Effects of testosterone on unit activity in rat hypothalamus and septum

Androgen Affects the Dynamics of Intrinsic Plasticity of Pyramidal Neurons in the CA1 Hippocampal Subfield in Adolescent Male Rats

Androgen receptor (AR) is abundantly expressed in the preoptico-hypothalamic area, bed nucleus of stria terminalis, and medial amygdala of the brain where androgen plays an important role in regulating male sociosexual, emotional and aggressive behaviors. In addition to these brain regions, AR is also highly expressed in the hippocampus, suggesting that the hippocampus is another major target of androgenic modulation. It is known that androgen can modulate synaptic plasticity in the CA1 hippocampal subfield. However, to date, the effects of androgen on the intrinsic plasticity of hippocampal neurons have not been clearly elucidated. In this study, the effects of androgen on the expression of AR in the hippocampus and on the dynamics of intrinsic plasticity of CA1 pyramidal neurons were examined using immunohistochemistry, Western blotting and whole-cell current-clamp recording in unoperated, sham-operated, orchiectomized (OCX), OCX + testosterone (T) or OCX + dihydrotestosterone (DHT)-primed adolescent male rats. Orchiectomy significantly decreased AR-immunoreactivity, resting membrane potential, action potential numbers, afterhyperpolarization amplitude and membrane resistance, whereas it significantly increased action potential threshold and membrane capacitance. These effects were successfully reversed by treatment with either aromatizable androgen T or non-aromatizable androgen DHT. Furthermore, administration of the AR-antagonist flutamide in intact rats showed similar changes to those in OCX rats, suggesting that androgens affect the excitability of CA1 pyramidal neurons possibly by acting on the AR. Our current study potentially clarifies the role of androgen in enhancing the basal excitability of the CA1 pyramidal neurons, which may influence selective neuronal excitation/activation to modulate certain hippocampal functions.

Sex and age modulate the visual perception of distance

An experiment was conducted to evaluate the ability of 28 younger and older adults to visually bisect distances in depth both indoors and outdoors; half of the observers were male and half were female. Observers viewed 15-m and 30-m distance extents in four different environmental settings (two outdoor grassy fields and an indoor hallway and atrium) and were required to adjust the position of a marker to place it at the midpoint of each stimulus distance interval. Overall, the observers' judgments were more accurate indoors than outdoors. In outdoor environments, many individual observers exhibited perceptual compression of farther distances (e.g., these observers placed the marker closer than the actual physical midpoints of the stimulus distance intervals). There were significant modulatory effects of both age and sex upon the accuracy and precision of the observers' judgments. The judgments of the male observers were more accurate than those of the female observers and they were less influenced by environmental context. In addition, the accuracies of the younger observers' judgments were less influenced by context than those of the older observers. With regard to the precision of the observers' judgments, the older females exhibited much more variability across repeated judgments than the other groups of observers (younger males, younger females, and older males). The results of our study demonstrate that age and sex are important variables that significantly affect the visual perception of distance.

The effects of flutamide on cell-cell junctions in the testis, epididymis, and prostate

In this review, we summarize recent findings on the effect of the anti-androgen flutamide on cell-cell junctions in the male reproductive system. We outline developmental aspects of flutamide action on the testis, epididymis, and prostate, and describe changes in junction protein expression and organization of junctional complexes in the adult boar following prenatal and postnatal exposure. We also discuss findings on the mechanisms by which flutamide induces alterations in cell-cell junctions in reproductive tissues of adult males, with special emphasis on cytoplasmic effects. Based on the results from in vivo and in vitro studies in the rat, we propose that flutamide affects the expression of junction proteins and junction complex structure not only by inhibiting androgen receptor activity, but equally important by modulating protein kinase-dependent signaling in testicular cells. Additionally, results from studies on prostate cancer cell lines point to a role for the cellular molecular outfit in response to flutamide.

Evolutionary Fate of the Androgen Receptor-Signaling Pathway in Ray-Finned Fishes with a Special Focus on Cichlids

The emergence of the steroid system is coupled to the evolution of multicellular animals. In vertebrates in particular, the steroid receptor repertoire has been shaped by genome duplications characteristic to this lineage. Here, we investigate for the first time the composition of the androgen receptor–signaling pathway in ray-finned fish genomes by focusing in particular on duplicates that emerged from the teleost-specific whole-genome duplication. We trace lineage- and species-specific duplications and gene losses for the genomic and nongenomic pathway of androgen signaling and subsequently investigate the sequence evolution of these genes. In one particular fish lineage, the cichlids, we find evidence for differing selection pressures acting on teleost-specific whole-genome duplication paralogs at a derived evolutionary stage. We then look into the expression of these duplicated genes in four cichlid species from Lake Tanganyika indicating, once more, rapid changes in expression patterns in closely related fish species. We focus on a particular case, the cichlid specific duplication of the rac1 GTPase, which shows possible signs of a neofunctionalization event.

