The effect of adolescent testosterone on hippocampal BDNF and TrkB mRNA expression: relationship with cell proliferation

The effect of supraphysiological dose of nandrolone decanoate administration on the inflammatory, neurotrophin and behavioral response in adult and old male mice

This study examined the effect of 6 weeks of supraphysiological nandrolone decanoate (ND) administration in adult mice (7 months) on cognitive function and neuroinflammation during aging. Male C57BL/6 mice were randomized into ND (10 mg·kg-1·wk-1) or control (CTL) groups. Half of the mice were tested at a young (Y) age (ND-Y and CTL-Y), 1 week following final ND administration, while the remaining mice were tested at 16 months (O) (ND-O and CTL-O). Learning and memory were better in young mice compared to older mice, regardless of treatment. ND-O displayed decreased anxiety as compared to all other groups. TNFα and IL1β expression were higher in older mice, regardless of treatment. ND administration in young mice appeared to attenuate the neuroinflammatory response in aging mice as evidenced by decreased COX2, IL-4 and increased IL-10 expression in ND-O compared to CTL-O. BDNF AR and ER expression increased in ND-O compared to CTL-O. Results of the study indicated that supraphysiological ND administration had no negative effect on learning and memory but may attenuate anxiety in older mice. In addition, ND administration in young adult mice may attenuate the inflammatory response during aging, which may be related to elevations in both AR and ER expression.

Influence of Testosterone depletion on Neurotrophin-4 in Hippocampal synaptic plasticity and its effects on learning and memory

Sex steroids are neuromodulators that play a crucial role in learning, memory, and synaptic plasticity, providing circuit flexibility and dynamic functional connectivity in mammals. Previous studies indicate that testosterone is crucial for neuronal functions and required further investigation on various frontiers. However, it is surprising to note that studies on testosterone-induced NT-4 expression and its influence on synaptic plasticity and learning and memory moderation are scanty. The present study is focused on analyzing the localized influence of neurotrophin-4 (NT4) on hippocampal synaptic plasticity and associated moderation in learning and memory under testosterone deprivation. Adult Wistar albino rats were randomly divided into various groups, control (Cont), orchidectomy (ORX), orchidectomy + testosterone supplementation (ORX+T) and control + testosterone (Cont+T). After two weeks, the serum testosterone level was undetectable in ORX rats. The behavioural assessment showed a decline in the learning ability of ORX rats with increased working and reference memory errors in the behavioural assessment in the 8-arm radial maze. The mRNA and protein expressions of NT-4 and androgen receptors were significantly reduced in the ORX group. In addition, there was a decrease in the number of neuronal dendrites in Golgi-Cox staining. These changes were not seen in ORX+T rats with improved learning behaviour. Indicating that testosterone exerts its protective effect on hippocampal synaptic plasticity through androgen receptor-dependent neurotrophin-4 regulation in learning and memory upgrade.

Steroid hormones and hippocampal neurogenesis in the adult mammalian brain

Hippocampal neurogenesis persists across the lifespan in many species, including rodents and humans, and is associated with cognitive performance and the pathogenesis of neurodegenerative disease and psychiatric disorders. Neurogenesis is modulated by steroid hormones that change across development and differ between the sexes in rodents and humans. Here, we discuss the effects of stress and glucocorticoid exposure from gestation to adulthood as well as the effects of androgens and estrogens in adulthood on neurogenesis in the hippocampus. Throughout the review we highlight sex differences in the effects of steroid hormones on neurogenesis and how they may relate to hippocampal function and disease. These data highlight the importance of examining age and sex when evaluating the effects of steroid hormones on hippocampal neurogenesis.

