Sex-Dependent Effects of Environmental Enrichment on Spatial Memory and Brain-Derived Neurotrophic Factor (BDNF) Signaling in a Developmental "Two-Hit" Mouse Model Combining BDNF Haploinsufficiency and Chronic Glucocorticoid Stimulation

Neural underpinnings of fine motor skills under stress and anxiety: A review

This review offers a comprehensive examination of how stress and anxiety affect motor behavior, particularly focusing on fine motor skills and gait adaptability. We explore the role of several neurochemicals, including brain-derived neurotrophic factor (BDNF) and dopamine, in modulating neural plasticity and motor control under these affective states. The review highlights the importance of developing therapeutic strategies that enhance motor performance by leveraging the interactions between key neurochemicals. Additionally, we investigate the complex interplay between emotional-cognitive states and sensorimotor behaviors, showing how stress and anxiety disrupt neural integration, leading to impairments in skilled movements and negatively impacting quality of life. Synthesizing evidence from human and rodent studies, we provide a detailed understanding of the relationships among stress, anxiety, and motor behavior. Our findings reveal neurophysiological pathways, behavioral outcomes, and potential therapeutic targets, emphasizing the intricate connections between neurobiological mechanisms, environmental factors, and motor performance.

Serotonergic agonism and pharmacologically-induced adolescent stress cause operant-based learning deficits in mice

BACKGROUND

The interplay between environmental stress and genetic factors is thought to play an important role in the pathogenesis and maintenance of obsessive-compulsive disorder (OCD). However, the relative contribution of these causative antecedents in the manifestation of cognitive inflexibility-a phenotype often seen in obsessive-compulsive (OC)- spectrum disorders-is not fully understood.

METHOD

In this study, we treated mice with 50 mg/L corticosterone (CORT, a glucocorticoid stress hormone) in their drinking water during adolescence. In adulthood, we assessed anxiety-like behaviour and locomotor activity; along with operant-based discrimination and reversal learning. RU-24969, a selective serotonin receptor 5-HT1A/1B receptor agonist, was used as an acute pharmacological model of OC-like behaviour. RU-24969 (5 mg/kg) was administered prior to each reversal learning testing session.

RESULTS

We found that acute treatment with 5 mg/kg RU-24969 induced stereotyped hyperlocomotion in vehicle- and CORT-treated mice. Furthermore, pre-treatment with CORT in adolescence produced subtle anxiety-like behaviour in adult mice, and also resulted in an impairment to late-stage discrimination learning and alterations to reversal learning. Finally, acute treatment with 5 mg/kg RU-24969 caused an impairment to early-stage reversal learning.

CONCLUSION

Whilst we revealed dissociable detrimental effects of adolescent CORT treatment and acute 5-HT1A/1B receptor agonism on discrimination and reversal learning, respectively, we did not find evidence of additive deleterious effects of these two treatments. We therefore suggest that while disrupted serotonergic signalling is likely to be involved in the cognitive phenotype of OC-spectrum disorders, distinct neuropathological pathways may be at play in mediating the role of stress as an antecedent in OCD and related illnesses.

Lactoferrin deficiency during lactation increases the risk of depressive-like behavior in adult mice

BACKGROUND

Lactoferrin is an active protein in breast milk that plays an important role in the growth and development of infants and is implicated as a neuroprotective agent. The incidence of depression is currently increasing, and it is unclear whether the lack of lactoferrin during lactation affects the incidence of depressive-like behavior in adulthood.

RESULTS

Lack of lactoferrin feeding during lactation affected the barrier and innate immune functions of the intestine, disrupted the intestinal microflora, and led to neuroimmune dysfunction and neurodevelopmental delay in the hippocampus. When exposed to external stimulation, adult lactoferrin feeding-deficient mice presented with worse depression-like symptoms; the mechanisms involved were activation of the LPS-TLR4 signalling pathway in the intestine and hippocampus, reduced BDNF-CREB signaling pathway in hippocampus, increased abundance of depression-related bacteria, and decreased abundance of beneficial bacteria.