Sex differences in anxiety and depression: role of testosterone

Compelling evidence exists for pervasive sex differences in pathological conditions, including anxiety and depressive disorders, with females more than twice as likely to be afflicted. Gonadal hormones may be a major factor in this disparity, given that women are more likely to experience mood disturbances during times of hormonal flux, and testosterone may have protective benefits against anxiety and depression. In this review we focus on the effects of testosterone in males and females, revealed in both human and animal studies. We also present possible neurobiological mechanisms underlying testosterone's mostly protective benefits, including the brain regions, neural circuits, and cellular and molecular pathways involved. While the precise underlying mechanisms remain unclear, both activational and organizational effects of testosterone appear to contribute to these effects. Future clinical studies are necessary in order to better understand when and how testosterone therapy may be effective in both sexes.

Blockade of androgen receptor in the medial amygdala inhibits noncontact erections in male rats

Our previous work demonstrated that androgens in the medial amygdala (MeA) of castrated male rats maintained noncontact erections (NCEs), which occur during exposure to an inaccessible receptive female, for one week after implantation. The present experiments investigated the effects of implantation into the MeA of either flutamide (F), a blocker of androgen receptors, or of 1,4,6-androstatrien-3,17-dione (ATD), which blocks aromatization of testosterone. One day after implantation of F, fewer males displayed NCEs, and had longer latencies to the first NCE and fewer NCEs, and spent less total time in genital grooming, compared to the control group. ATD had only weak facilitative effects on some measures of NCEs. These results suggest that androgen receptors in the MeA play a major role in the regulation of NCEs and that the MeA is one of the neuronal structures that regulate male sexual arousal. Furthermore, it is sensitive to relatively fast changes in the level of androgen receptors stimulation.

Membrane androgen receptors may mediate androgen reinforcement

Anabolic-androgenic steroid (AAS) abuse is widespread. Moreover, AAS are reinforcing, as shown by self-administration in rodents. However, the receptors that transduce the reinforcing effects of AAS are unclear. AAS may bind to classical nuclear androgen receptors (ARs) or membrane receptors. We used two approaches to examine the role of nuclear ARs in AAS self-administration. First, we tested androgen self-administration in rats with the testicular feminization mutation (Tfm), which interferes with androgen binding. If nuclear ARs are essential for AAS self-administration, Tfm males should not self-administer androgens. Tfm males and wild-type (WT) littermates self-administered the non-aromatizable androgen dihydrotestosterone (DHT) or vehicle intracerebroventricularly (ICV) at fixed-ratio (FR) schedules up to FR5. Both Tfm and WT rats acquired a preference for the active nose-poke during DHT self-administration (66.4+/-9.6 responses/4 h for Tfm and 79.2+/-11.5 for WT responses/4 h), and nose-pokes increased as the FR requirement increased. Preference scores were significantly lower in rats self-administering vehicle (42.3+/-5.3 responses/4 h for Tfm and 19.1+/-4.0 responses/4 h for WT). We also tested self-administration of DHT conjugated to bovine serum albumin (BSA) at C3 and C17, which is limited to actions at the cell surface. Hamsters were allowed to self-administer DHT, BSA and DHT-BSA conjugates for 15 days at FR1. The hamsters showed a significant preference for DHT (18.0+/-4.1 responses/4 h) or DHT-BSA conjugates (10.0+/-3.7 responses/4 h and 21.0+/-7.2 responses/4 h), but not for BSA (2.5+/-2.4 responses/4 h). Taken together, these data demonstrate that nuclear ARs are not required for androgen self-administration. Furthermore, androgen self-administration may be mediated by plasma membrane receptors.

Vertebrate sex steroid receptors: evolution, ligands, and neurodistribution

This review focuses on our current understanding of vertebrate sex steroid receptors, with an emphasis on their evolutionary relationships. These relationships are discussed based on nucleotide and amino acid sequence data, which provide clues to the process by which structure-function relations have originated, evolved, and been maintained over time. The importance of the distribution of sex steroid receptors in the vertebrate brain is discussed using the example of androgen receptor sites and their relatively conserved localizations in the vertebrate brain.