Androgens and Adult Neurogenesis in the Hippocampus

Adult neurogenesis in the hippocampus is modulated by steroid hormones, including androgens, in male rodents. In this review, we summarize research showing that chronic exposure to androgens, such as testosterone and dihydrotestosterone, enhances the survival of new neurons in the dentate gyrus of male, but not female, rodents, via the androgen receptor. However, the neurogenesis promoting the effect of androgens in the dentate gyrus may be limited to younger adulthood as it is not evident in middle-aged male rodents. Although direct exposure to androgens in adult or middle age does not significantly influence neurogenesis in female rodents, the aromatase inhibitor letrozole enhances neurogenesis in the hippocampus of middle-aged female mice. Unlike other androgens, androgenic anabolic steroids reduce neurogenesis in the hippocampus of male rodents. Collectively, the research indicates that the ability of androgens to enhance hippocampal neurogenesis in adult rodents is dependent on dose, androgen type, sex, duration, and age. We discuss these findings and how androgens may be influencing neuroprotection, via neurogenesis in the hippocampus, in the context of health and disease.

Dose-dependent effects of testosterone on spatial learning strategies and brain-derived neurotrophic factor in male rats

Studies suggest that males outperform females on some spatial tasks. This may be due to the effects of sex steroids on spatial strategy preferences. Past experiments with male rats have demonstrated that low doses of testosterone bias them toward a response strategy, whereas high doses of testosterone bias them toward a place strategy. We investigated the effect of different testosterone doses on the ability of male rats to effectively employ these two spatial learning strategies. Furthermore, we quantified concentrations of brain-derived neurotrophic factor (pro-, mature-, and total BDNF) in the prefrontal cortex, hippocampus, and striatum. All rats were bilaterally castrated and assigned to one of three daily injection doses of testosterone propionate (0.125, 0.250, or 0.500 mg/rat) or a control injection of the drug vehicle. Using a plus-maze protocol, we found that a lower testosterone dose (0.125 mg) significantly improved rats' performance on a response task, whereas a higher testosterone dose (0.500 mg) significantly improved rats' performance on a place task. In addition, we found that a low dose of testosterone (0.125 mg) increased total BDNF in the striatum, while a high dose (0.500 mg) increased total BDNF in the hippocampus. Taken altogether, these results suggest that high and low levels of testosterone enhance performance on place and response spatial tasks, respectively, and this effect is associated with changes in BDNF levels within relevant brain regions.

Beyond the Hippocampus and the SVZ: Adult Neurogenesis Throughout the Brain

Convincing evidence has repeatedly shown that new neurons are produced in the mammalian brain into adulthood. Adult neurogenesis has been best described in the hippocampus and the subventricular zone (SVZ), in which a series of distinct stages of neuronal development has been well characterized. However, more recently, new neurons have also been found in other brain regions of the adult mammalian brain, including the hypothalamus, striatum, substantia nigra, cortex, and amygdala. While some studies have suggested that these new neurons originate from endogenous stem cell pools located within these brain regions, others have shown the migration of neurons from the SVZ to these regions. Notably, it has been shown that the generation of new neurons in these brain regions is impacted by neurologic processes such as stroke/ischemia and neurodegenerative disorders. Furthermore, numerous factors such as neurotrophic support, pharmacologic interventions, environmental exposures, and stem cell therapy can modulate this endogenous process. While the presence and significance of adult neurogenesis in the human brain (and particularly outside of the classical neurogenic regions) is still an area of debate, this intrinsic neurogenic potential and its possible regulation through therapeutic measures present an exciting alternative for the treatment of several neurologic conditions. This review summarizes evidence in support of the classic and novel neurogenic zones present within the mammalian brain and discusses the functional significance of these new neurons as well as the factors that regulate their production. Finally, it also discusses the potential clinical applications of promoting neurogenesis outside of the classical neurogenic niches, particularly in the hypothalamus, cortex, striatum, substantia nigra, and amygdala.

Interplay between hormones and exercise on hippocampal plasticity across the lifespan

