Neural mechanism involved in the interaction between thermo- and osmoregulation: a role of median preoptic area in the hypothalamus

 

Kei Nagashima

Laboratory of Integrative Physiology, Health and Welfare, Faculty of Human Sciences, Waseda University

 

Dehydration attenuates autonomic heat loss responses in the heat.  In the present study, we hypothesized that hyperosmolality in the brain would play an important role in the attenuation and the hypothalamic areas would be involved in the mechanism.  Especially, the role of the preoptic area (POA) and median preoptic area (POA), which are involved in either thermoregulation or osmoregulation were investigated.  In anesthetized rats, isotonic (154 mM) or hypertonic (1500 mM) saline was injected to the internal carotid artery, and the POA in the hypothalamus was locally heated at ~40 °C using a thermode.  The same experiment was repeated on rats, of which the MnPO was lesioned with ibotenate.  The POA heating increased tail skin temperature (T_tail) by 3.4 ± 0.2 °C (means ± SE, n=11) during isotonic saline injection.  Hypertonic-saline injection suppressed (P<0.05) the increase in T_tail during warming of the dorsolateral area of the POA, but not the ventral area of the POA (n=13).  However, in the MnPO-lesioned rats, an increase in T_tail was similar between the isotonic and hypertonic saline trials during heating of the dorsolateral area of the POA (3.3 ± 0.4 and 3.2 ± 0.3 °C during the isotonic- and hypertonic-saline infusion, respectively, n=7).  Immunohistological analysis also indicates that there is neural connection between the POA and MnPO.  In addition, the MnPO sends inhibitory signal to the POA.  These results may suggest that hypermosmolality in the brain attenuated the neural response to the heat in the POA.  Moreover, the MnPO is necessary for this response.

 

Key words: osmolality, body temperature, median preoptic nucleus, vasodilatation, preoptic area