Rapid actions of androgens

The biological activity of androgens is thought to occur predominantly through binding to intracellular androgen-receptors, a member of the nuclear receptor family, that interact with specific nucleotide sequences to alter gene expression. This genomic-androgen effect typically takes at least more than half an hour. In contrast, the rapid or non-genomic actions of androgens are manifested within in seconds to few minutes. This rapid effect of androgens are manifold, ranging from activation of G-protein coupled membrane androgen-receptors or sex hormone-binding globulin receptors, stimulation of different protein kinases, to direct modulation of voltage- and ligand gated ion-channels and transporters. The physiological relevance of these non-genomic androgen actions has not yet been determined in detail. However, it may contribute to modulate several second messenger systems or transcription factors, which suggests a cross-talk between the fast non-genomic and the slow genomic pathway of androgens. This review will focus on the rapid effects of androgens on cell surface and cytoplasmic level.

Abuso de esteróides anabolizantes e seu impacto sobre a função tireóidea

A utilização de esteróides anabolizantes por indivíduos que desejam aumentar sua performance física, ou simplesmente para fins estéticos, tem atingido índices alarmantes nas últimas três décadas. Além dos efeitos desejados, uma infinidade de efeitos colaterais já foi bem descrita na literatura, como vários tipos de câncer, ginecomastia, peliosis hepatis, insuficiência renal, virilização, dentre outros. Sobre a função tireóidea, o efeito mais pronunciado em seres humanos é a diminuição da TBG, com conseqüente diminuição sérica de T3 e T4 totais, dependendo, porém, da susceptibilidade da molécula à aromatização e conseqüente transformação em estrógeno. Em ratos, o tratamento com esteróides anabolizantes altera a metabolização periférica dos hormônios tireóideos e também parece causar importante efeito proliferativo sobre as células tireóideas. Assim, o presente artigo visa rever os dados publicados acerca dos efeitos de doses suprafisiológicas de esteróides anabolizantes sobre a função tireóidea, reforçando o perigo que a utilização indiscriminada dessas drogas pode causar à saúde.

Non-classical actions of testosterone: an update

Androgens are known to exert their effects via genomic signalling, which involves intracellular androgen receptors that modulate gene expression on steroid binding. Whereas non-classical estrogen effects are well established, it is only recently that non-classical, rapid, membrane-initiated testosterone actions have received attention. Non-classical effects of testosterone have now been demonstrated convincingly in several tissues, in particular in the reproductive, cardiovascular, immune and musculoskeletal systems. There is evidence for the participation of the classical intracellular androgen receptor and for involvement of novel, membrane-associated androgen receptors in the non-classical actions of testosterone. Here we discuss evidence for rapid testosterone actions, which have clinical implications in fertility, cardiovascular disease and the treatment of prostate cancer.

Implants of estradiol conjugated to bovine serum albumin in the male rat medial preoptic area promote copulatory behavior

The expression of mating behavior in male rats is dependent on estrogen-responsive neurons in the medial preoptic area (MPO). Previous reports showed that mating is attenuated if the aromatization of testosterone to estradiol (E2) is blocked in the MPO and that mating is maintained by MPO E2 implants. However, the mechanisms by which E2 exerts its action are not fully understood. It had been thought that E2 acted exclusively by binding to nuclear estrogen receptors to exert it effects; however, recent reports suggest that E2 also binds to membrane-associated receptors activating downstream intracellular cascade responses. In this study, we aimed to determine if an action of E2 at the cell surface is sufficient to support mating behavior. Therefore, either vehicle, E2, or E2 conjugated to bovine serum albumin (BSA-E2: a complex of E2 and a large protein that will not cross the plasma membrane, thereby restricting the action of E2 to cell surface signaling) was chronically administered bilaterally to the MPO of castrated, dihydrotestosterone-treated male rats. Mating behavior was supported by MPO BSA-E2 implants, suggesting that E2 operates in the MPO via a cell surface mechanism to facilitate male rat mating behavior.

Novel cellular phenotypes and subcellular sites for androgen action in the forebrain

Historically, morphological studies of the distribution of androgen receptors in the brain led to conclusions that the major regional targets of androgen action are involved in reproduction, that the primary cellular targets are neurons, and that functional androgen receptors are exclusively nuclear, consistent with the classical view of steroid receptors as ligand-dependent transcription factors. In this review, we discuss three separate but interrelated recent studies highlighting observations made with newer methodologies while assessing the regional, cellular or subcellular distribution of androgen receptors containing cells in the forebrain. Regional studies demonstrated that the largest forebrain target for androgen action in terms of the number of androgen receptor expressing cells is the cerebral cortex, rather than the main hypothalamic and limbic centers for reproductive function. Cellular studies to determine the phenotype of androgen receptor expressing cells confirmed that most of these cells are neurons but also revealed that small subpopulations are astrocytes. The expression of androgen receptors in astrocytes is both region and age dependent. In contrast, reactive astrocytes in the lesioned adult rat brain do not express androgen receptors whereas reactive microglia do. Finally, androgen receptor immunoreactive axons were identified in the cerebral cortex of the rat and human. These observations do not overturn classical views of the cellular and subcellular locus of steroid action in the nervous system, but rather broaden our view of the potential direct impact of gonadal steroid hormones on cellular function and emphasize the regional and developmental specificity of these effects on the nervous system.

