Brain Research Bulletin,
Vol. 27,
pp. 725-730.
0361-9230/91
* Pergamon Press pk. 1991. printed in the U.S.A.
$3.00 t
.OO
RAPID CO~~U~ICATIO~
Dopaminergic Regulation of Quiet Biting Attack Behavior in the Cat MAJID B. SHAIKH,’ CHANG-LIN LU, MARGARET MACGREGOR AND ALLAN SIEGEL Department of Neurosciences, New Jersey Medical School, Newark, NJ 07103
Received 14 June 1991 SHAIKH, M. B., C.-L. LU, M. MA~GRBGQRAND A. SIEGEL. Dopaminer~ic regKlat~~nof #et biting attack be~vjor in the car. BRAIN RBS BULL 27(5) 725-730, 1991.-The present study provides evidence for the involvement of dopamine in the regulation of quiet biting attack behavior. Utilizing monopolar electrodes, quiet biting attack was elicited by electrical stimulation of lateral hypothalamus in five cats. After stable baseline response latency values were established, the nonselective dopamine agonist, apomorphine, was administered peripherally (IP, I .O, 1.4 and 1.8 mglkg), and its effects upon the attack response were identified. Apomorphine significantly facilitated the occurrence of quiet biting attack in a dose- and time-dependent manner. Conversely, quiet biting attack behavior was also suppressed in a dose- and time-dependent manner by the selective D2 antagonist, spiperone (0.2, 0.4 and 0.8 mgikg), but not by the selective Dl an~gonist, SCH 23390 (0.8 mgikg). Moreover, pre~eatment with spiperone (0.2 mgikgf completely blocked the facilitatory effects of 1.4 mg/kg of apomorphine, while SCH 23390 (0.8 mgikg) pretreatment failed to alter apomorphine-induced facilitation of the attack response. In addition, neither apomotphine nor spiperone altered response latencies for hypothalamically elicited circling behavior. The results suggest that dopamine plays a significant role in the regulation of quiet biting attack behavior. Apomorphine
Dopamine
Quiet biting attack
Hypothalamus
A number of investigators have attempted to identify what role the dopamine system plays in the regulation of aggressive behavior. Several studies employing the model of shock-induced fighting in rats have suggested that dopamine facilitates this response (1,3), possibly acting through D2 receptors (27). Similar m~ulato~ effects have been reported with respect to defensive rage behavior in the cat following peripheral administration of selective and nonselective agonists and antagonists (22, 23, 29, 38). Moreover, our laboratory has recently shown that feline defensive rage behavior can be modified following direct microinjections of dopaminergic compounds into the anterior hypothahunicpreoptic region (37). However, we have no knowledge of the role of the dopamine system in the regulation of feline quiet biting attack behavior, a response that occurs under natural conditions (19) and which can be elicited by electrical stimulation of the lateral perifornical hypothalamus (11,30). In the laboratory, this predatory response is characterized by stalking of the prey object, usually an anesthetized rat, followed by biting of the back of its neck. Accordingly, the present study was designed to identify the extent to which dopamine system contribute to the expression of this form of aggressive behavior. METHOD
Five adult cats of either sex that did not display any aggres-
Spiperone
SCH 23390
sive behavior when a rat was placed in their home cages and weighed between 2.5 and 4.0 kg, were employed in this study. The animals had free access to food and water during the entire course of these experiments. The cats were anesthetized with sodium pentobarbital (45 mglkgf for surgical procedures. Under aseptic conditions, 12 stainless-steel guide tubes (18 ga, 10 mm long) were stereotaxically mounted bilaterally [according to the atlas of Jasper and Ajmone Marson (15) over holes drilled through the skull overlying the hypothalamus. In addition, three stainless-steel stylets connected to 10 screws with wire, embedded in the skull, served as indifferent electrodes. The entire assembly was protected by three plastic bolts connected to the skull with dental acrylic to hold a plastic cap. One week postoperatively, the animals were placed in a wooden observation chamber (61 X 61 X 61 cm) with a Plexiglas door in the presence of an anesthetized rat and food. The stimulating electrodes (electrolytically sharpened stainless-steel stylets, insulated with oil-based paint except at the tip) were lowered vertically through the guide tubes in 0.5 mm steps, into the hyzealous for the elicitation of an attack response. Monopoly electrical stimulation was delivered to the freely moving animals as biphasic, rectangular electrical pulses (0.25 to 0.50 mA, 62.5 Hz, 1 ms half cycle duration) from a Grass S-88 stimulator which were led through a pair of constant current Grass isolation units to the cat. Peak-to-peak current was measured by a
‘Requests for reprints should be addressed to Dr. Majid B. Shaikh, Department of Neurosciences, MSB, H-519, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, 185 South Grange Avenue, Newark, NJ 07103.
