Serotonin 5-HT1A and 5-HT2/1C receptors in the midbrain periaqueductal gray differentially modulate defensive rage behavior elicited from the medial hypothalamus of the cat.

Recent studies have established that the expression of defensive rage behavior in the cat is mediated over a descending pathway from the medial hypothalamus to the dorsolateral quadrant of the midbrain periaqueductal gray matter (PAG). The present study was designed to determine the roles played by 5-HT1A and 5-HT2/1C receptors in this region of PAG in modulating defensive rage behavior elicited from the cat's medial hypothalamus. Monopolar stimulating electrodes were implanted into the medial hypothalamus from which defensive rage behavior could be elicited by electrical stimulation. During the course of the study, the 'hissing' component of the defensive rage response was used as a measure of defensive rage behavior. Cannula-electrodes were implanted into sites within the PAG from which defensive rage could also be elicited by electrical stimulation in order that 5-HT compounds could be microinjected into behaviorally identifiable regions of the PAG at a later time. Microinjections of the selective 5-HT1A agonist, (+)-8-hydroxy-dipropylaminotetralin hydrobromide (8-OHDPAT) (50 pmol, 2.0 and 3.0 nmol), into the PAG suppressed the hissing response in a dose-dependent manner. Administration of the selective 5-HT1A antagonist, 4-iodo-N-[2-[4-(methoxyphenyl)-1-piperazinyl] ethyl]-N-2-pyridinyl-benzamide hydrochloride (p-MPPI) (1.5 and 3.0 nmol), blocked the suppressive effects of 8-OHDPAT upon hissing. In contrast, microinjections of the 5-HT2/1C receptor agonist (+)-1-(4-iodo-2,5-dimethoxyphenyl)-2-aminopropane hydrochloride ((+)-DOI hydrochloride) (0.01, 1.0 and 1.5 nmol) facilitated the occurrence of hissing elicited from the medial hypothalamus in a dose-dependent manner. Immunohistochemical analysis revealed the presence of 5-HT axons and preterminals throughout the PAG, and in particular, in its dorsolateral aspect which receives major inputs from the medial hypothalamus in association with defensive rage behavior. The overall findings of the study provide evidence that activation of 5-HT1A and 5-HT2/1C receptors within the midbrain PAG differentially modulate the expression of defensive rage behavior elicited from the medial hypothalamus of the cat.

Ethanol enhances medial amygdaloid induced inhibition of predatory attack behaviour in the cat: role of GABAA receptors in the lateral hypothalamus.

The present study tested the hypothesis that the suppressive effects of ethanol upon predatory attack behaviour in the cat involve a pathway from the medial amygdala to the lateral hypothalamus, and that these suppressive effects are mediated by gamma-aminobutyric acid (GABAA) receptors located in the lateral hypothalamus. Cannula electrodes were implanted into the lateral hypothalamus for elicitation of predatory attack behaviour and for microinjections of the GABAA receptor antagonist, bicuculline. Monopolar stimulating electrodes were implanted into the medial amygdala from which subseizure levels of electrical stimulation suppressed predatory attack behaviour. In the first phase of the study, we compared response latencies for predatory attack behaviour following single stimulation of the lateral hypothalamus alone with those following paired trials of dual stimulation of the medial amygdala plus lateral hypothalamus. Dual stimulation significantly suppressed predatory attack. In the second phase of the study, peripheral ethanol administration (in doses of 0.01, 0.5 and 1.0 g/kg, i.p.) enhanced the suppressive effects of medial amygdaloid stimulation in a dose- and time-dependent manner in which peak effects were obtained 60 min post-injection. In the third phase of the study, bicuculline (0.15 nmol) was microinjected into the lateral hypothalamus both prior to and following paired trials of dual stimulation. Drug infusion blocked the suppressive effects of medial amygdaloid stimulation upon predatory attack behaviour elicited from the lateral hypothalamus, indicating the importance of GABAA receptors in mediating this suppression. In the fourth phase of the study, bicuculline, microinjected into the lateral hypothalamus at the time when ethanol's effects were maximal (i.e. 60-80 min post-ethanol administration), totally blocked the suppressive effects of medial amygdaloid stimulation as well as the enhancing effects of ethanol upon medial amygdaloid suppression of this form of aggressive behaviour. In the last phase of the study, bicuculline (0.15 nmol) infusion into the lateral hypothalamus significantly reduced the suppressive effects of ethanol (1.0 g/kg, i.p.) upon predatory attack behaviour elicited from the lateral hypothalamus. These results support the hypothesis that ethanol's suppressive effects upon predatory attack behaviour in the cat are mediated, at least in part, by GABAA receptors in the lateral hypothalamus. The present and recent findings in our laboratory support the view that GABAA receptors in the lateral hypothalamus are activated, in turn, by a GABAergic pathway which arises from the medial hypothalamus whose neurons receive inputs from the medial amygdala.

