Drugs and the Conditioned Avoidance Response

Drug dependence as a split object: Trajectories of neuroscientification and behavioralization at the Max Planck Institute of Psychiatry

Today, drug dependence is often understood as a "brain disease" and as an indication for behavioral therapy. In this article, I trace the historical development of the notions of drug dependence as a neuronal and behavioral problem in the local research context of the Max Planck Institute of Psychiatry in Munich, Germany. Focusing on the period from the 1950s to the 1980s, I argue that the neuroscientific and behaviorist understanding of "dependence" had two different trajectories that were yoked together under the same institution of self-proclaimed basic research: (a) the neuroscientific notion derived from an older toxicological approach to drug effects that was then accompanied by biochemical methods from the 1950s onwards, and neurochemical approaches from the 1960s and 1970s; and (b) the behaviorist notion had predecessors in psychotherapeutic approaches to addiction that emerged in the 1950s and took a psychodynamic orientation at the Institute. When the Institute positioned itself as a basic research establishment and developed a unified structure during the 1960s, these psychodynamic approaches were excluded for being "too applied." Soon afterward, behaviorist psychotherapeutic approaches to drug dependence emerged in the 1970s, emphasizing their foundation in basic research. Even though neuroscientific and behaviorist notions had some overlaps through the use of animal experimentation and by referring to basic research, researchers using the two approaches remained separate in their respective units during the time period under analysis. When conceptualizing the local scientific occupation with "drug dependence," I apply here the history of science concept of a "split object." Like the "boundary object," the split object is plastic enough to adapt to local conditions and robust enough to maintain its genuine identity. Compared with the boundary object, however, the split object does not invite scientific collaboration. It does, nonetheless, enable epistemic coexistence under a common institutional goal.

Effects of haloperidol and aripiprazole on the human mesolimbic motivational system: A pharmacological fMRI study

The atypical antipsychotic drug aripiprazole is a partial dopamine (DA) D2 receptor agonist, which differentiates it from most other antipsychotics. This study compares the brain activation characteristic produced by aripiprazole with that of haloperidol, a typical D2 receptor antagonist. Healthy participants received an acute oral dose of haloperidol, aripiprazole or placebo, and then performed an active aversive conditioning task with aversive and neutral events presented as sounds, while blood-oxygen-level-dependent (BOLD) functional magnetic resonance imaging (fMRI) was carried out. The fMRI task, targeting the mesolimbic motivational system that is thought to be disturbed in psychosis, was based on the conditioned avoidance response (CAR) animal model - a widely used test of therapeutic potential of antipsychotic drugs. In line with the CAR animal model, the present results show that subjects given haloperidol were not able to avoid more aversive than neutral task trials, even though the response times were shorter during aversive events. In the aripiprazole and placebo groups more aversive than neutral events were avoided. Accordingly, the task-related BOLD-fMRI response in the mesolimbic motivational system was diminished in the haloperidol group compared to the placebo group, particularly in the ventral striatum, whereas the aripiprazole group showed task-related activations intermediate of the placebo and haloperidol groups. The current results show differential effects on brain function by aripiprazole and haloperidol, probably related to altered DA transmission. This supports the use of pharmacological fMRI to study antipsychotic properties in humans.

Role of norepinephrine in mediating stress hormone regulation of long-term memory storage: a critical involvement of the amygdala

There is extensive evidence indicating that the noradrenergic system of the amygdala, particularly the basolateral nucleus of the amygdala (BLA), is involved in memory consolidation. Infusions of norepinephrine or beta-adrenoceptor agonists into the BLA enhance memory for inhibitory avoidance as well as water maze training. Other findings show that alpha 1-adrenoceptor activation also enhances memory for inhibitory avoidance training through an interaction with beta-adrenergic mechanisms. The central hypothesis guiding the research reviewed in this chapter is that stress hormones released during emotionally arousing experiences activate noradrenergic mechanisms in the BLA, resulting in enhanced memory for those events. Findings from experiments using rats have shown that the memory-modulatory effects of the adrenocortical stress hormones epinephrine and glucocorticoids are mediated by influences involving activation of beta-adrenoceptors in the BLA. In addition, both behavioral and microdialysis studies have shown that the noradrenergic system of the BLA also mediates the influences of other neuromodulatory systems such as opioid peptidergic and GABAergic systems on memory storage. Other findings indicate that this stress hormone-induced activation of noradrenergic mechanisms in the BLA regulates explicit/declarative memory storage in other brain regions.