726
Tektronix 5000 series oscilloscope. Following identification of an attack site, the electrode was cemented in place with dental acrylic. After obtaining an attack response, baseline threshold values for this response were determined over a period of one week. Testing of baseline values was conducted on alternate days (30 to 45 mm/day with an interstimulus interval of 3 min) utilizing the Method of Limits in which 10 ascending and descending series of trials were employed. Current levels were raised or lowered in 0.05 mA steps in a counterbalanced A-B-B-A design to avoid any order effects. The response threshold for quiet biting attack was defined as the current value at which responses were elicited on 50% of the trials and a stable threshold value was defined as one which remained constant over a period of at least three test sessions. After a stable threshold was obtained, baseline latency values at that current were then determined over 10 trials. The following drugs were utilized in the present study for peripheral administration: apomorphine hydrochloride (1 .O, 1.4, 1.8 mg/kg), a nonselective dopamine agonist (2); spiperone (0.2, 0.4, 0.8 mglkg), a selective D2 antagonist (9, 17, 28) and R (+ )-SCH 23390 hydrochloride (0.8 mg/kg). a selective Dl antagonist (13,14). Following establishment of stable baseline response thresholds and latencies for quiet biting attack behavior, various doses of the dopamine agonist, apomorphine and selective antagonists (SCH 23390 and spiperone) were administered peripherally. The rationale for the selection of specific dose levels for each of these drugs noted above was determined on the basis of a most recently published study from our laboratory (38). In this study. it was observed that facilitation of affective defense behavior in the cat followed administration of apomorphine at 0. l-l .O mg/kg doses. In the present study, pilot data indicated that 1.0 mglkg constituted the minimum effective dose for modulating predatory attack. Thus, the dose levels were titrated upwards in order to establish a dose-response relationship. In our recent study. we also reported that suppression of affective defense resulted from infusion of 0.1 mg/kg of SCH 23390, while receptor blockade of apomorphine followed pretreatment with 0.5 mg/kg of this drug (38). Other pilot data revealed that the SCH 23390 did not appear to alter the response latencies for elicitation of quiet biting attack behavior. Thus, we selected a dose of 0.8 mg/kg that was eight times greater than the effective dose against affective defense behavior in the cat when administered alone and 60% higher than the effective dose against this form of aggressive behavior when it was used as a pretreatment condition for apomorphine. Higher doses of the SCH 23390 were not employed because of the potential concern that, at such dose levels, it could have nonspecific properties (25). With respect to spiperone, our previous study in the cat established that 0.2 mg/kg was effective in suppressing affective defense behavior. Preliminary observations indicated that 0.4 mg/kg appeared to represent the lowest effective dose in suppressing quiet biting attack behavior. Therefore, the other doses were selected in order to establish that its effects are dose-dependent. Additionally, distilled water and 0.1% ascorbic acid were also utilized as vehicle controls and injected IP. Response latencies for quiet biting attack were determined over the following postinjection time periods of agonist or antagonist: 10-30, 30-60 and 120-150 min. Here, a paradigm for response latency testing identical to that employed in the predrug testing phase of this study was employed. After dose-response curves were obtained, each drug dose was tested one day per week with a test interval of 6 days. The paradigm for administration of each of the drugs as well
SHAIKH,
LU, MACGREGOR AND SIEGEL
