Prelimbic cortex extracellular signal-regulated kinase 1/2 activation is required for memory retrieval of long-term inhibitory avoidance.

Neural mechanism underlying memory retrieval has been extensively studied in the hippocampus and amygdala. However, little is known about the role of medial prefrontal cortex in long-term memory retrieval. We evaluate this issue in one-trial step-through inhibitory avoidance (IA) paradigm. Our results showed that, 1) inactivation of mPFC by local infusion of GABAA-receptor agonist muscimol caused severe deficits in retrieval of 1-day and 7-day but had no effects on 2-h inhibitory avoidance memory; 2) the protein level of phosphorylated-ERK1/2 in mPFC were significantly increased following retrieval of 1-day and 7-day IA memory, so did the numbers of phosphorylated-ERK (pERK) and phosphorylated-CREB (pCREB) labeled neurons; 3) intra-mPFC infusion of ERK kinase inhibitor PD98095 significantly reduced phosphorylated ERK1/2 levels and phosphorylated-ERK1/2 and phosphorylated-CREB labeled cells, and severely impaired retrieval of 7-day IA memory when the drugs were administrated 30min prior to test. The present study provides evidence that retrieval of long-lasting memory for inhibitory avoidance requires mPFC and involves the ERK-CREB signaling cascade.

Role of GABAA receptor in modulation of acute thermal pain using a rat model of cholestasis.

Increased activity of the endogenous opioid system in cholestasis results in analgesia. GABAA receptors have been ascribed both pronociceptive and antinociceptive roles in pain modulation. Considering the elevated endogenous opioid tone in cholestasis and the existence of close interaction between the GABAergic and opioidergic systems in pain control, the involvement of GABAA receptors in modulation of nociception in a model of elevated endogenous opioid tone, cholestasis, was investigated using muscimol and bicuculline as selective GABAA receptor agonist and antagonist respectively. Cholestasis was induced by ligation of the main bile duct using two ligatures and transsection of the duct between them. Cholestatic rats had increased tail-flick latencies (TFLs) compared to non-cholestatic rats. Administration of muscimol (0.2 and 0.4 mg/kg, s.c.) and bicuculline (0.5 and 1mg/kg, s.c.) to the cholestatic groups significantly increased and decreased respectively TFLs compared to the saline treated cholestatic group. Muscimol antinociception in cholestatic animals was attenuated by co-administration of naloxone or bicuculline. Furthermore, the combination of bicuculline and naloxone completely reversed the increased TFLs of cholestatic rats back to the level of unoperated animals. Muscimol and bicuculline injections into non-cholestatic animals did not alter TFLs. At the doses used here, none of the drugs impaired motor coordination, as revealed by the rotarod test. This study shows the involvement of GABAA receptors in pain modulation during cholestasis in rats.

Fungal hallucinogens psilocin, ibotenic acid, and muscimol: analytical methods and biologic activities.

Psychoactive drugs of fungal origin, psilocin, ibotenic acid, and muscimol among them have been proposed for recreational use and popularized since the 1960s, XX century. Despite their well-documented neurotoxicity, they reached reputation of being safe and nonaddictive. Scientific efforts to find any medical application for these hallucinogens in psychiatry, psychotherapy, and even for religious rituals support are highly controversial. Even if they show any healing potential, their usage in psychotherapy is in some cases inadequate and may additionally harm seriously suffering patients. Hallucinogens are thought to reduce cognitive functions. However, in case of indolealkylamines, such as psilocin, some recent findings suggest their ability to improve perception and mental skills, what would motivate the consumption of "magic mushrooms." The present article offers an opportunity to find out what are the main symptoms of intoxication with mushrooms containing psilocybin/psilocin, muscimol, and ibotenic acid. The progress in analytical methods for detection of them in fungal material, food, and body fluids is reviewed. Findings on the mechanisms of their biologic activity are summarized. Additionally, therapeutic potential of these fungal psychoactive compounds and health risk associated with their abuse are discussed.

The medial prefrontal cortex is critical for memory retrieval and resolving interference.

