Activation of Brainstem Neurons in Voluntarily Diving Rats after Bilateral Sectioning of the Anterior Ethmoidal Nerve

Abstract

This project was designed to investigate the functional role of the anterior ethmoidal nerve (AEN) during underwater diving in rats. The AEN innervates the nasal passages and is thought to be an important component of the afferent pathway that initiates the mammalian diving response. However recent evidence suggests that other nerves that innervate the nasal passages are also able to provide an afferent signal sufficient to initiate the autonomic responses to diving. To study this and the role of the AEN, 24 male Sprague‐Dawley rats were trained to swim and dive through a 5m underwater maze. Rats were subjected to either bilateral sectioning of the AENs (N=12) or a sham surgery (N=12). Twelve rats (6 surgical and 6 sham) had 24 post‐surgical dive trials over 2 hours to activate brainstem neurons to produce Fos, a neuronal activation marker. Twelve rats (6 surgical and 6 sham) were non‐diving controls. Brainstem tissues from all animals were immunohistochemically processed and analyzed for Fos and compared between the 4 groups. Brain regions inspected included the medullary dorsal horn, nucleus tractus solitarius, ventrolateral medulla, A5, and parabrachial region. This study further elucidates the afferent pathway(s) of the diving response and helps clarify the central integrative pathways involved in the mammalian diving response.