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

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.

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.

Effects of nandrolone on acute morphine responses, tolerance and dependence in mice

Anabolic-androgenic steroid exposure has been proposed to present a risk factor for the misuse of other drugs of abuse. We now examined whether the exposure to the anabolic-androgenic steroid, nandrolone, would affect the acute morphine responses, tolerance and dependence in rodents. For this purpose, mice received nandrolone using pre-exposure (for 14 days before morphine experiments) or co-administration (1 h before each morphine injection) procedures. Nandrolone treatments increased the acute hypothermic effects of morphine without modifying its acute antinociceptive and locomotor effects. Nandrolone also attenuated the development of tolerance to morphine antinociception in the hot plate test, but did not affect tolerance to its hypothermic effects, nor the sensitisation to morphine locomotor responses. After nandrolone pre-exposure, we observed an attenuation of morphine-induced place preference and an increase in the somatic manifestations of naloxone-precipitated morphine withdrawal. These results indicate that anabolic-androgenic steroid consumption may induce adaptations in neurobiological systems implicated in the development of morphine dependence.

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.

Action of cholecystokinin and serotonin on lateral hypothalamic neurons of rats

Discharges of spontaneously active lateral hypothalamic neurons were extracellularly recorded during iontophoretic administration of cholecystokinin (CCK-8S) or/and serotonin (5-HT) in anesthetized rats. The main results are the following. (1) The proportion of neurons responsive to CCK-8S was 62% (61/99) and that responsive to 5-HT 42% (33/78). (2) Out of the neuronal sample, 36% were influenced by both transmitters, allowing an interaction between the two systems. (3) Co-ejection of CCK and 5-HT elicited a response in 40% of the tested neurons, which was a significantly smaller responsiveness than with separate ejection of CCK-8S. The effect resulted from a reduced number of excited neurons whereas the number of inhibitions did not change. The results show that effects of 5-HT and CCK can converge on the same neuron within the lateral hypothalamus. This might be of relevance in the regulation of feeding behavior.

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.

Behavioural pharmacology of the serenic, eltoprazine

In this paper the effects of serenics (eltoprazine and fluprazine) are described in several animal models for offensive agonistic, defensive agonistic and predatory behaviour. They are compared with the effects of a number of other putative anti-aggressive compounds or drugs used clinically in order to ameliorate aggressive behaviour of psychiatric patients. In isolation-induced offensive aggression in mice, eltoprazine has a marked and potent anti-aggressive activity, although numerous other psychoactive drugs also exert anti-aggressive effects. The behavioural specificity of this anti-aggressive profile was investigated using an ethologically derived animal model, social interaction in male mice. In this model, eltoprazine has a very specific anti-aggressive (serenic) profile, inhibiting aggression while social interaction and exploration are not decreased but even enhanced; inactivity, a measure for sedation, is not affected. Such a profile contrasts sharply with that of neuroleptics (chlorpromazine, haloperidol), psychostimulants (d-amphetamine) or benzodiazepines (chlordiazepoxide), which exert severe sedation (neuroleptics) or even aggression-enhancing effects (BDZ). After subchronic treatment no tolerance for the anti-aggressive effects of eltoprazine occurred. The specific anti-aggressive effects of eltoprazine were also found in rat models of offensive agonistic behaviour. In one such model - resident-intruder aggression - eltoprazine reduced offensive behaviour specifically, leaving social interactions and exploration intact, and did not induce sedation or other unwanted side-effects. The neuroleptic haloperidol was very sedative in this model, as was the 5-HT1A-agonist buspirone. Benzodiazepines (chlordiazepoxide) have a biphasic effect in this paradigm, enhancing offence at low doses and decreasing it at higher doses, due to muscle relaxation. In another offensive model, colony-aggression, in which a dominant and subordinate male in a colony are confronted with a male intruder, eltoprazine reduced offensive behaviour of both the dominant and the subordinate against the intruder. In contrast, chlordiazepoxide enhanced aggression, at least at lower doses, whereas alcohol had, up to very high doses, no effect on the offensive behaviour. In a brain-stimulation induced offensive model--hypothalamically-induced aggression in rats--eltoprazine specifically reduces offence. Locomotion, a measure for sedation, was either unaffected or even somewhat enhanced, indicating the absence of any sedatory activity of this serenic compound. In contrast, haloperidol heavily sedated animals, making them incapable of aggression.(ABSTRACT TRUNCATED AT 400 WORDS)