Dose dependency of sex differences in the effects of repeated haloperidol administration in avoidance conditioning in mice

Sex differences in the effects of haloperidol in active avoidance conditioning in mice have previously been found in various studies carried out in our laboratory. Males were more affected than females by the disruptive effects of this neuroleptic. The work described here broadens the study of these sex differences to higher doses of haloperidol (0.1 and 0.2 mg/kg) using a repeated administration schedule (5 days). The results did not show sex differences in the deteriorating effects of this dopamine antagonist in the escape-avoidance response, but a tendency in the number of nonresponses was observed in the same direction as former results: male animals were more sensitive than females to the inhibitory effect of the low dose of haloperidol. It is concluded that the appearance of sex differences in the effects of haloperidol on active avoidance conditioning is a dose-dependent phenomenon.

The higher the dose, the greater the sex differences in escape-avoidance response in mice after acute administration of haloperidol

Sex differences in the effects of haloperidol in the escape-avoidance response have previously been found in various studies carried out in our laboratory in which mice were used as experimental subjects. Males were more affected than females by the disruptive effects of this neuroleptic of frequent clinical use. In the present work these sex differences were evaluated in a unique training session using several doses of the drug (0.075, 0.25, and 0.75 mg/kg i.p.). The number of avoidances, escapes, nonresponses, crossings during the adaptation period, crossings during intertrial intervals, and response latencies were analyzed. Statistically significant sex differences were found in the number of escapes and nonresponses: males showed fewer escape responses and more nonresponses than females. These sex differences were dose dependent: a positive correlation was obtained between doses of haloperidol and sex differences observed in the number of escapes and nonresponses. The higher the dose, the greater the sex differences. These are related not only to the impairment of motor activity, because no sex differences were found in the number of crossings during the adaptation period and intertrial intervals.

Effect of various psychotropic drugs on the performance of avoidance and escape behaviors in rats

The effect of different doses of nine psychotropic drugs upon conditioned avoidance responses (CARs) developed on a stable basis, after appropriate training, was investigated in rats and compared with their capacity to disrupt escape responses (ERs). Haloperidol (HAL), chlorpromazine (CPZ), morphine (MOR), pentobarbital (PENT), chlordiazepoxide (CDP), meprobamate (MPB), and amphetamine (AMPH) dose dependently inhibited both behaviors. Imipramine also disrupted CARs dose dependently, but did not affect ERs at maximal tolerated doses. Significant differences in the minimal effective doses, effective dose range, and time of onset and duration of action, as well as in potency, were observed. The quantitative determination of the level of selectivity, based upon the ratio ED50 escape failure/ED50 avoidance failure, indicated that all CNS depressants tested caused a selective inhibition of avoidance behavior. HAL was found to be the most specific, followed, in order, by CDP, MOR, CPZ, MPB, and PENT, whose ratio values were not significantly different. AMPH produced a nearly parallel impairment of both behaviors and quipazine only affected CARs at toxic doses. It is concluded that both neuroleptic and nonneuroleptic CNS depressant drugs have selective inhibitory effects on avoidance behavior. Data revealed differences that were more quantitative than qualitative.

Reversal of learning and memory impairments following lesion of the nucleus basalis magnocellularis (NBM) by concurrent noradrenergic depletion using DSP4 in the rat

In the following study the behavioural effects of simultaneous lesion of the nucleus basalis magnocellularis (NBM) using ibotenic acid and noradrenergic depletion following a single i.p. administration of DSP4 (50 mg/kg) were examined in the rat. NBM lesion induced a deficit in acquisition of a reinforced T-maze alternation task, a working memory adaptation of a spatial navigation task in a water maze and 24 h retention in a passive avoidance task compared to sham controls. No effect of the lesion on a reference memory version of spatial navigation in a water maze task was found. Animals that received a combination of NBM lesion and DSP4 treatment showed no impairment on any of the tasks that were impaired by NBM lesion alone. This indicates a reversal of the learning and memory deficits consequent to NBM lesion by simultaneous noradrenergic depletion. NBM lesion induced a significant reduction in choline-acetyltransferase activity in the frontal cortex, and DSP4 induced a significant decrease in noradrenaline concentration in occipital cortex and hippocampus, confirming the effects of these treatments. These results suggest an interaction between central noradrenergic and cholinergic systems in learning and memory processes.

