The ability to change strategies in different contexts is a form of behavioral flexibility that is crucial for adaptive behavior. The striatum has been shown to contribute to certain forms of behavioral flexibility such as reversal learning. Here we report on the contribution of striatal cholinergic interneurons-a key element in the striatal neuronal circuit-to strategy set-shifting in which an attentional shift from one stimulus dimension to another is required. We made lesions of rat cholinergic interneurons in dorsomedial or ventral striatum using a specific immunotoxin and investigated the effects on set-shifting paradigms and on reversal learning. In shifting to a set that required attention to a previously irrelevant cue, lesions of dorsomedial striatum significantly increased the number of perseverative errors. In this condition, the number of never-reinforced errors was significantly decreased in both types of lesions. When shifting to a set that required attention to a novel cue, rats with ventral striatum lesions made more perseverative errors. Neither lesion impaired learning of the initial response strategy nor a subsequent switch to a new strategy when response choice was indicated by a previously relevant cue. Reversal learning was not affected. These results suggest that in set-shifting the striatal cholinergic interneurons play a fundamental role, which is dissociable between dorsomedial and ventral striatum depending on behavioral context. We propose a common mechanism in which cholinergic interneurons inhibit neurons representing the old strategy and enhance plasticity underlying exploration of a new rule.

Pregnancy is associated with changes in mood and anxiety level as well as with marked hormonal fluctuations. Increases in the brain concentrations of neuroactive steroids during pregnancy in rats are accompanied by changes in expression of subunits of the GABA type A receptor (GABA A -R) in the brain. Granule cells of the dentate gyrus (DGGCs) exhibit two components of inhibitory GABAergic transmission: a phasic component mediated by synaptic GABA A -Rs, and a tonic component mediated by extrasynaptic GABA A -Rs. Recordings of GABAergic currents were obtained from hippocampal slices prepared from rats in estrus, at pregnancy day 15 (P15) or P19, or at 2 d after delivery. Exogenous GABA or 3␣,5␣-THP induced an increase in tonic current in DGGCs that was significantly greater at P19 than in estrus. Neither tonic nor phasic currents were affected by pregnancy in CA1 pyramidal cells. Immunohistochemical analysis revealed a marked increase in the abundance of the ␦ subunit of the GABA A -R and a concomitant decrease in that of the ␥ 2 subunit in the hippocampus at P19. Expression of the ␣ 4 subunit did not change during pregnancy but was increased 2 d after delivery. Treatment of rats from P12 to P18 with the 5␣-reductase inhibitor finasteride prevented the changes in tonic current and in ␦ and ␥ 2 subunit expression normally apparent at P19. These data suggest that the number of extrasynaptic GABA A -Rs is increased in DGGCs during late pregnancy as a consequence of the associated marked fluctuations in the brain levels of neuroactive steroids.

SUMMARY The G protein alpha subunit o (Gαo) is one of the most abundant proteins in the nervous system, and pathogenic mutations in its gene ( GNAO1 ) cause movement disorder. However, the function of Gαo is ill defined mechanistically. Here, we show that Gαo dictates neuromodulatory responsiveness of striatal neurons and is required for movement control. Using in vivo optical sensors and enzymatic assays, we determine that Gαo provides a separate transduction channel that modulates coupling of both inhibitory and stimulatory dopamine receptors to the cyclic AMP (cAMP)-generating enzyme adenylyl cyclase. Through a combination of cell-based assays and rodent models, we demonstrate that GNAO1 -associated mutations alter Gαo function in a neuron-type-specific fashion via a combination of a dominant-negative and loss-of-function mechanisms. Overall, our findings suggest that Gαo and its pathological variants function in specific circuits to regulate neuromodulatory signals essential for executing motor programs.

Fetal alcohol spectrum disorder (FASD) is associated with learning and memory alterations that could be, in part, a consequence of hippocampal damage. The CA3 hippocampal subfield is one of the regions affected by ethanol (EtOH), including exposure during the third trimester-equivalent (i.e., neonatal period in rats). However, the mechanism of action of EtOH is poorly understood. In CA3 pyramidal neurons from neonatal rats, dendritic BDNF release causes long-term potentiation of the frequency of GABA A receptormediated spontaneous postsynaptic currents (LTP-GABA A ) and this mechanism is thought to play a role in GABAergic synapse maturation. Here, we show that short-and long-term exposure of neonatal male rats to low EtOH concentrations abolishes LTP-GABA A by inhibiting L-type voltage-gated Ca 2ϩ channels. These findings support the recommendation that even light drinking should be avoided during pregnancy.

BackgroundFetal alcohol exposure affects 1 in 100 children making it the leading cause of mental retardation in the US. It has long been known that alcohol affects cerebellum development and function. However, the underlying molecular mechanism is unclear.Methodology/Principal FindingsWe demonstrate that CREB binding protein (CBP) is widely expressed in granule and Purkinje neurons of the developing cerebellar cortex of naïve rats. We also show that exposure to ethanol during the 3rd trimester-equivalent of human pregnancy reduces CBP levels. CBP is a histone acetyltransferase, a component of the epigenetic mechanism controlling neuronal gene expression. We further demonstrate that the acetylation of both histone H3 and H4 is reduced in the cerebellum of ethanol- treated rats.Conclusions/SignificanceThese findings indicate that ethanol exposure decreases the expression and function of CBP in the developing cerebellum. This effect of ethanol may be responsible for the motor coordination deficits that characterize fetal alcohol spectrum disorders.