Abstract. Rats were treated for 21 days with the selective. D-1 blocker SCH 23390 (0.1 mg/kg SC). Threshold doses of apomorphine for hypermotility (0.15 mg/kg ...
Psychopharmacology
Psychopharmacology (1987) 91 : 394-396
© Spfinger-Verlag 1987
Enhanced stereotyped response to apomorphine after chronic D-1 blockade with SCH 23390 A. Vaccheri, R. Dall'Olio, O. Gandolfi, P. Roncada, and N. Montanaro Institute of Pharmacology, University of Bologna, Via Irnerio 48, 1-40126 Bologna, Italy
Abstract. Rats were treated for 21 days with the selective D-1 blocker SCH 23390 (0.1 mg/kg SC). Threshold doses of apomorphine for hypermotility (0.15 mg/kg SC) and for stereotyped response (0.25 mg/kg SC) were given 7, 21, 35, and 77 days after discontinuation of the chronic treatment. The rats always showed enhanced stereotyped response to the higher dose of apomorphine but never any change in their motility response to the lower dose of dopamine agonist. This finding may represent a behavioral correlate of the reported supersensitivity of D-1 receptors induced by SCH 23390. Key words: Receptor supersensitivity - SCH 23390 Apomorphine - Stereotyped behavior - Locomotor activity
The acute administration to rats of SCH 23390, a newly synthesized benzazepine with strong D-I blocking activity (Iorio et al. 1983; Hyttel 1983), has been reported to antagonize apomorphine-induced hypermotility (Molloy and Waddington 1984), stereotyped behavior (Iorio et al. 1983; Molloy and Waddington 1984) and climbing behavior (Boyce et al. 1985), and to suppress conditioned avoidance response (Iorio etal. 1983). Recently, Creese and Chen (1985) have shown that repeated administration to rats of SCH 23390 elicits a highly significant increase in the Bm,x of D-I but not of D-2 binding sites in the striatum, thus demonstrating that selective D-1 supersensitivity can be obtained. To date, the behavioral correlates of selective D-1 receptor supersensitivity have not been assessed. In the present study, the potential changes in rat behavioral sensitivity to threshold doses of apomorphine for hypermotility and stereotypies were evaluated 7, 21, 35, and 77 days after discontinuation of daily administration of SCH 23390 for 3 weeks. The two doses of apomorphine (0.15 and 0.25 mg/kg SC, respectively) were the same as those employed in one of our previous investigations (Montanaro et al. 1982) to reveal enhanced dopaminergic sensitivity following chronic treatment with (-)-sulpiride and haloperidol. Materials and methods Male Sprague-Dawley rats (Nossan, Correzzana, Italy) were used that weighed 160-180 g at the beginning of the Offprint requests to: N. Montanaro
chronic treatment. There were four rats per cage under controlled conditions of light (from 7:00 a.m. to 7:00 p.m.), temperature (22_+ 2 C) and humidity (60%), with free access to standard laboratory diet and tap water. Rat locomotor activity was measured by means of eight actometric cages. These consisted of rectangular plastic boxes with a stainless-steel grid floor. A 65 V, 25 ~tA DC current was continuously delivered to the grid, the circuit being closed by the rat's feet; every circuit switch was recorded by a counter as 1 motility count. Only the horizontal movements of the animals across the cage were recorded: rearing or trampling did not cause a circuit switch unless associated with the animal's locomotion. Stereotyped behavior was evaluated in plastic rectangular boxes that had both a cover and front panel made of transparent Plexiglas so that detailed observation of the animals was possible. The rats were treated daily for 21 days with 0.1 mg/kg SC of SCH23390 (Schering-Plough, Bloomfield, N J, USA); controls received a daily injection of saline (1 ml/kg SC). Seven days after withdrawal, both saline- and SCH 23390-treated groups were divided into subgroups of eight animals. One subgroup from each group was employed to evaluate the motility response to 0.15 mg/kg SC apomorphine HC1 (Sigma, St. Louis, Mo, USA). The other two subgroups were used to assess the stereotyped response induced by 0.25 mg/kg SC apomorphine. The animals used for the hypermotility test were allowed to adapt to the actometric cages for 150 min. Then they were injected with the lower dose of apomorphine and placed once again in the actometers where their motilit response was recorded for 30 min, starting 10 min after the injection. A similar procedure was folldwed for the evaluation of stereotyped behavior. After being in the cages for 150 min, the rats were injected with the higher dose of apomorphine and placed in the observation cages. Stereotypy scores were assigned every 10 min for 30 min, starting 10 min after the injection, according to the following rating scale (Costall and Naylor 1973): 0 = no stereotypy; 1 = periodic sniffing; 2 = continuous sniffing; 3 = periodic licking or biting; 4 = continuous licking or biting. Individual data were the mean scores from three observations of each rat. The rats were also observed during the habituation period in order to assess the possible occurrence of spontaneous stereotyped movements. The tests described were repeated on the same groups of animals 3, 5, and 11 weeks after pretreatment withdrawal.