Dopamine functions in appetitive and defensive behaviours

The data reviewed here are compatible with the hypothesis that telencephalic dopamine activity is elicited by motivationally significant stimuli which in turn creates a neural state in which animals are more prepared to respond to significant stimuli in the environment. This analysis may be viewed as extensions of both the sensorimotor hypothesis, which depicts dopamine as potentiating the ability of stimuli to elicit responses (Clody and Carlton, 1980; Marshall et al., 1974; White, 1986) and of the incentive motivational hypothesis, which emphasizes the importance of dopamine in responding to stimuli that serve as signals of biologically significant events (Blackburn et al., 1989a; Crow, 1973; Mogenson and Phillips, 1976). In addition, we have sought to emphasize that not all responses are equally dependent upon the integrity of forebrain dopamine activity. Some responses, such as ingestion of standard foods by hungry animals, copulation, and escape, are relatively impervious to dopamine disruption. Further, once other behaviours, such as avoidance or appetitive operant responses, have been acquired, they can be maintained at an initially high rate despite perturbation of dopamine systems, although performance deteriorates with repeated testing. This analysis has emerged from the joint consideration of how both appetitive and defensive behaviours are influenced by dopamine antagonists, along with an examination of dopamine release during sequences of behaviour. The data reviewed suggest that dopamine is involved in fundamental psychological processes through which environmental stimuli come to exert control over certain aspects of behaviour. In the future, as knowledge in this field advances, there will have to be an integration of the literature on dopamine and motivation with the literature on dopamine and motor systems. We expect that dopamine release will be seen as a mechanism by which important environmental cues, of innate or learned significance, lead to a general enhancement of motor skeletal responses directed towards distal cues. We conclude with a caveat: Caution must be exercised when attempting to infer a general role of any neurotransmitter in motivated behaviour based on the study of a limited number of motivational systems. Although neurotransmitter pathways may figure prominently in the control of certain behaviours, it is incorrect to think of neurotransmitters as having a single role in behaviour. However, when comparative analyses reveal a common thread among different motivational systems, as is becoming apparent for the general role of mesotelencephalic dopamine pathways in behaviour, then the goal of generating coherent and comprehensive theory concerning a neurotransmitter's function in behaviour will begin to be realised.(ABSTRACT TRUNCATED AT 400 WORDS)

A general role for serotonin in the control of behavior: studies with intracerebral 5,7-dihydroxytryptamine

Multiple injections of 5,7-dihydroxytryptamine (5,7-DHT) into the rat brainstem reduced forebrain levels of serotonin and 5-hydroxyindoleacetic acid to 3-10% of the levels observed in control rats that had received intrabrainstem injection of a Locke's solution vehicle. This treatment reduced or abolished atropine-resistant cerebral activation (ARCA) in most cases. In rats in which ARCA was impaired or lost, a number of behavioral abnormalities were observed. These included: high levels of locomotion in an open field test; a deficiency in swimming to, and climbing upon, a visible platform in a water-filled tank; deficient social behavior; and impaired performance in a simple test of active avoidance. These deficits were not due to low level motor impairment. The 5,7-DHT-treated rats displayed a circadian rhythm of activity in running wheels. It is proposed that ascending serotonergic projections are an important component in the cerebral control of the Type 1 behavior with which the occurrence of ARCA is closely linked. Since Type 1 behavior includes such motor patterns as walking and manipulation of objects with the limbs, which are essential components of a great variety of behavioral performances, it is to be expected that a loss of ascending serotonergic function will result in a generalized deficit in behavior.

