Disruption of oral sensory relay to brain increased anxiety- and depression-like behaviours in rats.

OBJECTIVE: Sensory information plays an important role to determine psycho-emotional behaviours of individuals. Lingual nerve can be damaged by dental surgery or trauma, such as physical irritation, radiation, chemotherapy, or viral infection. This study was conducted to examine the psycho-emotional effects of lingual nerve damage in which oral sensory relay to the brain is disrupted. DESIGN: Male Sprague-Dawley rats were tested for anxiety and depression-related behaviours after bilateral transections of the lingual and chorda tympani nerves (Nx) or sham operation. Tissue contents of serotonin and its metabolite in the hippocampus, hypothalamus, and nucleus accumbens were analyzed by high-performance liquid chromatography. RESULTS: Sucrose preference was reduced in Nx rats compared with sham rats, suggesting the development of anhedonia, decreased pleasure seeking behaviour, by the lingual nerves transection. Ambulatory activity was decreased, anxiety-related behaviours during the activity test increased, time spent in the open arms during elevated plus maze test decreased, and immobility duration during forced swim test increased in Nx rats compared with sham rats. Serotonin level in the hippocampus of Nx rats was decreased significantly compared with sham rats. CONCLUSIONS: Results suggest that aberration of oral sensory relay to brain may lead to the development of depression- and anxiety-related disorders, and decreased serotonergic neurotransmission in the hippocampus may play a role in its underlying mechanism.

The psychosocial and affective burden of posttraumatic neuropathy following injuries to the trigeminal nerve.

AIMS: To explore the impact of trigeminal nerve injuries on quality of life, including the effect of pain on psychological and affective function. METHODS: An observational, cross-sectional survey design was employed. Fifty-six patients with inferior alveolar nerve injury (IANI) and 33 patients with lingual nerve injury (LNI) completed standardized self-report measures of pain intensity, pain catastrophizing, self-efficacy to cope with pain, and mood, in addition to generic and oral health-related quality of life (HRQoL) indicators. The impact of pain severity on these aspects of psychosocial function was examined. Summary statistics were calculated for all measures and compared with norms or values of other relevant studies, when available, using t tests. The impact of pain severity on these aspects of psychosocial function was examined using analysis of variance and hierarchical multivariate regression models. RESULTS: The majority of patients reported pain associated with their nerve injury (86%). Nerve injury had a significant impact on all investigated domains, and this was closely linked with reported pain levels. Patients with severe pain showed particularly elevated levels of depression and pain catastrophizing, as well as substantially reduced HRQoL and coping efficacy levels. Pain intensity level was a significant predictor in all models except anxiety, uniquely contributing between 17% and 26% of variance to the prediction of pain catastrophizing, depression, coping efficacy, and generic and oral HRQoL. CONCLUSION: Traumatic injury to the trigeminal nerve is associated with a substantial patient burden, particularly in patients who experience severe neuropathic pain as part of their condition. These findings highlight the need to identify, develop, and evaluate more effective treatments for neuropathic pain in trigeminal nerve injury that will not only provide clinically meaningful reductions in pain but also improve patients' quality of life.

Capsaicin avoidance as a measure of chemical hyperalgesia in orofacial nerve injury models.

Many patients suffer from trigeminal neuralgia and other types of orofacial pain that are poorly treated, necessitating preclininal animal models for development of mechanisms-based therapies. The present study assessed capsaicin avoidance and other nocifensive behavioral responses in three models of orofacial nerve injury in rats: chronic constriction injury (CCI) of the mental nerves, partial tight ligation of mental nerves, and CCI of lingual nerves. We additionally investigated if nerve injury resulted in enhanced capsaicin-evoked activation of neurons in trigeminal caudalis (Vc) or nucleus of the solitary tract (NTS) based on expression of Fos-like immunoreactivity (FLI). Mental nerve CCI resulted in an enhancement of capsaicin avoidance in a two-bottle preference paradigm, while neither mental nerve injury produced thermal hyperalgesia or mechanical allodynia. CCI of lingual nerves did not affect capsaicin avoidance. Counts of FLI in Vc were significantly higher in the lingual sham and mental nerve CCI groups compared to mental shams; FLI counts in NTS did not differ among groups. Mental nerve CCI may have induced central sensitization of chemical nociception since increased capsaicin avoidance was accompanied by greater activation of Vc neurons in response to oral capsaicin.