- Email: [email protected]
Behavioral cross-sensitization between cocaine and enkephalin in the A10 dopamine region
87
Behavioural Brain Research, 27 (1988) 87-91 Elsevier BBR 00744
Short Communication
Behavioral cross-sensitization between cocaine and enkephalin in the A 10 dopamine region Lee Ann DuMars,
L y n n D. R o d g e r a n d P e t e r W . K a l i v a s
Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology, Washington State University, Pullman, WA 99164 (U.S.A.) (Received 31 December 1986) (Revised version received 28 July 1987) (Accepted 8 August 1987)
Key words: Cocaine; Opioid; Enkephalin; Dopamine; Motor activity; Sensitization
The motor stimulant effect produced by cocaine and the injection of opioids onto A10 dopamine neurons is thought to be mediated by an increase in dopaminergic transmission in mesolimbic dopamine terminal fields such as the nucleus accumbens. Following daily administration, the behavioral stimulant effect of both cocaine and intra-A 10 injection of opioids is augmented. The data in this report demonstrate that rats receiving daily injection of enkephalin analogue into the A10 have an enhanced motor stimulant response to intraperitoneal cocaine, but not to saline. Conversely, rats receiving daily injection ofintraperitoneal cocaine have an enhanced motor stimulant response to intra-Al0 injection of enkephalin analogue.
Cocaine has a behavioral stimulant effect in mammals, that is, at least partially, dependent on dopamine (DA) transmission in the central nervous system 2'~1. The increase in locomotor and rearing behaviors produced by low doses of cocaine in rats is thought to be dependent on an increase in DA transmission in the nucleus accumbens 9, which results primarily from a blockade of DA re-uptake into presynaptic terminals 13. The motor stimulant effect of cocaine is known to become greater after daily administration 3'11"~2. Considering the importance of central DA systems in the behavioral stimulant action of acute cocaine administration, it has been proposed that the augmented response to daily cocaine injection may involve altered DA transmission ~z In support of this possibility, daily
cocaine administration decreases striatal levels of D A 2'14, and pretreatment with a DA receptor antagonist prevents the development of behavioral sensitization to daily cocaine injection ~. However, in another study, pretreatment with haloperidol was ineffective4. While a role for DA in the behavioral sensitization to daily cocaine remains largely Untested, it is known that injection of opioids into the A10 DA region produces a DA-dependent increase in motor activity 5,7,s,15 and that this motor stimulant effect is augmented after daily injections 5,7,~5. Furthermore, the enhanced behavioral response after daily intra-A10 administration of opioids is associated with an augmented increase in DA metabolism in the nucleus accumbens 6. Thus, it has been postulated that a hyper-responsiveness
Correspondence: P. Kalivas, Department of VCAPP, Washington State University, Pullman, WA 99164-6520, U.S.A. 0166-4328/88/$03.50 (~ 1988 Elsevier Science Publishers B.V. (Biomedical Division)
88 of the mesolimbic DA neurons projecting from the A10 region to the nucleus accumbens plays a critical role in the augmented behavioral response produced by daily intra-A 10 injection of opioids 6. Since a role by mesolimbic DA neurons in behavioral sensitization to intra-A10 opioids has been well documented, we sought to determine whether rats sensitized by the daily intra-A10 injection of opioids demonstrate an enhanced behavioral stimulant response to cocaine. Conversely, we also evaluated the possibility that rats sensitized to daily peripheral injections of cocaine have an enhanced motor stimulant response to the intra-A10 injection of opioids. If crosssensitization between opioids and cocaine could be shown, it would argue that a common neuroanatomical and/or neurochemical substrate(s) exists for sensitization to opioids and cocaine, and that a likely candidate is the mesolimbic DA system. Male Sprague-Dawley rats (Laboratory Animal Research Center, Pullman, WA) were individually housed under a 12/12 h light/dark cycle with food and water made available ad libitum. When rats attained a body weight of 250-350 g, they were stereotaxically implanted with injection cannulae (26-gauge stainless steel), 1 mm over the A10 region (2.6 mm A/P, 0.6 mm M/L, 2.5 mm D/V, relative to the interaural line) ~°. The cannulae were secured with stainless steel screws and dental acrylic, and one week recovery was allowed before drug injection. After completion of the behavioral studies, placement of the cannulae tips was determined in Cresyl violet-stained coronal sections (100 #m) obtained from the rat brain 7. A total of 48 rats were used in this study, and 37 were determined to have both cannulae placed in the A 10 DA region, including the ventral tegmental area, nucleus interfascicularis, or nucleus linearis v. Drugs given included cocaine (15 mg/kg, i.p.), the enkephalin analogue Tyr-D-Ala-Gly-NMePhe-Gly-ol (DAGO; 0.03 nmol/A10; 0.5 #l/side) and saline (1.0ml/kg, i.p., or 0.5 #l/side). The photocell cages were built by Omnitech, Inc., and have been described in detail elsewhere7. Eight photocell cages were located in individual wooden boxes with individual lighting and air
supply and were monitored simultaneously by an Apple lie computer. Visual observations of the rats were made through a one-way glass door. The rats were always adapted to the photocell apparatus for 60 min prior to drug injection, and behavior was monitored for 90 or 120 min after injection. Simultaneous bilateral microinjections (0.5#1/60 s) into the A10 region were made through a 33-gauge injection needle that was connected via PE-10 tubing with two I-FLI syringes mounted in an infusion pump. Two experiments were performed. To test if rats sensitized to D A G O demonstrate an enhanced behavioral stimulant response to cocaine, rats were injected in the photocell apparatus with saline, i.p., on day 1. On days 2-6, rats were injected with either saline or D A G O in the home cage. Two weeks later, rats were injected in the photocell apparatus with saline, i.p., followed the next day with cocaine, i.p. To test if rats sensitized to cocaine demonstrate an enhanced behavioral response to DAGO, rats were injected with saline, intra-A10, in the photocell cage on day one, and with D A G O in the photocell cage on day two. Cocaine or saline, i.p., was injected on days 3-5 in the home cage. Forty-eight h later, the rats were injected in the photocell cage with saline, intraA10, followed the next day with an injection of DAGO, intra-A 10. The daily treatment regimens of cocaine and D A G O have been shown to produce an augmented behavioral response to cocaine and DAGO, respectively, in preliminary studies in this laboratory and elsewhere r'~ In addition to photocell counts, human observations were recorded. The intensity of the rats' response to cocaine was rated by an observer ignorant of the pretreatment (i.e. daily saline or DAGO). The rats were rated for 10 s every 5 rain, beginning 5 min prior to injection, up to 40 min after injection, and once every 10 min from 40 to 90 min after injection. The scale ranged from 1 to 10 as follows: (1)asleep or still, (2)inactive, grooming, mild licking, (3) locomotion, rearing, or sniffing occurs, (4)any combination of two locomotion, rearing, or sniffing, (5)continuous sniffing without locomotion or rearing, (6)continuous sniffing with rearing or locomotion, (7) patterned continuous sniffing for 5 s, (8) pat-
89
30000
1500 Horizontal Movements
Horizontal Activity
,f
1000
20000
E
/ / / / / / / / /
500
10000
T
O~ o
Saline
I DAGO
0
200 ~ I 0 Saline DAGO
I ----/ / /
O
o0 t-
400
I/// ///
c-
Stereotypy
600
/ / / / /
Saline
/ / / / /
x
/ / / / /
DAGO
O
O
Vertical
Vertical Activity
d~ 0 0
Movements
c0
D.
200
I
50
0
0 Saline
DAGO
Saline
DAGO
Daily Treatment Fig. l. Effect o f daily D A G O administration on the acute motor response to cocaine. Rats were injected with saline, i.p., on day l (first open bar), and then injected daily for 5 days with either saline (0.5/d/A10; n = 9) or D A G O (0.03 nmol/A10; n = 9). Two weeks later the rats were reinjected with saline, i.p. (second open bar). The data are shown as m e a n + S.E.M. photocell counts. * P < 0.05, comparing cocaine treatment to the second saline treatment within each daily treatment group, using a repeatedmeasures analysis o f variance followed by a N e w m a n - K e u l s test. No significant difference was observed between the first and second saline treatments. + P < 0.05, comparing cocaine treatments between each daily treatment group, using a one-way analysis o f variance followed a N e w m a n - K e u l s test.
