Effects of affective touch on ultrasonic vocalization and c- FOS expression in rats

Abstract

The sense of touch has two functional dimensions: discriminative and affective. Discriminative properties of tactile stimuli are relayed via myelinated and fast conducting A fibers while affective properties are transmitted via unmyelinated, slowconducting C- tactile fibers. Gentle stimulation of CT- fibers was shown to elicit feeling of pleasantness and activate insular cortex. In the present study, hairy skin of male Wistar rats was stimulated with slow, moderate and fast velocities (3, 9, and 18 cm/s, respectively). Affective state was measured with ultrasonic vocalization recordings; neural activity was indicated by c-Fos expressions in primary somatosensory, posterior insular cortex and periaqueductal gray. Fast stimulation was shown to increase the amount and duration of 22- kHz USVs, yet not cause a difference in c-Fos expressions. Furthermore, number and duration of calls emitted in the last minute of stimulation were found to correlate with c-Fos expressions in PAG and contralateral S1. Thus, gentle stroking alters the affective state, albeit in a negative manner. Results of the current study may highlight the importance of the source of gentle touch. Gentle touch originating from con-specifics or familiar other sources may be processed more positively compared to unfamiliar sources. Therefore, future research may focus on this familiarity effect and mimic the setting of con-specific touch to study the processing of CT- afferent stimulation.|Keywords : C-tactile afferent, affective touch, rat vocalization, periaqueductal gray, somatosensory cortex, insular cortex.