Chronic D-amphetamine administered from childhood to adulthood dose-dependently increases the survival of new neurons in the hippocampus of male C57BL/6J mice

Amphetamine exposure alters behaviors, and neuronal and neurochemical activation in the brain of female prairie voles

Previous studies have shown that 3-day d-amphetamine (AMPH) treatment effectively induced conditioned place preferences (CPP) and impaired pair bonding behaviors in prairie voles (Microtus ochrogaster). Using this established animal model and treatment regimen, we examined the effects of the demonstrated threshold rewarding dose of AMPH on various behaviors and their potential underlying neurochemical systems in the brain of female prairie voles. Our data show that 3-day AMPH injections (0.2 mg/kg/day) impaired social recognition and decreased depressive-like behavior in females without affecting their locomotion and anxiety-like behaviors. AMPH treatment also decreased neuronal activation indicated by the labeling of the early growth response protein 1 (Egr-1) as well as the number of neurons double-labeled for Egr-1 and corticotrophin-releasing hormone (CRH) in the dentate gyrus (DG) of the hippocampus and paraventricular nucleus of the hypothalamus (PVN) in the brain. Further, AMPH treatment decreased the number of neurons double-labeled for Egr-1 and tyrosine hydroxylase (TH) but did not affect oxytocinergic neurons in the PVN or cell proliferation and neurogenesis markers in the DG. These data not only demonstrate potential roles of the brain CRH and dopamine systems in mediating disrupted social recognition and depressive-like behaviors by AMPH in female prairie voles, but also further confirm the utility of the prairie vole model for studying interactions between psychostimulants and social behaviors.

Electrically stimulated hind limb muscle contractions increase adult hippocampal astrogliogenesis but not neurogenesis or behavioral performance in male C57BL/6J mice

Regular exercise is crucial for maintaining cognitive health throughout life. Recent evidence suggests muscle contractions during exercise release factors into the blood which cross into the brain and stimulate adult hippocampal neurogenesis. However, no study has tested whether muscle contractions alone are sufficient to increase adult hippocampal neurogenesis and improve behavioral performance. Adult male, C57BL/6J mice were anesthetized and exposed to bilateral hind limb muscle contractions (both concentric and eccentric) via electrical stimulation (e-stim) of the sciatic nerve twice a week for 8 weeks. Each session lasted approximately 20 min and consisted of a total of 40 muscle contractions. The control group was treated similarly except without e-stim (sham). Acute neuronal activation of the dentate gyrus (DG) using cFos immunohistochemistry was measured as a negative control to confirm that the muscle contractions did not activate the hippocampus, and in agreement, no DG activation was observed. Relative to sham, e-stim training increased DG volume by approximately 10% and astrogliogenesis by 75%, but no difference in neurogenesis was detected and no improvement in behavioral performance was observed. E-stim also increased astrogliogenesis in CA1/CA2 hippocampal subfields but not in the cortex. Results demonstrate that muscle contractions alone, in absence of DG activation, are sufficient to increase adult hippocampal astrogliogenesis, but not neurogenesis or behavioral performance in mice.

From Gene to Behavior: L-Type Calcium Channel Mechanisms Underlying Neuropsychiatric Symptoms

The L-type calcium channels (LTCCs) Cav1.2 and Cav1.3, encoded by the CACNA1C and CACNA1D genes, respectively, are important regulators of calcium influx into cells and are critical for normal brain development and plasticity. In humans, CACNA1C has emerged as one of the most widely reproduced and prominent candidate risk genes for a range of neuropsychiatric disorders, including bipolar disorder (BD), schizophrenia (SCZ), major depressive disorder, autism spectrum disorder, and attention deficit hyperactivity disorder. Separately, CACNA1D has been found to be associated with BD and autism spectrum disorder, as well as cocaine dependence, a comorbid feature associated with psychiatric disorders. Despite growing evidence of a significant link between CACNA1C and CACNA1D and psychiatric disorders, our understanding of the biological mechanisms by which these LTCCs mediate neuropsychiatric-associated endophenotypes, many of which are shared across the different disorders, remains rudimentary. Clinical studies with LTCC blockers testing their efficacy to alleviate symptoms associated with BD, SCZ, and drug dependence have provided mixed results, underscoring the importance of further exploring the neurobiological consequences of dysregulated Cav1.2 and Cav1.3. Here, we provide a review of clinical studies that have evaluated LTCC blockers for BD, SCZ, and drug dependence-associated symptoms, as well as rodent studies that have identified Cav1.2- and Cav1.3-specific molecular and cellular cascades that underlie mood (anxiety, depression), social behavior, cognition, and addiction.

