Perinatal neurosteroid levels influence GABAergic interneuron localization in adult rat prefrontal cortex

GABA system as the cause and effect in early development

GABA is the primary inhibitory neurotransmitter in the adult brain and through its actions on GABAARs, it protects against excitotoxicity and seizure activity, ensures temporal fidelity of neurotransmission, and regulates concerted rhythmic activity of neuronal populations. In the developing brain, the development of GABAergic neurons precedes that of glutamatergic neurons and the GABA system serves as a guide and framework for the development of other brain systems. Despite this early start, the maturation of the GABA system also continues well into the early postnatal period. In this review, we organize evidence around two scenarios based on the essential and protracted nature of GABA system development: 1) disruptions in the development of the GABA system can lead to large scale disruptions in other developmental processes (i.e., GABA as the cause), 2) protracted maturation of this system makes it vulnerable to the effects of developmental insults (i.e., GABA as the effect). While ample evidence supports the importance of GABA/GABAAR system in both scenarios, large gaps in existing knowledge prevent strong mechanistic conclusions.

Gender and Neurosteroids: Implications for Brain Function, Neuroplasticity and Rehabilitation

Neurosteroids are synthesized de novo in the nervous system; they mainly moderate neuronal excitability, and reach target cells via the extracellular pathway. The synthesis of neurosteroids occurs in peripheral tissues such as gonads tissues, liver, and skin; then, because of their high lipophilia, they cross the blood-brain barrier and are stored in the brain structure. Neurosteroidogenesis occurs in brain regions such as the cortex, hippocampus, and amygdala by enzymes necessary for the in situ synthesis of progesterone from cholesterol. Neurosteroids could be considered the main players in both sexual steroid-induced hippocampal synaptic plasticity and normal transmission in the hippocampus. Moreover, they show a double function of increasing spine density and enhancing long term potentiation, and have been related to the memory-enhancing effects of sexual steroids. Estrogen and progesterone affect neuronal plasticity differently in males and females, especially regarding changes in the structure and function of neurons in different regions of the brain. Estradiol administration in postmenopausal women allowed for improving cognitive performance, and the combination with aerobic motor exercise seems to enhance this effect. The paired association between rehabilitation and neurosteroids treatment could provide a boosting effect in order to promote neuroplasticity and therefore functional recovery in neurological patients. The aim of this review is to investigate the mechanisms of action of neurosteroids as well as their sex-dependent differences in brain function and their role in neuroplasticity and rehabilitation.

Neurodegeneration in Niemann-Pick Type C Disease: An Updated Review on Pharmacological and Non-Pharmacological Approaches to Counteract Brain and Cognitive Impairment

Niemann–Pick type C (NPC) disease is an autosomal recessive storage disorder, characterized by abnormal sequestration of unesterified cholesterol in the late endo-lysosomal system of cells. Progressive neurological deterioration and the onset of symptoms, such as ataxia, seizures, cognitive decline, and severe dementia, are pathognomonic features of the disease. In addition, different pathological similarities, including degeneration of hippocampal and cortical neurons, hyperphosphorylated tau, and neurofibrillary tangle formation, have been identified between NPC disease and other neurodegenerative pathologies. However, the underlying pathophysiological mechanisms are not yet well understood, and even a real cure to counteract neurodegeneration has not been identified. Therefore, the combination of current pharmacological therapies, represented by miglustat and cyclodextrin, and non-pharmacological approaches, such as physical exercise and appropriate diet, could represent a strategy to improve the quality of life of NPC patients. Based on this evidence, in our review we focused on the neurodegenerative aspects of NPC disease, summarizing the current knowledge on the molecular and biochemical mechanisms responsible for cognitive impairment, and suggesting physical exercise and nutritional treatments as additional non-pharmacologic approaches to reduce the progression and neurodegenerative course of NPC disease.

