Brain Research, 512 (1990) 107-112
107
Elsevier BRES 15296
Multiple, but not acute, infusions of cocaine alter the release of prolactin in male rats Nancy S. Pilotte, Lawrence G. Sharpe and Elizabeth M. Dax Addiction Research Center, National Institute on Drug Abuse, Baltimore, MD 21224 (U.S.A.)
(Accepted 15 August 1989) Key words: Cocaine; Prolactin; Adrenocorticotropic hormone; Corticosterone
Hypothalamic dopamine tonically inhibits the release of prolactin (PRL) from the anterior pituitary gland. Cocaine, in turn, alters dopaminergic transmission. We compared the effects of acute and repeated injections of cocaine on the release of PRL in male rats to assess whether cocaine could affect dopaminergically mediated hormonal responses. We found that the concentration of PRL in plasma was not affected by single i.v. injections of 1, 3 or 10 mg/kg of cocaine. However, in rats infused repeatedly with 1 mg/kg of cocaine for 5 s every 12 min for 2 h over 10 days, the pre-infusion concentrations of PRL increased in a time-dependent manner whereas cocaine uniformly decreased post-infusion levels of PRL. Repeated administration of cocaine may produce long-term changes in either the tuberoinfundibular dopaminergic neurons or the adenohypophysiai dopamine D2-receptors, or both. Changes in the peripheral concentration of PRL after multiple injections of cocaine and during cocaine withdrawal may reflect dopaminergic activity in the hypothalamus. In contrast, single injections of cocaine increased adrenocorticotropin (ACTH) in a dose-dependent manner whereas repeated infusions did not increase peripheral concentrations of ACTH or corticosterone. It seems that repeated injections of cocaine do not result in persistent changes in the hypothalamo-pituitary-adrenal axis. INTRODUCTION T h e secretion of prolactin ( P R L ) from the anterior pituitary gland is u n d e r the tonic inhibitory control of d o p a m i n e ( D A ) released from the terminals of the t u b e r o i n f u n d i b u l a r d o p a m i n e r g i c ( T I D A ) neurons 5. In turn, circulating levels of P R L are thought to activate these neurons, increasing the release of D A 7'23. A single injection of cocaine to rats rapidly but briefly increases the concentration of extracellular D A 9'1s whereas rep e a t e d injections lead to long-term decreases in dopa accumulation and in 3,4-dihydroxyphenylacetic acid ( D O P A C ) formation xl, and reduce immunoreactive tyrosine hydroxylase throughout the mesolimbic D A system 24. Thus, the neurochemical effects of a single injection of cocaine on D A differ from those that occur after r e p e a t e d administration. Clinically, others have r e p o r t e d mild h y p e r p r o l a c t i n e m i a in humans upon cessation from the chronic use of cocaine 1'17. These observations are consistent with suggestions that the levels of central D A m a y be decreased after cocaine usage 25. Because of the close relationship between P R L and D A , we c o m p a r e d the release of P R L before and after one or multiple i.v. injections of cocaine as a means of assessing cocaine's effects on hypothalamic D A activity.
P R L and a d r e n o c o r t i c o t r o p i n ( A C T H ) are often released concomitantly in response to noxious (or 'stressful') stimuli. Because the physiological events following the administration of cocaine m a y be considered stressful, we examined w h e t h e r there was a d o s e - d e p e n d e n t relationship between cocaine and the release of P R L and A C T H . A C T H stimulates the secretion of corticosterone from the adrenal gland which in turn inhibits the further release of A C T H both by limiting the release of corticotropin releasing h o r m o n e centrally as well as directly at the adenohypophysis 19. With this in mind, we also examined whether r e p e a t e d , frequent infusions of cocaine would persistently alter the h y p o t h a l a m o - p i t u i t a r y adrenal axis by measuring A C T H and corticosterone before and after cocaine. MATERIALS AND METHODS
Subjects Male Lewis rats (225-250 g; Charles River, Wilmington, MA) were grouped 4 per cage. Food and water were available ad libitum. Lights were on between 06.00 and 18.00 h. All animals were catheterized 2 days (Expt. 1) or 7-10 days (Expt. 2) before use as described below and thereafter were housed individually. Experiment 1 Effects of acute cocaine administration on the release of PRL and ACTH. Two days before use, rats were anesthetized with Equithesin
Correspondence: N. Pilotte, Neuroendocrinology/Immunology Laboratory, Addiction Research Center, National Institute on Drug Abuse, Box 5180, Baltimore, MD 21224, U.S.A.
