Thalamocortical Connectivity in a Rat Brain Slice Preparation: Participation of the Ventrobasal Complex to Synchronous Activities
Abstract number :
1.165
Submission category :
Year :
2000
Submission ID :
2871
Source :
www.aesnet.org
Presentation date :
12/2/2000 12:00:00 AM
Published date :
Dec 1, 2000, 06:00 AM
Authors :
Virginia Tancredi, Giuseppe Biagini, Margherita D'Antuono, Rita Motalli, Jacques Louvel, Giovanna D'Arcangelo, Rene' Pumain, Richard A Warren, Massimo Avoli, Univ of Rome Tor Vergata, Rome, Italy; Univ of Modena and Reggio Emilia, Modena, Italy; Montreal
RATIONALE: The neocortex and thalamus are able to generate brain rhythms that are observed during sleep and in some pathological conditions such as absence seizures. In this study we used rat thalamocortical slices to analyze the relative contribution of thalamic and cortical networks to the synchronous activities induced by low (0.5?M) and high (50-100?M) concentrations of 4-aminopyridine (4AP). METHODS: Combined thalamocortical slices (550-650?m) were obtained from rat brain using hybrid coronal sections that were cut according to the procedures of Agmon & Connors (Neurosci 41:365-379, 1991). The presence of reciprocal thalamocortical connectivity in these slices was documented by diffusion of the fluorescent tracer Di-IC18 between the somatosensory cortex and the ventrobasal complex (VB) of the thalamus. Extracellular field potentials were recorded with glass pipettes that were positioned under visual control in cortex and VB. A bipolar stainless steel electrode was used to deliver extracellular stimuli (50-150?s; <200?A) to selected areas of the thalamocortical slice. RESULTS: Low concentrations of 4AP produced local spindle-like rhythmic oscillations in cortex and VB (duration=0.4-3.5s; frequency=9-16Hz). By contrast, high concentrations of 4AP induced widespread ictal-like epileptiform discharges (duration=8-45s) characterized by a 'tonic' component followed by a period of 'clonic' discharges in both cortex and VB. Spindle-like activity was abolished in cortex and thalamus by applying the excitatory amino acid receptor antagonist kynurenic acid in VB. In contrast, the same procedure exacerbated cortical ictal-like discharges, while depressing VB activity. CONCLUSIONS: Our results indicate that thalamus and cortex can generate synchronous activities in the thalamocortical network: spindle-like rhythmic oscillations are generated at the thalamic level and imposed upon the cortical network, whereas ictal-like discharges have a cortical origin and may be controlled by thalamocortical inputs arising within thalamic network.