Serotonin receptors 5-HT<Subscript>1A</Subscript> and 5-HT<Subscript>3</Subscript> reduce hyperexcitability of dorsal horn neurons after chronic spinal cord hemisection injury in rat

Spinal cord injury (SCI) results in abnormal pain syndromes in humans. In a rodent model of SCI, T13 spinal hemisection results in allodynia and hyperalgesia due in part to interruption of descending pathways, including serotonergic (5-HT) systems, that leads to hyperexcitability of dorsal horn neurons. To characterize further the role of 5-HT and 5-HT receptor subtypes 5-HT_1A and 5-HT₃ in neuronal activation after hemisection, we have examined the responsiveness of dorsal horn neurons to a variety of innocuous and noxious peripheral stimuli. Male Sprague-Dawley rats, 150–175 g, were spinally hemisected (n=40) at T13 and allowed 4 weeks for development of mechanical allodynia and thermal hyperalgesia. Animals then underwent electrophysiologic recording and the results were compared with those from sham controls (n=15). Evoked responses of convergent dorsal horn neurons (n=224 total) at L3–L5 to innocuous and noxious peripheral stimuli were characterized after administration of vehicle, 5-HT (25, 50, 100, and 200 μg), 5-HT (100 μg) in conjunction with the selective 5-HT_1A antagonist WAY 100135 (100 μg), the 5-HT₃ antagonist MDL 72222 (100 μg), the selective 5-HT_1A agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT, 150 μg), or the 5-HT₃ agonist 2-Me-5HT (75 μg), with or without pretreatment with antagonists; all treatments were delivered topically onto the cord adjacent to the recording electrode. In hemisected animals, increased responsiveness of convergent cells to all peripheral stimuli was observed bilaterally when compared to controls. No changes in ongoing background activity were present. In control animals, only the highest dose of 5-HT (200 μg) was sufficient to reduce evoked activity, whereas in hemisected animals a concentration-dependant decrease in response was observed. In hemisected animals, both 5-HT_1A and 5-HT₃ receptor antagonism reduced the effectiveness of 5-HT, restoring elevated evoked activity by up to 70% at the doses tested. Administration of 5-HT_1A and 5-HT₃ receptor agonists also decreased hyperexcitability, effects prevented by pretreatment with corresponding antagonists. These results demonstrate the development of denervation supersensitivity to 5-HT following SCI, corroborate behavioral studies showing the effectiveness of 5-HT in reducing allodynia and hyperalgesia after SCI, and contribute to a mechanistic understanding of the role of 5-HT receptor subtypes in chronic central pain. Electronic Publication     

Catecholamine-containing axon terminals in the hypoglossal nucleus of the rat: an immuno-electronmicroscopic study

Summary A correlative light and electron microscopic investigation was undertaken to determine the morphology and distribution of catecholamine (CA)-containing axon terminals in the hypoglossal nucleus (XII) of the rat. This was accomplished immunocytochemically with antibody to tyrosine hydroxylase (TH). The major findings in this study were the following: 1) Immunoreactive profiles were found throughout XII and included unmyelinated axons, varicosities, axon terminals and dendrites; 2) Nonsynaptic immunoreactive profiles (preterminal axons, varicosities) were more frequently observed (55.2%) than synaptic profiles (43.5%); 3) CA-containing axon terminals ending on dendrites were more numerous (71.8%) than those synapsing on somata (25.4%) or nonlabeled axon terminals (2.7%); 4) The morphology of labeled axon terminals was variable. Axodendritic terminals typically contained numerous small, round agranular vesicles, a few large dense-core vesicles and were associated with either a symmetric or no synaptic specialization, axosomatic terminals were often associated with a presynaptic membrane thickening or a symmetric synaptic specialization and contained small, round and a few elliptical-shaped vesicles, while axoaxonic synapses formed asymmetric postsynaptic specializations; and 5) CA-positive dendritic processes were identified in XII. These findings confirm the CA innervation of XII, and suggest a complex, multifunctional role for CA in controlling oro-lingual motor behavior.     

