To press or not to press? Differential receptor expression and response to novelty in rats learning an operant response for reward

Pregabalin- and topiramate-mediated regulation of cognitive and motor impulsivity in DBA/2 mice

BACKGROUND AND PURPOSE

Impulsivity is a core symptom in many neuropsychiatric disorders. The main objective of this study was to evaluate the effects of topiramate and pregabalin on the modulation of different impulsivity dimensions in DBA/2 mice.

EXPERIMENTAL APPROACH

The effects of acute and chronic administration of pregabalin (10, 20 and 40 mg·kg(-1) ) and topiramate (12.5, 25 and 50 mg·kg(-1) ) were evaluated in the light-dark box (LDB), hole board test (HBT) and delayed reinforcement task (DRT). α(2A) -Adrenoceptor, D(2) -receptor and TH gene expression were evaluated by real-time PCR in the prefrontal cortex (PFC), accumbens (ACC) and ventral tegmental area (VTA), respectively.

KEY RESULTS

Acute pregabalin administration showed a clear anxiolytic-like effect (LDB) but did not modify novelty-seeking behaviour (HBT). In contrast, topiramate produced an anxiolytic effect only at the highest dose, whereas it reduced novelty seeking at all doses tested. In the DRT, acute pregabalin had no effect, whereas topiramate only reduced motor impulsivity. Chronically, pregabalin significantly increased motor impulsivity and topiramate diminished cognitive impulsivity. Pregabalin decreased α(2A) -adrenoceptor and D(2) -receptor gene expression in the PFC and ACC, respectively, and increased TH in the VTA. In contrast, chronic administration of topiramate increased α(2A) -adrenoceptor and D(2) -receptor gene expression in the PFC and ACC, respectively, and also increased TH in the VTA.

CONCLUSIONS AND IMPLICATIONS

These results suggest that the usefulness of pregabalin in impulsivity-related disorders is related to its anxiolytic properties, whereas topiramate modulates impulsivity. These differences could be linked to their opposite effects on α(2A) -adrenoceptor and D(2) -receptor gene expression in the PFC and ACC, respectively.

Ethanol and phencyclidine interact with respect to nucleus accumbens dopamine release: differential effects of administration order and pretreatment protocol

Executive dysfunction is a common symptom among alcohol-dependent individuals. Phencyclidine (PCP) injection induces dysfunction in the prefrontal cortex of animals but little is known about how PCP affects the response to ethanol. Using the in vivo microdialysis technique in male Wistar rats, we investigated how systemic injection of 5 mg/kg PCP would affect the dopamine release induced by local infusion of 300 mM ethanol into the nucleus accumbens. PCP given 60 min before ethanol entirely blocked ethanol-induced dopamine release. However, when ethanol was administered 60 min before PCP, both drugs induced dopamine release and PCP's effect was potentiated by ethanol (180% increase vs 150%). To test the role of prefrontal cortex dysfunction in ethanol reinforcement, animals were pretreated for 5 days with 2.58 mg/kg PCP according to previously used 'PFC hypofunction protocols'. This, however, did not change the relative response to PCP or ethanol compared to saline-treated controls. qPCR illustrated that this low PCP dose did not significantly change expression of glucose transporters Glut1 (SLC2A1) or Glut3 (SLC2A3), monocarboxylate transporter MCT2 (SLC16A7), glutamate transporters GLT-1 (SLC1A2) or GLAST (SLC1A3), the immediate early gene Arc (Arg3.1) or GABAergic neuron markers GAT-1 (SLC6A1) and parvalbumin. Therefore, we concluded that PCP at a dose of 2.58 mg/kg for 5 days did not induce hypofunction in Wistar rats. However, PCP and ethanol do have overlapping mechanisms of action and these drugs differentially affect mesolimbic dopaminergic transmission depending on the order of administration.

5-HT(1B) receptor inhibition of alcohol-heightened aggression in mice: comparison to drinking and running

RATIONALE

Serotonin 5-HT(1B) receptors are promising targets for the management of several mood and impulse disorders.

OBJECTIVE

These experiments examine a 5-HT(1B) agonist, CP-94,253, and attempt to distinguish between its effects on seeking to perform three rewarding behaviors: aggression, drinking, and wheel running.

MATERIALS AND METHODS

Male CFW mice perform nose-poke responses that are maintained by a fixed interval schedules of 10-min (FI10) schedule to gain access to one of three rewarding activities. The first experiment studies mice reinforced by the opportunity to confront an intruder mouse after drinking water or alcohol; the second studies mice reinforced by the presentation of alcoholic or non-alcoholic solutions (i.e., 6% ethanol, 0.05% saccharin vs 0.05% saccharin); the third studies mice reinforced by access to a running wheel.

RESULTS

CP-94,253 (1.0-10 mg/kg i.p.) dose-dependently reduces aggression, drinking, and wheel running. Of these behaviors, alcohol-heightened aggression is the most sensitive to the 5-HT(1B) receptor agonist (ED50 = 4.8 mg/kg). Responding for the opportunity to drink or engage in alcohol-heightened aggression is suppressed by the highest dose of CP-94,253, whereas CP-94,253 does not affect responding that is reinforced by wheel running or species-typical aggression.

CONCLUSIONS

These results confirm the inhibitory effects of 5-HT(1B) receptor stimulation on aggressive performance and drinking. They also reveal an inhibition of voluntary wheel running, contrary to the stimulation of running in a novel, open arena. 5-HT(1B) receptor agonists may be particularly useful for the treatment of aggressive behavioral disorders, but their efficacy and potency appear to be sensitive to the intensity and context of the behavior.

The role of hypothalamic peptide gene expression in alcohol self-administration behavior

Self-administration of ethanol and food share many common features and Richter hypothesized that an increase in ethanol consumption would decrease feeding to balance the excess calories contained in the ethanol. Previously, we have shown that individual alcohol consumption correlates with neurotransmitter gene expression, especially in the prefrontal cortex. To test the hypothesis of Richter, we measured hypothalamic gene expression of receptors or neuropeptides of known relevance for the regulation of food intake using qPCR and correlated this to individual ethanol consumption in Wistar rats. For validation, gene expression was first correlated with body weight. We found a correlation of dynorphin, somatostatin, melanocortin-4 receptor and serotonin 5-HT(2C) with body weight and trends to correlation for CART, thus confirming the established role of the hypothalamus in the regulation of weight. For ethanol consumption, correlations were found for CRH receptors 1 and 2 and vasopressin while strong trends were observed for galanin receptor 1, orexin receptor 1, MCH and adrenoceptor alpha(1B). Therefore, alcohol consumption does seem to involve several hypothalamic systems which also mediate feeding responses and suggests that the hypothalamus, together with the prefrontal cortex, may determine the 'stopping point' of an individual.