Cellular and axonal constituents of neocortical molecular layer heterotopia.

Human neocortical molecular layer heterotopia consist of aggregations of hundreds of neurons and glia in the molecular layer (layer I) and are indicative of neuronal migration defect. Despite having been associated with dyslexia, epilepsy, cobblestone lissencephaly, polymicrogyria, and Fukuyama muscular dystrophy, a complete understanding of the cellular and axonal constituents of molecular layer heterotopia is lacking. Using a mouse model, we identify diverse excitatory and inhibitory neurons as well as glia in heterotopia based on molecular profiles. Using immunocytochemistry, we identify diverse afferents in heterotopia from subcortical neuromodulatory centers. Finally, we document intracortical projections to/from heterotopia. These data are relevant toward understanding how heterotopia affect brain function in diverse neurodevelopmental disorders.

BGC20-761, a novel tryptamine analog, enhances memory consolidation and reverses scopolamine-induced memory deficit in social and visuospatial memory tasks through a 5-HT6 receptor-mediated mechanism.

Inhibition of 5-HT(6) receptors has been shown to improve memory consolidation, thus we tested whether a novel tryptamine analog with high affinity for 5-HT(6) receptors, BGC20-761 (5-methoxy-2-phenyl-N,N-dimethyltryptamine, PMDT), can enhance long-term memory. BGC20-761 (10 mg/kg i.p.) alone had no effect on social recognition in young rats, however, at doses of 5 mg/kg and 10 mg/kg i.p, BGC20-761 dose-dependently reversed a deficit of social recognition induced by scopolamine (0.4 mg/kg i.p.), an anticholinergic drug that impairs memory. BGC20-761 (10 mg/kg i.p.), scopolamine (0.2 mg/kg i.p.) or BGC20-761 + scopolamine had no effects on novel object discrimination in young rats (2 months). In mature rats (6 months), recognition of the novel object was improved following administration of BGC20-761. Scopolamine had no effect in object recognition. However, the addition of scopolamine disrupted the memory-enhancing effect of BGC20-761. Based on the high affinity of BGC20-761 for 5-HT(6) receptors, these cognitive enhancing effects are most likely mediated by 5-HT(6) receptor inhibition. The difference in effects of BGC20-761 in young vs. mature rats may reflect the status of memory consolidation in these different age ranges.

Molecular layer heterotopia of the cerebellar vermis in mutant and transgenic mouse models on a C57BL/6 background.

C57BL/6 mice exhibit spontaneous cerebellar malformations consisting of heterotopic neurons and glia in the molecular layer of the vermis (Tanaka and Marunouchi, 2005; Mangaru et al., 2013). Malformations are only found between folia VIII and IX and are indicative of deficits of neuronal migration during cerebellar development. In the present report we test the prediction that mutant and transgenic mouse models on a C57BL/6 background will also exhibit these same cerebellar malformations. Consistent with our hypothesis, we found that 2 spontaneous mutant models of Parkinson's disease on a C57BL/6 background had cerebellar malformations. In addition, we found that numerous transgenic mouse lines on a full or partial C57BL/6 background including eGFP-, YFP- and Cre-transgenic mice also exhibited heterotopia. These data suggest that histological analyses be performed in studies of cerebellar function or development when using C57BL/6 or other mice on this background in order for correct interpretation of research results.

Overexpression of 5-HT(1B) mRNA in nucleus accumbens shell projection neurons differentially affects microarchitecture of initiation and maintenance of ethanol consumption.

Serotonin 1B (5-HT(1B)) heteroreceptors on nucleus accumbens shell (NAcSh) projection neurons have been shown to enhance the voluntary consumption of alcohol by rats, presumably by modulating the activity of the mesolimbic reward pathway. The present study examined whether increasing 5-HT(1B) receptors expressed on NAcSh projection neurons by means of virus-mediated gene transfer enhances ethanol consumption during the initiation or maintenance phase of drinking and alters the temporal pattern of drinking behavior. Animals received stereotaxic injections of viral vectors expressing either 5-HT(1B) receptor and green fluorescent protein (GFP) or GFP alone. Home cages equipped with a three-bottle (water and 6 and 12% ethanol) lickometer system recorded animals' drinking behaviors continuously, capturing either initiation or maintenance of drinking behavior patterns. Overexpression of 5-HT(1B) receptors during initiation increased consumption of 12% ethanol during both forced-access and free-choice consumption. There was a shift in drinking pattern for 6% ethanol with an increase in number of drinking bouts per day, although the total number of drinking bouts for 12% ethanol was not different. Finally, increased 5-HT(1B) expression induced more bouts with very high-frequency licking from the ethanol bottle sippers. During the maintenance phase of drinking, there were no differences between groups in total volume of ethanol consumed; however, there was a shift toward drinking bouts of longer duration, especially for 12% ethanol. This suggests that during maintenance drinking, increased 5-HT(1B) receptors facilitate longer drinking bouts of more modest volumes. Taken together, these results indicate that 5-HT(1B) receptors expressed on NAcSh projection neurons facilitate ethanol drinking, with different effects during initiation and maintenance of ethanol-drinking behavior.