Dual regulation by ethanol of the inhibitory effects of ketamine on spinal NMDA-induced pressor responses in rats.

BACKGROUND: Acute exposure of ethanol (alcohol) inhibits NMDA receptor function. Our previous study showed that acute ethanol inhibited the pressor responses induced by NMDA applied intrathecally; however, prolonged ethanol exposure may increase the levels of phosphorylated NMDA receptor subunits leading to changes in ethanol inhibitory potency on NMDA-induced responses. The present study was carried out to examine whether acute ethanol exposure influences the effects of ketamine, a noncompetitive NMDA receptor antagonist, on spinal NMDA-induced pressor responses. METHODS: The blood pressure responses induced by intrathecal injection of NMDA were recorded in urethane-anesthetized rats weighing 250-275 g. The levels of several phosphorylated residues on NMDA receptor GluN1 subunits were determined by western blot analysis. RESULTS: Intravenous injection of ethanol or ketamine inhibited spinal NMDA-induced pressor responses in a dose-dependent and reversible manner. Ketamine inhibition of NMDA-induced responses was synergistically potentiated by ethanol when ethanol was applied just before ketamine. However, ketamine inhibition was significantly reduced when applied at 10 min after ethanol administration. Western blot analysis showed that intravenous ethanol increased the levels of phosphoserine 897 on GluN1 subunits (pGluN1-serine 897), selectively phosphorylated by protein kinase A (PKA), in the lateral horn regions of spinal cord at 10 min after administration. Intrathecal administration of cAMPS-Sp, a PKA activator, at doses elevating the levels of pGluN1-serine 897, significantly blocked ketamine inhibition of spinal NMDA-induced responses. CONCLUSIONS: The results suggest that ethanol may differentially regulate ketamine inhibition of spinal NMDA receptor function depending on ethanol exposure time and the resulting changes in the levels of pGluN1-serine 897.

Expression and activity of cocaine- and amphetamine-regulated transcript peptide(1-39) in the rat.

Cocaine- and amphetamine-regulated transcript (CART) peptide consists of a family of peptides. Expression of the peptide fragment CART(1-39) was explored in the rat using an antiserum directed against CART(1-39) of the short form of the human CART prohormone. CART(1-39)-immunoreactivity, herein referred to as irCART, was detected in the rat central and peripheral nervous tissues with a pattern similar to that labeled with the antiserum CART(55-102) or CART(79-102). For example, irCART cells were detected in the hypothalamus, pons, medulla oblongata, spinal cord, and adrenal medulla. In urethane-anesthetized rats, CART(1-39) (0.05 to 2 nmol) by intrathecal injection did not cause a significant change of blood pressure or heart rate, but potentiated the pressor effects of glutamate injected intrathecally. Lastly, the effect of CART(1-39) on intracellular calcium concentrations [Ca2+]i was assessed and compared to that caused by CART(55-102) in cultured rat cortical neurons using the microfluorimetric method. CART(1-39) (100 nM) induced two types of responses in a population of cortical neurons: 1) a slowly rising increase in [Ca2+]i superimposed with oscillations, and 2) a fast increase followed by a sustained increase of [Ca2+]i. CART(55-102) caused only a slowly rising increase in [Ca2+]i in cortical neurons. Our result shows that the expression pattern of irCART in the rat nervous system and the potentiating action of CART(1-39) on glutamate-induced pressor response is similar to that reported for CART(55-102); but the calcium mobilizing action of CART(1-39) differs from that of CART(55-102), suggesting the possible existence of multiple CART receptors coupled to different calcium signaling pathways.

Inhibition by ethanol of NMDA-induced responses and acute tolerance to the inhibition in rat sympathetic preganglionic neurons in vitro and in vivo.

N-methyl-d-aspartate (NMDA) receptors have been demonstrated to be a pivotal target for ethanol action. The present study examined the actions of acute ethanol exposure on NMDA-induced responses and the acute tolerance to ethanol actions in rat sympathetic preganglionic neurons (SPNs) in vitro and in vivo. NMDA (50 microM) applied every 5 min induced reproducible membrane depolarizations of SPNs in neonatal spinal cord slice preparations. Ethanol (50 - 100 mM) applied by superfusion for 15 min caused a sustained decrease in NMDA-induced depolarizations in a dose-dependent and reversible manner. When the superfusion time of ethanol (100 mm) was increased to 50 min, NMDA-induced depolarizations were attenuated initially but a gradual recovery was seen in approximately 40% of SPNs tested. Repeated injections of NMDA (2 nM) intrathecally at 30 min interval caused reproducible increases in mean arterial pressure (MAP) in urethane-anesthetized rats. Intravenous injections of ethanol (0.16 or 0.32 g, 1 ml) inhibited NMDA-induced pressor effects in a blood concentration-dependent manner. The inhibition by ethanol of NMDA-induced pressor effects was reduced over time during continuous infusion of ethanol or on the second injection 3.5 h after prior injection of a higher dose of ethanol. Ethanol, at concentrations significantly inhibited NMDA-induced responses, had no significant effects on alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid-induced responses. The study demonstrated the selective inhibition by ethanol of NMDA-induced responses and the development of acute tolerance to the inhibitory effects in SPNs both in vitro and in vivo. These effects may play important roles in the ethanol regulation of cardiovascular function.