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Interaction between strychnine and γ-aminobutyric acid in chicks
EUROPEANJOURNAL OF PHARMACOLOGY24 (1973) 120-122. NORTH-HOLLANDPUBLISHINGCOMPANY
Short communication INTERACTION BETWEEN STRYCHNINE AND 7-AMINOBUTYRIC ACID IN CHICKS G. OSUIDE and P.O. ADEJOH Department of Pharmacy and Pharmacology, Ahmadu Bello University, Zaria, Nigeria
Accepted 30 July 1973
Received 19 July 1973
G. OSUIDE and P.O. ADEJOH, Interaction between strychnine and 7.aminobutyric acid in chicks, European J. Pharmacol. 24 (1973) 120-122. Domestic fowl chicks aged 2-10 days old were used in this study. Large doses of ~-aminobutyric acid (GABA) injected i.p. potentiated strychnine seizures. Equimolecular sucrose solutions produced similar but more intense potentiation of strychnine effects. It is suggested that the osmotic effects of injected GABAwere responsible for the excitatory effects produced in chicks. "r-Aminobutyricacid
Strychnine
1. Introduction In young chicks, 7-aminobutyric acid (GABA) penetrates the blood-brain barrier after i.p. injection, and produces depression of the central nervous system (Kramer and Seifter, 1966; Scholes, 1965). Hayashi (1958) has suggested that GABA is the parent substance of both a central excitatory and an inhibitory principle. In this communication, the interaction of GABA with strychnine in chicks has been studied.
2. Materials and methods White leghorn cockerels aged 2 - 1 0 days were used. Strychnine was injected s.c. in a range of doses into control chicks and into chicks which had been injected i.p. 90 min previously, with 20 ml/kg of a 2 M solution of GABA (equivalent to 4.12 g/kg) or with equimolecular solutions of sucrose (equivalent to 13.69 g/kg). The chicks were observed singly in an observation box 0.6X0.45X0.23 m for 1 hr; lethality was determined at 12 hr. Each chick was used only once. The drugs used were 7-aminobutyric acid ( K o c h -
Sucrose
Light), strychnine hydrochloride (British Drug Houses) and sucrose (British Drug Houses). The doses of strychnine refer to the base. Fresh solutions of sucrose were used.
3. Results In control chicks small doses of strychnine produced no seizure activity (table 1). ,~fter injection of strychnine to GABA-treated chicks they initially became more depressed and lost the righting reflex. After 5 - 1 0 m i n clonic seizures developed followed by tonic seizures. In chicks pretreated with equimolecular solutions of sucrose, strychnine-induced seizure activity was more severe than in GABA-treated chicks. In chicks treated either with GABA or with sucrose alone, no seizures were observed, but both produced death in 12% and 42% of chicks respectively within 12 hr (table 1).
4. Discussion A large dose of GABA was used in this study be-
121
G. Osuide, P.O. Ade]oh, GABA-strychnine interaction in chicks
Table 1 Influence of GABA and sucrose on strychnine effect in chicks. GABA and sucrose intensified the convulsant effect of strychnine. GABA and to a greater extent sucrose when injected alone produced lethal effects in chicks. Experiment
Dose of strychnine (mg/kg)
No. of chicks used
No. convulsing
Latency to tonic convulsion (min)
Control
0.35 0.5 O.6 0.7 0.85
0 0 3 7 10 10
8-23 8-23 3-10 2-6
0 0 0 0 1
1.0
10 15 10 10 10 10
GABApretreated chicks
0.35 0.5 0.6 0.7 0.85 1.0
50 10 29 10 10 10 10
-
5-28 9-15 4-14 3-11 3-5
6 0 0 0 0 8 10
Sucrosepretreated chicks
0.35 0.5 0.7
50 10 10 10
-
4-13 5-14 4-13
21
cause this dose produced obvious behavioural and ECoG depressant effects. In other studies on chicks, similar doses produce behavioural and ECoG depressant effects (Scholes, 1965; Kramer and Seifter, 1966), anticonvulsant effects against leptazol seizures (Kobrin and Seifter, 1966), and protection against semicarbazide and amino-oxyacetic acid seizures (Osuide and Adejoh, unpublished observation). The need for such large doses is probably due to a partial b l o o d - b r a i n barrier or synaptic barrier effect (McLennan, 1963), coupled with rapid metabolism to inactive products (Kramer and Seifter, 1966). Injection of concentrated solutions of GABA into the cerebrospinal fluid, produces generalized seizures in dogs (Hayashi, 1960). The potentiation of strychnine seizures was the only sign of excitation produced by GABA in the present experiments on chicks. Equimolecular solutions of sucrose also potentiated the convulsant effect o f strychnine. DeFeudis and Elliott (1967) have suggested that the brain is more sensitive than the spinal cord to the effects o f dehydration produced by increased osmolarity o f serum when
0 14 6 10 10 10 6 8 10
No. dead within 12 hr
0
5
7 8
hypertonic solutions of diverse substances, including GABA, are injected. This explains why increased serum osmolarity, and consequent brain dehydration, protected mice and rats from leptazol seizures, but did not affect strychnine seizures. Osuide ( 1 9 6 8 ) h a s suggested that the convulsant and lethal effects of strychnine in chicks are not confined to an action on the spinal cord, and that the brain is also involved. This may explain our finding that, in contrast to the results of DeFeudis and Elliott (1967) with mammals, osmotic effects appear to augment strychnine seizures in chicks. Potentiation o f the strychnine effect is probably due to increased osmolarity of the serum leading to stabilisation o f the neuronal membranes. Such an action would potentiate the local anaesthetic effects of strychnine observed by several workers (for references, see Curtis et al., 1971), and thus result in increased seizure susceptibility. Local anaesthetics are known to produce seizures. Sucrose was more effective than GABA in potentiating strychnine seizures, probably because, unlike GABA, it has no opposing central depressant action.
