Intrahypothalamic discriminative stimulus effects of neuropeptide Y

Neuropeptide Y (NPY) is one of the most ubiquitous neurotransmitters in the CNS and has been implicated in a variety of psychological and physiological functions. The current study investigated whether intrahypothalamic (I.H.) administrations of NPY were behaviorally discriminable from saline injections. Rats were trained to differentially respond based on whether they received I.H. injections of NPY (0.5 microg/0.5 microl) or saline (0.5 microl 0.9% NaCl). Subjects demonstrated discriminative control (85% correct in 8 out of 10 consecutive sessions) after a mean of 32 sessions. The ability of subjects to discriminate I.H. NPY from saline was dose dependent, with the lowest NPY dose tested (0.03 microg/0.5 microl) generalizing to saline. The opioid antagonist naloxone blocked the discrimination of NPY when administered I.P. (3.0 mg/kg) or I.H. (50 microg/0.5 microl).