Basolateral Amygdala Kindling Research Articles

Modification of post-traumatic epilepsy by fecal microbiota transfer

It has been well established that traumatic brain injury (TBI) modifies the composition of gut microbiome. Epilepsy, which represents one of the common sequelae of TBI, has been associated with dysbiosis. Earlier study showed that the risk of post-traumatic epilepsy (PTE) after lateral fluid percussion injury (LFPI) in rats can be stratified based on pre-existing (i.e., pre-TBI) gut microbiome profile. In the present study, we examined whether fecal microbiota transfer (FMT) from naïve rats with different prospective histories of PTE would affect the trajectory of PTE in recipients. Fecal samples were collected from naïve adult male Sprague–Dawley rats, followed by LFPI. Seven months later, upon four weeks of vide-EEG monitoring (vEEG), the rats were categorized as those with and without PTE. Recipients were subjected to LFPI, followed by FMT from donors with and without impending PTE. Control groups included auto-FMT and no-FMT subjects. Seven month after LFPI, recipients underwent four-week vEEG to detect spontaneous seizures. After completing vEEG, rats of all groups underwent kindling of basolateral amygdala. Fecal microbiota transfer from donors with impending PTE exerted mild-to-moderate pro-epileptic effects in recipients, evident as marginal increase in multiple spontaneous seizure incidence, and facilitation of kindling. Analysis of fecal samples in selected recipients and their respective donors confirmed that FMT modified microbiota in recipients along the donors’ lines, albeit without full microbiome conversion. The findings provide further evidence that gut microbiome may actively modulate the susceptibility to epilepsy.

Diversity of kindling of limbic seizures after lateral fluid percussion injury in the rat.

Lateral fluid percussion injury (LFPI) in rats is used to model post‐traumatic epilepsy (PTE), with spontaneous seizures occurring in up to ½ of the subjects. Using the kindling paradigm, we examined whether animals without detectable seizures had an altered seizure susceptibility. Male Sprague Dawley rats were subjected to LFPI. Seven‐nine months later, spontaneous seizures were monitored for two weeks. Afterward, the animals underwent kindling of basolateral amygdala. For kindling outcomes, the animals were categorized based on the 95% confidence intervals of mean number trials to kindling (ie 3 consecutive stage 4‐5 seizures). Spontaneous seizures were detected in 7 out of 24 rats. There was no correlation between the severity of LFPI and either baseline afterdischarge properties, or kindling rates. Six LFPI rats kindled at a rate comparable to those in sham‐LFPI (n = 10) and in naïve (n = 7) subjects. Ten LFPI rats kindled faster and 8—slower than controls. None of slow‐kindling rats had spontaneous seizures during the prekindling monitoring. During the same period, six fast‐kindling and three normal‐kindling rats had been seizure‐free. Thus, kindling reveals a diversity to seizure susceptibility after LFPI beyond an overt seizure symptomatology, ranging from the increased susceptibility to the increased resistance.

Preparation, Antiepileptic Activity, and Cardiovascular Safety of Dihydropyrazoles as Brain-Penetrant T-Type Calcium Channel Blockers.

A series of dihydropyrazole derivatives was developed as potent, selective, and brain-penetrating T-type calcium channel blockers. An optimized derivative, compound 6c, was advanced to in vivo studies, where it demonstrated efficacy in the WAG/Rij rat model of generalized nonconvulsive, absence-like epilepsy. Compound 6c was not efficacious in the basolateral amygdala kindling rat model of temporal lobe epilepsy, and it led to prolongation of the PR interval in ECG recordings in rodents.

Kindling of basolateral amygdala but not ventral hippocampus or perirhinal cortex disrupts sensorimotor gating in rats

The neural mechanisms mediating prepulse inhibition (PPI) appear to have relevance to neurological and psychiatric disorders. Patients with temporal lobe epilepsy exhibit psychotic symptoms and disrupted PPI, therefore the present experiments examined the consequences of seizures induced by kindling on PPI. Rats were chronically implanted with an electrode into the basolateral amygdala, perirhinal cortex, or ventral hippocampus and stimulated twice daily until 3 fully generalized, class 5 seizures were elicited. Kindling of basolateral amygdala, but not perirhinal cortex or ventral hippocampus, disrupted PPI when testing began 2 min, but not 48 h, following the elicitation of the third class 5 seizure. Startle amplitudes were unaffected by kindling. These results suggest that the anatomical origin of seizures is an important factor in determining their potentially disruptive effects on PPI.