The hippocampus is a brain structure known to play a central role in cognitive function (namely learning and memory) as well as mood regulation and affective behaviors due in part to its ability to undergo structural and functional changes in response to intrinsic and extrinsic stimuli. While structural changes are achieved through modulation of hippocampal neurogenesis as well as alterations in dendritic morphology and spine remodeling, functional (i.e., synaptic) changes can be noted through the strengthening (i.e., long-term potentiation) or weakening (i.e., long-term depression) of the synapses. While age, hormone homeostasis, and levels of physical activity are some of the factors known to module these forms of hippocampal plasticity, the exact mechanisms through which these factors interact with each other at a given moment in time are not completely understood. It is well known that hormonal levels vary throughout the lifespan of an individual and it is also known that physical exercise can impact hormonal homeostasis. Thus, it is reasonable to speculate that hormone modulation might be one of the various mechanisms through which physical exercise differently impacts hippocampal plasticity throughout distinct periods of an individual's life. The present review summarizes the potential relationship between physical exercise and different types of hormones (namely sex, metabolic, and stress hormones) and how this relationship may mediate the effects of physical activity during three distinct life periods, adolescence, adulthood, and senescence. Overall, the vast majority of studies support a beneficial role of exercise in maintaining hippocampal hormonal levels and consequently, hippocampal plasticity, cognition, and mood regulation.

Effect of adolescent androgen manipulation on psychosis-like behaviour in adulthood in BDNF heterozygous and control mice

RATIONALE

Males are more prone to psychosis, schizophrenia and substance abuse and addiction in adolescence and early adulthood than females. However, the role of androgens during this developmental period is poorly understood.

OBJECTIVES

This study aimed to examine how androgens in adolescence influence psychosis-like behaviour in adulthood and whether brain-derived neurotrophic factor (BDNF) is a mediator of these developmental effects.

METHODS

Wild-type and BDNF heterozygous male mice were castrated at pre-pubescence and implanted with testosterone or dihydrotestosterone (DHT). In adulthood, we assessed amphetamine- and MK-801-induced hyperlocomotion as a model of psychosis-like behaviour. Western blot analysis was used to quantify levels of the dopamine transporter (DAT) and N-methyl-d-aspartate (NMDA) receptor subunits.

RESULTS

While castration itself had little effect on behaviour, adolescent testosterone, but not DHT, significantly reduced amphetamine-induced hyperlocomotion, whereas both testosterone and DHT reduced the effect of MK-801. These effects were similar in mice of either genotype. In wildtype mice, both testosterone and DHT treatment reduced DAT expression in the medial prefrontal cortex (mPFC) but these effects were absent in BDNF heterozygous mice. There were no effects on NMDA receptor subunit levels.

CONCLUSIONS

The differential effect of adolescent testosterone and DHT on amphetamine-induced hyperlocomotion in adulthood suggests involvement of conversion of testosterone to estrogen and subsequent modulation of dopaminergic signalling. In contrast, the similar effect of testosterone and DHT treatment on NMDA receptor-mediated hyperlocomotion indicates it is mediated by androgen receptors. The involvement of BDNF in these hormone effects remains to be elucidated. These results demonstrate that, during adolescence, androgens significantly influence key pathways related to various mental illnesses prevalent in adolescence.

Sex-Dependent Signaling Pathways Underlying Seizure Susceptibility and the Role of Chloride Cotransporters

Seizure incidence, severity, and antiseizure medication (ASM) efficacy varies between males and females. Differences in sex-dependent signaling pathways that determine network excitability may be responsible. The identification and validation of sex-dependent molecular mechanisms that influence seizure susceptibility is an emerging focus of neuroscience research. The electroneutral cation-chloride cotransporters (CCCs) of the SLC12A gene family utilize Na⁺-K⁺-ATPase generated electrochemical gradients to transport chloride into or out of neurons. CCCs regulate neuronal chloride gradients, cell volume, and have a strong influence over the electrical response to the inhibitory neurotransmitter GABA. Acquired or genetic causes of CCCs dysfunction have been linked to seizures during early postnatal development, epileptogenesis, and refractoriness to ASMs. A growing number of studies suggest that the developmental expression of CCCs, such as KCC2, is sex-dependent. This review will summarize the reports of sexual dimorphism in epileptology while focusing on the role of chloride cotransporters and their associated modulators that can influence seizure susceptibility.

