A Descending Circuit Derived From the Superior Colliculus Modulates Vibrissal Movements.

The superior colliculus (SC) is an essential structure for the control of eye movements. In rodents, the SC is also considered to play an important role in whisking behavior, in which animals actively move their vibrissae (mechanosensors) to gather tactile information about the space around them during exploration. We investigated how the SC contributes to vibrissal movement control. We found that when the SC was unilaterally lesioned, the resting position of the vibrissae shifted backward on the side contralateral to the lesion. The unilateral SC lesion also induced an increase in the whisking amplitude on the contralateral side. To explore the anatomical basis for SC involvement in vibrissal movement control, we then quantitatively evaluated axonal projections from the SC to the brainstem using neuronal labeling with a virus vector. Neurons of the SC mainly sent axons to the contralateral side in the lower brainstem. We found that the facial nucleus received input directly from the SC, and that the descending projections from the SC also reached the intermediate reticular formation and pre-Bötzinger complex, which are both considered to contain neural oscillators generating rhythmic movements of the vibrissae. Together, these results indicate the existence of a neural circuit in which the SC modulates vibrissal movements mainly on the contralateral side, via direct connections to motoneurons, and via indirect connections including the central pattern generators.

Distribution of glucagon-like peptide 1-immunopositive neurons in human caudal medulla.

In rodents, glucagon-like peptide-1 (GLP-1)-positive neurons within the caudal medulla respond to a broad array of interoceptive signals that suppress food intake and drive the hypothalamic-pituitary-adrenal stress axis. The collective results of experiments utilizing cFos to identify activated neurons in rats and mice indicate that GLP-1 neurons are consistently activated by stimuli that present actual or anticipated threats to bodily homeostasis. The distribution of GLP-1-positive neurons in the human brain is unreported. The present study identified GLP-1-positive neurons and mapped their distribution within the caudal medulla in two adult human subjects (one female, one male). The goal of the study was to obtain structural evidence with which to challenge the general hypothesis that functions ascribed to GLP-1 neurons in rodent species may reflect parallel functions that exist in humans. In both human subjects, GLP-1-immunopositive neurons were located within the dorsal medullary region containing the caudal (visceral) nucleus of the solitary tract and in the nearby medullary reticular formation, similar to the distribution of GLP-1 neurons in rats, mice, and Old World monkeys. Quantitative analysis indicates the presence of approximately 6.5-9.3 K GLP-1-positive neurons bilaterally within the human caudal medulla. It will be important in future studies to map the distribution of GLP-1-positive fibers and terminals within higher regions of the human brain, to improve our understanding of how central GLP-1 signaling pathways might influence stress responsiveness, energy balance, and other physiological and behavioral functions.

[Effect of moxibustion-like thermal stimulation with different temperature and covering different areas of "zhongwan" (CV 12) on discharges of neurons in medullary subnucleus reticularis dorsalis of rats].

OBJECTIVE: To observe the effect of regional thermal (moxibustion-like) stimulation on discharges of neurons in the medullary subnucleus reticularis dorsalis (SRD) and to study the best thermal stimulation parameters in the rat. METHODS: Experiments were performed on 15 male Sprague-Dawley rats under anesthesia (10% urethane, 1.0-1.5 g/kg). Unit discharges of single neurons in the medullary SRD were recorded extracellularly with glass micropipettes. Thermal stimulation (warm water filled in a glass bottle) with different temperature (40 degrees C, 42 degrees C, 44 degrees C, 46 degrees C, 48 degrees C, 50 degrees C, 52 degrees C) and covering different area (diameter: 1.0 cm x 1.5 cm, 2.0 cm, 2.5 cm, 3.0 cm, 3.5 cm, 4.0 cm) was applied to "Zhongwan"(CV 12) region for 30 s. Firing rates of SRD neurons were analyzed by using Power-Lab Chart 5.0. RESULTS: When thermal stimulation with temperature of 40 degrees C and 42 degrees C and the stimulated area of 1.0-4.0 cm in diameter was applied to CV 12 region, discharges of the medullary SRD neurons had no obvious changes. When the temperature was increased to 44 degrees C and 46 degrees C, the electrical activities of SRD neurons were increased linearly along with the increase of the stimulated area of 1.0-4.0 cm in diameter. When the temperature was increased further from 48 degrees C to 52 degrees C, the increased electrical activities of SRD neurons peaked at the stimulated area of 3.5 cm in diameter. In addition, thermal stimulation at a temperature of 50 degrees C and an area of 4.0 cm in diameter induced a larger increase of discharges of SRD neurons in comparison with that of 46 degrees C plus an area of 3.5 cm/4.0 cm in diameter (P < 0.05). No significant differences were found between 50 degrees C and 52 degrees C at any stimulated areas mentioned above (P > 0.05). CONCLUSION: Noxious thermal (44-52 degrees C) stimulation of CV 12 region can activate SRD neuron, which reaches a plateau when the stimulated area is increased to a certain range.

