Neurosteroids: deficient cognitive performance in aged rats depends on low pregnenolone sulfate levels in the hippocampus

Pregnenolone sulfate (PREG S) is synthesized in the nervous system and is a major neurosteroid in the rat brain. Its concentrations were measured in the hippocampus and other brain areas of single adult and aged (22-24 month-old) male Sprague-Dawley rats. Significantly lower levels were found in aged rats, although the values were widely scattered and reached, in about half the animals, the same range as those of young ones. The spatial memory performances of aged rats were investigated in two different spatial memory tasks, the Morris water maze and Y-maze. Performances in both tests were significantly correlated and, accompanied by appropriate controls, likely evaluated genuine memory function. Importantly, individual hippocampal PREG S and distance to reach the platform in the water maze were linked by a significant correlation, i.e., those rats with lower memory deficit had the highest PREG S levels, whereas no relationship was found with the PREG S content in other brain areas (amygdala, prefrontal cortex, parietal cortex, striatum). Moreover, the memory deficit of cognitively impaired aged rats was transiently corrected after either intraperitoneal or bilateral intrahippocampal injection of PREG S. PREG S is both a gamma-aminobutyric acid antagonist and a positive allosteric modulator at the N-methyl-D-aspartate receptor, and may reinforce neurotransmitter system(s) that decline with age. Indeed, intracerebroventricular injection of PREG S was shown to stimulate acetylcholine release in the adult rat hippocampus. In conclusion, it is proposed that the hippocampal content of PREG S plays a physiological role in preserving and/or enhancing cognitive abilities in old animals, possibly via an interaction with central cholinergic systems. Thus, neurosteroids should be further studied in the context of prevention and/or treatment of age-related memory disorders.

Brain neurosteroids during the mouse oestrous cycle

Concentrations of the neuroactive steroid 3alpha,5alpha-tetrahydroprogesterone (TH PROG or allopregnanolone) and its precursors progesterone (PROG) and 5alpha-dihydroprogesterone (DH PROG) have been measured in mouse brain throughout the oestrous cycle. Plasma PROG concentrations were also measured for comparison. At each stage, circadian fluctuations were found in the concentrations of brain PROG and its metabolites. Such fluctuations were greater than those attributable to any particular stage of the oestrous cycle. Over the entire cycle, a significant correlation was found between brain TH PROG (or DH PROG) and PROG concentrations but not between brain TH PROG (or DH PROG) and plasma PROG concentrations. There was also no correlation between endogenous TH PROG (or DH PROG) and activity of the 5alpha-reductase converting 3H-PROG to 3H-DH PROG in whole brain homogenates. Concentrations of another neuroactive steroid, pregnenolone sulphate (PREG S), in the brain during the oestrous cycle were in phase with plasma PROG but not brain PROG concentrations. Our results indicate that circadian and ovarian influences on the concentrations of PROG and its metabolite TH PROG in female whole mouse brain are caused predominantly by changes in the supply of PROG from within the tissue, whatever the contribution of peripheral sources.

Neurosteroids in the mouse brain: behavioral and pharmacological effects of a 3 beta-hydroxysteroid dehydrogenase inhibitor

Inhibition of the aggressive behavior of castrated male mice toward lactating female intruders by dehydroepiandrosterone (DHEA) is correlated with a decrease of pregnenolone sulfate (PREG S) concentrations in brain. We attempted to establish a cause to effect relationship by preventing the decrease of PREG S with trilostane (TRIL), a competitive inhibitor of delta 5-3 beta-hydroxysteroid dehydrogenase delta 5 --> 4 isomerase enzyme. Indeed, TRIL elicited a large increase of PREG levels in brain. Those of PREG S were, however, unchanged, and TRIL unexpectedly decreased the aggressive behavior of control castrated males and did not counteract the inhibition elicited by DHEA. The neurosedative progesterone (PROG) metabolite, 3 alpha-hydroxy-5 alpha-pregnan-20-one (TH PROG), undetectable in the brain of control mice, reached nanomolar concentration range in TRIL-treated ones. However, injection of appropriate amounts of PROG, producing an even larger increase of brain TH PROG, had no antiaggressive effect. Finally, the latter was attributed to the large (up to 80 nM) TRIL-induced increase of brain 3 alpha,21-dihydroxy-5 alpha-pregnan-20-one, which like TH PROG potentiates inhibitory gamma-aminobutyric acid (GABA)ergic neurotransmission.