Anxiolytic and anxiogenic effects of kindling—role of baseline anxiety and anatomical location of the kindling electrode in response to kindling of the right and left basolateral amygdala

Effects of kindling of right and left basolateral amygdala (BLA) on plus maze anxiety was studied. Using a validated retest paradigm, it was possible to retest rats in the plus maze without increasing anxiety on retest. This permitted determining prekindling baseline levels of plus maze anxiety. Right BLA kindling of high baseline anxiety rats was anxiolytic one week after kindling. Right BLA kindling of low baseline anxiety rats was anxiogenic. In addition, left BLA kindling was either anxiogenic or without effect on plus maze anxiety, depending on baseline anxiety. Effects in left BLA differ from previous work showing anxiolytic effects of left BLA kindling. The discrepancy could be explained in part by prekindling baseline anxiety. These findings require modification of the previous conclusion that left hemisphere (left BLA) kindling is anxiolytic and right BLA kindling is anxiogenic in the plus maze. Rather the hemisphere difference may be due to an interaction between baseline anxiety level and kindling. If true, anxious disposition in rodents may interact with amygdala kindling to change amygdala function differently. Kindling and baseline anxiety effects on other behaviors (such as risk assessment and resistance to capture) are also described. Present data in the light of past studies suggest both premorbid anxiety state and location of the kindling electrode contribute to the effects of kindling on behavior.

Anxiolytic effects of kindling role of anatomical location of the kindling electrode in response to kindling of the right basolateral amygdala

Study of effects of kindling on affect has been complicated by the fact that anxiogenic, anxiolytic or no effects may be observed following kindling of the amygdala. Factors affecting behavioral outcome include strain of rat, hemisphere kindled, amygdala nucleus kindled and location of the kindling electrodes within particular AP planes of a given nucleus. Previous work has suggested that kindling of the right basolateral amygdala (BLA) is predominantly anxiogenic. This conclusion was based on kindling of anterior or posterior parts of the BLA. The present study sought to clarify this conclusion by examining behavioral effects of right BLA kindling in a mid-range of AP planes not yet studied. A variety of measures of rodent anxiety-like behavior were examined, including behavior in the hole board, elevated plus maze, light/dark box, social interaction test and unconditioned acoustic startle. Anhedonic effects of kindling were assessed by a sucrose preference test with controls for fluid consumption and taste sensitivities. All effects were assessed shortly after kindling (1–2 days) and at a longer time interval (7–8 days). Kindling to four stage 5 seizures in the mid-right BLA altered behavior at all time points after kindling in all tests except the hole board and light/dark box tests. The effect of kindling was anxiolytic like in the plus maze, social interaction and startle tests. Kindling in mid-BLA also increased sucrose consumption. Effects on sucrose consumption are consistent with previous studies showing no depressive-like effects of amygdala kindling in rodents. It is hypothesized that the focal nature of the behavioral consequences of amygdala kindling are best understood in the context of the circuitry in which the cells stimulated are imbedded and the impact of kindling on functioning of those circuits.

Stimulation site determines the conditioned effects of kindling in rats: anterior neocortex versus amygdala

Rats received 53 stimulations to either the left basolateral amygdala (BA) or left anterior neocortex (AN) in one environment (CS+) and 53 sham stimulations (the stimulation lead was attached but no current was delivered) in another environment (CS-), quasirandomly over 54 days. Confirming a previous report [Barnes, S.J., Pinel, J.P., Francis, L.H. & Wig, G.S. (2001) Behav. Neurosci., 115, 1065-1072], as BA kindling progressed, the CS+ began to elicit more defensive behaviours (i.e. less activity, more freezing and avoidance of the CS+) than the CS-, and at the end of the experiment, convulsions elicited in the CS+ were more severe than those elicited in the CS-. Like BA kindling, AN kindling led to less activity in the CS+; but unlike BA kindling, AN kindling led to more wet-dog-shakes and less, rather than more, severe convulsions in the CS+. During AN kindling, the mean number of wet-dog-shakes in the CS+ was negatively correlated with the mean convulsion class, suggesting that wet-dog-shakes contribute to the inherent variability of AN kindling. These findings confirm that inherent conditioned effects influence kindled convulsions and interictal behaviour and establish for the first time that the pattern of these conditioned effects is a function of the kindling site.

Antiepileptogenesis by Deep Brain Stimulation.

Low-frequency Stimulation of the Kindling Focus Delays Basolateral Amygdala Kindling in Immature Rats VelíŠek L, VelíŠkova J, Stanton PK Neurosci Lett 2002;326:61–63. Stimulation of deep brain sites is a new approach for treatment of intractable seizures. In adult rats, low-frequency stimulation (LFS; 1–3 Hz) of the kindling site interferes with the course of kindling epileptogenesis. In this study we determined whether the LFS is effective against the fast kindling in the basolateral amygdala in immature, 15-day-old rats. LFS (15 min of 1-Hz stimulation) was applied after each of the 1-s, 60-Hz kindling stimulus. LFS suppressed afterdischarge duration and seizure stage throughout the course of kindling, which indicates a strong antiepileptogenic potential. As the kindling and LFS stimulation patterns are similar to those used for induction of long-term potentiation and long-term depression (LTD), respectively, LTD or depotentiation may play a role in the mechanism of action.