The fine structure of serotonin and tyrosine hydroxylase immunoreactive terminals in the ventral posterior thalamic nucleus of cat and monkey

Summary Immunocytochemical methods have been combined with serial thin section analysis to study the synaptic organization of serotonin (5-HT) and tyrosine hydroxylase (TH) immunoreactive terminals in the ventral posterior nucleus of the cat and monkey thalamus. One hundred 5-HT immunoreactive terminals from the cat and approximately forty 5-HT and TH immunoreactive terminals from the monkey were selected for analysis in serial thin sections. Only 7–10% of the immunoreactive terminals could be revealed to form conventional synaptic contacts. Most of these could be identified as the asymmetrical type. Dendritic shafts belonging to relay neurons were the major targets of these monoamine immunoreactive terminals. The remainder made intimate membrane associations with relay cell dendrites and somata or with presynaptic dendrites of interneurons, but no overt membrane specializations could be detected. The present results suggest that the modulation of thalamocortical relay function by brainstem monoamine pathways in the somatosensory thalamus may occur by release of transmitters at atypical contact sites.     

Motor activity induces release of serotonin in the dorsal horn of the rat lumbar spinal cord

Literature highlights that serotonergic descending pathways are implicated in somatosensory functions in the spinal cord and that serotonin (5-HT) in the dorsal horn might play a role in motor function through proprioceptive feedback. We hypothesized that 5-HT release in dorsal horn might represent an important factor in the completion of locomotion by facilitation of the spinocerebellar tract and/or by modulation of spinal reflex pathways. The present study demonstrates that during locomotor activity, 5-HT is released in layers II, III, IV, V of Rexed. Microdialysis in combination with HPLC was used to measure concentrations of neurotransmitters in the lumbar dorsal horn before, during, and after a treadmill running exercise. Our results show a significant 41% increase of 5-HT release within the dorsal horn during the exercise. 5-HT release is temporally related to exercise. The present study demonstrates that dorsal horn 5-HT release might modulate locomotion.     

Evidence for a role of protein kinase C in the sustained activation of rat dorsal horn neurons evoked by cutaneous mustard oil application

The intracellular mechanisms involved in the sensitisation of spinal dorsal horn neurons brought about by sustained or repeated nociceptive inputs are unknown. The present experiments addressed any role of protein kinase (PKC) in sustained nociceptive responses of rat dorsal horn neurons by: (i) ionophoretic administration of PKC inhibitors whilst recording activity evoked by repeated cutaneous application of mustard oil; and (ii) assessing subcellular translocation of PKC evoked in spinal cord by cutaneous application of mustard oil. Both marked attenuation of mustard oil-induced neuronal activity by PKC inhibitors and selective translocation of PKC in spinal cord tissue ipsilateral to mustard oil application strongly supported a critical role of PKC in sustained nociceptive responses to mustard oil.     

Cytology, synaptology and immunocytochemistry of commissural neurons and their putative axonal terminals in the dorsal cochlear nucleus of the rat

The first binaural integration within the auditory system responsible for sound localization depends upon commissural neurons that connect the two symmetrical cochlear nuclei. These cells in the deep polymorphic layer of the rat dorsal cochlear nucleus were identified with the electron microscope after injection of the retrograde tracer, Wheat Germ Agglutinin conjugated to Horseradish Peroxydase, into the contralateral cochlear nucleus. Commissural neurons are multipolar or bipolar with an oval to fusiform shape. Few commissural neurons, most inhibitory but also excitatory, connect most of the divisions of the rat cochlear nuclei. The most common type is a glycinergic, sometimes GABAergic, moderately large cell. Its ergastoplasm is organized into peripheral stacks of cisternae, and few axo-somatic synaptic boutons are present. Another type of commissural neuron is a medium-sized, spindle-shaped cell, glycine and GABA-negative, with sparse ergastoplasm and synaptic coverage. A giant, rare type of commissural neuron is glycine-positive and GABA-negative, with short peripheral stacks of ergastoplasmic cisternae. It is covered with synaptic boutons, many of which contain round synaptic vesicles. Another rare type of commissural neuron is a moderately large cell, oval to fusiform in shape, immunonegative for both glycine and GABA, and contacted by many axo-somatic boutons. It contains large dense mitochondria and numerous dense core vesicles of peptidergic type. Some labelled boutons, mostly inhibitory and probably derived from commissural neurons, contact pyramidal, cartwheel, giant and tuberculo-ventral neurons. The prevalent inhibition of electrical activity in a cochlear nucleus observed after stimulation of the contralateral cochlear nucleus may be due to commissural inhibitory terminals which contact excitatory neurons such as pyramidal and giant cells. Other inhibitory commissural terminals which contact inhibitory neurons such as cartwheel and tuberculo-ventral neurons, may explain the stimulation of electrical activity in the DCN after contralateral stimulation.     

