Activation of Locus Coeruleus Somatostatin Receptors Induces an Increase of Growth Hormone Release in Male Rats

Abstract

Noradrenergic neurons of the locus coeruleus (LC) negatively regulate the endogenous rhythmicity of growth hormone (GH) secretion. These neurons express high concentrations of receptors for somatostatin (SRIH) and galanin (GAL), two neuropeptides which can affect electrical activity of LC neurons and also centrally modulate plasma GH levels. We thus investigated whether somatostatin and galanin receptors located in the LC are involved in GH regulation. Pulsatile patterns of endogenous GH secretion were monitored after unilateral infusion of the peptides into the lateral ventricle (ICV) or into the LC, after lesion of contralateral LC neurons by 6 hydroxydopamine. Neither unilateral LC lesions nor administration of saline affected GH release. When administered ICV, both SRIH (5 micrograms/microliter/15 min) and GAL (1 microgram/microliter/15 min) resulted in a marked increase in GH secretion. Infusion of SRIH into the LC induced a significant but weaker stimulation of plasma GH as compared to ICV injections. In contrast, infusion of GAL into the LC was ineffective. These results indicate that somatostatin can exhibit direct effects on noradrenergic neurons of the LC involved in GH regulation, whereas central effects of galanin on the hormone are mediated by distinct structures.

GalR1, but not GalR2 or GalR3, levels are regulated by galanin signaling in the locus coeruleus through a cyclic AMP‐dependent mechanism

“…Galanin has been shown to attenuate the firing rate of LC neurons (Nishibori et al 1988;Seutin et al 1989;Sevcik et al 1993), which correlates with the ability of galanin to attenuate opiate withdrawal symptoms (Zachariou et al 2003). Galanin has also been shown to have a direct and indirect effect on modulation of the noradrenaline-induced outward current of LC neurons (Xu et al 2001), but has no effect on LC-stimulated growth hormone release (Mounier et al 1996). Active wheel running (Van Hoomissen et al 2004) and estrogen treatment (Tseng et al 1997) correlate with an induction of galanin gene expression in the LC.…”

“…Galanin has also been shown to have a direct and indirect effect on modulation of the noradrenaline‐induced outward current of LC neurons (Xu et al . 2001), but has no effect on LC‐stimulated growth hormone release (Mounier et al . 1996).…”