Differential involvement of hippocampal vasoactive intestinal peptide in nociception of rats with a model of depression

The effects of VIP microinjected unilaterally (left or right) into the hippocampal CA1 area at a dose of 10 and 100 ng or bilaterally (10 ng), on nociception of male Wistar rats with a model of depression (bilateral olfactory bulbectomy—OBX) were studied. Nociception was examined applying mechanical pressure on the left hind paw of the rat (analgesy-meter test). It was found that in OBX rats the pain threshold is increased. VIP showed differential effects depending on the side and dose of administration. The pain threshold after left-side microinjections of VIP into the hippocampal CA1 area of OBX rats was significantly higher than that after injections into right-side. There are no significant differences between right-side VIP-treated and OBX rats. Bilateral microinjections of VIP also exerted antinociceptive effect. These findings suggest that the hippocampal lateralized antinociceptive effect of VIP in OBX rats depends on the hemisphere of injection and suggest that VIP-ergic neurons in the hippocampal CA1 area may play differential role in nociception of rats with a model of depression.