Neurotransmitters regulating defensive rage behavior in the cat.

This review summarizes recent findings of our laboratory that have been directed at: (1) identifying the neural circuits underlying the expression and modulation of defensive rage behavior in the cat and the neurotransmitters associated with these pathways; and (2) determining which components of the circuitry are affected by alcohol administration and which significantly alter the rage mechanism. The experiments described herein incorporated a number of converging methods, which include brain stimulation, behavioral pharmacology, immunocytochemistry, retrograde tract tracing and receptor binding. For behavioral pharmacological studies, monopolar electrodes and cannula-electrodes were implanted into selected regions along the limbic-midbrain axis for electrical stimulation and local microinfusion of drugs. The findings demonstrated: (1) a direct pathway from the anterior medial hypothalamus to the dorsal periaqueductal gray (PAG) over which this response is mediated. This pathway utilizes excitatory amino acids that act upon NMDA receptors within the midbrain PAG; (2) that the region of the dorsal PAG, from which defensive rage could be elicited, receives other inputs from the basal amygdala that facilitate this response by acting upon NMDA receptors; (3) a pathway from the medial amygdala to the medial hypothalamus that also facilitates defensive rage and whose functions are mediated by substance P receptors within the medial hypothalamus; (4) that the PAG also receives enkephalinergic inputs from the central nucleus of amygdala, which act upon mu receptors, and which powerfully suppress defensive rage; and (5) that recent findings reveal that ethanol administration facilitates defensive rage by virtue of its interactions with the medial hypothalamus, its descending projection to the PAG, and possibly with NMDA receptors within this pathway.

Differential effects of ethanol on feline rage and predatory attack behavior: an underlying neural mechanism.

Previous studies have shown that, at certain dose levels, ethanol can exert a powerful, facilitatory effect on aggressive behavior in both animals and humans. In the cat, however, it was discovered that ethanol differentially alters two forms of aggression that are common to this species. Defensive rage behavior is significantly enhanced, whereas predatory attack behavior is suppressed by ethanol administration. One possible mechanism governing alcohol's potentiation of defensive rage behavior is that it acts on the descending pathway from the medial hypothalamus to the midbrain periaqueductal gray (PAG)-an essential pathway for the expression of defensive rage behavior that uses excitatory amino acids as a neurotransmitter. This hypothesis is supported by the finding that the excitatory effects of alcohol on defensive rage behavior are blocked by administration of the N-methyl-D-aspartate antagonist alpha-2-amino-7-phosphoheptanoic acid (AP-7) when microinjected into the periaqueductal gray, a primary neuronal target of descending fibers from the medial hypothalamus that mediate the expression of defensive rage behavior. Thus, the present study establishes for the first time a specific component of the neural circuit for defensive rage behavior over which the potentiating effects of ethanol are mediated.

NMDA receptors in the midbrain periaqueductal gray mediate hypothalamically evoked hissing behavior in the cat.

