Basal ganglia organization in amphibians: chemoarchitecture.

Recent studies dealing with the investigation of the afferent and efferent connections of the basal ganglia of amphibians have revealed many similarities with basal ganglia structures of amniotes. In a further step, the chemoarchitecture of basal ganglia of the frog Rana perezi has been investigated. For use as main markers of amphibian basal ganglia structures, antibodies against tyrosine hydroxylase, substance P, and enkephalin were selected. Moreover, the distributions of nitric oxide synthase (nicotinamide adenine dinucleotide phosphate-diaphorase histochemistry), calretinin, dopamine-beta-hydroxylase, choline acetyltransferase, mesotocin, vasotocin, somatostatin, neuropeptide Y, neuropeptide FF, and serotonin were studied to corroborate a comparison with both basal ganglia and amygdaloid structures of amniotes. On the basis of connections and chemoarchitecture, a striatum proper, nucleus accumbens, dorsal and ventral pallidum, bed nucleus of the stria terminalis, and amygdaloid complex have been identified. Accordingly, a new terminology is proposed that is in line with our current understanding of basal ganglia organization in amphibians.