Biosynthesis and assay of neurosteroids in rats and mice: functional correlates

Pregnenolone (PREG), synthesized de novo in rodent brain, is the precursor of PREG sulfate (S) and progesterone (PROG). PROG is further converted to 5 alpha-pregnane 3, 20-dione (DH PROG) and to 3 alpha-hydroxy-5 alpha-pregnan-20-one (TH PROG). PROG, DH PROG and TH PROG have been measured in the brain of male and female rats. Neither PROG nor DH PROG disappeared from brain, contrary to plasma, after combined adrenalectomy (ADX) and gonadectomy (CX). Trilostane decreased PROG and increased PREG in the brain of CX+ADX rats and mice, in accordance with a precursor to product relationship. As previously described in CX male mice, the neurosteroid DHEA and its analog 3 beta-methyl-androst-5-en-17-one (CH3-DHEA) inhibited the aggressive behavior of female mice towards lactating female intruders. The decrease of biting attacks by DHEA was definitely more prominent in females neonatally imprinted with testosterone. The degree of inhibition of aggressive behavior was related to the decrease of PREG S concentrations in brain. The memory-enhancing effects of DHEA S and PREG S in male mice have been previously documented. Infusion of PREG S (12 fmol) into the nucleus basalis magnocellularis (NBM) of the rat after the acquisition trial enhanced memory performance in a two-trial recognition task (TTRT). Conversely, TH PROG (6 fmol), which potentiates GABAergic neurotransmission, disrupted performance when injected before the acquisition trial. Accordingly, we have found a positive correlation between the performances of 2-year-old rats in the TTRT and the concentrations of PREG S in the hippocampus, namely animals which performed best had the highest steroid levels.

Neurosteroids: 3 alpha-hydroxy-5 alpha-pregnan-20-one and its precursors in the brain, plasma, and steroidogenic glands of male and female rats

A RIA procedure for measuring progesterone (PROG), 5 alpha-pregnane-3,20-dione (5 alpha-DH PROG), and 3 alpha-hydroxy-5 alpha-pregnan-20-one (3 alpha,5 alpha-TH PROG) has been developed and validated by GLC/mass spectrometry. Measurements were made in intact and adrenalectomized (ADX) male rats, in cyclic, pregnant, spayed, and spayed-ADX females, and in both males and spayed females injected with PROG. The predominant contribution of the ovary to the concentrations of 3 alpha,5 alpha-TH PROG in plasma and brain, was indicated by its larger levels in females, in particular during pregnancy, and by its presence in ovarian tissue and disappearance after ovariectomy. An additional adrenal origin in both males and females was shown. Neither PROG nor 5 alpha-DH PROG disappeared from brain, contrary to plasma, after combined adrenalectomy and gonadectomy, thus suggesting that PROG might be synthetized de novo in brain. However, the concentrations of 3 alpha,5 alpha-TH PROG in plasma and brain of female rats were positively correlated with the concentrations of PROG in plasma, indicating that plasma PROG was the major precursor of 3 alpha,5 alpha-TH PROG. The direct formation of 3 alpha,5 alpha-TH PROG from PROG in brain was strongly suggested by the increased 3 alpha,5 alpha-TH PROG/PROG ratios in brain vs. plasma, when measured in control females, and after injection of PROG to both males and OVX females. It was previously reported that 3 alpha,5 alpha-TH PROG is a sedative/anxiolytic steroid, as a result of its binding to gamma-aminobutyric acid (GABA)A receptors and allosteric potentiation of GABAcergic neurotransmission. Its concentrations in brain reach indeed the neuroactive range in cyclic and pregnant females, and are compatible with a physiological role of this neurosteroid.

Neurosteroids: pregnenolone in human sciatic nerves

The characterization and quantification of pregnenolone in human sciatic nerves were undertaken, following previous demonstration of the synthesis of this steroid in rat brain oligodendrocytes, to explore the hypothesis that Schwann cells may demonstrate the same biosynthetic activity. Pregnenolone was definitively identified by mass spectrometry and quantified by specific radioimmunoassay. Its concentration (mean +/- SD, 63.9 +/- 45.9 ng/g of wet tissue, n = 12) was greater than or equal to 100 times the plasma level and concentration found in tendons and muscle. No correlation was found with sex or age. Free dehydroepiandrosterone as well as sulfate and fatty acid esters of pregnenolone and dehydroepiandrosterone were also measured. Results are discussed in terms of the concept that these "neurosteroids" may be synthesized in the peripheral nervous system.

