Effects of deoxycorticosterone and its ring A-reduced derivatives on the nervous system

Synthetic neuroactive steroids as new sedatives and anaesthetics: Back to the future

Since the 1990s, there has been waning interest in researching general anaesthetics (anaesthetics). Although currently used anaesthetics are mostly safe and effective, they are not without fault. In paediatric populations and neonatal animal models, they are associated with learning impairments and neurotoxicity. In an effort to research safer anaesthetics, we have gone back to re-examine neuroactive steroids as anaesthetics. Neuroactive steroids are steroids that have direct, local effects in the central nervous system. Since the discovery of their anaesthetic effects, neuroactive steroids have been consistently used in human or veterinary clinics as preferred anaesthetic agents. Although briefly abandoned for clinical use due to unwanted vehicle side effects, there has since been renewed interest in their therapeutic value. Neuroactive steroids are safe sedative/hypnotic and anaesthetic agents across various animal species. Importantly, unlike traditional anaesthetics, they do not cause extensive neurotoxicity in the developing rodent brain. Similar to traditional anaesthetics, neuroactive steroids are modulators of synaptic and extrasynaptic γ-aminobutyric acid type A (GABA_A ) receptors and their interactions at the GABA_A receptor are stereo- and enantioselective. Recent work has also shown that these agents act on other ion channels, such as high- and low-voltage-activated calcium channels. Through these mechanisms of action, neuroactive steroids modulate neuronal excitability, which results in characteristic burst suppression of the electroencephalogram, and a surgical plane of anaesthesia. However, in addition to their interactions with voltage and ligand gated ions channels, neuroactive steroids interact with membrane bound metabotropic receptors and xenobiotic receptors to facilitate signaling of prosurvival, antiapoptotic pathways. These pathways play a role in their neuroprotective effects in neuronal injury and may also prevent extensive apoptosis in the developing brain during anaesthesia. The current review explores the history of neuroactive steroids as anaesthetics in humans and animal models, their diverse mechanisms of action, and their neuroprotective properties.

Early and late effects of steroid hormones on the central nervous system

Steroids have fast and probably partly GABA-mediated central anaesthetic effects for which a strict structure-function correlation is required. They also affect short- and long-term activity in the CNS in other ways. One of these is long-term potentiation (the persistent facilitation of synaptic transmission), which occurs particularly in the hippocampus after repetitive stimulation of a fibre pathway. Two clearly distinguished components of the evoked response can be studied in the hippocampus: the excitatory postsynaptic potential (EPSP) which denotes the graded depolarization of the somadendritic region of the neuron and the population spike (PS), a manifestation of the all-or-none discharge of the cell action potential. Corticosterone had a significant depressant effect on the EPSP component of the evoked response immediately and 15 min after injection. Thereafter EPSP amplitudes were within normal values. Corticosterone significantly decreased the PS immediately after the train, the component remaining low 30 min after the train. 5 alpha-Dihydrocorticosterone (a ring A-reduced metabolite of corticosterone) significantly reduced the PS component of the response at all times after injection. 18-Hydroxydeoxycorticosterone and deoxycorticosterone significantly decreased both EPSP and PS components of the evoked response from the time of infusion. Contrary to expectation, tetrahydrodeoxycorticosterone was ineffective in decreasing, and if anything, enhanced the development of long-term potentiation. 18-Hydroxydeoxycorticosterone 21-acetate behaved like vehicle, except for the first 30 min after injection, when the EPSP was decreased. Different steroids can selectively affect different parts of a neuron and appear to show a different structure-function correlation for long-term potentiation from that required for anaesthesia.

