Long-lasting sensitization to the accelerating effects of amphetamine on the speed of an internal clock

Effect of alcohol on the sense of agency in healthy humans

Even at low to moderate doses, ingestion of the widely used recreational drug alcohol (ethanol) can impact cognitive and emotional processing. Recent studies show that the sense of agency (SoA; ie, the subjective experience of voluntary control over actions) can be modulated by specific pharmacological manipulations. The SoA, as quantified by the intentional binding (IB) paradigm, is enhanced by direct or indirect dopaminergic agonists in patients with Parkinson's disease and by ketamine (an N-methyl-D-aspartate (NMDA) receptor antagonist) in healthy individuals. These findings implicate dopaminergic and glutamatergic neurotransmission in mechanisms underlying SoA. Alcohol has a complex set of actions, including disinhibition of dopaminergic neurotransmission and allosteric antagonism at NMDA receptors. Here, we tested the hypothesis that low to moderate doses of alcohol would enhance SoA, and impact impulsivity and subjective emotional state. We conducted two experiments in 59 healthy male and female social drinkers, who ingested either a placebo "vehicle," or one of two doses of ethanol: 0.4 and 0.6 g/kg. In both experiments, we observed increased SoA/IB at both doses of alcohol exposure, relative to the placebo condition. We found no correlation between the effects of alcohol on IB and on impulsivity or subjective emotional state. Our findings might have implications for social and legal responsibility related to alcohol use, particularly in states prior to overt intoxication. Further studies are necessary to investigate the effects of alcohol and other addictive substances on the SoA.

Interval Timing, Dopamine, and Motivation

The dopamine clock hypothesis suggests that the dopamine level determines the speed of the hypothetical internal clock. However, dopaminergic function has also been implicated for motivation and thus the effect of dopaminergic manipulations on timing behavior might also be independently mediated by altered motivational state. Studies that investigated the effect of motivational manipulations on peak responding are reviewed in this paper. The majority of these studies show that a higher reward magnitude leads to a leftward shift, whereas reward devaluation leads to a rightward shift in the initiation of timed anticipatory behavior, typically in the absence of an effect on the timing of response termination. Similar behavioral effects are also present in a number of studies that investigated the effect of dopamine agonists and dopamine-related genetic factors on peak responding. These results can be readily accounted for by independent modulation of decision-thresholds for the initiation and termination of timed responding.

Increased drinking after intra-striatal injection of the dopamine D2/D3 receptor agonist quinpirole in the rat

RATIONALE

Dopamine D2 receptor hyperactivity has been implicated in the development of psychogenic polydipsia in schizophrenic patients. Repeated treatment with dopamine agonists, including the D2/D3 agonist quinpirole, has been shown to induce hyperdipsia in a number of animal models. Despite these observations, obtained with systemic administrations, little attempt has been made to investigate where in the brain dopamine agonists act to induce hyperdipsia.

OBJECTIVE

The present study investigates the effects of repeated intra-caudate infusions of quinpirole on the intake of water by rats tested under free-drinking conditions.

MATERIALS AND METHODS

Rats with bilateral cannulae placed into the anterior, central or posterior caudate received quinpirole microinfusions (1 μg/side) for five consecutive days in their home cage. Water intake was measured 15 and 60 min after the treatment.

RESULTS

When injected in the central caudate, quinpirole increased water intake, and this effect progressively increased over sessions, indicating the development of sensitization. When injected in the posterior caudate, the dipsogenic effect of quinpirole was less intense and did not undergo sensitization. The infusion of quinpirole in the anterior caudate did not affect drinking.

CONCLUSION

The present study shows that caudate D2/3 receptors play an important role in the development of quinpirole-induced hyperdipsia, an animal model of psychotic polydipsia.