terned continuous sniffing for 10 s, (9) continuous gnawing, and (10)bizarre diskinetic movements or seizures. Fig. 1 shows the effect of daily D A G O on the motor stimulant effect of acute cocaine injection. Compared with rats pretreated with daily saline, rats pretreated with daily D A G O demonstrated an increase in cocaine-induced horizontal activity. Total horizontal photocell counts, as well as number of horizontal movements and stereotypy, were increased. In contrast, no significant change was observed in rearing behavior produced by cocaine. Rats pretreated with D A G O also demonstrated an increase in the behavioral score obtained by an observer compared with scores from saline-pretreated rats (Fig. 2). In
6 (D 4 .0
3
nn
I 0
0~" ii'
ODsily DAGO
20
10
I'0 ' 2'0 3'0
40
50
~3
o
6'0
Time (min.) Fig. 2. Behavioral rating o f cocaine-induced motor behavior in rats pretreated with daily D A G O or saline. These data were obtained simultaneously with the acute cocaine treatment data shown in Fig. 1. Rats were pretreated with daily D A G O ( e , closed bar; 0.03 nmol/A10) or saline ( o , open bar) for 5 days. Time = 0 refers to the observations made 5 min prior to injection o f cocaine. See legend to Fig, 1 for more detail. * P < 0.05, using a one-way analysis o f variance.
90 3000
HorizontalActivity
2000 1000
1500
HorizontalMovements
1000 //,
.C 500 E
O 04 o 09 O 600
¢D •
Stereotypy
///
400
0 0
nt'-
',2,
z//
200
VerticalActivity
OL
100 ~ f 5[ ~ 0Vertical [- Movements~
o 1 2 78 Daily Saline
1 2 78 Daily Cocaine
Fig. 3. Effect of daily cocaine on the motor stimulant response to intra-A 10 injection of D A G O . Rats were injected intra-A10 with saline on days 1 and 7 (open bars), and with D A G O (0.03 nmol/A10) on days 2 and 8 (striped bars). On
DAGO-pretreated rats, the behavioral score was elevated between 25 and 35 min after injection of cocaine. No difference in the response to saline, i.p., given the day before cocaine administration was observed between daily saline- and daily DAGO-pretreated rats in any of the automated or observational measures (Fig. 1). Fig. 3 shows the effect of daily cocaine on the motor stimulant effect of DAGO. Rats treated with daily cocaine demonstrated an increase in horizontal and vertical photocell counts in response to D A G O on day 7 compared with the effect of D A G O on day 2. In contrast, the behavioral effect of D A G O on day 7 was not different from the effect of D A G O on day 2 in rats treated with saline, i.p., on days 3-5. When the response to D A G O on day 7 was compared between the daily saline- and daily cocainepretreated rats, only the stereotypy score was significantly elevated by daily cocaine. No difference was observed between daily saline- and daily cocaine-pretreated rats in response to acute saline, intra-A10, given on day 2 or 7 (Fig. 3). These data show that behavioral cross-sensitization can be demonstrated between cocaine and injection of an enkephalin analogue into the A 10 DA region. It has been known for many years that the behavioral stimulant effect of cocaine is enhanced following multiple daily injections TM, and a number of laboratories have recently demonstrated that the motor stimulant effect of intraAI0 injection of opioids is augmented after daily injections 5,7,1~. The fact that cross-sensitization occurs between cocaine and intra-A10 opioids argues for an overlap in the neurochemical and/or neuroanatomical substrate(s) mediating sensitization. It is known that the acute motor stimulant days 3-5, the rats received a daily injection of either saline, i.p. (n = 10), or cocaine (15 mg/kg, i.p.; n = 9). Data are shown as mean + S.E.M. photocell counts. * P < 0.05, comparing the effect of D A G O to the preceding injection of saline within each daily treatment group, using a repeated measures analysis of variance followed by a Newman-Keuls test. + P < 0.05, comparing the effect of D A G O on day 7 with D A G O on day 2 within each pretreatment group, using a repeated-measures analysis of variance followed by a N e w m a n - K e u l s test. '~ P < 0.05, comparing D A G O on day 7 between daily pretreatment groups, using a one-way analysis of variance followed by a N e w m a n - K e u l s test.