0006-8993/90/$03.50 © 1990 Elsevier Science Publishers B.V. (Biomedical Division)
108
(4.44 g chloral hydrate, 1 g pentobarbital sodium, 2.12 g magnesium sulfate, 44.4 ml propylene glycol, 12.0 ml ethanol, plus water q.s. to make 100 ml; 3 ml/kg i.p.) for implantation of a jugular catheter. The catheter consisted of 27 mm of Silastic (Dow Chemical Co., Midland, MI) tubing (0.51 mm i.d. × 0.94 mm o.d.) connected to 10 cm of single lumen vinyl tubing (Dural Plastics, New South Wales, Australia) by 23-gauge stainless steel tubing (1 cm). The Silastic end was inserted into the jugular vein to the level of the atrium and the other end was threaded subcutaneously over the shoulder and exteriorized at the back of the neck. The catheter was filled with 0.15 M NaCI (saline). Each rat was injected with penicillin (30,000 U i.m.) at the end of surgery. On the day of use, each rat was injected through the catheter with 50 U of heparin in saline. Blood (0.4 or 0.8 ml each) was withdrawn through the catheter, chilled briefly in an ice-water bath, and centrifuged for 1 rain at 10,000 g within l0 min of sampling. The plasma was measured and divided into aliquots for the determination of PRL and ACTH. The red cells were mixed with a volume of saline equal to the amount of plasma removed and returned to each rat via the catheter. Blood was removed and replaced in this manner 3 times at 15-min intervals prior to and 1, 10, 30, 45, and 60 min after the i.v. injection of cocaine (1, 3, or 10 mg/kg) or saline (Time 0). The larger volume (0.8 ml), required for measurement of ACTH, was withdrawn immediately before and 1, 10, and 45 min after the injection. Plasma reserved for measurement of A C T H was mixed with Trasylol and EDTA (to prevent degradation of the hormone) in ice-cold polypropylene tubes and was frozen immediately on dry ice. All other aliquots of plasma were frozen within 15 min after they were obtained and then stored at --70°C. They were assayed within 2 weeks of collection.
Experiment 2 Effects of repeated administrations of cocaine or saline on the release of PRL, A C T H and corticosterone. Ten to fourteen days before use, rats were catheterized, as described above, and a cannula connector pedestal (Plastic Products, Roanoke, VA) was affixed to the skull with four small screws (00-90) and dental acrylic. The catheter was filled with 50/~1 of gentamycin (0.075 mg/ml in saline) to prevent Pseudomonas-induced endocarditis 4 and was flushed daily with 100 ktl of this antibiotic solution, ensuring the patency of the catheter for up to 6 weeks. Cocaine (1 mg/kg, i.v.) or saline was administered repeatedly in the following manner. The rat was placed in a sound-attenuated environmental chamber lit by a 7-W light. Polyethylene tubing was threaded through a spring and attached to the animal's catheter by means a 23-gauge stainless steel tube. One end of the spring was attached to a swivel at the top of the chamber and the other end was screwed to the implanted pedestal to prevent any strain or pull on the tubing. Computer-controlled infusions of cocaine or saline were delivered to the rats via the catheter every 12 min for 2 h. The rationale for use of this paradigm was that this dosage schedule approximated the total dose and pattern of cocaine self-administration in rats given access to a close of 1 mg/kg/infusion at a rate of 100 td/kg in 5 s2°. Each animal thus received 10 injections of cocaine during the 2-h session. Sessions occurred between 07.00 and 12.00 h for 10 days. Blood (0.8 ml) was withdrawn from each rat and the red cells were mixed with saline and returned to each rat as described in Expt.1. Two aliquots of blood were withdrawn at 15-min intervals immediately before the session on days 1, 5 and 10 to establish presession hormone concentrations. Thus, pre-session samples taken on days 5 and 10 occurred 22 h after the last exposure to cocaine or saline. Immediately after sessions on days 1, 5 and 10, rats were removed from the chamber and given a final injection of cocaine (1 mg/kg) or saline and blood was withdrawn 1, 10, and 30 min later. Assays PRL was quantified by radioimmunoassay (RIA) with reagents obtained from the National Pituitary Hormone Distribution Pro-
A.
