Testosterone locally increases vasopressin content but fails to restore choline acetyltransferase activity in other regions in the senescent male rat brain

Testosterone abolishes implicit subordination in social anxiety

Neuro-evolutionary theories describe social anxiety as habitual subordinate tendencies acquired through a recursive cycle of social defeat and submissive reactions. If so, the steroid hormone testosterone might be of therapeutic value, as testosterone is a main force behind implicit dominance drive in many species including humans. We combined these two theories to investigate whether the tendency to submit to the dominance of others is an implicit mechanism in social anxiety (Study-1), and whether this can be relieved through testosterone administration (Study-2). Using interactive eye-tracking we demonstrate that socially anxious humans more rapidly avert gaze from subliminal angry eye contact (Study-1). We replicate this effect of implicit subordination in social anxiety in an independent sample, which is subsequently completely abolished after a single placebo-controlled sublingual testosterone administration (Study-2). These findings provide crucial evidence for hormonal and behavioral treatment strategies that specifically target mechanisms of dominance and subordination in social anxiety.

Approach–Avoidance versus Dominance–Submissiveness: A Multilevel Neural Framework on How Testosterone Promotes Social Status

Approach–avoidance generally describes appetitive motivation and fear of punishment. In a social context approach motivation is, however, also expressed as social aggression and dominance. We therefore link approach–avoidance to dominance–submissiveness, and provide a neural framework that describes how the steroid hormone testosterone shifts reflexive as well as deliberate behaviors towards dominance and promotion of social status. Testosterone inhibits acute fear at the level of the basolateral amygdala and hypothalamus and promotes reactive dominance through upregulation of vasopressin gene expression in the central-medial amygdala. Finally, the hormone can, depending on social context and prenatal hormone exposure, promote both pro- and antisocial behaviors and decisions through its effects on prefrontal–amygdala interactions. All these effects of testosterone, however, serve to increase and maintain social status.

Testosterone reduces amygdala-orbitofrontal cortex coupling

Testosterone influences various aspects of affective behavior, which is mediated by different brain regions within the emotion circuitry. Previous neuroimaging studies have demonstrated that testosterone increases neural activity in the amygdala. To investigate whether this could be due to altered regulation of amygdala functioning which is thought to be mediated by the prefrontal cortex, we studied the effects of exogenous testosterone on the interaction between the amygdala and other brain regions. Healthy middle-aged women received a single nasal testosterone dose in a randomized, placebo-controlled, crossover manner, and performed an emotional face matching task while their brain activity was measured with functional MRI. The results show that testosterone rapidly reduced functional coupling of the amygdala with the orbitofrontal cortex, and enhanced amygdala coupling with the thalamus. This suggests that testosterone may reduce the regulatory control over the amygdala, or that testosterone shifts amygdala output away from the orbitofrontal cortex towards the thalamus. Testosterone also reduced functional coupling with the contralateral amygdala. Because interhemispheric amygdala coupling is lower in men than in women, this result suggests that circulating testosterone may contribute to this sexual dimorphism.

Brain aging and Alzheimer's disease; use it or lose it

(1) Alzheimer's disease is a multifactorial disease in which age and APOE-epsilon 4 are important risk factors. (2) The neuropathological hallmarks of AD, i.e. amorphous plaques, neuritic plaques (NPs), pretangles, neurofibrillary tangles (NFT) and cell death are not part of a single pathogenetic cascade but may occur independently. (3) In brain areas where classical AD changes, i.e. NPs and NFTs, are present, such as the CA1 area of the hippocampus, the nucleus basalis of Meynert and the tuberomamillary nucleus, a decreased metabolic rate is found. The decreased metabolic rate appears not to be induced by the presence of pretangles, NFT or NPs. (4) Decreased metabolic rate may precede cognitive impairment and is thus an early occurring hallmark of AD, which, in principle, may be reversible. The observation that the administration of glucose or insulin enhances memory in AD patients also supports the view that AD has a metabolic basis. (5) Moreover, several observations in postmortem brain indicate that activated neurons are better able to withstand aging and AD, a phenomenon paraphrased by us as 'use it or lose it'. (6) It is, therefore, attractive to direct the development of therapeutic strategies towards restimulation of neuronal metabolic rate in order to improve cognition and other symptoms in AD. A number of pharmacological and non-pharmacological studies support the concept that activation of the brain has beneficial effects and may, to a certain degree, restore several aspects of cognition and other central functions. For instance, the circadian system may be restimulated in AD patients by exposing them to more light or transcutaneous nerve stimulation. A procedure has been developed to culture human postmortem brain tissue that allows testing of the efficacy of putative stimulatory compounds such as neurotrophins.