Neurosteroids, neuroactive steroids, and symptoms of affective disorders

Neurosteroids (NS) are steroids synthesized by the brain. Neuroactive steroids (NAS) refers to steroids that, independent of their origin, are capable of modifying neural activities. NAS bind and modulate different types of membrane receptors. The gamma amino butyric acid (GABA) and sigma receptor complexes have been the most extensively studied. Oxidized ring A reduced pregnanes, tetrahydroprogesterone (THP), and tetrahydrodeoxycorticosterone (THDOC) bind to the progesterone intracellular receptor (PR), and in this way can also regulate gene expression. Animal experimentation showed that salient symptoms of depression, viz., anxiety, sleep disturbances, and memory and sexual dysfunctions, are modulated by NAS. In turn, psychotropic drugs modulate NS and NAS levels. NS levels as well as NAS plasma concentrations change in patients with depression syndromes, the levels return to normal baseline with recovery, but normalization is not necessary for successful therapy. Results from current studies on the evolution of nervous systems, including evolutionary developmental biology as well as anatomical and physiological findings, almost preclude a categorical classification of the psychiatric ailments the human brain succumbs to. The persistence in maintaining such essentialist classifications may help to explain why up to now the search for biological markers in psychiatry has been an unrewarding effort. It is proposed that it would be more fruitful to focus on relationships between NAS and symptoms of psychiatric disorders, rather than with typologically defined disorders.

Systemic ethanol administration elevates deoxycorticosterone levels and chronic ethanol exposure attenuates this response

Systemic ethanol administration is known to elevate levels of the GABAergic neuroactive steroid 3alpha,21-dihydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THDOC). 3alpha,5alpha-THDOC is synthesized from deoxycorticosterone (DOC) by metabolism in adrenals and brain. The present study investigated DOC levels in plasma and brain following ethanol administration to naïve and ethanol-exposed rats. Rats were administered ethanol (2 g/kg, i.p.) or saline and DOC levels were measured in plasma and brain regions by radioimmunoassay. Chronic ethanol-exposed rats were administered an ethanol challenge (2 g/kg, i.p.) following 15 days of ethanol liquid diet consumption. Ethanol administration markedly increased DOC levels in plasma, cerebral cortex, hippocampus, hypothalamus, cerebellum, and olfactory tubercle of naïve rats. Ethanol challenge produced an attenuated elevation of DOC in rat plasma and brain following chronic ethanol consumption for 2 weeks. These findings suggest that acute ethanol increases DOC levels in ethanol naïve rats and chronic ethanol consumption induces tolerance to ethanol-induced increases in DOC levels.

Steroids, neuroactive steroids and neurosteroids in psychopathology

The term "neurosteroid" (NS) was introduced by Baulieu in 1981 to name a steroid hormone, dehydroepiandrosterone sulfate (DHEAS), that was found at high levels in the brain long after gonadectomy and adrenalectomy, and shown later to be synthetized by the brain. Later, androstenedione, pregnenolone and their sulfates and lipid derivatives as well as tetrahydrometabolites of progesterone (P) and deoxycorticosterone (DOC) were identified as neurosteroids. The term "neuroactive steroid" (NAS) refers to steroids which, independent of their origin, are capable of modifying neural activities. NASs bind and modulate different types of membrane receptors. The GABA and sigma receptor complexes have been the most extensively studied, while glycine-activated chloride channels, nicotinic acetylcholine receptors, voltage-activated calcium channels, although less explored, are also modulated by NASs. Within the glutamate receptor family, N-methyl-d-aspartate (NMDA) receptors, alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) receptors and kainate receptors have also been demonstrated to be a target for steroid modulation. Besides their membrane effects, once inside the neuron oxidation of Ring A reduced pregnanes, THP and THDOC, bind to the progesterone intracellular receptor and regulate gene expression through this path. The involvement of NASs on depression syndromes, anxiety disorders, stress responses to different stress stimuli, memory processes and related phenomena such as long-term potentiation are reviewed and critically evaluated. The importance of context for the interpretation of behavioral effects of hormones as well as for hormonal levels in body fluids is emphasized. Some suggestions for further research are given.

Effects of the active neurosteroid allotetrahydrodeoxycorticosterone on long-term potentiation in the rat hippocampus: implications for depression

We studied the effects of the active neurosteroid (ANS) allotetrahydrodeoxy corticosterone (ATHDOC) on long-term potentiation (LTP) in the dentate gyrus (DG) of intact, urethane anesthetized rats. Intravenous injection of the hormone at two doses, 0.1 and 0.5 mg/kg, produced a significant decrease in both components of the response: excitatory postsynaptic potentials (EPSP) and population spikes (PS). The effects were similar for the two doses. The results are discussed in terms of the potential mechanism by which ATHDOC modulates neural processes associated with symptoms present in depression syndromes.

