Dopamine manipulations limited to preexposure are sufficient to modulate latent inhibition

Antipsychotic drug-like facilitation of latent inhibition by a brain-penetrating neurotensin-1 receptor agonist

Latent inhibition (LI) is a measure of cognitive gating and refers to reduced conditioned learning when there is pre-exposure to the conditioned stimulus (CS) before it is paired with the unconditioned stimulus (US). Dysregulation of LI is associated with some neuropsychiatric disorders, including schizophrenia, and the ability to facilitate LI in rodents is a reasonably good predictive test for antipsychotic drugs. Converging evidence supports neurotensin-1 receptor (NTS1) agonists as novel drugs for schizophrenia. Therefore, we investigated the ability of a brain-penetrating, selective NTS1 agonist, PD149163, to facilitate LI in heterozygous Brattleboro rats, a strain that exhibits naturally low LI. Conditioned taste aversion to flavored water (FW; 0.1% saccharin) was induced by pairing it with malaise-inducing injections of lithium chloride (LiCl). Prior to LiCl-FW pairing, rats received subcutaneous injections of saline, or PD149163 (100 µg/kg or 200 µg/kg). Half the rats in each drug group had been allowed to drink FW the day before the LiCl-FW pairing (pre-exposed rats). Two days after pairing, the amount of FW each rat consumed was recorded. LI, defined as significantly greater FW drinking in the pre-exposed group compared with the non pre-exposed group, was exhibited only among rats that received 200 µg/kg of PD149163. These results further support NTS1 agonists as potentially novel drugs for the treatment of schizophrenia.

Effects of D- and L-govadine on the disruption of touchscreen object-location paired associates learning in rats by acute MK-801 treatment

RATIONALE

New pharmacological treatments for the cognitive deficits in schizophrenia are needed. Tetrahydroprotoberberines, such as govadine, are one class of compounds with dopaminergic activities that may be useful in treating some aspects of the cognitive symptoms of the disorder.

OBJECTIVE

The objective of the present studies was to test the effects of the D- and L-enantiomers of govadine on the impairment in a paired-associate learning (PAL) task produced by acute MK-801 in rats. We also assessed effects of the typical antipsychotic haloperidol as a comparator compound.

METHODS

MK-801 (0.05, 0.1, 0.15, and 0.2 mg/kg), D- and L-govadine (0.3, 1.0, and 3.0 mg/kg), and haloperidol (0.05, 0.1, and 0.25 mg/kg) were administered acutely to rats well trained on the PAL task in touchscreen-equipped operant conditioning chambers.

RESULTS

Acute MK-801 impaired performance of PAL in a dose-dependent manner by reducing accuracy and increasing correction trials. L-Govadine (1.0 mg/kg), but not D-govadine, blocked the disruptive effects of MK-801 (0.15 mg/kg) on PAL. Haloperidol failed to affect the MK-801-induced disruption of PAL. Higher doses of L-govadine and haloperidol dramatically impaired performance of the task which confounded interpretation of cognitive outcomes.

CONCLUSION

L-Govadine appears unique in its ability to improve performance of the MK-801-induced impairment in the PAL task. This behavioral effect may relate the ability of L-govadine to antagonize dopamine D2 receptors while also promoting dopamine efflux. Future research should further characterize the role of the dopamine system in the rodent PAL task to elucidate the mechanisms of its pro-cognitive effects.

Involvement of D1 and D2 dopamine receptor in the retrieval processes in latent inhibition

RATIONALE

Contemporary theories propose that latent inhibition (LI) is due to a process of interference with the context playing a key role as recovery cue. Physiological studies have demonstrated that LI is a process dependent on striatal dopamine. D2 dopamine receptors have been specifically associated with its expression, while D1 receptor has shown a limited function. However, to evaluate the role of dopamine receptors in LI, it is necessary to analyse their activity during recovery phase, where the mechanisms involved in interference processes are performed.

OBJECTIVE

The experiments studied the involvement of the dopaminergic system in the retrieval process of LI. We analysed the effect of the systemic administration of dopaminergic D1 (SCH-23390) and D2 (sulpiride) antagonist during the test phase on LI and on its contextual specificity.

METHODS

Animals were pre-exposed to saccharin solution and conditioned with a LiCl administration in conditioning phase. Dopaminergic antagonist drugs were administered during the test phase. Experiment 2 used the same context in all the phases. Experiment 3 used a new context during conditioning and test phase.

RESULTS

The D2 antagonist increased the LI effect and, in turn, diminished the normally suppressant effect of the context shift on LI. The opposite effect was observed under the D1 antagonist administration. This drug disrupted LI and enhanced the effect that the context shift had on this cognitive process.

CONCLUSIONS

D2 receptor had a relevant role on retrieval processes of pre-exposure learning, while D1 receptor was related with the contextual control of conditioning.

The prosocial psychopath: explaining the paradoxes of the creative personality

The literature on the creative personality is curiously equivocal in its characterization of the traits supposedly possessed by eminent creators. While acclaimed as revolutionary and pioneering visionaries, the same category of people can come across as unsocialized and discomfiting even to their close associates and admirers. This paper suggests that these ambiguities can be addressed by appealing to the potential psychobiological mechanisms that can give rise to the expression of both creative ability and "antisocial" traits. Work on latent inhibition, the somatic marker hypothesis, Eysenck's biosocial theory of crime and the dopamine hypothesis of addiction are reviewed and integrated into a model that examines the role of dopamine as a critical agent in the creative personality system. Finally, testable hypotheses stemming from the model are proposed.