AUDIBLE AND ULTRASONIC VOCALIZATION ELICITED BY A NOCICEPTIVE STIMULUS IN RAT - RELATIONSHIP WITH RESPIRATION

Brief electrical pulses applied to a rat's tail elicit complex vocal r esponses including audible (''peeps,'' ''chatters'') and ultrasonic co mponents. These responses, particularly the two first peeps which have been shown to be triggered by A delta- and C-fibers, could provide a useful tool in pain studies. In the present study, we aimed to optimiz e this test by investigating the influence of respiration on the vocal responses. The following results were obtained: 1) As expected, the v ocalization periods were concomitant with expiration; 2) The phase of the respiratory cycle at the onset of stimulation did not modify the m ean intensities of the peeps; 3) The lung volume at the onset of stimu lation significantly influenced the intensity and duration of the firs t peep and the latency of the second peep. Taking account of respirato ry parameters in pain tests based on a quantified analysis of vocal re sponses could improve their sensibility by reducing variability and th eir specificity by detecting confounding factors such as effects of dr ugs on respiratory centres or on motor function. (C) 1997 Elsevier Sci ence Inc.