The prefrontal cortex (PFC) is known to be critically involved in strategy switching, attentional set shifting, and inhibition of prepotent responses. A central feature of this kind of behavioral flexibility is the ability to resolve conflicting response tendencies, suggesting a general role of the PFC in resolving interference. If so, the PFC should also be involved in memory retrieval, which involves competition between potential retrieval targets. Moreover, the PFC should be needed whenever interference is high, regardless of the strategic or attentional requirements of the task. To test this hypothesis, we temporarily inactivated the mPFC with muscimol and tested rats on several olfactory learning tasks. Rats given muscimol were able to learn a few discrimination problems when they were learned one at a time. However, they were severely impaired when they had to learn and remember many odors concurrently. Rats given muscimol also suffered greater interference when learning two lists of conflicting odor discrimination problems. Additionally, temporary mPFC inactivation during the acquisition of one set of odor memories actually improved the ability to learn a new set of conflicting odor memories. This paradoxical release from interference suggests that the mPFC plays an important role in acquiring and promoting the long term retrieval of memories. These results suggest that the mPFC plays a general role in resolving interference and that this is a key aspect of behavioral flexibility.

Inactivation of the parietal reach region causes optic ataxia, impairing reaches but not saccades.

Lesions in human posterior parietal cortex can cause optic ataxia (OA), in which reaches but not saccades to visual objects are impaired, suggesting separate visuomotor pathways for the two effectors. In monkeys, one potentially crucial area for reach control is the parietal reach region (PRR), in which neurons respond preferentially during reach planning as compared to saccade planning. However, direct causal evidence linking the monkey PRR to the deficits observed in OA is missing. We thus inactivated part of the macaque PRR, in the medial wall of the intraparietal sulcus, and produced the hallmarks of OA, misreaching for peripheral targets but unimpaired saccades. Furthermore, reach errors were larger for the targets preferred by the neural population local to the injection site. These results demonstrate that PRR is causally involved in reach-specific visuomotor pathways, and reach goal disruption in PRR can be a neural basis of OA.

Long-term behavioral, electrophysiological, and neurochemical monitoring of the safety of an experimental antiepileptic implant, the muscimol-delivering Subdural Pharmacotherapy Device in monkeys.

OBJECT: The authors evaluated the extent to which the Subdural Pharmacotherapy Device (SPD), chronically implanted over the frontal cortex to perform periodic, localized muscimol-delivery/CSF removal cycles, affects overall behavior, motor performance, electroencephalography (EEG) activity, and blood and CSF neurochemistry in macaque monkeys. METHODS: Two monkeys were used to adjust methodology and 4 monkeys were subjected to comprehensive testing. Prior to surgery, the animals' behavior in a large test chamber was monitored, and the motor skills required to remove food pellets from food ports located on the walls of the chamber were determined. The monkeys underwent implantation of the subdural and extracranial SPD units. The subdural unit, a silicone strip integrating EEG electrodes and fluid-exchange ports, was positioned over the right frontal cortex. The control unit included a battery-powered, microprocessor-regulated dual minipump and radiofrequency module secured to the cranium. After implantation, the SPD automatically performed periodic saline or muscimol (1.0 mM) deliveries at 12-hour intervals, alternating with local CSF removals at 6-hour intervals. The antiepileptic efficacy of this muscimol concentration was verified by demonstrating its ability to prevent focal acetylcholine-induced seizures. During SPD treatment, the monkeys' behavior and motor performance were again monitored, and the power spectrum of their radiofrequency-transmitted EEG recordings was analyzed. Serum and CSF muscimol levels were measured with high-performance liquid chromatography electrochemical detection, and CSF protein levels were measured with turbidimetry. RESULTS: The SPD was well tolerated in all monkeys for up to 11 months. The behavioral study revealed that during both saline and muscimol SPD treatment, the monkeys could achieve the maximum motor performance of 40 food-pellet removals per session, as before surgery. The EEG study showed that local EEG power spectra were not affected by muscimol treatment with SPD. The neurochemical study demonstrated that the administration of 1.0 mM muscimol into the neocortical subarachnoid space led to no detectable levels of this compound in the blood and cisternal CSF, as measured 1-125 minutes after delivery. Total protein levels were within the normal range in the cisternal CSF, but protein levels in the cortical-site CSF were significantly higher than normal: 361 ± 81.6 mg/dl. Abrupt discontinuation of 3-month, periodic, subdural muscimol treatments induced withdrawal seizures, which could be completely prevented by gradually tapering off the subdural muscimol concentration from 1.0 mM to 0.12-0.03 mM over a period of 2 weeks. The monkeys' general health and weight were maintained. Infection occurred only in one monkey 9 months after surgery. CONCLUSIONS: Long-term, periodic, transmeningeal muscimol delivery with the SPD is essentially a safe procedure. If further improved and successfully adapted for use in humans, the SPD can be used for the treatment of intractable focal neocortical epilepsy affecting approximately 150,000 patients in the US.