as each drug dose were randomized and arranged in a counterbalanced manner. In four animals, the specificity of the facilitatory effects of apomorphine (1.8 mg/kg) was assessed by comparing its action against an unrelated response-i.e., ipsilateral circling, which was also elicited by electrical stimulation of the hypothalamus. The latency for circling behavior was defined as the time required for the cat to make one complete circle following onset of electrical stimulation. Response latency values for circling were determined for both pre- as well as postinjection periods in a manner identical to that described above for quiet biting attack behavior. At the completion of the experiments, the animals were perfused transcardially under deep (sodium pentobarbital) anesthesia with isotonic (0.9%) saline and 10% formalin. Then the brains were removed from the cranium, blocked, sectioned and stained with cresyl violet for identification of the electrode tips. A two-way repeated measures analysis of variance (ANOVA) was utilized to determine the effects of three doses of apomorphine (variable A) and vehicle over three periods of time (variable B) upon the latencies for quiet biting attack behavior. A similar analysis was conducted for the selective D2 antagonist, spiperone. For this analysis, variable B included two epochs of time for the lowest dose and three epochs of time for the higher doses. In addition, one-way repeated measures ANOVA’s were utilized for each drug dose to determine the time-dependent effects of drug administration upon quiet biting attack behavior. Here, changes in attack latencies were compared with predrug response values over time following each drug administration. For these analyses, N was defined as the number of animals employed in each group. Duncan’s Multiple Range Test was employed to compare the overall differences in the effects of different levels of drug treatment as well as to determine whether the time periods for individual dose levels of drug differed significantly from one another and baseline values. Here. the alpha level was set at p = 0.05. A two-way repeated measures ANOVA was also utilized to compare the effects of antagonist pretreatment (variable A) upon predatory attack latency values observed prior to and following drug delivery at different epochs of time (variable B) postagonist administration. The protocols involved in this experiment were approved by the Animal Care and Use Committee of New Jersey Medical School. RESULTS The data indicate that apomorphine, when injected peripherally, (IP) significantly facilitates the occurrence of predatory attack behavior in a dose-, F(3,12)=6.46, pcO.01, and time-, F(2,8)=7.40, p
Vol. 27,
pp. 725-730.
0361-9230/91
* Pergamon Press pk. 1991. printed in the U.S.A.
$3.00 t
.OO
RAPID CO~~U~ICATIO~
Dopaminergic Regulation of Quiet Biting Attack Behavior in the Cat MAJID B. SHAIKH,’ CHANG-LIN LU, MARGARET MACGREGOR AND ALLAN SIEGEL Department of Neurosciences, New Jersey Medical School, Newark, NJ 07103
Received 14 June 1991 SHAIKH, M. B., C.-L. LU, M. MA~GRBGQRAND A. SIEGEL. Dopaminer~ic regKlat~~nof #et biting attack be~vjor in the car. BRAIN RBS BULL 27(5) 725-730, 1991.-The present study provides evidence for the involvement of dopamine in the regulation of quiet biting attack behavior. Utilizing monopolar electrodes, quiet biting attack was elicited by electrical stimulation of lateral hypothalamus in five cats. After stable baseline response latency values were established, the nonselective dopamine agonist, apomorphine, was administered peripherally (IP, I .O, 1.4 and 1.8 mglkg), and its effects upon the attack response were identified. Apomorphine significantly facilitated the occurrence of quiet biting attack in a dose- and time-dependent manner. Conversely, quiet biting attack behavior was also suppressed in a dose- and time-dependent manner by the selective D2 antagonist, spiperone (0.2, 0.4 and 0.8 mgikg), but not by the selective Dl an~gonist, SCH 23390 (0.8 mgikg). Moreover, pre~eatment with spiperone (0.2 mgikgf completely blocked the facilitatory effects of 1.4 mg/kg of apomorphine, while SCH 23390 (0.8 mgikg) pretreatment failed to alter apomorphine-induced facilitation of the attack response. In addition, neither apomotphine nor spiperone altered response latencies for hypothalamically elicited circling behavior. The results suggest that dopamine plays a significant role in the regulation of quiet biting attack behavior. Apomorphine
Dopamine
Quiet biting attack
Hypothalamus
A number of investigators have attempted to identify what role the dopamine system plays in the regulation of aggressive behavior. Several studies employing the model of shock-induced fighting in rats have suggested that dopamine facilitates this response (1,3), possibly acting through D2 receptors (27). Similar m~ulato~ effects have been reported with respect to defensive rage behavior in the cat following peripheral administration of selective and nonselective agonists and antagonists (22, 23, 29, 38). Moreover, our laboratory has recently shown that feline defensive rage behavior can be modified following direct microinjections of dopaminergic compounds into the anterior hypothahunicpreoptic region (37). However, we have no knowledge of the role of the dopamine system in the regulation of feline quiet biting attack behavior, a response that occurs under natural conditions (19) and which can be elicited by electrical stimulation of the lateral perifornical hypothalamus (11,30). In the laboratory, this predatory response is characterized by stalking of the prey object, usually an anesthetized rat, followed by biting of the back of its neck. Accordingly, the present study was designed to identify the extent to which dopamine system contribute to the expression of this form of aggressive behavior. METHOD
