Concurrent alternating stimulation of two limbic sites culminates in typical kindling of generalized seizures from one site (dominant), whereas the other site (suppressed) supports only nongeneralized seizures for as long as stimulation of the dominant site continues (kindling antagonism). Burchfiel and Applegate (1989; 1990) claimed that antagonism reflects a frank arrest of kindling from the suppressed site at an intermediate stage. They argued, moreover, that the eventual generalization of seizures provoked from the suppressed site after the termination of stimulation of the dominant site reflects a resumption of kindling from its previous state of arrest. Burchfiel and Applegate also claimed that the behaviorally stereotyped arrest of kindling from the suppressed site reveals critical transitions between sequentially expressed mechanisms that govern both antagonism and kindling. They therefore viewed kindling as a stepwise process that is mediated by qualitatively and temporally distinct mechanisms. This position hinges on the assumption that antagonism reflects a true arrest of kindling from the suppressed site rather than a transient inhibition of seizures. I conducted the following experiments to determine whether the assumption is justified, In Experiment 1, I replicated and extended the observations of Burchfiel and Applegate concerning the expression of antagonism during alternating stimulation of limbic as well as nonlimbic sites. The results of Experiment 1 thus indicate that antagonism is indeed a robust phenomenon and therefore worthy of further study. In Experiment 2, the imposition of a prolonged stimulation-free period (30 d) after the termination of stimulation of the dominant site (amygdala) did not significantly reduce the number of stimulations of the suppressed site (septal area) required to elicit a generalized seizure. Also, epileptiform after discharge provoked from the septal area increased during alternating stimulation, and the septal area supported generalized seizures after fewer stimulations in rats previously expressing antagonism as compared to control rats previously kindled from the amygdala. Collectively, these data are consistent with the view of Burchfiel and Applegate that kindling from the suppressed site progresses to an intermediate stage during alternating stimulation and resumes after the termination of stimulation of the dominant site. The results of Experiment 2 also suggest the possibility that the development of seizures from the suppressed site after the termination of stimulation of the dominant site is dictated by the additive expression of: first, the well-documented facilitation of kindling from one site that reliably follows kindling from another (i.e., transfer between the amygdala, which supported generalized seizures, and the septal area); second, (partial) kindling from the septal area, which previously supported nonconvulsive or partial seizures, during the Initial Phase. The results of Experiment 3 revealed that the facilitation of seizure development from the septal area observed in rats previously exposed to alternating stimulation, which perhaps is attributable to partial kindling from the suppressed site, was site specific. Rats subjected to alternating stimulation of the left amygdala and right septal area and control rats previously stimulated only in the left amygdala subsequently demonstrated generalized seizures following similar numbers of stimulations of the previously unstimulated right amygdala. Another plausible view is that antagonism reflects a long-lasting (> 30 d) form of inhibition that is perhaps uniquely invoked by alternating stimulation, While the results of Experiments 1 - 3 do not rule out this possibility, the results of Experiment 4 clearly indicate that the persistence of any such effects of alternating stimulation is not mediated by continuing influences of the dominant site: After the establishment of antagonism, radio-frequency lesions of the dominant site (amygdala) failed to alter the development of seizures provoked by stimulation of the suppressed site (septal area). / Graduate

Thesis (doctoral)--Lund University, 1997. / Added t.p. with thesis statement inserted.

Thesis (doctoral)--Lund University, 1997. / Added t.p. with thesis statement inserted.

Thesis (Ph. D.)--Carleton University, 1995. / Also available in electronic format on the Internet.

Thesis (Ph.D.) -- McMaster University, 1999. / Includes bibliographical references (leaves 130-151). Also available via World Wide Web.

It has been reported previously that systemic administration of clonidine, an agonist of α-2 receptors for noradrenaline, significantly retards amygdaloid kindling, by delaying the emergence from partial seizure, Conversely, systemic administration of α-2 antagonists has been reported to facilitate amygdaloid kindling, The experiments I conducted attempted to discover whether α-2 adrenoceptors in the amygdala participated in these effects, I examined the effect of either systemic administration (i,p.) or intraamygdaloid infusions of a variety of noradrenergic drugs on the kindling of seizures with electrical stimulation of the amygdala, Rats received either low-frequency stimulation of the amygdala, to induce rapid kindling, or conventional high-frequency stimulation, Drugs and electrical stimulation were administered once every 48 hrs, I observed a significant retardation of kindling in rats receiving i,p. injections of clonidine (0.1 mg/kg) or unilateral infusions of clonidine in concentrations of [special characters omitted] to [special characters omitted] M, regardless of the stimulation frequency. The prophylactic effect was due to a delay in the progression out of partial seizure. I observed similar effects with infusions of xylazine, also an α-2 adrenoceptor agonist, The effect was specific to the amygdala/pyriform region, because infusions of clonidine dorsal lo the amygdala were without effect. Power spectral analysis of the AD from the stimulated and the contralateral amygdala during the initial occurrence of bilateral AD failed to reveal differences attributable to clonidine, Therefore, clonidine might retard kindling by modifying the propagation of AD from the stimulated amygdala to a midbrain or pontine brainstem area critical, for the expression of generalized seizures. Clonidine had no effect on established generalized seizures, suggesting that it was producing a genuine prophylactic effect against kindling. Unexpectedly, intraamygdaloid infusions of either idazoxan, yohimbine, or SK&F 104856, antagonists of α-2 receptors, failed to accelerate kindling. Simultaneous infusion of idazoxan blocked clonidine’s prophylactic effect, which suggests strongly that this effect was mediated at the α-2 adrenoceptor. Blockade of amygdaloid α-1 adrenoceptors with corynanthine failed to affect kindling. I conclude that the population of α-2 adrenoceptors in the amygdala/pyriform region contributes to the antiepileptogenic effect observed after systemic administration of clonidine and that the facilitation of kindling observed after systemic administration of α-2 antagonists reported previously may have been mediated by the blockade of a population of α -2 adrenoceptors in addition to, or outside of, the amygdala/pyriform region. / Graduate