395 Table 1. Stereotyped response (mean scores) induced by 0.25 mg/kg
SC apomorphine and motility response (30-min motility counts + SEM) induced by 0.15 mg/kg SC apomorphine. Pre-APO lines show the baseline values (last 30 rain of habituation) of each group; no stereotyped behavior was observed before APO administration. Rats were pretreated with saline or SCH 23390 for 21 days and tested at various times after withdrawal Weeks after withdrawal
Stereotypy score
Motility counts
Saline SCH 23390 Saline
SCH 23390
1 Pre-APO APO
0.92
1.83"*
69.63+_ 9.19 75.25_+15.56
43.28+ 9.65 73.88_+15.65
3 Pre-APO APO
1.41
2.08**
45.63_+ 9.38 65.38+_23.13
42.13_+ 7.29 54.00+_ 4.29
5 Pre-APO APO 11 Pre-APO APO
1.50
2.41"* 2.79*
48.25_+10.10 54.63+12.77 59.25_+11.29 64.88_+16.30 4 6 . 5 0 _ + 1 0 . 0 057.25_+14.75 80.00_+ 15.60 77.75_+12.50
1.79
* P < 0.05 and ** P < 0.01: comparison with the respective salinepretreated group (two-tailed Mann-Whitney U test)
Thirty-minute motility counts were submitted to 2 x 4 ("treatment" x " t i m e s " ) factorial A N O V A with repeated measurements on the factor "times." Stereotypy scores were analyzed by means of individual Mann-Whitney U tests (two-tailed). Results
Administration of 0.25 mg/kg apomorphine to the control rats only induced continuous or intermittent sniffing, which lasted 30-40 min. SCH 23390-pretreated animals exhibited significantly higher stereotypy scores, which corresponded to continuous sniffing and to intermittent or continuous licking and biting. The differences between saline- and SCH 23390-pretreated animals remained approximately the same during the whole experiment. On the other hand, the stereotyped response to apomorphine of both saline- and SCH 23390pretreated animals progressively increased as we repeated the trials. Chronic treatment with SCH 23390 did not affect the locomotor response to 0.15 mg/kg apomorphine. Factorial A N O V A of the 30-min motility counts did not yield any significant F ratio (treatment: F(1,14)< 1; times: F(3,42)= 1.10; interaction treatment x times: F(3,42) < 1). Discussion
Chronic pretreatment of rats with 0.1 mg/kg SCH 23390 was followed by enhanced stereotyped response to the threshold dose of 0.25 mg/kg apomorphine, whereas the same pretreatment failed to modify the sensitivity of the rats to a threshold dose of apomorphine (0.15 mg/kg) for hypermotility. The increased stereotyped response to apomorphine lasted at least 11 weeks. The stereotypy scores of both saline- and SCH 23390pretreated animals progressively increased as the trials were repeated. A similar finding has been already reported by Czernansky et al. (1984). Although the mechanism underlying this phenomenon is not clear, it has been demonstrated
that repeated apomorphine exposure can lead to hyposensitivity as well as to hypersensitivity, depending on the interval between the administrations (Castro et al. 1985). In our experiments, the increased response to repeated apomorphine exposure did not influence the differences between saline- and SCH 23390-treated groups. Enhancement o f stereotyped response to apomorphine after withdrawal from SCH 23390 seems to be the behavioral correlate of the neurochemical D-1 selective supersensitivity observed by Creese and Chen (1985) and by Porceddu et al. (1985) after SCH 23390 chronic administration. This finding is consistent with some reports indicating that D-1 receptors play a role in certain dopamine-mediated behaviors (Molloy and Waddington 1984; Christensen etal. 1984; Arnt 1985) either directly or by interacting with D-2 sites (Pugh et al. 1985). The repeated blockade of D-1 receptors with SCH 23390 failed to modify the sensitivity of rats to the lower dose of apomorphine we used to induce hypermotility. This was an unexpected finding because SCH 23390, when given acutely, appears to be as effective as the classic neuroleptics in inhibiting locomotor response in rodents (see Introduction). As is well known, classic neuroleptics are either D - l / D - 2 unselective or D-2 selective blockers, whereas SCH 23390 only blocks D-1 receptors. There is evidence that D-1 receptors, at least in