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At least 37 records · Page 2Linked to original sources
PubMed2003

Selective alleviation of compulsive lever-pressing in rats by D1, but not D2, blockade: possible implications for the involvement of D1 receptors in obsessive-compulsive disorder.

Rats undergoing extinction of lever-pressing for food after the attenuation of an external feedback for this behavior exhibit excessive lever-pressing unaccompanied by an attempt to collect a reward. This behavior may be analogous to the excessive and unreasonable behavior seen in obsessive-compulsive disorder. In the present study, we tested the hypothesis that the compulsive behavior induced by signal attenuation is mediated via D(1) rather than D(2) receptors. Administration of 0.005, 0.01 and 0.03 mg/kg of the D(1) antagonist SCH 23390 reduced the number of compulsive lever-presses without affecting the number of lever-presses followed by an attempt to collect a reward. In contrast, administration of 0.005, 0.01, 0.024, 0.036 and 0.05 of the D(2) antagonist haloperidol dose-dependently decreased both types of lever-presses. In addition, haloperidol at doses that decreased lever-pressing in the post-training signal attenuation procedure (0.036 and 0.05 mg/kg) had a similar effect in regular extinction, whereas an SCH 23390 dose that decreased compulsive lever-pressing in the post-training signal attenuation procedure (0.01 mg/kg) had no effect on regular extinction. On the basis of electrophysiological data on the response of dopamine neurons to the omission of an expected reward, these results were interpreted as suggesting that compulsive lever-pressing depends on a phasic decrease in the stimulation of D(1) receptors. The implications of these results for the pathophysiology and treatment of obsessive-compulsive disorder are discussed.

Animals↗
PubMedDate not supplied

Sudden death in the laboratory rat.

Vulnerability to sudden death was produced in laboratory rats by manipulating their developmental history. Rats who were reared in isolation died suddenly when placed in a stressful swimming situation. Handling of these singly-housed rats from 25 to 100 days of age potentiated the phenomenon. However, animals who were group housed did not die even when they had been previously handled.

Animals↗
PubMed1996

Unsignaled morphine delivery does not disrupt the development of associative morphine tolerance in the rat.

When morphine administration is paired with a distinctive context, tolerance to morphine's analgesic effects comes readily under the associative control of the drug-paired context. These associative tolerance effects are eliminated when a relatively short (i.e., 6 h) interdose interval (IDI) is used for conditioning. Contemporary models of learned tolerance explain the absence of learning at short IDIs by positing that residual morphine effects from a recent drug exposure disrupt the formation of drug-context associations. The present studies examined the impact of unsignaled morphine injections given 6 h prior to drug-context pairings on the development of associative tolerance. Analgesia was measured by the tail-flick method, and tolerance levels were assessed by dose-response curve methodology. Morphine preexposure had no detectable influence on the acquisition of associative tolerance when rats were tested immediately after conditioning, after a 30-day rest interval, or after a 30-day period of daily saline injections in their home-cage environment. These data suggest disruption of associative tolerance effects at short IDIs is not attributable to residual effects of morphine from the immediately preceding trial.

Animals↗
PubMed1991

Norepinephrine-induced plasticity and one-trial olfactory learning in neonatal rats.

The influence of norepinephrine (NE) on the acquisition of a conditioned odor preference and enhanced focal uptake of [14C]2-deoxyglucose (2-DG) within the olfactory bulb was assessed in neonatal rat pups. On postnatal day (PN) 6, pups were injected with either an NE receptor agonist (isoproterenol), NE receptor antagonist (propranolol or timolol), or saline before one-trial odor conditioning. The experimental conditioning group received a 10-min exposure to an odor (peppermint) and reinforcing tactile stimulation similar to that received from the dam. Control groups received only the odor, only the tactile stimulation, backwards presentation of the odor and tactile stimulation or neither of these stimuli. The next day, pups were either tested for an olfactory preference (Expts. 1 and 2) or assessed for differential olfactory bulb activity using the 2-DG technique (Expt. 3). The results indicate that early odor experience with either tactile stimulation or isoproterenol is sufficient to produce a learned behavioral preference and enhanced focal 2-DG uptake within the olfactory bulb. Moreover, an NE receptor blocker injected prior to training with odor and tactile stimulation blocks the acquisition of both behavioral preference and the enhanced 2-DG uptake. In Expt. 4, the effects of tactile stimulation and isoproterenol were further assessed. An odor paired with a moderate level of either of these stimuli produces learning. However, the simultaneous presentation of a moderate level of these stimuli paired with an odor does not result in an odor preference. An odor preference may be reinstated by simultaneous presentation of these stimuli, provided the level of each of these stimuli is too low to produce an odor preference when presented alone with an odor. These data suggest that exogenous NE and tactile stimulation are additive in their effect on learning. These results are discussed in terms of the neural mechanisms underlying reinforcement in infant rats.

Animals↗
PubMed1999

Extending the spontaneous preference test of recognition: evidence of object-location and object-context recognition.

The natural preference for novel objects which is displayed by rats has been used as a behavioural index to test object recognition. In this series of experiments the standard spontaneous recognition task was extended to look at other types of recognition memory; memory for place (recognition that an object is in a location where previously there had been no object), memory for object in place (recognition that a specific object has changed position with another object) and memory for context (recognition that a familiar object is in a context different to that in which it was previously encountered). We also included a standard test of object recognition in which successful discrimination relied primarily on visual cues. In addition, we looked at how the differential exploration of objects varied within the 3 min of the test phase. The results showed that rats were sensitive to the changes made in all of the test conditions and that the level of discrimination varied within the 3 min test phase. In the standard condition and the context condition, the first 2 min were found to be the most sensitive period. In the two conditions involving a position change, discrimination was only evident in the first minute.

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