Neurochemistry of bulbospinal presympathetic neurons of the medulla oblongata.

This review focuses on presympathetic neurons in the medulla oblongata including the adrenergic cell groups C1-C3 in the rostral ventrolateral medulla and the serotonergic, GABAergic and glycinergic neurons in the ventromedial medulla. The phenotypes of these neurons including colocalized neuropeptides (e.g., neuropeptide Y, enkephalin, thyrotropin-releasing hormone, substance P) as well as their relative anatomical location are considered in relation to predicting their function in control of sympathetic outflow, in particular the sympathetic outflows controlling blood pressure and thermoregulation. Several explanations are considered for how the neuroeffectors coexisting in these neurons might be functioning, although their exact purpose remains unknown. Although there is abundant data on potential neurotransmitters and neuropeptides contained in the presympathetic neurons, we are still unable to predict function and physiology based solely on the phenotype of these neurons.

Hypoglossal premotor neurons of the intermediate medullary reticular region express cholinergic markers.

The inspiratory drive to hypoglossal (XII) motoneurons originates in the caudal medullary intermediate reticular (IRt) region. This drive is mainly glutamatergic, but little is known about the neurochemical features of IRt XII premotor neurons. Prompted by the evidence that XII motoneuronal activity is controlled by both muscarinic (M) and nicotinic cholinergic inputs and that the IRt region contains cells that express choline acetyltransferase (ChAT), a marker of cholinergic neurons, we investigated whether some IRt XII premotor neurons are cholinergic. In seven rats, we applied single-cell reverse transcription-polymerase chain reaction to acutely dissociated IRt neurons retrogradely labeled from the XII nucleus. We found that over half (21/37) of such neurons expressed mRNA for ChAT and one-third (13/37) also had M2 receptor mRNA. In contrast, among the IRt neurons not retrogradely labeled, only 4 of 29 expressed ChAT mRNA (P < 0.0008) and only 3 of 29 expressed M2 receptor mRNA (P < 0.04). The distributions of other cholinergic receptor mRNAs (M1, M3, M4, M5, and nicotinic alpha4-subunit) did not differ between IRt XII premotor neurons and unlabeled IRt neurons. In an additional three rats with retrograde tracers injected into the XII nucleus and ChAT immunohistochemistry, 5-11% of IRt XII premotor neurons located at, and caudal to, the area postrema were ChAT positive, and 27-48% of ChAT-positive caudal IRt neurons were retrogradely labeled from the XII nucleus. Thus the pre- and postsynaptic cholinergic effects previously described in XII motoneurons may originate, at least in part, in medullary IRt neurons.

A quantitative study of the brainstem cholinergic projections to the ventral part of the oral pontine reticular nucleus (REM sleep induction site) in the cat.

