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Male (N = 9) and female (N = 7) infant albino rats sustained bilateral lateral preoptic area (LPO) destruction on the tenth day of life. During development and as adults, these brain-damaged rats were subjected to repeated testing of drinking behaviors in response to cellular and extracellular dehydration. Immediately following LPO destruction the pups ceased suckling and most rats required tube-feeding to maintain life; however, all pups were maintaining body weight through voluntary suckling and/or feeding-drinking by 20-21 days of age. Daily water intakes were elevated from 30-42 days of age, following which intakes decreased to control vonse to water deprivation, polyethylene glycol injection and food deprivation treatments. These results are consistent with the suggestion that the LPO contains osmoreceptors for drinking behavior, and the present results suggest that such osmoreceptors, may be functional by the tenth day of life for rats.

Single-unit recordings were made from lateral hypothalamic area (LHA) neurons of infant (8 through 21 days of age) male and female albino rats. Basal (or spontaneous) firing rates of LHA neurons were recorded for 20 min from rats 8 through 21 days of age, and mean basal firing rates did not differ across ages. Basal firing rates of LHA neurons in infant rats ranged from less than 1 spike/sec up to 27 spikes/sec, with 56% of the basal rates less than 1 spike/sec. Infant rats also received hypertonic saline injections (and control injections) to determine osmosensitivity characteristics of LHA neurons. Across ages, 56%--88% of LHA neurons were osmosensitive, with the highest percentages of osmosensitive units found in rats 14--21 days of age. Infant rats showed LHA unit electrophysiological characteristics that were quite similar to those obtained from LHA neurons in adult rats with respect to basal firing rates and osmosensitivity, however, LHA neuron activity in infants was not modulated by sensory stimuli as is frequently reported for adults. The results are discussed in terms of functional development of the LHA.

Donor tectal tissue from fetal rats was transplanted to the tectal region of intact host newborn rats. Histological and ultrastructural characteristics of mature tectal grafts were examined with special emphasis placed on glial elements and the interface between transplant and host brain. Most transplants survived, proliferated, and differentiated to mature neurons and glial cells. Mature transplants were found to contain small and medium sized neurons which formed clusters along the transplant border. Neurites traversed the interface between transplant and host brain. There was an absence of phagocytosis, inflammatory reactions and chromatolytic neurons throughout the transplant. Classical staining techniques and GFAP immunoreactive stains revealed only mild focal astrogliosis confined mostly to the subpial and perivascular regions of the transplant-host interface. Ultrastructural examination of the transplant revealed numerous axodendritic synapses with aggregates of synaptic vesicles and well formed postsynaptic membranes. The absence of a leptomeningeal membrane at several points along the transplant-host interface may allow neurites from both sides to establish functional synaptic contacts. Single unit recording combined with anterograde WGA-HRP neuronal tract tracing was used to determine the presence and extent of host retinal innervation of tectal transplants.