Sex differences in androgen receptor immunoreactivity in basal forebrain nuclei of elderly and Alzheimer patients

The vertical limb of the diagonal band of Broca (VDB or Ch2) and the nucleus basalis of Meynert (NBM or Ch4) are major cholinergic nuclei of the human basal forebrain, a complex that is affected in Alzheimer's disease (AD). Sex hormones influence the function of these cholinergic neurons in animals and humans and we showed earlier that estrogen and androgen receptors (AR) are present in both the VDB and the NBM of young patients of 20-39 years of age. The aim of the present study was to investigate whether AR expression changes in relation to aging and AD. In both brain areas of male and female patients over the age of 56 nuclear staining had almost disappeared and cytoplasmic AR expression was decreased. This decrease was most pronounced in the VDB of men. In addition, the proportion of neurons showing cytoplasmic AR expression was higher in control aged women than in control aged men in both the VDB and the NBM. Surprisingly, cytoplasmic ARs were significantly decreased in the VDB and the NBM only in AD women and not in AD men. These observations suggest the possible involvement of androgens in the functional changes of the basal forebrain nuclei in aging and AD.

Effects of gonadectomy on immunoreactivity for choline acetyltransferase in the cortex, hippocampus, and basal forebrain of adult male rats

Androgens are known to affect cognitive and mnemonic aspects of spatial processing. The cholinergic system is thought to play an important role in cognition and memory, but little is known about the interaction between androgen and cholinergic neurons. The present study focused on the effects of testosterone on the cholinergic neurons in the anterior cingulate cortex, the posterior parietal cortex, the hippocampus, and the basal forebrain including the medial septum, i.e., regions related to spatial processing. We examined choline acetyltransferase (ChAT) immunoreactivity in three groups of adult male rats: sham-operated (Sham), 28-day gonadectomized (GDX), and 28-day gonadectomized with immediate implantation of testosterone propionate (GDX+TP). Comparison of the Sham and GDX+TP groups demonstrated that the GDX group had significantly decreased cell counts of ChAT-immunoreactive neurons in anterior cingulate cortex layer II/III, posterior parietal cortex layer II/III, and the medial septum, but not in the other basal forebrain subregions examined (the horizontal part of the diagonal band of Broca and the substantia innominata). The GDX group also had significantly reduced hippocampal ChAT-immunoreactive fiber pixel density. The GDX+TP group maintained ChAT-immunoreactive cell counts in the anterior cingulate cortex, posterior parietal cortex, and medial septum equivalent to those in the Sham group. Less than 1% of identified cells showed colocalization of immunoreactivity for ChAT and androgen receptor in the cell bodies of the cortex and basal forebrain. Our observations demonstrate that the presence or absence of testosterone for 4 weeks influenced the cholinergic population region-specifically in the adult rat brain.

Social behavior functions and related anatomical characteristics of vasotocin/vasopressin systems in vertebrates

The neuropeptide arginine vasotocin (AVT; non-mammals) and its mammalian homologue, arginine vasopressin (AVP) influence a variety of sex-typical and species-specific behaviors, and provide an integrational neural substrate for the dynamic modulation of those behaviors by endocrine and sensory stimuli. Although AVT/AVP behavioral functions and related anatomical features are increasingly well-known for individual species, ubiquitous species-specificity presents ever increasing challenges for identifying consistent structure-function patterns that are broadly meaningful. Towards this end, we provide a comprehensive review of the available literature on social behavior functions of AVT/AVP and related anatomical characteristics, inclusive of seasonal plasticity, sexual dimorphism, and steroid sensitivity. Based on this foundation, we then advance three major questions which are fundamental to a broad conceptualization of AVT/AVP social behavior functions: (1) Are there sufficient data to suggest that certain peptide functions or anatomical characteristics (neuron, fiber, and receptor distributions) are conserved across the vertebrate classes? (2) Are independently-evolved but similar behavior patterns (e.g. similar social structures) supported by convergent modifications of neuropeptide mechanisms, and if so, what mechanisms? (3) How does AVT/AVP influence behavior - by modulation of sensorimotor processes, motivational processes, or both? Hypotheses based upon these questions, rather than those based on individual organisms, should generate comparative data that will foster cross-class comparisons which are at present underrepresented in the available literature.

