Localization of the serotonergic terminal fields modulating seizures in the genetically epilepsy-prone rat.

Serotonin (5-HT) has been shown to exert antiepileptic effects in a variety of generalized convulsive seizure models, particularly the genetically epilepsy-prone rat (GEPR). The present study was designed to identify the region/site(s) where 5-HT exerts anticonvulsant effects in the GEPR-9, a model in which sound-evoked generalized tonic-clonic seizures (GTCS) are highly sensitive to manipulations in 5-HT concentration. Because the 5-HT reuptake inhibitor, fluoxetine, was known to exert anticonvulsant effects in GEPR-9s via a 5-HT-dependent mechanism, we utilized selective regional 5-HT depletion in combination with systemic fluoxetine administration to find the site where a 5-HT deficit would prevent the anticonvulsant action of fluoxetine. Widespread destruction of serotonergic terminal fields or regionally specific terminal field destruction was achieved using intracerebroventricular and more target specific infusions of 5,7-dihydroxytryptamine. The capacity of fluoxetine to suppress seizures in GEPR-9s following a loss of 5-HT was then examined. The present findings show the anticonvulsant action of fluoxetine is markedly attenuated following the loss of midbrain 5-HT, particularly in the region of the superior colliculus, while forebrain and spinal cord 5-HT do not appear to play a role in the action of fluoxetine. The importance of the deep layers of the SC was confirmed by demonstrating that direct microinfusion of fluoxetine into the SC can suppress seizures in rats pretreated with the 5-HT(1A) receptor antagonist pindolol.

Vagus nerve stimulation may protect GABAergic neurons following traumatic brain injury in rats: An immunocytochemical study.

Seizures and subclinical seizures occur following experimental brain injury in rats and may result from inhibitory neuron loss. This study numerically compares cortical and hippocampal glutamic acid decarboxylase (GAD) positive neurons between sham fluid percussion injury (FPI), FPI with sham Vagus Nerve Simulation (VNS), and FPI with chronic intermittent VNS initiated at 24 h post FPI in rats. Rats (n=8/group) were prepared for immunocytochemistry of GAD at 15 days post FPI. Serial sections were collected and GAD immunoreactive neurons were counted in the hippocampal hilus and two levels of the cerebral cortex. Numbers of quantifiable GAD cells in the rostral cerebral cortices were different between groups, both ipsilateral and contralateral to the FPI. Post hoc analysis of cell counts rostral to the ipsilateral epicenter, revealed a significant 26% reduction in the number of GAD cells/unit area of cerebral cortex following FPI. In the FPI-VNS group, this percentage loss was attenuated to only an 8.5% reduction, a value not significantly different from the sham group. In the contralateral side of the rostral cerebral cortex, FPI induced a significant 24% reduction in GAD cells/unit area; whereas, the VNS-treated rats showed no appreciable diminution of GAD cells rostral to the contralateral epicenter. Hippocampal analysis revealed a similar reduction of GAD cells in the FPI group; however, unlike the cortex this was not statistically significant. In the FPI-VNS group, a trend towards increased numbers of hilar GAD cells was observed, even over and above that of the sham FPI group; however, this was also not statistically significant. Together, these data suggest that VNS protects cortical GAD cells from death subsequent to FPI and may increase GAD cell counts in the hippocampal hilus of the injured brain.

Recovery of function after vagus nerve stimulation initiated 24 hours after fluid percussion brain injury.

Recent evidence from our laboratory demonstrated in laboratory rats that stimulation of the vagus nerve (VNS) initiated 2 h after lateral fluid percussion brain injury (FPI) accelerates the rate of recovery on a variety of behavioral and cognitive tests. VNS animals exhibited a level of performance comparable to that of sham-operated uninjured animals by the end of a 2-week testing period. The effectiveness of VNS was further evaluated in the present study in which initiation of stimulation was delayed until 24 h post-injury. Rats were subjected to a moderate FPI and tested on the beam walk, skilled forelimb reaching, locomotor placing, forelimb flexion and Morris water maze tasks for 2 weeks following injury. VNS (30 sec trains of 0.5 mA, 20.0-Hz biphasic pulses) was initiated 24 h post-injury and continued at 30-min intervals for the duration of the study, except for brief periods when the animals were detached for behavioral assessments. Consistent with our previous findings when stimulation was initiated 2 h post-injury, VNS animals showed significantly faster rates of recovery compared to controls. By the last day of testing (day 14 post-injury), the FPI-VNS animals were performing significantly better than the FPI-no-VNS animals and were not significantly different from shams in all motor and sensorimotor tasks. Performance in the Morris water maze indicated that the VNS animals acquired the task more rapidly on days 11-13 post-injury. On day 14, the FPI-VNS animals did not differ in the latency to find the platform from sham controls, whereas the injured controls did; however, the FPI-VNS animals and injured controls were not significantly different. Despite the lack of significant histological differences between the FPI groups, VNS, when initiated 24 h following injury, clearly attenuated the ensuing behavioral deficits and enhanced acquisition of the cognitive task. The results are discussed with respect to the norepinephrine hypothesis.

