Abstracts

The substantia nigra pars reticulata (SNR) plays an important role in the control of generalized seizures. In adult male rats, the SNR has two topographically separate segments, anterior and posterior, that play distinct roles in the modulation of seizures. We investigated the involvement of the two distinct SNR regions during different stages of flurothyl seizures. Flurothyl is a volatile convulsant, which allows the examination of discrete seizure stages by changing the delivery rate. We measured changes in cerebral metabolic activity in the SNR and its major input and output structures using the 2[14C] deoxyglucose (2DG) technique during the preictal, ictal and postical periods.
Adult male rats were divided into the following groups based on the seizure stage: controls without or with flurothyl exposure but no seizure; preictal clonic; preictal tonic-clonic; ictal; postictal clonic, and postictal tonic-clonic. 2DG was injected subcutaneously (0.05[micro]Ci/g). Coronal sections were cut throughout the entire brain. The sections were digitized and the gray level variation was measured using NIH image.
The two SNR regions can be distinguished based on their differential involvement at distinct stages of flurothyl seizures, as well as on their afferent and efferent networks. During the preictal clonic stage, the SNRposterior, subthalamic nucleus and ventromedial thalamus were affected. During the preictal tonic-clonic stage, both SNRanterior and SNRposterior, ventromedial thalamus, striatum and globus pallidus were affected. Both SNR regions, including all input and output structures studied, were active during the ictal stage. During the postictal stages, the activity within the SNR was not different from controls.
The data suggest that in adult male rats, the activity of the two SNR regions and their major input and output pathways are differentially influenced during preictal periods, and as a function of seizure type.
[Supported by: NS 20253, NS 30387 and Heffer Family Medical foundation]