Influence of prenatal and postnatal acclimation on nervous and peripheral thermoregulation.

The aim of the present study was to investigate whether prenatal and postnatal adaptation to different ambient temperatures affects the autonomic (heat production, heat loss, rectal or colonic temperature), behavioral (preferred ambient temperature) and nervous mechanisms (neuronal thermosensitivity of the preoptical area of the anterior hypothalamus) of thermoregulation. The experiments were carried out in postnatal, differently acclimated adult rabbits (60 days at 6-7, 20 and 30 degrees C) and adult rats (3 to 6 weeks at 5 and 21 degrees C) and in differently incubated 1- to 10-day-old Muscovy ducklings and turkeys (last week of incubation at 34.5, 37.5 and 38.5 degrees C). The results of the experiments are summarized as follows: (1) Postnatal acclimation changes the threshold ambient temperature of heat loss and heat production. For example, cold-acclimated rabbits have a lower threshold temperature for evaporative heat loss and thermoregulatory heat production than heat-acclimated ones. (2) Prenatal acclimation changes postnatal thermoregulatory behavior as well as autonomic thermoregulatory mechanisms. Birds incubated at higher (38.5 degrees C) or lower (34.5 degrees C) temperatures than the usual 37.5 degrees C for the last week of embryonic development have higher or lower preferred ambient temperatures during the first 10 days post hatching. Besides this, cold-incubated birds have a higher heat/ production and clonic temperature in the first days post hatching than normally/ incubated or heat-incubated ones. (3) Extracellular recordings from hypothalamic neurons in brain slices from differently acclimated rats have shown that adaptation to different ambient temperatures changes firstly the temperature sensitivity of the hypothalamic neurons and secondly the modulatory action of the neuropeptides bombesin and thyrotropin releasing hormone.