Biochemical characterization of a membrane androgen receptor in the ovary of the atlantic croaker (Micropogonias undulatus)

Membrane androgen receptors have been biochemically characterized in only a few vertebrate species to date. Therefore, the purpose of the current study was to comprehensively investigate the binding characteristics of a putative membrane androgen receptor in the ovary of the teleost, Atlantic croaker (Micropogonias undulatus). Specific androgen binding to an ovarian plasma membrane fraction was demonstrated using a radioreceptor assay protocol consisting of a short-term incubation with [(3)H]testosterone (T) and subsequent filtration of bound steroid from free steroid. Saturation and Scatchard analyses of T binding to an ovarian plasma membrane fraction indicated the presence of a single, high-affinity (K(d) = 15.32 +/- 2.68 nM [mean +/- SEM]), low-capacity (B(max) = 2.81 +/- 0.31 pmol/mg protein), androgen-binding site. Specific androgen binding to the receptor was readily displaceable, and the association and dissociation kinetics were rapid (half-time = 3.7 +/- 1.7 and 4.7 +/- 0.2 min, respectively). Competitive binding assays showed that 5alpha-dihydrotestosterone, T, and 11-ketotestosterone had relative binding affinities (RBAs) of 193%, 100%, and 13%, respectively, whereas none of the C(18) or C(21) steroids tested bound with high affinity except for progesterone (RBA = 191%). This androgen-binding moiety with high affinity for progesterone is unlikely to mediate the physiological actions of progestins in croaker, because it has low binding affinity for fish progestin hormones. Androgen-binding sites were also detected in membrane fractions of the brain, liver, kidney, and drumming muscle, whereas little or no binding was detected in the trunk muscle, heart, gills, or intestine. Receptor levels increased 10-fold during ovarian recrudescence, reaching maximum levels in fully mature ovaries, which suggests a likely physiological role for this receptor during the reproductive cycle of female croaker. It is concluded that the androgen-binding moiety identified in the plasma membrane fraction of Atlantic croaker ovarian tissue fulfils all the criteria for its designation as a steroid receptor.

The roles of androgen receptors and androgen-binding proteins in nongenomic androgen actions

The biological activity of testosterone and dihydrotestosterone is thought to occur predominantly through binding to the androgen receptor (AR), a member of the nuclear receptor superfamily that functions as a ligand-activated transcription factor. However, androgens have also been reported to induce the rapid activation of kinase-signaling cascades and modulate intracellular calcium levels. These effects are considered to be nongenomic because they occur in cell types that lack a functional AR, in the presence of inhibitors of transcription and translation, or are observed to occur too rapidly to involve changes in gene transcription. Such nongenomic effects of androgens may occur through AR functioning in the cytoplasm to induce the MAPK signal cascade. In addition, androgens may function through the sex hormone binding globulin receptor and possibly a distinct G protein-coupled receptor to activate second messenger signaling mechanisms. The physiological effect of nongenomic androgen action has yet to be determined. However, it may ultimately contribute to regulation of transcription factor activity, including mediation of the transcriptional activity of AR.

Testosterone restoration of copulatory behavior correlates with medial preoptic dopamine release in castrated male rats

The medial preoptic area (MPOA) is an important integrative site for male sexual behavior. We have reported an increase in dopamine (DA) release in the MPOA of male rats shortly before and during copulation. Postcastration loss of copulatory ability mirrored the loss of the precopulatory DA response to an estrous female. The present study investigated the time courses of restoration, rather than loss, of the MPOA DA response to a receptive female and of copulation in long-term castrates. Male rats were castrated and tested for loss of copulatory ability 21 days later. They then received 2, 5, or 10 daily subcutaneous injections of testosterone propionate (TP, 500 microg) or oil. Microdialysate samples were collected from the MPOA during baseline, exposure to a female behind a barrier, and copulation. Extracellular DA was measured using HPLC-EC. None of the six 2-day-TP-treated animals copulated, nor did they show elevated DA release in the MPOA in the presence of a receptive female. Five of the nine 5-day-TP-treated animals ejaculated; three intromitted without ejaculating; and one failed to copulate, with all but the noncopulating animal showing elevated DA release. All of the six 10-day-TP-treated animals copulated and also demonstrated an increase in MPOA DA. None of the oil controls copulated or showed an increase in DA release. Therefore, a consistent relationship between MPOA DA release during exposure to a receptive female and the subsequent ability of the male to copulate was observed.