Reduced neuronal activity and reactivation in Alzheimer's disease

1. Alzheimer's disease is a multifactorial disease in which age and APOE-epsilon 4 are important risk factors. Various mutations and even viral infections such as herpes simplex (Itzhaki et al., 1997) may play an additional role. 2. The neuropathological hallmarks of Alzheimer's disease (AD), i.e. amorphous plaques, neuritic plaques (NPs), pretangles, neurofibrillary tangles (NFT) and cell death are not part of a single pathogenetic cascade but are basically independent phenomena. 3. Pretangles can occur in neurons from which the metabolic rate is not altered. However, in brain areas where classical AD changes, i.e. NPs and NFTs, are present, such as the CA1 area of the hippocampus, the nucleus basalis of Meynert and the tuberomamillary nucleus, a decreased metabolic rate is found. Decreased metabolic rate appears to be an independent phenomenon in Alzheimer's disease. It is not induced by the presence of pretangles, NFT or NPs. 4. Decreased metabolic rate may precede cognitive impairment and is thus an early occurring hallmark of Alzheimer's disease, which, in principle, may be reversible. The observation that the administration of glucose or insulin enhances memory in Alzheimer patients also supports the view that Alzheimer's disease is basically a metabolic disease. Moreover, several observations indicate that activated neurons are better able to withstand aging and AD, a phenomenon paraphrased by us as "use it or lose it". It is, therefore, attractive to direct the development of therapeutic strategies towards restimulation of neuronal metabolic rate in order to improve cognition and other symptoms in Alzheimer's disease. A number of pharmacological and non-pharmacological studies support the concept that activation of the brain indeed has beneficial effects on several aspects of cognition and other central functions.

Testosterone effects on vasotocinergic innervation of sexually dimorphic medial preoptic nucleus and lateral septum during aging in male quail

Vasotocin fibers are known to innervate regions important in the regulation of sexual behavior and neuroendocrine systems in quail. In this experiment, vasotocinergic innervation of the lateral septum and of the sexually dimorphic medial preoptic nucleus was studied during reproductive aging relative to sexual behavior or following testosterone (T). There were 4 groups of male Japanese quail (Coturnix japonica) studied: adult reproductive (6 month, n = 4), photoregressed adult (n = 5), old senescent (36 month, n = 4), and old testosterone-treated (n = 5). Immunocytochemistry for vasotocin (VT) was performed on serial sections and quantification of the density of VT-positive fibers was performed by image analysis. Results showed a highly significant decrease in VT-immunocytochemical staining in photoregressed and in old senescent males; whereas T-treatment in old males was associated with recovery of VT-immunocyto-chemical staining, comparable to the adult reproductive male. Previous experiments have shown that T treatment restimulates sexual behavior in senescent males similar to the recovery of sexual behavior in T-treated castrates. These results indicate that the VT system may be associated with the behavioral recovery observed in senescent T-treated males.

Effects of testosterone on the rat renal medullary vasopressin receptor concentration and the antidiuretic response

The renal concentrating ability declines with age in humans and animals. Studies suggest that the concentrating defect is due to a decrease in renal vasopressin sensitivity. With ageing, expression of the renal vasopressin V2 receptor in rat is impaired; the normal receptor expression is restored by testosterone treatment. The effect of testosterone on the renal sensitivity to vasopressin was investigated in young rats. Male rats after orchidectomy and chronic antiandrogen cyproterone acetate treatment, and female rats after chronic testosterone phenylpropionate treatment, were used. The plasma arginine-vasopressin (AVP) and testosterone concentrations, and the antidiuretic responses to AVP and the V2 agonist deamino-[8-D-arginine]-vasopressin (dDAVP) after volume loading were measured, and the renal [3H]AVP binding density was determined. The plasma AVP level decreased slightly, but not significantly, in male rats after orchidectomy and cyproterone acetate treatment, but did not alter in female rats after testosterone treatment. The AVP and dDAVP sensitivities decreased in male rats after orchidectomy and cyproterone acetate administration, and increased in female rats treated with testosterone, as compared with the animals with a normal gonadal function. [3H]AVP binding to the renal inner medullary membranes was decreased following orchidectomy or antiandrogen treatment in male rats, and increased in testosterone-treated female rats. The results suggest that testosterone may play a physiological role in maintenance of the V2 vasopressin receptor expression and hence in the normal urinary concentrating ability in rat.

