DISTRIBUTION OF AVP AND CA2-DEPENDENT PKC-ISOZYMES IN THE SUPRACBIASMATIC NUCLEUS OF THE MOUSE AND RABBIT()

The suprachiasmatic nucleus (SCN) is the circadian pacemaker in mammal s and contains a network of arginine-vasopressin-immunoreactive (AVP-i r) neurons. AVP-recipient cells contain the V1a class of receptors lin ked to phosphoinositol turnover and protein kinase C (PKC). The presen t study describes the localization of AVP and the four Ca2+-dependent PKC-isoforms in the mouse and rabbit SCN. An estimate of the numerical density of AVP-ir neurons at the rostral, medial, and caudal level of the SCN revealed that the mouse SCN contains more than twice the numb er of AVP-ir neurons than the rabbit SCN. Neurons immunostained for AV P or PKC dominated in the dorsomedial and ventrolateral aspects of the mouse SCN, while the central area of the SCN revealed only weakly sta ined neurons. The rabbit SCN was characterized by a more homogeneous d istribution of AVP-ir and PKC-ir neurons. PKC alpha was the most abund antly expressed isozyme in both species, whereas the presence of the o ther isoforms differed (mouse: PKC alpha > PKC beta I > > PKC beta II > PKC gamma; rabbit: PKC alpha:> PKC beta II greater than or equal to PKC gamma> PKC beta I). Clear PKC gamma-positive neurons were only obs erved in the rabbit SCN, while the mouse SCN predominantly contained i mmunolabeled fiber tracts for this PKC isozyme. Astrocytes immunoreact ive for each PKC isoform. were frequently encountered in the rabbit SC N, but were absent in mice. Immunofluorescence double labeling showed that numerous AVP-recipient cells in the mouse SCN were immunopositive for PKC alpha, and that nearly all AVP-ir neurons express PKC alpha a bundantly. These results substantiate the putative role for PKC alpha in vasopressinergic signal transduction in the SCN. The differential e xpression in degree and cell type of the Ca2+-dependent PKC-isoforms i n the mouse and rabbit SCN may be related to the differences observed in circadian timekeeping between the two species.