Effects of cerebral depletion of norepinephrine on conditioned avoidance responding in Sprague-Dawley and Fischer rats

Block of conditioned avoidance responding (CAR) in the rat is a property of all antipsychotic agents. To determine whether cerebral norepinephrine (NE) is crucial for CAR, the effect of depletion of cerebral NE was examined both during acquisition and retention of a CAR task in Sprague-Dawley and Fischer 344 male rats. In examining acquisition of CAR, DSP-4 [N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine] (50 mg/kg, IP) was given to naive rats from each strain. In one control group, desmethylimipramine (DMI, 20 mg/kg, IP -30 min), which inhibits the uptake of DSP-4 and its subsequent neurotoxic effect, was given prior to DSP-4. After DSP-4, all animals were tested for acquisition of CAR in a discrete trial paradigm in striatum, and brain stem were removed for NE and dopamine assay using HPLC. In examining retention of CAR, the effect of DSP-4 on the CAR of trained rats were observed. DSP-4 produced an almost total depletion of cortical NE and about 50% reduction of NE in the brain stem in both strains and in both tests. In the first experiment, DSP-4 failed to significantly diminish CAR acquisition in either strain, although there was a trend towards a DSP-4-induced deficit. Interestingly, DSP-4 caused no decrement in CAR in trained rats of either strain, but did significantly impair further acquisition of CAR in Sprague-Dawley rats. The data demonstrate cerebral NE is not critical for retention of CAR, but suggest a possible role for NE in the acquisition of CAR.

Action of a chronic administration of mescaline in dynamic behavioural situations

The modifications of the rat behaviour caused by a chronic administration of mescaline were studied in two schedules of operant conditioning. In the "periodic conditioning" test, the schedule of reinforcement was changed from a fixed ratio to a fixed interval schedule. Mescaline (4 mg/kg/day and 10 mg/kg/day) caused no modification of the ability of the rat to adapt its behaviour to the new experimental situation. In the "reversal test" the contingency for food delivery was switched from one lever, where responses were previously reinforced to the other lever where responses had no programmed consequences. A chronic administration of mescaline (4 mg/kg/day) caused a total incapacity of the rat to switch to the lever which became reinforced in the reversal trial. A chronic administration of 9 mg/kg/day of mescaline had an excitatory effect and the number of reinforced responses in the II and III reversals exceeded the unreinforced responses in a measure greater than in the controls.

Dopamine-receptor agonists: mechanisms underlying autoreceptor selectivity. I. Review of the evidence

The behavioural, biochemical, neuroendocrinological and electrophysiological actions of the enantiomers of the dopamine (DA) analogue 3-(3-hydroxyphenyl)-N-n-propylpiperidine, 3-PPP, are extensively reviewed. (+)-3-PPP acts in a fashion similar to classical direct-acting DA agonists, stimulating both DA autoreceptors and postsynaptic DA receptors, although in some situations the drug appears to exhibit partial agonist activity. (-)-3-PPP exerts a variety of actions in different pharmacological models. Either agonistic, antagonistic or both agonistic and antagonistic activity are observed depending on the anatomical location of the relevant DA receptors and the experimental conditions. The actions of transdihydrolisuride (TDHL) and the trans-fused 7-OH-1,2,3,4,4a,5,6,10b-octahydrobenzo(f)quinoline (HW 165) are also discussed. These agents possess a similar spectrum of action to (-)-3-PPP suggesting a new generation of DA agonists which exhibit variable intrinsic activity at different DA receptors. Finally, evidence is presented indicating that the 3-PPP enantiomers display selectivity for DA receptors.

Central depressant action of cesium in mice

Cesium chloride (CsCl) at several dose levels (1.25-20.0 mEq/kg IP) was administered acutely to albino mice whose behavior was compared with that in corresponding saline controls. Motor activity decreased and Straub tail occurred in a dose-related manner. Signs of autonomic disturbance, diarrhea, and salivation were seen with toxic doses. Subchronic administration of CsCl (5.0 mEq/kg/day IP for 7 days) exerted a phenothiazine-like effect in mice, reducing amphetamine-induced aggregation toxicity and enhancing pentobarbital-induced hypnosis. The antinociceptive action of morphine was unaltered by identical multiple administrations of CsCl. These results indicate a specific neurosuppressant action of CsCl on mouse CNS and suggest exploration of this alkali earth metal for antipsychotic-like activity.

