Electrophysiological and immunofluorescence characterization of Ca2+ channels of acutely isolated rat sphenopalatine ganglion neurons

Abstract

The sphenopalatine ganglion (SPG) is the main parasympathetic ganglion that is involved in regulating cerebral vascular tone and gland secretion. SPG neurons have been implicated in some types of migraine headaches but their precise role has yet to be determined. In addition, very little information is available regarding ion channel modulation by neurotransmitters that are involved in the parasympathetic drive of SPG neurons. In this study, acute isolation of adult rat SPG neurons was developed in order to begin the electrophysiological characterization of this ganglion. Under our dissociation conditions, the average number of neurons obtained per ganglion was greater than 1200. Immunofluorescence imaging results showed positive labeling with acetylcholinesterase (AChE), confirming the parasympathetic nature of SPG neurons. On the other hand, weak tyrosine hydroxylase immunostaining was observed in these neurons. Whole-cell patch-clamp recordings revealed that most of the Ca(2+) current is carried by N-type (53%) and SNX-482 resistant R-type (30%) Ca(2+) channels. In addition, Ca(2+) currents were inhibited in a voltage-dependent manner following exposure to oxotremorine-M (Oxo-M), norepinephrine and ATP via muscarinic acetylcholine receptor 2 (M(2) AChR) subtype, adrenergic and P2Y purinergic receptors, respectively. The peptides VIP and angiotensin II failed to modulate Ca(2+) currents, suggesting that these receptors are not present on the SPG soma or do not couple to Ca(2+) channels. In summary, our data suggest that the Ca(2+) current inhibition mediated by Oxo-M, NE and ATP in adult rat SPG neurons plays an integral part in maintaining parasympathetic control of cranial functions.