Distribution and morphology of vasopressin‐, neurophysin II‐, and oxytocin‐immunoreactive cell bodies in the forebrain of the cat

Experiments were done to provide a detailed map of the location and a description of morphological characteristics of vasopressin (AVP‐IR)‐, neurophysin II (NII‐IR)‐ and oxytocin (OXY‐IR)‐immunoreactive neuronal perikarya in the forebrain of the cat. In addition, the location of cells in the forebrain retrogradely labeled following injections of tracers into the neurohypophysis was determined. The distribution of AVP‐IR and NII‐IR was similar in all cases studied. Most of the cells containing AVP‐IR and OXY‐IR were observed in the hypothalamic paraventricular (PVH) and supraoptic (SON) nuclei. In addition, AVP‐IR and OXY‐IR cell bodies were found in the regions of the nucleus of the diagonal band of Broca, the dorsal chiasmatic nucleus, the anterior hypothalamic‐preoptic area, the periventricular area, the nucleus circularis, the perifornical area of the lateral hypothalamus, the accessory SON, the area of the tuber cinereum (Tca), and the medial nucleus of the amygdala. The density of AVP‐IR cells was greater than that of OXY‐IR cells in these regions. Several forebrain areas were also observed to contain only AVP‐IR perikarya: the suprachiasmatic nucleus (Sc), the bed nucleus of the stria terminalis, and the region of the substantia innominata and ventral globus pallidus (SI/GP). In addition, the dorsomedial nucleus of the hypothalamus only contained OXY‐IR perikarya. Most of the cells immunoreactive to AVP were multipolar and had spinelike processes over their somata and proximal dendrites. In addition, the majority of cells in the PVH and SON were round or oval, whereas those outside these nuclei were fusiform or triangular. The mean somal area of AVP‐IR cells in the region of the SI/GP was significantly ( P < 0.05) larger than that of AVP‐IR cells in all other regions examined, whereas the mean somal area of Sc AVP‐IR cells was significantly ( P < 0.05) smaller than that of all other groups of AVP‐IR cells examined. Most OXY‐IR cells were similar morphologically to those immunoreactive to AVP, except that OXY‐IR cell bodies and their appendages did not have spinelike processes. In addition, OXY‐IR perikarya were generally of uniform size. OXY‐IR cells in the PVH and accessory SON were significantly ( P < 0.05) larger than AVP‐IR cells in the same regions, but were not different from AVP‐IR cells in the lateral hypothalamus and SON. After the injection of either horseradish peroxidase or Fast Blue into the neurohypophysis, retrogradely labeled cells were found in essentially the same forebrain structures as those containing AVP‐IR and OXY‐IR cells, except for the dorsal chiasmatic nucleus, Sc, and the ventral GP region. In addition, there were considerably fewer retrogradely labeled cells than cells immunoreactive for AVP and OXY in all regions examined, except for the SON, where all cells appeared to be retrogradely labeled. Most of the retrogradely labeled cells were found in the PVH, SON and region of the Tca. These combined data indicate that AVP and OXY cells projecting to the neurohypophysis are found in several forebrain structures. In addition, their number and restricted distribution in these forebrain structures suggests that AVP and OXY cells are also likely to be involved in other physiological functions such as neurotransmission.