PROLACTIN
200
150
--I UJ > U.I .-I
100
50
.,-I i
|
03 B. tl O
600
ACTH
COCAINE,
~
/z
/T
Z uJ
\
[]
0
,
1
m g / k g
N = 6 - 8
•
r~ uJ O.
0
'
BL
0
|
15
|
|
!
30
45
60
MINUTES
Fig. 1. A: percent change from pre-injection concentrations of PRL (mean + S.E.M.) in conscious, catheterized male rats after the i.v. injection of saline (1.0 m l / k g ) o r cocaine (1, 3 or 10 mg/kg). Each point represents observations made on 6-8 rats. The dotted line represents the pre-injection (100%) levels. The mean (_+S.E,M.) pre-injection concentrations between groups were not different and were as follows (in ng/ml): saline, 10.3 + 1.4; cocaine, 1 mg/kg, 12.9 + 2.1; 3 mg/kg, 9.4 + 0.7; and 10 mg/kg, 12.6 _+ 1.4. B: percent change from pre-injection levels of A C T H (mean + S.E.M.) after the i.v. injection of saline or cocaine from the same rats depicted in A. The dotted line represents the pre-injection (100%) levels of ACTH. The mean ( + S.E.M.) pre-injection concentrations between groups were not different and were as follows (in pg/ml): saline, 29.6 _+ 2.8; cocaine, 1 mg/kg, 55.7 +_ 18.4; 3 mg/kg, 33.4 + 4.1; 10 mg/kg, 37.4 _+ 2.2.
gram of the NIDDK, and evaluated against the rPRL-RP-3 reference preparation. Plasma was assayed in duplicate at two dilutions and the limit of detection was 2 ng/ml. A C T H and corticosterone were quantified using double antibody RIA kits (Radioassay Systems Laboratories, Carson, CA). Plasma was assayed in duplicate with detection limits of 16 pg/ml for A C T H and 25 ng/ml for corticosterone. All plasmas from each experiment were evaluated in the same RIA.
Statistical analyses Two-way A N O V A and A N C O V A were used to analyse dose and time (repeated measures). All dose- and time-dependent effects were evaluated with linear regression analysis. Post hoc comparisons were made with the Duncan's multiple range statistic. Differences were considered significant at P < 0.05. Materials Cocaine hydrochloride was provided by the National Institute on Drug Abuse. Dosages reflect the concentration of free base. Trasylol and EDTA were purchased from Sigma (St. Louis, MO).
109
30
A.
SALINE
100---
A. SALINE
[~, [] DAY 1
80
[--1, [ ] DAY '
[], '~ DAY 5 20
~, •
[~], • DAY 5
DAYIO
60 40
_~
=-
30
~/,/]rrT~, •
o
DAY10 ~
~
I
,
m
,
,
,
I
E
¢: 0,. 2o
PRE-SESSION
0 0 PRE-SESSION
10 20 POST-SESSION
30 (MIN)
Fig. 2. Peripheral concentrations of PRL from conscious catheterized male rats before and after 11 i.v. infusions of saline (0.1 ml/kg; Panel A) or cocaine (1 mg/kg; Panel B) on each of days 1, 5 and 10 of passive administration. Column heights and symbols represent the mean; vertical lines denote the S.E.M. Numbers at the base of column denote the n. Two pre-session determinations were made 15 min and immediately before the i.v. infusions began. These values did not differ from each other and so were combined and are denoted by the bars at the left of the graph.
