Differential patterns of expression of neuropeptide Y throughout abstinence in outbred Swiss mice classified as susceptible or resistant to ethanol-induced locomotor sensitization

Anxiety-like behavior in acute and protracted withdrawal after morphine-induced locomotor sensitization in C57BL/6 male mice: The role of context

Contextual memory plays an important role in development and maintenance of drug addiction. However, little is known about of the role contextual memory in the emergence of a negative emotional state in the withdrawal period. Therefore, this study investigated anxiety-like behavior in acute and protracted morphine withdrawal of mice submitted to a locomotor sensitization protocol and the influence of contextual memory on this behavior. Male adult C57Bl6 mice were subjected to morphine locomotor sensitization and anxiety-like behavior was assessed by using the elevated plus maze test (EPM). To evaluate associative memory, the mice were re-exposed to the context of locomotor sensitization immediately before EPM. As expected, repeated morphine administrations promoted locomotor sensitization, seen as a gradual increase in the distance traveled during the acquisition phase. There was an increase in anxiety-like behavior upon acute withdrawal, as indicated by a decrease in open arms activity (OAA), but this effect dissipated over time. However, when the context was presented, mice in protracted withdrawal showed enhanced anxiety-like behavior, indicated by an increase in closed arms activity (CAA). This effect was context specific since re-exposure in an alternative context did not change the anxiety-like behavior. Treatment with diazepam counteracted the decrease in OAA in acute withdrawal and the increase in CAA induced by context re- exposure during protracted abstinence. Thus, repeated morphine administration induced a negative emotional state when the drug was discontinued. The context associated with drug exposure played a pivotal role in the appearance of anxiety-like behavior, even long after drug discontinuation. There were differences in the patterns of anxiety behaviors in acute (unconditioned anxiety-like behavior) and protracted (conditioned anxiety-like behavior) withdrawal since the former was characterized by a passive behavioral strategy and the latter by an active behavioral strategy.

Neuropeptide Y response to alcohol is altered in nucleus accumbens of mice selectively bred for drinking to intoxication

The High Drinking in the Dark (HDID) mice have been selectively bred for drinking to intoxicating blood alcohol levels and represent a genetic model of risk for binge-like drinking. Presently, little is known about the specific genetic factors that promote excessive intake in these mice. Previous studies have identified neuropeptide Y (NPY) as a potential target for modulating alcohol intake. NPY expression differs in some rodent lines that have been selected for high and low alcohol drinking phenotypes, as well as inbred mouse strains that differ in alcohol preference. Alcohol drinking and alcohol withdrawal also produce differential effects on NPY expression in the brain. Here, we assessed brain NPY protein levels in HDID mice of two replicates of selection and control heterogeneous stock (HS) mice at baseline (water drinking) and after binge-like alcohol drinking to determine whether selection is associated with differences in NPY expression and its sensitivity to alcohol. NPY levels did not differ between HDID and HS mice in any brain region in the water-drinking animals. HS mice showed a reduction in NPY levels in the nucleus accumbens (NAc) - especially in the shell - in ethanol-drinking animals vs. water-drinking controls. However, HDID mice showed a blunted NPY response to alcohol in the NAc core and shell compared to HS mice. These findings suggest that the NPY response to alcohol has been altered by selection for drinking to intoxication in a region-specific manner. Thus, the NPY system may represent a potential target for altering binge-like alcohol drinking in these mice.