preproenkephalin and Learning-Disabilities

We hypothesized that mice subjected to prolonged stress would demonstrate decreased performance in a learning and memory task attributable to the endogenous activation of the kappa opioid receptor (KOR). C57BL/6J mice were tested using the novel object recognition (NOR) assay at various time points after exposure to repeated forced swim stress (FSS). Unstressed mice demonstrated recognition of the novel object at the end of a procedure using three 10-min object interaction phases, with a recognition index (RI) for the novel object of 71.7+/-3.4%. However, 1 h after exposure to FSS, vehicle-pretreated mice displayed a significant deficit in performance (RI=58.2+/-4.1%) compared with unstressed animals. NOR was still significantly reduced 4 but not 24 h after FSS. Treatment with the KOR-selective antagonist norbinaltorphimine (10 mg/kg, i.p.) prevented the decline in learning and memory performance. Moreover, direct activation of the KOR induced performance deficits in NOR, as exogenous administration of the KOR agonist U50,488 [(+/-)-trans-3,4-dichloro-N-methyl-N-[2-(1-pyrrolidinyl)cyclohexyl]-benzeneacetamide] (0.3 mg/kg, i.p.) suppressed NOR (RI=56.0+/-3.9%). The effect of FSS on NOR performance was further examined in mice lacking the gene for the endogenous KOR agonist dynorphin (Dyn). Dyn gene-disrupted mice exposed to FSS did not show the subsequent learning and memory deficits (RI=66.8+/-3.8%) demonstrated by their wild-type littermates (RI=49.7+/-2.9%). Overall, these results suggest that stress-induced activation of the KOR may be both necessary and sufficient to produce subsequent deficits in novel object recognition.

Topics: 3,4-Dichloro-N-methyl-N-(2-(1-pyrrolidinyl)-cyclohexyl)-benzeneacetamide, (trans)-Isomer; Analgesics, Non-Narcotic; Analysis of Variance; Animals; Behavior, Animal; Enkephalins; Gene Expression Regulation; Immobility Response, Tonic; Learning Disabilities; Male; Memory Disorders; Mice; Mice, Inbred C57BL; Mice, Knockout; Motor Activity; Naltrexone; Narcotic Antagonists; Protein Precursors; Receptors, Opioid, kappa; Recognition, Psychology; Stress, Psychological; Swimming; Time Factors

The misuse of anabolic androgenic steroids has in several reports been associated with effects resulting in altered behavior. This study used the Morris water maze task to investigate the effect of high doses of the anabolic androgenic steroid nandrolone on spatial learning and memory in male rats. During the experiment, we observed a significantly impaired Morris water maze performance in the nandrolone-treated rats compared with controls. The hippocampus, a brain region associated with cognitive function, was analyzed for mRNA expression of prodynorphin, the precursor of dynorphinergic peptides. The results indicated that the transcription levels of prodynorphin were significantly elevated in the animals treated with nandrolone compared with controls. Thus, the findings suggest that administration of nandrolone to male rats impairs memory function, possibly via dynorphinergic actions.

Topics: Anabolic Agents; Animals; Enkephalins; Gene Expression Regulation; Hippocampus; Learning Disabilities; Male; Maze Learning; Nandrolone; Protein Precursors; Rats; Rats, Sprague-Dawley; RNA, Messenger; Transcriptional Activation