Journal of Neurochemistry Lippincott--Raven Publishers, Philadelphia © 1997 International Society for Neurochemistry Sulphur-Containing Amino Acids Modulate Noradrenaline Release from Hippocampal Slices G. Selema, R. M. Cristèfol, S. Gassó, *R. Griffiths, and E. RodrIguez-Farré Department of Pharmacology and Toxicology, Instituto de Investigaciones Biomédicas de Barcelona, Consejo Superior c/c Investigaciones CientIficas, Barcelona, Spain; and * Neurochemistry Group, Division of Cell and Molecular Biology, University of St. Andrews, St. Andrews, Fife, Scotland Abstract: The L- and n-enantiomers of the sulphur-con- taining amino acids (SAAs)—homocysteate, homocys- teine sulphinate, cysteate, cysteine sulphinate, and S- sulphocysteine—stimulated [ 3H] noradrenaline release from rat hippocampal slices in a concentration-depen- dent manner. The relative potencies of the L-isomers (EC 50 values of 1.05—1.96 mM) were of similar order to that of glutamate (1.56 mM), which was 10-fold lower than that of NMDA (0.15 mM), whereas the D-isomers exhibited a wider range of potencies (0.75 to >5 mM). All stimulatory effects of the SAAs were significantly inhib- ited by the voltage-sensitive Na~ channel blocker tetro- dotoxin (55—71%) and completely blocked by addition of Mg 2~ or 002+ to the incubation medium. All SAA-evoked responses were concentration-dependently antagonized by the selective NMDA receptor antagonist D-(—)-2- amino-5-phosphonopentanoic acid (lC~~ values of 3.2— 49.5 1iM). 6-Cyano-7-nitroquinoxaline-2,3-dione (CNQX), a non-NMDA receptor antagonist, at 100 1jM inhibited the [ 3H]noradrenaline release induced by glutamate and NMDA (65 and 76%, respectively) and by all SAAs stud- ied (65—85%), whereas 10 ~M CNQX only inhibited the effects of S-sulpho-L-cysteine and L- and D-homocys- teate(33, 32, and 44%, respectively). However, the more selective AMPA/kainic acid receptor antagonist 6-nitro- 7-sulphamoylbenzo( f ) quinoxaline-2,3-dione (100 tiM), which did not antagonize the [3H]noradrenaline release induced by glutamate and NMDA, reduced only the S- sulpho-L-cysteine-evoked response (25%). Thus, the stimulation of Ca2~ -dependent [3H] noradrenaline release from hippocampal slices elicited by the majority of the SAAs appears to be mediated by the NMDA receptor. Key Words: Noradrenaline release—Sulphur-containing amino acids—Excitatory amino acid receptors—Hippo- campal slices—Rat. J. Neurochem. 68, 1534—1541 (1997). Although glutamate is the main excitatory neuro- transmitter in the CNS, several sulphur-containing amino acids (SAAs) such as homocysteate (HCA), homocysteine sulphinate (HCSA), cysteate (CA), cysteine sulphinate (CSA), and S-sulphocysteine (SC), which are structurally related to aspartate and glutamate, have also been shown to exert excitatory actions on CNS neurones (Mewett et al., 1983). Sev- eral lines of evidence suggest that some of these SAAs may act as neurotransmitters in the brain. Their endo- genous location and heterogeneous CNS distribution have been established (Do et al., 1986, 1988; Ku- patrick and Mozley, 1986). Certain SAAs can be re- leased in a Ca2~ -dependent manner from various brain regions following K~-induceddepolarization (Do et al., 1986), whereas more recently the evoked release of CSA and HCA following electrical stimulation of the Schaffer collateral—CA I neural pathway has been demonstrated (Klancnik et al., 1992). Astrocytes and neurones exhibit transport systems with both high and low affinity for the SAAs (Grieve et al., 1991). Elec- trophysiological and neurochemical studies have shown that both L- and D-enantiomers of several SAAs depolarize neurones (Curtis and Watkins, 1963) and elicit release of other neurotransmitters (acetylcholine, aspartate, GABA, and dopamine) from brain slices (Lehmann et al., 1988) and neuronal cultures (Dunlop et al., 1989, 1990, 1991, 1992; Mount et al., 1990). All these effects appear to be mediated by stimulation of glutamate receptors. The excitatory and cytotoxic actions of glutamate Received July 15, 1996; revised manuscript received November 26, 1996; accepted December 6, 1996. Address correspondence and reprint requests to Dr. R. M. CristO- fol at Department of Pharmacology and Toxicology, Instituto de Investigaciones Biombdicas de Barcelona, Consejo Superior de In- vestigaciones CientIficas, Jordi Girona 18-26, E-08034 Barcelona, Spain. The present address of Dr. G. Selema is Instituto Nacional de Toxicologia, Hospital “Carlos Finley,” La Habana, Cuba. Abbreviations used: D-AP5, D-( — )-2-amino-5-phosphonopenta- noic acid; AMPA, cr-amino-3-hydroxy-5-methyl-4-isoxazolepropio- nic acid; CA, cysteale; CNQX, 6-cyano-7-nitroquinoxaline-2,3-di- one; CSA, cysteine sulphinate; EAA, excitatory amino acid; HCA, homocysteate; HCSA, homocysteine sulphinate; KA, kainic acid; NA, noradrenaline; NBQX, 6-nitro-7-sulphamoylbenzo (f ) quinoxa- line-2,3-dione; NMDA, N-methyl-D-aspartate; SAA, sulphur-con- taining amino acid; SC, S-sulphocysteine; TTX, tetrodotoxin. 1534