The effects of nucleus raphe magnus lesions on an ascending thermal pathway in the rat.

Abstract

SUMMARY1. In the thalamus and hypothalamus of rats, anaesthetized with Urethane, single unit recordings have been made from cells which respond to small innocuous changes in scrotal skin temperature applied with a water-perfused brass thermode.2. Once a scrotal temperature-sensitive neurone had been isolated the brain stem was electrolytically lesioned through implanted tungsten electrodes to determine whether the input from the scrotal skin temperature sensors ascends through the brain stem lemniscal pathways or the mid-line raphe nuclei. All recording sites and lesions were identified histologically.3. Thirty-six neurones have been studied of which half were located in the ventrobasal thalamus, six were located in the anterior thalamic nuclei and the remainder were in the medial hypothalamus.4. The nucleus raphe magnus was lesioned on eighteen separate occasions; in each case the temperature-responsive activity of the thalamic or hypothalamic neurone was abolished.5. Extensive brain-stem lesions which spared only the mid-line nucleus raphe magnus had no discernible effect on the responses of the thalamic or hypothalamic neurones to scrotal skin temperature.6. The ascending pathway from the thermal sensors of the rat scrotal skin must pass through, or relay in, the nucleus raphe magnus.

In situ histochemical localization of type I interleukin-1 receptor messenger RNA in the central nervous system, pituitary, and adrenal gland of the mouse

“…Second, 5-HT is well known to suppress appetite, most probably via hypothalamic projections (see Curson, 1990). Third, a number of lines of evidence have implicated the raphe and 5-HT in thermoregulation, including (1) the presence ofthermosensitive neurons in the rostra1 raphe (Cronin and Baker, 1976;Hori and Harada, 1976); (2) enhanced firing of neurons in the preoptic area of the hypothalamus following rostra1 raphe stimulation (Bruck and Hinckel, 1980;Werner and Bienek, 1985) and (3) abolition of the thermoresponsiveness of preoptic neurons following lesions of the rostra1 raphe (Taylor, 1982;Werner and Bienek, 1985). Interestingly, the fever induced by administering bacterial pyrogens may be attenuated by raphe lesions (Kadlecova et al, 1977) or by depleting (Harvey and Milton, 1974;Kandasamy, 1977;Matuszek and Ishikawa, 198 1) or antagonizing (Kandasamy, 1977) central 5-HT (see Myers, 1980).…”

More Than a Marker: Interaction Between the Circadian Regulation of Temperature and Sleep, Age-Related Changes, and Treatment Possibilities

“…Local thermosensitive neurons with a prevalence similar to those of the POAH have been demonstrated in rat tissue in vitro in several thalamic nuclei, particularly, but not exclusively, in the arousal-related midline reuniens nucleus (Taylor 1982;Dean et al 1992;Travis et al 1995). The majority of local thermosensitive cells are intrinsically warm sensitive (Dean and Boulant 1992;Travis et al 1995).…”

The preoptic area in the hypothalamus is the source of the additional respiratory drive at raised body temperature in anaesthetised rats

“…Again it is possible that the collaterals to the brainstem (Taylor, 1982;Hellon & Taylor, 1982) from spinothalamic afferents, or raising the temperature of brainstem itself, may have limited facilitatory effects on the respiratory network. Such effects are slight, however, because their activation only sustains the breathing that is already present and cannot itself cause breathing to reappear.…”

“…Such hypotension could provide an additional drive to breathe by reducing the perfusion of peripheral chemoreceptors sufficiently to increase their stimulation. Thirdly, it remains possible that such high temperatures either stimulate the respiratory network in the brainstem directly, or stimulate sufficient activity in collaterals from thermoreceptor afferents travelling in the spinothalamic tract (Taylor, 1982;Hellon & Taylor, 1982) to facilitate activity in the respiratory network. One further observation indicates that regions caudal to the hypothalamus may provide a weak but additional influence on breathing at raised temperature.…”