Voltage Stimulation of the Anterior Ethmoidal Nerve in Rats Produces a Cardiorespiratory Response Similar to the Diving Response

Abstract

The diving response, initiated when animals submerge under water, includes a decrease in heart rate, peripheral vasoconstriction, and apnea. Electrical stimulation of the anterior ethmoidal nerve (AEN), the nerve that innervates the nasal passages, can produce similar reflex responses. The purpose of the present research in Sprague‐Dawley rats was to electrically stimulate the AEN using silver coated copper wire and a voltage stimulus supplied through an iWorx TA‐220 Control Module and Labscribe software. Our hypothesis was that increasing the intensity of the AEN electrical stimulation would increase the intensity of the resultant cardiorespiratory responses. Accordingly, we isolated the AEN at the base of the orbit, hooked the electrodes around the nerve, and insulated the nerve and orbit with dental impression material. While recording heart rate, arterial blood pressure and respiration, we varied 5 s of AEN electrical stimulation between 0.1 and 1.1 volts. Stimulation threshold of 0.2 volts would elicit slight bradycardia, slight alterations in BPa, and a slight decrease in respiratory rate. With increasing voltages, the response intensified. When maximally stimulated, HR decreased from 438 ± 28 to 181 ± 37 bpm, and BPa decreased from 127 ± 5 to 121 ± 14 mmHg. The respiratory rate decreased from 93 ± 3 to 0 breaths/min with an apnea duration of 5.0 ± 0.2 s. Our studies found that the intensity of the cardiorespiratory responses and the voltage of the AEN stimulation varied somewhat linearly. This technique and these findings can be used in future research to investigate the brainstem pathways of the mammalian diving response.