122
G. Osuide, P.O. Ade/oh, GABA-strychnine interaction in chicks
Acknowledgements This work was financed by the United Kingdom Medical Research Council. We are grateful to Mr. E.A. Imoni and Aminu Abimbola for technical assistance.
References Curtis, D.R., A.W. Duggan and G.A.R. Johnston, 1971, The specificity of strychnine as a glycine antagonist in the mammalian spinal cord, Exptl. Brain Res. 12, 547. DeFeudis, F.V. and K.A.C. Elliot, 1967, Delay or inhibition of convulsion by i.p. injections of diverse substances, Can. J. Physiol. Pharmacol. 45,857. Hayashi, T., 1958, Inhibition and excitation due to "r-aminobutyric acid in the central nervous system, Nature 182, 1076.
Hayashi, To, 1960, Comparison of inhibitory action of amino butyric acid and #-hydroxy-3,-aminobutyric acid on th~ motor system of higher animals, in: Inhibition in the Cen tral Nervous System and GABA, ed. E. Roberts (Per gamon Press, Oxford) p. 515. Kobrin, S. and J° Seifter, 1966, to-Amino acids and variou! biogenic amines as antagonists to pentylenetetrazol, J. Pharmacol. Exptl. Therap. 154, 646. Kramer, S.Z. and J. Seffter, 1966, The effects of GABA and biogenic amines on behaviour and brain electrical activity in chicks, Life Sci. 5,527. McLennan, H., 1963, Synaptic transmission (W.B. Saunder,~ Company, Philadelphia and London). Osuide, G., 1968, Effects of some centrally acting drugs i~ conscious chicks and on spinal reflexes, European J. Pharmacol. 3,283. Scholes, N.W., 1965, Effects of parenterally administered ~. aminobutyric acid on the general behaviour of the youn~ chick, Life Sci. 4, 1945.
Short communication INTERACTION BETWEEN STRYCHNINE AND 7-AMINOBUTYRIC ACID IN CHICKS G. OSUIDE and P.O. ADEJOH Department of Pharmacy and Pharmacology, Ahmadu Bello University, Zaria, Nigeria
Accepted 30 July 1973
Received 19 July 1973
G. OSUIDE and P.O. ADEJOH, Interaction between strychnine and 7.aminobutyric acid in chicks, European J. Pharmacol. 24 (1973) 120-122. Domestic fowl chicks aged 2-10 days old were used in this study. Large doses of ~-aminobutyric acid (GABA) injected i.p. potentiated strychnine seizures. Equimolecular sucrose solutions produced similar but more intense potentiation of strychnine effects. It is suggested that the osmotic effects of injected GABAwere responsible for the excitatory effects produced in chicks. "r-Aminobutyricacid
Strychnine
1. Introduction In young chicks, 7-aminobutyric acid (GABA) penetrates the blood-brain barrier after i.p. injection, and produces depression of the central nervous system (Kramer and Seifter, 1966; Scholes, 1965). Hayashi (1958) has suggested that GABA is the parent substance of both a central excitatory and an inhibitory principle. In this communication, the interaction of GABA with strychnine in chicks has been studied.
2. Materials and methods White leghorn cockerels aged 2 - 1 0 days were used. Strychnine was injected s.c. in a range of doses into control chicks and into chicks which had been injected i.p. 90 min previously, with 20 ml/kg of a 2 M solution of GABA (equivalent to 4.12 g/kg) or with equimolecular solutions of sucrose (equivalent to 13.69 g/kg). The chicks were observed singly in an observation box 0.6X0.45X0.23 m for 1 hr; lethality was determined at 12 hr. Each chick was used only once. The drugs used were 7-aminobutyric acid ( K o c h -
Sucrose
Light), strychnine hydrochloride (British Drug Houses) and sucrose (British Drug Houses). The doses of strychnine refer to the base. Fresh solutions of sucrose were used.
3. Results In control chicks small doses of strychnine produced no seizure activity (table 1). ,~fter injection of strychnine to GABA-treated chicks they initially became more depressed and lost the righting reflex. After 5 - 1 0 m i n clonic seizures developed followed by tonic seizures. In chicks pretreated with equimolecular solutions of sucrose, strychnine-induced seizure activity was more severe than in GABA-treated chicks. In chicks treated either with GABA or with sucrose alone, no seizures were observed, but both produced death in 12% and 42% of chicks respectively within 12 hr (table 1).
