RAPID COMMUNICATION Potentiation of NMDA Currents by Pituitary Adenylate Cyclase Activating Polypeptide in Neonatal Rat Sympathetic Preganglionic Neurons

Wu, S. Y. and N. J. Dun. Potentiation of NMDA currents by long-lasting potentiation of glutamate responses in central pituitary adenylate cyclase activating polypeptide in neonatal rat synapses, which may represent a form of synaptic plasticity sympathetic preganglionic neurons. J. Neurophysiol. 78: 1175– (Greengard et al. 1991; Siegelbaum and Kandel 1991; Wang 1179, 1997. Whole cell patch-clamp recordings were made from et al. 1991). sympathetic preganglionic neurons (SPNs) in the intermediolateral The present study was undertaken to test the hypothesis cell column of thoracolumbar spinal cord slices of 12to 16-daythat PACAP acting via the adenylate cyclase pathway may old rats, and the effects of pituitary adenylate cyclase activating modulate glutamate responses in rat sympathetic preganglipolypeptide (PACAP)-38 on N-methyl-D-aspartate (NMDA)and onic neurons (SPNs). SPNs appear to be a suitable model kainate (KA)-induced inward currents were examined. PACAP, system because nerve terminals containing PACAP-like imin concentrations (10–30 nM) that caused no significant change of holding currents, reversibly increased NMDA-induced currents munoreactivity have been shown to make synaptic-like conbut not KA-induced currents. At higher concentrations (ú30 nM), tacts with retrogradely labeled SPNs in the rat intermediolatthe peptide produced a sustained inward current. The potentiating eral cell column (Chiba et al. 1996; Dun et al. 1996b). effect of PACAP was nullified by prior incubation of the slices with Some of the results have appeared as an abstract (Wu and the adenylate cyclase inhibitor MDL-12,330A (25 mM). Further, Dun 1996a). superfusing the slices with the membrane-permeable cyclic AMP analogue N,2 *-0-dibutyryladenosine 3 *:5 *-cyclic monophosphate (100–300 mM) in the presence of the phosphodiesterase inhibitor M E T H O D S 3-isobutyl-1-methylxanthine (700 mM) increased the NMDA currents. This result suggests that PACAP selectively increases Procedures used in obtaining 500-mm transverse thoracolumbar NMDA-receptor-mediated responses in the rat SPNs, probably via spinal cord slices from 12to 16-day-old Sprague-Dawley rats a cyclic-AMP-dependent mechanism, providing evidence that the have been described (Shen and Dun 1990; Wu and Dun 1996b). peptide may be involved in synaptic plasticity. Spinal slices were superfused with a Krebs solution of the following composition (in mM): 117 NaCl, 2.0 KCl, 1.2 KH2PO4, 2.3 CaCl2 , 1.3 MgCl2 , 26 NaHCO3, and 10 glucose. The solution was I N T R O D U C T I O N saturated with 95% O2-5% CO2. In preparing Mg-free Krebs solution, MgCl2 was omitted and replaced with an isomolar amount of NaCl. Whole cell recordings were made from SPNs under voltPituitary adenylate cyclase activating polypeptide age-clamp mode with the use of an Axoclamp 2A (Wu and Dun (PACAP), a relatively new peptide first isolated from the 1996b). When filled with the solution containing (in mM) 130 ovine hypothalamus, occurs as a 38-amino-acid or a trunK gluconate, 1 MgCl2 , 2 CaCl2 , 4 ATP, 10 ethylene glycolcated 27-amino-acid peptide, the former being the prevailing bis(b-aminoethyl ether)-N,N,N *,N *-tetraacetic acid, and 10 N-2form in mammalian tissues (Arimura 1992). The amino acid hydroxyethylpiperazine-N *-2-ethanesulfonic acid, patch electrodes sequence of PACAP-38 is well preserved in different species had a resistance of 3–5 MV. With the exception of glutamate and is identical in sheep, rat, and human (Arimura 1992). agonists, pharmacological agents were dissolved in Krebs solution More interestingly, PACAP is homologous to a peptide enin known concentrations and applied to the slices by superfusion. coded by the Drosophila memory gene amnesiac, which is N-methyl-D-aspartate (NMDA, 1 mM) or kainate (KA, 1 mM) thought to be involved in memory storage in the fruit fly was pressure ejected to the recording neuron from a glass pipette with the use of a Picospritzer (General Valve) . A bipolar concen(Feany and Quinn 1995). The possibility that PACAP may tric electrode was placed close to the ventral rootlets for antidromic also be involved in synaptic plasticity in the mammalian identification of SPNs (Shen and Dun 1990). Experiments were nervous system has yet to be explored (Kandel and Abel carried out at room temperature (21 { 17C). Results are expressed 1995). as means { SD and analyzed statistically with the use of Student’s Biochemical studies have revealed two seven-transmemt-test. brane-domain PACAP receptors that are coupled to different NMDA, KA, D-2-amino-phosphonopentanoic acid (AP5), and intracellular pathways (Shivers et al. 1991). Type I receptors 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) were purchased are positively coupled to adenylate cyclase and phospholifrom Tocris Cookson (St. Louis, MO); PACAP-38 was purchased pase C, whereas type II receptors are linked to adenylate from Peninsula Laboratories (Belmont, CA); MDL-12,330A and cyclase only (Spengler et al. 1993). Activation of intracellutetrodotoxin were purchased from RBI (Natick, MA); and other chemicals were from Sigma (St. Louis, MO). lar adenylate cyclase cascade has been shown to underlie