Sex and species differences in the effects of cohabitation on vasopressin messenger RNA expression in the bed nucleus of the stria terminalis in prairie voles (Microtus ochrogaster) and meadow voles (Microtus pennsylvanicus)

Three days of male and female cohabitation dramatically reduces the density of vasopressin-immunoreactive (AVP-ir) fibers in the lateral septum and lateral habenular nucleus of male, but not of female prairie voles. Here we tested whether this reduction is associated with changes in AVP messenger RNA (mRNA) expression in the bed nucleus of the stria terminalis (BST), the presumed source of these fibers, and with changes in testosterone levels, which may influence AVP biosynthesis in the BST. In addition, we tested whether similar changes can be found in meadow voles, which unlike prairie voles do not dramatically change their social behaviors after mating. In both species, males showed more AVP mRNA-labeled cells in the BST and more grains per labeled cell than females. In prairie vole males, cohabitation increased the number of AVP mRNA labeled BST cells and the density of grains per labeled cells. It also raised plasma testosterone levels. No changes were found in prairie vole females nor in meadow voles of either sex. The changes in prairie vole male suggest that cohabitation stimulates AVP biosynthesis. The previously observed decrease in AVP-ir fiber density in the lateral septum and lateral habenular nucleus may therefore reflect increased synaptic release of AVP, which may contribute to mating-induced changes in social behaviors in prairie vole males.

Decreased number of vasopressin immunoreactive neurons in the medial amygdala and locus coeruleus of the aged rat

The earlier described age-related decreases in vasopressin innervation of extra-hypothalamic rat brain regions were found to coincide with a decrease in vasopressin expression in the cells where these fibers originated. A significant age-related decrease in the number of vasopressin-immunoreactive cell bodies was found in the medial amygdala and locus coeruleus of senescent Brown-Norway (BN/BiRij) rats (33 months) when compared to middle-aged (19 months) and young (3 months) rats. In addition, total testosterone plasma levels were significantly reduced in middle-aged and old rats as compared to young animals and the number of vasopressin-immunoreactive cells in both the medial amygdala and locus coeruleus correlated significantly with the decreased testosterone levels in a similar way as found earlier for vasopressin terminals.

Convergent cholinergic activities in aging and Alzheimer's disease

Choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) activities have been examined postmortem in a series of 66 individuals with no evidence of CNS disease, ranging in age from 24 gestational weeks to 95 years and in 33 cases of Alzheimer's disease (AD) aged 57-89 years. In the normal human hippocampus a striking and highly significant age-related decline in ChAT occurred from middle to old age (between 40 and 100 years); a trend apparent at a later stage and to a lesser extent in the hippocampal gyrus. In both areas enzyme activity in AD was inversely related to age at death; reductions compared with the normal were on average 70-80% in the 60-70 year old groups compared with 30-40% in the 80-90 year old group. A similar trend was apparent with respect to acetylcholinesterase (AchE) histochemical activity associated with fibers and terminals (predominantly cholinergic and concentrated in CA3 and 4 of the hippocampus) but not with reactive perikarya (considered to be noncholinergic) present in both hippocampus and cortex. These data indicate that the normal aging human hippocampus may constitute a useful model for investigating the dysfunction or degeneration of basal forebrain cholinergic neurons in AD.

Central monoamine metabolism in the male Brown-Norway rat in relation to aging and testosterone

Concentrations of dopamine (DA), 3,4-dihydroxyphenylacetic acid (DOPAC), homovanillic acid (HVA), noradrenaline (NA), free 3-methoxy-4-hydroxyphenylethyleneglycol (MHPG), serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) were determined in brain regions of 5-, 20-, and 32-month-old male Brown-Norway rats using high pressure liquid chromatography. In view of the activating effects of sex steroids on peptide and monoamine transmitter systems and the declining plasma testosterone levels with aging, the effects of testosterone supplementation on age-related changes in central monoamine metabolism were also studied. Age-related decreases in monoamine metabolism were observed in nigrostriatal, mesocortical and coeruleohippocampal systems. Marked reductions in DOPAC (35%) and HVA (50%) occurred in the ventral tegmental area between 20 and 32 months of age. 5-HT and 5-HIAA levels showed reductions and increases depending on the brain region. Testosterone administration resulted in elevations of HVA in the substantia nigra and MHPG in the locus coeruleus and hippocampus, which were most pronounced in young animals. It is concluded that there are marked differences in age-related changes between nigrostriatal, mesocortical and coeruleohippocampal systems and that testosterone exerts a stimulatory influence on some aspects of monoamine metabolism in young but not in aged animals.

Spatial memory deficits in aged rats: contributions of the cholinergic system assessed by ChAT

Activity of choline acetylase (ChAT) was measured in basal forebrain cholinergic nuclei and in projection sites of these cells in the hippocampus and cortex of young rats and of aged rats who showed impaired performance on the radial arm maze. Decreased ChAT activity was found in the vertical diagonal band nucleus, the dentate gyrus and striatum of aged rats.