Purinergic modulation of area postrema neuronal excitability in rat brain slices

Abstract

ATP has been shown to excite neurons in various regions of the central nervous system. Whereas immunohistochemical studies show P2X receptors in the area postrema, the responsiveness of area postrema neurons to extracellular ATP has not been studied. To investigate the effects of purinoceptor activation on area postrema neuronal excitability, we performed whole-cell recordings from area postrema neurons in rat brain slices. Most area postrema neurons responded to ATP application, and most responses were excitatory. Voltage-clamp recordings showed three different types of response: (1) a postsynaptic or extrasynaptic excitatory response (inward currents; n=26/51 cells), (2) a presynaptic excitatory response (increased frequency of miniature excitatory postsynaptic currents with only a small direct postsynaptic current; n=24/51 cells, or (3) a postsynaptic inhibitory response (outward current; n=1/51). The excitatory responses were found in both of the two major electrophysiological cell classes, i.e. cells displaying I(h) and cells not displaying I(h), while the inhibitory responses were found in only cells not displaying I(h). Current-clamp recordings showed ATP-induced depolarization (n=13/15) or hyperpolarization (n=2/15) of membrane potential that modulated the frequency of action potentials. In the presence of CNQX, mEPSCs were abolished and bath-applied ATP did not generate mEPSCs, indicating that glutamate release was facilitated by the activation of presynaptically located ATP receptors. Our pharmacological results from studies with ATP, alphabetame-ATP, betame-ATP and PPADS indicate that the post- and/or extrasynaptic responses are most likely mediated by P2X(7) receptors and/or receptors composed of P2X(2) and P2X(5) subunits. We conclude that half of the presynaptic responses are most likely mediated by P2X(7) receptors and/or receptors composed of P2X(2) and P2X(5) subunits while the others also contain P2X(1) subunits. It is well known that P2X(7) subunit forms only homomultimeric P2X receptors. Finally, the present study suggests that purinoceptor activation may contribute to the control of several autonomic functions by area postrema neurons.

Circumventricular Organs

“…Binding sites/receptors for amylin (Sexton et al, 1994), canabinoid CB1 receptor, cholecystokinin CCK-1 receptor (Moran et al, 1986), angiotensin II AT 1 (Lenkei et al, 1997;Allen et al, 2000), atrial natriuretic peptide Saavedra et al, 1992), GLP-1 (Göke et al,1995), Ghrelin-GHRS receptor (Zigman et al, 2006); neuropeptide Y, Peptide YY and pancreatic polypeptide-Y1, Y2, Y4 and Y5 receptors (Martel et al, 1986;Kishi et al, 2005); purinergic P2X2 and P2X7 receptors (Kodama et al, 2007;Mangano et al, 2012), somatostatin (Patel et al, 1986), substance P NK-1 receptor (Baude and Shigemoto, 1998), vasoactive intestinal polypeptide (Shaffer and Moody, 1986), vasopressin (Phillips et al, 1988), and insulin (Werther et al, 1987) have been observed in the area postrema. Like the other sensory CVOs, the area postrema exhibits the CD14 lipopolysacharide receptor (Lacroix et al, 1998).…”

Facilitation of Neurotransmitter and Hormone Release by P2X Purinergic Receptors

“…It has been suggested that endogenously released ATP acts at postsynaptic P2XRs to mediate synaptic currents in the hippocampus (Edwards et al, 1992). This classical view, however, is challenged by a series of recent studies that showed that ATP acts rather as a modulator that stimulates the release of other neurotransmitters (Li et al, 1998;Sperlagh et al, 2002;Watano et al, 2004;Rodrigues et al, 2005;Kodama et al, 2007;Sperlagh et al, 2007;Donato et al, 2008). In the SON neurons, for instance, all spontaneous synaptic currents were inhibited by blockers of glutamate and GABAA receptors and application of ATP stimulated about 2300 % increase in frequency of both spontaneous inhibitory and excitatory postsynaptic currents without changes in their amplitude (Fig.3) (Vavra et al, 2011).…”

“…Furthermore, inhibiting P2XRs by application of PPADS has been shown to abolish the glutamate-dependent postsynaptic currents evoked by focal application of ATP in dorsal horn neurons (Li et al, 1998 Nakatsuka andGu, 2001). PPADS-sensitive P2X2Rs have been shown in glutamatergic terminals of neurons in trigeminal mesencephalic motor nucleus (Khakh and Henderson, 1998), the nucleus tractus solitari (Shigetomi and Kato, 2004) and the area postrema (Kodama et al, 2007). The presynaptic P2X2Rs have been shown to underlie increase in GABA release in a subset of GABAergic interneurons in the spinal cord (Hugel and Schlichter, 2000) and in Purkinje cells in rat cerebellar slices (Donato et al, 2008).…”

Chemical phenotypes of P2X2 purinoreceptor immunoreactive cell bodies in the area postrema

“…It has been shown that purinergic P2X receptor activation via intraperitoneal injection of a slowly degradable ATP analog, α,β-methyleneATP (α,β-meATP), induces emetic responses in ferrets and Suncus murinus (house musk shrews) [15]. Moreover, ATP has been shown to have an excitatory effect on isolated rat area postrema neurons, an effect that can be inhibited by P2X receptor antagonists [16,17].…”