Bombesin immunoreactive neurons in the hypothalamic paraventricular nucleus innervate the dorsal vagal complex in the rat.

Bombesin-like immunoreactivity has been localized within neuronal cell bodies of the hypothalamus and nerve terminals within the dorsal vagal complex. The possibility that the hypothalamus is a source for bombesin-like immunoreactive terminals within the dorsal vagal complex was examined using the combined retrograde tracing and immunohistochemical technique. After injections of retrograde tracer were made into the dorsal vagal complex, cells in the hypothalamus labeled with both retrograde tracer and bombesin immunoreactivity were localized in the parvocellular part of the paraventricular nucleus. In the paraventricular nucleus most of the vagal projecting bombesin immunoreactive neurons were located within the medial parvocellular subdivision. Approximately 30% of the bombesin immunoreactive neurons in this subnucleus projected to the dorsal vagal complex. The results suggest that the paraventricular hypothalamic nucleus is a major source of bombesin terminals within the dorsal vagal complex. This pathway may mediate some of the autonomic nervous system changes that are observed when bombesin is injected within the central nervous system. Additionally, this data adds to a growing amount of evidence supporting the role of bombesin as a peptide neurotransmitter.