The present study was designed to test the hypothesis that the descending pathway from the medial hypothalamus to the dorsal periaqueductal gray (PAG) is critical for the expression of defensive rage behavior in the cat and utilizes excitatory amino acids as a neurotransmitter. In the first phase of the study, monopolar stimulating electrodes were implanted into the medial hypothalamus from which defensive rage behavior could be elicited by electrical stimulation. For the entire study, the hissing response was used as a measure of defensive rage behavior. Cannula electrodes were implanted into the PAG from which defensive rage sites could be identified and were later used for microinfusion of the NMDA receptor antagonist, DL-2-amino-7-phosphoheptanoic acid (AP-7), into behaviorally identified sites within the PAG. Initially, intracerbral microinjections of the NMDA receptor antagonist, AP-7 (0.2, 2.0 nmol), which were placed directly into sites within the PAG from which defensive rage had been elicited, blocked the occurrence of hypothalamic hissing. Microinjections of similar doses of AP-7 into the PAG also blocked the facilitatory effects of medial hypothalamic stimulation upon hissing behavior elicited from the PAG. However, microinjections of 2 nmol into the PAG had no effect upon hissing that was also elicited from the region of the injection site. This finding indicates that AP-7 selectively blocks hissing elicited from the medial hypothalamus and that the suppressive effects of AP-7 cannot be the result of anesthetic or other nonselective properties of the drug. The next phase of the study, which employed immunohistochemical, receptor autoradiographic techniques, identified NMDA receptors to be present in highest concentrations in the dorsolateral aspect of the PAG where defensive rage is typically elicited. The final phase of the study, which employed a combination of retrograde labeling procedures following microinjections of Fluoro-Gold into defensive rage sites in the dorsal PAG and the immunocytochemical labeling of glutamatergic neurons, identified large numbers of neurons in the medial hypothalamus that were labeled positively for both Fluoro-Gold and glutamate. The overall findings of this study support the hypothesis that descending fibers of the medial hypothalamus that supply the dorsal aspect of the PAG mediate defensive rage behavior and utilize excitatory amino acids that act upon NMDA receptors within the dorsal PAG.

Medial amygdaloid suppression of predatory attack behavior in the cat: I Role of a substance P pathway from the medial amygdala to the medial hypothalamus.

The medial amygdala is known to powerfully suppress predatory attack behavior in the cat, but the mechanisms underlying such modulation remain unknown. The present study tested the hypothesis that medial amygdaloid suppression of predatory attack is mediated, in part, by a pathway from the medial amygdala to the medial hypothalamus which utilizes substance P as a neurotransmitter. Stimulating electrodes were implanted into the medial amygdala and cannula electrodes were implanted into both the medial and lateral hypothalamus. Predatory attack behavior was elicited by electrical stimulation of the lateral hypothalamus. In the first phase of the study, paired trials compared attack latencies of single stimulation of the lateral hypothalamus with those following dual stimulation of the lateral hypothalamus and medial amygdala. Attack latencies were significantly elevated following dual stimulation of the medial amygdala and lateral hypothalamus. In the second phase of the study, dose and time dependent decreases in response suppression were noted following the infusion of the substance P (NK1) receptor antagonist, CP96.345 (in doses of 0.05, 0.5 and 2.5 nmol) into the medial hypothalamus. In third phase of the study, the effects of microinjections of the substance P receptor agonist, [Sar9.Met(O2)11]-substance P (in doses of 0.5, 1.0 and 2.0 nmol), directly into the medial hypothalamus upon lateral hypothalamically elicited predatory attack behavior were determined. Microinfusion of this drug elevated attack response latencies in a dose- and time-dependent manner. In addition, pretreatment with CP96,345 into the medial hypothalamus blocked the suppressive effects of subsequent delivery of [Sar9,Met(O2)11]-substance P into the same medial hypothalamic site. Other parts of the study demonstrated the presence of: (1) high densities of substance P receptors in the ventromedial hypothalamus, and (2) neurons that are positively labeled for substance P that project from the medial amygdala to the ventromedial hypothalamus as demonstrated by retrograde labeling with Fluoro-Gold. These findings provide support for the hypothesis that medial amygdaloid suppression of lateral hypothalamically elicited predatory attack behavior includes a substance P pathway from the medial amygdala to the medial hypothalamus. The findings further suggest that stimulation of the medial amygdala activates substance P receptors in the medial hypothalamus, thus triggering an inhibitory mechanism from the medial to the lateral hypothalamus, resulting in suppression of predatory attack behavior.

Medial amygdaloid suppression of predatory attack behavior in the cat: II. Role of a GABAergic pathway from the medial to the lateral hypothalamus.