A morte súbita inexplicável na epilepsia (SUDEP) ainda está sujeita a várias controvérsias na literatura. No entanto, uma das possíveis causas de óbito são as apnéias observadas durante o sono, promovendo aumento dos níveis de CO2 (hipercapnia) e/ou diminuição dos níveis de O2 (hipoxemia). Tem sido especulado que essas alterações podem estar associadas às disfunções na atividade dos neurônios quimiossensíveis localizados no tronco encefálico. Além disso, é possível que os distúrbios respiratórios poderiam envolver alterações na neurotransmissão serotoninérgica. Os neurônios quimiossensíveis, localizados no núcleo retrotrapezoide (RTN), constituem um dos principais grupamentos responsáveis por controlar a atividade respiratória. O RTN recebe uma densa inervação serotoninérgica dos vários subnúcleos da rafe. Diante das várias lacunas na literatura, sobre as alterações respiratórias como possíveis causadoras de morte inexplicável na epilepsia, o presente estudo procurou entender quais eram as possíveis alterações respiratórias e neuroanatômicas no tronco encefálico observadas em dois modelos experimentais de epilepsia: ratos Wistar audiogênicos (cepa WAR) e animais submetidos à estimulação da amígdala (kindling rápido da amígdala - ARK). Os animais WAR apresentaram uma redução da ventilação (VE) basal (332 ± 105, vs. Wistar: 505 ± 36 ml/kg/min) e uma redução da resposta ventilatória a hipercapnia (7% CO2) (813 ± 341, vs. Wistar: 1661 ± 177 ml/kg/min). No modelo ARK, observamos apenas que a resposta de taquipnéia ao aumento do CO2 foi reduzida (126 ± 6 vs controle: 143 ± 6 rpm) comparado com o grupo controle. Em outro protocolo experimental, os animais WAR foram submetidos à exposição em hipercapnia durante um período de 3 horas para a expressão da proteína fos. Nesses animais, observamos uma redução no número de neurônios imunorreativos para fos na região do RTN e na região da rafe pálido e obscurus. Por outro lado, observamos um aumento do número de neurônios imunorreativos para fos na região do locus coeruleus. Os animais WAR também apresentaram uma redução significante do número de varicosidades serotoninérgicas na superfície ventral da região do RTN, quando comparados com os ratos Wistar. Essa redução foi devida a uma redução no número de neurônios imunorreativos para serotonina na rafe pallidus e obscurus. Por fim, observamos também que aumento da VE produzida pela injeção unilateral de serotonina no RTN foi menor nos animais WAR quando comparado aos animais Wistar. No modelo de epilepsia de ARK quando submetidos à hipercapnia de 3 horas, observamos também uma redução no número de neurônios imunorreativos a expressão de fos na região do RTN e na região do núcleo do trato solitário. Da mesma maneira aos animais WAR, observamos um aumento do número de neurônios imunorreativos para fos na região do locus coeruleus. Considerando estes resultados, sugere-se que nos modelos experimentais de epilepsia utilizados no presente estudo, observamos uma redução da atividade respiratória basal e na resposta ventilatória à hipercapnia, bem como uma alteração neuroanatômica no tronco encefálico. Assim, gostaríamos de sugerir que ambos os modelos experimentais de epilepsia, utilizados no presente estudo, podem ser considerados modelos experimentais de epilepsia com o objetivo de se estudar distúrbios respiratórios e possivelmente correlacionar com mortes súbitas e inexplicáveis na epilepsia. / Unexplained sudden death in epilepsy (SUDEP) is still subject to several controversies in the literature. However, one of the possible causes of death are the apneas observed during sleep, promoting an increase in CO2 levels (hypercapnia) and/or a decrease in O2 levels (hypoxemia). It has been speculated that these changes may be associated with dysfunctions in chemosensitive neurons. In addition, it is possible that respiratory disorders may involve changes in serotonergic neurotransmission. The chemosensitive neurons located in the retrotrapezoid nucleus (RTN) are one of the main groups responsible for controlling respiratory activity. The RTN receives a dense serotonergic innervation of the various subnuclei of rafe. The present study sought to understand the possible respiratory alterations observed in two models of epilepsy: audiogenic Wistar rats (WAR strain) and rapid amygdala kindling (ARK). WAR animals showed a reduction in baseline ventilation (332 ± 105, vs. Wistar: 505 ± 36 ml/kg/min) and a reduction in hypercapnic (7% CO2) ventilatory response (813 ± 341, vs. Wistar: 1661 ± 177 ml/kg/min). In the ARK model, we only observed that the tachypnea response to CO2 was reduced (126 ± 6 vs control: 143 ± 6 rpm). In a different experimental protocol, WAR animals were exposed to hypercapnia for a period of 3 hours in order to have the fos protein expression. In these animals, we observed a reduction in the number of fos-immunoreactive neurons in the RTN region and in the raphe pallidus and obscurus. On the other hand, we observed an increase in the number of fos-immunoreactive neurons of the locus coeruleus. WAR animals also showed a significant reduction in the number of serotonergic varicosities of the ventral medullary surface. This reduction was due to a reduction in the number of serotonin-immunoreactive neurons in raphe pallidus and obscurus. Finally, we also observed that the increase in VE produced by the unilateral injection of serotonin in the RTN was lower in the WAR animals when compared to the Wistar rats. In the ARK epilepsy model submitted to 3 hour of hypercapnia, we also observed a reduction in the number of fos-immunoreactive neurons in the RTN region and in the region of the nucleus of the solitary tract. In the same way as WAR animals, we observed an increase in the number of fos-immunoreactive neurons in the locus coeruleus region. Considering these results, it is suggested that in the experimental models of epilepsy used in the present study, we observed a reduction of basal respiratory activity and hypercapnic ventilatory response, as well as a neuroanatomic changes in the brainstem. Thus, we would like to suggest that both experimental models of epilepsy used in the present study can be considered good experimental models of epilepsy in order to study respiratory disorders and possibly correlate with sudden and unexplained deaths in epilepsy.

