Immunoelectron microscopic study of beta-endorphinergic synaptic innervation of GABAergic neurons in the dorsal raphe nucleus

Using a preembedding double immunoreactive technique by immunostaining with antirat beta -endorphin and antisynthetic glutamic acid decarboxylase anti sera sequentially, the synaptic relationships between beta -endorphinergic neuronal fibers and GABAergic neurons in the dorsal raphe nucleus of the ra t were examined at the ultrastructural level. Although both beta -endorphin -like immunoreactive fibers and glutamic acid decarboxylase-like immunoreac tive neurons can be found in the mediodorsal and medioventral parts of the dorsal raphe nucleus, the synapses between them were found only in the medi odorsal part. Most of the beta -endorphin-like immunoreactive neuronal fibe rs contained many dense-cored vesicles. The synapses made by beta -endorphi n-like immunoreactive neuronal axon terminals on glutamic acid decarboxylas e-like immunoreactive neurons were both symmetrical and asymmetrical, with the latter predominant, especially in the axo-dendritic synapses. Perikarya with beta -endorphin-like immunoreactivity were found only in the ventroba sal hypothalamus. These findings suggest the possibility that the beta -end orphin-producing neurons in the ventrobasal hypothalamus could influence GA BAergic neurons in the dorsal raphe nucleus directly by synaptic relationsh ips. (C) 2001 Wiley-Liss, Inc.