NEUROTENSIN IN THE LATERAL HYPOTHALAMIC AREA - ORIGIN AND FUNCTION

The origin of neurotensin in the lateral hypothalamus was investigated by means of fluorescent retrograde tract tracing and neurotensin-like immunoreactivity. Following fluorescent retrograde tract tracing with FluoroGold combined with neurotensin immunohistochemistry in the rat brain, numerous neurotensin-immunoreactive neurons with projections to the posterior lateral hypothalamic area were identified in the centra l nucleus of the amygdala, perifornical area and the parabrachial nucl eus. Fewer numbers of neurotensin-positive neurons with projections to the lateral hypothalamic area were observed in the bed nucleus of the stria terminalis, lateral septal nucleus, medial preoptic area, peri- and paraventricular nuclei of the hypothalamus, anterior lateral hypo thalamic area and dorsal raphe nucleus. In addition, the role of neuro tensin in the modulation of autonomic regulatory input from the insula was investigated. The lateral hypothalamic area was surveyed for sing le units responding to electrical stimulation (500-900 mu A, 0.5 Hz) o f sites in the insular cortex from which cardiovascular presser or dep ressor responses could be elicited. These units were tested for the in fluence of neurotensin on responses to stimulation of the insular cort ex. Of 60 spontaneously firing neurons, 27 units responded to electric al stimulation of cardiovascular sites in the insula. Of the units res ponding to stimulation of cardiovascular sites in the insula, 14 units showed excitation only, 10 units showed excitation followed by inhibi tion and three units showed inhibition. Iontophoresis of 0.1-1.0 mM ne urotensin (25-100 nA, pH 5.0-6.0) potentiated six of the excitatory re sponses and showed no effect on the inhibitory responses. In addition, nine neurons showed an increase in spontaneous activity with iontopho resis of neurotensin. Of these neurons, three were excited by insular stimulation and six did not respond. These findings indicate the likel y origin of neurotensin in the lateral hypothalamic area and demonstra te that neurotensin has a role in the modulation of some of the cardio vascular regulatory input from the insular cortex.