Five adult cats of either sex that did not display any aggres-
Spiperone
SCH 23390
sive behavior when a rat was placed in their home cages and weighed between 2.5 and 4.0 kg, were employed in this study. The animals had free access to food and water during the entire course of these experiments. The cats were anesthetized with sodium pentobarbital (45 mglkgf for surgical procedures. Under aseptic conditions, 12 stainless-steel guide tubes (18 ga, 10 mm long) were stereotaxically mounted bilaterally [according to the atlas of Jasper and Ajmone Marson (15) over holes drilled through the skull overlying the hypothalamus. In addition, three stainless-steel stylets connected to 10 screws with wire, embedded in the skull, served as indifferent electrodes. The entire assembly was protected by three plastic bolts connected to the skull with dental acrylic to hold a plastic cap. One week postoperatively, the animals were placed in a wooden observation chamber (61 X 61 X 61 cm) with a Plexiglas door in the presence of an anesthetized rat and food. The stimulating electrodes (electrolytically sharpened stainless-steel stylets, insulated with oil-based paint except at the tip) were lowered vertically through the guide tubes in 0.5 mm steps, into the hyzealous for the elicitation of an attack response. Monopoly electrical stimulation was delivered to the freely moving animals as biphasic, rectangular electrical pulses (0.25 to 0.50 mA, 62.5 Hz, 1 ms half cycle duration) from a Grass S-88 stimulator which were led through a pair of constant current Grass isolation units to the cat. Peak-to-peak current was measured by a
‘Requests for reprints should be addressed to Dr. Majid B. Shaikh, Department of Neurosciences, MSB, H-519, New Jersey Medical School, University of Medicine and Dentistry of New Jersey, 185 South Grange Avenue, Newark, NJ 07103.
726
Tektronix 5000 series oscilloscope. Following identification of an attack site, the electrode was cemented in place with dental acrylic. After obtaining an attack response, baseline threshold values for this response were determined over a period of one week. Testing of baseline values was conducted on alternate days (30 to 45 mm/day with an interstimulus interval of 3 min) utilizing the Method of Limits in which 10 ascending and descending series of trials were employed. Current levels were raised or lowered in 0.05 mA steps in a counterbalanced A-B-B-A design to avoid any order effects. The response threshold for quiet biting attack was defined as the current value at which responses were elicited on 50% of the trials and a stable threshold value was defined as one which remained constant over a period of at least three test sessions. After a stable threshold was obtained, baseline latency values at that current were then determined over 10 trials. The following drugs were utilized in the present study for peripheral administration: apomorphine hydrochloride (1 .O, 1.4, 1.8 mg/kg), a nonselective dopamine agonist (2); spiperone (0.2, 0.4, 0.8 mglkg), a selective D2 antagonist (9, 17, 28) and R (+ )-SCH 23390 hydrochloride (0.8 mg/kg). a selective Dl antagonist (13,14). Following establishment of stable baseline response thresholds and latencies for quiet biting attack behavior, various doses of the dopamine agonist, apomorphine and selective antagonists (SCH 23390 and spiperone) were administered peripherally. The rationale for the selection of specific dose levels for each of these drugs noted above was determined on the basis of a most recently published study from our laboratory (38). In this study. it was observed that facilitation of affective defense behavior in the cat followed administration of apomorphine at 0. l-l .O mg/kg doses. In the present study, pilot data indicated that 1.0 mglkg constituted the minimum effective dose for modulating predatory attack. Thus, the dose levels were titrated upwards in