Effects of androstenedione on long term potentiation in the rat dentate gyrus. Relevance for affective and degenerative diseases

We studied the effects of the androgenic hormone androstenedione, a 17-ketosteroid, on long term potentiation (LTP) in the dentate gyrus (DG) of intact, urethane anesthetized rats. Intravenous injection of 10mg of the hormone dissolved in Nutralipid produced a significant increase of the population spike (PS), but not of the excitatory post-synaptic potentials (EPSPs). The results are discussed in terms of the potential enhancement that androstenedione may have on some aspects of memory processes as reported for other androgenic steroids. Also noted are the plausible beneficial effects of the hormone on depression as well as in recovery following both central and peripheral neural injury.

Androsterone sulfate increases dentate gyrus population spike amplitude following tetanic stimulation

We studied the effects of the androgenic hormone, androsterone sulfate, a 17-ketosteroid, on long term potentiation in the dentate gyrus (DG) of urethane anesthesized rats. Intravenous injection of 10 mg of the hormone dissolved in Nutralipid produced a significant increase of the population spike (PS), but not of the excitatory post-synaptic potentials (EPSP). The results are discussed in terms of the potential enhancement that androsterone sulfate may have on memory as was described for one of its parent compounds, dehydroepiandrosterone (DHEA) and its potential use as an antidepressant.

The specificity of stress responses to different nocuous stimuli: neurosteroids and depression

The role that adrenal cortex and neurosteroid hormones may have in the etiology and/or maintenance of depressive diseases is discussed. Selye's concept of stress as the summation of unspecific body responses of the autonomic central nervous system (CNS) and hypothalamic pituitary adrenal axis (HPAA) as the main characteristic of it is contrasted with Mason's view of stress responses as being specific for different stimuli, i.e., the neuroendocrine system responds with the production of a hormonal profile individualized and characteristic for the various stimuli applied. The data reviewed provides support for Mason's interpretation of stress as fundamentally a behavioral response. In turn, the high relevance of emotional factors in the determination of stress responses led to a reconsideration of cognitive-affective interactions in nervous systems. Recent results revealed that improvement in depression treated with antidepressants (ADs) is associated with an increase in the neurosteroid 3alpha 5alpha tetrahydroprogesterone, both in the blood and cerebrospinal fluid of recovered patients. The increase occurs with both selective serotonin reuptake inhibitors and tricyclic ADs. An evaluation of the possible and putative roles for neurosteroids in the CNS is presented and suggestions for enhancing the type of supporting data from the laboratory diagnosis of depressions are advanced.

Natural steroids counteracting some actions of putative depressogenic steroids on the central nervous system: potential therapeutic benefits

Psychological similarities in the symptomatology of Cushing's and depressive diseases led to repeated attempts of treatment of the affective disease by suppression of adrenocortical secretion. While successful in many patients, all drugs employed-metyrapone, ketoconazole and aminoglutethimide-carry the danger of inducing adrenal insufficiency. In addition, their undesirable side effects were also a main reason for treatment suspension. In our 1990 proposal for the treatment of depression through control of adrenal steroid levels, we set as one of the goals the identification of steroids which can antagonize each other on their effects on the central nervous system. Specifically, we looked first at steroids that could counter each other's effects on long-term potentiation, a putative memory mechanism in the central nervous system. One reason for this was the consensus that memory mechanisms are affected in both Cushing's and depressive patients. Another was the fact that cortisol-type hormones which underlie, at least in part, the depressogenic actions of adrenal steroids also have inhibitory effects on LTP. We conjectured, then, that a steroid with opposite effects, one that could enhance long-term potentiation and, further, that could counter the depressant effects of corticosterone on long-term potentiation, could be of use in the treatment of depression. Dehydroepiandrosterone sulfate increases long-term potentiation in a dose-related manner, and preliminary data suggest that it also counteracts the depressant effects of corticosterone on long-term potentiation when injected simultaneously on experimental animals. Potentially at least, rather than resort to total suppression of adrenocortical activity, it may be possible to treat depression just by counteracting some of the effects of cortisol-like hormone actions in the central nervous system. Further, both in clinical trials as well as in experimental animals, dehydroepiandro-sterone sulfate has been shown to enhance performance in memory-requiring tasks.