The ventral part of the cat oral pontine reticular nucleus (vRPO) is the site in which microinjections of small dose and volume of cholinergic agonists produce long-lasting rapid eye movement sleep with short latency. The present study determined the precise location and proportions of the cholinergic brainstem neuronal population that projects to the vRPO using a double-labeling method that combines the neuronal tracer horseradish peroxidase-wheat germ agglutinin with choline acetyltransferase immunocytochemistry in cats. Our results show that 88.9% of the double-labeled neurons in the brainstem were located, noticeably bilaterally, in the cholinergic structures of the pontine tegmentum. These neurons occupied not only the pedunculopontine and laterodorsal tegmental nuclei, which have been described to project to other pontine tegmentum structures, but also the locus ceruleus complex principally the locus ceruleus alpha and peri-alpha, and the parabrachial nuclei. Most double-labeled neurons were found in the pedunculopontine tegmental nucleus and locus ceruleus complex and, much less abundantly, in the laterodorsal tegmental nucleus and the parabrachial nuclei. The proportions of these neurons among all choline acetyltransferase positive neurons within each structure were highest in the locus ceruleus complex, followed in descending order by the pedunculopontine and laterodorsal tegmental nuclei and then, the parabrachial nuclei. The remaining 11.1% of double-labeled neurons were found bilaterally in other cholinergic brainstem structures: around the oculomotor, facial and masticatory nuclei, the caudal pontine tegmentum and the praepositus hypoglossi nucleus. The disperse origins of the cholinergic neurons projecting to the vRPO, in addition to the abundant noncholinergic afferents to this nucleus may indicate that cholinergic stimulation is not the only or even the most decisive event in the generation of REM sleep.

Projections from the cat posterior lateral hypothalamus to the ventral part of the oral pontine reticular nucleus contain a GABAergic component.

The posterior lateral hypothalamus (PLH) has long been considered crucial to normal wakefulness while the ventral part of the oral pontine reticular nucleus (vRPO) is involved in the generation and maintenance of rapid eye movement (REM) sleep. However, to date, there is no information on the ultrastructure or neurotransmitter content of the hypothalamo-reticular projection. In the present study, we examined the morphology and synaptic organization of PLH terminals in the vRPO using PLH injections of biotinylated dextran amine (BDA) as well as of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP). Since some PLH neurons are GABAergic, we used a post-embedding immunogold technique to determine whether any anterogradely labeled terminals were GABA-immunopositive. Electron microscope analyses revealed a variety of ultrastructural features in the vRPO anterogradely labeled terminals. Although most labeled terminals (over 63%) formed symmetric synapses on vRPO somata and dendrites, others made asymmetric synapses on vRPO dendrites. The relative percentages of labeled terminals observed on large, medium and small diameter dendrites were 44.3 +/- 5.5%, 35.3 +/- 3.0% and 20.4 +/- 3.1%, respectively. Finally, post-embedding immunogold technique revealed that there are GABA-immunopositive and immunonegative components to this projection, indicating that GABA is one of the transmitters used by the PLH cells that project to the vRPO. Furthermore, most, if not all, of the GABA-labeled axon terminals formed symmetric synapsis. In conclusion, our results suggest that the PLH could modulate the physiological responses of vRPO neurons through a GABAergic pathway as well as by other inhibitory and/or excitatory pathways. Activation of the descending PLH GABAergic projection may inhibit the REM sleep-inducing neurons within the vRPO and thus contribute to the suppression of REM sleep activation during wakefulness.

Response of NADPH-diaphorase-exhibiting neurons in the medullar reticular formation to high spinal cord injury.

1. The effect of hemisection of the cervical spinal cord on NADPH-diaphorase staining in the reticular nuclei of the rabbit medulla was investigated using histochemical technique. 2. A quantitative assessment of somal and neuropil NADPH-diaphorase staining was made by an image analyzer in a selected area of each reticular nucleus of the rabbit medulla. 3. On the 7th postsurgery day, the highest up-regulation of somatic NADPH-diaphorase staining was observed in regions regulating cardiorespiratory processes; however, the highest increase of neuropil NADPH-diaphorase staining was found in the reticular nuclei modulating the tonus of postural muscles. 4. The degeneration of non-NADPH-diaphorase-stained neurons was detected throughout the reticular formation of the medulla, but the extent of neuronal death did not correlate with the up-regulation of the NADPH-diaphorase staining in the reticular nuclei of the medulla. 5. The findings provide evidence that NADPH-diaphorase-exhibiting neurons are refractory to the hemisection of the cervical spinal cord and that the neuronal up-regulation of NADPH-diaphorase at the medullar level is probably not a causative factor leading to the death of the reticulospinal neurons.