A C T H increased significantly ( P < 0.05) 1.6-fold within 1 min of saline (Fig. 1B). H o w e v e r , cocaine in doses of 1, 3, or 10 mg/kg increased A C T H an average of 2.3-, 4-
200 "A. SALINE 15o
RESULTS
POST-SESSION (MIN)
Fig. 3. Peripheral concentrations of ACTH from the rats depicted in Fig. 2. Refer to Fig. 2 for legend.
~"
100
I-1,[] oAY , D , $ oar s ~'
•
T _~ l
DAYIO
Experiment 1 Basal levels of P R L were low and similar in all groups before the i.v. administration of saline or cocaine. The m e a n ( + S . E . M . ) pre-injection concentrations between groups were as follows (in ng/ml): saline, 10.3 + 1.4; cocaine, 1 mg/kg, 12.9 + 2.1; 3 mg/kg, 9.4 + 0.7; and 10 mg/kg, 12.6 + 1.4. N e i t h e r cocaine nor saline inhibited the release of P R L throughout the 60 min sampling period. Cocaine was followed by a transient, nonsignificant increase of 2 4 - 4 7 % in P R L at 1 min which r e t u r n e d to basal levels by 10 min (Fig. 1A). No c o c a i n e - t r e a t e d group was significantly different from the saline controls or from each o t h e r at any sampling period. Basal levels of A C T H were not different between any groups prior to the i.v. infusion of saline or cocaine. The m e a n ( + S . E . M . ) pre-injection concentrations were as follows (in pg/ml): saline, 29.6 + 2.8; cocaine, 1 mg/kg, 55.7 + 18.4; 3 mg/kg, 33.4 + 4.1; 10 mg/kg, 37.4 + 2.2.
so
.
,
_.
o
.=
u
!
0
PRE-SESSION
20
30
POST-SESSION
10
(MIN)
Fig. 4. Peripheral concentrations of corticosterone from rats depicted in Fig. 2. Refer to Fig. 2 for legend.
110 or 6-fold respectively. An ANCOVA (with basal levels held constant) revealed significant effects between doses (P < 0.05) and across time (P < 0.01). Regression analysis showed a significant linear relationship between dose and the percentage of increase (r = 0.59, 1 min post-injection, P
107
Elsevier BRES 15296
Multiple, but not acute, infusions of cocaine alter the release of prolactin in male rats Nancy S. Pilotte, Lawrence G. Sharpe and Elizabeth M. Dax Addiction Research Center, National Institute on Drug Abuse, Baltimore, MD 21224 (U.S.A.)
(Accepted 15 August 1989) Key words: Cocaine; Prolactin; Adrenocorticotropic hormone; Corticosterone
Hypothalamic dopamine tonically inhibits the release of prolactin (PRL) from the anterior pituitary gland. Cocaine, in turn, alters dopaminergic transmission. We compared the effects of acute and repeated injections of cocaine on the release of PRL in male rats to assess whether cocaine could affect dopaminergically mediated hormonal responses. We found that the concentration of PRL in plasma was not affected by single i.v. injections of 1, 3 or 10 mg/kg of cocaine. However, in rats infused repeatedly with 1 mg/kg of cocaine for 5 s every 12 min for 2 h over 10 days, the pre-infusion concentrations of PRL increased in a time-dependent manner whereas cocaine uniformly decreased post-infusion levels of PRL. Repeated administration of cocaine may produce long-term changes in either the tuberoinfundibular dopaminergic neurons or the adenohypophysiai dopamine D2-receptors, or both. Changes in the peripheral concentration of PRL after multiple injections of cocaine and during cocaine withdrawal may reflect dopaminergic activity in the hypothalamus. In contrast, single injections of cocaine increased adrenocorticotropin (ACTH) in a dose-dependent manner whereas repeated infusions did not increase peripheral concentrations of ACTH or corticosterone. It seems that repeated injections of cocaine do not result in persistent changes in the hypothalamo-pituitary-adrenal axis. INTRODUCTION T h e secretion of prolactin ( P R L ) from the anterior pituitary gland is u n d e r the tonic inhibitory control of d o p a m i n e ( D A ) released from the terminals of the t u b e r o i n f u n d i b u l a r d o p a m i n e r g i c ( T I D A ) neurons 5. In turn, circulating levels of P R L are thought to activate these neurons, increasing the release of D A 7'23. A single injection of cocaine to rats rapidly but briefly increases the concentration of extracellular D A 9'1s whereas rep e a t e d injections lead to long-term decreases in dopa accumulation and in 3,4-dihydroxyphenylacetic acid ( D O P A C ) formation xl, and reduce immunoreactive tyrosine hydroxylase throughout the mesolimbic D A system 24. Thus, the neurochemical effects of a single injection of cocaine on D A differ from those that occur after r e p e a t e d administration. Clinically, others have r e p o r t e d mild h y p e r p r o l a c t i n e m i a in humans upon cessation from the chronic use of cocaine 1'17. These observations are consistent with suggestions that the levels of central D A m a y be decreased after cocaine usage 25. Because of the close relationship between P R L and D A , we c o m p a r e d the release of P R L before and after one or multiple i.v. injections of cocaine as a means of assessing cocaine's effects on hypothalamic D A activity.
