Richard H. Rech

Conditioned drug effects and absence of tolerance to d-amphetamine induced motor activity ☆

Tolerance development to d-amphetamine induced motor motor activity was studied under various experimental conditions. Following seven daily habituation sessions, female, albino rats were subjected to 7 daily sessions in which NaCl was injected IP 30 min before placement into activity cages (NaCl controls). In the next 9 days, the rats underwent 3 drug sessions, each separated by 2 NaCl controls, in which d-amphetamine (0.5, 10. or 1.7 mg/kg) was likewise injected before placement. A course of repeated drug administration followed for the next 14 days. One group of rats was injected with the drug 30 min before placement into the activity cage, a second group received the drug 30 min after each session as a control for conditioned activity effects, while a third group received NaCl. On the fifteenth day, all rats recieved d-aphetamine 30 min before placement as a test for tolerance development. This session was followed the next day by a test for conditioned motor effects in which NaCl was injected IP 30 min before the session. Dose related increases in motor activity were observed during the drug control sessions. The magnitude of the drug effect did not decrease following any of the conditions during the course of repeated drug administration. Animals repeatedly injected with the drug 30 min after or with NaCl 30 min before each session were affected by d-amphetamine approximately the same as they were before repeated injections. Rats administered d-amphetamine 30 min before sessions during the course of repeated injections showed an enhanced response to d-amphetamine during the test for tolerance. The magnitude of the change was related to the magnitude of the conditioned motor activity response. These experiments emphasize the importance of learned or conditioned variables that may result from repeated drug administration in conjunction with behavioral tests.

Comparison of anti-conflict drug effects in three experimental animal models of anxiety.

A novel form of experimentally-induced conflict behavior based on the conditioned suppression of drinking (CSD) is described and compared with two conventional animal models of human anxiety — a modified Geller-Seifter and an Estes-Skinner (Conditioned Emotional Response) procedure. The CSD procedure offered significant advantages over the two operant procudures in that the session duration was short (10 min) and the acquisition of stable behavioral baselines was rapid (approximately 2 weeks). Like the more conventional procedures, the CSD paradigm permitted the simultaneous determination of drug effects on shock-suppressed and nonsuppressed responding as estimates of antianxiety and sedative properties, respectively. With the CSD procedure, the anticonflict profiles for the benzodiazepines were highly correlated with their relative clinical antianxiety potency. Therefore, the CSD procedure appears to be a valuable tool in screening for possible antianxiety agents as well as in the behavioral testing of mechanism of action hypotheses regarding such agents.

Hyperalgesia during withdrawal as a means of measuring the degree of dependence in morphine dependent rats.

A modified flinch-jump procedure was used to detect changes in sensitivity to electric footshock in rats. In preliminary studies, dose-related increases in reaction thresholds (analgesia) were observed following intraperitoneal administration of 3, 6, or 9 mg/kg of morphine with the peak effect 60 min after injection. Analgesia and development of tolerance to the analgesic effects of morphine were detected 2–6 h and 12–24 h, respectively, after the subcutaneous (s.c.) implantation of a morphine pellet (75 mg base). In studies of withdrawal, rats made dependent by the s.c. implantation of morphine pellets showed significant decreases in reaction thresholds (hyperalgesia) and correlated decreases in body weight following removal of the pellet. The greatest changes during withdrawal occurred 12–36 h after pellet removal and the return of the reaction threshold to preremoval levels was associated with the return of normal diurnal fluctuation of body weight. Rats made dependent by s.c. administration of varying doses of morphine every 8 h for 11 days showed similar decreases in body weight and reaction threshold following abrupt cessation of drug injections. Animals receiving larger doses of morphine showed greater changes in the two measures, as well as a more rapid onset and more prolonged duration of effect. Peak effects were observed 48–60 h after the last injection of morphine. In another experiment, rats were made dependent to morphine by the pellet implantation procedure. Following i.p. administration of varying doses of naloxone, a morphine antagonist, there were dose-related decreases in reaction threshold and in body weight with the greatest decrease occurring 60–120 min after the injection. These investigations indicate that the hyperalgesia during withdrawal is a useful index of the degree of physical dependence in rats.

