Neuronal projections to the lateral retrochiasmatic area of sheep with special reference to catecholaminergic afferents: immunohistochemical and retrograde tract-tracing studies

The retrochiasmatic area contains the A15 catecholaminergic group and numer ous monoaminergic afferents whose discrete cell origins are unknown in shee p. Using tract-tracing methods with a specific retrograde fluorescent trace r, fluorogold, we examined the cells of origin of afferents to the retrochi asmatic area in sheep. The retrogradely labeled cells were seen by observat ion of the tracer by direct fluorescence or by immunohistochemistry with sp ecific antibodies raised in rabbits or horses. Among the retrogradely label ed neurons. double immunohistochemistry for tyrosine hydroxylase, dopamine- beta-hydroxylase, and serotonin were used to characterize catecholamine and serotonin FG labeled neurons. The retrochiasmatic area, which included the A15 dopaminergic group and the accessory supraoptic nucleus (SON), receive d major inputs from the lateral septum (LS), the bed nucleus of the stria t erminalis (BNST), the thalamic paraventricular nucleus, hypothalamic parave ntricular and supraoptic nuclei, the perimamillary area, the amygdala, the ventral part of the hippocampus and the parabrachial nucleus (PBN). Further , numerous scattered retrogradely labeled neurons were observed in the preo ptic area, the ventromedial part of the hypothalamus, the periventricular a rea, the periaqueductal central gray (CG), the ventrolateral medulla and th e dorsal vagal complex. Most of the noradrenergic afferents came from the v entro-lateral medulla (A1 group). and only a few from the locus coeruleus c omplex (A6/A7 groups). A few dopaminergic neurons retrogradely labeled with flurogold were observed in the periventricular area of the hypothalamus. R are serotoninergic fluorogold labeled neurons belonged to the dorsal raphe nucleus. Most of these afferents came from both sides of the brain, except for hypothalamic supraoptic and paraventricular nuclei. In the light of the se anatomical data, we compared our results with data obtained from rats, a nd we discussed the putative role of these afferents in sheep in the regula tion of several specific functions in which the retrochiasmatic area may be involved, such as reproduction. (C) 2000 Elsevier Science B.V. All rights reserved.