Sympathetic modulation of cold‐receptive neurones in the trigeminal system of the rat.

Abstract

SUMMARY1. The effects of cervical sympathetic electrical stimulation on the activity of cold-receptive neurones in the trigeminal system of the rat have been studied.2. Sympathetic stimulation caused excitation and/or suppression of cold-receptive cells in the trigeminal nucleus caudalis. The responses were complex but within any one cell low-frequency stimulation (below 5 Hz) usually (81 % of cells) caused excitation, while high-frequency stimulation (above 10 Hz) caused excitation and suppression.3. The temperature of the cutaneous receptive fields was 'clamped' with a thermode. Measurements of surface and intradermal temperatures suggested that the temperature fall caused by sympathetic stimulation was not sufficient to account for the increased firing rate observed.4. The suppression was blocked by a low dose of phentolamine; it was mimicked by carotid occlusion and may be a consequence of vasoconstriction.5. The excitation was resistant to ,8-blockade; it was best mimicked by the z-agonist phenylephrine.6. Similar frequency-dependent excitations and suppressions, and responses to pharmacological agonists, were obtained in recordings from cold-receptive primary afferent neurones in the trigeminal ganglion.7. The excitation may be a complex secondary effect, or there may be a direct c-receptor-mediated excitation of cold-receptive primary afferent fibres by the sympathetic system.

Two Periods in the Response of the Skin Cold Receptors to Intravenous Infusion of Noradrenaline

“…There is a phasic increase in firing rate followed by a decrease irrespective of the initial activity of the skin cold receptors during the first period. This supports the previous results and, once again, confirms that the peripheral thermoreceptors are sensitive to the rise in NA concentration caused by NA injection 1,2,4 or sympathetic electrical stimulation 6 …”

“…This supports the previous results and, once again, confirms that the peripheral thermoreceptors are sensitive to the rise in NA concentration caused by NA i n j e c t i~n ' .~,~ or sympathetic electric d stimulation. 6 The similarity between the response of the cold receptors to a rapid rise in NA concentration and their dynamic response to fast cooling are noteworthy. Possibly, the recorded dynamic response of the receptors to cooling is a manifestation of not only a direct thermal excitation of the receptor, but also of an associated activation of the sympathetic nervous system.…”

Validity of contact skin temperature sensors under different environmental conditions with and without fabric coverage: characterisation and correction

“…Challenges of using human skin include spatial and temporal temperature variability (Pennes 1948;Webb 1992), particularly with cooler T sk (Frim et al 1990), and that a reference T sk measurement may have its own limitations relating to thermal equilibrium with the skin and modified heat exchange with the skin and its surroundings. Careful measurements utilising non-contact (Hardy and Soderstrom 1937) or invasive methods (just below the skin surface; Davies 1985) are possible but lack practicality for widespread use.…”

Vertebrate behavioral thermoregulation: knowledge and future directions

“…Notably, this behavioral change could arise due to two broad classes of effects: The sensation of temperature could simply be altered—the thermal preference changes because at the sensory level 30°C now feels like 29°C; alternatively, a sense of absolute temperature is maintained, but the transformation of thermosensory information to thermoregulatory behaviors is altered. There are indications that sympathetic stimulation can influence the response of trigeminal cold-responsive neurons, 121 and prostaglandin E2, a major mediator of fever, can directly sensitize the capsaicin response of TRPV1 channels in the lung. 122 However, this latter effect should rather reduce preferred temperatures as it would increase the feeling of warmth.…”