Lack of central 5-hydroxytryptamine influence on the anticonflict activity of diazepam

This study examined the effects of various drug treatments (IP injections) proposed to modify central 5-hydroxytryptamine (5-HT) activity on a conditioned suppression of drinking behavior in water-deprived rats. The subjects were trained to drink their daily water requirement during a 10-min session. Intermittent tone periods of 7 s were then introduced, the last 5 s of which the drinking tube was electrified. The animals gradually suppressed tube contacts during the tone to a low constant level within 2 weeks of training. Diazepam increased punished responding dramatically. The 5-HT antagonists methysergide (1–18 mg/kg), cyproheptadine (1–18 mg/kg), metergoline (0,25–2.0 mg/kg) and cinanserin (10–100 mg/kg) failed to induce large, reliable increases in punished responding. When a low dose of diazepam was combined with 5-HT antagonists, only one treatment, methysergide at 3 mg/kg, potentiated the anticonflict activity of diazepam. Acute or chronic treatment with PCPA increased behavior suppressed by punishment, but this effect was weak, brief, and poorly related to the depletion of brain 5-HT. LSD (0.3–100 μg/kg) administered 1,10, or 30 min before the test was ineffective in overcoming suppression by punishment. Mescaline (6–30 mg/kg) had no significant effect on punished responding. 5-HTP (18 mg/kg) decreased the number of shocks accepted, but not after pretreating with carbidopa. Pretreatment with carbidopa plus 5-HTP potentiated the anticonflict effect of diazepam. The 5-HT agonist mCPP (0.25–2.0 mg/kg) enhanced suppression due to punishment, but only in doses that interfered with unpunished responding. The 5-HT-releasing agent fenfluramine (0.25–1.0 mg/kg) did not affect this behavior. Amitriptyline pretreatment in a dose not affecting unpunished behavior (5.6 mg/kg) potentiated the diazepam-induced increase in punished responding. These results are difficult to reconcile with the proposal that suppression of behavior consequent to punishment is related to brain 5-HT activity.

Interactions of metergoline with diazepam, quipazine, and hallucinogenic drugs on a conflict behavior in the rat

The effects of diazepam quipazine, lysergic acid diethylamide (LSD), and 2,5-dimethoxy-4-methylamphetamine (DOM) were examined on a conditioned suppression paradigm. Food-deprived rats were trained to drink a liquid diet from a tube. Subsequently, intermittent 7-s tones were presented during the daily 10-min sessions, the tube being electrified during the last 5 s of each tone. The subject gradually learned to suppress contact with the tube during the tone periods to a low stable level (punished responding) and consumed stable volumes of the liquid diet during the silent periods (unpunished responding). Treatment with diazepam caused large increases (1,000% of control) in punished responding. The hallucinogens produced only modest increases (200–300%), while quipazine did not significantly increase punished responding. Metergoline pretreatment (0.1–2.0 mg/kg, 180 min) had no effect on punished responding itself, and there was no significant alteration of the diazepam dose-response pattern. The weak increase in punished responding by LSD was antagonized by metergoline, but the interaction between metergoline and DOM was variable and inconsistent. Diazepam, quipazine, LSD, and DOM caused dose-dependent decreases in unpunished responding (fluid intake). Metergoline alone decreased unpunished responding only at 2.0 mg/kg. Metergoline pretreatment (1.0 mg/kg) only slightly antagonized the LSD effect on unpunished behavior, but shifted the dose-response curves of DOM and quipazine for decrease in fluid intake to the right approximately eight fold. On the contrary, the dose-response curve of diazepam to decrease fluid intake was shifted to the left by metergoline pretreatment. These data suggest that altered activity of brain serotonin (5-HT) neurons is not responsible for the dramatic increase in punished responding by diazepam. The hallucinogens, quipazine, and diazepam all produce a decrease in unpunished responding, but they appear to do so by different neuropharmacological mechanisms. In addition, there may be at least slight differences in the mechanism by which LSD produces its effects as compared with that of quipazine and DOM.

