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Effects of nikethamide, picrotoxin and strychnine on ‘amphetamine-state’
European Journal of Pharmacology 29 (1974) 175-178
© North-Holland Publishing Company Short communication
E F F E C T S O F N 1 K E T H A M I D E , P I C R O T O X I N A N D S T R Y C H N I N E ON 'AMPHETAMINE-STATE' Jen-Tzaw HUANG 1 and Beng T. HO 2 Texas Research Institute of Mental Sciences and University of Texas at Houston, Houston, Texas 77025, U.S.A.
Received 5 August 1974, accepted 11 September 1974 J.-T. HUANGand B.T. HO, Effects of nikethamide, picrotoxin and strychnine on 'amphetamine-state', European J. Pharmacol. 29 (1974) 175-178. Rats were trained to discriminate between d-amphetamine sulfate (0.8 mg/kg) or saline by selectively pressing two levers programmed on differential response at low rate 15-sec schedule for food reinforcement. Nikethamide (26-75 mg/kg), strychnine (0.5 and 10 mg/kg) and picrotoxin (1.0 and 2.0 mg/kg) did not produce d-amphetamine-like responding in the animals. Results indicated that in order for drugs to produce similar discriminative cue they should possess a specific pharmacologicalproperty in common. State-dependent learning Discriminative cue
Picrotoxin
Nikethamide
1. Introduction For chemicals of the same pharmacological class to exert similar discriminative property has been investigated. Hirschhorn and Winter (1971) and Schechter and Rosecrans (1972) reported that hallucinogens such as mescaline, LSD and psilocybin all produce the similar discriminative cue in animals. We (Huang and Ho, 1974a) have shown that ~-phenethylamine, a compound of weak amphetamine-like action produces d-amphetamine-like responding after its metabolism being prevented by iproniazid. Furthermore, methylphenidate and cocaine (Huang and Ho, 1974b) which were classified as psychomotor stimulants as d-amphetamine were also found to generalize the discriminative cue produced by d-amphetamine. These results seem to be in accord with the proposal of Overton (1971) that chemicals with similar pharma-
i Present address: Department of Pharmacology,University of Minnesota, Minneapolis, Minnesota 55455, U.S.A. 2 To whom reprint requests should be addressed, Texas Research Institute of Mental Sciences, 1300 Moursund Avenue, Houston, Texas 77025, U.S.A.
d-Amphetamine
Strychnine
cological actions can produce similar interoceptive cues. For further substantiation of this hypothesis the present study was carried out with CNS stimulants, such as nikethamide, picrotoxin and strychnine, to test for generalization to discriminative control induced by d-amphetamine.
2. Materials and methods Male Sprague-Dawley rats (350-450 g) were deprived of food until they stabilized to approximately 85% of their normal weight and were then used for training to discriminate between amphetamine (0.8 mg/kg) and saline as previously described (Huang and Ho, 1974a). 5 2-1ever sound attenuate operant chambers (Scientific Prototype Model PLS-1000) were used for behavioral training and testing. Each chamber was programmed with solid state equipment (GrasonStadler 1200 series) which controlled reinforcement ~and recording of response. Animals were trained to perform a differential reinforcement of low response rate (DRL) 1-sec schedule for 30 rain every day for 4
176
J.-T. Huang, B.T. Ho, CNS stimulants and amphetamine cue
days, followed by 4 days each on D R L 5-sec, D R L 10-sec and finally on DRL 15-sec schedule. Reinforcement was given on alternating levers (doublealternating schedule) with a delivery of a 45-mg Noyes pellet for each correct response. After the animals have been stabilized on D R L 15-sec (16 days) d-amphetamine sulfate (0.8 mg/kg) or 0.9% saline (1 ml/kg) was administered i.p. 15 min before the daily 30-min training session. The left lever was designated as the 'amphetamine correct' lever and the right lever as the 'saline correct' lever. Animals were reinforced only when pressing the designated correct lever according to the administration o f amphetamine or saline. After 32 training sessions with 4 days for each training block (2 days on the amphetamine lever and 2 days on the saline lever) all animals' responses were more than 80% lever correct during 10-min extinction test in which the reinforcement delivery was disconnected. Extinction sessions were then performed with nikethamide, picrotoxin and strychnine sulfate for the purpose o f testing the degree of generalization to the d-amphetamine-induced interoceptive cue. Each drug in saline was injected i.p. to animals 15-min prior to the test session and results are expressed as the number of correct responses divided by the total number of responses.