Low-frequency stimulation of the kindling focus delays basolateral amygdala kindling in immature rats

Stimulation of deep brain sites is a new approach for treatment of intractable seizures. In adult rats, low-frequency stimulation (LFS; 1–3 Hz) of the kindling site interferes with the course of kindling epileptogenesis. In this study we determined whether the LFS will be effective against the fast kindling in the basolateral amygdala in immature, 15 day old rats. LFS (15 min of 1 Hz stimulation) was applied after each of the 1 s, 60 Hz kindling stimulus. LFS suppressed afterdischarge duration and seizure stage throughout the course of kindling, which indicates a strong antiepileptogenic potential. As the kindling and LFS stimulation patterns are similar to those used for induction of long-term potentiation and long-term depression (LTD), respectively, LTD or depotentiation may play a role in the mechanism of action.

Loss of dendritic synapses in the medial amygdala associated with kindling

Kindling stimulation was given in the basolateral amygdala (BLA), the septal area or the corpus callosum in the right hemisphere of adult rats. The density of dendritic synapses was electron microscopically studied in the medial amygdaloid nucleus (MAN) ipsi- and contralateral to the stimulation side. The number of dendritic synapses was markedly decreased in both sides of the MAN of 3 groups of kindled rats. Such reduction occurred in both dendritic shaft and spine synapses. The most remarkable decrease was obtained in the BLA kindling. These results suggest that a decrease of synapses may provide a morphological basis for kindling.

Sleep and kindling: I. Effects of initial afterdischarge threshold determination

Recent work indicated a significant correlation between seizure latencies following exposure to the convulsant drug monomethylhydrazine (MMH) and afterdischarge (AD) thresholds obtained at the beginning of basolateral amygdala kindling in cats. A profound alteration in state physiology is an early and sustained feature of the prodrome with MMH but has not been shown in relation to initial AD thresholds. The present experiment examined state variables during the earliest phase of kindling in an effort to determine if other similarities exist between these two experimental models of epilepsy. Eighteen cats (experimental, N = 12; control, N = 6) were surgically prepared for basolateral amygdala stimulation and for the evaluation of standard state variables. Postoperatively, two baseline, 12-h, polygraphic recordings were obtained in the experimental group. AD thresholds were then established using a method of limits procedure, after which a third 12-h polygraphic recording was obtained as long as 48 h later. Control animals underwent the same polygraphic recording sequence but never received amygdala stimulation. AD thresholds in experimental animals varied considerably. Threshold values were not systematically related either to histologically verified electrode sites throughout the basolateral amygdala or to changes in the sleep-waking cycle. State evaluation indicated that the experimental animals showed a sustained facilitation of waking and a suppression of slow-wave sleep during the poststimulation recording compared with their own baseline and with controls. These findings indicate a further resemblance between the MMH and kindling models of epilepsy, which, in conjunction with other similarities, could be indicative of a common pathological mechanism.

Relation of monomethylhydrazine (MMH) seizure thresholds to afterdischarge thresholds with amygdaloid stimulation in cats

Studies conducted in our laboratory for the last 15 years focused on an acute seizure model involving exposure to the convulsant compound, monomethylhydrazine (MMH). An important feature of this model is the latency in minutes postinjection to the onset of generalized tonic clonic convulsions. This index varies between naive animals but is systematically altered by procedures which facilitate or protect against seizures in other experimental animal models and human seizure disorders. MMH latencies may therefore provide a sensitive index of seizure susceptibility in general, despite its systemic and acute nature. To further test this hypothesis, the present study compared postoperative MMH latencies in eight naive cats with subsequent afterdischarge thresholds (in μA) obtained from basolateral amygdala kindling electrodes. The correlation between those two indices was statistically significant. In addition, animals divided on the basis of the median population value into high or low MMH seizure latencies differed significantly from one another on that index. Afterdischarge thresholds evaluated in the same animals also differed significantly and in the same direction. Thus, animals with prolonged seizure latencies also showed significantly higher afterdischarge thresholds, whereas shorter latencies accompanied lower afterdischarge thresholds. Finally, the gender, weight, electrode impedance, or electrode sites of individuals did not account for this relationship. Given the dissimilarity of the two models used, the results suggested endogenous differences in seizure susceptibility that are definable regardless of procedure. Alternatively, common features of the two models may have contributed to the present findings.