# Alpha-pinene modulates feeding behavior and hypothalamic orexin-A expression in a rat model of painful temporomandibular disorder

## TL;DR

Alpha-pinene reduces pain and improves feeding behavior in rats with temporomandibular joint inflammation.

## Contribution

Alpha-pinene's effect on feeding behavior and hypothalamic orexin-A in a TMD rat model is newly demonstrated.

## Key findings

- Alpha-pinene at 0.4 μg/rat improved pain thresholds and feeding behavior in CFA-treated rats.
- Alpha-pinene restored hypothalamic orexin A expression in rats with TMJ inflammation.
- CFA-treated rats showed anxiety-like behavior and impaired feeding patterns.

## Abstract

Background: Temporomandibular disorders (TMDs) are common conditions
involving the temporomandibular joint (TMJ) and masticatory muscles, often
presenting with pain and impaired orofacial function. Painful TMD can disrupt jaw
motor activities, including chewing and feeding behavior, reflecting alteration
in muscle performance and central neuroregulation. The hypothalamic neuropeptide
orexin A integrates pain, arousal, and energy balance and may be involved in
these disturbances. This study examined whether intracerebroventricular (ICV)
administration of alpha-pinene, an anti-inflammatory monoterpene, could modulate
pain-related impairments in feeding behavior and orexin A expression in a rat
model of inflammatory TMD. Methods: TMJ inflammation was
induced in male Wistar rats via Complete Freund’s Adjuvant (CFA) injection. Rats
received ICV alpha-pinene (0.1, 0.2, or 0.4 μg/rat). Feeding
behavior parameters—including meal frequency, duration, and total intake—were
recorded with an automated monitoring system as functional readouts of
masticatory muscle activity during food processing. Anxiety-like behavior was
evaluated using the elevated plus maze, and hypothalamic orexin A expression was
assessed by immunohistochemistry. Results: CFA-treated rats showed
reduced pain thresholds, anxiety-like behavior, and impaired feeding behavior,
including fewer meals, shorter feeding duration, and reduced intake.
Alpha-pinene, particularly at 0.4 μg/rat, significantly improved
these behavioral outcomes and restored hypothalamic orexin A expression compared
with untreated CFA rats. Conclusions: Alpha-pinene mitigated
pain-related disruptions in feeding behavior and restored hypothalamic orexin A
expression in a rat model of TMJ inflammation. These findings highlight the
interplay between orofacial pain, altered oral motor function, and central
neuroregulation. The observed behavioral improvements suggest that alpha-pinene
may offer therapeutic benefits for managing functional impairments associated
with both muscular and joint-related TMD pain, supporting its potential as a
candidate for integrative TMD management.