91
effect of cocaine is mediated, at least partially, by enhanced DA transmission in the nucleus accumbens 9, and it is suspected that alterations in DA transmission may mediate the sensitized behavioral response to cocaine 11. The acute motor stimulant effect of intra-A10 injection of opioids is associated with an increase in DA transmission in the nucleus accumbens, and the augmentation of this effect by dally injection is associated with an augmentation of DA transmission in the nucleus accumbens 6. Taken together, these data argue that the common neuroanatomical and neurochemical substrate mediating behavioral cross-sensitization may be the mesolimbic DA projection from the A10 region to the nucleus accumbens. However, this possibility remains to be evaluated experimentally. The conditioning of behavioral sensitization to dally injections of both cocaine and intra-A10 opioids has been demonstrated I ~,~5. While a role of conditioning to environmental cues cannot be entirely eliminated in the present study, a number of factors argue for minimal involvement. (1) The rats received the behavioral stimulants in the home cage prior to the test day in the photocell cage, eliminating the photocell cage as a conditioning cue. (2)The response to saline in the photocell cage was not significantly altered by dally treatment with a motor stimulant. (3) D A G O injection was made via microinjection into the brain, and cocaine was given i.p. These procedures were sufficiently different to minimize the injection procedure as a conditioning variable. In summary, behavioral cross-sensitization was demonstrated between peripheral cocaine administration and intra-A10 injection of enkephalin analogue. Increased mesolimbic DA transmission by these drugs argues that this may be the mechanism by which cross-sensitization is produced, and direct testing of this possibility will be the subject of future studies. This research was supported in part by U.S. Public Health Service Grants DA-03906 and MH-40817.
1 Beninger, R.J. and Herz, R.S., Pimozide blocks establishment but not expression of cocaine-produced environment-specific conditioning, Life Sci., 38 (1986) 1425-1431. 2 Dackis, C.A. and Gold, M.S., New concepts in cocaine addiction: the dopamine depletion hypothesis, Neurosci. Biobehav. Rev., 9 (1985) 469-477. 3 Downs, A.W. and Eddy, N.B., The effect of repeated doses of cocaine on the rat, J. Pharmacol. Exp. Ther., 46 (1932) 199-202. 4 Gale, K., Catecholamine-independent behavioral and neurochemical effects of cocaine in rats, NIDA Research Monogr., 54 (1984) 323-332. 5 Joyce, E.M. and Iversen, S.D., The effect of morphine applied locally to mesencephalic dopamine cell bodies on spontaneous motor activity in the rat, Neurosci. Lett., 14 (1979) 207-212. 6 Kalivas, P.W., Sensitization to repeated enkephalin administration into the ventral tegmental area of the rat. II. Involvement of the mesolimbic dopamine system, J. Pharmacol. Exp. Ther., 235 (1985) 544-550. 7 Kalivas, P.W., Taylor, S. and Miller, J.S., Sensitization of repeated enkephalin administration into the ventral tegmental area of the rat. I. Behavioral characterization, J. Pharmacol. Exp. Ther., 235 (1985) 537-543. 8 Kelley, A.E., Stinus, L. and Iversen, S.D., Interaction between D-Ala-Met-enkephalin, AI0 dopaminergic neurons, and spontaneous behavior in the rat, Behav. Brain Res., 1 (1980) 3-24. 9 Kelley, P.H. and Iversen, S.D., Selective 6-OHDAinduced destruction of mesolimbic dopamine neurons: abolition of psychostimulant-induced locomotor activity in rats, Eur. J. Pharmacol., 40 (1975) 45-56. 10 Pellegrino, L.K., Pellegrino, A.S. and Cushman, A.J., A Sterotaxic Atlas of the Rat Brain, Plenum, New York, 1979. 11 Post, R.M. and Contel, N.R., Human and animal studies of cocaine: implications for development of behavioral pathology. In I. Cresse (Ed.), Stimulants: Neurochemical, Behavioral and Clinical Perspectives, Raven, New York, 1983, pp. 169-203. 12 Post, R.M., Lockfeld, A., Squillace, K.H. and Cantel, N.R., Drug-environment interaction: context dependency of cocaine-induced behavioral sensitization, Life Sci., 28 (1981) 755-760. 13 Reith, M.E.A., Meisler, B.E., Sershen, H. and Lastha, A., Structural requirements for cocaine congeners to interact with dopamine and serotonin uptake sites in mouse brain and to induce sterotyped behavior, Biochem. Pharmacol., 35 (1986) 1123-1129. 14 Taylor, D. and Ho, B.T., Neurochemical effects of cocaine following acute and repeated injection, J. Neurosci. Res., 3 (1977) 95-101. 15 Vezina, P. and Stewart, J., Conditioning and placespecific sensitization of increases in activity induced by morphine in the VTA, Pharmacol. Biochem. Behav., 20 (1984) 925-934.