Suppressive effects of dehydroepiandrosterone and 3 beta-methyl-androst-5-en-17-one on attack towards lactating female intruders by castrated male mice. II. Brain neurosteroids

Dehydroepiandrosterone (DHA) and 3 beta-methyl-androst-5-en-17-one (CH3-DHA) suppress attacks by castrated male mice towards lactating female intruders (Haug et al. Physiol. Behav. 46:955, 1989). Their effects on the concentrations of DHA, pregnenolone (delta 5P), and their sulfate ester (S) have been investigated in the brain of control and treated mice. A more than 2 fold, significant, decrease of delta 5P-S was the only change common to both steroids. DHA and CH3-DHA effects might be related to the antagonistic action of delta 5P-S on GABAA receptors.

Neuro-steroids: 3 beta-hydroxy-delta 5-derivatives in rat and monkey brain

The rat brain accumulates pregnenolone (P) as the unconjugated steroid, the sulfate ester (S) and fatty acid esters (L). P + PS do not disappear from rat brain after combined adrenalectomy (adx) and castration (orx). PL does not serve a source of P after adx + orx. P is metabolized by several rat brain regions to progesterone and to PL. Brain microsomes contain the acyl-transferase which converts P to PL using endogenous substrates. Brain P and dehydroepiandrosterone (D) undergo a prominent circadian variation with their acrophases at the beginning of the dark span. The circadian variation of brain D persists after adx + orx. The monkey brain (Macaca fascicularis) also accumulates P and D. Adrenal suppression with dexamethasone for 4 days does not decrease the concentrations of brain P and 3rd ventricle CSFP and D. The concentrations of brain D are decreased to a much smaller extent than plasma D. D inhibits the aggressive behavior of castrated male mice exposed to lactating female intruders. This is not the case for DS or androst-5-ene-3 beta, 17 beta-diol. The D analog 3 beta-methyl-androst-5-en-17-one, which is not estrogenic and cannot be metabolized to testosterone or estradiol, is as active as D in inhibiting the aggressive behavior of castrated mice.

Neurosteroids: regulatory mechanisms in male rat brain during heterosexual exposure

Pregnenolone (delta 5-P) and dehydroepiandrosterone (DHEA) were measured in the limbic system of young adult male rats (M) exposed for several days to the scent of cycling females but in absence of sexual contacts (M/F), and compared to levels obtained in males similarly exposed to other males (M/M). delta 5-P was highest in the olfactory bulbs of M/M, as compared to other regions of the limbic system. It decreased greater than 50% in M/F olfactory bulbs, but was identical in the olfactory tubercles, the amygdalas and the hypothalamus of M/M and M/F, as well as in the plasma, the adrenals and the spleen (taken as a representative non-endocrine organ). In comparison with M/M levels, DHEA selectively increased in the hypothalamus of M/F. These results demonstrate very different steroid concentrations in different regions of the brain, and they reveal their selective and eventually opposite changes upon heterosexual exposure. Therefore, they suggest regulatory mechanisms specific to various parts of the brain which are not directly related to the hormonal levels in the blood, and which could be part of the response to still undefined signals emitted by animals of the other sex.

Pregnenolone and its sulfate ester in the rat brain

Pregnenolone (P) and its sulfate ester (PS) have been characterized in the brain of adult male rats. The concentration of P (38.4 +/- 6.9 and 22.1 +/- 2.9 ng/g, mean +/- S.D., in anterior and posterior brain, respectively) exceeded that of PS in brain (15.8 +/- 3.0 and 5.7 +/- 2.1 ng/g in the same fractions) and largely those of P and PS in plasma (1.3 +/- 0.2 and 1.4 +/- 0.3 ng/g, respectively). The level of P in brain was much larger than that of dehydroepiandrosterone sulfate (DS), characterized and measured previously (Corpéchot et al.). Brain P and PS levels did not seem to depend on steroidogenic gland secretion: no meaningful difference occurred in brain 15 days after adrenalectomy plus orchiectomy, compared with sham-operated controls. It is proposed that, as that of DS (ref. 5) P and PS formation or accumulation (or both) in the rat brain depend on in situ mechanisms unrelated to the peripheral endocrine gland system.