The effects of p-chlorophenylalanine on morphine analgesia, tolerance and dependence development in two strains of rats

The effects of p-chlorophenylalanine (p-CPA; 100 mg/kg/day for 3 days) on morphine analgesia and the development of tolerance and physical dependence were investigated in Sprague-Dawley (SD) and Fisher (F) strains of albino rats. Using a modified flinch-jump method to detect changes in reactivity to electric footshock, F strain rats were more reactive to the footshock than SD rats, but showed less relative increase in threshold (analgesia) than SD rats following various doses of morphine. Pretreatment with p-CPA attenuated significantly morphine analgesia in SD, but not F rats. In animals implanted subcutaneously with morphine pellets, p-CPA appeared to delay the development of tolerance to morphine in both strains of rats. Hyperalgesia and loss of body weight resulted from administration of naloxone to pellet-implanted rats and p-CPA pretreatment lessened these withdrawal effects significantly in SD rats only. These results emphasize the importance of strain differences in the study of morphine analgesia and development of tolerance and dependence. Assuming differences in the function of the serotonergic inhibitory system in the two strains of rats, these data provide general support for the involvement of brain 5-HT mechanisms in modulating, if not mediating the effects of morphine.

Prior drug experience and effects of amphetamine on schedule controlled behavior

Abstract Food deprived rats were trained to lever press for food pellets on a fixed ratio 40 schedule of reinforcement. Following 18 days of training, rats received d -amphetamine IP (1.0 mg/kg) as a drug control. Three days later, half of the animals were given d -amphetamine and half were given NaCl for six days. Tolerance to the disruptive effects of d -amphetamine on FR responding was not noted in the drugged group. Both groups received 14 more daily sessions with NaCl followed by 12 additional days of drug. Rats with previous drug experience exhibited tolerance in 6 days, while the other group required 12 days. In a second study, rats were trained to respond on an unsignalled continuous avoidance schedule for 8–10 weeks. Two groups of rats were given 7 daily drug sessions in which d -amphetamine (1.0 mg/kg) was administered IP. Each drug session was followed by 2 daily NaCl control sessions. In the first 3 drug sessions of one group, d -amphetamine was injected IP 30 min after the end of the session. All other injections were given immediately before placement into the operant chamber. During the first session in which the drug was injected before placement into the chamber, response increases were significantly higher in rats with drug experience outside the behavioral situation than in drug naive subjects. These studies emphasize the importance of prior drug exposure when investigating behavioral effects of drugs.

Effects of acute and chronic interactions of diazepam and d-amphetamine on punished behavior of rats.

Drinking of water-deprived rats was punished by delivery of either 0.03 or 0.1 mA shocks through the drinking tube during the last 5 of 7-s tone components during a 15-min daily exposure to water. These sessions consisted of 66 alternating components marked by the presence or absence of a tone. Drinking was not punished during the 33 components without tones or during the first 2 s of each tone. The baseline number of shocks accepted by the rats at 0.1 mA was less than half that at 0.03 mA. Acute diazepam markedly increased shocks delivered from the baseline values for both shock intensities, while acute d-amphetamine either had no effect or decreased the number of shocks accepted. The combination of acute diazepam and d-amphetamine caused a decrease in shock rates as compared to diazepam alone. Daily treatment with the combination of 10 mg/kg diazepam and 1 mg/kg d-amphetamine caused a gradual increase in punished responding over 25 days under either shock intensity. Gross observation of these rats after daily treatments indicated the development of hyperreactivity and a pattern resembling stereotyped behavior. At the end of the chronic treatment with the drug combination the shock rates were significantly greater than those caused by diazepam alone. Nevertheless, neither the effect of diazepam nor that of d-amphetamine, when administered singly after the period of chronic treatment with the combination, differed significantly from initial effect of the respective drugs on punished responding.