Impact of Auditory Integration Therapy (AIT) on the Plasma Levels of Human Glial Cell Line-Derived Neurotrophic Factor (GDNF) in Autism Spectrum Disorder

Neurotrophic factors, including the glial cell line-derived neurotrophic factor (GDNF), are of importance for synaptic plasticity regulation, intended as the synapses' ability to strengthen or weaken their responses to differences in neuronal activity. Such plasticity is essential for sensory processing, which has been shown to be impaired in autism spectrum disorder (ASD). This study is the first to investigate the impact of auditory integration therapy (AIT) of sensory processing abnormalities in autism on plasma GDNF levels. Fifteen ASD children, aged between 5 and 12 years, were enrolled and underwent the present research study. AIT was performed throughout 10 days with a 30-min session twice a day. Before and after AIT, Childhood Autism Rating Scale (CARS), Social Responsiveness Scale (SRS), and Short Sensory Profile (SSP) scores were calculated, and plasma GDNF levels were assayed by an EIA test. A substantial decline in autistic behavior was observed after AIT in the scaling parameters used. Median plasma GDNF level was 52.142 pg/ml before AIT. This level greatly increased immediately after AIT to 242.05 pg/ml (P < 0.001). The levels were depressed to 154.00 pg/ml and 125.594 pg/ml 1 month and 3 months later, respectively, but they were still significantly higher compared with the levels before the treatment (P = 0.001, P = 0.01, respectively). There was an improvement in the measures of autism severity as an effect of AIT which induced the up-regulation of GDNF in plasma. Further research, on a large scale, is needed to evaluate if the cognitive improvement of ASD children after AIT is related or not connected to the up-regulation of GDNF.

Sex hormones modulate pathogenic processes in experimental traumatic brain injury

Clinical and animal studies have revealed sex-specific differences in histopathological and neurological outcome after traumatic brain injury (TBI). The impact of perioperative administration of sex steroid inhibitors on TBI is still elusive. Here, we subjected male and female C57Bl/6N mice to the controlled cortical impact (CCI) model of TBI and applied pharmacological inhibitors of steroid hormone synthesis, that is, letrozole (LET, inhibiting estradiol synthesis by aromatase) and finasteride (FIN, inhibiting dihydrotestosterone synthesis by 5α-reductase), respectively, starting 72 h prior CCI, and continuing for a further 48 h after CCI. Initial gene expression analyses showed that androgen (Ar) and estrogen receptors (Esr1) were sex-specifically altered 72 h after CCI. When examining brain lesion size, we found larger lesions in male than in female mice, but did not observe effects of FIN or LET treatment. However, LET treatment exacerbated neurological deficits 24 and 72 h after CCI. On the molecular level, FIN administration reduced calpain-dependent spectrin breakdown products, a proxy of excitotoxicity and disturbed Ca²⁺ homeostasis, specifically in males, whereas LET increased the reactive astrocyte marker glial fibrillary acid protein specifically in females. Examination of neurotrophins (brain-derived neurotrophic factor, neuronal growth factor, NT-3) and their receptors (p75^NTR , TrkA, TrkB, TrkC) revealed CCI-induced down-regulation of TrkB and TrkC protein expression, which was reduced by LET in both sexes. Interestingly, FIN decreased neuronal growth factor mRNA expression and protein levels of its receptor TrkA only in males. Taken together, our data suggest a sex-specific impact on pathogenic processes in the injured brain after TBI. Sex hormones may thus modulate pathogenic processes in experimental TBI.

Sex Differences in Sex Hormone Profiles and Prediction of Consciousness Recovery After Severe Traumatic Brain Injury

Objective: The clinical course of unconsciousness after traumatic brain injury (TBI) is commonly unpredictable and it remains a challenge with limited therapeutic options. The aim of this study was to evaluate the early changes in serum sex hormone levels after severe TBI (sTBI) and the use of these hormones to predict recovery from unconsciousness with regard to sex. Methods: We performed a retrospective study including patients with sTBI. A statistical of analysis of serum sex hormone levels and recovery of consciousness at 6 months was made to identify the effective prognostic indicators. Results: Fifty-five male patients gained recovery of consciousness, and 37 did not. Of the female patients, 22 out of 32 patients regained consciousness. Male patients (n = 92) with sTBI, compared with healthy subjects (n = 60), had significantly lower levels of follicular stimulating hormone (FSH), testosterone and progesterone and higher levels of prolactin. Female patients (n = 32) with sTBI, compared with controls (n = 60), had significantly lower levels of estradiol, progesterone, and testosterone and significantly higher levels of FSH and prolactin. Testosterone significantly predicted consciousness recovery in male patients. Normal or elevated testosterone levels in the serum were associated with a reduced risk of the unconscious state in male patients with sTBI. For women patients with sTBI, sex hormone levels did not contribute to the prediction of consciousness recovery. Conclusion: These findings indicate that TBI differentially affects the levels of sex-steroid hormones in men and women patients. Plasma levels of testosterone could be a good candidate blood marker to predict recovery from unconsciousness after sTBI for male patients.