order to establish a dose-response relationship. In our recent study. we also reported that suppression of affective defense resulted from infusion of 0.1 mg/kg of SCH 23390, while receptor blockade of apomorphine followed pretreatment with 0.5 mg/kg of this drug (38). Other pilot data revealed that the SCH 23390 did not appear to alter the response latencies for elicitation of quiet biting attack behavior. Thus, we selected a dose of 0.8 mg/kg that was eight times greater than the effective dose against affective defense behavior in the cat when administered alone and 60% higher than the effective dose against this form of aggressive behavior when it was used as a pretreatment condition for apomorphine. Higher doses of the SCH 23390 were not employed because of the potential concern that, at such dose levels, it could have nonspecific properties (25). With respect to spiperone, our previous study in the cat established that 0.2 mg/kg was effective in suppressing affective defense behavior. Preliminary observations indicated that 0.4 mg/kg appeared to represent the lowest effective dose in suppressing quiet biting attack behavior. Therefore, the other doses were selected in order to establish that its effects are dose-dependent. Additionally, distilled water and 0.1% ascorbic acid were also utilized as vehicle controls and injected IP. Response latencies for quiet biting attack were determined over the following postinjection time periods of agonist or antagonist: 10-30, 30-60 and 120-150 min. Here, a paradigm for response latency testing identical to that employed in the predrug testing phase of this study was employed. After dose-response curves were obtained, each drug dose was tested one day per week with a test interval of 6 days. The paradigm for administration of each of the drugs as well
SHAIKH,
LU, MACGREGOR AND SIEGEL
as each drug dose were randomized and arranged in a counterbalanced manner. In four animals, the specificity of the facilitatory effects of apomorphine (1.8 mg/kg) was assessed by comparing its action against an unrelated response-i.e., ipsilateral circling, which was also elicited by electrical stimulation of the hypothalamus. The latency for circling behavior was defined as the time required for the cat to make one complete circle following onset of electrical stimulation. Response latency values for circling were determined for both pre- as well as postinjection periods in a manner identical to that described above for quiet biting attack behavior. At the completion of the experiments, the animals were perfused transcardially under deep (sodium pentobarbital) anesthesia with isotonic (0.9%) saline and 10% formalin. Then the brains were removed from the cranium, blocked, sectioned and stained with cresyl violet for identification of the electrode tips. A two-way repeated measures analysis of variance (ANOVA) was utilized to determine the effects of three doses of apomorphine (variable A) and vehicle over three periods of time (variable B) upon the latencies for quiet biting attack behavior. A similar analysis was conducted for the selective D2 antagonist, spiperone. For this analysis, variable B included two epochs of time for the lowest dose and three epochs of time for the higher doses. In addition, one-way repeated measures ANOVA’s were utilized for each drug dose to determine the time-dependent effects of drug administration upon quiet biting attack behavior. Here, changes in attack latencies were compared with predrug response values over time following each drug administration. For these analyses, N was defined as the number of animals employed in each group. Duncan’s Multiple Range Test was employed to compare the overall differences in the effects of different levels of drug treatment as well as to determine whether the time periods for individual dose levels of drug differed significantly from one another and baseline values. Here. the alpha level was set at p = 0.05. A two-way repeated measures ANOVA was also utilized to compare the effects of antagonist pretreatment (variable A) upon predatory attack latency values observed prior to and following drug delivery at different epochs of time (variable B) postagonist administration. The protocols involved in this experiment were approved by the Animal Care and Use Committee of New Jersey Medical School. RESULTS The data indicate that apomorphine, when injected peripherally, (IP) significantly facilitates the occurrence of predatory attack behavior in a dose-, F(3,12)=6.46, pcO.01, and time-, F(2,8)=7.40, p
