Reduction of learned helplessness by central administration of quaternary naltrexone

Prior research has established that escape impairment resulting from prior inescapable shock (IS) could be reversed by the peripheral administration of the opiate antagonist naltrexone (NTX), but not the quaternary form of naltrexone (QNTX), which when systemically administered, does not readily pass the blood-brain barrier. As it was unclear whether the failure of systemically administered QNTX to reduce shuttle escape deficits following exposure to IS could be attributed to reasons other than the restricted access of QNTX to receptor sites in the brain, rats were affixed with chronic indwelling ventricular cannulae to allow direct brain administration of QNTX. The present experiment found a significant attenuation of the escape deficit produced by prior inescapable shock following the intracerebroventricular (ICV) administration of QNTX (10 micrograms/rat). These data provide further evidence of a mediational role for central opiate receptors in the expression of escape interference following inescapable shock.