Chemosensory representation of first-time oral exposure to ethanol in the orbitofrontal cortex of mice.

Intermittent ethanol consumption changes the neuronal activity of the orbitofrontal cortex (OFC) in rodents, which has been attributed to important participation in the development of addiction, particularly alcoholism. The OFC participates in gustatory sensory integration. However, it is unknown whether this region can encode chemosensory elements of oral ethanol administration independently of the consumption movement (orofacial motor response) when administered for the first time (naïve mice). To answer this question, we used a sedated mouse model and a temporary analysis protocol to register extracellular neuronal responses during the oral administration of ethanol. Our results show an increase in neuronal frequency (in the first 500 ms) when low (0.6, 1, and 2.1 M) and high (3.2, 4.3, and 8.6 M) concentrations of ethanol are orally administered. The modulatory effect of ethanol was observed from low and high concentrations and differed from the tastants. There was consistent neuronal activity independent of the concentration of ethanol. Our results demonstrate a sensory representation of oral ethanol stimulation in the OFC neurons of naïve mice under sedation.

Sensory-motor response elicited by first time intraoral administered ethanol after trigeminal neuropathic injury.

Recent findings have shown a relationship between alcohol use disorders (AUD) and chronic pain. Preclinical models have demonstrated that chronic pain, including trigeminal nerve injury, increases ethanol consumption throughout extended administration periods. Nevertheless, it remains unclear whether chronic pain induces a greater susceptibility to developing AUD by altering motor control consumption regardless of the symptomatology of neuropathic pain, and whether sex influences this susceptibility. We used a former prolonged pain experience model induced by a constriction of the mental nerve (mNC) to answer this question. We analyzed ethanol consumption in a short-access protocol to reduce the post-ingestional effects and compared licking microstructure between groups. The constriction of the mental nerve induced evoked and spontaneous pain and reduction in the hedonic value of sucrose. The differences in alcohol consumption were not reflective of the former prolonged pain experience. Female mice showed a more efficient dynamic of consumption of alcohol, reflected in a long burst of licking and a less variable licking rate within a cluster.

Encoding signs of orofacial neuropathic pain from facial expressions in mice.

OBJECTIVE: To evaluate the effects of mental nerve injury in the facial reactions elicited by mechanical stimulation of different intensities and detect and quantify spontaneous facial pain-like expressions during a period free of stimuli, as signs of evoked and spontaneous pain in a mouse model for neuropathic orofacial pain. DESIGN: We recorded mouse heads in a fixed position during a stimulus-free period and with mechanical stimulation with 3 different Von Frey filaments. We extracted the Histograms of Oriented Gradients of each frame of the video recordings to be compared with a prototypical pain-like facial expression. The similarity score was then used to register and quantify the percentage of spontaneous pain-like facial reactions and evaluate the increased similarity to the prototypical pain-like face evoked by mechanical stimuli. The assessments were made one day before and four days after a unilateral mental nerve compression. RESULTS: Our findings show that mental nerve injury promotes an increase in spontaneous facial pain-like expressions and reduced mechanical threshold, reflected in a higher similarity to our pain-like face prototype, regardless of the intensity of the stimuli applied. CONCLUSIONS: Machine vision encodes the facial expression associated with evoked and spontaneous pain after mental nerve injury for up to four days. Facial expression quantitatively reflects the increased mechanical sensitivity elicited by mental nerve injury. We also show that this technique can detect spontaneous pain-like responses from facial reactions. Artificial vision can be applied to evaluate signs of orofacial neuropathic pain to study the involved neural circuits.