Possible presence of the ATP-sensitive K channel in isolated spinal dorsal horn neurons of the rat

The ATP-sensitive K⁺ channel (K_ATP channel) is a K⁺ channel inhibited by cytoplasmic ATP. It was originally found in cardiac cells and recently in neuronal cells. Here, we present evidence indicating that the K_ATP channel also exists in spinal dorsal horn neurons: membrane currents were recorded by whole-cell voltage-clamp in spinal dorsal horn neurons isolated from young rats. The outward current was augmented by K_ATP channel activators nicorandil and minoxidil and reduced by the blocker glibenclamide. This glibenclamide-induced change in the current was augmented when the intracellular ATP was lowered and the reversal potential was shifted according to the external K⁺ concentration.     

Dose dependence of the 5-HT agonist quipazine in facilitating spinal stepping in the rat with epidural stimulation

Epidural electrical stimulation (ES) at spinal cord segment L2 can produce coordinated step-like movements in completely spinalized adult rats [R.M. Ichiyama, Y.P. Gerasimenko, H. Zhong, R.R. Roy, V.R. Edgerton, Hindlimb stepping movements in complete spinal rats induced by epidural spinal cord stimulation, Neurosci. Lett. 383 (2005) 339-344]. Plantar placement of the paws, however, was rarely observed. Here, we sought to determine the dose dependence of a 5-HT agonist (quipazine) on stepping kinematics when administered in combination with ES. Six adult female Sprague-Dawley rats received a complete mid-thoracic spinal cord transection and were implanted with epidural electrodes at the L2 spinal cord level. Quipazine (i.p.) was tested at doses of 0.1, 0.2, 0.3, 0.4, and 0.5 mg/kg. Rats were placed in a body weight support system, allowing them to walk bipedally on a moving treadmill belt (7 cm/s). 3D step kinematics analysis revealed that coordinated alternating bilateral stepping was induced by L2 stimulation (50 Hz) alone and by quipazine alone. Furthermore, the combination treatment produced significantly greater numbers of plantar steps and improved quality of stepping compared to either intervention alone. Both number and quality of stepping peaked at the intermediate dose of 0.3-0.4 mg/kg. The results indicate that quipazine and ES can have complementary effects on spinal circuits and that quipazine dosage is an important factor in differentially modulating these circuitries to improve the quality of the bipedal stepping on a treadmill belt.     

Reduction of substance P binding sites in the spinal dorsal horn after perineural capsaicin treatment in the rat

The long-term effect of perineural capsaicin treatment on the distribution of substance P (SP) binding sites was studied in the rat spinal dorsal horn using ¹²⁵I-labelled Bolton-Hunter-SP. Three months after local application of capsaicin onto the sciatic nerve quantitative evaluation of the autoradiograms revealed a significant decrease in the densiy of SP binding sites of up to 48% in regions of laminae I and II of the spinal dorsal horn somatotopically related to the capsaicin treated sciatic nerve. It is suggested that reduction in SP binding may result from transganglionic and transsynaptic degenerative changes affecting postsynaptic structures. Changes in the distribution of SP binding sites may significantly contribute to functional alterations observed after perineural treatment with capsaicin.     

Localization of 5-HT2A, 5-HT3, 5-HT5A and 5-HT7 receptor-like immunoreactivity in the rat cerebellum

Although serotonin (5-hydroxytryptamine, 5-HT) is known to exert a modulatory action on cerebellar function, our current knowledge of the nature of receptor subtypes mediating serotonergic activity in this part of the brain remains fragmentary. In this study, we report the presence and distribution of 5-HT3, 5-HT5A and 5-HT7 receptor-like immunoreactivity in the rat cerebellum using immunofluorescence histochemistry. 5-HT3 immunoreactivity was found in fibers sparsely distributed throughout the cerebellum. Most of them were seen in the cerebellar cortex as fine varicose 5-HT3-positive axonal processes. 5-HT5A immunoreactivity, on the other hand, was observed in neuronal somata of the cerebellar cortex and deep cerebellar nuclei. Based upon cell morphology and the use of cell-specific markers, Purkinje cells, molecular layer interneurons and Golgi cells were found to be 5-HT5A immunopositive. In addition, the use of cell-specific markers allowed us to identify previously reported large 5-HT2A-positive cells in the granular layer as being Golgi cells. Finally, 5-HT7 immunoreactivity was observed only in Purkinje cells. Corroborating previous radioligand-binding, in situ hybridization and immunohistochemical studies, our data relate serotonin receptor subtypes to specific cerebellar cell types and may consequently contribute to the elucidation of serotonergic actions in the cerebellum.     

