Psychopharmacologia (Berl.) 42, 41-45 (1975) 9 by Springer-Verlag 1975
The Duration of Tolerance to the Anorexigenic Effect of Amphetamine in Rats K. GUNNAR GOTESTAM and TOMMY LEWANDER Psychiatric Research Center, University of Uppsala, Uller~tker Hospital, Uppsala, Sweden Received September 28, 1974
Abstract. Rats were given d/-amphetamine 16 mg/kg twice daily for 15 days. Complete tolerance to the anorexigenic effect of amphetamine developed from day 7-11. A single injection of 16 mg/kg amphetamine was given to the am-
phetamine pretreated rats and to saline pretreated controls at different time-points after withdrawal, and their food intakes were compared. Signs of tolerance were present at 16 but not 20 days after withdrawal.
Key words: Amphetamine - Anorexia - Tolerance - Drug Dependence - Rats.
During chronic administration of amphetamine, tolerance develops to some, but not all, of its effects, e.g. the anorexigenic and hypothermic effects (cf. K o s m a n and Unna, 1968; Kalant etal., 1971; Lewander, 1971). No reference to the duration of tolerance after a m p h e t a m i n e withdrawal has been found in the literature. The present investigation was carried out in order to study the duration of tolerance to the anorexigenic effect of a m p h e t a m i n e in rats. Two groups of rats were treated chronically with a m p h e t a m i n e and saline, respectively until tolerance to the anorexigenic effect of a m p h e t a m i n e had developed. At different timepoints during 20 days after a m p h e t a m i n e withdrawal, subgroups of the a m p h e t a m i n e and saline treated rats were given a single a m p h e t a m i n e injection and their food intakes were compared.
Method Subjects. Sixty male Sprague-Dawley rats (Anticimex, Sollentuna) about 8 weeks old and weighing 244-265 g at the beginning of the experiment were kept in individual cages of 26 x 36 x 12 cm. The experiment was carried out in a windowless room with a constant temperature of 22 ~C, and with the lights on from 10 p.m. to 10 a.m. The daily experiments started at 10 a.m. Pre-Experimental Training. Prior to the study the rats were trained on the reversed light-dark schedule for two weeks, and to eat the food pellets (Anticimex lab chow pellets 210)
from 10 a.m. to 3 p.m. for 6 days. Water was available ad lib. The experiment started when the mean food intake was about 20 g/rat/5 hrs for two consecutive days. The two last days of this training are included in Fig. 1 and Fig. 2.
Chronic Amphetamine Administration Period (Fig. 1A and 2A). The rats were divided into 6 experimental groups (n = 5), which received intraperitoneal injections of 16 mg/kg dl-amphetamine sulphate (dissolved in physiological saline 8 mg/ml) twice daily at 10 a.m. and 5 p.m. for 15 days and 6 control groups (n = 5) receiving saline injections. The rats were weighed prior to the first daily injection. Each experimental group of 5 rats had a weight-matched control group. Immediately following the first daily injection, a weighed quantity of food was placed on the cages. At 3 p.m. the remaining food was collected, weighed and the food intake was calculated. Cleaning and filling up with water was made after this 5 hrs feeding period. During the chronic administration period the control rats received the same amount of food as the experimental rats by pair-feeding on a group basis. This was accomplished by giving a control group the average amount of food eaten by the corresponding experimental group on the preceeding day. The chronic amphetamine administration period was determined to 15 days since by that time according to previous experiments (Lewander, 1971) tolerance to the anorexigenic effect of amphetamine has developed. Tolerance Duration Assessment (Fig. 1 B and 2 B). At 1, 2, 4, 8, 12, 16, and 20 days after amphetamine withdrawal one experimental group (n = 5) and its pair fed control group, was injected with a single dose of amphetamine (16 mg/kg i.p.) at 10 a.m. The food intake was measured at hourly intervals from 10 a.m. to 3 p.m.
42
Psychopharmacologia (Berl.), Vol. 42, Fasc. 1 (1975) Total food i n t a k e o---. Q Exp. [] Controls
B.