Kindling involves the progressive development of epileptiform activity that culminates in generalized seizures in response to repeated electrical stimulation of the brain. Kindling induces widespread changes in synaptic sensitivity and neuronal reactivity. These neuroplastic changes are evident in altered memory and behavior. This research was designed to further our understanding of kindling-induced deficits in spatial cognition. Two questions were examined: 1)does entorhinal cortex kindling disrupt spatial cognition; and 2)can bilateral bifocal kindling, of two brain regions known to participate in spatial cognition, produce larger cognitive deficits than unifocal kindling? This research attempted to confirm the spatial cognitive effects produced by unifocal dorsal hippocampal (dHPC) kindling, as a positive control. In contrast, the spatial cognitive effects produce by unifocal entorhinal cortex (EC) and bifocal kindling (i.e., EC kindling with subsequent contralateral dHPC kindling) are unknown and were examined here. Rats were subjected to unifocal EC kindling, unifocal dHPC kindling, or bifocal kindling. Rats exhibited fully generalized seizures prior to Morris water maze training from days 2 to 31. Visible platform trials were used to examine escape motivation and gross motor coordination, and all groups performed adequately. Consistent with previous research, dHPC kindling disrupted performance during acquisition trials; however, EC and bifocal kindling failed to disrupt acquisition. During retention trials, the bifocal kindling group displayed a disruption in performance; however, dHPC and lateral EC kindling failed to affect retention. The bifocal kindled group failed to display larger deficits than the unifocal kindled groups. These data suggest that the number of kindling stimulations given to a particular site may play a critical role in site-dependent disruption of memory.

Kindling involves the progressive development of epileptiform activity that culminates in generalized seizures in response to repeated electrical stimulation of the brain. Kindling induces widespread changes in synaptic sensitivity and neuronal reactivity. These neuroplastic changes are evident in altered memory and behavior. This research was designed to further our understanding of kindling-induced deficits in spatial cognition. Two questions were examined: 1)does entorhinal cortex kindling disrupt spatial cognition; and 2)can bilateral bifocal kindling, of two brain regions known to participate in spatial cognition, produce larger cognitive deficits than unifocal kindling? This research attempted to confirm the spatial cognitive effects produced by unifocal dorsal hippocampal (dHPC) kindling, as a positive control. In contrast, the spatial cognitive effects produce by unifocal entorhinal cortex (EC) and bifocal kindling (i.e., EC kindling with subsequent contralateral dHPC kindling) are unknown and were examined here. Rats were subjected to unifocal EC kindling, unifocal dHPC kindling, or bifocal kindling. Rats exhibited fully generalized seizures prior to Morris water maze training from days 2 to 31. Visible platform trials were used to examine escape motivation and gross motor coordination, and all groups performed adequately. Consistent with previous research, dHPC kindling disrupted performance during acquisition trials; however, EC and bifocal kindling failed to disrupt acquisition. During retention trials, the bifocal kindling group displayed a disruption in performance; however, dHPC and lateral EC kindling failed to affect retention. The bifocal kindled group failed to display larger deficits than the unifocal kindled groups. These data suggest that the number of kindling stimulations given to a particular site may play a critical role in site-dependent disruption of memory.

Thesis (M.Sc.)--Memorial University of Newfoundland, 2001. / Bibliography: leaves 47-54.