Hibernation-related changes in the immunoreactivity of neuropeptide systems in the suprachiasmatic nucleus of the ground squirrel, Spermophilus richardsonii

Abstract

The pattern of distribution and reactivity of the neuropeptides vasopressin (AVP), vasoactive intestinal peptide (VIP), neuropeptide Y (NPY), substance P (SP), and thyrotropin-releasing hormone (TRH) were studied in the suprachiasmatic nucleus (NSC) of 20 Richardson's ground squirrels (and 7 European hedgehogs) of both sexes during hibernation and euthermia. The total area of immunostained structures revealed by application of the individual immunocytochemical techniques was measured by means of computer-aided image analysis. In both species, elements of all peptide systems examined were related to particular subdivisions of the NSC. The pattern of immunoreactivity was strongly correlated with the physiological stage of hibernation or euthermia both in ground squirrels and hedgehogs. The immunoreactivities to AVP and SP increased in area during hibernation (AVP: 25%; SP: 25%), whereas the respective area immunoreactive to NPY and VIP decreased (NPY: 45%; VIP: 100%) in comparison to nonhibernating controls. The TRH-immunoreactive nerve fibers were rare and rather scattered; thus, the quantitative procedure was not applicable for this immunoreaction.