Systemic 5-bromo-2-deoxyuridine induces conditioned flavor aversion and c-Fos in the visceral neuraxis

Prior experience with flavored alcohol increases preference for flavored alcohol but flavor does not influence binge-like drinking behavior in mice

BACKGROUND

Binge drinking can lead to various negative consequences and in non-experimental settings, alcohol usually contains flavoring, which may promote increased binge drinking. Preclinical models of binge-like drinking have been well established, however, the influence of flavor on alcohol preference and binge-like drinking has not been fully explored.

METHODS

Male and female C57BL/6 J mice were tested via two-bottle choice with alcohol flavored with different concentrations of unsweetened Cherry flavor Kool-Aid and water. Next, mice were tested for preference for flavored alcohol over plain alcohol. Consumption of flavored alcohol versus water was examined over 48 h. Binge-like drinking with flavored alcohol was validated via drinking in the dark (DID). A separate cohort of mice underwent chronic DID for 6 weeks with either flavored or plain alcohol. After chronic DID, mice were then tested for preference for flavored versus plain alcohol and then alcohol consumption despite adverse effects was examined using the quinine adulteration test.

RESULTS

The 0.1% Kool-Aid concentration was chosen to use for further testing based on intake. Mice preferred Kool-Aid flavored alcohol over plain alcohol after the concentration test, but mice with no prior exposure to plain or flavored alcohol preferred plain over flavored alcohol. Throughout all initial testing, female mice showed increased alcohol intake compared to male mice. Both male and female mice showed binge-like drinking of flavored alcohol, with females having higher intake and blood alcohol levels. Kool-Aid flavor did not increase alcohol intake during chronic binge-like drinking. Previous exposure to flavored alcohol during DID increased the preference for flavored alcohol over plain alcohol but did not influence alcohol consumption despite adverse effects.

CONCLUSION

The present study indicates that prior experience with flavored alcohol increases preference and intake, suggesting an effect of learned safety from neophobia. However, flavor does not impact binge-like alcohol consumption or alcohol drinking despite negative consequences. Additionally, the current study shows that female mice will consume more flavored alcohol than males, similar to findings from other alcohol studies.

Forty-eight hour conditioning produces a robust long lasting flavor preference in rats

Conditioned flavor preference (CFP) learning is a form of associative learning in ingestive behavior. CFP Learning can be rapid and produces preferences of varying strengths that can be exceptionally persistent. We sought to establish a method to produce a robust long-lasting CFP in rats. Rats were given 48-h access (conditioning) to a CS+ flavor (grape or cherry 0.05% Kool-Aid, counterbalanced) mixed with 8% glucose and 0.05% saccharin. In order to determine the strength of conditioning rats were given 14 consecutive days of 24-h access to CS+ and CS- flavors mixed only with 0.05% Kool-Aid and 0.05% saccharin (extinction), then further tested 34 days after the last extinction test (48 days post conditioning) for 2 consecutive days with the CS+ and CS-. We found that not only did the learned CFP fail to extinguish over 14 days of testing, but it also persisted for at least 48 days after conditioning. These data provide a method to produce a robust, long lasting and persistent CFP for use in future ingestive behavior research.

Genetic evidence for p75NTR-dependent tetraploidy in cortical projection neurons from adult mice

A subpopulation of chick retinal projection neurons becomes tetraploid during development, an event prevented by blocking antibodies against p75 neurotrophin receptor (p75(NTR)). We have used an optimized flow cytometric assay, based on the analysis of unfixed brain cell nuclei, to study whether p75(NTR)-dependent neuronal tetraploidization takes place in the cerebral cortex, giving rise to projection neurons as well. We show that 3% of neurons in both murine neocortex and chick telencephalic derivatives are tetraploid, and that in the mouse ~85% of these neurons express the immediate early genes Erg-1 and c-Fos, indicating that they are functionally active. Tetraploid cortical neurons (65-80%) express CTIP2, a transcription factor specific for subcortical projection neurons in the mouse neocortex. During the period in which these neurons are born, p75(NTR) is detected in differentiating neurons undergoing DNA replication. Accordingly, p75(NTR)-deficient mice contain a reduced proportion of both NeuN and CTIP2-positive neocortical tetraploid neurons, thus providing genetic evidence for the participation of p75(NTR) in the induction of neuronal tetraploidy in the mouse neocortex. In the striatum tetraploidy is mainly associated with long-range projection neurons as well since ~80% of tetraploid neurons in this structure express calbindin, a marker of neostriatal-matrix spiny neurons, known to establish long-range projections to the substantia nigra and globus pallidus. In contrast, only 20% of tetraploid cortical neurons express calbindin, which is mainly expressed in layers II-III, where CTIP2 is absent. We conclude that tetraploidy mainly affects long-range projection neurons, being facilitated by p75(NTR) in the neocortex.

Cardiomyocyte proliferation and progenitor cell recruitment underlie therapeutic regeneration after myocardial infarction in the adult mouse heart

Cardiosphere-derived cells (CDCs) have been shown to regenerate infarcted myocardium in patients after myocardial infarction (MI). However, whether the cells of the newly formed myocardium originate from the proliferation of adult cardiomyocytes or from the differentiation of endogenous stem cells remains unknown. Using genetic fate mapping to mark resident myocytes in combination with long-term BrdU pulsing, we investigated the origins of postnatal cardiomyogenesis in the normal, infarcted and cell-treated adult mammalian heart. In the normal mouse heart, cardiomyocyte turnover occurs predominantly through proliferation of resident cardiomyocytes at a rate of ∼1.3–4%/year. After MI, new cardiomyocytes arise from both progenitors as well as pre-existing cardiomyocytes. Transplantation of CDCs upregulates host cardiomyocyte cycling and recruitment of endogenous progenitors, while boosting heart function and increasing viable myocardium. The observed phenomena cannot be explained by cardiomyocyte polyploidization, bi/multinucleation, cell fusion or DNA repair. Thus, CDCs induce myocardial regeneration by differentially upregulating two mechanisms of endogenous cell proliferation.