3. Results
Data in table 1 show that after more than 32 sessions of discriminative training the subjects were able to discriminate between saline and d-amphetamine, i.e. when injected with 0.8 mg/kg of d-amphetamine they responded more than 8 out of 10 on the 'amphetamine lever' and less than twice on the 'saline lever' even at the discontinuation o f reinforcement. However, when these subjects were tested with nikethamide, picrotoxin or strychnine, their responses were dissimilar to responses obtained with d-amphetamine: low doses of these drugs produced saline-like responses and higher doses gave responses only in the change (around 50%) level. Also, some rats either underwent convulsion or failed to press the lever. To mention an example, 2 mg/kg of picroto~dn caused only two rats to respond while others showed slight convulsion or just sat in the corner of the cage. The effects of a high dose (75 mg/kg) o f nikethamide on d-amphetamine-induced discriminative cue are shown in table 2. Rats showed convulsion, lacrimation and salivation and marked reduction of responding. Normally rats pressed levers more than 50 times within a 10-min extinction test, but in the nikethamide-treated animals two only pressed levers twice within 30 min. Table 2 also shows that better performance was not achieved by extending the duration period of the extinction test.
Table 1 Effect of nikethamide, picrotoxin and strychnine on d-amphetamine-induced discriminative control. Drug
d-Amphetamine sulfate Saline Nikethamide Picrotoxin Strychnine sulfate
Dose (mg/kg) 0.8 25 50 1.0 2.0 0.5 1.0
Percent amphetamine lever choice a 5 min
10 min
88.1 ± 2.1 13.2 ± 3.2 18.8 ± 3.3 56.2 ± 10.3 35.6 + 13.1 58.8 ± 19.0 19.8 ± 7.6 12.5 ± 4.2
89.3 10.8 18.2 49.3 35.0 48.1 18.6 11.7
± 1.9 ± 2.6 ± 3.5 ± 11.6 ± 14.8 ± 15.9 b ± 6.4 ± 4.0
a Calculated from the number of responses on the amphetamine lever divided by total number of responses on the two levers during 5 and 10 min extinction test period. Each value represents mean ± S.E.M. of 5 animals. b 3 of the 5 animals failed to respond to the lever.
J.-T. Huang, B.T. Ho, CNS stimulants and amphetamine cue
177
Table 2 Effect of nikethamide (75 mg/kg) on d-amphetamine-induced discriminative control. Animal
Number of lever responses a,b
no.
11 12 13 14 15
5 min
10 min
L R%toL
L
R%toL
L
R%toL
L
2 1 2 7 6
2 2 2 11 7
2 0 0 5 8
13 2 2 20 8
4 0 0 9 10
19 2 2 22 9
Average c
2 50 0 0 3 70 6 50 56.6
15 min
50 69 47
20 min
55.3
76 69 44
25 min
30 min
R%toL
L
R%tok
L
R%toL
8 0 0 13 11
22 2 2 26 10
13 0 0 16 12
22 2 2 28 13
13 0 0 16 14
63
70 63 45 62.6
63 62 45 56.6
63 64 48 58.3
a Nikethamide was injected i.p. 15 min before placing the animal into the operant chamber. b L: amphetamine lever. R: saline lever. Percent of response on the left lever during the extinction test period was calculated as stated in footnote a of table 1. c Calculated from data obtained with No. 11, 14 and 15 rats. Percent of the amphetamine-lever response during 30-min extinction test with d-amphetamine sulfate (0.8 mg/kg): 90.2 + 3.0, 90.4 ± 2.8, 90.9 ± 2.4, 91.2 ± 1.5, 88.9 ± 2.5, 85.7 ± 2.9 for 5, 10, 15, 20, 25 and 30 min respectively.
4. Discussion
The present results indicate that the d-amphetamine-induced discriminative cue was not generalized by nikethamide, picrotoxin or strychnine. Although d-amphetamine has the same potency of central excitatory and analeptic properties as nikethamide, picrotoxin, strychnine and methylphenidate (Innes and Nickerson, 1970), only methylphenidate which is classified as psychomotor stimulant produced damphetamine-like cueing effect (Harris and BaNter, 1971; Huang and Ho, 1974b). Therefore, it seems that the production of the 'amphetamine-state' is not solely related to the general excitatory property of the drug, but may require a more specific property, which methylphenidate and amphetamine have in common. Many previous reports (Costa and Garattini, 1970) have demonstrated that various amphetamine actions were due to its effects on catecholamine neurons. Our previous report (Ho and Huang, 1973) further suggested that dopaminergic neurons were involved in producing the discriminative cue of amphetamine. The finding that strychnine and picrotoxin affect primarily the glycine and GABA systems may also explain why these two drugs failed to produce the discriminative cueing effect similar to d-amphetamine. This difference in effects of nikethamide, picrotoxin and strychnine from that of amphetamine could not
be due to an insufficient amount of the drug for action, because low doses of these drugs produced saline-like responses but high doses showed responses undefined for either saline or d-amphetamine. It is thus concluded that these drugs are different from d-amphetamine in regard to their discriminative stimulus properties.
