Amino acid transmitters in the mammalian central nervous system

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148 D.R. CURTIS and G.A.R. JOHNSTON: ..-., ~o 2- ~o 2- Z ~ ~'~ ~o ~,~ z .~ ~,~ o < Z Z ~o~ o ~ < ~,o ~Zz~ ~z Z Z © © 2~ © ;> ~. o r-: er~ "2. ~ o.~.~ ;> o, #" ,,~ ~.~ ,q. ~. o~a~a ;> -#'0o c9 r',l ~ m 0 Z ~ N oG'~, cD ~ ~,.h t¢3 t ~ ~.m. ,d ¢q "R. ,q oq ",O O'~ '-~ o, m ~
Amino Acid Transmitters in the Mammalian Central Nervous System 149 Table 9. Enzyme levels in extracts of cat spinal cord and roots (~tmole/hr/g wet tissue) Enzyme Dorsal Dorsal Dorsal Ventral Ventral Ventral Reference roots white grey grey white roots Aspartate 545 2 454 5 412 5 418 2 480 537 GRAHAM and APRISON transaminase (1969) Glutamate 17 149 446 448 139 16 GRAHAM and APRISON dehydrogenase (1969) Glutamine 7 20 67 67 19 4 GRAHAM and APRISON synthetase (I 969) Glutaminase 12 67 397 331 66 13 GRAHAM and APRISON (1969) Glutamate 4 0 13 a 7 0 3 GRAHAM and APR1SON decarboxylase (1969) GABA 1 3 14 13 3 1 GRAHAM and APRISON transaminase (1969) D-Amino acid 0.8 2.2 2.1 0.4 DE MARCHI and oxidase JOHNSTON (1969) Glycine 6.6 9.9 9.6 7 JOHNSTON, VITALI transaminase and ALEXANDER (1970) Serine hydroxy- 2.5 4.3 a 5 2.5 DAVIES and methyltransferase JOHNSTON (1973) a Levels in dorsal grey significantly different from those in ventral grey. (DAvIDOFF et al., 1967). In these animals, which showed no response to nociceptive cutaneous stimulation in the affected segments, spinal monosynaptic reflexes were enhanced, polysynaptic reflexes were reduced, and although some evidence has been obtained for antidromic inhibition mediated by Renshaw cells, details have not been published regarding other types of spinal inhibition (MuRAYAMA and SMITH, 1965). In the rat; however, hindlimb rigidity produced in the same fashion is accompanied by reduced responses to painful cutaneous stimulation, enhanced monosynaptic and reduced polysynaptic reflexes, and reduction of two types of inhibition of ankle extensor motoneurones: short latency ("postsynaptic") inhibition by impulses in the deep peroneal nerve and prolonged (" presynaptic ") inhibition by repetitive impulses in the posterior biceps nerve (MATSUSHITA and SMITH, 1970). There is thus evidence in these studies of a loss of both excitatory and inhibitory spinal mechanisms associated with interneurones. Useful information might also. be provided by transection of dorsal roots, although subsequent alterations in amino acid levels and associated enzymes may be complicated by disturbances of the blood supply (Rat: SUGAR and GER- ARD, 1940. Cat: CHAMBERS, ELDRED, and EGGETT, 1972) in addition to loss of primary afferent fibres. With both aortic occlusion and de-afferentation, histological control and unchanged levels of some metabolites are required to exclude "non-specific" loses of amino acids produced by infarction, oedema, gliosis or cavity formation (see DAVIDOEE et al., 1967).
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Amino acid transmitters in the mammalian central nervous system

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