The medial amygdala is known to powerfully suppress predatory attack behavior elicited by electrical stimulation of the lateral hypothalamus of the cat. In the preceding paper, it was shown that the initial limb of a pathway subserving suppression of predatory attack from the medial amygdala to the lateral hypothalamus projects to the ventromedial hypothalamus and its functions are mediated by substance P. The present study tested the hypothesis that the second limb of the pathway subserving medial amygdaloid suppression of predatory attack behavior projects from the medial to lateral hypothalamus and its functions are mediated by GABA. Cannula electrodes were implanted into the lateral hypothalamus for elicitation of predatory attack behavior as well as for the microinfusion of GABA compounds. Monopolar stimulating electrodes were implanted into sites within the medial amygdala from which subseizure levels of stimulation could suppress predatory attack behavior. Initially, the effects of dual stimulation of the medial amygdala and lateral hypothalamus upon response latencies for predatory attack were compared with single stimulation of the lateral hypothalamus alone. Dual stimulation was shown to significantly suppress predatory attack elicited from the lateral hypothalamus. Then, the GABAA receptor antagonist, bicuculline, was microinjected into sites within the lateral hypothalamus from which predatory attack was elicited in doses of 0.015, 0.075 and 0.15 nmol and paired trials of single and dual stimulation were again repeated in a manner identical to that applied prior to drug administration. Drug infusion produced a blockade of medial amygdaloid suppression of predatory attack in a time- and dose-dependent manner. Conversely, microinfusions of the GABAA receptor agonist, muscimol (10, 25 and 50 pmol), into the same lateral hypothalamic 'attack' site in the absence of medial amygdaloid stimulation suppressed predatory attack, thus simulating the effects of medial amygdaloid stimulation. Furthermore, pretreatment with bicuculline microinjected into the lateral hypothalamus blocked the suppressive effects of substance P, that was infused into the ventromedial hypothalamus, upon predatory attack. Receptor autoradiography demonstrated the presence of high affinity binding for GABAA receptors in the lateral hypothalamus. A combination of immunocytochemical and retrograde axonal tract tracing procedures, in which Fluoro-Gold was microinjected into the lateral hypothalamic attack sites, revealed the presence of populations of neurons labeled for both Fluoro-Gold and GABA in the ventromedial hypothalamus. These findings provide new evidence for the existence of a pathway from the medial to lateral hypothalamus whose functions are mediated by GABA. Thus, the overall findings provide support for the view that the pathway from the medial amygdala to the lateral hypothalamus underlying suppression of predatory attack behavior involves a two-neuronal arc: the first neuron projects from the medial amygdala to the medial hypothalamus and its functions are mediated by substance P: the second neuron involves a GABAergic pathway originating in the ventromedial hypothalamus and which projects to the lateral hypothalamus.

Neuroanatomical and neurochemical mechanisms underlying amygdaloid control of defensive rage behavior in the cat.

1. It is well established that the hypothalamus and midbrain periaqueductal gray (PAG) play important roles in the expression of defensive rage behavior. While defensive rage is not elicited from the amygdala, this region of the limbic system nevertheless serves an important role in the modulation of defensive rage behavior. The present paper attempts to address the question of how the amygdala modulates defensive rage behavior in the cat. The studies were conducted using brain stimulation, pharmacological, neuroanatomical and immunocytochemical methods to identify the likely neural pathways and their associated neurotransmitters by which different regions of the amygdala modulate defensive rage behavior in the cat. 2. The experimental evidence provided thus far establishes that three regions of the amygdala have been identified as powerful modulators of defensive rage behavior. These include the medial nucleus, basal complex and central nucleus of the amygdala. Experiments involving dual stimulation of an amygdaloid nucleus and sites within the medial hypothalamus or PAG from which defensive rage behavior was elicited demonstrated that two of the regions facilitated defensive rage --the medial nucleus and basal complex--and a third region--the central nucleus--suppressed defensive rage. The mechanisms and substrates underlying modulation for each of these regions are different. Medial amygdaloid facilitation of defensive rage involves a pathway (i.e., the stria terminalis) that projects directly to the medial hypothalamus and utilizes substance P as a neurotransmitter. Basal amygdaloid facilitation of defensive rage behavior makes use of a pathway to the PAG in which excitatory amino acids acting on NMDA receptors are utilized as a neurotransmitter. The central nucleus also projects to the PAG. However, it is strongly inhibitory and utilizes enkephalins that act upon mu receptors within the PAG.

Basal amygdaloid facilitation of midbrain periaqueductal gray elicited defensive rage behavior in the cat is mediated through NMDA receptors.

