Dissecting the role of TRPV1 in detecting multiple trigeminal irritants in three behavioral assays for sensory irritation.

Polymodal neurons of the trigeminal nerve innervate the nasal cavity, nasopharynx, oral cavity and cornea. Trigeminal nociceptive fibers express a diverse collection of receptors and are stimulated by a wide variety of chemicals. However, the mechanism of stimulation is known only for relatively few of these compounds. Capsaicin, for example, activates transient receptor potential vanilloid 1 (TRPV1) channels. In the present study, wildtype (C57Bl/6J) and TRPV1 knockout mice were tested in three behavioral assays for irritation to determine if TRPV1 is necessary to detect trigeminal irritants in addition to capsaicin. In one assay mice were presented with a chemical via a cotton swab and their response scored on a 5 level scale. In another assay, a modified two bottle preference test, which avoids the confound of mixing irritants with the animal's drinking water, was used to assess aversion. In the final assay, an air dilution olfactometer was used to administer volatile compounds to mice restrained in a double-chambered plethysmograph where respiratory reflexes were monitored. TRPV1 knockouts showed deficiencies in the detection of benzaldehyde, cyclohexanone and eugenol in at least one assay. However, cyclohexanone was the only substance tested that appears to act solely through TRPV1.

Atomoxetine changes rat's HR response to stress from tachycardia to bradycardia via alterations in autonomic function.

Atomoxetine is a central norepinephrine reuptake inhibitor used to treat attention deficit hyperactivity disorder. We tested the effects of atomoxetine upon the heart rate (HR) and mean arterial blood pressure (mBP) response to aversive conditioning. In Protocol 1 the mBP and HR responses to a stress (15s tone followed by shock) were tested in 8 Sprague-Dawley rats given saline pretreatment for 3 days; the rats' responses were then tested for 3 additional days following atomoxetine (1mg/kg, sc). Atomoxetine decreased (p<0.05) baseline mBP from 128+/-11 mm Hg (mean+/-SD) to 117+/-19 mm Hg; baseline HR slowed from 380+/-23 bpm to 351+/-21 bpm. The mBP increase to acute stress was similar after saline vs. after drug, but the peak was attained more slowly. After atomoxetine HR tended to slow during stress rather than accelerate. In Protocol 2 the cardiovascular responses were tested (n=6) for 3 days post-saline and for 3 days after a higher dose of atomoxetine (2mg/kg, sc). The average HR acceleration during the last 10s of the stress after saline (+7.5+/-14.7 bpm) was replaced by a HR slowing (-6.2+/-10.5 bpm). We conclude that drug treatment (a) decreases baseline sympathetic tone and/or elevates cardiac parasympathetic tone; (b) slows sympathetic arousal to acute stress without changing its magnitude; and, (c) enables the emergence of elevated parasympathetic tone during the stress. These autonomic consequences are consistent with atomoxetine's anxiolytic and transient sedative effects.