SYNAPTIC INPUTS OF TACHYKININ-CONTAINING NERVE-TERMINALS TO TARGET TYROSINE-HYDROXYLASE-, BETA-ENDORPHIN- AND NEUROPEPTIDE Y-PRODUCING NEURONS OF THE ARCUATE NUCLEUS - DOUBLE PREEMBEDDING IMMUNOCYTOCHEMICAL STUDY IN THE RAT

Anatomical connections between tachykinin-containing terminals and thr ee neuronal populations of the arcuate nucleus, chemically defined res pectively by beta-endorphin (beta-END), tyrosine-hydroxylase or neurop eptide Y (NPY) and well represented in the arcuate nucleus, were studi ed using electron microscope double pre-embedding immunocytochemistry involving a combination of two sensitive chromogens: diaminobenzidine and tetramethylbenzidine. Following tachykinin immunodetection by diam inobenzidine, and tyrosine-hydroxylase, beta-END or NPY immunolabellin g by tetramethylbenzidine, tachykinin-immunoreactive terminals were se en presynaptic to tyrosine-hydroxylase immunopositive cells and dendri tes principally in the dorsomedial portion of the arcuate nucleus. Tac hykinin-immunoreactive processes were also seen in synaptic contact wi th ventrolaterally located beta-END immunopositive perikarya. Tachykin in-immunopositive terminals also contacted NPY- immunoreactive cells a nd dendritic processes ventromedially. These results demonstrate the e xistence of a direct tachykinergic input onto three neuronal populatio ns expected to play a role in the control of reproductive events. Cons equently, they suggest, at least, an indirect action for tachykinins i n the regulation of reproduction. Especially, tachykinins may indirect ly control the luteinizing hormone-releasing hormone neurons via dopam ine, beta-END and NPY cells and thereby influence luteinizing hormone secretion.