Abolition of conditioned heart-rate responses in rabbits following central administration of [N-MePhe3, D-Pro4] morphiceptin

Rabbits were initially habituated to a tone and then give 15-20 paired trials where the tone was followed by periorbital shock resulting in conditioned heart-rate decelerations to tone onset and an acceleration of heart-rate following shock offset. The animals were matched for learning performance and divided into two groups. Each animal received a microinfusion into the region of the fourth ventricle of either the opiate [N-MePhe3,D-Pro4] morphiceptin, a highly selective mu receptor agonist, or a mixture of the morphiceptin analogue and the opiate antagonist naltrexone. Administration of the morphiceptin analogue eliminated the conditioned bradycardia to the tone but not the acceleration to the shock. Rabbits given the mixture continued to show conditioned heart-rate decelerations. Previous studies have shown that opiates abolish a recently learned conditioned nictitating membrane response. These effects are consistent with the hypothesis that the opiate effect on conditioning is due to an attenuation of conditioned fear.

The effect of the enantiomers of 3-PPP on conditioned avoidance responding in the rat

The effects of the enantiomers of 3-PPP on the maintenance of conditioned avoidance responding (CAR) were studied. The weak classical dopamine (DA) agonist (+)-3-PPP failed to interfere with CAR at any dose tested (0.8-13.6 mg/kg). Low doses of the drug produced sedation, while high doses produced behavioural stimulation. (-)-3-PPP, which acts as an antagonist on postsynaptic and as an agonist on autoreceptor DA sites, reduced avoidance with no effect on escape behaviour (6.8-13.6 mg/kg). However, this reduction of CAR occurred at doses much higher than those previously demonstrated to inhibit locomotor activity. This profile is discussed in relation to the behavioural effects of classical postsynaptic DA receptor antagonists.

A screening method for substances potentially active on learning and memory

A series of substances from different pharmacological classes was examined by two different tests for their activity on learning and memory. A concomitant evaluation was performed by use of a one-trial passive avoidance immediately followed by electroshock in mice and the pole-climbing test in rats. Only doses not producing changes in gross behavior (Irwin's test) were used. A facilitating action on all the considered parameters was observed for d-amphetamine, caffeine, L-glutamine, Mg pemoline, phosphorylserine, piracetam, strychnine, and tricyanoaminopropene. A worsening action was found for atropine, cycloheximide, diazepam, and morphine. Chlorpheniramine, diphenylhydantoin, GABA, imipramine, meclizine, mescaline, metrazol, and testosterone showed no or doubtful activity. Our results suggest that the parallel use of these relatively simple tests supplies information that is satisfactory for screening purposes and that has a high degree of predictability as substantiated by literature data.

Correlation between antiavoidance activities of antipsychotic drugs in rats and daily clinical doses

Effects of oral antipsychotic drugs, 12 phenothiazines, 3 thioxanthenes, 5 butyrophenones and 8 other derivatives on Sidman and discriminated avoidance responses in rats were investigated and compared to their clinical doses routinely used PO. Almost all drugs except sulpiride and clozapine suppressed the avoidance responses with a dose-dependent decrease in the response rate (lever-pressing) and increase in the shock rate in the Sidman avoidance performance or a decrease in both the response and avoidance rates in the discriminated one. Sulpiride (80-640 mg/kg) produced no marked change in the avoidance responses. Clozapine (2.5-10 mg/kg) increased the shock rate or decreased the avoidance rate without eliciting any change in the response rate. The avoidance-suppressing activities of the antipsychotic drugs were well correlated with their clinical daily doses. However, the avoidance-suppressing effects of carpipramine, clocapramine, thiothixene and sulpiride were relatively less potent, while that of clotiapine was more potent than in the clinical activities. The potencies of the avoidance-suppressing effects of each drug on the Sidman and the discriminated avoidance responses were almost identical except for triflupromazine, pimozide, thioridazine, spiclomazine and propericiazine. The former two drugs suppressed the Sidman avoidance response more than the discriminated avoidance response. However, the latter three drugs suppressed the discriminated avoidance response more markedly than the Sidman avoidance response. The present results suggest that the avoidance response in rats is applicable in evaluating the clinical efficacies of antipsychotic drugs.