Effects of adrenocortical steroids on long-term potentiation in the limbic system: basic mechanisms and behavioral consequences

Hippocampal structures are a major target for adrenal steroid hormones, and hence these neural regions are some of the most likely mediators of the effects of adrenocortical steroids on behavior. Memory disturbance, in particular biasing toward negative contents, are part of the symptomatology presented by depressive patients. In turn, a sizeable subset of depression also presents with hypercortisolemia. Adrenocortical hormones are also known to affect memory processes. Hippocampal formation is essential for declarative memory. We thought it appropriate then to study the effects of adrenal steroids on long-term potentiation, a putative memory mechanism in the hippocampus. Two clearly distinguished components of the evoked response to perforant path stimulation can be studied in the hippocampus: the excitatory postsynaptic potential (EPSP) which denotes the graded depolarization of the somatodendritic region of the neuron and the population spike (PS), a manifestation of the all-or-none-discharge of the cell action potential. Corticosterone had a significant depressant effect on the EPSP component of the evoked response immediately and 15 min after injection. Thereafter EPSP amplitudes were within normal values. Corticosterone significantly decreased the PS immediately after the train, the component remaining low 30 min after the train. 5 alpha-Dihydrocorticosterone (a ring A-reduced metabolite of corticosterone) significantly reduced the PS component of the response at all times after injection. 18-Hydroxydeoxycorticosterone and deoxycorticosterone significantly decreased both EPSP and PS components of the evoked response from the time of infusion. Contrary to expectation, tetrahydrodeoxycorticosterone was ineffective in decreasing and if anything, enhanced the development of long-term potentiation. 18-Hydroxydeoxycorticosterone 21-acetate behaved like vehicle, except for the first 30 min after injection when the EPSP was decreased. Allotetrahydroprogesterone decreased all EPSP's values and had no effect in the PS development in comparison with vehicle. The suggestion is made that the study of steroidal effects on hippocampal LTP can serve as a preclinical model of some aspects of depression in a specific subset of the disease.

Adrenal steroids and the physiopathology of a subset of depressive disorders

Patients suffering from Cushing's disorders (syndrome and disease) are significantly affected by psychological disturbances that overlap with depressive disorders. In turn, a subset of patients with affective disorders present with hypercortisolemia, and non-suppression in the Dexamethasone Suppression Test (DST). We have shown that long-term potentiation (LTP), a putative memory mechanism, is significantly affected by steroids when tested on the hippocampus, a crucial structure for memory processes. We propose that an imbalance of adrenal steroids and their metabolites, interacting at the level of the hippocampus, play a fundamental role in the psychophysiopathology of Cushing's and depressive disorders. By biasing memory mechanisms, the imbalance of these hormones sets both distorted mood, and hence memory contents, and distorted cognition based on recollection and present experiences.

Modulation by adrenal steroids of limbic function

The effects of various steroid hormones on the long-term potentiation (LTP) of the rat hippocampus were evaluated. LTP was elicited in the dentate gyrus of adrenalectomized animals with priming tetanic stimulation (200 Hz-0.03 cps) of its main afferent, the perforant pathway. Single pulse EPSP (excitatory post-synaptic potential) slope, and PS (population spike) amplitude values were compared before and after the i.v. injection of the hormones and subsequently after the priming stimulation every 15 min up to 1 h. 18-OH-deoxycorticosterone (18-OH-DOC) produced a significant decrease of the EPSP LTP and arrested the PS enhancement in comparison with vehicle at every time post-tetanic stimulation. Its 21-acetate derivative produced a moderate decrease of the EPSP and had no effect on the PS LTP in comparison with vehicle. Deoxycorticosterone (DOC) exhibited similar effects on the EPSP although less marked than with 18-OH-DOC while the PS only decreased in the first 30 min post-train. Corticosterone decreased both EPSP and PS for the first 15 and 30 min after priming stimulation, respectively, matching values with those of vehicle afterwards. Its 21-acetate produced an initial decrease of the EPSP and had no effect on the PS LTP. Allo-tetrahydro-DOC produced little, if any, initial enhancement of the PS LTP in comparison with vehicle. These results show that the adrenal steroids tested can modulate hippocampal LTP, a plastic phenomenon in the mammalian CNS which is known to be related to memory and learning processes. Moreover, adrenal steroids can independently modify the PS or EPSP components of the LTP, suggesting different loci of action at the neuronal level.

