POSTNATAL-DEVELOPMENT OF THE VASOPRESSINERGIC SYSTEM IN GOLDEN-HAMSTERS

Adult golden hamsters, as compared to rats, lack several parvicellular vasopressinergic cell groups. We looked at the development of the vas opressinergic system in hamsters to draw comparisons with maturing rat s. Arginine-vasopressin-immunoreactive (AVP-ir) neurons, their fibers and associated AVP binding sites were observed at several intervals af ter birth. Different rates of maturation were observed between differe nt populations of vasopressinergic neurons. Within the suprachiasmatic nucleus (SCN), small AVP-ir neurons, their fibers and related binding sites maturated gradually during the first month after birth. In comp arison, large AVP-ir neurons were apparent in newborn animals. Similar ly, AVP-ir fibers and AVP binding sites were also present in the brain of newborns within areas not related to small vasopressinergic neuron s from the SCN, such as the central amygdala (CeA) or the cerebral cor tex. During the following weeks, a heterogenous pattern of development was observed within such areas. As the neurosecretory vasopressinergi c system appeared to develop gradually, projections to the brain and t heir associated binding sites developed rapidly during the first week of life. Transient patterns of maturation were observed within certain sites. Indeed, some of the labelling observed in newborns regressed l ater. As similar reports were made in rats, our observations draw anal ogies between the vasopressinergic systems of these two species, besid e their apparent dissimilarities in adult animals. Furthermore, our da ta also reinforce the concept that large vasopressinergic neurons do n ot constitute a homogenous population.