References Costa, E. and S. Garattini (eds.), 1970, International symposium on amphetamines and related compounds (Raven Press, New York). Harris, R.T. and R.L. Balster, 1971, An analysis of the function of drugs in stimulus control of operant behavior, in: Stimulus Properties of Drugs, eds. T. Thompson and P. Pickens (Appleton-Century-Crafts, New York) p. 111. Hirschhorn, I.P. and J.C. Winter, 1971, Mescaline and lysergic acid diethylamine (LSD) as discriminative stimuli, Psychopharmacologia (Berlin) 23, 64. Ho, B.T. and J.T. Huang, 1973, The role of monoamines in discriminative response control by amphetamines, Society for Neuroscience, Third Ann. Meeting, San Diego, U.S.A. p. 340. Huang, J.T. and B.T. Ho, 1974a, The effect of pretreatment with iproniazid on behavioral activities of #-phenylethylamine in rats, Psychopharmacologia (Berlin) 35, 77. Huang, J.T. and B.T. Ho, 1974b, Discriminative stimulus properties of d-amphetamine and related compounds in rats, Pharmacol. Behav. Biochem. 2, (in press).
178
J.-T. Huang, B.T. Ho, CNS stimulants and amphetamine cue
lnnes, I.R. and M. Nickerson, 1970, Drug action on postganglionic adrenergic nerve endings and structures innervated by them (sympathomimetic drugs), in: Pharmacological Basis of Therapeutics, eds. L.S. Goodman and A. Gilman (MacMillan, New York) p. 502. Overton, D.A., 1971, Discriminative control of behavior by drug state, in: Stimulus Properties of Drugs, eds. T.
Thompson and P. Pickens (Appleton-Century-Crafts, New York) p. 87. Schechter, M.D. and J.A. Rosecrans, 1972, Lysergic acid diethylamide (LSD) as a discriminative cue: Drugs with similar stimulus properties, Psychopharmacologia (Berlin) 26, 313.
© North-Holland Publishing Company Short communication
E F F E C T S O F N 1 K E T H A M I D E , P I C R O T O X I N A N D S T R Y C H N I N E ON 'AMPHETAMINE-STATE' Jen-Tzaw HUANG 1 and Beng T. HO 2 Texas Research Institute of Mental Sciences and University of Texas at Houston, Houston, Texas 77025, U.S.A.
Received 5 August 1974, accepted 11 September 1974 J.-T. HUANGand B.T. HO, Effects of nikethamide, picrotoxin and strychnine on 'amphetamine-state', European J. Pharmacol. 29 (1974) 175-178. Rats were trained to discriminate between d-amphetamine sulfate (0.8 mg/kg) or saline by selectively pressing two levers programmed on differential response at low rate 15-sec schedule for food reinforcement. Nikethamide (26-75 mg/kg), strychnine (0.5 and 10 mg/kg) and picrotoxin (1.0 and 2.0 mg/kg) did not produce d-amphetamine-like responding in the animals. Results indicated that in order for drugs to produce similar discriminative cue they should possess a specific pharmacologicalproperty in common. State-dependent learning Discriminative cue
Picrotoxin
Nikethamide
1. Introduction For chemicals of the same pharmacological class to exert similar discriminative property has been investigated. Hirschhorn and Winter (1971) and Schechter and Rosecrans (1972) reported that hallucinogens such as mescaline, LSD and psilocybin all produce the similar discriminative cue in animals. We (Huang and Ho, 1974a) have shown that ~-phenethylamine, a compound of weak amphetamine-like action produces d-amphetamine-like responding after its metabolism being prevented by iproniazid. Furthermore, methylphenidate and cocaine (Huang and Ho, 1974b) which were classified as psychomotor stimulants as d-amphetamine were also found to generalize the discriminative cue produced by d-amphetamine. These results seem to be in accord with the proposal of Overton (1971) that chemicals with similar pharma-
i Present address: Department of Pharmacology,University of Minnesota, Minneapolis, Minnesota 55455, U.S.A. 2 To whom reprint requests should be addressed, Texas Research Institute of Mental Sciences, 1300 Moursund Avenue, Houston, Texas 77025, U.S.A.
d-Amphetamine
Strychnine
cological actions can produce similar interoceptive cues. For further substantiation of this hypothesis the present study was carried out with CNS stimulants, such as nikethamide, picrotoxin and strychnine, to test for generalization to discriminative control induced by d-amphetamine.