Steroids and depression

Patients with endogenous depression (major affective disorder) frequently have high cortisol levels, but the diurnal rhythm is usually maintained and they do not develop the physical signs of Cushing's syndrome. On the other hand, depression is a frequent feature of Cushing's syndrome regardless of etiology, and it is often relieved when the cortisol levels are reduced, by whatever means. The mechanisms of the hypercortisolemia and resistance to dexamethasone suppression commonly found in endogenous depression are poorly understood; contrary to expectations, ACTH levels are not clearly elevated. There is a striking difference in the psychiatric features seen in endogenous hypercorticism compared to those seen after exogenous administration of glucocorticoids or ACTH. This suggests that either there are other stimulating or modifying factors besides ACTH or that the steroids stimulated by ACTH or other peptides differ from those in control subjects, i.e. there may be an alteration in the metabolism of steroids in depression. Little is known about the metabolic changes or the many steroids besides glucocorticoids produced by the hyperactive steroid-producing tissue. Preliminary studies suggest that major depression may be improved by steroid suppression. It is hypothesized that steroids themselves may be important in causing and perpetuating depression.

Effects of adrenal steroids and their reduced metabolites on hippocampal long-term potentiation

We studied the effects of steroid hormones on the hippocampal long-term potentiation (LTP), a putative mechanism of neuronal plasticity and memory storage in the CNS. In vivo experiments were performed in rats under chloral hydrate anesthesia (0.4 mg/kg i.p.). All animals were adrenalectomized 48 h before recording. LTP was induced after priming tetanic stimulation at the perforant pathway (PP) and single pulse field potentials were obtained from the dentate gyrus (DG). The excitatory post-synaptic potential (EPSP) slope and population spike (PS) amplitude were analyzed before and after the i.v. injection of the steroids and after the induction of LTP, and followed up to 1 h. Results obtained with the hormones were compared with matched control animals injected with vehicle alone, Nutralipid 10%. Previous results from our laboratory showed that deoxycorticosterone (DOC) decreased the magnitude of the EPSP at all times after priming stimulation and the PS decreased during the first 30 min of the LTP. Corticosterone decreased the EPSP in the first 15 min and the PS during the first 30 min after priming stimuli. In these experiments the mineralocorticoids aldosterone and 18-OH-DOC elicited a decrease of the EPSP at all times post-train; and no significant difference against vehicle was observed in the PS. Post-injection values were not changed except for 18-OH-DOC at a dose of 1 mg, where a decrease of both the EPSP (P less than 0.01) and the PS (P less than 0.02) was observed against vehicle. ATH-progesterone at 0.1 mg/rat also decreased the EPSP values significantly after priming stimulation and no significant changes against vehicle were observed in the PS. These results show that adrenal steroids can modulate hippocampal LTP, that they can act at different neuronal loci and with different time courses in the development of the phenomena.

Testosterone 5 alpha-reductase activity in the rat brain is highly concentrated in white matter structures and in purified myelin sheaths of axons

Previous results obtained in this laboratory indicate that in the rat brain the 5 alpha-reductase, the enzymatic activity involved in metabolizing testosterone into 5 alpha-androstan-17 beta-ol-3-one (dihydrotestosterone), is particularly concentrated in the white matter. In the present experiments, this enzymatic activity was studied in the following white matter structures, which were microdissected using the punch technique of Palkovits: anterior commissure (CA), fornix (FX), habenulo-interpeduncular tract (HP), corpus callosum (CC), stria medullaris (SM), optic chiasm (CO), fimbria of the hippocampus (FI), cerebral peduncle (PC), pontine fibers (FP), cerebellar medulla (CMD) and corticospinal tract (TCS). Moreover brain myelin was isolated and purified by sucrose density gradient ultracentrifugation. The results obtained confirm that, in the rat brain, the enzymes involved in testosterone 5 alpha-reduction are preferentially localized in the white matter. However, clearcut differences in the metabolic activity exist between the different structures examined so far. DHT formation increases rostro-caudally, so that the highest activity has been recorded in the white matter structures punched at the level of pons (FP), medulla oblungata (TCS) and cerebellum (CMD). The high metabolic activity associated with the white matter structures appears to be linked to the presence of myelin, since the specific activity of the enzyme is particularly elevated in purified preparations of myelin sheaths.

