# Differences in the autonomic regulation of temperature in the lower lip and tongue during activation of the lingual nerve

## TL;DR

This study shows that the parasympathetic nervous system helps regulate temperature more strongly in the tongue than in the lower lip of rats.

## Contribution

The study reveals that noncholinergic parasympathetic vasodilation plays a key role in orofacial temperature regulation, with stronger effects in intraoral tissues.

## Key findings

- Parasympathetic reflex vasodilation increases blood flow and temperature more in the tongue than in the lower lip.
- Sympathetic nerve activation reduces blood flow and temperature in both tissues, but parasympathetic reflexes counteract this more in the tongue.
- The noncholinergic parasympathetic system is crucial for maintaining orofacial temperature.

## Abstract

Orofacial temperature influences orofacial functions and is related to hemodynamics mediated by the autonomic nerves. Although the properties of autonomic vasomotor responses differ in orofacial tissues, differences in the autonomic regulation of orofacial temperature are unclear. We examined the differences in blood flow (BF) and temperature (Tm) between the extraoral (lower lip) and intraoral tissues (tongue) of urethane-anesthetized rats. Noncholinergic parasympathetic vasodilation evoked by trigeminal-mediated reflex elicited significant increases in BF and Tm in both tissues, and these increases were larger in the tongue than in the lower lip. Activation of cervical sympathetic nerves significantly decreased BF and Tm in both tissues. These decreases were restored by parasympathetic reflex vasodilation; the effects were larger in the tongue than in the lower lip. Our results suggest that parasympathetic vasodilation is involved in the maintenance of BF and Tm, and that the effects may be greater in intraoral than in extraoral tissues.

•Prominent parasympathetic vasodilation exists in the intraoral tissues.•The noncholinergic system contributes to orofacial temperature regulation.•Parasympathetic vasodilation inhibits orofacial temperature decrease.

Prominent parasympathetic vasodilation exists in the intraoral tissues.

The noncholinergic system contributes to orofacial temperature regulation.

Parasympathetic vasodilation inhibits orofacial temperature decrease.