P R L and a d r e n o c o r t i c o t r o p i n ( A C T H ) are often released concomitantly in response to noxious (or 'stressful') stimuli. Because the physiological events following the administration of cocaine m a y be considered stressful, we examined w h e t h e r there was a d o s e - d e p e n d e n t relationship between cocaine and the release of P R L and A C T H . A C T H stimulates the secretion of corticosterone from the adrenal gland which in turn inhibits the further release of A C T H both by limiting the release of corticotropin releasing h o r m o n e centrally as well as directly at the adenohypophysis 19. With this in mind, we also examined whether r e p e a t e d , frequent infusions of cocaine would persistently alter the h y p o t h a l a m o - p i t u i t a r y adrenal axis by measuring A C T H and corticosterone before and after cocaine. MATERIALS AND METHODS
Subjects Male Lewis rats (225-250 g; Charles River, Wilmington, MA) were grouped 4 per cage. Food and water were available ad libitum. Lights were on between 06.00 and 18.00 h. All animals were catheterized 2 days (Expt. 1) or 7-10 days (Expt. 2) before use as described below and thereafter were housed individually. Experiment 1 Effects of acute cocaine administration on the release of PRL and ACTH. Two days before use, rats were anesthetized with Equithesin
Correspondence: N. Pilotte, Neuroendocrinology/Immunology Laboratory, Addiction Research Center, National Institute on Drug Abuse, Box 5180, Baltimore, MD 21224, U.S.A.
0006-8993/90/$03.50 © 1990 Elsevier Science Publishers B.V. (Biomedical Division)
108
(4.44 g chloral hydrate, 1 g pentobarbital sodium, 2.12 g magnesium sulfate, 44.4 ml propylene glycol, 12.0 ml ethanol, plus water q.s. to make 100 ml; 3 ml/kg i.p.) for implantation of a jugular catheter. The catheter consisted of 27 mm of Silastic (Dow Chemical Co., Midland, MI) tubing (0.51 mm i.d. × 0.94 mm o.d.) connected to 10 cm of single lumen vinyl tubing (Dural Plastics, New South Wales, Australia) by 23-gauge stainless steel tubing (1 cm). The Silastic end was inserted into the jugular vein to the level of the atrium and the other end was threaded subcutaneously over the shoulder and exteriorized at the back of the neck. The catheter was filled with 0.15 M NaCI (saline). Each rat was injected with penicillin (30,000 U i.m.) at the end of surgery. On the day of use, each rat was injected through the catheter with 50 U of heparin in saline. Blood (0.4 or 0.8 ml each) was withdrawn through the catheter, chilled briefly in an ice-water bath, and centrifuged for 1 rain at 10,000 g within l0 min of sampling. The plasma was measured and divided into aliquots for the determination of PRL and ACTH. The red cells were mixed with a volume of saline equal to the amount of plasma removed and returned to each rat via the catheter. Blood was removed and replaced in this manner 3 times at 15-min intervals prior to and 1, 10, 30, 45, and 60 min after the i.v. injection of cocaine (1, 3, or 10 mg/kg) or saline (Time 0). The larger volume (0.8 ml), required for measurement of ACTH, was withdrawn immediately before and 1, 10, and 45 min after the injection. Plasma reserved for measurement of A C T H was mixed with Trasylol and EDTA (to prevent degradation of the hormone) in ice-cold polypropylene tubes and was frozen immediately on dry ice. All other aliquots of plasma were frozen within 15 min after they were obtained and then stored at --70°C. They were assayed within 2 weeks of collection.