Inhibitory influences of the adrenal steroid, 3 alpha, 5 alpha-tetrahydrodeoxycorticosterone [correction of tetrahydroxycorticosterone] on aggression and defeat-induced analgesia in mice

The effects of intraperitoneal administrations of the deoxycorticosterone metabolite, 5 alpha-pregnane-, 21 diol-20-one (3 alpha, 5 alpha-tetrahydrodeoxycorticosterone; alpha-THDOC) on the responses to aggression and defeat-induced analgesia were examined in subordinate intruder male mice in "resident-intruder" pairings. alpha-THDOC reduced in a dose-dependent mannter (1-20 mg/kg) the number of bites and time to obtain defeat in subordinate mice during the agonistic encounters, as well as attenuating defeat-induced analgesia. These inhibitory effects of alpha-THDOC were separate from its sedative actions at 20-30 mg/kg. In addition, the stereo-isomer, 3 beta-pregnane-3 alpha, 21 diol-20-one (20 mg/kg) had no significant effects on the agonistic encounters and defeat, indicating that the inhibitory effects of alpha-THDOC on agonistic interactions are stereospecific. Pretreatment with the benzodiazepine antagonist Ro 15-1788 (5 and 10 mg/kg) attenuated the inhibitory effects of alpha-THDOC on defeat-induced analgesia. Ro 15-1788 (5, 10 mg/kg) by itself, however, had minimal effects on these agonistic interactions and subsequent defeat-induced analgesia. These results indicate that the naturally occurring steroid, alpha-THDOC, has significant effects on responses to aggression and defeat-induced analgesia.

Effects of 5 alpha-dihydrocorticosterone on evoked responses and long-term potentiation

The effect of a Ring A-reduced metabolite of corticosterone, 5 alpha-dihydrocorticosterone (DHB) on long-term potentiation (LTP) in the dentate gyrus (DG) of the rat were studied in barbiturate-anaesthetised animals. It was observed that DHB significantly impairs the development of LTP, more particularly the population spike (PS) component of the evoked potential (EP) to perforant path (PP) stimulation. Nutralipid, an inert control solvent of the steroid, did not affect LTP development. We argue that both, membrane and intracellular effects of DHB, are involved in the mechanisms responsible for DHB blocking of LTP.

Effects of 18-hydroxydeoxycorticosterone on central nervous system excitability

The effects of 18-hydroxydeoxycorticosterone (18-OH-DOC) on central nervous system excitability were studied in adrenalectomized rats. Sixty-four evoked potentials (EP) recorded from the pontine reticular formation were averaged before and after the injection of vehicle and hormone. 750 micrograms of 18-OH-DOC dissolved in 0.5 ml of a 4:1 saline Cremophor-EL solution were injected i.v. A decrease of 55.7 +/- 6.1% in the amplitude of the EPs was observed with the hormone 16.3 min +/- 2.7 (SE) after injection. Amplitude values returned to baseline levels 38 min +/- 6.8 (SE) after injection. The secretion of 18-OH-DOC is greatly increased by ACTH and might modulate central nervous system function.

Steroid hormone metabolites are barbiturate-like modulators of the GABA receptor

Two metabolites of the steroid hormones progesterone and deoxycorticosterone, 3 alpha-hydroxy-5 alpha-dihydroprogesterone and 3 alpha, 5 alpha-tetrahydrodeoxycorticosterone, are potent barbiturate-like ligands of the gamma-aminobutyric acid (GABA) receptor-chloride ion channel complex. At concentrations between 10(-7) and 10(-5)M both steroids inhibited binding of the convulsant t-butylbicyclophosphorothionate to the GABA-receptor complex and increased the binding of the benzodiazepine flunitrazepam; they also stimulated chloride uptake (as measured by uptake of 36Cl-) into isolated brain vesicles, and potentiated the inhibitory actions of GABA in cultured rat hippocampal and spinal cord neurons. These data may explain the ability of certain steroid hormones to rapidly alter neuronal excitability and may provide a mechanism for the anesthetic and hypnotic actions of naturally occurring and synthetic anesthetic steroids.