20
0 "0
10 E
0
','0
6
I,,1 i
15
20
II
I
Base- E:d[-AM 16 mg/kg,2 (n=30) Line C:Saline*2 (pairfed, n=30)
5 I
30
I
HI
35 Days
!
dI-AM 16mg/kg (n=5)
Fig. 1A and B. Total food intake (g/rat/day) before (baseline, n = 60), during administration and after withdrawal of chronic administration of d/-amphetamine 16 mg/kg twice daily for 15 days. After the tolerance phase (Fig. 1A) the chronically amphetamine treated rats (experimental rats, n = 30) and the chronically saline treated animals (control rats, n = 30) were divided into groups of five rats
and tested for amphetamine anorexia with a single injection of 16 mg/kg all-amphetamine at different time points after withdrawal (Fig. 1B). S.E.M. (vertical bars) are indicated for baseline days, and test days after withdrawal. Filled circles indicate statistically significant differences (P < 0.01, ttests) from baseline (day 0)
Body weight
[] o---. Exp. [] . . . .
Controls
300
A.
B.
E
O L. (.9
250 .a_a~ - ' * ~ ' ~ ' ~ "
9
i
0
5
10
20
15
II Base- E:dI-AM 16 mg/kg*2 (n=30) line C:Saline*2 (n=30)
I
25 I
30 I
I
35 Days I
dI-AM 16 mg/kg (n=5)
Fig. 2A and B. Body weight (g) before (baseline), during (Fig. 2A) and after withdrawal (Fig. 2B) of amphetamine treatment with 16 mg/kg twice daily for 15 days for the same groups of rats described in the legend to Fig. 1. S.E.M. (vet-
tical bars) are indicated for baseline days and test days after withdrawal. Filled circles indicate statistically significant differences (P < 0.01, t tests) between experimental and control rats
On day 1 after amphetamine withdrawal one experimental and one control group were compared on the 16th day of chronic amphetamine administration. These two groups were tested again at 20 days after amphetamine withdrawal. This control group had thus received a single
dose of 16 mg/kg amphetamine 20 days before the second test. Analyses of variance (one-way classification and splitplot) were computed according to Kirk (1968). When overall significance in the F test was obtained, differences be-
K. G. G6testam and T. Lewander: Tolerance Duration to Amphetamine in Rats tween means were computed with multiple t tests (ibid.). The overall results were considered significant at the 5 % level, and the multiple t tests at the 1% level.
15
O
43
DAY 1 (p
The Duration of Tolerance to the Anorexigenic Effect of Amphetamine in Rats K. GUNNAR GOTESTAM and TOMMY LEWANDER Psychiatric Research Center, University of Uppsala, Uller~tker Hospital, Uppsala, Sweden Received September 28, 1974
Abstract. Rats were given d/-amphetamine 16 mg/kg twice daily for 15 days. Complete tolerance to the anorexigenic effect of amphetamine developed from day 7-11. A single injection of 16 mg/kg amphetamine was given to the am-
phetamine pretreated rats and to saline pretreated controls at different time-points after withdrawal, and their food intakes were compared. Signs of tolerance were present at 16 but not 20 days after withdrawal.
Key words: Amphetamine - Anorexia - Tolerance - Drug Dependence - Rats.
During chronic administration of amphetamine, tolerance develops to some, but not all, of its effects, e.g. the anorexigenic and hypothermic effects (cf. K o s m a n and Unna, 1968; Kalant etal., 1971; Lewander, 1971). No reference to the duration of tolerance after a m p h e t a m i n e withdrawal has been found in the literature. The present investigation was carried out in order to study the duration of tolerance to the anorexigenic effect of a m p h e t a m i n e in rats. Two groups of rats were treated chronically with a m p h e t a m i n e and saline, respectively until tolerance to the anorexigenic effect of a m p h e t a m i n e had developed. At different timepoints during 20 days after a m p h e t a m i n e withdrawal, subgroups of the a m p h e t a m i n e and saline treated rats were given a single a m p h e t a m i n e injection and their food intakes were compared.
Method Subjects. Sixty male Sprague-Dawley rats (Anticimex, Sollentuna) about 8 weeks old and weighing 244-265 g at the beginning of the experiment were kept in individual cages of 26 x 36 x 12 cm. The experiment was carried out in a windowless room with a constant temperature of 22 ~C, and with the lights on from 10 p.m. to 10 a.m. The daily experiments started at 10 a.m. Pre-Experimental Training. Prior to the study the rats were trained on the reversed light-dark schedule for two weeks, and to eat the food pellets (Anticimex lab chow pellets 210)
from 10 a.m. to 3 p.m. for 6 days. Water was available ad lib. The experiment started when the mean food intake was about 20 g/rat/5 hrs for two consecutive days. The two last days of this training are included in Fig. 1 and Fig. 2.