Structure-activity relationships of steroid hormones on muscarinic receptor binding

A total of fifty steroidal compounds were tested for their inhibition on the binding of muscarinic receptor antagonist, [3H]quinuclidinyl benzilate ([3H](-)QNB), to the hypothalamic membranes prepared from male rats. Among the compounds tested, the active structures (with IC50 values less than or equal to 100 microM in parentheses) are: progesterone (40), 5 beta-pregnane-3,20-dione (40), deoxy-corticosterone (50), 5 beta-pregnane-17 alpha,21-diol-3,20-dione (30), 11-desoxy-17-hydroxycorticosterone (22), 17 alpha-hydroxyprogesterone (20), 5 beta-pregnan-17 alpha-ol-3,20-dione (24), 5 beta-androstane-3,17-dione (100), and 5 beta-dihydrotestosterone (100). By examining all the compounds tested, the following structure-activity relationship became apparent: (a) The ring A-reduced steroidal structures with a 5 beta-conformation were more potent than those with a 5 alpha-conformation; (b) 17 alpha-hydroxylation of the steroidal ring increased the steroid's inhibitory activity; (c) The C3 carbonyl group was essential for activity; (d) Reduction of the C3 carbonyl group or aromatization of the ring A abolished the steroid's inhibitory activity; (e) Oxidation of the C11 position of ring C resulted in a decrease or loss of inhibitory activity; and (f) Different modifications of the side chain of ring D by acetylation resulted in either an increase or a decrease in the inhibitory activity. The structure-activity relationship as revealed in this study might provide an insight for the synthesis of a steroidal molecule with a high affinity for the muscarinic receptor as well as for the search of a more potent and physiologically relevant steroidal metabolite possessing the ability to interact with the muscarinic receptor.

Opposite effects of ecdysone and 20-hydroxyecdysone on in vitro uterus motility of a tsetse fly

In order to examine the possible effects of ecdysteroids on parturition, we studied in vitro the influence of ecdysone and 20-hydroxyecdysone on the motility of isolated uterus from virgin and pregnant female tsetse fly (Glossina fuscipes). Ecdysone initiates phasic uterine contractions or enhances the frequency of preexisting contractile activity. In contrast, uterine contractions are decreased or abolished by 20-hydroxyecdysone. Pharmacological data indicate that tsetse fly uterus exhibits myogenic and nerve-evoked contractions. Ecdysteroids mainly act on nervous structures that control muscle contractions. Our results provide evidence for a specific action of ecdysteroids on a nerve-muscle target involved in female reproduction.

Direct effects of androgens on lateral hypothalamic neuronal activity in the male rat: II. A pressure ejection study

Direct excitatory effects of sex steroids on lateral hypothalamic-medial forebrain bundle (LHA-MFB) neurons have been demonstrated in a previous study using the microiontophoretic ejection of charged hormone derivatives. In the present study neuronal discharge frequency was recorded during the local pressure ejection of the physiologically active form of these hormones. Of 56 neurones studied, 12 increased in activity due to testosterone application. Twenty-eight of these cells were tested with both testosterone and estradiol. Five were activated by both hormones, 4 were specifically excited by 17 Beta-estradiol, 3 were specifically excited by testosterone, and 16 were unaffected. The short latency of neuronal responses and the efficacy of nanomolar hormonal concentrations suggest the existence of high affinity specific sites in the plasma membrane of responsive neurons. The physiological significance of these neurons is discussed.