RAPID COMMUNICATION ATP P21 Receptors and Sensory Synaptic Transmission Between Primary Afferent Fibers and Spinal Dorsal Horn Neurons in Rats

Li, Ping, Amelita A. Calean, and Min Zhuo. ATP P21 receptors stock and Wood 1996; Kennedy and Leff 1995 for reviews). and sensory synaptic transmission between primary afferent fibers In the spinal dorsal horn, several ATP receptor subtypes inand spinal dorsal horn neurons in rats. J. Neurophysiol. 80: 3356– cluding P212,4,6 receptor subtypes are expressed in presynap3360, 1998. Glutamate is a major fast transmitter between primary tic terminals of primary afferent fibers and postsynaptic dorsal afferent fibers and dorsal horn neurons in the spinal cord. Recent horn neurons (Brake et al. 1994; Buell et al. 1996; Collo et evidence indicates that ATP acts as another fast transmitter at the al. 1996; Cook et al. 1997; Vulchanova et al. 1996; see Burnrat cervical spinal cord and is proposed to serve as a transmitter stock and Wood 1996 for a review). Although a presynaptic for nociception and pain. Sensory synaptic transmission between action of ATP P21 receptors on glutamate release was recently dorsal root afferent fibers and neurons in the superficial dorsal horn reported (Gu and MacDermott 1997), the involvement of of the lumbar spinal cord were examined by whole cell patchclamp recording techniques. Experiments were designed to test postsynaptic P21 receptors in synaptic transmission between if ATP could serve as a transmitter at the lumbar spinal cord. primary afferent fibers and dorsal horn neurons is still unclear. Monosynaptic excitatory postsynaptic currents (EPSCs) were comATP may serve as a neuromodulator to enhance glutamate pletely abolished after the blockade of both glutamatergic a-aminoinduced responses by a postsynaptic mechanism (Li and Perl 3-hydroxy-5-methyl-4-isoxazolepropionic acid/kainate and N1995) or induce postsynaptic currents in a subpopulation of methyl-D-aspartate receptors. No residual current was detected, dorsal horn neurons (Bardoni et al. 1997). In this study, we indicating that glutamate but not ATP is a fast transmitter at the used in vitro whole cell patch-clamp recording techniques and dorsal horn of the lumbar spinal cord. Pyridoxal-phosphate-6-azoin vivo behavioral tests to examine the role of P21 receptors phenyl-2 *,4 *-disulfonic acid (PPADS), a selective P21 receptor in sensory synaptic transmission and behavioral nociception. antagonist, produced an inhibitory modulatory effect on fast EPSCs and altered responses to paired-pulse stimulation, suggesting the involvement of a presynaptic mechanism. Intrathecal administraM E T H O D S tion of PPADS did not produce any antinociceptive effect in two different types of behavioral nociceptive tests. The present results Slice preparation suggest that ATP P212 receptors modulate excitatory synaptic transmission in the superficial dorsal horn of the lumbar spinal cord by Transverse spinal cord slices from postnatal (P4–P17) rats a presynaptic mechanism, and such a mechanism does not play an (Sprague-Dawley; Harlan) were prepared with the method of Takaimportant role in behavioral responses to noxious heating. The hashi (1990) with some modifications. Rats were deeply anestheinvolvement of other P21 subtype receptors, which is are less sensitized with halothane and then cooled on ice for 10 min. The lumbar tive to PPADS, in acute nociceptive modulation and persistent pain spinal cord was exposed, and ice-cold physiological saline solution remains to be investigated. (all in mM: 113 NaCl, 3 KCl, 25 NaHCO3, 1 NaH2PO3, 2 CaCl2 , 1 MgCl2 , and 25 D-glucose, equilibrated with 95% O2-5% CO2, pH 7.3) was poured over it to cool the spinal cord. A segment of I N T R O D U C T I O N lumbar spinal cord was quickly removed and immersed in oxygenThe superficial dorsal horn of the spinal cord is important ated, ice-cold saline for ¢3 min. The dura was removed and crossfor sensory transmission, including information coding nocisection slices (150–200 mm in thickness) were cut with a Vibratome. The slices were kept in a filtering funnel filled with oxygenceptive information (Christensen and Perl 1970; Light et al. ated saline at room temperature for ¢2 h. 1979; Light and Perl 1979; Kumazawa and Perl 1978; Pearson 1952; Rethelyi et al. 1989; Sugiura et al. 1986). Glutamate is a major neurotransmitter, and fast synaptic transmission in Whole cell patch-clamp recording the dorsal horn is mainly mediated by a-amino-3-hydroxy-5methyl-4-isoxazolepropionic acid (AMPA)/kainate and NWhole cell voltage-clamp experiments were performed with an methyl-D-aspartate (NMDA) receptors (Glaum et al. 1994; Axopatch 200B patch-clamp amplifier. The slice was continuously Hori et al. 1996; Nastrom et al. 1994; Randic et al. 1993; perfused with oxygenated saline. Visually guided whole cell patchSchneider and Perl 1988, 1994; Yoshimura and Jessell 1990; clamp recordings were performed with the aid of an Axioskop see Yaksh and Malmberg 1994 for a review). ATP is also microscope. The exact sites of recorded neurons were determined by biocytin labeling. Biocytin (0.5%) was added into the recording proposed as another fast transmitter for nociception (see Burnsolution to label the cell. Whole cell patch-clamp recordings were made with 5–10 MV electrodes without fire polishing. The reThe costs of publication of this article were defrayed in part by the cording pipette solution contained (in mM) 110 CsMeSO3, 5 payment of page charges. The article must therefore be hereby marked MgCl2 , 1 ethylene glycol-bis(b-aminoethyl ether)-N,N,N*,N*-tet‘‘advertisement’’ in accordance with 18 U.S.C. Section 1734 solely to indicate this fact. raacetic acid (EGTA), 40 N-2-hydroxdyethylpiperazine-N *-2-eth-