Neurotoxicity of triorthotolyl phosphate in chickens of different genotypes in the presence and absence of deoxycorticosterone

Indices of acute and delayed toxicity following administration of triorthotolyl phosphate (TOTP) were measured in roosters from lines of chickens originating from the Cornell randombred population. Matings were designed to produce individuals that had presence or absence of allele 21 of the B blood system. Non-B21 individuals had allele 13 or 31. Acute inhibition of esterases (neurotoxic esterase, liver cholinesterase, plasma cholinesterases, and plasma carboxylesterases) occurred in all birds within 24 hr of a single oral dose of 360 mg/kg TOTP. Clinical signs of delayed neuropathy were evident within 12 days of TOTP administration, with no significant difference between genotypes. Dietary deoxycorticosterone (40 to 200 ppm) appeared incapable of statistically significant modification of the strong effects of TOTP. Activities of blood esterases were different between roosters having B21/B21 and those with B13 and/or B31.

In vivo secretion of 3 alpha-hydroxy-5 alpha-pregnan-20-one, a potent anaesthetic steroid, by the adrenal gland of the rat

3 alpha OH-5 alpha-Pregnan-20-one (allo-THP), a steroid with strong anaesthetic properties, was found to be secreted by the adrenal gland of the rat in quantities similar to those secreted by the rat ovary. From the hypnotic potencies established for this and other endogenous steroids there can be little doubt that the total amount of steroids with anaesthetic properties produced in a female rat are sufficient to exert a depressant action on certain cells of the brain. In rats with intact adrenal glands a positive correlation existed between the adrenal secretion of allo-THP and pregnenolone or progesterone, whereas that between allo-THP and DOC was negative. This could be the result of a competition between the enzymes responsible for the oxidation and reduction of progesterone, the common precursor of allo-THP and DOC. The possibility that allo-THP could have hypotensive actions was suggested.

Effects of corticosterone and 5 alpha-dihydrocorticosterone on brain excitability in the rat

The effects of corticosterone (B) and its reduced metabolite 5 alpha-dihydrocorticosterone (DHB) on CNS activity in the rat were examined. Two indices of brain excitability were evaluated: 1) amplitude of population responses (evoked potentials [EP] to sciatic nerve stimulation) and 2) changes in the rate of firing of tonically discharging neurons--both at pontine brainstem regions of the reticular formation. Experiments were carried out in adrenalectomized rats, and recordings were obtained from animals under urethane anesthesia. Steroids were dissolved in a 4:1 saline:Cremophor-El (Sigma) solution and doses of 750 micrograms/0.5 ml were injected (IV). The effects of B on EPs were bidirectional. Increases (8 animals) and decreases (6 animals) of the amplitude responses in different animals were observed. In 4 animals, no changes were detected. In contrast, injection of DHB produced a consistent and significant reduction of brainstem sciatic evoked potentials in 10 of 12 animals tested; 2 animals did not respond to the steroid. At the neuronal level, the effects of the steroids were evaluated by the changes they induced in the mean firing frequency (P less than 0.01) measured during 5-min intervals as determined by a one-way analysis of variance and analysis with a test of multiple comparisons. Only cells that fired in a stationary mode for 15 min before the steroid injection were studied. A more consistent pattern of responses to B was observed at the single-cell level. From 31 neurons that responded to the hormone, of 76 examined, 27 showed an increase in their firing rate and only 4 neurons showed a decrease. The increase in firing rate had an onset latency of 2-5 min (means = 3.5, SE 0.43) with a duration of 16-25 min (means = 17.5, SE 2.7). Of 69 neurons that were tested with DHB, 51 showed a significant decrease in their mean firing frequency. Onset latency of the effect was 2-8 min (means = 4.0, SE 1.21) and the duration of the induced changes was 16-40 min (means = 30.0, SE 3.47). Central interactions of DHB and B when sequentially administered were examined in 28 neurons. Of these, 21 responded to DHB administration with a significant decrease in their firing rates. In 11 of these neurons, injection of B, 5 min after DHB, was followed by a rapid (1-2 min) return of the neurons to baseline firing rates.(ABSTRACT TRUNCATED AT 400 WORDS)