Colocalization of androgen, estrogen and cholinergic receptors on cultured astrocytes of rat central nervous system

By means of immunohistochemical and electrophysiological methods, we have investigated the presence of androgen receptors on astrocytes in explant and primary cultures from various regions of rat central nervous system. Our studies have shown that a great number of astrocytes and neurones express androgen receptors as recognized by a specific monoclonal antibody. Immunoreactivity was mainly distributed over the soma of the astrocytes, the nuclei being intensely stained. In contrast, glial processes were only faintly stained or not stained. Double-immunostaining studies have provided evidence for a colocalization of androgen and estrogen alpha- and beta-receptors on many astrocytes. Furthermore, there was also a coexistence of glial androgen receptors with cholinergic muscarinic and nicotinic sites. Our immunohistochemical findings are supported by electrophysiological investigations demonstrating that 5alpha-androstan, 17beta-estradiol as well as the cholinergic agonists muscarine and nicotine caused hyperpolarizations on the same astrocytes. Our studies suggest that there is a coexistence of functional receptors for androgen, estrogen as well as for the cholinergic agonists on glial cells. Further investigations are needed to elucidate the physiological role of glial androgen, estrogen and cholinergic receptors and to define their function in neurodegenerative diseases.

Emerging diversities in the mechanism of action of steroid hormones

The classical genomic action of steroid hormones acting through intracellular receptors is well recognized. Within this concept of action, questions regarding the ultimate fate of the hormone and lack of a tight correlation between tissue uptake and biological activity with receptor binding remain unanswered. Evidence has accumulated that steroid hormones can exert non-classical action that is characterized by rapid effect of short duration. In most of these cases, the hormone effects occurs at the membrane level and is not associated with entry into the cell. The possible mechanisms for these non-classical actions are: (a) changes in membrane fluidity; (b) steroid hormone acting on receptors on plasma membranes; (c) steroid hormones regulating GABAA receptors on plasma membranes; and (d) activation of steroid receptors by factors such as EGF, IGF-1 and dopamine. Data have also been obtained indicating that receptor-mediated insertion of steroid hormones into DNA may take place with the steroid acting as a transcription factor. These new proposed mechanism of action of steroid hormones should not be viewed as a challenge to the classical mechanism. These diverse modes of action provide for an integrated action of hormones which may be rapid and of short duration or prolonged to address the physiological needs of the individual.

A re-evaluation of the effects of gonadal steroids on neuronal activity in the male rat

Single unit activity (SUA) was recorded from 77 cells located in the arcuate nucleus (ARC) and medial preoptic area (MPA) of anesthetized, intact male rats. Animals were administered vehicle, testosterone (T; 5 or 50 micrograms) or 17 beta-estradiol (E; 0.5 microgram) intravenously and SUA was monitored for 8-12 min. T (50 micrograms) reduced SUA in 50% of ARC units and 44% of MPA units within 2.1 +/- 0.46 and 3.3 +/- 0.92 min, respectively. Inhibition of ARC SUA was more pronounced than MPA SUA. A small percentage (9%) of ARC units were excited by T. E reduced SUA in 29% of ARC units and 27% of MPA units. Single doses of 5 micrograms T did not affect ARC activity. However, when followed within 10 min by an additional dose of 5 or 50 micrograms T, 30% and 43% of ARC units were inhibited, respectively. Doses (10 micrograms) of T produced plasma T concentrations within physiological limits, although 50 micrograms doses produced supraphysiological T levels. Neither dose affected circulating LH concentrations. We conclude that physiological and supraphysiological concentrations of T can rapidly affect SUA within the ARC.

Prenatal exposure to methadone affects central cholinergic neuronal activity in the weanling rat

The effect of prenatal exposure to methadone via maternal osmotic minipumps was studied on brain regional acetylcholine (ACh) turnover and dopamine (DA), norepinephrine (NE), serotonin (5-hydroxytryptamine, 5-HT) and their metabolites in 21-day-old female and male rats. ACh content was not affected in any region studied. However, the turnover rate of ACh (TRAch) was increased significantly in the striata and parietal cortices of both sexes. Two gender-specific changes were observed: a profound decrease in hypothalamic TRACh in the females and an increase in hippocampal TRACh in the males. No changes were observed in TRACh in the medulla-pons or the frontal cortex of either sex. The reduction in TRACh was accompanied by a threefold increase in DA content in the hypothalamus of the methadone-exposed females. No other changes were observed in DA, NE, or 5-HT, save for increased 5-HT content in the medulla-pons of the male methadone-exposed rats. Thus, prenatal methadone exposure produces several lingering changes in cholinergic function, many of which were not apparent in the immediate postnatal period. Although striatal ACh content was no longer reduced in methadone-exposed rats, striatal cholinergic function remains disrupted. It remains to be proven whether these differences are a direct effect of methadone exposure or are a consequence of neonatal withdrawal.

