Changes in vasoactive intestinal peptide and arginine vasopressin expression in the suprachiasmatic nucleus of the rat brain following footshock stress

Abstract

The neuropeptides, arginine vasopressin (AVP) and vasoactive intestinal polypeptide (VIP) are synthesized by neurons of the suprachiasmatic nucleus (SCN) of the hypothalamus and are important regulators of SCN function. Previous studies have demonstrated that acute exposure to stressors can disrupt circadian activity rhythms, suggesting the possibility of stress-related alterations in the expression of these neuropeptides within SCN neurons. In this study, we examined the effect of intermittent footshock stress on AVP mRNA and heterogeneous nuclear RNA (hnRNA) and VIP mRNA expression in neurons of the SCN. Young adult male Sprague/Dawley rats were subjected to 15 s of scrambled intermittent footshock (0.50 mA pulses, 1 pulse/s, 300 ms duration) every 5 min for 30 min. Animals were sacrificed 75 or 135 min after the onset of stress and brains examined for AVP mRNA and hnRNA, and VIP mRNA using in situ hybridization. Footshock stress increased AVP hnRNA levels at the 75 min time point whereas AVP mRNA was elevated at both the 75 and 135 min time points. In contrast, footshock stress decreased the number of cells expressing VIP mRNA in the SCN without changing hybridization level per cell. These data indicate that the disruptive effect of stress on activity rhythms correlate with alterations in the expression of regulatory peptides within the SCN.

Figure 1

Effect of footshock stress on VIP mRNA in the SCN. Adult male rats were sacrificed either 75 min. or 135 min. after receiving 30 min of intermittent footshock. Each bar represents the group means (± SEM). Figure 1A depicts the data obtained following density analysis of film autoradiograms. Figure 1B depicts the results of VIP mRNA levels following grain density estimates from emulsion coated slides expressed as the ratio of labeled cells to unlabeled cells. Ratios for individual animals were derived from analyses performed on 55-74 neurons. No differences in the density of the individual labeled neurons were observed between. N=5/group. NS = nonstressed. *p<0.05 from control group.

Figure 2

Effect of footshock stress on AVP mRNA expression in the SCN, PVN and SON of adult male rats. mRNA levels were measured using optical density of film autoradiograms. Each bar represents the mean +/- SEM of 5 animals/group. *p<0.05 from control group.

Figure 3

AVP mRNA and heteronuclear RNA levels in individual neurons of the SCN. Data shown are the mean (± SEM) number of grains (minus background) over individual SCN neurons. The analysis measured 60-75 cells per animal with 5 animals representing each group. *p<0.05 from control group.