Chronic Amphetamine Administration Period (Fig. 1A and 2A). The rats were divided into 6 experimental groups (n = 5), which received intraperitoneal injections of 16 mg/kg dl-amphetamine sulphate (dissolved in physiological saline 8 mg/ml) twice daily at 10 a.m. and 5 p.m. for 15 days and 6 control groups (n = 5) receiving saline injections. The rats were weighed prior to the first daily injection. Each experimental group of 5 rats had a weight-matched control group. Immediately following the first daily injection, a weighed quantity of food was placed on the cages. At 3 p.m. the remaining food was collected, weighed and the food intake was calculated. Cleaning and filling up with water was made after this 5 hrs feeding period. During the chronic administration period the control rats received the same amount of food as the experimental rats by pair-feeding on a group basis. This was accomplished by giving a control group the average amount of food eaten by the corresponding experimental group on the preceeding day. The chronic amphetamine administration period was determined to 15 days since by that time according to previous experiments (Lewander, 1971) tolerance to the anorexigenic effect of amphetamine has developed. Tolerance Duration Assessment (Fig. 1 B and 2 B). At 1, 2, 4, 8, 12, 16, and 20 days after amphetamine withdrawal one experimental group (n = 5) and its pair fed control group, was injected with a single dose of amphetamine (16 mg/kg i.p.) at 10 a.m. The food intake was measured at hourly intervals from 10 a.m. to 3 p.m.
42
Psychopharmacologia (Berl.), Vol. 42, Fasc. 1 (1975) Total food i n t a k e o---. Q Exp. [] Controls
B.
20
0 "0
10 E
0
','0
6
I,,1 i
15
20
II
I
Base- E:d[-AM 16 mg/kg,2 (n=30) Line C:Saline*2 (pairfed, n=30)
5 I
30
I
HI
35 Days
!
dI-AM 16mg/kg (n=5)
Fig. 1A and B. Total food intake (g/rat/day) before (baseline, n = 60), during administration and after withdrawal of chronic administration of d/-amphetamine 16 mg/kg twice daily for 15 days. After the tolerance phase (Fig. 1A) the chronically amphetamine treated rats (experimental rats, n = 30) and the chronically saline treated animals (control rats, n = 30) were divided into groups of five rats
and tested for amphetamine anorexia with a single injection of 16 mg/kg all-amphetamine at different time points after withdrawal (Fig. 1B). S.E.M. (vertical bars) are indicated for baseline days, and test days after withdrawal. Filled circles indicate statistically significant differences (P < 0.01, ttests) from baseline (day 0)
Body weight
[] o---. Exp. [] . . . .
Controls
300
A.
B.
E
O L. (.9
250 .a_a~ - ' * ~ ' ~ ' ~ "
9
i
0
5
10
20
15
II Base- E:dI-AM 16 mg/kg*2 (n=30) line C:Saline*2 (n=30)
I
25 I
30 I
I
35 Days I
dI-AM 16 mg/kg (n=5)
Fig. 2A and B. Body weight (g) before (baseline), during (Fig. 2A) and after withdrawal (Fig. 2B) of amphetamine treatment with 16 mg/kg twice daily for 15 days for the same groups of rats described in the legend to Fig. 1. S.E.M. (vet-
tical bars) are indicated for baseline days and test days after withdrawal. Filled circles indicate statistically significant differences (P < 0.01, t tests) between experimental and control rats
On day 1 after amphetamine withdrawal one experimental and one control group were compared on the 16th day of chronic amphetamine administration. These two groups were tested again at 20 days after amphetamine withdrawal. This control group had thus received a single
dose of 16 mg/kg amphetamine 20 days before the second test. Analyses of variance (one-way classification and splitplot) were computed according to Kirk (1968). When overall significance in the F test was obtained, differences be-
K. G. G6testam and T. Lewander: Tolerance Duration to Amphetamine in Rats tween means were computed with multiple t tests (ibid.). The overall results were considered significant at the 5 % level, and the multiple t tests at the 1% level.
15
O
43
DAY 1 (p