Hormonal regulation of adult sympathetic neurons: the effects of castration on neuropeptide Y, norepinephrine, and tyrosine hydroxylase activity

Previous studies utilizing the hypogastric ganglia (HG) have indicated that gonadal steroids exert organizational and activational effects on noradrenergic biochemistry. Bilateral castration of male rodents at birth prevents the normal maturation of tyrosine hydroxylase (T-OH) activity in the HG; castration during adulthood results in a progressive decline in T-OH activity. Testosterone replacement corrects both the ontogenetic and adult functional alterations in the neurotransmitter-synthesizing enzyme. The present studies in adult male rats extend these previous observations and asked the question whether gonadal steroids regulate the neurotransmitters neuropeptide Y (NPY) and norepinephrine (NE) in the HG. Adult rodents were castrated and ganglia T-OH, NPY, and NE were examined at various time points after surgery. All three indices of sympathetic neuron biochemistry declined following castration, but they exhibited different profiles. It appears that hormones may affect enzyme activity and neurotransmitter pools differently within neurons. Testosterone replacement therapy fully restored T-OH activity, and NPY and NE levels in the HG. These studies extend the activational role of testosterone in regulating sympathetic neuron neurotransmitter and neuropeptide levels as well as neurotransmitter-synthesizing enzymes.

Organizational role of testosterone on the biochemical and morphological development of the hypogastric ganglion

Previous reports have demonstrated that after postnatal day 10 testosterone influences hypogastric ganglion (HG) development by 'activating' morphological and biochemical indices. We now report an 'organizational' influence on the developing HG during the first 10 postnatal days. To investigate the organizational effects of testosterone, male rats were castrated within 12 h of birth. Testosterone replacement therapy initiated following castration maintained the normal number of neurons in the HG. Conversely, delayed replacement therapy starting at day 10 or vehicle treatment only, resulted in a significant decrease in neuron number. Castration also produced a significant decrease in somal and nuclear cross-sectional areas. Testosterone replacement, whether initiated immediately or if delayed until day 10, restored somal and nuclear cross-sectional areas to normal. Tyrosine hydroxylase (TH) and choline acetyltransferase (ChAT) activities were sensitive to both testosterone dosage and the time of administration. Testosterone decanoate administered subsequent to castration was not able to completely reverse the enzyme activity deficits, while delayed replacement therapy was even less effective in restoring enzyme activities. In contrast, higher doses of testosterone completely reversed enzyme activity deficits, and in fact produced a significant increase in TH activity. Again, delayed testosterone replacement did not fully restore deficits in enzyme activity. In summary, the hormonal environment during the first 10 days of life is critical for the organization of HG cell number; in contrast, nuclear and cell size appear to be dependent on testosterone for activation. TH and ChAT activities also appear to be organized during this dose- and time-dependent developmental period.

Central control of sexual behavior

Neuronal activity changes in the medial preoptic area (MPOA) of the male monkey were related to the commencement of sexual behavior, penile erection and the refractory period following ejaculation. Similarly, changes in the female MPOA were related to the commencement of sexual behavior and presentation. Increased neuronal activity in the dorsomedial hypothalamic nucleus (DMH) in the male monkey and in the ventromedial hypothalamic nucleus (VMH) in the female monkey was synchronized to each mating act. Stimulation study and neuronal activity recordings in the MPOA, DMH and VMH suggest involvement of MPOA neurons in sexual arousal, and of male DMH and female VMH neurons in the copulatory act. Stimulation experiment on the various parts in the hypothalamus of the female monkey also supports the conclusion.

Neuronal sensitivities in preoptic tissue slices: interactions among homeostatic systems

The preoptic area participates in many homeostatic systems, which include the regulation of body temperature, fluid and metabolite balance, and reproduction. Some preoptic neurons have been shown to be sensitive to either temperature, osmotic pressure, glucose, testosterone or estradiol. While previous studies have treated these as separate and distinct neuronal populations, this paper reviews recent experiments which show that many neurons have multiple sensitivities to these endogenous factors. Neurons in preoptic tissue slices were tested for their responses to changes in temperature, as well as various perfusion media containing 30 pg/ml testosterone or estradiol, low glucose (1.0 mM) or increased osmotic pressure (309 mosmol/kg). The steroid-sensitive, osmosensitive and glucosensitive neurons were not confined to the temperature insensitive neurons; but instead nearly half of the thermosensitive neurons responded to these nonthermal stimuli. In addition, many osmosensitive neurons showed glucosensitivity and steroid-sensitivity. This suggests that, even at the neuronal level, there is a basis for interactions between homeostatic systems.

