Abstract
We previously reported that s.c. hypertonic-saline increased operant heat-escape/warm-seeking behavior in rats. In this study, to assess the mechanism involved, the behavior was measured in rats of which the median preoptic nucleus (MnPO) was chemically ablated (ibotenic acid, 5 μg). The lesion was verified success by an attenuation of the drink after i.c.v. injection of angiotensin II. Thirty minutes after s.c. injection of either 2500- or 154-mM saline (1.0 ml/100 g), rats were successively placed at 26, 35 and 40°C for 1 h each. They could trigger 0°C-air for 45s when entered a specific area (i.e. operant behavior). In the sham-operated rats, counts of the operant behavior was greater (p<0.05) in 2500-mM than 154-mM saline during 35 and 40°C-heat. However, in the lesioned-rats, the counts did not differ between the two trials, and were at the same level as those in the sham-operated rats in 154-mM saline trial. These results suggest that the MnPO is involved in the mechanism which activates heat-escape/warm-seeking behavior after hypertonic-saline injection. Howeover, the MnPO is not associated with the behavior in euhydrated condition. [Jpn J Physiol 54 Suppl:S230 (2004)]
