Laryngeal effects of stimulation of the dorsolateral Periaqueductal Grey Matter in spontaneously breathing anaesthetized rats

Abstract

The stimulation of the Periaqueductal Gray matter (PAG) and nucleus retroambiguus (nRA) produces vocalization. A high expression of FOXP2 protein at mesencephalic (PAG) and pontine regions involved in cardiorespiratory control has been described. The aim of this study was to characterize the possible role of the dlPAG in modulating laryngeal activity and their effects on vocalization. Experimental studies were carried out with non-inbred male rats (n=27), Sprague-Dawley (250-300 g). Animals were anesthetized with sodium pentobarbitone (60 mg/kg i.p., initial dose, supplemented 2mg/ kg, i.v., as necessary). Neuromorphological study (n=6) The pattern of staining for c-Fos and FOXP2 protein immunoreactivity (c-Fos-ir) were examinated throughout the rostrocaudal extent of the nRa/nA region during electrical stimulation of the dlPAG. Neuropharmacological study (n=21) A double tracheal cannulation was used to obtain an “isolated glottis in situ” and to record respiratory airflow. Bilateral parietostomy allowed access to the dlPAG. Electrical stimulations (n=7) of this region using concentric bipolar electrodes (1ms pulses, 20-40µA, 100Hz for 5s) were performed. Microinjections of PBS-Evans Blue (250nl, pH 7.4±0.1, 5-s duration) (n=7) or glutamate (0,25M, 250nl) (n=7) were performed. Respiratory flow, pleural pressure, blood pressure and heart rate were also recorded. Activation of the dlPAG elicited a selective increase in c-Fos-ir with an ipsilateral predominance in nRA/nA somatas (p<0.01) and confirm the expression of FOXP2 bilaterally in both nuclei. dlPAG PBS-Evans Blue microinjections did not produce any significant changes in any of the cardiorespiratory variables recorded. dlPAG stimulations evoked a decrease of laryngeal resistance (subglottal pressure) (p<0,001) accompanied with an inspiratory facilitatory response consisted of an increase in respiratory rate (p<0,001), together with a pressor (p<0,001) and tachycardic response (p<0,001).