The present study tested the hypotheses that: (1) defensive rage behavior elicited from the midbrain periaqueductal gray (PAG) in the cat is facilitated from the basal complex of amygdala; and (2) such facilitation from this region of amygdala is mediated via a pathway in which excitatory amino acids acting upon NMDA receptors within the PAG are utilized as a neurotransmitter. In the first phase of this study, cannula electrodes were implanted into PAG sites for the elicitation of defensive rage behavior as well as for drug delivery. Then, a second monopolar electrode was implanted into the basal nucleus of amygdala from which facilitation of defensive rage could be obtained. As a result of dual stimulation of the basal amygdala and PAG, response latencies for defensive rage were significantly lowered relative to PAG stimulation alone (P < 0.01). In the second phase of this experiment, 3 doses of a selective NMDA receptor antagonist, AP-7 (0.1, 0.5, 1.0 mg/kg), were peripherally (i.p.) administered in 5 animals. The results indicated a significant decrease in the facilitatory effects of amygdaloid stimulation in a dose and time dependent manner (P < 0.001). In the third phase, AP-7 was administered intracerebrally into PAG defensive rage sites in doses of 0.2 and 2.0 nmol. It was noted that intracerebral microinjections of AP-7 at the higher dose (2.0 nmol) also significantly suppressed the facilitatory effects of amygdaloid stimulation (P < 0.01); however, these effects were somewhat less potent then those observed following peripheral drug administration. A fourth phase of the study was conducted at the completion of the pharmacological experiments.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence that substance P is utilized in medial amygdaloid facilitation of defensive rage behavior in the cat.

The present study was designed to test the hypothesis that a major excitatory mechanism for the expression of feline defensive rage behavior involves the medial nucleus of the amygdala which utilizes substance P as a neurotransmitter in a direct output pathway that supplies the medial hypothalamus. In phase I of the experiment, stimulating electrodes were implanted into the medial amygdala and cannula electrodes were implanted into the medial and lateral hypothalamus from which defensive rage and predatory attack behavior could be elicited by electrical stimulation, respectively. Response latencies for defensive rage were significantly lowered after dual stimulation of the medial amygdala and medial hypothalamus relative to single stimulation of the medial hypothalamus alone. In phase II, dose- and time-dependent decreases in medial amygdaloid-induced facilitation of defensive rage were observed after the i.p. administration of the NK1 antagonist, CP-96,345 (0.05, 2 and 4 mg/kg). In phase III of the study, the effects of microinjections of CP-96,345 placed directly into defensive rage sites within the medial hypothalamus (0.05, 0.5 and 2.5 nmol) upon medial amygdaloid modulation of this response were assessed. Again, intracerebral administration of this antagonist blocked the facilitatory effects of medial amygdaloid-induced facilitation of defensive rage in a manner parallel to that observed with peripheral administration of the NK1 antagonist. The results suggest that the medial amygdala facilitates defensive rage by acting through a substance P mechanism at the level of the medial hypothalamus. Other experiments revealed that peripheral administration of the NK1 antagonist: (1) had little upon the latency or threshold for elicitation of defensive rage, suggesting that the medial amygdaloid-substance P facilitatory mechanism acts in a phasic rather than tonic manner; and (2) also blocks the suppressive effects of medial amygdaloid stimulation upon predatory attack behavior elicited from the lateral hypothalamus. The latter finding suggest that similar neurochemical mechanisms regulate medial amygdaloid modulation of both forms of hypothalamically elicited aggression. The final aspect of this study utilized the combination of retrograde-tracing of amygdaloid neurons into the medial hypothalamus after microinjections of Fluoro-Gold into defensive rage sites, and the immunocytochemical analysis of substance P neurons within the amygdala. The data indicated that large numbers of retrogradely and immunocytochemically positive labeled cells were identified in the medial nucleus, including many that were double-labeled.(ABSTRACT TRUNCATED AT 400 WORDS)

Electromyographic activity in the masseter muscle resulting from stimulation of hypothalamic behavioral sites in the cat.

This study examined the relationship between hypothalamically elicited emotional behaviors and electromyographic activity in the masseter muscle of the cat. Electromyographic amplitudes resulting from stimulation at hypothalamic sites at which affective defense and quiet biting attack behaviors were elicited were compared with those recorded during stick biting that simulated mastication. The electromyographic activity elicited by hypothalamic stimulation was greater than that found from stick biting for all behavioral sites. At control sites, from which no behavior could be elicited, the electromyographic activity associated with stick biting exceeded that observed from the hypothalamic sites. These findings suggest a relationship between hypothalamically elicited behaviors and increased levels of jaw muscle activity.

Role of NMDA receptors in hypothalamic facilitation of feline defensive rage elicited from the midbrain periaqueductal gray.

