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Role of Brainstem Structures in Seizures Initiated from the Deep Prepiriform Cortex of Rats
Author(s) -
Browning Ronald,
Maggio Roberto,
Sahibzada Niaz,
Gale Karen
Publication year - 1993
Publication title -
epilepsia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.687
H-Index - 191
eISSN - 1528-1167
pISSN - 0013-9580
DOI - 10.1111/j.1528-1157.1993.tb02579.x
Subject(s) - brainstem , forebrain , cerebrum , neuroscience , basal forebrain , medial forebrain bundle , anatomy , medicine , psychology , central nervous system , striatum , dopamine
Summary: Previous studies showed that brainstem sei zures can still be evoked after transections that separate forebrain from brainstem. We sought to determine wheth er forebrain‐evoked electrographic seizures require brain stem connections for initiation and generalization. Male Sprague‐Dawley rats weighing 295–320 g implanted with epidural electrodes had brain transections placed at the pre‐, mid‐, or postcollicular level. In experiment 1, the transections were limited to severing the brainstem, spar ing the telencephalon laterally; these are referred to as “core” transections. In experiment 2, the transections severed the brainstem and also cut through the lateral telencephalon. These “extended” transections were ei ther (a) bilateral, (b) unilateral (i.e., a hemitransection confined to one hemisphere), or (c) partial (sparing path ways ventral to the pretectal nuclei). All transections were performed under ether anesthesia, and seizures were initiated 3 h later by focal infusion of bicuculline (BIC) into the area tempestas (AT) through a previously implanted guide cannula. In experiment 1, bilateral fore brain electrographic seizures occurred in the complete absence of connections between forebrain and brainstem, showing that the brainstem is not required for forebrain evoked seizures. In experiment 2, forebrain seizures evoked by BIC in AT were suppressed by bilateral ex tended transections which interrupted connections be tween AT and the caudal lateral telencephalon. Under these circumstances, application of carbachol with BIC reinstated the forebrain seizure response. These results indicate that carbachol application served to compensate for loss of an excitatory influence on AT resulting from the severing of connections with the caudal telencepha lon. The demonstration of direct projections from ento rhinal cortex to AT using Fluoro‐Gold tracing together with the finding that extended brain transections caudal to the telencephalon do not suppress focally evoked fore brain seizures provided further support for the notion that AT afferents from the caudal telencephalon regulate the sensitivity of AT to BIC. The present findings provide further evidence that seizure substrates in the forebrain and brainstem are separable and independent.