Amino acid transmitters in the mammalian central nervous system

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).