Characterization and measurement of dehydroepiandrosterone sulfate in rat brain

Dehydroepiandrosterone (3 beta-hydroxy-5-androsten-17-one, I) sulfate (Ia) has been characterized in the anterior and the posterior parts of the brain of adult male rats. Its level (1.58 +/- 0.14 and 4.89 +/- 1.06 ng/g, mean +/- SD, in anterior and posterior brain, respectively) largely exceeded that of I in brain (0.42 +/- 0.10 and 0.12 +/- 0.03 ng/g in anterior and posterior brain, respectively) and of Ia in plasma (0.26 +/- 0.13 ng/ml). Brain Ia level did not seem to depend on adrenal secretion; it was unchanged after administration of corticotropin or dexamethasone for 3 days, and no meaningful change occurred in brain 15 days after adrenalectomy plus orchiectomy, compared with sham-operated controls. In contrast, stress conditions prevailing 2 days after adrenalectomy plus orchiectomy or after the corresponding sham operation resulted in a significantly increased concentration of Ia in the brain. Changes of Ia level in brain occurred irrespective of changes in corresponding plasma samples. It is proposed that Ia formation or accumulation (or both) in the rat brain depends on in situ mechanisms unrelated to the peripheral endocrine gland system.

[Free and sulfo-conjugated dehydroepiandrosterone in the brain of mice with myelin biosynthesis disorders]

Dehydroepiandrosterone, either unconjugated (D) or conjugated to sulfuric acid (DS), has been identified in the brain of male Mice; DS had been previously found in Rat brain. DS amounts in posterior brain, were 0.8-2.0 ng/g in controls, and very much lower in dysmyelinic jimpy and quaking Mice of the same age. Conversely, amounts of D were increased in affected Mice, suggesting an impaired sulfoconjugation. Results may be explained by accumulation of D and DS in brain, unrelated to the endocrine system.

Testosterone, dihydrotestosterone and androstanediols in plasma, testes and prostates of rats during development

Testosterone (T). 5α-dihydrotestosterone (DHT), 5α-androstane-3α, 17β-diol (3α-diol), and 5α-androstane-3β,17β-diol (3β-diol) have been measured in the plasma, ventral prostate, and testes of Sprague-Dawley rats with a specific radio-immunoassay, at birth, and then weekly until the 12th week.

In plasma, the T concentration is ∼ 0.3 ng/ml at birth and up to the 4th week; thereafter it increases steadily and reaches the adult level of ∼ 3 ng/ml by the 8th week. In male foetuses of 18 days gestation, the plasma concentration is 0.6 ng/ml. The 5α-metabolites taken together are at a higher concentration than that of T until the 7th week, and each one, after a broad maximum between 5–9 weeks, decreases promptly by the 10th week. The larger formation of 5α-metabolites from T in young rats has been confirmed by injection of the hormone to castrated males, which showed relatively more conversion at 5 than at 10 weeks.

In the ventral prostate, DHT is already high at 4 weeks (11 ng/g), and remain between 7 and 15 ng/g until the 12th week. T concentration is also larger than in plasma at 4th week (2 ng/g) and becomes approximately equal to the plasma value at puberty. A sharp peak of 3α-diol and 3β-diol is observed at the 8th week.

In the testes, T concentration is high at birth (183 ng/g), then declines rapidly, and increases again from the 5th week onward in parallel with plasma concentration. The concentrations of 5α-metabolites per testis vary in parallel to those in plasma, with the exception of sustained elevation of 3β-diol.

Simultaneous radioimmunoassay of tesosterone, dihydrotestosterone, 5 alpha-androstane-3alpha, 17beta-diol and 5alpha-androstane-3beta, 17beta-diol in the plasms of adult male rats

A single thin layer chromatography and three antibodies were used for the specific radioimmunoassay of four androgens in pooled rat plasma (Sprague-Dawley adult males). The following values were found (pg/ml +/- SD). Testosterone: 3, 138 +/-173; dihydrotestosterone: 374 +/-20; 5alpha-androstane-3alpha, 17beta-diol: 284+/-24; 5alpha-androstane-3beta, 17beta-diol: 223+/-11.