The therapeutic contribution of nanomedicine to treat neurodegenerative diseases via neural stem cell differentiation

The discovery of adult neurogenesis drastically changed the therapeutic approaches of central nervous system regenerative medicine. The stimulation of this physiologic process can increase memory and motor performances in patients affected by neurodegenerative diseases. Neural stem cells contribute to the neurogenesis process through their differentiation into specialized neuronal cells. In this review, we describe the most important methods developed to restore neurological functions via neural stem cell differentiation. In particular, we focused on the role of nanomedicine. The application of nanostructured scaffolds, nanoparticulate drug delivery systems, and nanotechnology-based real-time imaging has significantly improved the safety and the efficacy of neural stem cell-based treatments. This review provides a comprehensive background on the contribution of nanomedicine to the modulation of neurogenesis via neural stem cell differentiation.

The Neuropsychiatric Disease-Associated Gene cacna1c Mediates Survival of Young Hippocampal Neurons

Genetic variations in CACNA1C, which encodes the Cav1.2 subunit of L-type calcium channels (LTCCs), are associated with multiple forms of neuropsychiatric disease that manifest high anxiety in patients. In parallel, mice harboring forebrain-specific conditional knockout of cacna1c (forebrain-Cav1.2 cKO) display unusually high anxiety-like behavior. LTCCs in general, including the Cav1.3 subunit, have been shown to mediate differentiation of neural precursor cells (NPCs). However, it has not previously been determined whether Cav1.2 affects postnatal hippocampal neurogenesis in vivo. Here, we show that forebrain-Cav1.2 cKO mice exhibit enhanced cell death of young hippocampal neurons, with no change in NPC proliferation, hippocampal size, dentate gyrus thickness, or corticosterone levels compared with wild-type littermates. These mice also exhibit deficits in brain levels of brain-derived neurotrophic factor (BDNF), and Cre recombinase-mediated knockdown of adult hippocampal Cav1.2 recapitulates the deficit in young hippocampal neurons survival. Treatment of forebrain-Cav1.2 cKO mice with the neuroprotective agent P7C3-A20 restored the net magnitude of postnatal hippocampal neurogenesis to wild-type levels without ameliorating their deficit in BDNF expression. The role of Cav1.2 in young hippocampal neurons survival may provide new approaches for understanding and treating neuropsychiatric disease associated with aberrations in CACNA1C. Visual Abstract.

Effects of addictive drugs on adult neural stem/progenitor cells

Neural stem/progenitor cells (NSPCs) undergo a series of developmental processes before giving rise to newborn neurons, astrocytes and oligodendrocytes in adult neurogenesis. During the past decade, the role of NSPCs has been highlighted by studies on adult neurogenesis modulated by addictive drugs. It has been proven that these drugs regulate the proliferation, differentiation and survival of adult NSPCs in different manners, which results in the varying consequences of adult neurogenesis. The effects of addictive drugs on NSPCs are exerted via a variety of different mechanisms and pathways, which interact with one another and contribute to the complexity of NSPC regulation. Here, we review the effects of different addictive drugs on NSPCs, and the related experimental methods and paradigms. We also discuss the current understanding of major signaling molecules, especially the putative common mechanisms, underlying such effects. Finally, we review the future directions of research in this area.