Inactivation of the left auditory cortex impairs temporal discrimination in the rat.

The left auditory cortex (AC) in humans is involved in the processing of the temporal parameters of acoustical signals, specifically in speech perception, whereas the right AC plays the dominant role in pitch and melody perception. The hemispheric lateralization of acoustical signal processing in non-human mammals is less explored. The present study examined the ability of rats to detect or discriminate a series of gaps in continuous noise under conditions of unilateral or bilateral reversible inactivation of the AC. The results showed that muscimol-induced reversible inactivation of the left AC suppresses the ability of rats to discriminate between acoustical stimuli of different temporal parameters (duration or repetition rate), whereas inactivation of the right AC results in no change or only a mild decrease in discrimination ability. Hemispheric asymmetry was observed only in the case of gap discrimination tasks, but not in a gap detection task. Our findings demonstrate that, similarly as in humans, the left AC in the rat plays the dominant role in temporal discrimination. These data provide further evidence for the functional asymmetry of the mammalian brain, which appears in a relatively early phase of evolution.

Roles of perirhinal and posterior piriform cortices in control and generation of seizures: a microinfusion study in rats exposed to soman.

Identification of critical receptors in seizure controlling brain regions may facilitate the development of more efficacious pharmacological therapies against nerve agent intoxication. In the present study, a number of drugs with anticonvulsant potency were microinfused into the perirhinal cortex (PRC) or posterior piriform cortex (PPC) in rats. The drugs used exert cholinergic antagonism (scopolamine), glutamatergic antagonism (ketamine, NBQX), both cholinergic and glutamatergic antagonism (procyclidine, caramiphen), or GABAergic agonism (muscimol). The results showed that in the PRC anticonvulsant efficacy against soman-induced seizures (subcutaneously administered) was achieved by procyclidine or NBQX, but not by ketamine, scopolamine, caramiphen, or muscimol (Experiment 1). Hence, both muscarinic and glutamatergic NMDA receptors had to be antagonized simultaneously or AMPA receptors alone, suggesting increased glutamatergic activation in the PRC before onset of seizures. In the PPC, anticonvulsant effects were assured by scopolamine or muscimol, but not by procyclidine, caramiphen, NBQX, or ketamine (Experiment 2). Thus, muscarinic and GABA(A) receptors appear to be the critical ones in the PPC. Microinfusion of soman into the PRC or PPC resulted in sustained seizure activity in the majority of the rats of both infusion categories. The rhinal structures encompassed in this study apparently have critical functions as both control and trigger sites for nerve agent-evoked seizures.

Inactivation of the infralimbic but not the prelimbic cortex impairs consolidation and retrieval of fear extinction.

Rats were subjected to one or two cycles of context fear conditioning and extinction to study the roles of the prelimbic cortex (PL) and infralimbic cortex (IL) in learning and relearning to inhibit fear responses. Inactivation of the PL depressed fear responses across the first or second extinction but did not impair learning or relearning fear inhibition (experiment 1). Inactivation of the IL did not affect inhibition across the first extinction but disrupted its long-term retention. Inactivation of the IL impaired inhibition across the second extinction, and inactivation before or after this extinction impaired long-term retention (experiments 2 and 3). Inactivation of the IL before the retention test restored extinguished fear responses (experiment 4). These results show for the first time that neuronal activity in the PL is involved in the expression of fear responses but not in the learning that underlies long-term fear inhibition. They also confirm that the IL is involved in this inhibitory learning: Specifically, they show that the IL is critical for consolidation and retrieval of this inhibitory learning. The role of the IL is discussed in terms of a contemporary neural model of fear extinction.