Psychotropic drugs and Sidman avoidance in rats: IRT distribution changes

The effects of d-amphetamine, caffeine, chlorpromazine, diazepam and and pentobarbital on Sidman avoidance responding (R-S interval, 30 sec; S-S interval, 3 sec) in rats, especially on the interresponse time (IRT) distribution, were studied. d-Amphetamine and caffeine increased the total number of responses. Short IRTs were increased, while longer ones were decreased. Chlorpromazine, diazepam and pentobarbital all increased the number of shocks delivered. After chlorpromazine, no marked change was observed in the total number of responses. However, response bursts and escape reponses increased, while IRTs between 3 and 30 sec decreased. After diazepam and pentobarbital, the burst response scarcely increased, and the IRTs in the 3-15 sec range decreased, while the IRTs longer than 33 sec increased. These changes were more marked after diazepam than after pentobarbital. Total number of responses was decreased by both drugs. The present results suggest that in utilizing the Sidman avoidance procedure for psychotropic drug assessment, changes in the IRT distribution give a more precise profile of the drug than is afforded by the total number of responses and shocks delivered.

Effects of chronic ingestion and withdrawal of sodium barbitone on learning in rats

Rats were submitted to three different manipulations: chronic ingestion of sodium barbitone, which was added to the drinking water; chronic administration of barbitone and subsequent withdrawal of the drug; and drinking water only. Both groups of experimental animals showed deficient acquisition in both shuttle-box avoidance and passive-avoidance response when compared to the control animals. Nevertheless, no impairment was observed in passive avoidance when the period of withdrawal was 15 days. Neither was impairment observed when the animals were tested in a T-maze or in another appetitive task. These results cannot be explained by differences in weight or fluid consumption.

Schizophrenic psychology, associative learning and the role of forebrain dopamine

It is suggested that schizophrenic thinking can be explained as a lowering of levels of significance for acceptance of conclusions based on inductive logic. The formal similarity between inductive logic and operant, or classical conditioning is pointed out. It is thus possible to explain the therapeutic effects of neuroleptic drugs by referring to the effect of these, and related drugs, and of lesions of ascending dopamine pathways, on acquisition of conditioned responses. It is tentatively suggested that recognition of association of related features of the environment, whether in humans or animals occurs in the basal ganglia by a dopamine dependent process. A role is suggested for neocortical noradrenaline in consolidaton of newly acquired associations. Implications and tests of this hypothesis are discussed.

Decreased intracranial self-stimulation after neuroleptics or 6-hydroxydopamine: evidence for mediation by motor deficits rather than by reduced reward

Rats were implanted with electrodes in the lateral hypothalamus, put on a 22-h food deprivation schedule and trained to bar-press for ICS and for food on a CRF schedule. Haloperidol (0.08 mg/kg) and pimozide (0.22 mg/kg) significantly decreased responding for both reinforces, although responding for ICS was decreased more than it was for food. The same doses of these drugs did not decrease food consumption of a 15-min ad libitum test after 22-h of food deprivation, suggesting that the decreased bar-pressing for food was not the result of anorexia or reduced motivation for food. When similar rates of responding for ICS and for food were obtained on a V1 60 schedule, haloperidol (0.1 mg/kg) reduced responding for food and ICS to a similar extent. Thus, when baseline rate is controlled for, neuroleptics do not selectively reduce responding for ICS. In addition, examination of cumulative response records revealed that rather than producing an extinction curve, as would be predicted if neuroleptics reduced the rewarding properties of ICS, haloperidol produced a uniform decrease in the rate of responding throughout the experimental session. Similar results were obtained with intraventricular 6-hydroxydopamine (6-OHDA) injections. While these experiments do not exclude the possibility that dopaminergic (DA) systems participate in some central reinforcement mechanisms, they suggest that neuroleptics and 6-OHDA decrease responding for food or ICS primarily by impairing the function of DA systems critically involved in the initiation or maintenance of operant behaviour rather than by interfering with reward.