Impaired spatial navigation in adult female but not adult male rats exposed to alcohol during the brain growth spurt

Two groups of male and female rats were given the same dose of alcohol using an artificial rearing procedure on postnatal days 4-10. One group received the alcohol in a condensed manner each day which caused cyclic blood alcohol concentrations (BACs) with high peaks. A second group received the alcohol in a uniform manner over each day which resulted in moderate, stable BACs. Two control groups consisted of male and female rats artificially reared but not exposed to alcohol and rats reared normally by dams. All rats were raised to 90 days of age and then tested for spatial navigation ability in the Morris water maze, which involved locating a hidden underwater platform using distal extramaze cues. Neither the alcohol treatments nor the artificial rearing had any effects on performance of adult male rats relative to suckle controls in this task. In contrast, the condensed alcohol exposure but not the uniform alcohol exposure resulted in detrimental performance in the Morris water maze by adult female rats. When the ability to locate and escape onto a visible platform was examined, there were no differences between the female groups given condensed alcohol exposure or artificially reared on milk solution alone. Thus, exposure to high BACs during the brain growth spurt has a lasting and selective detrimental effect on spatial navigation learning in adult female but not adult male rats.

A miniaturized method for multiple and inexpensive electrophoreses on polyacrylamide slab gels

The design, construction, and use of a simple inexpensive system for multiple slab gel electrophoreses are described. Each gel slab is cooled from both sides by an electrode buffer. The electrophoresis time of each gel can be easily controlled independently from the others in the set. Because this set is very simple, it was completely handmade by the author. Depending on the purpose for which the set is to be used, its size, thickness, and shape can be changed.

Direct effects of androgens on lateral hypothalamic neuronal activity in the male rat: I. A microiontophoretic study

Unit neuronal activity in the lateral hypothalamic-medial forebrain bundle region (LHA-MFB) of the male rat is modified following an increase of plasma testosterone level. In order to determine possible direct action of hormones on LHA-MFB neurons, unit discharge frequencies were recorded during local microiontophoresis of testosterone and estradiol, and electroosmotic application of cholesterol. Thirteen cells did not respond, 9 were nonspecifically depressed by all the steroids tested, 13 were excited by both sex-steroids, and 11 were specifically activated by testosterone. The short latencies of the responses suggest a direct effect of steroids on the plasma membrane sites.

Medial preoptic neuronal responses to connatural females in sexually inactive male monkeys (Macaca fuscata)

Neuronal responses to a connatural female were investigated in the medial preoptic area of two sexually inactive male monkeys. Of 72 neurons tested, the presence of the female elicited a phasic excitatory response in 11 neurons and a tonic excitatory response in 5 neurons. These findings suggest that a small number of medial preoptic neurons are involved in coding the presence of the female in the sexually inactive male monkey.

Isoelectric focusing with reduced cathodic drift and migration into the anode chamber

An apparatus has been developed to reduce cathodic drift and migration into the anode chamber in vertical gel rod isoelectric focusing (IEF). In contrast to commercially available apparatuses, this apparatus can easily handle many more gels at one time, and the length, diameter and shape of its gel can be arbitrarily changed. In addition, high concentrations of detergent can be used to dissolve the protein samples, and removal of the gel cylinders from the glass tubes is easy.

Gradient flattening of sodium dodecyl sulfate (SDS) and isoelectric focusing (IEF) gels

In addition to our previously reported versatile methods for sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis [1] and isoelectric focusing (IEF)-gel [2], I have achieved molecular weight gradient flattening of the SDS-polyacrylamide gel and pH gradient flattening of the IEF gel at any segment using the same electrophoresis system. Any crowded gel segment where congregated components are not separated well can easily be widened for good separation and any dispersed gel segment where components are too far apart can easily be narrowed. Therefore, every gel segment can be used effectively and meaningfully because the gradient curve can be adjusted to any distribution of the components. In the crowded area, any small spots of components which could not be detected previously because of nearby heavy staining or strong radioactivity of an abundant component can be sufficiently separated from the nearby spots in a small gel without sacrificing other areas.

Hormonal control of sexual differentiation: changes in electric organ discharge waveform

Males and females of some mormyrid electric fishes generate electrical pulses that differ in waveform and duration. For one such species, testosterone or dihydrotestosterone induces females and immature males to produce the mature male electric organ discharge which is two times the duration of the female or immature discharge. Estradiol has only a weak effect. For a second species where males and females have similar electric organ discharges, testosterone produces no effect. The data suggest that androgens affect the electric organ itself.

