Rat Submandibular Gland Perfusion Method for Clarifying Inhibitory Regulation of GABAA Receptor

Abstract

Abstract. GABA is an inhibitory transmitter found in rat salivary gland. However, the inhibitory potential of GABA on salivary secretion is unclear. Using an in vivo cannulation method, intraperitoneal administration of GABA was ineffective in the absence of gabaculine, a GABA transaminase inhibitor, on pilocarpine-induced salivary secretion, suggesting that GABA was rendered metabolically inactive before reaching the salivary gland. We hypothesized that the action of a drug on the salivary glands could be measured directly using a submandibular gland perfusion system. The submandibular gland artery, veins, and duct were cannulated in situ so that physiological functions such as innervation would not be compromised. Hank's balanced salt solution (pH 7.4) was perfused at a rate of 0.5 ml/min together with 1 M carbachol (CCh) over a 5-min period every 30 min. Amount of secreted saliva showed no change to the recurrent addition of CCh to the perfusate. GABA or muscimol dose-dependently inhibited CCh-induced salivary secretion. This effect was blocked by bicuculline, a GABA A -receptor (GABA A -R) antagonist, and enhanced by clonazepam, a central-type benzodiazepine-receptor agonist. These results suggest that salivary secretion is suppressed by GABA A -R in rat salivary gland and that the perfusion method used was effective in clarifying inhibitory regulation of GABA A -R.

Effects of Benzodiazepines on Acinar and Myoepithelial Cells

“…GABA A receptors can be both central and peripheral (located in the salivary glands) (Okubo and Kawaguchi, 2013 ). Kosuge et al ( 2009 ) demonstrated the presence of peripheral GABA A receptors in the acinar cells of parotid and submandibular glands of rats.…”

“…Numerous studies, both on human and animals, have demonstrated that BZDs cause a reduction in salivary flow, with severe oral side effects (De Almeida Pdel et al, 2008 ; Femiano et al, 2008 ). BZDs act to induce reduction in salivary flow through GABA A receptors located in the salivary glands as well as through indirect actions of the CNS on the salivary glands mediating central GABA A receptors (Kujirai et al, 2002 ; Okubo and Kawaguchi, 2013 ). In addition to inhibiting the muscarinic receptors present in the salivary glands, which are responsible for the salivary flow, BZDs also can affect the transport of chloride and the calcium influx, which can lead to fluid secretion.…”

“…As a result, a reduction in the salivary secretion activity occurs. BZDs can also inhibit β-adrenergic receptors, in turn blocking the release of amylase from rat parotid glands (Okubo and Kawaguchi, 2013 ).…”

Localization of Vesicular Inhibitory Amino Acid Transporter (VIAAT) in the Submandibular Salivary Gland Throughout the Postnatal Development of Mice

“…These findings are in contrast to the fact that most physiological studies on the effect of GABA in the saliva secretion have been done in adult rodents (Okubo & Kawaguchi, 2013;Ouchi et al, 2011). From this chronological feature of the present immunoreactivity, it is more plausible to consider the regulatory role of GABA in the development of the glandular cells rather than the saliva…”

Rebamipide, an anti‐ulcerative drug, inhibits induction of salivary dysfunction by benzodiazepines

“…Our group has already reported on the mechanism underlying this side effect in a number of earlier studies. Central‐ and peripheral‐type BDZ receptors were involved in suppression of salivary secretion induced by cholinergic or adrenergic stimulation in rat salivary gland (Yamagishi and Kawaguchi, ; Okubo and Kawaguchi, , ). Another study demonstrated that DZP increased intracellular Cl − levels by preventing Ca 2+ release from intracellular calcium ([Ca 2+ ] i ) stores, and suppressed Cl − efflux through Ca 2+ ‐dependent Cl − channels in the apical membrane of acinar cells (Kawaguchi and Yamagishi, ; Kujirai et al , ).…”