Experiment 2 Effects of repeated administrations of cocaine or saline on the release of PRL, A C T H and corticosterone. Ten to fourteen days before use, rats were catheterized, as described above, and a cannula connector pedestal (Plastic Products, Roanoke, VA) was affixed to the skull with four small screws (00-90) and dental acrylic. The catheter was filled with 50/~1 of gentamycin (0.075 mg/ml in saline) to prevent Pseudomonas-induced endocarditis 4 and was flushed daily with 100 ktl of this antibiotic solution, ensuring the patency of the catheter for up to 6 weeks. Cocaine (1 mg/kg, i.v.) or saline was administered repeatedly in the following manner. The rat was placed in a sound-attenuated environmental chamber lit by a 7-W light. Polyethylene tubing was threaded through a spring and attached to the animal's catheter by means a 23-gauge stainless steel tube. One end of the spring was attached to a swivel at the top of the chamber and the other end was screwed to the implanted pedestal to prevent any strain or pull on the tubing. Computer-controlled infusions of cocaine or saline were delivered to the rats via the catheter every 12 min for 2 h. The rationale for use of this paradigm was that this dosage schedule approximated the total dose and pattern of cocaine self-administration in rats given access to a close of 1 mg/kg/infusion at a rate of 100 td/kg in 5 s2°. Each animal thus received 10 injections of cocaine during the 2-h session. Sessions occurred between 07.00 and 12.00 h for 10 days. Blood (0.8 ml) was withdrawn from each rat and the red cells were mixed with saline and returned to each rat as described in Expt.1. Two aliquots of blood were withdrawn at 15-min intervals immediately before the session on days 1, 5 and 10 to establish presession hormone concentrations. Thus, pre-session samples taken on days 5 and 10 occurred 22 h after the last exposure to cocaine or saline. Immediately after sessions on days 1, 5 and 10, rats were removed from the chamber and given a final injection of cocaine (1 mg/kg) or saline and blood was withdrawn 1, 10, and 30 min later. Assays PRL was quantified by radioimmunoassay (RIA) with reagents obtained from the National Pituitary Hormone Distribution Pro-
A.
PROLACTIN
200
150
--I UJ > U.I .-I
100
50
.,-I i
|
03 B. tl O
600
ACTH
COCAINE,
~
/z
/T
Z uJ
\
[]
0
,
1
m g / k g
N = 6 - 8
•
r~ uJ O.
0
'
BL
0
|
15
|
|
!
30
45
60
MINUTES
Fig. 1. A: percent change from pre-injection concentrations of PRL (mean + S.E.M.) in conscious, catheterized male rats after the i.v. injection of saline (1.0 m l / k g ) o r cocaine (1, 3 or 10 mg/kg). Each point represents observations made on 6-8 rats. The dotted line represents the pre-injection (100%) levels. The mean (_+S.E,M.) pre-injection concentrations between groups were not different and were as follows (in ng/ml): saline, 10.3 + 1.4; cocaine, 1 mg/kg, 12.9 + 2.1; 3 mg/kg, 9.4 + 0.7; and 10 mg/kg, 12.6 _+ 1.4. B: percent change from pre-injection levels of A C T H (mean + S.E.M.) after the i.v. injection of saline or cocaine from the same rats depicted in A. The dotted line represents the pre-injection (100%) levels of ACTH. The mean ( + S.E.M.) pre-injection concentrations between groups were not different and were as follows (in pg/ml): saline, 29.6 _+ 2.8; cocaine, 1 mg/kg, 55.7 +_ 18.4; 3 mg/kg, 33.4 + 4.1; 10 mg/kg, 37.4 _+ 2.2.
gram of the NIDDK, and evaluated against the rPRL-RP-3 reference preparation. Plasma was assayed in duplicate at two dilutions and the limit of detection was 2 ng/ml. A C T H and corticosterone were quantified using double antibody RIA kits (Radioassay Systems Laboratories, Carson, CA). Plasma was assayed in duplicate with detection limits of 16 pg/ml for A C T H and 25 ng/ml for corticosterone. All plasmas from each experiment were evaluated in the same RIA.