2. Materials and methods Male Sprague-Dawley rats (350-450 g) were deprived of food until they stabilized to approximately 85% of their normal weight and were then used for training to discriminate between amphetamine (0.8 mg/kg) and saline as previously described (Huang and Ho, 1974a). 5 2-1ever sound attenuate operant chambers (Scientific Prototype Model PLS-1000) were used for behavioral training and testing. Each chamber was programmed with solid state equipment (GrasonStadler 1200 series) which controlled reinforcement ~and recording of response. Animals were trained to perform a differential reinforcement of low response rate (DRL) 1-sec schedule for 30 rain every day for 4
176
J.-T. Huang, B.T. Ho, CNS stimulants and amphetamine cue
days, followed by 4 days each on D R L 5-sec, D R L 10-sec and finally on DRL 15-sec schedule. Reinforcement was given on alternating levers (doublealternating schedule) with a delivery of a 45-mg Noyes pellet for each correct response. After the animals have been stabilized on D R L 15-sec (16 days) d-amphetamine sulfate (0.8 mg/kg) or 0.9% saline (1 ml/kg) was administered i.p. 15 min before the daily 30-min training session. The left lever was designated as the 'amphetamine correct' lever and the right lever as the 'saline correct' lever. Animals were reinforced only when pressing the designated correct lever according to the administration o f amphetamine or saline. After 32 training sessions with 4 days for each training block (2 days on the amphetamine lever and 2 days on the saline lever) all animals' responses were more than 80% lever correct during 10-min extinction test in which the reinforcement delivery was disconnected. Extinction sessions were then performed with nikethamide, picrotoxin and strychnine sulfate for the purpose o f testing the degree of generalization to the d-amphetamine-induced interoceptive cue. Each drug in saline was injected i.p. to animals 15-min prior to the test session and results are expressed as the number of correct responses divided by the total number of responses.
3. Results
Data in table 1 show that after more than 32 sessions of discriminative training the subjects were able to discriminate between saline and d-amphetamine, i.e. when injected with 0.8 mg/kg of d-amphetamine they responded more than 8 out of 10 on the 'amphetamine lever' and less than twice on the 'saline lever' even at the discontinuation o f reinforcement. However, when these subjects were tested with nikethamide, picrotoxin or strychnine, their responses were dissimilar to responses obtained with d-amphetamine: low doses of these drugs produced saline-like responses and higher doses gave responses only in the change (around 50%) level. Also, some rats either underwent convulsion or failed to press the lever. To mention an example, 2 mg/kg of picroto~dn caused only two rats to respond while others showed slight convulsion or just sat in the corner of the cage. The effects of a high dose (75 mg/kg) o f nikethamide on d-amphetamine-induced discriminative cue are shown in table 2. Rats showed convulsion, lacrimation and salivation and marked reduction of responding. Normally rats pressed levers more than 50 times within a 10-min extinction test, but in the nikethamide-treated animals two only pressed levers twice within 30 min. Table 2 also shows that better performance was not achieved by extending the duration period of the extinction test.
Table 1 Effect of nikethamide, picrotoxin and strychnine on d-amphetamine-induced discriminative control. Drug
d-Amphetamine sulfate Saline Nikethamide Picrotoxin Strychnine sulfate
Dose (mg/kg) 0.8 25 50 1.0 2.0 0.5 1.0
Percent amphetamine lever choice a 5 min
10 min
88.1 ± 2.1 13.2 ± 3.2 18.8 ± 3.3 56.2 ± 10.3 35.6 + 13.1 58.8 ± 19.0 19.8 ± 7.6 12.5 ± 4.2
89.3 10.8 18.2 49.3 35.0 48.1 18.6 11.7
± 1.9 ± 2.6 ± 3.5 ± 11.6 ± 14.8 ± 15.9 b ± 6.4 ± 4.0
a Calculated from the number of responses on the amphetamine lever divided by total number of responses on the two levers during 5 and 10 min extinction test period. Each value represents mean ± S.E.M. of 5 animals. b 3 of the 5 animals failed to respond to the lever.
J.-T. Huang, B.T. Ho, CNS stimulants and amphetamine cue
177
Table 2 Effect of nikethamide (75 mg/kg) on d-amphetamine-induced discriminative control. Animal
Number of lever responses a,b
no.