Electrophoresis in gel slabs of any thickness: a rapid, multiple, adaptable, facile and inexpensive method

A new apparatus has been developed to facilitate a good, effective transfer of protein from a first-dimension gel into a second-dimension gel. This new simple apparatus makes running time of the slab gel short and is convenient for the simultaneous processing of many polyacrylamide gel slabs and ultra-thin (100 micrometers) gels. Many gels can be run at the same time in a small space and be readily inserted or removed. Multiple gels can easily be prepared. The plates can have any desired shape and dimension, and their thickness can easily be changed. The present method is very simple and inexpensive, has a wide application and has many other advantages.

Androgen influence on lateral hypothalamus in the male rat: possible behavioral significance

The lateral hypothalamus and other structures in the forebrain were explored with microelectrodes in the male rat under urethane anesthesia before and after IV injections of testosterone. In the lateral hypothalamus, significant proportion of neurons responded after a few minutes to the hormonal increases by changes in firing rate. These responses could be attributed neither to a solvent effect nor to generalized changes in cerebral activity as indicated by EEG monitoring. The rapid onset implies that the steroid molecule exerted a non-genomic effect on target cells. The brain cells detected here were either such testosterone target cells or other neurons transsynaptically connected to them. All units tested with estradiol and testosterone reacted in the same way to both steroids, suggesting that testosterone acts after being aromatized into estradiol. This supports a possible role of these neurons in the regulation of male sexual behavior. Their involvement in the modulation of motivation during the appetitive component of sexual behavior, according to the hormonal state of the subject, is discussed.

Hormonal regulation of axonal sprouting in the hippocampus

Removal of septal fibers to the rat hippocampal formation is followed by an ingrowth of sympathetic axons into the deafferented regions. We have shown previously that the pattern of sprouting is more restricted in males than in females when the lesions are made in mature animals, but is almost the same if lesions are made during the early postnatal period. In the present study, the relationship of circulating sex hormones to the sprouting response was investigated by comparing the extent of sympathetic axon ingrowth following fimbrial lesions in intact or gonadectomized adult male and female rats. The effects of manipulating sex steroids during development was examined by comparing sympathetic axonal sprouting after fimbrial lesions in rats which were castrated (male) or treated with testosterone (females and castrated males) on postnatal day 2. We find that (1) gonadectomy of either adult female or male rats does not affect the sprouting response, but (2) neonatal castration of male rats permits sprouting in a pattern similar to normal females, and neonatal testosterone treatment of females or castrated males results in the more limited sprouting response characteristic of normal males. These results indicate that the sex-related differential response to fimbrial lesions may be determined by developmental differences in endogenous steroid levels.

Hypothalamic neurons responsive to increased plasma level of testosterone in the male rat

Unitary activity was recorded from several forebrain structures. Out of 108 cells, 35 reacted to a testosterone i.v. injection by an increase (24 cells) or a decrease (11 cells) of firing rate. This response was early (latency: 5.0 +/- 0.6 min), lasted 25.7 +/- 1.9 min and was reproducible. Responsive neurons were found to be significantly more numerous in the lateral hypothalamic area than in other structures.

Neural gonadal steroid actions

Neurons sensitive to gonadal steroids are located strategically within neural circuits that mediate behaviors broadly related to the reproductive process. Some neuronal events and properties are regulated by these hormones. Variability in the occurrence and distribution of particular neural hormonal sensitivities across species may be related to variations in the hormonal requirements for sexual differentiation and for activation of reproductive behaviors.

Sexual dimorphism in extent of axonal sprouting in rat hippocampus

Sympathetic axons, normally innervating the extracerebral vasculature, sprout into denervated regions of the hippocampal formation after lesions of the medial septal nucleus or fimbria in adult female rats. Similar lesions in adult males also elicit the sympathetic ingrowth; however, the number of anomalous axons is greatly reduced and their distribution is altered. In adult males the sympathetic axons do not send out collaterals within the stratum oriens of region CA3 or the molecular layer or deep hilar regions of the area dentata, as they do in adult females. Lesions in juveniles of both sexes result in more vigorous sprouting than in their adult counterparts. In the young males the anomalous axons are distributed more extensively into the dentate molecular layer; in the young females the axons merely send out more collaterals within the same regions as in the adults. This sexually dimorphic response to central nervous system damage suggests either that the sprouting is affected by the hormonal environment of the mature hippocampal system or that this brain region, like the hypothalamus, may express permanent morphological or physiological differences as a result of exposure to sex steroids during development.

Gonadal steroids: humoral modulators of nerve-cell function

The gonadal steroids, estradiol, testosterone and progesterone, alter neuroendocrine function and behavior in adult mammals and do so by acting on the central nervous system and pituitary gland. Besides intracellular receptor sites, various cellular and chemical actions of gonadal steroids are being studied within the brain and pituitary. The review summarizes the present state of such research and points as well to new advances in our understanding of the cellular basis of developmental events such as brain sexual differentiation and puberty, which are influenced by gonadal steroids.