GABA and opioid binding distribution in the brain of the seizure-resistant Proechimys guyannensis: an autoradiography study.

Proechimys guyannensis rodents present resistance to epilepsy. Autoradiography was used to map GABA(A) ((3)H-Muscimol), benzodiazepine ((3)H-Flunitrazepam), mu ((3)H-DAMGO), and delta ((3)H-DPDPE) opioid receptor binding in adult Proechimys guyannensis brain under normal conditions. Results were compared with values obtained from adult Wistar rats. Proechimys presented reduced (3)H-Muscimol binding in several cortices, thalamus, medial amygdala nucleus, and dorsal dentate gyrus. (3)H-Flunitrazepam binding was reduced in periaqueductal gray, frontal and entorhinal cortices, and enhanced in piriform cortex and ventral CA2 field of Ammons horn. Concerning (3)H-DAMGO binding, high values were found in several cortices, medial amygdala nucleus, dorsal dentate gyrus, and periaqueductal gray, whereas reduced binding was detected in anterior olfactory tubercle, cingulated cortex, thalamus, basolateral amygdala, substantia nigra, and dorsal and ventral CA fields. High (3)H-DPDPE binding was noticed in CA1 field from dorsal hippocampus, while reduced values were found in cingulate cortex, olfactory tubercle, thalamus, and substantia nigra. These findings provide the first description of receptor binding distribution of the Proechimys brain and suggest natural endogenous anticonvulsant mechanisms of theses rodents under normal conditions.