Habit formation and the loss of control of an internal clock: inverse relationship between the level of baseline training and the clock-speed enhancing effects of methamphetamine

Prenatal choline supplementation alters the timing, emotion, and memory performance (TEMP) of adult male and female rats as indexed by differential reinforcement of low-rate schedule behavior

Choline availability in the maternal diet has a lasting effect on brain and behavior of the offspring. To further delineate the impact of early nutritional status, we examined effects of prenatal-choline supplementation on timing, emotion, and memory performance of adult male and female rats. Rats that were given sufficient choline (CON: 1.1 g/kg) or supplemental choline (SUP: 5.0 g/kg) during embryonic days (ED) 12-17 were trained with a differential reinforcement of low-rate (DRL) schedule that was gradually transitioned through 5-, 10-, 18-, 36-, and 72-sec criterion times. We observed that SUP-females emitted more reinforced responses than CON-females, which were more efficient than both groups of males. In addition, SUP-males and SUP-females exhibited a reduction in burst responding (response latencies <2 sec) compared with both groups of CON rats. Furthermore, despite a reduced level of burst responding, the SUP-males made more nonreinforced responses prior to the DRL criterion as a result of maintaining the previous DRL criterion following transition to a new criterion. In summary, long-lasting effects of prenatal-choline supplementation were exhibited by reduced frustrative DRL responding in conjunction with the persistence of temporal memory in SUP-males and enhanced temporal exploration and response efficiency in SUP-females.

Acute ethanol potentiates the clock-speed enhancing effects of nicotine on timing and temporal memory

BACKGROUND

Acute ethanol administration potentiates some of the behavioral effects of nicotine, although the extent of this effect is unknown. The present investigation assessed the ability of ethanol to potentiate nicotine's effect on the overestimation of multisecond durations as a result of an increase in the speed of an internal clock.

METHODS

Adult male rats were exposed to the acute effects of ethanol (0.0, 0.5, 1.5, and 3.0 g/kg; IG) which was given 10 minutes prior to the administration of nicotine (0.0, 0.3, 0.6, and 1.0 mg/kg; IP). The effects of these combined treatments on timing and temporal memory were assessed using 18- and 36-second peak-interval procedures with separate visual/spatial cues for responding.

RESULTS

When administered alone, ethanol had no consistent effect on peak time, but decreased peak rate, and increased peak spread as a function of dose. In contrast, nicotine alone shifted the peak times of the response distributions leftward in a proportional manner as a function of dose. When administered after pretreatment with ethanol, nicotine's effect on the horizontal placement of the peak functions was potentiated.

CONCLUSIONS

The observation that ethanol pretreatment potentiates the clock-speed enhancing effects of subsequently administered nicotine is discussed in terms of the role of alpha7-nicotinic acetylcholine receptors and dopamine-glutamate interactions in cortico-striatal circuits thought to subserve interval timing.

Evidence for the sensitivity of operant timing behaviour to stimulation of D1 dopamine receptors

RATIONALE

Temporal differentiation of operant behaviour is sensitive to dopaminergic manipulations. Previous studies using the fixed-interval peak procedure implicated D(2)-like dopamine receptors in these effects. However, recent findings suggest that d-amphetamine alters timing performance on the free-operant psychophysical procedure via D(1)-like receptors. It is not known whether this effect of d-amphetamine is mimicked by direct D(1)-like receptor stimulation.

OBJECTIVE

The effects of a D(1)-like receptor agonist 6-chloro-2,3,4,5-tetrahydro-1-phenyl-1H-3-benzazepine (SKF-81297) on performance on the free-operant psychophysical procedure and the interaction between SKF-81297 and a D(1)-like receptor antagonist 8-bromo-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepin-7-ol (SKF-83566) and a D(2)-like receptor antagonist haloperidol, were examined.

MATERIALS AND METHODS

Rats were trained to respond on two levers (A and B) under a free-operant psychophysical schedule, in which sucrose reinforcement was provided intermittently for responding on A during the first half and on B during the second half of 50-s trials. Logistic psychometric functions were fitted to the relative response rate data (percent responding on B [%B] vs time from trial onset [t]) under each treatment condition, and quantitative indices of timing (T(50) [value of t corresponding to %B = 50] and the Weber fraction [(T(75)-T(25))/2T(50); T(25) and T(75) are values of t corresponding to %B = 25 and %B = 75] were compared among treatments.