some cases, do not directly mediate some behaviors but exert their influence on responses mediated by D-2 activation (Pugh et al. 1985). In this regard, further studies from our laboratory (submitted for publication) seem to indicate that D-1 receptors may play a permissive role on certain dopamine-mediated functions. This would explain the inability of SCH 23390 to induce behavioral supersensitivity to the threshold dose of apomorphine for hypermotility. If D-1 receptors play a permissive role at the mesolimbic level for the expression of the D-2 mediated motor response, their acute blockade may well impair such a response, but an increase in their density does not necessarily have to be followed by enhanced hypermotility. This interpretation may account for the motility response, but not for the stereotyped behavior that appeared to be augmented after withdrawal from repeated SCH 23390 administration. At the striatal level, where stereotyped behavior is considered to be expressed (Costall and Naylor 1979), there is a high density of D-1 receptors, and the interaction between D-1 and D-2 receptors may be different from the one hypothesized at the mesolimbic level. This report represents a preliminary study in which D-1 receptor supersensitivity was assessed by employing a mixed D - l / D - 2 agonist such as apomorphine. Further studies are in progress involving the challenge of rats withdrawn from SCH 23390 with selective D-I or D-2 agonists, in order better to understand the role of these receptors in dopamine-stimulated behaviors.
Acknowledgements. The present work was supported by a grant from the Italian Ministry of Education. We thank Mr. Josef Vesely for helpful technical assistance. References
Arnt J (1985) Hyperactivity induced by stimulation of separate dopamine D-1 and D-2 receptors in rats with bilateral 6-OHDA lesions. Life Sci 37:71%723 Boyce S, Kelly E, Davis A, Fleminger S, Jenner P, Marsden CD
396 (1985) SCH 23390 may alter dopamine-mediated motor behavior via striatal D-1 receptors. Biochem Pharmacol 34:1665-1669 Castro R, Abreu P, Calzadilla CH, Rodriguez M (1985) Increased or decreased locomotor response in rats following repeated administration of apomorphine depends on dosage intervals. Psychopharmacology 85 : 333-339 Christensen AV, Arnt J, Hyttel J, Larsen JJ, Svendsen O (1984) Pharmacological effect of a specific dopamine D-I antagonist SCH 23390 in comparison with neuroleptics. Life Sci 34:1529-1540 Costall B, Naylor RJ (1973) On the mode of action of apomorphine. Eur J Pharmacol 21:350-361 Costall B, Naylor RJ (1979) Behavioral aspects of dopamine agonists and antagonists. In: Horn AS, Korf J, Westerink BHC (eds) The neurobiology of dopamine. Academic Press, London, pp 555-576 Creese I, Chen A (1985) Selective D-1 dopamine receptor increase following chronic treatment with SCH 23390. Eur J Pharmacol 109:127-128 Csernansky JG, Csernansky CA, Hollister LE (1984) Distinct effects of two stresses on the behavioral response to apomorphine. Life Sci 35:1513-1518
Hyttel J (1983) SCH 23390 - the first selective dopamine D-1 antagonist. Eur J Pharmacol 91:153-154 Iorio LC, Barnett A, Leitz FH, Houser VP, Korduba CA (1983) SCH 23390, a potential benzazepine antipsychotic with unique interactions on dopaminergic system. J Pharmacol Exp Ther 226:462 468 Molloy AG, Waddington IL (1984) Dopaminergic behaviour stereospecifically promoted by the D1 agonist R-SK&F 38393 and selectively blocked by the D1 antagonist SCH 23390. Psychopharmacology 82: 409 410 Montanaro N, Dall'Olio R, Gandolfi O, Vaccheri A (1982) Differential enhancement of behavioral sensitivity to apomorphine following chronic treatment of rats with (-)-sulpiride and haloperidol. Eur J Pharmacol 81 : 1-9 Porceddu ML, Ongini E, Biggio G (1985) 3H-SCH 23390 binding sites increase after chronic blockade of D-1 dopamine receptors. Eur J Pharmacol 118:367-370 Pugh MT, O'Boyle KM, Molloy AG, Waddington JL (1985) Effects of the putative D-1 antagonist SCH 23390 on stereotyped behaviour induced by the D-2 agonist RU24213. Psychopharmacology 87: 308-312 Received October 10, 1986/Final version November 20, 1986