4. Discussion A large dose of GABA was used in this study be-
121
G. Osuide, P.O. Ade]oh, GABA-strychnine interaction in chicks
Table 1 Influence of GABA and sucrose on strychnine effect in chicks. GABA and sucrose intensified the convulsant effect of strychnine. GABA and to a greater extent sucrose when injected alone produced lethal effects in chicks. Experiment
Dose of strychnine (mg/kg)
No. of chicks used
No. convulsing
Latency to tonic convulsion (min)
Control
0.35 0.5 O.6 0.7 0.85
0 0 3 7 10 10
8-23 8-23 3-10 2-6
0 0 0 0 1
1.0
10 15 10 10 10 10
GABApretreated chicks
0.35 0.5 0.6 0.7 0.85 1.0
50 10 29 10 10 10 10
-
5-28 9-15 4-14 3-11 3-5
6 0 0 0 0 8 10
Sucrosepretreated chicks
0.35 0.5 0.7
50 10 10 10
-
4-13 5-14 4-13
21
cause this dose produced obvious behavioural and ECoG depressant effects. In other studies on chicks, similar doses produce behavioural and ECoG depressant effects (Scholes, 1965; Kramer and Seifter, 1966), anticonvulsant effects against leptazol seizures (Kobrin and Seifter, 1966), and protection against semicarbazide and amino-oxyacetic acid seizures (Osuide and Adejoh, unpublished observation). The need for such large doses is probably due to a partial b l o o d - b r a i n barrier or synaptic barrier effect (McLennan, 1963), coupled with rapid metabolism to inactive products (Kramer and Seifter, 1966). Injection of concentrated solutions of GABA into the cerebrospinal fluid, produces generalized seizures in dogs (Hayashi, 1960). The potentiation of strychnine seizures was the only sign of excitation produced by GABA in the present experiments on chicks. Equimolecular solutions of sucrose also potentiated the convulsant effect o f strychnine. DeFeudis and Elliott (1967) have suggested that the brain is more sensitive than the spinal cord to the effects o f dehydration produced by increased osmolarity o f serum when
0 14 6 10 10 10 6 8 10
No. dead within 12 hr
0
5
7 8
hypertonic solutions of diverse substances, including GABA, are injected. This explains why increased serum osmolarity, and consequent brain dehydration, protected mice and rats from leptazol seizures, but did not affect strychnine seizures. Osuide ( 1 9 6 8 ) h a s suggested that the convulsant and lethal effects of strychnine in chicks are not confined to an action on the spinal cord, and that the brain is also involved. This may explain our finding that, in contrast to the results of DeFeudis and Elliott (1967) with mammals, osmotic effects appear to augment strychnine seizures in chicks. Potentiation o f the strychnine effect is probably due to increased osmolarity of the serum leading to stabilisation o f the neuronal membranes. Such an action would potentiate the local anaesthetic effects of strychnine observed by several workers (for references, see Curtis et al., 1971), and thus result in increased seizure susceptibility. Local anaesthetics are known to produce seizures. Sucrose was more effective than GABA in potentiating strychnine seizures, probably because, unlike GABA, it has no opposing central depressant action.
122
G. Osuide, P.O. Ade/oh, GABA-strychnine interaction in chicks
Acknowledgements This work was financed by the United Kingdom Medical Research Council. We are grateful to Mr. E.A. Imoni and Aminu Abimbola for technical assistance.
References Curtis, D.R., A.W. Duggan and G.A.R. Johnston, 1971, The specificity of strychnine as a glycine antagonist in the mammalian spinal cord, Exptl. Brain Res. 12, 547. DeFeudis, F.V. and K.A.C. Elliot, 1967, Delay or inhibition of convulsion by i.p. injections of diverse substances, Can. J. Physiol. Pharmacol. 45,857. Hayashi, T., 1958, Inhibition and excitation due to "r-aminobutyric acid in the central nervous system, Nature 182, 1076.
Hayashi, To, 1960, Comparison of inhibitory action of amino butyric acid and #-hydroxy-3,-aminobutyric acid on th~ motor system of higher animals, in: Inhibition in the Cen tral Nervous System and GABA, ed. E. Roberts (Per gamon Press, Oxford) p. 515. Kobrin, S. and J° Seifter, 1966, to-Amino acids and variou! biogenic amines as antagonists to pentylenetetrazol, J. Pharmacol. Exptl. Therap. 154, 646. Kramer, S.Z. and J. Seffter, 1966, The effects of GABA and biogenic amines on behaviour and brain electrical activity in chicks, Life Sci. 5,527. McLennan, H., 1963, Synaptic transmission (W.B. Saunder,~ Company, Philadelphia and London). Osuide, G., 1968, Effects of some centrally acting drugs i~ conscious chicks and on spinal reflexes, European J. Pharmacol. 3,283. Scholes, N.W., 1965, Effects of parenterally administered ~. aminobutyric acid on the general behaviour of the youn~ chick, Life Sci. 4, 1945.