Saccadic omnipause and burst neurons in monkey and human are ensheathed by perineuronal nets but differ in their expression of calcium-binding proteins.

The extracellular matrix of the brain contains large aggregates of chondroitin sulfate proteoglycans (CSPG), which form lattice-like cell coatings around distinct neuron populations and are termed perineuronal nets. The function of perineuronal nets is not fully understood, but they are often found around neurons containing the calcium-binding protein parvalbumin, suggesting a function in primarily highly active neurons. In the present paper the distribution of perineuronal nets was studied in two functional cell groups of the primate oculomotor system with well-known firing properties: 1) the saccadic omnipause neurons in the nucleus raphe interpositus (RIP) exhibit a high tonic firing rate, which is only interrupted during saccades; they are inhibitory and use glycine as a transmitter; and 2) premotor burst neurons for vertical saccades in the rostral interstitial nucleus of the medial longitudinal fascicle (RiMLF) fire with high-frequency bursts during saccades; they are excitatory and use glutamate and/or aspartate as a transmitter. In the macaque monkey, both cell populations were identified by their parvalbumin immunoreactivity and were studied for the presence of perineuronal nets using CSPG antibodies or lectin binding with Wisteria floribunda agglutinin. In addition, the expression of another calcium-binding protein, calretinin, was studied in both cell groups. Double- and triple-immunofluorescence methods revealed that both omnipause and burst neurons are selectively ensheathed with strongly labeled perineuronal nets. Calretinin was coexpressed in at least 70% of the saccadic burst neurons, but not in the omnipause neurons. Parallel staining of human tissue revealed strongly labeled perineuronal nets around the saccadic omnipause and burst neurons, in corresponding brainstem regions, which specifically highlighted these neurons within the poorly structured reticular formation. These findings support the hypothesis that perineuronal nets may provide a specialized microenvironment for highly active neurons to maintain their fast-spiking activity and are not related to the transmitter or the postsynaptic action of the ensheathed neurons.

Ultrastructural organization of lamprey reticulospinal synapses in three dimensions.

The giant reticulospinal synapse in lamprey provides a unique model to study synaptic vesicle traffic. The axon permits microinjections, and the active zones are often separated from each other, which makes it possible to track vesicle cycling at individual release sites. However, the proportion of reticulospinal synapses with individual active zones ("simple synapses") is unknown and a quantitative description of their organization is lacking. Here, we report such data obtained by serial section analysis, intermediate-voltage electron microscopy, and electron tomography. The simple synapse was the most common type (78%). It consisted of one active zone contacting one dendritic process. The remaining synapses were "complex," mostly containing one vesicle cluster and two to three active zones synapsing with distinct dendritic shafts. Occasional axosomatic synapses with multiple active zones forming synapses with the same cell were also observed. The vast majority of active zones in all synapse types contained both chemical and electrotonic synaptic specializations. Quantitative analysis of simple synapses showed that the majority had active zones with a diameter of 0.8-1.8 microm. The number of synaptic vesicles and the height of the vesicle cluster in middle sections of serially cut synapses correlated with the active zone length within, but not above, this size range. Electron tomography of simple synapses revealed small filaments between the clustered synaptic vesicles. A single vesicle could be in contact with up to 12 filaments. Another type of filament, also associated with synaptic vesicles, emerged from dense projections. Up to six filaments could be traced from one dense projection.

Hypocretin receptor protein and mRNA expression in the dorsolateral pons of rats.