Dysfunction of the subthalamic nucleus induces behavioral and movement disorders in monkeys.

High-frequency stimulation of the subthalamic nucleus (STN) in parkinsonian patients is reported to induce psychiatric effects. The likely explanation for these effects is the partitioning of the STN into sensorimotor, associative, and limbic anatomo-functional territories. Thus, a specific neuronal dysfunction of the STN sensorimotor territory could lead to abnormal movements, whereas a dysfunction of the associative or limbic territory could lead to behavioral disturbances. To test this hypothesis, neuronal dysfunction of the STN was induced by microinjections of the GABA agonist muscimol, or antagonist bicucculline, in various parts of the nucleus in three monkeys. Stereotyped behaviors (licking and biting fingers) and/or violent hyperactivity were obtained with bicuculline injected into the anteromedial, associative, and limbic territories, whereas injections of muscimol induced no major effects. Abnormal limb movements (contralateral ballism) were obtained after muscimol or bicuculline injections into the posterolateral, sensorimotor territory. Control injections localized around the STN induced other effects (mainly torticollis), which underlines the specificity of STN injection effects. Our study supports the hypothesis that the anteromedial part of the STN is involved in behavioral control.

Hippocampal infusions of glucose reverse memory deficits produced by co-infusions of a GABA receptor agonist.

Although septal infusions of glucose typically have positive effects on memory, we have shown repeatedly that this treatment exacerbates memory deficits produced by co-infusions of gamma-aminobutyric acid (GABA) receptor agonists. The present experiments tested whether this negative interaction between glucose and GABA in the medial septum would be observed in the hippocampus, a brain region where glucose typically has positive effects on memory. Specifically, we determined whether hippocampal infusions of glucose would reverse or exacerbate memory deficits produced by hippocampal co-infusions of the GABA receptor agonist muscimol. Fifteen minutes prior to either assessing spontaneous alternation (SA) or continuous multiple trial inhibitory avoidance (CMIA) training, male Sprague-Dawley-derived rats were given bilateral hippocampal infusions of vehicle (phosphate-buffered saline [PBS], 1 microl/2 min), glucose (33 or 50 nmol), muscimol (0.3 or 0.4 microg, SA or 3 microg, CMIA) or muscimol and glucose combined in one solution. The results indicated that hippocampal infusions of muscimol alone decreased SA scores and CMIA retention latencies. More importantly, hippocampal infusions of glucose, at doses that had no effect when infused alone, attenuated (33 nmol) or reversed (50 nmol) the muscimol-induced memory deficits. Thus, although co-infusions of glucose with muscimol into the medial septum impair memory, the present findings show that an opposite effect is observed in the hippocampus. Collectively, these findings suggest that the memory-impairing interaction between glucose and GABA in the medial septum is not a general property of the brain, but rather is brain region-dependent.

Retrograde amnesia induced by drugs acting on different molecular systems.

The gamma aminobutyric acid-A (GABA-sub(A)) agonist, muscimol, the glutamate N-methyl-D-aspartate (NMDA) receptor antagonist, D-2-amino-5-phosphonopentanoic acid (AP5), and the inhibitor of the extracellularly regulated kinases (ERKs), UO 126, cause retrograde amnesia when administered to the hippocampus. In the present study, the authors found that they all cause retrograde amnesia for 1-trial inhibitory avoidance, not only when infused into the dorsal CA1 region of the hippocampus, but also when infused into the basolateral amygdala or the entorhinal, parietal, and posterior cingulate cortices. The posttraining time course of the effect of each drug was, however, quite different across brain structures. Thus, in all of them, NMDA receptors and the ERK pathway are indispensable for memory consolidation, and GABA-sub(A) receptor activation inhibits memory consolidation: but in each case, their influence is interwoven differently.

Sex differences and hormonal effects in a model of preterm infant brain injury.

Premature infants are at an exceptionally high risk for brain injury, with damage resulting in permanent behavioral deficits. A contributing factor to the severity of brain injury is gender, with males more sensitive to insult than females. The role of gender and early hormonal environment in addressed in our novel model of prenatal brain damage.

