Er. Ribeiro-barbosa et al., Projections of the basal retrochiasmatic area: a neural site involved in the photic control of pineal metabolism, BRAIN RES, 839(1), 1999, pp. 35-40
It has been shown that the basal retrochiasmatic area (RCHb), situated imme
diately ventral to the third ventricle behind the suprachiasmatic nucleus a
nd in front of the arcuate nucleus, is implicated in the nocturnal inhibito
ry process of melatonin production induced by short-term retinal photo-stim
ulation. In the present study, the projections of the RCHb have been examin
ed using the Phaseolus vulgaris leucoagglutinin (PHA-L) method in the rat.
Considering the putative role of the RCHb in contributing to the short-term
photo-inhibition of the pineal gland during the night, it is reasonable to
suppose that the RCHb may ultimately inhibit the sympathetic outflow of th
e upper thoracic segments, known to be critically involved in the control o
f melatonin secretion. Of particular interest, the present anterograde trac
t-tracing study indicates all possible paths from the RCHb which may concei
vably be involved in influencing the sympathetic outflow and, therefore, me
latonin production. Thus, apart from a direct projection to the intermediol
ateral column at thoracic levels of the spinal cord, the RCHb is in a posit
ion to control the sympathetic outflow through other potential routes, such
as the dorsal parvicellular part of the paraventricular nucleus of the hyp
othalamus, lateral hypothalamic area, ventromedial nucleus of the hypothala
mus, lateral part of the periaqueductal gray and Barrington's nucleus. (C)
1999 Elsevier Science B.V. All rights reserved.