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Radioautographic determinations of 125I-[Tyr0,D-Trp8]somatostatin-14 (125I-SRIF) binding sites were performed on frozen serial sections of the locus coeruleus (LC) of control rats and of rats subjected to either bilateral microinjections of 6 hydroxydopamine (6-OHDA) into the LC or unilateral microinjection into the ascending noradrenergic bundles. These experiments were performed in order to determine whether 125I-SRIF binding was localized to noradrenergic-containing cells and in which regions the cells which contain the binding sites are projecting. The extent of the lesions was assessed by measuring norepinephrine (NE) levels in the hippocampus (88% decrease as compared to sham-operated animals) for bilateral LC lesions and in the frontal cortex (87% reduction vs. contralateral side) for unilateral bundle lesions. In control rats, 125I-SRIF binding sites were restricted to the boundaries of the LC and followed closely the distribution of tyrosine hydroxylase-labeled cells. Three weeks after bilateral injections of 6-OHDA, 125I-SRIF binding decreased by 79% in all regions of the LC. In contrast, unilateral destruction of the ascending noradrenergic bundles resulted in a moderate decrease only in the middle part of the LC with a more important effect in the dorsal (55%) than in the ventral (24%) portion of the nucleus. These data demonstrate that: 1) most SRIF receptors in the LC are located in the vicinity of NE-containing cell bodies and 2) NE-containing cells bearing SRIF receptors project to the forebrain as well as to other terminal areas located more caudally in the brain. These data suggest a general role for SRIF in the control of the multiple functions of the LC.

Effects of vasoactive intestinal peptide (VIP) on growth hormone (GH) secretion were investigated both in vivo on freely moving, intact or mediobasal hypothalamic lesioned rats, and in vitro in incubation or superfusion systems of anterior pituitary tissue. In vivo, IV injection of VIP induced a rapid but transient increase in plasma GH levels in all animals and in vitro, VIP stimulated GH release from incubated or superfused rat pituitaries in a concentration dependent manner. This increase was potentiated by forskolin, a potent activator of adenylate cyclase. These findings indicate that VIP exerts a direct stimulating action on somatotrophs and that the effect seems to imply a coupling of VIP receptors with cAMP production.