Attenuation of Fos expression to airpuff startle stimuli following tympanic membrane rupture.

The airpuff startle stimulus consists of two modalities, tactile and acoustic. Tympanic membrane rupture (TMR) effectively deafens a rat, thus preventing it from perceiving the acoustic component of the airpuff and permitting study of the tactile component in isolation. Previous studies have shown that the tactile modality is sufficient to drive the cardiovascular response to the airpuff, but cannot elicit the full behavioral startle response. In the present study Fos protein was used as a marker of neuronal activation to identify brain regions activated by the airpuff in both intact and TMR rats. Results show an attenuation of Fos expression following TMR in the dorsal and ventral cochlear nuclei, ventral nucleus of the lateral lemniscus and medial geniculate nucleus. In contrast, Fos expression following TMR was unchanged in the locus coeruleus, the laterodorsal tegmental nucleus, the supramammilary nucleus, and the ventromedial hypothalamic nucleus. Analysis of behavioral data confirmed that the startle response to the airpuff was diminished following TMR. These data are the first of which we know to employ an immediate early gene approach to discriminate between brain regions activated by the tactile and acoustic startle stimulus modalities. The results are discussed in terms of the classical acoustic startle circuit, and the central autonomic pathways activated by the tactile component of the airpuff.