The present study tested the hypothesis that the pathway from the medial hypothalamus to the midbrain periaqueductal gray (PAG) subserving defensive rage behavior in the cat facilitates the occurrence of this response when elicited from the PAG by utilizing excitatory amino acids as a neurotransmitter or neuromodulator. Cannula electrodes were implanted into the PAG for the elicitation of defensive rage behavior as well as for microinjections of excitatory amino acid antagonists and N-methyl-D-aspartic acid (NMDA). Monopolar stimulating electrodes were also implanted into the medial hypothalamus from which this response could also be elicited and, when stimulated at subthreshold levels for elicitation of behavior, could also facilitate the occurrence of PAG elicited defensive rage. Initially, dual stimulation of the PAG and medial hypothalamus facilitated the occurrence of defensive rage elicited from the PAG. Then, the identical dual stimulation paradigm was repeated with the same current parameters following the infusion of various antagonists for different receptors into the PAG defensive rage sites. The results indicate that infusion of either kynurenic acid [(0.1-2.0 nmol), a non-selective excitatory amino acid receptor antagonist] or D-2-amino-7-phosphonoheptanoic acid (AP7) [(0.1-2.0 nmol), a specific NMDA receptor antagonist], produced a dose and time dependent blockade of the facilitatory effects of medial hypothalamic stimulation. In contrast, microinjections of relatively larger doses of 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) [(4 nmol), a non-NMDA receptor (quisqualate and kainate) antagonist] or atropine [(4.4 nmol), a muscarinic receptor antagonist] had little effect upon medial hypothalamically elicited facilitation of the PAG response. In a second experiment, NMDA [0.1-1.0 nmol] was microinjected directly into PAG defensive rage sites in the absence of medial hypothalamic stimulation. In these animals, drug infusion mimicked the effects of dual stimulation by producing a dose and time dependent decrease in response latencies. A third experiment was designed to further test the hypothesis by neuroanatomical methods. Here, the retrograde label, Fluoro-Gold, was microinjected into defensive rage sites within the PAG and following a survival time of 5-6 days, the animals were sacrificed. The brains were then processed for immunocytochemical analysis of cells that immunoreact positively for aspartate and glutamate. The results indicated the presence of many retrogradely labelled and immunocytochemically positive cells within the rostro-caudal extent of the medial hypothalamus as well as others that were double labelled.(ABSTRACT TRUNCATED AT 400 WORDS)

Dopaminergic regulation of quiet biting attack behavior in the cat.

The present study provides evidence for the involvement of dopamine in the regulation of quiet biting attack behavior. Utilizing monopolar electrodes, quiet biting attack was elicited by electrical stimulation of lateral hypothalamus in five cats. After stable baseline response latency values were established, the nonselective dopamine agonist, apomorphine, was administered peripherally (IP, 1.0, 1.4 and 1.8 mg/kg), and its effects upon the attack response were identified. Apomorphine significantly facilitated the occurrence of quiet biting attack in a dose- and time-dependent manner. Conversely, quiet biting attack behavior was also suppressed in a dose- and time-dependent manner by the selective D2 antagonist, spiperone (0.2, 0.4 and 0.8 mg/kg), but not by the selective D1 antagonist, SCH 23390 (0.8 mg/kg). Moreover, pretreatment with spiperone (0.2 mg/kg) completely blocked the facilitatory effects of 1.4 mg/kg of apomorphine, while SCH 23390 (0.8 mg/kg) pretreatment failed to alter apomorphine-induced facilitation of the attack response. In addition, neither apomorphine nor spiperone altered response latencies for hypothalamically elicited circling behavior. The results suggest that dopamine plays a significant role in the regulation of quiet biting attack behavior.

An enkephalinergic mechanism involved in amygdaloid suppression of affective defence behavior elicited from the midbrain periaqueductal gray in the cat.

A series of recent studies in our laboratory have provided evidence that opioid peptides powerfully suppress feline affective defense behavior at the level of the midbrain periaqueductal gray (PAG). In the present study, we tested the hypothesis that the central (CE) nucleus of the amygdala constitutes a significant inhibitory input to the PAG which utilizes enkephalins as its neurotransmitter or neuromodulator. Cannula-electrodes were implanted into the PAG for the elicitation of affective defense behavior as well as for infusion of opioid antagonists. Monopolar stimulating electrodes were also implanted into the central, lateral and medial amygdaloid nuclei from which suppression or facilitation of affective defense behavior could be obtained. Initially, 4 trials of concurrent, subseizure stimulation of the CE or lateral amygdala at very low (100 microA, 60 Hz) currents and PAG resulted in an immediate suppression of this response which displayed a time dependent decline after 30 min. In the next stage of the experiment, naloxone (2.7, 18.9 and 27.5 nM) was microinjected through the cannula-electrode into the PAG affective defense site and the experimental procedures noted above were repeated. Naloxone treatment (at 27.5 and 18.9 nM) blocked the suppressive effects of CE and lateral amygdaloid stimulation in a dose and time dependent manner. Further analysis revealed that this effect is likely mediated via the mu receptor since the suppressive effects of amygdaloid stimulation were blocked by the selective mu antagonist, beta-Funaltrexamine (0.05 and 0.2 nM) but not by the selective delta-antagonist, ICI 174,864 (0.7 nM).(ABSTRACT TRUNCATED AT 250 WORDS)