RESULTS

SKF-81297 (0.8 mg kg(-1)) reduced T(50); this effect was antagonized by SKF-83566 (0.03 mg kg(-1)) but not by haloperidol (0.05, 0.1 mg kg(-1)).

CONCLUSIONS

Stimulation of D(1)-like dopamine receptors affects performance in the free-operant psychophysical procedure.

Prenatal choline supplementation increases sensitivity to time by reducing non-scalar sources of variance in adult temporal processing

Choline supplementation of the maternal diet has a long-term facilitative effect on timing and temporal memory of the offspring. To further delineate the impact of early nutritional status on interval timing, we examined effects of prenatal choline supplementation on the temporal sensitivity of adult (6 months) male rats. Rats that were given sufficient choline in their chow (CON: 1.1 g/kg) or supplemental choline added to their drinking water (SUP: 3.5 g/kg) during embryonic days (ED) 12-17 were trained with a peak-interval procedure that was shifted among 75%, 50%, and 25% probabilities of reinforcement with transitions from 18 s-->36 s-->72 s temporal criteria. Prenatal choline supplementation systematically sharpened interval timing functions by reducing the associative/non-temporal response enhancing effects of reinforcement probability on the Start response threshold, thereby reducing non-scalar sources of variance in the left-hand portion of the Gaussian-shaped response functions. No effect was observed for the Stop response threshold as a function of any of these manipulations. In addition, independence of peak time and peak rate was demonstrated as a function of reinforcement probability for both prenatal choline-supplemented and control rats. Overall, these results suggest that prenatal choline supplementation facilitates timing by reducing impulsive responding early in the interval, thereby improving the superimposition of peak functions for different temporal criteria.

Impairments in timing, temporal memory, and reversal learning linked to neurotoxic regimens of methamphetamine intoxication

Methamphetamine intoxication has long-term consequences on dopaminergic function and corticostriatal-mediated behaviors in humans and other animals. In order to determine the potential impact on timing and temporal memory, we examined methamphetamine dose regimens that have been linked to neurotoxicity in adult (8 months) male rats. Rats that were given repetitive, high-dose methamphetamine (3.0 mg/kg ip x 4 injections/2 h) or saline injections were trained on a 2-s vs 8-s bisection procedure using auditory and visual signal durations. Following the high-dose regimen, baseline timing performance was reestablished prior to the rats' receiving reversal training in which the spatial/temporal mapping of the anchor durations (2 s and 8 s) to response options (left or right lever) was reversed. Low-dose methamphetamine (0.5 mg/kg ip) or saline injections were subsequently used to evaluate the effectiveness of the neurotoxic doses in terms of modifying the horizontal leftward shifts associated with increases in clock speed. Overall, the results indicate that MAP intoxication leads to reduced auditory/visual differences in clock speed, deficits in reversal learning, distortions in temporal memory, and lowered dopaminergic regulation of clock speed consistent with damage to prefrontal cortex and corticostriatal circuitry.

Ketamine “unlocks” the reduced clock-speed effects of cocaine following extended training: Evidence for dopamine–glutamate interactions in timing and time perception

The present study examined the clock-speed modulating effects of acute cocaine administration in groups of male rats that received different amounts of baseline training on a 36-s peak-interval procedure prior to initial drug injection. After injection of cocaine (10, 15, or 20mg/kg, ip), rats that had received a minimal amount of training (e.g., <or=30 sessions) prior to drug administration displayed a horizontal leftward shift in their timing functions indicating that the speed of the internal clock was increased. In contrast, rats that had received an extended amount of training (e.g., >or=180 sessions) prior to cocaine (15 mg/kg, ip) administration did not produce this "classic" curve-shift effect, but instead displayed a general disruption of temporal control following drug administration. Importantly, when co-administered with a behaviorally ineffective dose of ketamine (10mg/kg, ip) the ability of cocaine to modulate clock speed in rats receiving extended training was restored. A glutamate "lock/unlock" hypothesis is used to explain the observed dopamine-glutamate interactions as a function of timing behaviors becoming learned habits.