Activation of central neurotensin receptors reinstates cocaine seeking in the rat: modulation by a D1/D5, but not D2/D3, receptor antagonist.

RATIONALE: Neurotensin (NT) has been implicated in some of the behavioral effects of psychostimulants. Thus, there is reason to think that NT may play a role in the reinstatement of cocaine seeking, and that it may do so via an interaction with dopamine (DA). OBJECTIVES: To assess (1) whether NT and an NT analog, D-TYR[11]NT, induce reinstatement of cocaine seeking; (2) whether the effects of NT receptor activation on reinstatement can be modulated by D1/D5 or D2/D3 antagonists; (3) the specificity of the effects of NT receptor activation on the reinstatement of cocaine seeking. METHODS: In Experiment 1, rats were initially trained to self-administer cocaine. Following a subsequent period of extinction training, they were tested for the reinstatement of cocaine seeking by NT or D-TYR[11]NT (15, 30 microg i.c.v.). In Experiment 2, rats were pretreated with the D1/D5 antagonist, SCH 23390 (0.05, 0.10 mg/kg i.p.) or the D2/D3 antagonist, raclopride (0.25, 0.50 mg/kg i.p.), prior to testing for reinstatement by D-TYR[11]NT (15 microg i.c.v.). In Experiment 3, rats that had been trained to self-administer sucrose pellets were tested for the reinstatement of sucrose seeking by D-TYR[11]NT (15, 30 microg i.c.v.). RESULTS: (1) Both NT and D-TYR[11]NT produced robust reinstatement of cocaine seeking; (2) the effect of the analog was attenuated by pretreatment with the D1/D5, but not D2/D3, receptor antagonist; (3) the analog did not induce the reinstatement of sucrose seeking. CONCLUSIONS: The findings suggest that an interaction between NT and DA may contribute to the neurobiology of reinstatement in animals with a history of cocaine self-administration.

Modulation of the pair housing induced feeding suppression.

The present experiments explored how manipulating the period of individual housing, partner novelty, or short periods of conspecific interaction affected the feeding suppression evident when young adult male rats were moved from individual to pair housing. In the first experiment, after a period of pair housing, rats were individually housed for 0, 3, 10, or 14 days before being rehoused with either the same or a novel partner. There was an increase in the feeding suppression as the duration of individual housing grew, and at 3 days, the novel partner produced a stronger suppression than did the familiar partner. In the second experiment, four 15-min exposures to a conspecific in a novel place preference environment did not eliminate the feeding suppression at pair housing. The third experiment found that four 90-min exposures to a conspecific reduced the feeding suppression evident at rehousing. In Experiments 2 and 3, an environment previously paired with a conspecific did not produce a place aversion. Together, these experiments suggest that the feeding suppression evident when male rats are moved from individual to pair housing can be considered a graded effect open to modulation by a variety of behavioral manipulations.