Affective defense behavior elicited from the feline midbrain periqueductal gray is regulated by mu and delta opioid receptors.

The present study sought to identify specific opioid receptor subtypes involved in the modulation of affective defense behavior (AD) at the level of the midbrain periaqueductal gray (PAG). Cannula electrodes were utilized for eliciting AD from the PAG as well as for microinjecting mu, delta and kappa agonists and antagonists into these sites. Following microinjections of morphiceptin, D-Pen2,D-Pen5 enkephalin (DPDPE), or U-488H into sites from which AD was elicited, threshold values were determined. The results indicated that morphiceptin and DPDPE significantly suppressed AD in a dose- and time-dependent manner. Pretreatment with mu and delta opioid antagonists, B-FNA and ICI 174,864, completely blocked the suppressive effects of morphiceptin and DPDPE, respectively. Microinjections of morphiceptin and DPDPE failed to alter response thresholds for circling behavior also elicited from electrical stimulation of dorsal PAG. Administration of the selective kappa agonist, U-488H, or vehicle alone, did not alter the threshold for AD. The results of this study indicate that opioid peptides interact with mu and delta receptors within the midbrain PAG to powerfully suppress AD.

Enkephalinergic involvement in periaqueductal gray control of hypothalamically elicited predatory attack in the cat.

The effects of central infusion of naloxone into the midbrain periaqueductal gray (PAG) upon predatory attack behavior in the cat were studied in 12 cats. Initially, quiet biting attack was elicited by electrical stimulation of sites within the lateral hypothalamus using monopolar electrodes. Then cannula-electrodes were implanted into sites within the PAG from which electrical stimulation facilitated or suppressed the attack response. Following identification of modulatory sites within the PAG, naloxone (1.0 micrograms/0.5 microliter) was microinjected into those sites and the effects upon hypothalamically elicited attack were assessed. At nine of twelve sites in the PAG where suppression was obtained, administration of naloxone served to block those effects. Similarly, at six of eight facilitatory sites within the PAG, naloxone also blocked the modulatory effects of PAG stimulation. However, vehicle (isotonic saline) alone did not alter the modulatory effects of PAG stimulation. Administration of DAME (250 ng/0.3 microliter) into PAG modulatory sites in four cats, two which facilitated and two that suppressed the attack response, reversed the effects of naloxone at these sites. These results demonstrate that opioid peptides within the PAG play a complex role in the expression of predatory attack behavior in the cat.

GABA-mediated regulation of feline aggression elicited from midbrain periaqueductal gray.

The midbrain periaqueductal gray (PAG) is now recognized as a critical structure for the initiation and regulation of aggressive behavior in the cat. The PAG is also known to be rich in gamma-aminobutyric acid (GABA) receptors. In the present study, we sought to examine the possible role of this putative neurotransmitter in the modulation of affective defense and quiet biting attack behavior elicited by electrical stimulation of the PAG. Cannula-electrodes were employed for electrical stimulation as well as for microinjections of a GABA agonist (muscimol: 3, 12 and 22 pmol/0.25 microliters) and GABA antagonist (bicuculline: 22 and 68 pmol/0.25 microliters). After establishing predrug response threshold values for affective defense and quiet biting attack, these drugs were microinjected into the PAG sites from which these responses were elicited. Microinjections of muscimol (12 and 22 pmol) significantly suppressed the affective defense response in a dose- and time-dependent manner. Pretreatment with bicuculline (68 pmol) blocked the suppressive effects of muscimol (12 pmol) upon affective defense behavior. In contrast, this dose of muscimol failed to alter the response threshold for quiet biting attack behavior. Microinjections of vehicle alone (0.25 microliter of saline, pH = 7.4) did not modify the thresholds for either of these responses. These results indicate that, at the level of the PAG, GABA-ergic mechanisms are selectively involved in the regulation of affective defense behavior in the cat.