Statistical analyses Two-way A N O V A and A N C O V A were used to analyse dose and time (repeated measures). All dose- and time-dependent effects were evaluated with linear regression analysis. Post hoc comparisons were made with the Duncan's multiple range statistic. Differences were considered significant at P < 0.05. Materials Cocaine hydrochloride was provided by the National Institute on Drug Abuse. Dosages reflect the concentration of free base. Trasylol and EDTA were purchased from Sigma (St. Louis, MO).
109
30
A.
SALINE
100---
A. SALINE
[~, [] DAY 1
80
[--1, [ ] DAY '
[], '~ DAY 5 20
~, •
[~], • DAY 5
DAYIO
60 40
_~
=-
30
~/,/]rrT~, •
o
DAY10 ~
~
I
,
m
,
,
,
I
E
¢: 0,. 2o
PRE-SESSION
0 0 PRE-SESSION
10 20 POST-SESSION
30 (MIN)
Fig. 2. Peripheral concentrations of PRL from conscious catheterized male rats before and after 11 i.v. infusions of saline (0.1 ml/kg; Panel A) or cocaine (1 mg/kg; Panel B) on each of days 1, 5 and 10 of passive administration. Column heights and symbols represent the mean; vertical lines denote the S.E.M. Numbers at the base of column denote the n. Two pre-session determinations were made 15 min and immediately before the i.v. infusions began. These values did not differ from each other and so were combined and are denoted by the bars at the left of the graph.
A C T H increased significantly ( P < 0.05) 1.6-fold within 1 min of saline (Fig. 1B). H o w e v e r , cocaine in doses of 1, 3, or 10 mg/kg increased A C T H an average of 2.3-, 4-
200 "A. SALINE 15o
RESULTS
POST-SESSION (MIN)
Fig. 3. Peripheral concentrations of ACTH from the rats depicted in Fig. 2. Refer to Fig. 2 for legend.
~"
100
I-1,[] oAY , D , $ oar s ~'
•
T _~ l
DAYIO
Experiment 1 Basal levels of P R L were low and similar in all groups before the i.v. administration of saline or cocaine. The m e a n ( + S . E . M . ) pre-injection concentrations between groups were as follows (in ng/ml): saline, 10.3 + 1.4; cocaine, 1 mg/kg, 12.9 + 2.1; 3 mg/kg, 9.4 + 0.7; and 10 mg/kg, 12.6 + 1.4. N e i t h e r cocaine nor saline inhibited the release of P R L throughout the 60 min sampling period. Cocaine was followed by a transient, nonsignificant increase of 2 4 - 4 7 % in P R L at 1 min which r e t u r n e d to basal levels by 10 min (Fig. 1A). No c o c a i n e - t r e a t e d group was significantly different from the saline controls or from each o t h e r at any sampling period. Basal levels of A C T H were not different between any groups prior to the i.v. infusion of saline or cocaine. The m e a n ( + S . E . M . ) pre-injection concentrations were as follows (in pg/ml): saline, 29.6 + 2.8; cocaine, 1 mg/kg, 55.7 + 18.4; 3 mg/kg, 33.4 + 4.1; 10 mg/kg, 37.4 + 2.2.
so
.
,
_.
o
.=
u
!
0
PRE-SESSION
20
30
POST-SESSION
10
(MIN)
Fig. 4. Peripheral concentrations of corticosterone from rats depicted in Fig. 2. Refer to Fig. 2 for legend.
110 or 6-fold respectively. An ANCOVA (with basal levels held constant) revealed significant effects between doses (P < 0.05) and across time (P < 0.01). Regression analysis showed a significant linear relationship between dose and the percentage of increase (r = 0.59, 1 min post-injection, P