Behavioural Brain Research, 27 (1988) 87-91 Elsevier BBR 00744
Short Communication
Behavioral cross-sensitization between cocaine and enkephalin in the A 10 dopamine region Lee Ann DuMars,
L y n n D. R o d g e r a n d P e t e r W . K a l i v a s
Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology, Washington State University, Pullman, WA 99164 (U.S.A.) (Received 31 December 1986) (Revised version received 28 July 1987) (Accepted 8 August 1987)
Key words: Cocaine; Opioid; Enkephalin; Dopamine; Motor activity; Sensitization
The motor stimulant effect produced by cocaine and the injection of opioids onto A10 dopamine neurons is thought to be mediated by an increase in dopaminergic transmission in mesolimbic dopamine terminal fields such as the nucleus accumbens. Following daily administration, the behavioral stimulant effect of both cocaine and intra-A 10 injection of opioids is augmented. The data in this report demonstrate that rats receiving daily injection of enkephalin analogue into the A10 have an enhanced motor stimulant response to intraperitoneal cocaine, but not to saline. Conversely, rats receiving daily injection ofintraperitoneal cocaine have an enhanced motor stimulant response to intra-Al0 injection of enkephalin analogue.
Cocaine has a behavioral stimulant effect in mammals, that is, at least partially, dependent on dopamine (DA) transmission in the central nervous system 2'~1. The increase in locomotor and rearing behaviors produced by low doses of cocaine in rats is thought to be dependent on an increase in DA transmission in the nucleus accumbens 9, which results primarily from a blockade of DA re-uptake into presynaptic terminals 13. The motor stimulant effect of cocaine is known to become greater after daily administration 3'11"~2. Considering the importance of central DA systems in the behavioral stimulant action of acute cocaine administration, it has been proposed that the augmented response to daily cocaine injection may involve altered DA transmission ~z In support of this possibility, daily
cocaine administration decreases striatal levels of D A 2'14, and pretreatment with a DA receptor antagonist prevents the development of behavioral sensitization to daily cocaine injection ~. However, in another study, pretreatment with haloperidol was ineffective4. While a role for DA in the behavioral sensitization to daily cocaine remains largely Untested, it is known that injection of opioids into the A10 DA region produces a DA-dependent increase in motor activity 5,7,s,15 and that this motor stimulant effect is augmented after daily injections 5,7,~5. Furthermore, the enhanced behavioral response after daily intra-A10 administration of opioids is associated with an augmented increase in DA metabolism in the nucleus accumbens 6. Thus, it has been postulated that a hyper-responsiveness
Correspondence: P. Kalivas, Department of VCAPP, Washington State University, Pullman, WA 99164-6520, U.S.A. 0166-4328/88/$03.50 (~ 1988 Elsevier Science Publishers B.V. (Biomedical Division)
88 of the mesolimbic DA neurons projecting from the A10 region to the nucleus accumbens plays a critical role in the augmented behavioral response produced by daily intra-A 10 injection of opioids 6. Since a role by mesolimbic DA neurons in behavioral sensitization to intra-A10 opioids has been well documented, we sought to determine whether rats sensitized by the daily intra-A10 injection of opioids demonstrate an enhanced behavioral stimulant response to cocaine. Conversely, we also evaluated the possibility that rats sensitized to daily peripheral injections of cocaine have an enhanced motor stimulant response to the intra-A10 injection of opioids. If crosssensitization between opioids and cocaine could be shown, it would argue that a common neuroanatomical and/or neurochemical substrate(s) exists for sensitization to opioids and cocaine, and that a likely candidate is the mesolimbic DA system. Male Sprague-Dawley rats (Laboratory Animal Research Center, Pullman, WA) were individually housed under a 12/12 h light/dark cycle with food and water made available ad libitum. When rats attained a body weight of 250-350 g, they were stereotaxically implanted with injection cannulae (26-gauge stainless steel), 1 mm over the A10 region (2.6 mm A/P, 0.6 mm M/L, 2.5 mm D/V, relative to the interaural