Increased extracellular concentrations of norepinephrine in cortex and hippocampus following vagus nerve stimulation in the rat.

The vagus nerve is an important source of afferent information about visceral states and it provides input to the locus coeruleus (LC), the major source of norepinephrine (NE) in the brain. It has been suggested that the effects of electrical stimulation of the vagus nerve on learning and memory, mood, seizure suppression, and recovery of function following brain damage are mediated, in part, by the release of brain NE. The hypothesis that left vagus nerve stimulation (VNS) at the cervical level results in increased extracellular NE concentrations in the cortex and hippocampus was tested at four stimulus intensities: 0.0, 0.25, 0.5, and 1.0 mA. Stimulation at 0.0 and 0.25 mA had no effect on NE concentrations, while the 0.5 mA stimulation increased NE concentrations significantly in the hippocampus (23%), but not the cortex. However, 1.0 mA stimulation significantly increased NE concentrations in both the cortex (39%) and hippocampus (28%) bilaterally. The increases in NE were transient and confined to the stimulation periods. VNS did not alter NE concentrations in either structure during the inter-stimulation baseline periods. No differences were observed between NE levels in the initial baseline and the post-stimulation baselines. These findings support the hypothesis that VNS increases extracellular NE concentrations in both the hippocampus and cortex.

Reeler homozygous mice exhibit enhanced susceptibility to epileptiform activity.

PURPOSE: Seizures are observed frequently in humans with diffuse neuronal migration disorders. The reeler mutant mouse also exhibits a diffuse disruption of migration, yet no pro-epileptic phenotype has been reported for this model. Whether this disparity reflects a phenotypic difference that can be used to delineate the mechanisms associated with increasing seizure susceptibility or reflects a paucity of knowledge is unclear. Consequently, this study examined whether seizure susceptibility is altered in reeler mutant mice. METHODS: In vivo (minimal electroshock delivered transcorneally) and in vitro techniques (field-potential recordings in neocortical and hippocampal brain slice preparations exposed to bicuculline methiodide) were used to determine whether the susceptibility to epileptiform activity is enhanced in reeler homozygous mice relative to controls. Adult (3-7 months) male reeler homozygotes (rl/rl) and controls (+/?) were identified based on their behavioral phenotype and were used in all experiments. RESULTS: Minimal electroshock revealed that rl/rl mice, compared with controls, exhibited a lower threshold for electroshock-induced seizures (4.5 +/- 0.52 vs. 6.7 +/- 0.35 mA), and a higher incidence of behavioral seizures (median seizure score, class 4 vs. class 0) when animals were subjected to a 5-mA electroshock stimulus. Additionally, neocortical and hippocampal slices from rl/rl mice were more likely to generate spontaneous epileptiform activity after bicuculline application, compared with controls, and the duration of the epileptiform events elicited in 10-30 muM bicuculline was longer in slices from rl/rl mice. CONCLUSIONS: These data demonstrate that rl/rl mice have enhanced seizure susceptibility that is in part intrinsic to the malformed neocortex and hippocampus. Thus in contrast to prior belief, most animal models of diffuse neuronal migration disorders do exhibit a pro-epileptic phenotype.

Electrical stimulation of the vagus nerve enhances cognitive and motor recovery following moderate fluid percussion injury in the rat.