Evaluation of a C57BL/6J × 129S1/SvImJ Hybrid Nestin-Thymidine Kinase Transgenic Mouse Model for Studying the Functional Significance of Exercise-Induced Adult Hippocampal Neurogenesis

New neurons are continuously generated in the adult hippocampus but their function remains a mystery. The nestin thymidine kinase (nestin-TK) transgenic method has been used for selective and conditional reduction of neurogenesis for the purpose of testing the functional significance of new neurons in learning, memory and motor performance. Here we explored the nestin-TK model on a hybrid genetic background (to increase heterozygosity, and “hybrid vigor”). Transgenic C57BL/6J (B6) were crossed with 129S1/SvImJ (129) producing hybrid offspring (F1) with the B6 half of the genome carrying a herpes simplex virus thymidine kinase (TK) transgene regulated by a modified nestin promoter. In the presence of exogenously administered valganciclovir, new neurons expressing TK undergo apoptosis. Female B6 nestin-TK mice (n = 80) were evaluated for neurogenesis reduction as a positive control. Male and female F1 nestin-TK mice (n = 223) were used to determine the impact of neurogenesis reduction on the Morris water maze (MWM) and rotarod. All mice received BrdU injections to label dividing cells and either valganciclovir or control chow, with or without a running wheel for 30 days. Both the F1 and B6 background displayed approximately 50% reduction in neurogenesis, a difference that did not impair learning and memory on the MWM or rotarod performance. Running enhanced neurogenesis and performance on the rotarod but not MWM suggesting the F1 background may not be suitable for studying pro-cognitive effects of exercise on MWM. Greater reduction of neurogenesis may be required to observe behavioral impacts. Alternatively, new neurons may not play a critical role in learning, or compensatory mechanisms in pre-existing neurons could have masked the deficits. Further work using these and other models for selectively reducing neurogenesis are needed to establish the functional significance of adult hippocampal neurogenesis in behavior.

Behavioral and pharmacological evaluation of a selectively bred mouse model of home cage hyperactivity

Daily levels of physical activity vary greatly across individuals and are strongly influenced by genetic background. While moderate levels of physical activity are associated with improved physical and mental health, extremely high levels of physical activity are associated with behavioral disorders such as attention deficit hyperactivity disorder (ADHD). However, the genetic and neurobiological mechanisms relating hyperactivity to ADHD or other behavioral disorders remain unclear. Therefore, we conducted a selective breeding experiment for increased home cage activity starting with a highly genetically variable population of house mice and evaluated the line for correlated responses in other relevant phenotypes. Here we report results through Generation 10. Relative to the Control line, the High-Active line traveled approximately 4 times as far in the home cage (on days 5 and 6 of a 6-day test), displayed reduced body mass at maturity, reduced reproductive success, increased wheel running and open field behavior, decreased performance on the rotarod, decreased performance on the Morris water maze that was not rescued by acute administration of d-amphetamine, reduced hyperactivity from chronically administered low clinical doses of d-amphetamine, and increased numbers of new cells and neuronal activation of the dentate gyrus. Standardized phenotypic differences between the lines were compared to estimates expected from genetic drift to evaluate whether the line differences could have resulted from random effects as opposed to correlated responses to selection. Results indicated line differences in body mass and locomotor responses to low doses of amphetamine were more likely due to selection than drift. The efficacy of low doses of d-amphetamine in ameliorating hyperactivity support the High-Active line as a useful model for exploring the etiology of hyperactivity-associated comorbid behavioral disorders.

Psychostimulants and brain dysfunction: a review of the relevant neurotoxic effects

Psychostimulants abuse is a major public concern because is associated with serious health complications, including devastating consequences on the central nervous system (CNS). The neurotoxic effects of these drugs have been extensively studied. Nevertheless, numerous questions and uncertainties remain in our understanding of these toxic events. Thus, the purpose of the present manuscript is to review cellular and molecular mechanisms that might be responsible for brain dysfunction induced by psychostimulants. Topics reviewed include some classical aspects of neurotoxicity, such as monoaminergic system and mitochondrial dysfunction, oxidative stress, excitotoxicity and hyperthermia. Moreover, recent literature has suggested new phenomena regarding the toxic effects of psychostimulants. Thus, we also reviewed the impact of these drugs on neuroinflammatory response, blood-brain barrier (BBB) function and neurogenesis. Assessing the relative importance of these mechanisms on psychostimulants-induced brain dysfunction presents an exciting challenge for future research efforts. This article is part of the Special Issue entitled 'CNS Stimulants'.