line) ~°. The cannulae were secured with stainless steel screws and dental acrylic, and one week recovery was allowed before drug injection. After completion of the behavioral studies, placement of the cannulae tips was determined in Cresyl violet-stained coronal sections (100 #m) obtained from the rat brain 7. A total of 48 rats were used in this study, and 37 were determined to have both cannulae placed in the A 10 DA region, including the ventral tegmental area, nucleus interfascicularis, or nucleus linearis v. Drugs given included cocaine (15 mg/kg, i.p.), the enkephalin analogue Tyr-D-Ala-Gly-NMePhe-Gly-ol (DAGO; 0.03 nmol/A10; 0.5 #l/side) and saline (1.0ml/kg, i.p., or 0.5 #l/side). The photocell cages were built by Omnitech, Inc., and have been described in detail elsewhere7. Eight photocell cages were located in individual wooden boxes with individual lighting and air
supply and were monitored simultaneously by an Apple lie computer. Visual observations of the rats were made through a one-way glass door. The rats were always adapted to the photocell apparatus for 60 min prior to drug injection, and behavior was monitored for 90 or 120 min after injection. Simultaneous bilateral microinjections (0.5#1/60 s) into the A10 region were made through a 33-gauge injection needle that was connected via PE-10 tubing with two I-FLI syringes mounted in an infusion pump. Two experiments were performed. To test if rats sensitized to D A G O demonstrate an enhanced behavioral stimulant response to cocaine, rats were injected in the photocell apparatus with saline, i.p., on day 1. On days 2-6, rats were injected with either saline or D A G O in the home cage. Two weeks later, rats were injected in the photocell apparatus with saline, i.p., followed the next day with cocaine, i.p. To test if rats sensitized to cocaine demonstrate an enhanced behavioral response to DAGO, rats were injected with saline, intra-A10, in the photocell cage on day one, and with D A G O in the photocell cage on day two. Cocaine or saline, i.p., was injected on days 3-5 in the home cage. Forty-eight h later, the rats were injected in the photocell cage with saline, intraA10, followed the next day with an injection of DAGO, intra-A 10. The daily treatment regimens of cocaine and D A G O have been shown to produce an augmented behavioral response to cocaine and DAGO, respectively, in preliminary studies in this laboratory and elsewhere r'~ In addition to photocell counts, human observations were recorded. The intensity of the rats' response to cocaine was rated by an observer ignorant of the pretreatment (i.e. daily saline or DAGO). The rats were rated for 10 s every 5 rain, beginning 5 min prior to injection, up to 40 min after injection, and once every 10 min from 40 to 90 min after injection. The scale ranged from 1 to 10 as follows: (1)asleep or still, (2)inactive, grooming, mild licking, (3) locomotion, rearing, or sniffing occurs, (4)any combination of two locomotion, rearing, or sniffing, (5)continuous sniffing without locomotion or rearing, (6)continuous sniffing with rearing or locomotion, (7) patterned continuous sniffing for 5 s, (8) pat-
89
30000
1500 Horizontal Movements
Horizontal Activity
,f
1000
20000
E
/ / / / / / / / /
500
10000
T
O~ o
Saline
I DAGO
0
200 ~ I 0 Saline DAGO
I ----/ / /
O
o0 t-
400
I/// ///
c-
Stereotypy
600
/ / / / /
Saline
/ / / / /
x
/ / / / /
DAGO
O
O
Vertical
Vertical Activity
d~ 0 0
Movements
c0
D.
200
I
50
0
0 Saline
DAGO
Saline
DAGO
Daily Treatment Fig. l. Effect o f daily D A G O administration on the acute motor response to cocaine. Rats were injected with saline, i.p., on day l (first open bar), and then injected daily for 5 days with either saline (0.5/d/A10; n = 9) or D A G O (0.03 nmol/A10; n = 9). Two weeks later the rats were reinjected with saline, i.p. (second open bar). The data are shown as m e a n + S.E.M. photocell counts. * P < 0.05, comparing cocaine treatment to the second saline treatment within each daily treatment group, using a repeatedmeasures analysis o f variance followed by a N e w m a n - K e u l s test. No significant difference was observed between the first and second saline treatments. + P < 0.05, comparing cocaine treatments between each daily treatment group, using a one-way analysis o f variance followed a N e w m a n - K e u l s test.
