The influence of paraventricular nucleus of the hypothalamus soluble guanylate cyclase on autonomic and neuroendocrine responses to acute restraint stress in rats

Abstract

The paraventricular nucleus of the hypothalamus (PVN) regulates physiological and behavioural responses evoked by stressful stimuli, but the local neurochemical and signalling mechanisms involved are not completely understood. The soluble guanylate cyclase (sGC) within the PVN is implicated in autonomic and cardiovascular control in rodents under resting conditions. However, the involvement of PVN sGC-mediated signalling in stress responses is unknown. Therefore, we investigated the role of sGC within the PVN in cardiovascular, autonomic, neuroendocrine, and local neuronal responses to acute restraint stress in rats. Bilateral microinjection of the selective sGC inhibitor ODQ (1 nmol/100 nl) into the PVN reduced both the increased arterial pressure and the drop in cutaneous tail temperature evoked by restraint stress, while the tachycardia was enhanced. Intra-PVN injection of ODQ did not alter the number of Fos-immunoreactive neurons in either the dorsal cap parvocellular (PaDC), ventromedial (PaV), medial parvocellular (PaMP), or lateral magnocelllular (PaLM) portions of the PVN following acute restraint stress. Local microinjection of ODQ into the PVN did not affect the restraint-induced increases in plasma corticosterone concentration. Taken together, these findings suggest that sGC-mediated signalling in the PVN plays a key role in acute stress-induced pressor responses and sympathetically mediated cutaneous vasoconstriction, whereas the tachycardiac response is inhibited. Absence of an effect of ODQ on corticosterone and PVN neuronal activation in and the PaV and PaMP suggests that PVN sGC is not involved in restraint-evoked hypothalamus-pituitary-adrenal (HPA) axis activation and further indicates that autonomic and neuroendocrine responses are dissociable at the level of the PVN.

Keywords: PVN, sGC; cardiovascular responses; corticosterone; sympathetic activity.

Figure 1 –

A diagrammatic representation modified from the rat brain atlas of Paxinos and Watson (1986) indicating the dispersion of microinjection sites throughout the PVN (filled circles) of rats used in the present experiments. PVN— paraventricular nucleus of the hypothalamus; f—fornix; opt—optic chiasm.

Figure 2 –

Mean arterial pressure (MAP), pulsatile arterial pressure (PAP), and heart rate (HR) recordings of representative rats illustrating the effects of the pretreatment with Dimethyl sulfoxide (DMSO, vehicle, 100nL) or the selective sGC inhibitor 1H-[1,2,4] oxadiazolol [4,3-a]quinoxalin-1-one (ODQ, 1 nmol/100 nL) into the paraventricular nucleus of hypothalamus (PVN), before and during the restraint.

Figure 3 -

Tail infrared digital images of representative rats that received Dimethyl sulfoxide (DMSO, vehicle, 100nL) or the selective sGC inhibitor 1H-[1,2,4] oxadiazolol [4,3-a]quinoxalin-1-one (ODQ, 1 nmol/100 nL) into the paraventricular nucleus of hypothalamus (PVN) in their home cages and on the first and last minute of the restraint. Note that the drop in the cutaneous tail temperature during the restraint is reversed in animals treated with ODQ. All images use the same color coding to indicate the temperature.

Figure 4 –

A) Mean arterial pressure (ΔMAP) and heart rate (ΔHR) changes over time during the restraint that were observed in rats with the bilateral paraventricular nucleus of hypothalamus (PVN) pretreated with Dimethyl sulfoxide (DMSO, vehicle, 100nL, n=5) or the selective sGC inhibitor 1H-[1,2,4] oxadiazolol [4,3-a]quinoxalin-1-one (ODQ, 1 nmol/100 nL, n=9) B) Tail skin temperature changes over time before and during restraint observed in animals with the bilateral PVN pretreated Dimethyl sulfoxide (DMSO, vehicle, 100nL, n=5) or the selective sGC inhibitor 1H-[1,2,4] oxadiazolol [4,3-a]quinoxalin-1-one (ODQ, 1 nmol/100 nL, n=9). C) Corticosterone plasma concentration over time before and during the restraint in animals with the bilateral PVN Dimethyl sulfoxide (DMSO, vehicle, 100nL, n=9) or the selective sGC inhibitor 1H-[1,2,4] oxadiazolol [4,3-a]quinoxalin-1-one (ODQ, 1 nmol/100 nL, n=8). The acute restraint stress was started at time 0 and ended at 60 minutes. Points represent the mean and bars the SEM. *significantly different from vehicle (P<0.05).

Figure 5 –

Average of number of c-Fos-immunoreactive cells per mm² × 1000 in the portions of PVN: dorsal cap (PaDC), lateral magnocellular (PaLM), medial parvocellular (PaMP) and ventral (PaV), after the bilateral PVN microinjection of Dimethyl sulfoxide (DMSO, vehicle, 100nL, n=9) or the selective sGC inhibitor 1H-[1,2,4] oxadiazolol [4,3-a]quinoxalin-1-one (ODQ, 1 nmol/100 nL, n=8). followed by 60 min of acute restraint stress.