Ultrastructural evidence for co-localization of corticotropin-releasing factor receptor and mu-opioid receptor in the rat nucleus locus coeruleus

Previous studies have shown that corticotropin-releasing factor (CRF), an integral mediator of the stress response, and opioids regulate the activity of the locus-coeruleus-norepinephrine (LC-NE) system during stress in a reciprocal manner. Furthermore, repeated opiate exposure sensitizes noradrenergic neurons to CRF. Previous studies have shown that mu-opioid receptors (muORs) are prominently distributed within somatodendritic processes of catecholaminergic neurons in the LC and axon terminals containing opioid peptides and CRF converge within the LC. To further examine cellular sites for interactions between CRF receptor type 1 (CRFr) and muOR, immunofluorescence and electron microscopic analysis of the rat LC was conducted. Triple immunofluorescence showed prominent co-localization of the CRFr and muOR in noradrenergic somata in the LC. Ultrastructural analysis confirmed dual localization of CRFr and muOR in common dendritic processes in the LC. Semi-quantitative analysis showed that of the dendrites exhibiting CRFr immunolabeling, 57% expressed muOR immunoreactivity. These data provide ultrastructural evidence that CRFr and muOR are co-localized in LC neurons, a cellular substrate that may underlie opiate-induced sensitization of brain noradrenergic neurons to CRF.     

Stimulation of the lateral hypothalamus produces antinociception mediated by 5-HT1A, 5-HT1B and 5-HT3 receptors in the rat spinal cord dorsal horn

The lateral hypothalamus is part of an efferent system that modifies pain at the spinal cord dorsal horn, but the mechanisms by which lateral hypothalamus-induced antinociception occur are not fully understood. Previous work has shown that antinociception produced from electrical stimulation of the lateral hypothalamus is mediated in part by spinally projecting 5-hydroxytryptamine (5-HT) neurons in the ventromedial medulla. To further examine the role of the lateral hypothalamus in antinociception, the cholinergic agonist carbamylcholine chloride (125 nmol) was microinjected into the lateral hypothalamus of female Sprague-Dawley rats and nociceptive responses measured on the tail-flick and foot-withdrawal tests. Intrathecal injections of the selective 5-HT1A, 5-HT1B, 5-HT3 receptor antagonists, WAY 100135, SB-224289, and tropisetron, respectively, and the non-specific antagonist methysergide, were given. Lateral hypothalamus stimulation with carbamylcholine chloride produced significant antinociception that was blocked by WAY 100135, tropisetron, and SB-224289 on both the tail-flick and foot-withdrawal tests. Methysergide was not different from controls on the tail flick test, but increased foot-withdrawal latencies compared with controls. These results suggest that the lateral hypothalamus modifies nociception in part by activating spinally projecting serotonin neurons that act at 5-HT1A, 5-HT1B, and 5-HT3 receptors in the dorsal horn.     

5-羟色胺3A型受体在成年小鼠杏仁体基底外侧核中间神经元内的表达

目的:研究5-羟色胺3A型受体(5-HT3Areceptor;5-HT3AR)在杏仁体基底外侧核中间神经元内的表达。方法:以成年5-HT3AR-BACEGFP转基因小鼠作为材料,利用免疫组织化学技术在激光共聚焦显微镜下观察成年小鼠杏仁体基底外侧核中5-HT3AR在不同类型中间神经元内的表达。结果:杏仁体基底外侧核中分布着大量的5-HT3AR免疫阳性神经元。5-HT3AR在小鼠杏仁体基底外侧核中Calretinin(CR)、血管活性肠肽(Vasoactive in-testinal peptide,VIP)和Reelin免疫阳性的中间神经元中大量表达,而在Calbindin(CB)、Parvalbumin(PV)或Neu-ropeptide Y(NPY)免疫阳性的中间神经元中很少表达。结论:杏仁体基底外侧核中存在5-HT3AR免疫阳性中间神经元,不同类型的中间神经元中5-HT3AR的表达比例不同。     

