Effects of stimulation of cuneiform nucleus and the dorsomedial Hypothalamic nucleus and Perifornical area on the mechanisms involved in the control of laryngeal activity and subglottic pressure in spontaneously breathing anaesthetized rats.

Abstract

The dorsomedial Hypothalamic nucleus and Perifornical area (DMH-PeF) and the mesencephalic Cuneiform nucleus (CnF) have been involved in sympathetic activity due their connectivity with several nuclei involved in cardiorespiratory control. In previous studies we have demonstrated a functional interaction between hypothalamic and mesencephalic structures (DMH-PeF, dlPAG) with several pontine regions (PBc, A5) (2, 3). We have also shown that rostral and ventral pontine structures are involved in the changes of laryngeal caliber (4). The aim of this study was to characterize the relations between hypothalamic and mesencephalic regions involved in cardiorespiratory control and their possible role in modulating laryngeal activity and their possible effects on vocalization. Experimental studies were carried out with non-inbred male rats (n=42), Sprague-Dawley (250-300g). Animals were anesthetized with sodium pentobarbitone (60 mg/kg i.p., initial dose, supplemented 2mg/kg, i.v., as necessary). A double tracheal cannulation was used to obtain an “isolated glottis in situ” and to record respiratory airflow. Bilateral parietostomy allowed access to the DMH-PeF and CnF. Electrical (n=14) and chemical (n=14) stimulations of these regions using bipolar electrodes or glutamate was performed. Microinjections (n=14) of PBS-Evans Blue served as control purpose. Respiratory flow, pleural pressure, blood pressure and heart rate were also recorded. DMH-PeF and CnF PBS-Evans Blue microinjections did not produce any significant changes in any of the cardiorespiratory variables recorded. Glutamate microinjections within the DMH-PeF and CnF evoked a decrease of laryngeal resistance (subglottal pressure) (p<0,01 and p<0,001 respectively) with an inspiratory facilitatory response consisted of an increase in respiratory rate (p<0,001 in both cases), together with a pressor (p<0,001 and p<0,01 respectively) and tachycardic response (p<0,001in both cases)