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. 1983 Apr;337:441–450. doi: 10.1113/jphysiol.1983.sp014634

A role for an indoleamine other than 5-hydroxytryptamine in the hypothalamic thermoregulatory pathways of the rat

B Cox 1, A Davis 1, Valerie Juxon 1, T F Lee 1,*, Deborah Martin 1
PMCID: PMC1199117  PMID: 6875941

Abstract

1. Intrahypothalamic injection of either 5-hydroxytryptamine (5-HT) (20 μg) or tryptamine (1 μg) caused hypothermia and hyperthermia respectively in lightly restrained rats maintained at an ambient temperature of 20 ± 1 °C.

2. Both the 5-HT- and the tryptamine-sensitive sites were located within the same region of the preoptic area.

3. When rats were tested at different ambient temperatures (4, 20 and 29 °C), intrahypothalamic injection of 5-HT caused a marked fall in core temperature (-1·3 °C) in rats maintained at 4 °C, but smaller responses were obtained at 20 and 29 °C (-0·9 and -0·5 °C respectively). Tryptamine caused a significant hyperthermia in rats kept at 20 °C, but had no significant effect in rats maintained at either 4 or 29 °C.

4. The hypothermic effect of 5-HT was selectively antagonized by systemic pre-treatment with cyproheptadine (2·5 mg/kg), but not by methergoline (0·625 mg/kg) and methysergide (0·2 mg/kg). In contrast, the hyperthermic effect of tryptamine was blocked by methergoline and methysergide, but not by cyproheptadine.

5. Cyproheptadine (2·5 mg/kg) reduced the ability of rats to cope with a heat load but had no effect on the response to cold. In contrast, methergoline (0·625 mg/kg) and methysergide (0·2 mg/kg) reduced the ability to cope with cold but the rats' ability to cope with a heat load remained intact.

6. These results suggest the existence of two indoleamine pathways within the preoptic anterior hypothalamus involved in the control of body temperature: a serotonergic pathway mediating heat loss and a non-serotonergic pathway mediating heat gain. The non-serotonergic system may exert its effects by modulating the activity of a central serotonergic system.

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Selected References

These references are in PubMed. This may not be the complete list of references from this article.

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