terned continuous sniffing for 10 s, (9) continuous gnawing, and (10)bizarre diskinetic movements or seizures. Fig. 1 shows the effect of daily D A G O on the motor stimulant effect of acute cocaine injection. Compared with rats pretreated with daily saline, rats pretreated with daily D A G O demonstrated an increase in cocaine-induced horizontal activity. Total horizontal photocell counts, as well as number of horizontal movements and stereotypy, were increased. In contrast, no significant change was observed in rearing behavior produced by cocaine. Rats pretreated with D A G O also demonstrated an increase in the behavioral score obtained by an observer compared with scores from saline-pretreated rats (Fig. 2). In
6 (D 4 .0
3
nn
I 0
0~" ii'
ODsily DAGO
20
10
I'0 ' 2'0 3'0
40
50
~3
o
6'0
Time (min.) Fig. 2. Behavioral rating o f cocaine-induced motor behavior in rats pretreated with daily D A G O or saline. These data were obtained simultaneously with the acute cocaine treatment data shown in Fig. 1. Rats were pretreated with daily D A G O ( e , closed bar; 0.03 nmol/A10) or saline ( o , open bar) for 5 days. Time = 0 refers to the observations made 5 min prior to injection o f cocaine. See legend to Fig, 1 for more detail. * P < 0.05, using a one-way analysis o f variance.
90 3000
HorizontalActivity
2000 1000
1500
HorizontalMovements
1000 //,
.C 500 E
O 04 o 09 O 600
¢D •
Stereotypy
///
400
0 0
nt'-
',2,
z//
200
VerticalActivity
OL
100 ~ f 5[ ~ 0Vertical [- Movements~
o 1 2 78 Daily Saline
1 2 78 Daily Cocaine
Fig. 3. Effect of daily cocaine on the motor stimulant response to intra-A 10 injection of D A G O . Rats were injected intra-A10 with saline on days 1 and 7 (open bars), and with D A G O (0.03 nmol/A10) on days 2 and 8 (striped bars). On
DAGO-pretreated rats, the behavioral score was elevated between 25 and 35 min after injection of cocaine. No difference in the response to saline, i.p., given the day before cocaine administration was observed between daily saline- and daily DAGO-pretreated rats in any of the automated or observational measures (Fig. 1). Fig. 3 shows the effect of daily cocaine on the motor stimulant effect of DAGO. Rats treated with daily cocaine demonstrated an increase in horizontal and vertical photocell counts in response to D A G O on day 7 compared with the effect of D A G O on day 2. In contrast, the behavioral effect of D A G O on day 7 was not different from the effect of D A G O on day 2 in rats treated with saline, i.p., on days 3-5. When the response to D A G O on day 7 was compared between the daily saline- and daily cocainepretreated rats, only the stereotypy score was significantly elevated by daily cocaine. No difference was observed between daily saline- and daily cocaine-pretreated rats in response to acute saline, intra-A10, given on day 2 or 7 (Fig. 3). These data show that behavioral cross-sensitization can be demonstrated between cocaine and injection of an enkephalin analogue into the A 10 DA region. It has been known for many years that the behavioral stimulant effect of cocaine is enhanced following multiple daily injections TM, and a number of laboratories have recently demonstrated that the motor stimulant effect of intraAI0 injection of opioids is augmented after daily injections 5,7,1~. The fact that cross-sensitization occurs between cocaine and intra-A10 opioids argues for an overlap in the neurochemical and/or neuroanatomical substrate(s) mediating sensitization. It is known that the acute motor stimulant days 3-5, the rats received a daily injection of either saline, i.p. (n = 10), or cocaine (15 mg/kg, i.p.; n = 9). Data are shown as mean + S.E.M. photocell counts. * P < 0.05, comparing the effect of D A G O to the preceding injection of saline within each daily treatment group, using a repeated measures analysis of variance followed by a Newman-Keuls test. + P < 0.05, comparing the effect of D A G O on day 7 with D A G O on day 2 within each pretreatment group, using a repeated-measures analysis of variance followed by a N e w m a n - K e u l s test. '~ P < 0.05, comparing D A G O on day 7 between daily pretreatment groups, using a one-way analysis of variance followed by a N e w m a n - K e u l s test.