Naloxone-induced modulation of feline aggression elicited from midbrain periaqueductal gray.

In the present study, peripheral administration of naloxone hydrochloride (IP) was employed to identify the role of endogenous opioid peptides in the regulation of two forms of aggressive behavior in the cat--affective defense and quiet biting attack behavior. These forms of aggressive behavior were elicited by electrical stimulation of dorsal and ventral aspects of the midbrain periaqueductal gray, respectively, utilizing monopolar electrodes. Following the establishment of stable baseline thresholds for affective defense and quiet biting attack behavior, naloxone (0.5, 1.0, 4.0 and 7.0 mg/kg) and saline (vehicle control) were administered peripherally (IP). The response thresholds were tested 5-30, 30-60, 60-90, 180-210 and 1440-1470 min following naloxone administration. These results indicated that a dose level of 7.0 mg/kg of naloxone had a profound facilitatory effect on affective defense behavior. Response threshold values returned to prenaloxone baseline levels at 1440-1470 min postinjection. Administration of lower doses of naloxone (1.0 and 4.0 mg/kg) also resulted in a significant facilitation of this response but of shorter durations. Neither the lowest dose of naloxone (0.5 mg/kg) nor saline (vehicle control) were effective in modifying the threshold for affective defense behavior. In contrast, when tested for its effects upon quiet biting attack, the maximum dose utilized in this study (7.0 mg/kg) tended to suppress this response although the overall effect was not significant. The selective dose-dependent facilitatory effects of naloxone upon affective defense behavior in the cat suggests that the opioid peptide system plays a significant (inhibitory) role in the regulation of this response.

Opioid peptides within the midbrain periaqueductal gray suppress affective defense behavior in the cat.

The effects of the methionine-enkephalin analog [D-Ala2-Met5]-enkephalinamide (DAME) upon the threshold for affective defense behavior were determined following microinjections placed into midbrain periaqueductal gray sites from which this response was elicited. Affective defense behavior was elicited by electrical stimulation through a cannula electrode situated in the dorsal aspect of the midbrain periaqueductal gray. Dose-response curves characterizing the effects of DAME upon affective defense behavior were determined utilizing the following doses: 0.25, 0.5 and 1.0 microgram in 0.5 microliter saline, pH = 7.4 or vehicle control (saline). Response thresholds were tested 10-30, 30-60, 60-90, 120-150, 180-210, 1440-1470 and 2880-2910 min postinjection. The results obtained indicated that injections of DAME at a dose of 1.0 microgram/0.5 microliter produced significant, long duration elevations in affective defense thresholds, lasting up to 1440-1470 min postinjection. Lower doses of DAME (0.25 and 0.5 microgram/0.5 microliter) also resulted in significant increases in affective defense thresholds, but these effects were of shorter durations (60-90 and 120-150 min) postinjection, respectively. The suppressive effects of DAME were blocked when animals were pretreated with naloxone (10 micrograms/0.5 microliter) microinjected into the same midbrain periaqueductal gray site into which 0.25 microgram DAME was injected and affective defense behavior was elicited.

Carbamazepine regulates feline aggression elicited from the midbrain periaqueductal gray.

Carbamazepine has been utilized both as an anticonvulsant and as a psychotropic drug for the treatment of complex partial seizures and various mood and other emotional disorders such as the episodic dyscontrol syndrome. In the present study, we sought to identify the role of carbamazepine in the regulation of two forms of aggressive behavior--affective defense and quiet biting attack behavior--elicited by electrical stimulation of the midbrain periaqueductal gray matter of the cat in the absence of convulsive activity. The experimental paradigm involved establishment of stable baseline thresholds for affective defense and quiet biting attack responses. Following establishment of a stable baseline, carbamazepine (2.5, 5, or 10 mg/kg) and propylene glycol (vehicle control) were administered peripherally (IP). The response thresholds were tested 5-30, 30-60, 60-90, 120-150, 1440-1470, and 2160-2190 minutes following drug administration. It was observed that carbamazepine administration at 5 and 10 mg/kg dose levels preferentially suppressed affective defense behavior but had no effect upon quiet biting attack, indicating that the selective effects of carbamazepine upon affective attack are not due to any possible sedative effects upon motor responses. The effects of carbamazepine upon affective defense were dose dependent and of long duration when administered at the highest dose level (10 mg/kg).