TY - JOUR
T1 - The dorsal midbrain anticonvulsant zone-I. Effects of locally administered excitatory amino acids or bicuculline on maximal electroshock seizures
AU - Shehab, S.
AU - Simkins, M.
AU - Dean, P.
AU - Redgrave, P.
N1 - Funding Information:
Acknowledgements--This work was supported by MRC Grant G8814995N. We also thank Natalie Wood for histological assistance and Len Hetherington for producing the photomicrographs.
PY - 1995/4
Y1 - 1995/4
N2 - Microinjections of bicuculline methiodide into the dorsal midbrain anticonvulsant zone, a region which includes the caudal deep layers of the superior colliculus, the adjacent mesencephalic reticular formation and the intercollicular nucleus, suppress tonic hindlimb extension induced by maximal electroshock. The purpose of the present experiments was to establish the most effective and convenient method for eliciting anticonvulsant properties from the dorsal midbrain using the electroshock model of epilepsy. A comparison of different injections of excitatory amino acids and bicuculline into the dorsal midbrain of the rat showed: (i) injections of kainate suppressed hindlimb extension but only at substantially larger doses (i.e. 200-400 pmol) than 50 pmol of bicuculline, which produced generally superior effects; (ii) quisqualate provided only weak protection against tonic seizures at doses that produced neurotoxic effects (2-40 nmol); (iii)N-methyl-d-aspartate was ineffective at doses which produced mild clonic seizure in their own right (2-4 nmol) and also produced some evidence of neurotoxicity; (iv) the suppression of hindlimb extension by bicuculline was dose related, and the lowest bilateral dose for producing reliable suppression was 50 pmol/400 nl per side; and (v) a unilateral injection of 100 pmol/400 nl also reliably suppressed hindlimb extension. The latter finding had important implications for the design and interpretation of the following lesion study. Injections of bicuculline into the dorsal midbrain also produced defence-like behavioural responses that included running and biting; the intensity of these responses correlated with the suppression of hindlimb extension. In contrast, the excitatory amino acids produced initial defensive reactions which were followed by a state of frozen immobility at the time of the electroshock test.
AB - Microinjections of bicuculline methiodide into the dorsal midbrain anticonvulsant zone, a region which includes the caudal deep layers of the superior colliculus, the adjacent mesencephalic reticular formation and the intercollicular nucleus, suppress tonic hindlimb extension induced by maximal electroshock. The purpose of the present experiments was to establish the most effective and convenient method for eliciting anticonvulsant properties from the dorsal midbrain using the electroshock model of epilepsy. A comparison of different injections of excitatory amino acids and bicuculline into the dorsal midbrain of the rat showed: (i) injections of kainate suppressed hindlimb extension but only at substantially larger doses (i.e. 200-400 pmol) than 50 pmol of bicuculline, which produced generally superior effects; (ii) quisqualate provided only weak protection against tonic seizures at doses that produced neurotoxic effects (2-40 nmol); (iii)N-methyl-d-aspartate was ineffective at doses which produced mild clonic seizure in their own right (2-4 nmol) and also produced some evidence of neurotoxicity; (iv) the suppression of hindlimb extension by bicuculline was dose related, and the lowest bilateral dose for producing reliable suppression was 50 pmol/400 nl per side; and (v) a unilateral injection of 100 pmol/400 nl also reliably suppressed hindlimb extension. The latter finding had important implications for the design and interpretation of the following lesion study. Injections of bicuculline into the dorsal midbrain also produced defence-like behavioural responses that included running and biting; the intensity of these responses correlated with the suppression of hindlimb extension. In contrast, the excitatory amino acids produced initial defensive reactions which were followed by a state of frozen immobility at the time of the electroshock test.
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U2 - 10.1016/0306-4522(94)00515-7
DO - 10.1016/0306-4522(94)00515-7
M3 - Article
C2 - 7609869
AN - SCOPUS:0028937649
SN - 0306-4522
VL - 65
SP - 671
EP - 679
JO - Neuroscience
JF - Neuroscience
IS - 3
ER -