Intermittent, chronically delivered electrical stimulation of the vagus nerve (VNS) is an FDA-approved procedure for the treatment of refractory complex/partial epilepsy in humans. Stimulation of the vagus has also been shown to enhance memory storage processes in laboratory rats and human subjects. Recent evidence suggests that some of these effects of VNS may be due to the activation of neurons in the nucleus locus coeruleus resulting in the release of norepinephrine (NE) throughout the neuraxis. Because antagonism of NE systems has been shown to delay recovery of function following brain damage, it is possible that enhanced release of NE in the CNS may facilitate recovery of function. To evaluate this hypothesis the lateral fluid percussion injury (LFP) model of traumatic brain injury was used and a variety of motor and cognitive behavioral tests were employed to assess recovery in pre-trained stimulated, control, and sham-injured laboratory rats. Two hours following moderate LFP, vagus nerve stimulation (30.0-sec trains of 0.5 mA, 20.0 Hz, biphasic pulses) was initiated. Stimulation continued in each animal's home cage at 30-min intervals for a period of 14 days, with the exception of brief periods when the animals were disconnected for behavioral assessments. Motor behaviors were evaluated every other day following LFP and tests included beam walk, locomotor placing, and skilled forelimb reaching. In each measure an enhanced rate of recovery and /or level of final performance was observed in the VNS-LFP animals compared to nonstimulated LFP controls. Behavior in the Morris water maze was assessed on days 11-14 following injury. Stimulated LFP animals showed significantly shorter latencies to find the hidden platform than did controls. Despite these behavioral effects, neurohistological examination did not reveal significant differences in lesion extent, density of fluorojade positive neurons, reactive astrocytes or numbers of spared neurons in the CA3 subarea of the hippocampus, at least at the one time point studied 15 days post-injury. These results support the idea that vagus nerve stimulation enhances the neural plasticity that underlies recovery of function following brain damage and provides indirect support for the hypothesis that enhanced NE release may mediate the effect. Importantly, since VNS facilitated both the rate of recovery and the extent of motor and cognitive recovery, these findings suggest that electrical stimulation of the vagus nerve may prove to be an effective non-pharmacological treatment for traumatic brain injury.

The serotonergic and noradrenergic effects of antidepressant drugs are anticonvulsant, not proconvulsant.

Contrary to existing evidence, convulsant liability of the antidepressants has been attributed to noradrenergic and serotonergic increments. This is a classic case of confusing treatment effects with the manifestations of illness. In fact, the remarkable anticonvulsant effectiveness of antidepressant-induced noradrenergic and serotonergic activation has been ignored. Some antidepressant drugs such as the specific serotonin reuptake inhibitor (SSRI) fluoxetine may be devoid of convulsant liability entirely, while having distinct anticonvulsant properties. Some authorities advance the notion that the seizure predisposition of patients with epilepsy increases risks for antidepressant-induced seizures. However, evidence does not support this contention. Instead, data increasingly support the concept that noradrenergic and serotonergic deficiencies contribute to seizure predisposition. Indeed, the antidepressants have the potential to overcome seizure predisposition in epilepsy. Whereas therapeutic doses of antidepressants elevate noradrenergic and serotonergic transmission, larger doses can activate other biological processes that may be convulsant.

Brainstem seizure severity regulates forebrain seizure expression in the audiogenic kindling model.

PURPOSE: Although sound-induced (audiogenic) seizures in the genetically epilepsy-prone rat (GEPR) initially occur independent of the forebrain, repeated audiogenic seizures recruit forebrain seizure circuits in a process referred to as audiogenic kindling. In GEPR-3s, audiogenic kindling results in facial and forelimb (F&F) clonic seizures that are typical of forebrain seizures. However, in GEPR-9s, audiogenic kindling produces posttonic all-limb clonus not usually observed during forebrain seizures. We hypothesized that the more severe brainstem seizures of the GEPR-9 prevent the expression of F&F clonic seizures during audiogenic kindling. Therefore attenuation of audiogenic seizures during audiogenic kindling in GEPR-9s should allow F&F clonic seizures to be expressed. Likewise, intensifying audiogenic seizure severity in GEPR-3s should inhibit audiogenically kindled F&F clonic seizures. We have tested this hypothesis in the present study. METHODS: Lesions of the superior colliculus or treatment with low-dose phenytoin were used to suppress audiogenic seizure severity in GEPR-9s. Depletion of brain serotonin was used to increase the seizure severity in GEPR-3s. All GEPRs were then subjected to audiogenic kindling. Behavioral and electrographic seizures were assessed. RESULTS: Suppression of audiogenic seizure severity during audiogenic kindling in GEPR-9s increased the incidence forebrain seizure behavior. Kindled GEPR-9s that continued to display full tonic seizures did not exhibit forebrain convulsions, but did show posttonic clonus and forebrain seizure activity in the EEG. GEPR-3s chronically depleted of brain serotonin, along with displaying tonic brainstem seizures, tended to display less severe forebrain seizures during audiogenic kindling. CONCLUSIONS: These findings support the concept that severe brainstem seizures prevent the behavioral expression of forebrain seizures in audiogenically kindled GEPR-9s. It appears that the severe brainstem seizure of the GEPR-9 does not allow the forebrain seizure to manifest its typical behavioral concomitants despite electrographic evidence that spike-wave discharge is occurring in the forebrain.

