Effects of hypothalamic thermal stimuli on sympathetic neurones innervating skin and skeletal muscle of the cat hindlimb.

Abstract

1. Postganglionic neurones supplying hairless and hairy skin of the cat hindlimb were analysed for their responses to thermal stimuli applied to the anterior hypothalamus and spinal cord in anaesthetized and artificially ventilated cats. Activity was recorded from multi-and single-unit bundles which were isolated from peripheral nerves. The neurones were functionally identified as cutaneous vasoconstrictor (CVC) and muscle vasoconstrictor (MVC) neurones. Activity in sudomotor (SM) neurones was either monitored indirectly by recording the phasic negative deflections of the skin potential from the surface of the hairless skin, or in some experiments additionally by recording activity directly from the SM axons. 2. The activity in forty-one out of forty-four multi-unit and six out of six single-unit CVC bundles was inhibited, in a graded manner, by hypothalamic warming. An increase in the temperature of the surface of hairless skin followed the decrease in activity of the CVC neurones supplying it. Large changes in skin temperature only followed decreases in CVC activity of more than 40%. Cooling of the hypothalamus had only weak transient effects on CVC neurones. 3. Simultaneous warming of hypothalamus and spinal cord had multiplicative effects on the activity in CVC neurones. Subthreshold warming of one structure increased the response to warming of the other one and reduced the threshold temperature. 4. SM neurones were not affected by hypothalamic warming, but activated during hypothalamic cooling. 5. MVC neurones were weakly activated during hypothalamic warming only if arterial blood pressure decreased, otherwise they were unaffected. It is likely that this activation was due to secondary unloading of arterial baroreceptors. 6. Two silent postganglionic neurones projecting to skin were activated during hypothalamic warming. These neurones may have had a vasodilatory function. 7. Rhythmicity of the activity in CVC neurones, related to the cycle of artificial ventilation, increased during hypothalamic warming whereas that of MVC neurones was unchanged. 8. The functionally highly specific responses to hypothalamic warming in CVC neurones indicate a pathway from the hypothalamus that is specific for CVC neurones, in contrast to MVC and SM neurones. This central pathway is integrated with other spinal and supraspinal reflex pathways that determine the characteristic reflex pattern of CVC neurones to somatic and visceral stimuli and possibly with pathways that generate other physiological changes during hypothalamic warming (e.g. increase in respiratory drive).Most neurones of the sympathetic outflow to skin and reciprocal fashion in the anaesthetized animal, although a skeletal muscle of the cat hindlimb have vasoconstrictor minority of cutaneous vasoconstrictor (CVC) neurones functions and exhibit distinct reflexes to stimulation of behave like muscle vasoconstrictor (MVC) neurones. These cutaneous receptors, visceral receptors, arterial discharge patterns depend on the integration of spinal and baroreceptors and...

Central pathway for spontaneous and prostaglandin E2-evoked cutaneous vasoconstriction

“…Our experiments were conducted in anesthetized animals, and chloralose, one component of our anesthetic regimen, may have lowered the threshold temperature and reduced the response dynamics of thermoregulation in our rats (10). Thus, we expect that the thermoregulatory balance point temperature (48) and the response gains might be lower in our experiments than they would be in unanesthetized rats, but such differences would not affect the validity of our conclusions regarding the thermoregulatory pathways that we have investigated.…”

Location of cat brain stem neurons that drive sweating

“…Hasama (14) produced reproducible sweating from the paw pads when the base of the hypothalamus was heated in conscious cats, indicating a thermoregulatory role. In anesthetized cats, Magoun et al (23) sometimes found sweating from the paw pads when the anterior hypothalamus/preoptic area was heated with a thermode, but Grewe et al (12) found none when the hypothalamus and spinal cord were heated sufficiently to cause cutaneous vasodilatation; yet vibration and noxious stimulation did cause sweating in this preparation. A role in improving grip was postulated (12).…”

“…In anesthetized cats, Magoun et al (23) sometimes found sweating from the paw pads when the anterior hypothalamus/preoptic area was heated with a thermode, but Grewe et al (12) found none when the hypothalamus and spinal cord were heated sufficiently to cause cutaneous vasodilatation; yet vibration and noxious stimulation did cause sweating in this preparation. A role in improving grip was postulated (12). It is possible that sweating on the cat's paw is analogous with sweating on the human hand, which is involved in both thermoregulatory and stress responses; it also serves to improve grip (41).…”

Reduced Rearing Temperature Augments Responses in Sympathetic Outflow to Brown Adipose Tissue

“…Our finding that both the mean threshold temperature (35.5°C) and the mean operating point temperature (35.1°C) were markedly less than the normal core temperature of the awake rat (37.5°C) would suggest that the temperature regulatory mechanisms in these animals are suppressed by anesthesia. Chloralose, one component of the anesthesia used in these experiments, has been suggested to lower the threshold temperature and reduce the response dynamics of thermoregulation (Grewe et al, 1995). Additionally, our stimulus for producing an acute hypothermia involved ventral contact with a chilled surface, which would likely have activated cutaneous cold receptors before reducing core temperature.…”