Distribution of preprovasopressin mRNA in the rat central nervous system

Vasopressin released in the central nervous system has been shown to be inv olved both in homeostatic mechanisms (e.g., water balance, thermoregulation , cardiovascular regulation, metabolism, and antinociception) and in higher brain functions (e.g., social recognition and communication, and learning and memory). Many nuclear groups have been proposed to synthesize vasopress in, but available data are conflicting. We have used a sensitive in situ hy bridization technique to identify the distribution of the neurons that may be the origin of the vasopressin in the central nervous system of the male Sprague-Dawley rat. Vasopressin mRNA-expressing neurons were most abundant in the hypothalamus (e.g., the paraventricular, supraoptic, and suprachiasm atic nuclei) but were also seen in the medial amygdaloid nucleus, the bed n ucleus of stria terminalis, and the nucleus of the horizontal diagonal band . Previously unreported vasopressinergic neurons were seen in the entorhina l and piriform cortices, the ventral lateral portion of the parabrachial nu cleus, the pedunculopontine nucleus, and the rostral part of the ventral pe riaqueductal gray matter and the adjacent portion of the mesencephalic reti cular nucleus. Vasopressin mRNA expression suggestive of neuronal labeling was seen in the pyramidal layer of the CA1-3 fields and the dentate gyrus o f the hippocampus. In addition, vasopressin mRNA expression, probably repre senting axonal mRNA, was detected over the hypothalamopituitary tract. No o r insignificant preprovasopressin mRNA expression was present in the cerebe llum, locus coeruleus, subcoeruleus, or the spinal cord. These findings pro vide novel information on the distribution of vasopressin neurons that are important for our understanding of how vasopressin acts in the brain. (C) 1 999 Wiley-Liss, Inc.