The hypocretins (also known as orexins) are hypothalamic peptides that have been implicated in feeding and sleep regulation. Previous reports have described the distribution of the mRNAs encoding two hypocretin receptors (HCRT-R), but the pattern of protein expression has not been investigated. Here we examine the distribution of the mRNA and protein for the HCRT receptor 1 (HCRT-R1) and HCRT receptor 2 (HCRT-R2) in the pontine brainstem and demonstrate that they are present in many pontine nuclei including those associated with REM sleep. Immunohistochemistry indicates that one or both of the receptor subtypes are expressed in the dorsal raphe, the lateral dorsal tegmental (LDT), the pedunculo pontine (PPT), the locus coeruleus (LC), the locus subcoeruleus, pontis oralis, Barrington's, the trigeminal complex (mesencephalic trigeminal and motor nucleus of the trigeminal nerve), the dorsal tegmental nucleus of Gudden (DTG), the ventral cochlear nucleus (VCA), trapezoid nucleus (TZ), pontine raphe nucleus and the pontine reticular formation. These regions have been shown to be involved in mastication, bladder control, gastrointestinal function and in arousal. Given these projection sites and the functions associated with these sites, we suggest that HCRT may play a role in maintaining alertness and vigilance while the animal is engaged in consummatory behavior.

Thalamic distribution of zinc-rich terminal fields and neurons of origin in the rat.

Several cortico-cortical and limbic-related circuits are enriched in zinc, which is considered as an important modulator of glutamatergic transmission. While heavy metals have been detected in the thalamus, the specific presence of zinc has not been examined in this region. We have used two highly sensitive variations of the Timm method to study the zinc-rich innervation in the rat thalamus, which was compared to the distribution of acetylcholinesterase activity. The origin of some of these zinc-rich projections was also investigated by means of retrograde transport after intracerebral infusions of sodium selenium (Na2SeO3). The overall zinc staining in the thalamus was much lower than in the neocortex, striatum or basal forebrain; however, densely stained terminal fields were observed in the dorsal tip of the reticular thalamic nucleus, the anterodorsal and lateral dorsal thalamic nuclei and the zona incerta. In addition, moderately stained zinc-rich terminal fields were found in the rostral intralaminar nuclei, nucleus reuniens and lateral habenula. Intracerebral infusions of Na2SeO3 in the lateral dorsal nucleus resulted in retrogradely labeled neurons that were located in the postsubiculum, and also in the pre- and parasubiculum. These results are the first to establish the existence of a zinc-rich subicular-thalamic projection. Similar infusions in either the intralaminar nuclei or the zona incerta resulted in labeling of neurons in several brainstem structures related to the reticular formation. Our results provide morphological evidence for zinc modulation of glutamatergic inputs to highly selective thalamic nuclei, arising differentially from either cortical limbic areas or from brainstem ascending activation systems.

Aggregates of cAMP-dependent kinase RIalpha characterize a type of cholinergic neurons in the rat brain.

Acetylcholine is synthesized by different types of neurons, showing a distinct biochemical phenotype. Aggregates of RIalpha regulatory subunit of cAMP-dependent protein kinases are visualized by immunohistochemistry only in some cholinergic neurons, since they tightly colocalize with two different markers, choline acetyltransferase (ChAT) and vesicular acetylcholine transporter (VAChT). These neurons are present mainly in brain areas related to the limbic system. None of the other regulatory subunits of cAMP dependent kinases colocalize with cholinergic markers.

Serotonergic connections to the ventral oral pontine reticular nucleus: implication in paradoxical sleep modulation.