Discriminated escape learning and response to electric shock after 6-hydroxydopamine lesions of the nigro-neostriatal dopaminergic projection

In an earlier report it was observed that bilateral stereotaxic injections of 6-hydroxydopamine (6-OHDA) into the zone compacta of the substantia nigra deficits in the acquisition of a conditioned avoidance response [8], The present experiments were designed to determine if either a generalized learning impairment or a decreased sensitivity to foot shock might be the basis for the avoidance deficit. It was found that rats subjected to bilateral 6-OHDA lesions of the substantia nigra learned a light discrimination shock escape habit in as few trials as unoperated controls. This observation indicates that the integrity of the dopaminergic nigro-neostriatal system is not essential for the formation of learned associations between sensory cues and motor responses. In a second experiment it was observed that neither the shock-induced flinch nor the jump threshold was elevated after nigral lesions, suggesting that these lesions do not decrease the aversive motivational properties of foot shock. In view of these findings, the nature of the avoidance deficit produced by substantia nigra lesions is discussed with reference to the possibility that they selectively block the initiation of voluntary motor responses. According to this hypothesis, the failure of these lesions to disrupt escape responding may be due to the fact that the unconditioned stimulus generates reflexive motor responses (flinch, jump, etc.) which are sufficient to begin the motor sequences that cannot be initiated voluntarily in response to the conditioned stimulus.

Haloperidol-induced disruption of conditioned avoidance responding: attenuation by prior training or by anticholinergic drugs

Rats injected daily with haloperidol (0.15 mg/kg) failed to acquire a one-way avoidance response over a 9 day period (10 trails/day). When these animals were subsequently tested without haloperidol, on the first drug-free day they preformed as well as animals given saline throughout the training period and significantly better than naive saline-treated animals on the first day of training. The performance of rats which were trained for two days before receiving haloperidol was only partly blocked by the drug, while animals trained for 9 days before drug administration were immune to the disruptive effects. Three anticholinergic (muscarinic) drugs, atropine (10 mg/kg), scopolamine (1 mg/kg) and benztropine (2 mg/kg) significantly reversed the effect of haloperidol on the acquisition of the nigroneostriatal projection and support the view that this system is critically involved in the acquistion of learned instrumental responses. The nature of the avoidance deficit produced by these treatments is discussed with reference to the possibility that they selectively block the initiation of boluntary motor responses. According to this hypothesis, the failure of these teratments to disrupt escape responding may be due to the fact that the unconditioned stimulus generates reflexive motor responses (flinch, jump, etc.) which are sufficient to begin the motoric sequences that cannot be initiated voluntarily in response to the conditioned stimulus.

Pharmacological properties of centrally-administered agents which interfere with neurotransmitter function: a comparison with the central depressant effects of ouabain

1. Centrally administered sodium diethyldithiocarbamate (DDC) produced hypothermia, central nervous depression and potentiation of the antinociceptive effect of morphine. These effects resemble those seen with centrally administered ouabain. Furthermore, the interactions of (+)-amphetamine, desmethylimipramine and nialamide with DDC and ouabain were similar.2. 6-Hydroxydopamine by the same route also produced central nervous depressant effects including hypothermia, decreased locomotor activity and catalepsy but not ptosis.3. Both ouabain and chlorpromazine produced similar effects on behaviour and body temperature including selective abolition of a conditioned avoidance response.4. Although centrally administered tetrabenazine produced ptosis, decreased locomotor activity and catalepsy, it had no significant effect on body temperature. However, the hypothermia produced by peripherally administered reserpine was reversed by centrally administered dibutyryl cyclic 3',5'-adenosine monophosphate.5. Centrally administered cocaine and desmethylimipramine produced no depressant effects but an increased excitability and responsiveness were apparent in both cases.6. Although the observed behavioural depression and hypothermia can occur independently both seem to involve an interference with dopaminergic systems.