脊髓损伤后5-HT2A受体的变化与鼠尾痉挛关系的分析

目的　通过损伤大鼠脊髓腰1节段来探讨损伤下段5-HT2A受体免疫反应变化与鼠尾痉挛状态的关系,为治疗患者脊髓损伤后肢体痉挛提供理论依据。 方法　60只雄性Wistar大鼠随机分为空白组、打击组和横断组（n=20）,用免疫组化法研究5-HT2A受体免疫反应的变化,并分析与鼠尾痉挛状态的关系。所得数据统计学处理。 结果　(1)打击组和横断组5-HT2A受体免疫反应的密度比空白组增高,横断组增高更显著,差异有统计学意义。(2)脊髓损伤后鼠尾痉挛状态与5-HT2A受体的密度和脊髓损伤的程度呈正相关。 结论　脊髓损伤后鼠尾痉挛状态与5-HT2A受体密度的变化呈正相关,应用5-HT2A受体阻滞剂治疗患者的肢体痉挛提供了理论依据。     

Differential distribution of MAP1A isoforms in the adult mouse barrel cortex and comparison with the serotonin 5-HT2A receptor

Microtubule-associated protein 1A (MAP1A) is essential during the late differentiation phase of neuronal development. Here, we demonstrated the presence of two MAP1A isoforms with a differential spatial distribution in the adult mouse barrel cortex. Antibody A stained MAP1A in pyramidal and stellate cells, including dendrites that crossed layer IV in the septa between barrels. The other antibody, BW6 recognized a MAP1A isoform that was mainly confined to the barrel hollow and identified smaller caliber dendrites. Previously, an interaction of MAP1A and the serotonin 5-hydroxytryptamine 2A (5-HT(2A)) receptor was shown in the rat cortex. Here, we identified, by double-immunofluorescent labeling, MAP1A isoform and serotonin 5-HT(2A) receptor distribution. MAP1A co-localized mainly with 5-HT(2A) receptor in larger apical dendrites situated in septa. This differential staining of MAP1A and a serotonin receptor in defined barrel compartments may be due to changes in the expression or processing of MAP1A during dendritic transport as a consequence of functional differences in processing of whisker-related sensory input.     

Reversal of the antinociceptive effects of intrathecally administered serotonin in the rat by a selective 5-HT3 receptor antagonist

The ability of the highly selective 5-HT3 receptor antagonist ICS 205-930 (3 alpha-tropanyl-1H-indole-3-carboxylic acid ester) to block the increase in tail flick (TFL) and hot plate latencies (HPL) produced by intrathecally (i.t.) administered serotonin (5-HT) was examined in pargyline pretreated rats. ICS 205-930 (0.1 microgram, i.t.) blocked the ability of 5-HT (200 micrograms) to increase TFL and HPL. Significant hyperalgesia, as measured by a decrease in TFL and HPL compared to saline controls, also resulted from either the coadministration of ICS 205-930 (10 micrograms) and 5-HT (200 micrograms) or from ICS 205-930 (100 micrograms) alone. These data suggest an important role for 5-HT3 receptors in modulating spinal nociceptive responses.     

Somatostatin immunoreactivity in axon terminals in rat nucleus tractus solitarii arising from central nucleus of amygdala: coexistence with GABA and postsynaptic expression of sst2A receptor