Weaving basic and social sciences into a case-based, clinically oriented medical curriculum: one school's approach.

Southern Illinois University School of Medicine recently completed its fourth year of a resource-session-enhanced, case-based, tutor-group-oriented curriculum. As an example of a curricular unit, the authors describe the implementation of the basic and clinical sciences in one of the four units in year one, and detail that unit's organization, logistics, content, rationale, and other characteristics. The Sensorimotor Systems and Behavior (SSB) unit is preceded by a cardio-respiratory-renal unit and is followed by an endocrine-reproductive-gastrointestinal unit. A Doctoring unit temporally spans each of these three units. The SSB unit is allotted an 11.5-week period that includes an aggregate of 2.5 weeks of available clinical time, 1.5 weeks for examinations and exam study time, and approximately 8.5 weeks for tutor-group sessions, mandatory laboratory sessions, and self-directed learning. Optional resource sessions are offered during a two- to four-hour block on a single morning each week. Clinical training in the SSB unit augments self-directed, laboratory, and tutor-group learning of neuroscience, gross anatomy, cell biology, physiology, biochemistry, behavioral and social science, embryology, limited pharmacology and genetics, and basic clinical neurology for first-year students. Although it is fast-paced and places heavy responsibility for independent learning on the students, the SSB unit culminates in significant achievement in the basic and clinical sciences. The unit provides substantial clinical training and practical experience in physical and neurological examinations that directly integrate with basic science knowledge. The unit reduces lecture-based instruction, demands self-determination, and promotes experience in team effort, professionalism, peer interaction, empathy in clinical medicine, and practical use of basic science knowledge.

Platelet monoamine oxidase B activity changes across 31 days of smoking abstinence.

Although recent studies demonstrate that tobacco cigarette smoke substantially inhibits both central nervous system and blood platelet monoamine oxidase (MAO) activity, little is known about the time course of MAO increases after smoking cessation. Therefore, changes in platelet MAO-B activity and mood were assessed before and at multiple times after quitting smoking. Quitting smoking was associated with a significant (22%) increase in MAO activity by day 3 and with a maximum increase (about 50%) by day 10 that was maintained through day 31 of abstinence. However, abstinence-related increases in depressive mood peaked at day 2 of abstinence, a week more rapidly than the peak increase in MAO-B activity. Neither mood nor MAO-B activity returned to baseline or smoking control levels across the 31-day abstinence period. The asynchrony of increased negative affect and MAO-B activity during the first few days of abstinence may reflect any of several possibilities. First, the duration of the platelet life cycle may not reflect central MAO-B or MAO-A activity. Second, MAO-B may not contribute to or index mood changes during the first days of abstinence though it may contribute to protracted abstinence-induced negative affect. These findings are discussed in terms of the hypothesis that platelet MAO activity reflects central nervous system MAO changes that promote increased depressive affect resulting from smoking abstinence.

Role of the superior colliculus and the intercollicular nucleus in the brainstem seizure circuitry of the genetically epilepsy-prone rat.

PURPOSE: The neuronal network responsible for the convulsive behavior associated with sound-induced seizures in genetically epilepsy-prone rats (GEPRs) is believed to include the inferior colliculus and other brainstem structures such as the deep layers of the superior colliculus (DLSC), periaqueductal gray, and pontine reticular formation. However, previous studies also suggested that the DLSC and the nearby intercollicular nucleus (ICN) are part of a midbrain anticonvulsant zone capable of suppressing tonic convulsions when activated with bicuculline. Our aim in this study was to investigate the role of the superior colliculus (SC) and the ICN in generalized tonic-clonic seizures (GTCSs). METHODS: Bilateral lesions of the SC and the ICN as well as bicuculline infusions into the ICN were used to assess the role of this dorsal midbrain region in brainstem seizures induced by sound stimulation in GEPR-9s and GEPR-3s. RESULTS: Lesions of the SC markedly attenuated audiogenic seizure (AGS) severity by abolishing all behavioral components except the wild running. Lesions of the ICN significantly reduced seizure severity in GEPR-9s, but were somewhat less effective than SC lesions. Bicuculline infusion into the deep layers of the SC and/or the ICN produced audiogenic-like seizures in GEPR-9s. CONCLUSIONS: These findings support the hypothesis that the SC and ICN are important components of the brainstem seizure network, but suggest they are not necessary for the wild-running component of the seizure. The results further indicate that stimulation of the tectum facilitates GTCSs. Thus these findings suggest that the dorsal midbrain, when stimulated, is proconvulsant rather than anticonvulsant regarding brainstem seizures in GEPRs.