Elsevier

Brain Research

Volume 416, Issue 2, 28 July 1987, Pages 283-288
Brain Research

Self-administration of morphine into the lateral hypothalamus in the mouse

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Abstract

BALB/c mice were chronically and unilaterally implanted with a guide cannula, the tip of which was positioned 1 mm above the lateral hypothalamus (LH). On each experimental day, a stainless-steel injection cannula was inserted into the LH, and self-administration of morphine or vehicle in this brain area was studied by using a spatial discrimination test in a Y-maze. In a first experiment, we observed that when mice had access to morphine (0.1 μg by injection) they rapidly discriminated the reinforced arm from the neutral arm of the maze in order to self-administer, with increasing frequency, the drug into the LH. In contrast when only vehicle was present, the two arms were no longer discriminated. In a second experiment we compared the effects of 3 doses of morphine (0.1 μg, 0.05 μg and 0.025 μg by injection); optimal discrimination was obtained with the lowest dose used. In a third experiment we observed that subcutaneous injections of naloxone (4 mg/kg) progressively reduced the number of self-administrations of morphine into the LH, a result which suggests that this response is dependent on an opiate receptor mechanism.

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