CONCLUSIONS

Overall, our findings reveal that lactoferrin feeding deficient during lactation can increase the risk of depressive-like behavior in adults. The mechanism is related to the regulatory effect of lactoferrin on the development of the "microbial-intestinal-brain" axis.

Canalization and plasticity in psychopathology

This theoretical article revives a classical bridging construct, canalization, to describe a new model of a general factor of psychopathology. To achieve this, we have distinguished between two types of plasticity, an early one that we call 'TEMP' for 'Temperature or Entropy Mediated Plasticity', and another, we call 'canalization', which is close to Hebbian plasticity. These two forms of plasticity can be most easily distinguished by their relationship to 'precision' or inverse variance; TEMP relates to increased model variance or decreased precision, whereas the opposite is true for canalization. TEMP also subsumes increased learning rate, (Ising) temperature and entropy. Dictionary definitions of 'plasticity' describe it as the property of being easily shaped or molded; TEMP is the better match for this. Importantly, we propose that 'pathological' phenotypes develop via mechanisms of canalization or increased model precision, as a defensive response to adversity and associated distress or dysphoria. Our model states that canalization entrenches in psychopathology, narrowing the phenotypic state-space as the agent develops expertise in their pathology. We suggest that TEMP - combined with gently guiding psychological support - can counter canalization. We address questions of whether and when canalization is adaptive versus maladaptive, furnish our model with references to basic and human neuroscience, and offer concrete experiments and measures to test its main hypotheses and implications. This article is part of the Special Issue on "National Institutes of Health Psilocybin Research Speaker Series".

The Molecular Effects of Environmental Enrichment on Alzheimer's Disease

Environmental enrichment (EE) is an environmental paradigm encompassing sensory, cognitive, and physical stimulation at a heightened level. Previous studies have reported the beneficial effects of EE in the brain, particularly in the hippocampus. EE improves cognitive function as well as ameliorates depressive and anxiety-like behaviors, making it a potentially effective neuroprotective strategy against neurodegenerative diseases such as Alzheimer's disease (AD). Here, we summarize the current evidence for EE as a neuroprotective strategy as well as the potential molecular pathways that can explain the effects of EE from a biochemical perspective using animal models. The effectiveness of EE in enhancing brain activity against neurodegeneration is explored with a view to differences present in early and late life EE exposure, with its potential application in human being discussed. We discuss EE as one of the non pharmacological approaches in preventing or delaying the onset of AD for future research.

A Novel and Selective Dopamine Transporter Inhibitor, (S)-MK-26, Promotes Hippocampal Synaptic Plasticity and Restores Effort-Related Motivational Dysfunctions

Dopamine (DA), the most abundant human brain catecholaminergic neurotransmitter, modulates key behavioral and neurological processes in young and senescent brains, including motricity, sleep, attention, emotion, learning and memory, and social and reward-seeking behaviors. The DA transporter (DAT) regulates transsynaptic DA levels, influencing all these processes. Compounds targeting DAT (e.g., cocaine and amphetamines) were historically used to shape mood and cognition, but these substances typically lead to severe negative side effects (tolerance, abuse, addiction, and dependence). DA/DAT signaling dysfunctions are associated with neuropsychiatric and progressive brain disorders, including Parkinson’s and Alzheimer diseases, drug addiction and dementia, resulting in devastating personal and familial concerns and high socioeconomic costs worldwide. The development of low-side-effect, new/selective medicaments with reduced abuse-liability and which ameliorate DA/DAT-related dysfunctions is therefore crucial in the fields of medicine and healthcare. Using the rat as experimental animal model, the present work describes the synthesis and pharmacological profile of (S)-MK-26, a new modafinil analogue with markedly improved potency and selectivity for DAT over parent drug. Ex vivo electrophysiology revealed significantly augmented hippocampal long-term synaptic potentiation upon acute, intraperitoneally delivered (S)-MK-26 treatment, whereas in vivo experiments in the hole-board test showed only lesser effects on reference memory performance in aged rats. However, in effort-related FR5/chow and PROG/chow feeding choice experiments, (S)-MK-26 treatment reversed the depression-like behavior induced by the dopamine-depleting drug tetrabenazine (TBZ) and increased the selection of high-effort alternatives. Moreover, in in vivo microdialysis experiments, (S)-MK-26 significantly increased extracellular DA levels in the prefrontal cortex and in nucleus accumbens core and shell. These studies highlight (S)-MK-26 as a potent enhancer of transsynaptic DA and promoter of synaptic plasticity, with predominant beneficial effects on effort-related behaviors, thus proposing therapeutic potentials for (S)-MK-26 in the treatment of low-effort exertion and motivational dysfunctions characteristic of depression and aging-related disorders.