11 12 13 14 15
5 min
10 min
L R%toL
L
R%toL
L
R%toL
L
2 1 2 7 6
2 2 2 11 7
2 0 0 5 8
13 2 2 20 8
4 0 0 9 10
19 2 2 22 9
Average c
2 50 0 0 3 70 6 50 56.6
15 min
50 69 47
20 min
55.3
76 69 44
25 min
30 min
R%toL
L
R%tok
L
R%toL
8 0 0 13 11
22 2 2 26 10
13 0 0 16 12
22 2 2 28 13
13 0 0 16 14
63
70 63 45 62.6
63 62 45 56.6
63 64 48 58.3
a Nikethamide was injected i.p. 15 min before placing the animal into the operant chamber. b L: amphetamine lever. R: saline lever. Percent of response on the left lever during the extinction test period was calculated as stated in footnote a of table 1. c Calculated from data obtained with No. 11, 14 and 15 rats. Percent of the amphetamine-lever response during 30-min extinction test with d-amphetamine sulfate (0.8 mg/kg): 90.2 + 3.0, 90.4 ± 2.8, 90.9 ± 2.4, 91.2 ± 1.5, 88.9 ± 2.5, 85.7 ± 2.9 for 5, 10, 15, 20, 25 and 30 min respectively.
4. Discussion
The present results indicate that the d-amphetamine-induced discriminative cue was not generalized by nikethamide, picrotoxin or strychnine. Although d-amphetamine has the same potency of central excitatory and analeptic properties as nikethamide, picrotoxin, strychnine and methylphenidate (Innes and Nickerson, 1970), only methylphenidate which is classified as psychomotor stimulant produced damphetamine-like cueing effect (Harris and BaNter, 1971; Huang and Ho, 1974b). Therefore, it seems that the production of the 'amphetamine-state' is not solely related to the general excitatory property of the drug, but may require a more specific property, which methylphenidate and amphetamine have in common. Many previous reports (Costa and Garattini, 1970) have demonstrated that various amphetamine actions were due to its effects on catecholamine neurons. Our previous report (Ho and Huang, 1973) further suggested that dopaminergic neurons were involved in producing the discriminative cue of amphetamine. The finding that strychnine and picrotoxin affect primarily the glycine and GABA systems may also explain why these two drugs failed to produce the discriminative cueing effect similar to d-amphetamine. This difference in effects of nikethamide, picrotoxin and strychnine from that of amphetamine could not
be due to an insufficient amount of the drug for action, because low doses of these drugs produced saline-like responses but high doses showed responses undefined for either saline or d-amphetamine. It is thus concluded that these drugs are different from d-amphetamine in regard to their discriminative stimulus properties.
References Costa, E. and S. Garattini (eds.), 1970, International symposium on amphetamines and related compounds (Raven Press, New York). Harris, R.T. and R.L. Balster, 1971, An analysis of the function of drugs in stimulus control of operant behavior, in: Stimulus Properties of Drugs, eds. T. Thompson and P. Pickens (Appleton-Century-Crafts, New York) p. 111. Hirschhorn, I.P. and J.C. Winter, 1971, Mescaline and lysergic acid diethylamine (LSD) as discriminative stimuli, Psychopharmacologia (Berlin) 23, 64. Ho, B.T. and J.T. Huang, 1973, The role of monoamines in discriminative response control by amphetamines, Society for Neuroscience, Third Ann. Meeting, San Diego, U.S.A. p. 340. Huang, J.T. and B.T. Ho, 1974a, The effect of pretreatment with iproniazid on behavioral activities of #-phenylethylamine in rats, Psychopharmacologia (Berlin) 35, 77. Huang, J.T. and B.T. Ho, 1974b, Discriminative stimulus properties of d-amphetamine and related compounds in rats, Pharmacol. Behav. Biochem. 2, (in press).
178
J.-T. Huang, B.T. Ho, CNS stimulants and amphetamine cue
lnnes, I.R. and M. Nickerson, 1970, Drug action on postganglionic adrenergic nerve endings and structures innervated by them (sympathomimetic drugs), in: Pharmacological Basis of Therapeutics, eds. L.S. Goodman and A. Gilman (MacMillan, New York) p. 502. Overton, D.A., 1971, Discriminative control of behavior by drug state, in: Stimulus Properties of Drugs, eds. T.
Thompson and P. Pickens (Appleton-Century-Crafts, New York) p. 87. Schechter, M.D. and J.A. Rosecrans, 1972, Lysergic acid diethylamide (LSD) as a discriminative cue: Drugs with similar stimulus properties, Psychopharmacologia (Berlin) 26, 313.