Compulsive-like effects of repeated administration of quinpirole on drinking behavior in rats

We have previously reported that repeated administrations of quinpirole, a D2/D3 dopamine receptor agonist, facilitate instrumental behavior in rats given the choice between operant and free access to water (contrafreeloading: CFL). The goal of the present study was to investigate the effects of repeated daily administrations of quinpirole (0.5 mg/kg i.p.) on the appetitive versus the consummatory component of water-reinforced behavior, under two experimental conditions. Under one condition, the rats were given access to tap water according to an FR3 schedule of reinforcement. Under the second condition, the rats were given the choice between operant and free access to water. Five major findings were obtained. First, acutely quinpirole suppressed operant behavior and, therefore, water intake for at least 1h. Second, upon repeated administrations tolerance developed to the suppressant effect of quinpirole on instrumental behavior but only to a lesser extent to the antidipsic effect, dissociating the appetitive from the consummatory components of water-reinforced behavior. Third, in CFL conditions quinpirole induced a progressively larger preference for the operant access. Fourth, even when the rats were given the choice between free access to highly palatable saccharine (0.05 or 0.01%) solutions and operant access to tap water, quinpirole shifted the animals towards the operant access. Fifth, repeated quinpirole produced lasting consequences on drinking behavior, since after rehydration and under drug-free conditions quinpirole-pretreated rats ingested larger amounts of water than control rats. In conclusion, the repeated activation of D2/D3 receptors appears to induce the rats to perseverate in performing needless instrumental behavior.

Dopamine D1 activation shortens the duration of phases in stereotyped grooming sequences

Rats frequently emit grooming actions in a highly stereotyped, syntactic chain in which three distinct phases of facially directed forearm movements are sequentially emitted in a rule-governed pattern and followed by body-directed licking. The present study evaluated the effects of the full dopamine D1 agonist, SKF 81297, and the partial dopamine D1 agonist, SKF 38393, on the duration of individual phases of stereotyped grooming chains. We found that systemic administration of SKF 81297 significantly shortened grooming chain duration. An examination of the fine temporal structure of syntactic grooming chain actions showed that duration changes were correlated with decreased numbers of actions in phases I and IV of the chain. Phases II and III were not changed in duration, although there were some structural distortions introduced. The partial D1 agonist, SKF 38393, had no effect on duration or number of component actions in the grooming chain. Based on these results, we hypothesize that the timing of syntactic grooming phase transitions may involve a D1-mediated internal clock process that is altered by full D1 agonist activation. By this model, SKF 81297 increases the speed of the clock used for the temporal control of grooming actions, and thus shortens phase durations.

A time contraction effect of acute tail-pinch stress on the associative learning of rats

The effect of tail-pinch stress interpolated between the saccharin conditioned stimulus (CS) and the illness-inducing unconditioned stimulus (US) during long-trace taste-aversion conditioning was examined in young- and old adult rats with a two-cylinder (saccharin versus water) test. A 2 x 2 x 4 factorial ANOVA was performed on percent-preference-for-saccharin data, with age (young, old), stress condition (stressed, non-stressed), and CS-US interval (22.5-, 45-, 90-, and 180-min) being the factors under consideration. The ANOVA yielded only significant main effects of stress condition and CS-US interval. These findings indicate that stress weakens the CS-US association as evidenced by a higher percent preference for saccharin in the stressed rats than in non-stressed rats at all CS-US intervals. A comparison of the stressed and non-stressed conditioned rats with pseudo-conditioned controls showed that the non-stressed rats formed strong aversions up to the 45-min CS-US interval whereas the stressed rats showed no conditioning beyond the 22.5 min CS-US interval, indicating that stress decreases the effective CS-US interval. Results were interpreted in terms of time-contraction and an internal biological countdown timer hypothesized to govern processes involved in associative learning over long delays.