Cholinergic microstimulation of the ventral part of the oral pontine reticular nucleus (vRPO) in cats generates and maintains paradoxical sleep. The implication of rostral raphe nuclei in modulating the sleep-wakefulness cycle has been based on their serotonergic projections to the pontine structures responsible for the induction of paradoxical sleep. However, serotonergic neurons have also been described in brainstem structures other than the raphe nuclei. The aim of the present work is to trace the origin of the serotonergic afferents to the vRPO and to the locus coeruleus alpha and perilocus coeruleu alpha nuclei, closely related with different paradoxical sleep events. Anterograde and retrograde horseradish peroxidase conjugated with wheat germ agglutinin tracer injections in these nuclei in cats were combined with serotonin antiserum immunohistochemistry. Our results demonstrate that reciprocal connections linking the rostral raphe nuclei to those oral pontine nuclei are scarce. The percentage of double-labeled neurons after injections in the vRPO averaged 18% in rostral raphe nuclei, while a level of 82% was estimated in mesopontine tegmentum structures other than the raphe nuclei. These results showed that the main source of serotonin to the vRPO, implicated in generation and maintenance of paradoxical sleep, arises from these mesopontine tegmentum structures. This indicates that the serotonin modulation of paradoxical sleep could be the result of activation in non-raphe mesopontine tegmentum structures. The existence of a complicated network in the vRPO, which maintains a balance between different neurotransmitters responsible for the generation and alternance of paradoxical sleep episodes, is discussed.

Cholinergic projections to the visual thalamus and superior colliculus.

The parabrachial region of the brainstem reticular formation projects to the dorsal lateral geniculate nucleus of the thalamus and to the intermediate gray layer of the superior colliculus. We used the retrograde axonal transport of two fluorescent labels to demonstrate that individual parabrachial cells project to both structures. The results suggest that cholinergic cells of the parabrachial region may coordinate the relay of visuosensory information to the cortex with the onset of orienting movements.

Immunohistochemical evidence for the brevican-tenascin-R interaction: colocalization in perineuronal nets suggests a physiological role for the interaction in the adult rat brain.

Brevican is one of the most abundant chondroitin sulfate proteoglycans in the adult rat brain. We have recently shown that the C-type lectin domain of brevican binds fibronectin type III domains 3-5 of tenascin-R. Here we report strong evidence for a physiological basis for this interaction. Substantial brevican immunoreactivity was detected in a number of nuclei and in the reticular formations throughout the midbrain and hindbrain, including, but not limited to, the deep cerebellar nuclei, the trapezoid body, the red nucleus, the oculomotor nucleus, the vestibular nucleus, the cochlear nucleus, the gigantocellular reticular nucleus, the motor trigeminal nucleus, and the lateral superior olive. Most of the brevican immunoreactivity exhibited pericellular and reticular staining patterns. In almost all of these sites, brevican immunoreactivity colocalized with that of tenascin-R, which was also substantially codistributed with versican, another member of the lectican family. Detailed analysis revealed that the pericellular staining of brevican resembled that in perineuronal nets in which tenascin-R has been localized. Immunoelectron microscopy identified brevican immunoreactivity in the intercellular spaces surrounding presynaptic boutons and on their surfaces, but not in the synaptic clefts or in their immediate vicinity, a distribution pattern consistent with perineuronal nets. Taken together, our results provide strong evidence that the previously reported interactions between brevican and tenascin-R may play a functional role within the perineuronal nets.

Origins of the glycinergic inputs to the rat locus coeruleus and dorsal raphe nuclei: a study combining retrograde tracing with glycine immunohistochemistry.

The amino acid glycine is a major inhibitory neurotransmitter in the brainstem and is likely involved in the tonic inhibition of the monoaminergic neurons during all sleep-waking stages. In order to determine the neurons at the origin of the glycinergic innervation of the two principal monoaminergic nuclei, the locus coeruleus and the dorsal raphe of the rat, we applied a double-labelling technique, combining retrograde transport of cholera-toxin B subunit with glycine immunohistochemistry. Using this technique, we found that the locus coeruleus and dorsal raphe nuclei receive a common glycinergic innervation from the ventral and ventrolateral periaqueductal grey, including the adjacent deep mesencephalic reticular nucleus. Small additional glycinergic inputs to these nuclei originated from the lateral paragigantocellular nucleus and the rostral ventromedial medullary reticular formation. The potential role of these glycinergic inputs in the control of the excitability of the monoaminergic neurons of the locus coeruleus and dorsal raphe nuclei is discussed.