TREK-1 pathway mediates isoflurane-induced memory impairment in middle-aged mice

Post-operative cognitive dysfunction (POCD) has been widely reported, especially in elderly patients. An association between POCD and inhalational anesthetics, such as isoflurane, has been suggested. The TWIK-related K⁺ channel-1 (TREK-1) controls several major cellular responses involved in memory formation and is believed to participate in the development of depression, cerebral ischemia and blood-brain barrier dysfunction. However, the specific role of TREK-1 in mediating anesthesia-induced POCD remains unknown. In the current study, we determined that exposure to isoflurane affected memory in middle-aged mice and altered TREK-1 expression. In addition, TREK-1 over-expression exacerbated isoflurane-induced memory impairment, while TREK-1 silence attenuated the impairment. Taken together, our data demonstrate that inhibition of TREK-1 protects mice from cognitive impairment induced by anesthesia and TREK-1 is a potential therapeutic target against memory impairment induced by volatile anesthetics.

Improvement of spatial learning and memory, cortical gyrification patterns and brain oxidative stress markers in diabetic rats treated with Ficus deltoidea leaf extract and vitexin

Despite the fact that Ficus deltoidea and vitexin played important roles in controlling hyperglycemia, an effective mitigation strategy dealing with cognitive deficit observed in diabetes, little is known about its neuroprotective effects. The study is aimed to determine changes in behavioral, gyrification patterns and brain oxidative stress markers in streptozotocin (STZ)-induced diabetic rats following F. deltoidea and vitexin treatments. Diabetic rats were treated orally with metformin, methanolic extract of F. deltoidea leaves and vitexin for eight weeks. Morris water maze (MWM) test was performed to evaluate learning and memory functions. The patterns of cortical gyrification were subsequently visualized using micro-computed tomography (micro-CT). Quantification of brain oxidative stress biomarkers, insulin, amylin as well as serum testosterone were measured using a spectrophotometer. The brain fatty acid composition was determined using gas chromatography (GC). Biochemical variation in brain was estimated using Fourier transform infrared (FT-IR) spectroscopy. Results showed that oral administration of F. deltoidea extract and vitexin to diabetic rats attenuated learning and memory impairment, along with several clusters of improved gyrification. Both treatments also caused a significant increase in the superoxide dismutase (SOD) and glutathione peroxidase (GPx) values, as well as a significant reduction of TBARS. Strikingly, improvement of cortical gyrification, spatial learning and memory are supported by serum testosterone levels, fatty acid composition of brain and FT-IR spectra.

Cognitive impairment in first-episode drug-naïve patients with schizophrenia: Relationships with serum concentrations of brain-derived neurotrophic factor and glial cell line-derived neurotrophic factor

OBJECTIVES

Evidence suggests that brain-derived neurotrophic factor (BDNF) and glial cell line -derived neurotrophic factor (GDNF) are important in the regulation of synaptic plasticity, which plays a key role in the cognitive processes in psychiatric disorders. Our work aimed at exploring the associations between serum BDNF and GDNF levels and cognitive functions in first-episode drug-naïve (FEDN) patients with schizophrenia.

METHODS

The BDNF and GDNF levels of 58 FEDN patients and 55 age- and sex-matched healthy controls were measured and test subjects were examined using several neurocognitive tests including the verbal fluency test (VFT), the trail making test (TMT), the digit span test (DST), and the Stroop test.

