Chronic light deprivation inhibits appetitive associative learning induced by ethanol and its respective c-Fos and pCREB expression

Chemogenetic inhibition of amygdala excitatory neurons impairs rhEPO-enhanced contextual fear memory after TBI

Erythropoietin (EPO) is a hypoxia-responsive cytokine that induces neuroprotective effect in hypoxic-ischaemic, traumatic, excitotoxic and inflammatory injuries. Recently, utilizing a clinically relevant murine model of TBI and delayed hypoxemia, we have found that ongoing recombinant human EPO (rhEPO) administration influenced neurogenesis, neuroprotection, synaptic density and, behavioral outcomes early after TBI, and the impact on long-lasting outcomes 6 months after injury. We also demonstrated that the 1-month behavioral improvement was associated with mitogen-activated protein kinase (MAPK)/cAMP response element-binding protein (CREB) signaling activation and increased of excitatory synaptic density in the amygdala. However, we did not uncover which type of cells were involved in fear memory response enhancement after rhEPO treatment in the setting of TBI with delayed hypoxemia. In this report, using chemogenetic tools in our controlled cortical impact (CCI) model, we were able to inactivate excitatory neurons and eliminate rhEPO-induced fear memory recall enhancement. In summary, these data demonstrate that rhEPO treatment initiated after TBI enhances contextual fear memory in the injured brain via activation of excitatory neurons in the amygdala.

Exposure to Running Wheels Prevents Ethanol Rewarding Effects: The Role of CREB and Deacetylases SIRT-1 and SIRT-2 in the Nucleus Accumbens and Prefrontal Cortex

Alcohol use disorder is one of the most prevalent addictions, strongly influenced by environmental factors. Voluntary physical activity (VPA) has proven to be intrinsically reinforcing and we hypothesized that, as a non-drug reinforcer, VPA could mitigate ethanol-induced rewarding effects. The transcriptional factor cAMP response element binding protein (CREB), and deacetylases isozymes sirtuins 1 and 2 (SIRT-1 and SIRT-2) have a complex interplay and both play a role in the rewarding effects of ethanol. To test whether the exposure of mice to running wheels inhibits the development of ethanol-induced conditioned place preference (CPP), mice were assigned into four groups: housed in home cages with locked ("Sedentary") or unlocked running wheels (VPA), and treated with saline or 1.8 g/kg ethanol during the conditioning phase. The groups were referred as Saline-Sedentary, Saline-VPA, Ethanol-Sedentary and Ethanol-VPA. The expression of CREB, SIRT-1 and SIRT-2 were evaluated in the prefrontal cortex (PFC) and nucleus accumbens (NAc). VPA prevented the development of ethanol-induced CPP. VPA, ethanol and the combination of both inhibited pCREB and pCREB/CREB ratio in the NAc, suggesting that both reward stimuli can share similar patterns of CREB activation. However, we have found that ethanol-induced increased CREB levels were prevented by VPA. Both VPA groups presented lower SIRT-1 levels in the NAc compared to the Sedentary groups. Thus, exposure to running wheels prevented ethanol-rewarding effects and ethanol-induced increases in CREB in the NAc. The molecular alterations underlying CPP prevention may be related to a lower expression of CREB in the NAc of Ethanol-VPA compared to the respective Sedentary group, given the positive correlation between CPP and CREB levels in the Ethanol-Sedentary group.

The offspring of rats selected for high or low ethanol intake at adolescence exhibit differential ethanol-induced Fos immunoreactivity in the central amygdala and in nucleus accumbens core

Adolescents exhibit, when compared to adults, altered responsivity to the unconditional effects of ethanol. It is unclear if this has a role in the excessive ethanol intake of adolescents. Wistar rats from the third filial generation (F₃) of a short-term breeding program which were selected for high (STDRHI) vs. low (STDRLO) ethanol intake during adolescence, were assessed for ethanol-induced (0.0, 1.25 or 2.5 g/kg) Fos immunoreactivity (Fos-ir) in the central (Ce), basolateral (BLA) and medial (Me) amygdaloid nuclei; nucleus accumbens core and shell (AcbC, AcbSh), ventral tegmental area (VTA), as well as prelimbic and infralimbic (PrL, IL) prefrontal cortices. Following i.p. administration of saline, and across the structures measured, Fos-ir was significantly greater in STDRHI than in STDRLO rats. Across both lines, baseline Fos-ir was significantly lower in BLA than in any other structure, whereas PrL, IL and Shell did not differ between each other and exhibited significantly greater level of baseline neural activation than Ce, Me, AcbC and VTA. STDRLO, but not STDRHI, rats exhibited ethanol-induced Fos-ir in Ce. STRDHI, but not STDRLO, rats exhibited an ethanol-induced Fos-ir depression in AcbC. Key maternal care behaviors (i.e., grooming of the pups, latency to retrieve the pups, time spent in the nest and time adopting a kiphotic posture) were fairly similar across lines. There were significant intergenerational variations in the amount self-licking behaviors in STDRHI dams as well as an increased amount of exploration of the cage in these animals, when compared to STDRLO counterparts. These results indicate that short term selection for differential alcohol intake during adolescence yields heightened neural activity at baseline (i.e., after vehicle) in STRDHI vs. STDRLO adolescent rats, and differential sensitivity to ethanol-induced Fos immunoreactivity in Ce and in AcbC. It is unlikely that rearing patterns explained the neural differences reported, between STDRHI and STDRLO rats.