The effect of GABA receptor ligands in experimental spina bifida occulta.

BACKGROUND: The pathophysiology behind spina bifida and other neural tube defects (NTDs) is unclear. Folic acid is one variable, but other factors remain. Studies suggest that substances active at the GABA receptor may produce NTDs. To test this hypothesis pregnant rats were exposed to either the GABA a agonist muscimol (1, 2 or 4 mg/kg), the GABA a antagonist bicuculline (.5, 1, or 2 mg/kg), the GABA b agonist baclofen (15, 30, 60 mg/kg), or the GABA b antagonist hydroxysaclofen (1, 3, or 5 mg/kg) during neural tube formation. Normal saline was used as a control and valproic acid (600 mg/kg) as a positive control. The embryos were analyzed for the presence of a spina bifida like NTD. RESULTS: After drug administration the pregnancies were allowed to proceed to the 21st day of gestation. Then embryos were removed and skeletons staining and cleared. Vertebral arch closure was measured. Results indicate that the GABAa receptor agonist muscimol, the GABAa receptor antagonist bicuculline, and the GABAb agonist baclofen produced NTDs characterized by widening of the vertebral arch. Oppositely the GABAb antagonist hydroxysaclofen produced narrowing of the vertebral arches. CONCLUSIONS: The findings indicate that GABA a or b ligands are capable of altering neural formation. GABA may play a greater than appreciated role in neural tube formation and may be important in NTDs. The narrowing of the vertebral arch produced by the GABA b antagonist hydroxysalcofen suggests that GABA b receptor may play an undefined role in neural tube closure that differs from the GABA a receptor.

Vestibular influence on the binocular control of vertical-torsional nystagmus after lesions in the interstitial nucleus of Cajal.

The interstitial nucleus of Cajal (iC) is a center of the velocity-to-position integration for vertical and torsional eye movements. In addition, iC has projections to and from the vestibular nuclei. Therefore the vestibular influence on the binocular alignment of vertical-torsional nystagmus after unilateral reversible iC inactivations was investigated in the alert monkey using 3D binocular search-coil recordings. The nystagmus was compared with the eye muscle rotation axes, which were corrected for the tonic ocular torsion elicited by the iC inactivation. Rotation axes of nystagmus were different for both eyes and revealed a co-activation of eye muscles similar to the effects of electrical stimulation of the anterior canal nerve. This suggests that, in addition to the deficient neural integrator, a vestibular imbalance contributes to the vertical-torsional nystagmus after iC inactivations.

[Antinociceptive effects of intrathecally administered GABA agonists at the spinal cord level].

The present study was designed to investigate antinociceptive effect of GABA agonists regarding visceral as well as somatic noxious stimuli. Following the approval by the institutional animal care committee, an intrathecal catheter was implanted in the subarachnoid space at the L 4/5 level in male Sprague-Dawley rats. The tail flick (TF) test and the colorectal distension test (CD) were used to measure responses to somatic and visceral stimuli, respectively. Threshold in TF test and CD test were measured at 5, 10, 15, 20, 30, 60, 90, 120 and 180 min after the intrathecal injection of 0.1, 1, 5, 20 micrograms of muscimol, 0.01, 0.1, 0.3, 1 microgram of baclofen or normal saline. Percent of maximum possible effect (%MPE) and %area under the curve (%AUC) were calculated by transforming response threshold in TF and CD tests. Repeated measure ANOVA followed by Fisher's PLSD test were used for statistical analysis. Muscimol 0.1 microgram increased mean %MPE in TF test at 10 min to 15% but not in CD test. Muscimol 1, 5 and 20 micrograms significantly increased %MPE at 5 min in TF and CD tests. Muscimol 20 micrograms produced 100%MPE for 180 min after drug injection. Baclofen 0.1, 0.3 and 1 microgram significantly increased %MPE at 5 min in TF and CD test. Antinociceptive effect in TF test seems to be greater than that in CD test. Muscimol caused motor disturbance but baclofen did not. It is concluded that intrathecally administered muscimol and baclofen produced somatic and visceral antinociception in a dose dependent fashion.