RESULTS

Patients performed significantly worse than controls in nearly all neurocognitive performances except the forward subscale part of the DST. BDNF levels were inversely correlated to TMT-part B scores and positively correlated to VFT-action in the FEDN group. GDNF levels showed a positive correlation with VFT-action scores and a negative correlation with TMT-part B scores of these patients.

CONCLUSION

Current data suggests that cognitive dysfunction widely exists in the early stages of schizophrenia. BDNF and GDNF may be jointly contributed to the pathological mechanisms involved in cognitive impairment in FEDN patients with schizophrenia.

Dissociable effects of age and testosterone on adolescent impatience

The onset of adolescence is associated with an increase in transgressive behaviours-from juvenile delinquency to substance use and unprotected sex-that are often attributed to increased impulsiveness. In the past, this increase was ascribed to "raging hormones"; more recently, to an imbalance in the maturation of different brain regions. However, it remains unclear how these large-scale biological changes impact specific processes that result in impulsive decisions, namely, sensitivity to immediate rewards and general discounting of future options. To gain further insight into these questions, we used an intertemporal choice task to investigate the role of testosterone in impatient decision-making in boys at the developmental transition to adolescence (N=72, ages 11-14). Our results suggest that increased testosterone (but not age) is related to increased sensitivity to immediate rewards, whereas increased age (but not testosterone) is related to a reduction in general impatience. These results are discussed in the context of recent neurobiological models of adolescent development.

Multiple Mechanisms Linking Type 2 Diabetes and Alzheimer's Disease: Testosterone as a Modifier

Evidence in support of links between type-2 diabetes mellitus (T2DM) and Alzheimer's disease (AD) has increased considerably in recent years. AD pathological hallmarks include the accumulation of extracellular amyloid-β (Aβ) and intracellular hyperphosphorylated tau in the brain, which are hypothesized to promote inflammation, oxidative stress, and neuronal loss. T2DM exhibits many AD pathological features, including reduced brain insulin uptake, lipid dysregulation, inflammation, oxidative stress, and depression; T2DM has also been shown to increase AD risk, and with increasing age, the prevalence of both conditions increases. In addition, amylin deposition in the pancreas is more common in AD than in normal aging, and although there is no significant increase in cerebral Aβ deposition in T2DM, the extent of Aβ accumulation in AD correlates with T2DM duration. Given these similarities and correlations, there may be common underlying mechanism(s) that predispose to both T2DM and AD. In other studies, an age-related gradual loss of testosterone and an increase in testosterone resistance has been shown in men; low testosterone levels can also occur in women. In this review, we focus on the evidence for low testosterone levels contributing to an increased risk of T2DM and AD, and the potential of testosterone treatment in reducing this risk in both men and women. However, such testosterone treatment may need to be long-term, and would need regular monitoring to maintain testosterone at physiological levels. It is possible that a combination of testosterone therapy together with a healthy lifestyle approach, including improved diet and exercise, may significantly reduce AD risk.

Hippocampal serotonin-2A receptor-immunoreactive neurons density increases after testosterone therapy in the gonadectomized male mice

The change of steroid levels may also exert different modulatory effects on the number and class of serotonin receptors present in the plasma membrane. The effects of chronic treatment of testosterone for anxiety were examined and expression of 5-HT_2A serotonergic receptor, neuron, astrocyte, and dark neuron density in the hippocampus of gonadectomized male mice was determined. Thirty-six adult male NMRI mice were randomly divided into six groups: intact-no testosterone treatment (No T), gonadectomy (GDX)-No T, GDX-Vehicle, GDX-6.25 mg/kg testosterone (T), GDX-12.5 mg/kg T, and GDX-25 mg/kg T. Anxiety-related behavior was evaluated using elevated plus maze apparatus. The animals were anesthetized after 48 hours after behavioral testing, and decapitated and micron slices were prepared for immunohistochemical as well as histopathological assessment. Subcutaneous injection of testosterone (25 mg/kg) may induce anxiogenic-like behavior in male mice. In addition, immunohistochemical data reveal reduced expression of 5-HT_2A serotonergic receptor after gonadectomy in all areas of the hippocampus. However, treatment with testosterone could increase the mean number of dark neurons as well as immunoreactive neurons in CA1 and CA3 area, dose dependently. The density of 5-HT_2A receptor-immunoreactive neurons may play a crucial role in the induction of anxiety like behavior. As reduction in such receptor expression have shown to significantly enhance anxiety behaviors. However, replacement of testosterone dose dependently enhances the number of 5-HT_2A receptor-immunoreactive neurons and interestingly also reduced anxiety like behaviors.

