Effects of pentazocine and other opiates on shock detection in the rat: involvement of opiate and dopamine receptors

The involvement of nucleus accumbens dopamine in appetitive and aversive motivation

In recent years, considerable emphasis has been placed upon the putative role of nucleus accumbens dopamine systems in appetitive motivation and positive reinforcement. However, considerable evidence indicates that brain dopamine in general, and nucleus accumbens dopamine in particular, is involved in aspects of aversive motivation. Administration of dopamine antagonists or localized interference with nucleus accumbens dopamine systems has been shown to disrupt active avoidance behavior. In addition, accumbens dopamine release and metabolism is activated by a wide variety of stressful conditions. A review of the literature indicates that there are substantial similarities between the characteristics of dopaminergic involvement in appetitive and aversive motivation. There is conflicting evidence about the role of dopamine in emotion, and little evidence to suggest that the profound and consistent changes in instrumental behavior produced by interference with DA systems are due to direct dopaminergic mediation of positive affective responses such as hedonia. It is suggested that nucleus accumbens dopamine is involved in aspects of sensorimotor functions that are involved in both appetitive and aversive motivation.

Interactions of opioids with caffeine: evaluation by ambulatory activity in mice

Morphine (up to 10 mg kg-1), buprenorphine (up to 0.1 mg kg-1), pentazocine (30 mg kg-1) and caffeine (up to 10 mg kg-1), significantly increased mouse ambulation. The combination of morphine, buprenorphine and pentazocine with caffeine generally enhanced the effect. Dopamine D1- and D2-receptor bockade, depletion of stored dopamine, and inhibition of dopamine synthesis could reduce the ambulation increased by single administration of morphine, buprenorphine and caffeine, and by combined administration of morphine and buprenorphine with caffeine. Although naloxone (0.1-3 mg kg-1) itself did not change mouse ambulation, at 3 mg kg-1, it reduced the effect of caffeine. The repeated administration of morphine (10 mg kg-1) induced a sensitization to the ambulation-increasing effect, and was inhibited by the combination of caffeine (10 mg kg-1) in the repeated administration schedule. The repeated administration of caffeine (10 mg kg-1) with buprenorphine (0.3 mg kg-1) resulted in a decrease in the effect to the level of caffeine alone. The development of cross-sensitization to morphine (10 mg kg-1) by the repeated treatment with buprenorphine (0.3 mg kg-1) was inhibited by caffeine (10 mg kg-1). Our results suggest that the dopaminergic systems are involved in the enhanced interaction of opioids having agonistic action on mu- or sigma-receptors with caffeine. However, it is also considered that, following the repeated administration, caffeine acts to reduce the sensitivity to the ambulation-increasing effect of opioids, probably inducing up-regulation of adenosinergic systems.

Effects of repeated administration of pentazocine on ambulatory activity in mice: comparison with the effects of morphine and methamphetamine

Effects of single and repeated administration of pentazocine (5 times at intervals of 3-4 days) were compared with those of morphine and methamphetamine by means of ambulatory activity in mice. The interactions among these 3 drugs were also investigated. Pentazocine (25 mg/kg, s.c.), morphine (10 and 20 mg/kg, s.c.) and methamphetamine (2 mg/kg, s.c.) significantly increased the activity, and the effect progressively enhanced (defined here as development of reverse tolerance) during the repeated administration schedule. The induction of reverse tolerance to pentazocine was less dependent on the environmental conditions, and it was abolished within 2 months. A cross reverse tolerance was demonstrated from methamphetamine to pentazocine and to morphine, and from morphine to pentazocine. However, no significant cross reverse tolerance was induced from pentazocine to morphine and to methamphetamine, and from morphine to methamphetamine. The present results suggest that pentazocine possesses an ambulation-increasing effect, although the characteristics are different from that of either morphine or methamphetamine.

The role of dopamine in the effects of pentazocine and tripelennamine

CNS dopamine has been suggested as a mediator in the effects of many drugs of abuse. The present study was conducted to assess the potential dopaminergic activity of pentazocine and tripelennamine combinations (T's and Blues). The effects of pentazocine and tripelennamine, administered alone and in combination with several dopaminergic drugs, on milk drinking were assessed in the rat. Both the opioid and antihistamine were tested in combination with apomorphine and haloperidol. Pentazocine was also tested in combination with the D1- and D2-receptor selective antagonists SCH 23390 and raclopride, and with the D2-receptor agonist quinpirole. Tripelennamine was additionally tested in combination with methamphetamine. Haloperidol and quinpirole pretreatment produced leftward shifts in the pentazocine dose-effect curve while raclopride and SCH 23390 shifted the opioid curve to the right. Doses of apomorphine shifted tripelennamine's dose-effect curve to the left, tripelennamine enhanced the effects of methamphetamine, but haloperidol did not alter the antihistamine's effects. These data suggest dopaminergic involvement in the effects of the opioid and antihistamine.