Axon terminals synapsing on neurones in the nucleus tractus solitarii (NTS) that originate from the central nucleus of the amygdala (CeA) have been shown to contain gamma-aminobutyric acid (GABA) immunoreactivity. Here we investigated whether such terminals also contain somatostatin (SOM), a neuropeptide found in axons distributed throughout the NTS and in somata in the CeA, and known to modulate cardiovascular reflexes when microinjected into the NTS. With fluorescence microscopy, SOM immunoreactivity was seen in the varicosities of some axons throughout the NTS that were anterogradely labelled with biotin dextran amine injected into the CeA. Such varicosities were frequently observed in close proximity to dendrites of NTS neurones that were immunoreactive for the SOM receptor sst(2A) subtype, and in many cases also for catecholamine synthesising enzymes. In the caudal, cardioregulatory zone of NTS, SOM immunoreactivity was localised by electron microscopic pre-embedding gold labelling to boutons containing dense-cored and clear pleomorphic vesicles and forming symmetrical synapses, mostly onto dendrites. Additional post-embedding gold labelling for GABA suggested that a subpopulation (29%) of GABAergic terminals sampled in this area of NTS contained SOM. Almost all boutons anterogradely labelled from the amygdala were GABA-immunoreactive (-IR) and 21% of these were SOM-IR. A similar proportion of these boutons (22%) formed synapses onto dendrites containing immunoreactivity for the SOM receptor sst(2A) subtype. These observations provide evidence that some of the GABAergic projection neurones in the CeA that inhibit baroreceptor reflex responses in the NTS in response to fear or emotional stimuli could release SOM, which might modulate the activity of NTS neurones via an action on sst(2A) receptors.     

Activity-dependent modulation of axonal excitability in unmyelinated peripheral rat nerve fibers by the 5-HT(3) serotonin receptor

Activity-dependent fluctuations in axonal excitability and changes in interspike intervals modify the conduction of trains of action potentials in unmyelinated peripheral nerve fibers. During inflammation of a nerve trunk, long stretches of axons are exposed to inflammatory mediators such as 5-hydroxytryptamine [5-HT]. In the present study, we have tested the effects of m-chlorophenylbiguanide (mCPBG), an agonist at the 5-HT(3) serotonin receptor, on activity- and potential-dependent variations in membrane threshold and conduction velocity of unmyelinated C-fiber axons of isolated rat sural nerve segments. The increase in axonal excitability during application of mCPBG was much stronger at higher frequencies of action potentials and/or during axonal membrane hyperpolarization. The effects on the postspike recovery cycle also depended on the rate of stimulation. At an action potential frequency of 1 Hz or in hyperpolarized axons, mCPBG produced a loss of superexcitability. In contrast, at 0.33 Hz, a small increase in the postspike subexcitability was observed. Similar effects on excitability changes were found when latency instead of threshold was recorded, but only at higher action potential frequencies: at 1.8 Hz, mCPBG increased conduction velocity and reduced postspike supernormality. The latter effect would increase the interspike interval if pairs of action potentials were conducted along several cm in an inflamed nerve trunk. These data indicate that activation of axonal 5-HT(3) receptors not only enhances membrane excitability but also modulates action potential trains in unmyelinated, including nociceptive, nerve fibers at high impulse rates.     

Raloxifene blocks estradiol induction of the serotonin transporter and 5-hydroxytryptamine2A receptor in female rat brain

Sex steroids have potent effects on mood, mental state and cognition. Our previous findings and those of others suggest that these effects may be due at least in part to estradiol actions on central serotonergic mechanisms. Specifically, estradiol-17beta in its acute positive feedback mode for gonadotropin release in the female rat induces expression of the genes for the 5-hydroxytryptamine(2A) receptor (5-HT(2A)R) and the serotonin transporter (SERT) in the dorsal raphe nucleus (DRN). This is accompanied by an increase in the densities of 5-HT(2A)R and the SERT in forebrain regions which in the human are concerned with the control of mood, mental state, cognition and emotion. Here we report that raloxifene, a benzothiophene and selective estrogen receptor modulator (SERM), completely blocked estradiol stimulation of brain 5-HT(2A)R and SERT expression in acutely ovariectomized rats. Raloxifene also blocked the estrogen-induced surge of luteinizing hormone. Treatment of acutely ovariectomized rats with raloxifene alone increased the density of SERT sites in the mid-frontal cortex and decreased the density of 5-HT(2A)R in the posterior olfactory tubercle. The inhibitory effects of raloxifene on acute estrogen-induction of central serotonergic mechanisms were similar to those of tamoxifen even though there are major differences between the two SERMs in their affinity for the two estrogen receptor subtypes and their actions on the uterus. These findings provide robust evidence that estradiol induction of the 5-HT(2A)R and the SERT in brain is mediated by nuclear estrogen receptors. Our data may provide the basis for obtaining a better understanding of the effects of sex steroids on mood and mental state in the human and the possible rational development of congeners of sex steroids for the treatment of mental disorders.