Differential Modulation of Clock Speed by the Administration of Intermittent Versus Continuous Cocaine

The roles that psychostimulant sensitization and tolerance play in temporal perception in the seconds-to-minutes range were assessed in rats. Cocaine (20 mg/kg/day) was administered for 2 weeks either intermittently via daily injections (induces sensitization) or continuously via an osmotic minipump (induces tolerance). Interval timing was evaluated throughout administration and withdrawal. Injections of cocaine caused immediate, proportional, leftward shifts in peak times, indicating an increase in the speed of an internal clock. These shifts grew progressively larger with repeated administration, indicating that stimulant-induced increases in clock speed can be sensitized. Continuous cocaine administration produced no reliable effects. These results suggest that the mechanisms of sensitization may play a considerable role in drug-induced alterations of the perception of time.

Tolerance to amphetamine hypophagia: a microstructural analysis of licking behavior in the rat

The development of tolerance to amphetamine-induced hypophagia was assessed by recording changes in lick parameters in rats given chronic administration of the drug (2 mg/kg) and access to sweetened milk. Although licking and milk intake gradually recovered, the volume of milk ingested per lick remained suppressed. Amphetamine had no effect on the interlick interval or the force per lick. In contrast, the drug caused a sustained increase in the number of lick bursts (defined by pause criteria of 0.5-2.0 s) and a decrease in the number of licks per burst (but only at pause criteria of 0.5 and 1.0 s). These results suggest that tolerant rats frequently interrupt licking, resulting in less efficient capture of milk.

Dissociation in the effects of the D2/D3 dopaminergic agonist quinpirole on drinking and on vasopressin levels in the rat

In the present study, we investigated the role of vasopressin in the development of quinpirole-induced hyperdipsia in the rat. We report that: (1), an acute intraperitoneal (i.p.) injection of 0.56 mg/kg of quinpirole increased plasma vasopressin (radioimmunoassay) at 15 min but not at 30 or 120 min; (2), nine daily injections of quinpirole (0.56 mg/kg, i.p.) progressively increased water intake and diuresis for a period of several hours after each treatment; (3), quinpirole hyperdipsia was associated with apparently normal levels of vasopressin (which might be considered inappropriately high in the presence of excessive drinking); (4), quinpirole reduced vasopressin and oxytocin, but not angiotensin, immunoreactivity in the supraoptic nucleus. These findings suggest that quinpirole hyperdipsia is a sound animal model of psychotic polydipsia.

Quinpirole- and amphetamine-induced hyperdipsia: influence of fluid palatability and behavioral cost

Daily administration of moderate doses of amphetamine or of the dopaminergic D2 agonist quinpirole is associated with the development of excessive, non-regulatory drinking. Here we compared the influence of manipulating fluid palatability and behavioral cost on the development of this drinking augmentation. Experiment 1 was based on the phenomenon of contrafreeloading (CFL): animals work for a resource even though the same resource is freely available. The effects of 15 daily injections of amphetamine (1.0 and 1.7 mg/kg i.p. ) or quinpirole (0.1 and 0.56 mg/kg i.p.) were evaluated in mildly water-deprived rats. For the first 6 days the rats obtained water by lever pressing (FR3) only; over the following 9 days water was also freely available (CFL). Initially, 0.56 mg/kg quinpirole reduced lever pressing for water. A complete recover of responding was then obtained, and was followed by a progressive increment in the amount water obtained by lever pressing during the CFL phase (from 10 to 50%). Amphetamine did not affect percent CFL, but at the highest dose (1.7 mg/kg) reduced total water intake during the last 3 days of treatment. In experiment 2 the rats had free access to two bottles, one of which contained tap water, and the other contained either an ethanol (6%) or a sucrose (5%) solution. After habituation to this regimen, the rats received 10 daily i.p. injections of vehicle, amphetamine (1.0 or 3 mg/kg), or quinpirole (0.1 or 0.56 mg/kg). Quinpirole 0.56 mg/kg enhanced daily fluid intake under both sucrose and ethanol conditions, but selectively reduced ethanol preference. The higher amphetamine dose reduced fluid intake and sucrose preference. In conclusion, chronic exposure to a dopaminergic D2 agonist, but not to amphetamine, produced an increment of drinking that was resistant to manipulation of either palatability or the behavioral cost of the fluid.