Interactions between depressants (alcohol-type) and stimulants (amphetamine-type) ☆

Abstract The rotarod disruption in rats by 1.5 g/kg of ethanol was prolonged by combining the depressant with 2 or 8 mg/kg d-amphetamine, but not after combinations with 4 or 6 mg/kg of the stimulant. The combination with 8 mg/kg d-amphetamine also induced a prolonged coma and lethality. Cocaine or methylphenidate in combination form with ethanol also showed prolonged disruption of rotarod performance, but severe depression and lethality were not observed at any dose combination. d-Amphetamine in combination with pentobarbital or diazepam also increased the duration of rotarod impairment. Amphetamine plus methaqualone did not prolong rotarod disruption, but rather showed a trend toward antagonism. These combinations of 8 mg/kg d-amphetamine with depressants other than alcohol did not cause prolonged coma and lethality. Lower doses of ethanol (0.25 and 0.5 g/kg) plus 8 mg/kg d-amphetamine induced a delayed impairment of rotarod performance in rats as well as a comatose state and lethality. Mice showed a similar trend for these interactions between alcohol and d-amphetamine but the influence was much less predictable. Analysis of alcohol levels in rat serum and brain indicated little effect of d-amphetamine on the rate of elimination of ethanol. On the other hand, 1.5 g/kg of ethanol prolonged the d-amphetamine decay from brain and serum. This latter interaction was not observed in rats treated with 8 mg/kg d-amphetamine plus 0.5 g/kg ethanol. Mice treated with 8 mg/kg d-amphetamine plus 2.25 g/kg alcohol showed little trend for changes in rate of elimination of either drug. The behavioral effects of the combination of d-amphetamine and ethanol cannot be explained adequately on the basis of altered pharmacokinetics of either drug.

The effects of d-lysergic acid diethylamide (LSD), 2,5-dimethoxy-4-methylamphetamine (DOM), pentobarbital and methaqualone on punished responding in control and 5,7-dihydroxytryptamine-treated rats

The purpose of the present study was to determine the role of central 5-hydroxytryptamine (5-HT) neuronal systems in the effects of d-lysergic acid diethylamide (LSD), 2,5-methoxy-4-methylamphetamine (DOM), pentobarbital (PB) and methaqualone (MQ) on punished responding in rats. Water-deprived rats were trained to drink from a tube that was electrified at intervals (variable interval 21 sec; 0.03 mA current intensity), electrification being signalled by a tone. In daily 10-min control sessions, these animals accepted a relatively constant number of shocks; water consumption was also quite stable. At maximally effective doses PB, and to a lesser extent MQ, produced large (400-600 percent of control) increases in punished responding with little decrease in water intake. Higher doses of these agents produced a significant depression of unpunished responding (water intake). The hallucinogens, on the other hand, produced only moderate (125-175 percent of control) increases in the number of shock received, yet a similar depression of unpunished responding. Selective destruction of 5-HT neurons by intracerebroventricular administration of the neurotoxin 5,7-dihydroxytryptamine per se produced little change in the number of shocks received or water consumed in controls sessions. This destruction of 5-HT neurons failed to alter the effects of PB or MQ on punished or unpunished responding. The increase in punished responding produced by the hallucinogens, however, was blocked by this destruction of 5-HT neurons. Furthermore, the capacity of the hallucinogens to decrease water intake was significantly potentiated by the neurotoxin pretreatment. These data demonstrate that the effects of the hallucinogens LSD and DOM on conditioned suppression are quite different from those of PB and MQ, and that this difference may be due to the extent of 5-HT involvement in the effects of these agents.