Prolactin-releasing peptide-immunoreactivity in A1 and A2 noradrenergic neurons of the rat medulla.

Distribution of prolactin-releasing peptide-like immunoreactivity (PrRP-LI) was investigated in the rat medulla with the use of a rabbit polyclonal antiserum against the human PrRP-31 peptide. PrRP-positive neurons were noted mainly in two areas of the caudal medulla: ventrolateral reticular formation and commissural nucleus of the nucleus of the solitary tract (NTS), corresponding to the A1 and A2 areas. PrRP-LI neurons were absent in the medulla rostral to the area postrema. Double-labeling the sections with PrRP antisera and tyrosine hydroxylase (TH) monoclonal antibodies revealed extensive colocalization of PrRP- and TH-like immunoreactivity (TH-LI) in neurons of the A1 and A2 areas. Our results show that PrRP-LI is expressed in a population of A1 and A2 noradrenergic neurons of the rat caudal medulla.

Modulation of the audiogenic seizure network by noradrenergic and glutamatergic receptors of the deep layers of superior colliculus.

Recent studies suggest that the deep layers of superior colliculus (DLSC) play a role in the network for audiogenic seizures (AGS) in genetically epilepsy-prone rats (GEPR-9s). The present study examined the role of glutamatergic and noradrenergic receptors in DLSC in modulation of AGS susceptibility. The study examined effects of a competitive NMDA receptor antagonist [dl-2-amino-7-phosphonoheptanoic acid (AP7)] or an alpha1 noradrenergic agonist (phenylephrine) focally microinjected into DLSC as compared to effects in the inferior colliculus (IC) and pontine reticular formation (PRF), which are major established components of the AGS network. The results demonstrated that blockade of NMDA receptors in DLSC suppressed AGS susceptibility. AP7 microinjection was effective at relatively low doses in IC, but required higher doses in DLSC and PRF. The DLSC was relatively more sensitive to seizure reduction by the alpha1 noradrenergic agonist as compared to the IC and PRF. The anticonvulsant effect of AP7 was longer-lasting than phenylephrine in the DLSC and IC but not in the PRF. These data suggest that neurons in the DLSC are a requisite component for the neuronal network for AGS in GEPR-9s and that NMDA and alpha1 adrenoreceptors in this site may play important roles in the modulation of AGS propagation. The relatively greater sensitivity of DLSC to phenylephrine as compared to IC and PRF indicates that norepinephrine may be more important in the modulation of AGS in DLSC, which contrasts to the role of glutamate modulation. These data support recent neuronal recording data, which indicate that DLSC neurons play a critical role in AGS.

The medullary dorsal reticular nucleus facilitates pain behaviour induced by formalin in the rat.

The influence of the dorsal reticular nucleus (DRt) on pain behaviour during the formalin test was studied in the rat by lesioning the nucleus through local application of electrical current or quinolinic acid. Animals in which the DRt was lesioned ipsilaterally to the paw injected with formalin spent less time in focused (licking, biting or scratching the injected paw) and total (focused pain behaviour plus protection of the injected paw during movements) pain behaviour, and showed paw-jerks less frequently than non-lesioned animals in both phases 1 and 2 of the test. Animals in which the DRt was lesioned contralaterally to the injected paw presented a decrease in total pain behaviour and number of paw-jerks only during phase 2. The number of superficial (laminae I-II) and deep (laminae III-VI) spinal dorsal horn cells expressing the c-fos proto-oncogene 2 h after subcutaneous injection of formalin was reduced by 34% and 50%, respectively, in animals with an ipsilateral DRt lesion as compared to non-lesioned rats. No differences in c-fos expression were observed after lesioning the DRt contralateral to the formalin injection. The results indicate that the DRt is involved in the facilitation of nociception during the formalin test by enhancing the response capacity of dorsal horn neurons to noxious stimulation. It is suggested that the pronociceptive action of the DRt is mediated by the reciprocal connections it establishes with the spinal dorsal horn.