Early postnatal neuroactive steroid manipulation differentially affects recognition memory and passive avoidance performance in male rats

Early postnatal neuroactive steroids (NAS) play a significant role in the neurodevelopment. Their alteration can modify adult behavior, such as anxiety or learning. For this reason, we set out to observe if neonatal NAS levels alteration affects two types of learning implying low or high levels of emotional content, such as recognition memory and aversive learning respectively. Thus, we tested allopregnanolone or finasteride administered from postnatal days 5-9. In adulthood, recognition memory was assessed using the object recognition test, as well as aversive learning throughout the passive avoidance test (PA). Because of the important emotional component of PA, which can be influencing learning, we evaluated anxiety-like behavior by means of the open field test (OF). The results indicated that those animals administered with finasteride showed higher recognition levels of a familiar object. On the other hand, they showed an impairment in a stressful learning, such as PA. However, no effects of finasteride were observed on anxiety-like behavior in OF, despite it has been reported that neonatal finasteride treatment can promote an anxiety-like profile in the elevated plus-maze test in adulthood. Regarding neonatal allopregnanolone, animals showed higher levels in OF exploration only when they were already familiar with the apparatus. Furthermore, neonatal allopregnanolone did not affect recognition memory or aversive learning. In conclusion, the neonatal NAS manipulation by means of finasteride differently affected two types of learning implying distinct stress levels. Altogether, the results show the importance of the emotional content to explain the effects of neonatal NAS manipulation on learning.

Early postnatal allopregnanolone levels alteration and adult behavioral disruption in rats: Implication for drug abuse

Several studies have highlighted the role that early postnatal levels of allopregnanolone play in the development of the CNS and adult behavior. Changes in allopregnanolone levels related to stress have been observed during early postnatal periods, and perinatal stress has been linked to neuropsychiatric disorders. The alteration of early postnatal allopregnanolone levels in the first weeks of life has been proven to affect adult behaviors, such as anxiety-related behaviors and the processing of sensory inputs. This review focuses on the first studies about the possible relationship between the early postnatal allopregnanolone levels and the vulnerability to abuse of drugs such as alcohol in adulthood, given that (1) changes in neonatal allopregnanolone levels affect novelty exploration and novelty seeking has been linked to vulnerability to drug abuse; (2) early postnatal administration of progesterone, the main allopregnanolone precursor, affects the maturation of dopaminergic meso-striatal systems, which have been related to novelty seeking and drug abuse; and (3) alcohol consumption increases plasma and brain allopregnanolone levels in animals and humans. Manipulating neonatal allopregnanolone by administering finasteride, an inhibitor of the 5α-reductase enzyme that participates in allopregnanolone synthesis, increases alcohol consumption and decreases the locomotor stimulant effects of low alcohol doses. At a molecular level, finasteride decreases dopamine and serotonin in ventral striatum and dopamine release in nucleus accumbens. Preliminary results suggest that serotonin 5HT3 receptors could also be affected. Although an in-depth study is necessary, evidence suggests that there is a relation between early postnatal allopregnanolone and vulnerability to drug use/abuse.

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Early postnatal AlloP levels alteration affects brain maturation and adult behavior.

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Early stress interacts to AlloP influencing neuropsychiatric disorders vulnerability.

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Fluctuations in neonatal AlloP levels play a role in alcohol abuse vulnerability.

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Neonatal finasteride induces novelty-seeking profile and increases ethanol intake.

The Mitochondrion as Potential Interface in Early-Life Stress Brain Programming

Mitochondria play a central role in cellular energy-generating processes and are master regulators of cell life. They provide the energy necessary to reinstate and sustain homeostasis in response to stress, and to launch energy intensive adaptation programs to ensure an organism’s survival and future well-being. By this means, mitochondria are particularly apt to mediate brain programming by early-life stress (ELS) and to serve at the same time as subcellular substrate in the programming process. With a focus on mitochondria’s integrated role in metabolism, steroidogenesis and oxidative stress, we review current findings on altered mitochondrial function in the brain, the placenta and peripheral blood cells following ELS-dependent programming in rodents and recent insights from humans exposed to early life adversity (ELA). Concluding, we propose a role of the mitochondrion as subcellular intersection point connecting ELS, brain programming and mental well-being, and a role as a potential site for therapeutic interventions in individuals exposed to severe ELS.

