| Brief airpuffs delivered to the dorsal thorax of conscious, normotensive, chronically-catheterized rats elicited startle reactions consisting of large and transient motor (jumping), pressor, tachycardia and bradycardia responses. The neural pathways of these responses were investigated with psychophysiological, neurological, and pharmacological techniques.; The motor response to the airpuff is driven primarily by an acoustic component since it was abolished by: (a) disruption of hearing with tympanic membrane rupture (TMR) or transection of Cranial Nerve VIII; (b) radiofrequency lesions of Ventral Cochlear Nucleus or Nucleus Reticularis Pontis Caudalis, and (c) addition of masking noise during testing. These interventions minimally altered pressor, tachycardia or bradycardia components demonstrating dissociation between somatomotor and cardiovascular systems. The airpuff motor pathway is likely identical to the acoustic motor pathway.; Studies addressed cross-modality interactions. Motor responses to airpuffs were much larger than acoustic and tactile responses combined suggesting synergism. Small increases in background noise affected motor but not cardiovascular responses to airpuff stimuli. Cross-modal interactions masked any intensity-dependence of airpuff responses since TMR animals exhibited relatively large intensity-dependence.; Complex neural pathways mediate airpuff responses. Lesions of the dorsal column nuclei at the obex in TMR animals did not alter cardiovascular responses, suggesting involvement of other somatosensory pathways. However, local anesthetic injections into Cranial Nerve V selectively reduced pressor responses, as did lesions spanning the dorsal and dorsolateral PAG. Therefore, the pressor response pathway likely includes trigeminal afferents and is modulated at the dorsal/dorsolateral periaqueductal gray (PAG).; The bradycardia response pathway involves central cholinergic receptors. Intracerebroventricular (ICV) injection of hemicholinium-3 abolished bradycardic responses in Wistar-Kyoto (WKY) rats. ICV scopolamine, pirenzapine, methoctramine, or hexamethonium lowered the pressor response, but only scopolamine or pirenzapine abolished bradycardia. ICV physostigmine enhanced bradycardia in WKY rats, and revealed bradycardia in Spontaneously Hypertensive rats (SHR), which do not normally exhibit bradycardia. ICV clonidine abolished the pressor response in WKY and SHR, and the bradycardia response in WKY. These results suggest a deficiency in a central cholinergic pathway in SHR.; The airpuff startle paradigm is an excellent model for the processing of sensory stimuli into behavioral and autonomic responses. |