Effects of Treadmill Exercise on Social Behavior in Rats Exposed to Thimerosal with Respect to the Hippocampal Level of GluN1, GluN2A, and GluN2B

Thimerosal (THIM) kills brain neurons via induction of apoptosis and necrosis and induces the pathological features of autism spectrum disorder (ASD) in rats. THIM also affects the function of glutamatergic receptors. On the other hand, exercise induces both improvement and impairment effects on memory, depending on intensity, type, and duration. Treadmill exercise can also alter the expression of glutamatergic receptors. In this study, we aimed to investigate the effect of THIM and three protocols of treadmill exercise on social interaction memory and hippocampal expression of GluN1, GluN2A, and GluN2B in rats. THIM was injected intramuscularly at the dose of 300 µg/kg. The three-chamber apparatus was used to evaluate social interaction memory, and western blotting was used to assess protein expression. The results showed that THIM impaired social memory. Exercise 1 impaired social affiliation in controls. Social memory was impaired in all exercise groups of controls. Exercise 1 + 2 impaired social affiliation in THIM rats. Social memory was impaired in all groups of THIM rats. Exercises 2 and 1 + 2 decreased the expression of GluN1, and exercise 1 increased the expression of GluN2A and GluN2B in controls. THIM increased the expression of GluN2B, while exercise 1 reversed this effect. All exercise protocols increased the expression of GluN2A, and exercises 2 and 1 + 2 increased the expression of GluN1 in THIM rats. In conclusion, both THIM and exercise impaired social memory. Of note, the results did not show a separate and influential role for glutamatergic subunits in modulating memory processes following THIM injection or exercise.

Age-Dependent and Pathway-Specific Bimodal Action of Nicotine on Synaptic Plasticity in the Hippocampus of Mice Lacking the miR-132/212 Genes

Nicotine addiction develops predominantly during human adolescence through smoking. Self-administration experiments in rodents verify this biological preponderance to adolescence, suggesting evolutionary-conserved and age-defined mechanisms which influence the susceptibility to nicotine addiction. The hippocampus, a brain region linked to drug-related memory storage, undergoes major morpho-functional restructuring during adolescence and is strongly affected by nicotine stimulation. However, the signaling mechanisms shaping the effects of nicotine in young vs. adult brains remain unclear. MicroRNAs (miRNAs) emerged recently as modulators of brain neuroplasticity, learning and memory, and addiction. Nevertheless, the age-dependent interplay between miRNAs regulation and hippocampal nicotinergic signaling remains poorly explored. We here combined biophysical and pharmacological methods to examine the impact of miRNA-132/212 gene-deletion (miRNA-132/212-/-) and nicotine stimulation on synaptic functions in adolescent and mature adult mice at two hippocampal synaptic circuits: the medial perforant pathway (MPP) to dentate yrus (DG) synapses (MPP-DG) and CA3 Schaffer collaterals to CA1 synapses (CA3-CA1). Basal synaptic transmission and short-term (paired-pulse-induced) synaptic plasticity was unaltered in adolescent and adult miRNA-132/212-/- mice hippocampi, compared with wild-type controls. However, nicotine stimulation promoted CA3-CA1 synaptic potentiation in mature adult (not adolescent) wild-type and suppressed MPP-DG synaptic potentiation in miRNA-132/212-/- mice. Altered levels of CREB, Phospho-CREB, and acetylcholinesterase (AChE) expression were further detected in adult miRNA-132/212-/- mice hippocampi. These observations propose miRNAs as age-sensitive bimodal regulators of hippocampal nicotinergic signaling and, given the relevance of the hippocampus for drug-related memory storage, encourage further research on the influence of miRNAs 132 and 212 in nicotine addiction in the young and the adult brain.