The Potential of Gonadal Hormone Signalling Pathways as Therapeutics for Dementia

Dementia is an ever-expanding problem facing an ageing society. Currently, there is a sharp paucity of treatment strategies. It has long been known that sex hormones, namely 17β-estradiol and testosterone, possess neuroprotective- and cognitive-enhancing qualities. However, certain lacunae in the knowledge underlying their molecular mechanisms have delayed their use as treatment strategies in dementia. With recent advancements in pharmacology and molecular biology, especially in the development of safer selective oestrogen receptor modulators and the recent discovery of the small-molecule brain-derived neurotrophic factor receptor agonist, 7,8-dihydroxyflavone, the exploitation of these signalling pathways for clinical use has become possible. This review aims to adumbrate the evidence and hurdles underscoring the use of sex hormones in the treatment of dementia as well as discussing some direction that is required to advance the translation of evidence into practise.

Association of testosterone and BDNF serum levels with craving during alcohol withdrawal

Preclinical and clinical studies show associations between testosterone and brain-derived neurotrophic growth factor (BDNF) serum levels. BDNF and testosterone have been independently reported to influence alcohol consumption. Therefore, we aimed to investigate a possible interplay of testosterone and BDNF contributing to alcohol dependence. Regarding possible interplay of testosterone and BDNF and the activity of the hypothalamic pituitary axis (HPA), we included cortisol serum levels in our research. We investigated testosterone and BDNF serum levels in a sample of 99 male alcohol-dependent patients during alcohol withdrawal (day 1, 7, and 14) and compared them to a healthy male control group (n = 17). The testosterone serum levels were significantly (p < 0.001) higher in the patients' group than in the control group and decreased significantly during alcohol withdrawal (p < 0.001). The decrease of testosterone serum levels during alcohol withdrawal (days 1-7) was significantly associated with the BDNF serum levels (day 1: p = 0.008). In a subgroup of patients showing high cortisol serum levels (putatively mirroring high HPA activity), we found a significant association of BDNF and testosterone as well as with alcohol craving measured by the Obsessive and Compulsive Drinking Scale (OCDS). Our data suggest a possible association of BDNF and testosterone serum levels, which may be relevant for the symptomatology of alcohol dependence. Further studies are needed to clarify our results.

Sex hormones and adult hippocampal neurogenesis: Regulation, implications, and potential mechanisms

Neurogenesis within the adult hippocampus is modulated by endogenous and exogenous factors. Here, we review the role of sex hormones in the regulation of adult hippocampal neurogenesis in males and females. The review is framed around the potential functional implications of sex hormone regulation of adult hippocampal neurogenesis, with a focus on cognitive function and mood regulation, which may be related to sex differences in incidence and severity of dementia and depression. We present findings from preclinical studies of endogenous fluctuations in sex hormones relating to reproductive function and ageing, and from studies of exogenous hormone manipulations. In addition, we discuss the modulating roles of sex, age, and reproductive history on the relationship between sex hormones and neurogenesis. Because sex hormones have diverse targets in the central nervous system, we overview potential mechanisms through which sex hormones may influence hippocampal neurogenesis. Lastly, we advocate for a more systematic consideration of sex and sex hormones in studying the functional implications of adult hippocampal neurogenesis.

Social behavior, hormones and adult neurogenesis

A variety of experiences have been shown to affect the production of neurons in the adult hippocampus. These effects may be mediated by experience-driven hormonal changes, which, in turn, interact with factors such as sex, age and life history to alter brain plasticity. Although the effects of physical experience and stress have been extensively characterized, various types of social experience across the lifespan trigger profound neuroendocrine changes in parallel with changes in adult neurogenesis. This review article focuses on the influence of specific social experiences on adult neurogenesis in the dentate gyrus and the potential role of hormones in these effects.