Dim Light at Night and Constant Darkness: Two Frequently Used Lighting Conditions That Jeopardize the Health and Well-being of Laboratory Rodents

The influence of light on mammalian physiology and behavior is due to the entrainment of circadian rhythms complemented with a direct modulation of light that would be unlikely an outcome of circadian system. In mammals, physiological and behavioral circadian rhythms are regulated by the suprachiasmatic nucleus (SCN) of the hypothalamus. This central control allows organisms to predict and anticipate environmental change, as well as to coordinate different rhythmic modalities within an individual. In adult mammals, direct retinal projections to the SCN are responsible for resetting and synchronizing physiological and behavioral rhythms to the light-dark (LD) cycle. Apart from its circadian effects, light also has direct effects on certain biological functions in such a way that the participation of the SCN would not be fundamental for this network. The objective of this review is to increase awareness, within the scientific community and commercial providers, of the fact that laboratory rodents can experience a number of adverse health and welfare outcomes attributed to commonly-used lighting conditions in animal facilities during routine husbandry and scientific procedures, widely considered as “environmentally friendly.” There is increasing evidence that exposure to dim light at night, as well as chronic constant darkness, challenges mammalian physiology and behavior resulting in disrupted circadian rhythms, neural death, a depressive-behavioral phenotype, cognitive impairment, and the deregulation of metabolic, physiological, and synaptic plasticity in both the short and long terms. The normal development and good health of laboratory rodents requires cyclical light entrainment, adapted to the solar cycle of day and night, with null light at night and safe illuminating qualities during the day. We therefore recommend increased awareness of the limited information available with regards to lighting conditions, and therefore that lighting protocols must be taken into consideration when designing experiments and duly highlighted in scientific papers. This practice will help to ensure the welfare of laboratory animals and increase the likelihood of producing reliable and reproducible results.

Enhanced motivation to alcohol in transgenic mice expressing human α-synuclein

α-Synuclein (αSYN) is the neuropathological hallmark protein of Parkinson's disease (PD) and related neurodegenerative disorders. Moreover, the gene encoding αSYN (SNCA) is a major genetic contributor to PD. Interestingly, independent genome-wide association studies also identified SNCA as the most important candidate gene for alcoholism. Furthermore, single-nucleotide-polymorphisms have been associated with alcohol-craving behavior and alcohol-craving patients showed augmented αSYN expression in blood. To investigate the effect of αSYN on the addictive properties of chronic alcohol use, we examined consumption, motivation, and seeking responses induced by environmental stimuli and relapse behavior in transgenic mice expressing the human mutant [A30P]αSYN throughout the brain. The primary reinforcing effects of alcohol under operant self-administration conditions were increased, while consumption and the alcohol deprivation effect were not altered in the transgenic mice. The same mice were subjected to immunohistochemical measurements of immediate-early gene inductions in brain regions involved in addiction-related behaviors. Acute ethanol injection enhanced immunostaining for the phosphorylated form of cAMP response element binding protein in both amygdala and nucleus accumbens of αSYN transgenic mice, while in wild-type mice no effect was visible. However, at the same time, levels of cFos remain unchanged in both genotypes. These results provide experimental confirmation of SNCA as a candidate gene for alcoholism in addition to its known link to PD.

Involvement of TLR4 in the long-term epigenetic changes, rewarding and anxiety effects induced by intermittent ethanol treatment in adolescence

Studies in humans and experimental animals have demonstrated the vulnerability of the adolescent brain to actions of ethanol and the long-term consequences of binge drinking, including the behavioral and cognitive deficits that result from alcohol neurotoxicity, and increased risk to alcohol abuse and dependence. Although the mechanisms that participate in these effects are largely unknown, we have shown that ethanol by activating innate immune receptors, toll-like receptor 4 (TLR4), induces neuroinflammation, impairs myelin proteins and causes cognitive dysfunctions in adolescent mice. Since neuroimmune signaling is also involved in alcohol abuse, the aim of this study was to assess whether ethanol treatment in adolescence promotes the long-term synaptic and molecular events associated with alcohol abuse and addiction. Using wild-type (WT) and TLR4-deficient (TLR4-KO) adolescent mice treated intermittently with ethanol (3g/kg) for 2 weeks, we showed that binge-like ethanol treatment in adolescent mice promotes short- and long-term alterations in synaptic plasticity and epigenetic changes in the promoter region of bdnf and fosb, which increased their expression in the mPFC of young adult animals. These molecular events were associated with long-term rewarding and anxiogenic-related behavioral effects, along with increased alcohol preference. Our results further showed the participation of neuroimmune system activation and the TLR4 signaling response since deficient mice in TLR4 (TLR4-KO) are protected against molecular and behavioral alterations of ethanol in the adolescent brain. Our results highlight a new role of the neuroimmune function and open up new avenues to develop pharmacological treatments that can normalize the immune signaling responsible for long-term effects in adolescence, including alcohol abuse and related disorders.