Effects of morphine, clonidine, and intensity change on electric-shock discrimination

The effects of morphine, clonidine, and changes in stimulus intensity were examined in squirrel monkeys responding on one of two levers following brief presentations of one of two electric-shock intensities (0.1 and 0.5 mA). Responses were designated as correct or incorrect depending on which shock intensity had been presented and which lever was pressed. Morphine (0.42 to 1.80 mg/kg) and clonidine (0.075 to 0.18 mg/kg) decreased percentage correct responding. Morphine and clonidine also increased response latency and the number of shock presentations that were not followed by responses. Changes in shock intensity also decreased percentage correct responding but had no effect on response latency or on the number of shock presentations not followed by responses.

External stimulus control in a "drug-discrimination" procedure: drug effects and inter-animal variation

Rats (N = 12) were trained to discriminate between two stimulus conditions S1 and S2, consisting of combinations of visual and tactile stimuli [S1: box lighted (L) and wooden floor insert present (W); S2: box dark (D) and grid floor present (G)] in a two-lever discrimination procedure. S1 was continuously present during half of the sessions, and S2 was continuously present during the remaining sessions. Morphine (0.3--6 mg/kg) and haloperidol (0.04--0.08 mg/kg), but not chlorpromazine (1--4 mg/kg) and scopolamine (0.031--0.125 mg/kg), decreased the accuracy of discriminative responding during S1 sessions. None of the drugs significantly affected discrimination accuracy during S2 sessions. After drug testing was completed, reversed combinations of the visual and tactile stimuli were tested (i.e. L + G, and D + W). Inter-animal variation in the control by the component stimuli was observed. The results suggest that "intermediate results" (i.e. equal responding on drug and saline lever) in drug discrimination research, if observed at the highest dose of a drug at which animals still respond, may be interpreted in terms of a drug-induced disruption of discriminative responding. The results further suggest that inter-animal variation in the outcome of drug generalization tests may be partly related to inter-animal variation in the degree of stimulus control by different components of the training drug stimulus.

Effects of d-amphetamine and morphine on discrimination: signal detection analysis and assessment of response repetition in the performance deficits

Signal detection analysis was used to examine the effects of d-amphetamine and of morphine on auditory discrimination in female rats. The probability of response repetition in the discrete trial two-choice discrimination procedure was used as an additional behavioral measure. d-Amphetamine (0.4-3.2 mg/kg) and morphine (1.88-15.0 mg/kg) decreased the sensitivity measures (A' and SI) but did not consistently affect the response bias measures (B" and RI). The probability of response repetition was increased by d-amphetamine and was not affected by morphine. It is concluded that the response bias measure B", derived from signal detection theory, and the empirical response bias measure RI, do not discriminate between the different ways in which d-amphetamine and morphine affect discriminative responding, under the conditions of this study.

Effects of immobilization stress on shock discrimination performance in rats

It has been suggested that acute stress induces analgesia in rats and mice. However, stress can have a myriad of debilitating effects on organisms, and it is not clear whether stress decreases the perceived intensity of the painful stimulus (i.e., a change in sensitivity) or decreases the willingness or ability of the organism to carry out the appropriate bodily movement (i.e., a change in responsivity). Since traditional animal analgesia tests confound sensitivity with responsivity, we assessed the effects of immobilization stress on rats trained on a two-choice, two-shock discrimination task, in which the dependent measures are presumably less reflective of alterations in pain responsivity. Immobilization stress significantly disrupted shock discrimination performance, with the disruption occurring primarily in choice performance signalled by the higher intensity shock discriminative stimulus. These effects completely dissipated with successive daily exposures to stress. The data suggest that immobilization stress has a specific effect on pain sensitivity which is separate from its possible effects on pain responsivity.

Drugs and visual perception: effects of LSD, morphine and chloropromazine on accuracy, bias and speed

Ten pigeons were trained to discriminate between the intensities of two white lights (projected behind a center response "key") using a discrete trial procedure in which choice behavior involved pecking at red or green lights projected behind left or right side keys. LSD (0.02-0.08 mg/kg) did not alter the accuracy of the brightness discrimination (percent correct) although it did lower response speed and may have differentially affected spatial (position) bias. Morphine (2.5--10.0 mg/kg) decreased accuracy of discrimination as well as response speed and had greater effects on trials when the bright stimulus was presented than when the dim stimulus was presented. Chlorpromazine (7.5-3.0 mg/kg) lowered accuracy without significantly altering any other measure of performance.

Effects of morphine, d-amphetamine, and pentobarbital on shock and light discrimination performance in rats

The effects of 2 and 4 mg/kg morphine sulfate, 0.5 and 1 mg/kg d-amphetamine sulfate, and 6 and 12 mg/kg pentobaribital sodium were tested in rats in two different discrete-trial two-choice discrimination tasks. The discriminative stimuli for one task were high and low intensity shocks. In the other, correct choices were signaled by the position of a brief light flash. Morphine (4 mg/kg) significantly disrupted performance of both tasks, with more reliable disturbance occurring in the shock discrimination animals. Pentobarbital (12 mg/kg), while exerting noticeable effects on gross motor behavior, had little effect on discrimination performance; d-amphetamine (1 mg/kg) was disruptive of discrimination performance in only some animals. The results indicate that much of the effect of relatively low doses of morphine on the shock discrimination performance of rats may be due not to its putative specific antinociceptive properties, but to alterations in conceptual-judgmental processes or decreases in motivation (e.g., hunger) unrelated to pain.