91
effect of cocaine is mediated, at least partially, by enhanced DA transmission in the nucleus accumbens 9, and it is suspected that alterations in DA transmission may mediate the sensitized behavioral response to cocaine 11. The acute motor stimulant effect of intra-A10 injection of opioids is associated with an increase in DA transmission in the nucleus accumbens, and the augmentation of this effect by dally injection is associated with an augmentation of DA transmission in the nucleus accumbens 6. Taken together, these data argue that the common neuroanatomical and neurochemical substrate mediating behavioral cross-sensitization may be the mesolimbic DA projection from the A10 region to the nucleus accumbens. However, this possibility remains to be evaluated experimentally. The conditioning of behavioral sensitization to dally injections of both cocaine and intra-A10 opioids has been demonstrated I ~,~5. While a role of conditioning to environmental cues cannot be entirely eliminated in the present study, a number of factors argue for minimal involvement. (1) The rats received the behavioral stimulants in the home cage prior to the test day in the photocell cage, eliminating the photocell cage as a conditioning cue. (2)The response to saline in the photocell cage was not significantly altered by dally treatment with a motor stimulant. (3) D A G O injection was made via microinjection into the brain, and cocaine was given i.p. These procedures were sufficiently different to minimize the injection procedure as a conditioning variable. In summary, behavioral cross-sensitization was demonstrated between peripheral cocaine administration and intra-A10 injection of enkephalin analogue. Increased mesolimbic DA transmission by these drugs argues that this may be the mechanism by which cross-sensitization is produced, and direct testing of this possibility will be the subject of future studies. This research was supported in part by U.S. Public Health Service Grants DA-03906 and MH-40817.
1 Beninger, R.J. and Herz, R.S., Pimozide blocks establishment but not expression of cocaine-produced environment-specific conditioning, Life Sci., 38 (1986) 1425-1431. 2 Dackis, C.A. and Gold, M.S., New concepts in cocaine addiction: the dopamine depletion hypothesis, Neurosci. Biobehav. Rev., 9 (1985) 469-477. 3 Downs, A.W. and Eddy, N.B., The effect of repeated doses of cocaine on the rat, J. Pharmacol. Exp. Ther., 46 (1932) 199-202. 4 Gale, K., Catecholamine-independent behavioral and neurochemical effects of cocaine in rats, NIDA Research Monogr., 54 (1984) 323-332. 5 Joyce, E.M. and Iversen, S.D., The effect of morphine applied locally to mesencephalic dopamine cell bodies on spontaneous motor activity in the rat, Neurosci. Lett., 14 (1979) 207-212. 6 Kalivas, P.W., Sensitization to repeated enkephalin administration into the ventral tegmental area of the rat. II. Involvement of the mesolimbic dopamine system, J. Pharmacol. Exp. Ther., 235 (1985) 544-550. 7 Kalivas, P.W., Taylor, S. and Miller, J.S., Sensitization of repeated enkephalin administration into the ventral tegmental area of the rat. I. Behavioral characterization, J. Pharmacol. Exp. Ther., 235 (1985) 537-543. 8 Kelley, A.E., Stinus, L. and Iversen, S.D., Interaction between D-Ala-Met-enkephalin, AI0 dopaminergic neurons, and spontaneous behavior in the rat, Behav. Brain Res., 1 (1980) 3-24. 9 Kelley, P.H. and Iversen, S.D., Selective 6-OHDAinduced destruction of mesolimbic dopamine neurons: abolition of psychostimulant-induced locomotor activity in rats, Eur. J. Pharmacol., 40 (1975) 45-56. 10 Pellegrino, L.K., Pellegrino, A.S. and Cushman, A.J., A Sterotaxic Atlas of the Rat Brain, Plenum, New York, 1979. 11 Post, R.M. and Contel, N.R., Human and animal studies of cocaine: implications for development of behavioral pathology. In I. Cresse (Ed.), Stimulants: Neurochemical, Behavioral and Clinical Perspectives, Raven, New York, 1983, pp. 169-203. 12 Post, R.M., Lockfeld, A., Squillace, K.H. and Cantel, N.R., Drug-environment interaction: context dependency of cocaine-induced behavioral sensitization, Life Sci., 28 (1981) 755-760. 13 Reith, M.E.A., Meisler, B.E., Sershen, H. and Lastha, A., Structural requirements for cocaine congeners to interact with dopamine and serotonin uptake sites in mouse brain and to induce sterotyped behavior, Biochem. Pharmacol., 35 (1986) 1123-1129. 14 Taylor, D. and Ho, B.T., Neurochemical effects of cocaine following acute and repeated injection, J. Neurosci. Res., 3 (1977) 95-101. 15 Vezina, P. and Stewart, J., Conditioning and placespecific sensitization of increases in activity induced by morphine in the VTA, Pharmacol. Biochem. Behav., 20 (1984) 925-934.