Towards an improved serum-free, chemically defined medium for long-term culturing of cerebral cortex tissue

The present study describes a series of experiments which have led to a substantially improved serum-free, chemically defined medium (CDM) for long-term culturing of reaggregated fetal rat cerebral cortex tissue. A reduction of the original medium concentrations of the hormones insuline, T3 and corticosterone, on the one hand, and an enrichment of the medium with the vitamins A, C and E, the unsaturated fatty acids linoleic and linolenic acid, and biotin, L-carnitine, D(+)-galactose, glutathione (reduced) and ethanolamine, on the other hand, formed the most important chemical adjustments of the medium. With the aid of this CDM (encoded R12), the light- and electron microscopic architecture of the tissue could be kept in a good condition (superior to that seen earlier in serum-supplemented medium) up to 23 days in vitro. From that time on, the neuronal network lying between the reaggregates degenerated for the largest part, while a portion of the large neurons (probably pyramidal cells) plus some of the neuronal network within the reaggregates degenerated too. This degeneration process continued during the following weeks, but the reaggregates nevertheless retained most of their mass, so that both small and large neuronal cell bodies (visible in transparent regions at the edge of the reaggregates) remained in good condition up to at least 103 DIV. Stout, thick nerve bundles interconnecting the reaggregates, also survived up to this point. Electron microscopic evaluation of such 'aged' reaggregates revealed degenerating as well as healthy regions. The latter had indeed retained healthy-looking pyramidal and non-pyramidal neurons, embedded within a dense neuropil which was often traversed by myelinated axons. The numerical synapse density in such selected, healthy tissue regions reached its maximum during the sixth week in vitro, followed by a rapid decrease and a stabilization at about half the peak values. The present culture system has opened the possibility for performing controlled quantitative studies on the relationship between structure and function of cerebral cortex tissues during development and aging, on its dependence on nutrients, hormones and drugs, and on special factors synthesized by the tissue and released into the nutrient medium.

Localization of aldosterone and corticosterone in the central nervous system, assessed by quantitative autoradiography

Nuclear localization of tritiated aldosterone in the CNS was studied in rats by numerical evaluation of silver grains, deposited over neuronal cell nuclei in thaw-mounted autoradiograms, and compared with the localization obtained after prior administration of a 100-fold excess of radioinert aldosterone, corticosterone or 18-hydroxy-11-deoxycorticosterone (18-OH-DOC). Corticosterone and 18-OH-DOC completely prevented nuclear localization in most regions examined. However, in contrast to pretreatment with aldosterone, pretreatment with corticosterone and 18-OH-DOC did not completely prevent the concentration of radioactivity in the cell nuclei of the indusium griseum. Traces of radioactivity were, furthermore, retained in areas CA1 and CA2 and the dentate gyrus in rats exposed to corticosterone, but not to 18-OH-DOC, prior to [3H]aldosterone. A similar profile of silver grain distribution to that noted with aldosterone was found for corticosterone except that with tritiated corticosterone the most intense concentration of radioactivity occurred in hippocampal areas CA1 and CA2 and not in the indusium griseum. Prior administration of excess deoxycorticosterone acetate abolished nuclear accumulation of tritiated corticosterone. Dihydrotestosterone, on the other hand, failed to compete with tritiated corticosterone at a dose 200-fold in excess of the tritiated steroid. We conclude that (1) a receptor readily shared by aldosterone, corticosterone, 18-OH-DOC and DOC, but not by dihydrotestosterone, is widely distributed throughout the CNS, (2) a receptor shared by aldosterone and 18-OH-DOC, but not by corticosterone may be present in hippocampal areas CA1 and CA2, (3) that both these as well as the receptor accepting dihydrotestosterone can be located within the same cell.