Early-life stress effects on BDNF DNA methylation in first-episode psychosis and in rats reared in isolation

Stressful events during early-life are risk factors for psychiatric disorders. Brain-derived neurotrophic factor (BDNF) is implicated in psychosis pathophysiology and deficits in BDNF mRNA in animal models of psychiatric disease are reported. DNA methylation can control gene expression and may be influenced by environmental factors such as early-life stress. We investigated BDNF methylation in first-episode psychosis (FEP) patients (n = 58), their unaffected siblings (n = 29) and community-based controls (n = 59), each of whom completed the Childhood Trauma Questionnaire (CTQ); BDNF methylation was also tested in male Wistar rats housed isolated or grouped from weaning. DNA was extracted from human blood and rat brain (prefrontal cortex and hippocampus), bisulphite-converted and the methylation of equivalent sequences within BDNF exon IV determined by pyrosequencing. BDNF methylation did not differ significantly between diagnostic groups; however, individuals who had experienced trauma presented higher levels of methylation. We found association between the mean BDNF methylation and total CTQ score in FEP, as well as between individual CpG sites and subtypes of trauma. No significant correlations were found for controls or siblings with child trauma. These results were independent of age, gender, body mass index, BDNF genotype or LINE-1, a measure of global methylation, which showed no significant association with trauma. Isolation rearing resulted in increased BDNF methylation in both brain regions compared to group-housed animals, a correlate of previously reported changes in gene expression. Our results suggest that childhood maltreatment may result in increased BDNF methylation, providing a mechanism underlying the association between early-life stress and psychosis.

Environmental Complexity and Research Outcomes

Environmental complexity is an experimental paradigm as well as a potential part of animals' everyday housing experiences. In experimental uses, researchers add complexity to stimulate brain development, delay degenerative brain changes, elicit more naturalistic behaviors, and test learning and memory. Complexity can exacerbate or mitigate behavioral problems, give animals a sense of control, and allow for expression of highly driven, species-typical behaviors that can improve animal welfare. Complex environments should be designed thoughtfully with the animal's natural behaviors in mind, reported faithfully in the literature, and evaluated carefully for unexpected effects.

The neuroprotective effect of Riparin IV on oxidative stress and neuroinflammation related to chronic stress-induced cognitive impairment

BACKGROUND

Cognitive impairment is identified as one of the diagnostic criteria for major depressive disorder and can extensively affect the quality of life of patients. Based on these findings, this study aimed to investigate the possible effects of Riparin IV (Rip IV) on cognitive impairment induced by chronic administration of corticosterone in mice.

METHODS

Female Swiss mice were divided into four groups: control (Control), corticosterone (Cort), Riparin IV (Cort + Rip IV), and Fluvoxamine (Cort + Flu). Three groups were administered corticosterone (20 mg/kg) subcutaneously during the 22-day study, while the control group received only vehicle. After the 14th day, the groups were administered medications: Riparin IV (Rip IV), fluvoxamine (Flu), or distilled water, by gavage, 1 h after the subcutaneous injections. After treatment, mice underwent behavioral testing, and brain areas were removed for oxidative stress and cytokine content assays.

RESULTS

The results revealed that Cort-treated mice developed a cognitive impairment and exhibited a neuroinflammatory profile with an oxidative load and Th1/Th2 cytokine imbalance. Rip IV treatment significantly ameliorated the cognitive deficit induced by Cort and displayed a neuroprotective effect.

CONCLUSION

The antidepressant-like ability of Rip IV treatment against chronic Cort-induced stress may be due to its potential to mitigate inflammatory damage and oxidative stress. The antioxidant and anti-inflammatory effect observed indicates Rip IV as a possible drug for antidepressant treatment of non-responsive patients with severe and cognitive symptoms.