Expression of VIP and/or PACAP receptor mRNA in peptide synthesizing cells within the suprachiasmatic nucleus of the rat and in its efferent target sites

Jun 4, 2004The Journal of comparative neurology

Presence of VIP and PACAP receptor messages in peptide-producing cells of the rat's body clock and its output areas

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Abstract

Nearly 100% of arginine-vasopressin (AVP) neurons in the rat suprachiasmatic nucleus (SCN) express VPAC(2) mRNA.

VPAC(2) mRNA is found in 41% of vasoactive intestinal peptide (VIP) neurons and 23% of somatostatin (SST) neurons in the SCN.
PAC(1) mRNA is detected in 45% of VIP neurons, 40% of SST neurons, and 32% of AVP neurons.
VPAC(2) mRNA is also present in several diencephalic areas that receive signals from SCN VIP neurons.
The distribution of PAC(1) mRNA within the SCN indicates that PACAP's effects may extend beyond the retinorecipient region.
The presence of VPAC(2) mRNA in AVP neurons suggests a potential regulatory connection between SCN VIP neurons and AVP systems.

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The suprachiasmatic nucleus (SCN) contains the predominant circadian pacemaker in mammals. Considerable evidence indicates that VPAC(2) and PAC(1), receptors for vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP), play critical roles in maintaining and entraining circadian rhythms. Retinal projections to the rat SCN contain PACAP and terminate mostly in the ventral SCN, the site of VIP neurons. The incidence of VPAC(2) and PAC(1) mRNAs within distinct neuronal populations of the rat SCN has been determined using double-label in situ hybridization. VPAC(2) mRNA was detected in almost all arginine-vasopressin (AVP) neurons of the dorsomedial SCN and in 41% of the VIP neurons; somatostatin (SST) neurons, predominantly in dorsomedial and intermediate regions, showed a decreased incidence (23%). PAC(1) mRNA was present in nearly half of the VIP and SST neurons (45% and 40%, respectively) and in one-third of the AVP neurons (32%). Cells expressing VPAC(2) mRNA also were detected in diencephalic areas that receive VIP-immunoreactive SCN efferents, such as the peri-suprachiasmatic region, lateral subparaventricular zone, parvocellular hypothalamic paraventricular subdivisions, dorsomedial hypothalamic nucleus, and anterior thalamic paraventricular and paratenial nuclei. The extensive distribution of PAC(1) mRNA within the SCN suggests that actions of PACAP are not restricted to the predominantly retinorecipient region. The presence of VPAC(2) mRNA in nearly half the VIP neurons, in almost all the AVP neurons, and at sites receiving VIP-immunoreactive SCN efferents suggests that the SCN VIP neurons are coupled and/or autoregulated and also influence the AVP-containing dorsomedial SCN and distal sites via VPAC(2).

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Expression of VIP and/or PACAP receptor mRNA in peptide synthesizing cells within the suprachiasmatic nucleus of the rat and in its efferent target sites

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