Activation of GABAA but not GABAB receptors in the NTSblocked bradycardia of chemoreflex in awake rats.

In the present study we analyzed effects of bilateral microinjections of muscimol (a GABAA agonist) and baclofen (a GABAB agonist) into the nucleus tractus solitarius (NTS) on bradycardic and pressor responses to chemoreflex activation (potassium cyanide, 40 micrograms/rat iv) in awake rats. Bilateral microinjections of muscimol (25 and 50 pmol/50 nl) into the NTS increased baseline mean arterial pressure (MAP): 119 +/- 8 vs. 107 +/- 2 mmHg (n = 6) and 121 +/- 8 vs. 103 +/- 3 mmHg (n = 6), respectively. Muscimol at 25 pmol/50 nl reduced the bradycardic response to chemoreflex activation 5 min after microinjection; with 50 pmol/50 nl the bradycardic response to chemoreflex activation was reduced 5, 15, 30, and 60 min after microinjection. Neither muscimol dose produced an effect on the pressor response of the chemoreflex. Effects of muscimol (50 pmol/50 nl) on basal MAP and on the bradycardic response of the chemoreflex were prevented by prior microinjection of bicuculline (a GABAA antagonist, 40 pmol/50 nl) into the NTS. Bilateral microinjections of baclofen (12.5 and 25 pmol/50 nl) into the NTS produced an increase in baseline MAP [137 +/- 9 vs. 108 +/- 4 (n = 7) and 145 +/- 5 vs. 105 +/- 2 mmHg (n = 7), respectively], no changes in basal heart rate, and no effects on the bradycardic response; 25 pmol/50 nl only attenuated the pressor response to chemoreflex activation. The data show that activation of GABAA receptors in the NTS produces a significant reduction in the bradycardic response, whereas activation of GABAB receptors produces a significant reduction in the pressor response of the chemoreflex. We conclude that 1) GABAA but not GABAB plays an inhibitory role in neurons of the lateral commissural NTS involved in the parasympathetic component of the chemoreflex and 2) attenuation of the pressor response of the chemoreflex by activation of GABAB receptors may be due to inhibition of sympathoexcitatory neurons in the NTS or may be secondary to the large increase in baseline MAP produced by baclofen.

Muscimol induces retrograde amnesia for changes in reward magnitude.

These experiments examined the effect of the GABAA agonist, muscimol (MUS), on memory for changes in reward magnitude. In Experiment 1 rats were trained to run a straight alley for either a large or small food reward. After reaching asymptotic performance rats in the high reward group were shifted to the small food reward. Half the animals received 1.0 or 3.0 mg/kg (ip) of MUS or the equivalent volume of saline immediately after training. Shifted training continued for 3 more days and no further injections were given. Shifted saline animals displayed an increase in response latencies compared to unshifted controls with a sharp peak on the day after the shift. Shifted MUS receiving 1.0 mg/kg performed comparably to shifted saline animals. In contrast, Shifted MUS animals receiving 3.0 mg/kg displayed performance comparable to shifted saline animals on the day of the shift but displayed a sharp increase in response latencies on the second day after the shift. These findings indicate that post-training systemic MUS injections delay the peak increase in response latencies and suggest that MUS induces retrograde amnesia for reward reduction. Experiment 2 examined the effect of MUS on the memory of a reward increase. Rats were first trained as in Experiment 1 and rats under the high reward condition were then shifted to the small reward. On the next training session, the large food reward was reinstated.(ABSTRACT TRUNCATED AT 250 WORDS)

Symptomatic treatment of tardive dyskinesia: a word of caution.

The search for a treatment of tardive dyskinesia (TD) has focused largely on cholinergic and GABAergic agents that are believed to attenuate striatal imbalances and bring about symptomatic control of dyskinetic movements. While numerous reports of the partial effectiveness of acute treatment with cholinergic or GABAergic agents have appeared, the effects of chronic administration of these substance are unclear. Results of chronic administration of cholinergic or GABAergic agents to animals are presented, and it is argued that these substances have the potential of eventually worsening TD. Alternative approaches aimed at modifying the theorized pathophysiology of TD, as opposed to symptom control methods, are presented.