Effects of progesterone on the neonatal brain following hypoxia-ischemia

Progesterone displays a strong potential for the treatment of neonatal hypoxic-ischemic encephalopathy since it has been shown to be beneficial in the treatment of the central nervous system injuries in adult animals. Here, we evaluated the effects of the administration of progesterone (10 mg/kg) in seven-days-old male Wistar rats submitted to neonatal hypoxia-ischemia (HI). Progesterone was administered immediately before ischemia and/or 6 and 24 h after the onset of hypoxia. The body weight of the animals, the volume of brain lesion and the expression of p-Akt and procaspase-3 in the hippocampus were evaluated. All animals submitted to HI showed a reduction in the body weight. However, this reduction was more remarkable in those animals which received progesterone before surgery. Administration of progesterone was unable to reduce the volume of brain damage caused by HI. Moreover, no significant differences were observed in the expression of p-Akt and procaspase-3 in animals submitted to HI and treated with either progesterone or vehicle. In summary, progesterone did not show a neuroprotective effect on the volume of brain lesion in neonatal rats submitted to hypoxia-ischemia. Furthermore, progesterone was unable to modulate p-Akt and procaspase-3 signaling pathways, which may explain the absence of neuroprotection. On the other hand, it seems that administration of progesterone before ischemia exerts some systemic effect, leading to a remarkable reduction in the body weight.

Endogenous neurosteroids influence synaptic GABAA receptors during postnatal development

GABA plays a key role in both embryonic and neonatal brain development. For example, during early neonatal nervous system maturation, synaptic transmission, mediated by GABA_A receptors (GABA_A Rs), undergoes a temporally specific form of synaptic plasticity to accommodate the changing requirements of maturing neural networks. Specifically, the duration of miniature inhibitory postsynaptic currents (mIPSCs), resulting from vesicular GABA activating synaptic GABA_A Rs, is reduced, permitting neurones to appropriately influence the window for postsynaptic excitation. Conventionally, programmed expression changes to the subtype of synaptic GABA_A R are primarily implicated in this plasticity. However, it is now evident that, in developing thalamic and cortical principal- and inter-neurones, an endogenous neurosteroid tone (eg, allopregnanolone) enhances synaptic GABA_A R function. Furthermore, a cessation of steroidogenesis, as a result of a lack of substrate, or a co-factor, appears to be primarily responsible for early neonatal changes to GABAergic synaptic transmission, followed by further refinement, which results from subsequent alterations of the GABA_A R subtype. The timing of this cessation of neurosteroid influence is neurone-specific, occurring by postnatal day (P)10 in the thalamus but approximately 1 week later in the cortex. Neurosteroid levels are not static and change dynamically in a variety of physiological and pathophysiological scenarios. Given that GABA plays an important role in brain development, abnormal perturbations of neonatal GABA_A R-active neurosteroids may have not only a considerable immediate, but also a longer-term impact upon neural network activity. Here, we review recent evidence indicating that changes in neurosteroidogenesis substantially influence neonatal GABAergic synaptic transmission. We discuss the physiological relevance of these findings and how the interference of neurosteroid-GABA_A R interaction early in life may contribute to psychiatric conditions later in life.

Effects of neonatal allopregnanolone manipulations and early maternal separation on adult alcohol intake and monoamine levels in ventral striatum of male rats

Changes in endogenous neonatal levels of the neurosteroid allopregnanolone (AlloP) as well as a single 24h period of early maternal separation (EMS) on postnatal day (PND) 9 affect the development of the central nervous system (CNS), causing adolescent/adult alterations including systems and behavioural traits that could be related to vulnerability to drug abuse. In rats, some behavioural alterations caused by EMS can be neutralised by previous administration of AlloP. Thus, the aim of the present work is to analyse if manipulations of neonatal AlloP could increase adult alcohol consumption, and if EMS could change these effects. We administered AlloP or finasteride, a 5α-reductase inhibitor, from PND5 to PND9, followed by 24h of EMS at PND9. At PND70 we measured alcohol consumption using a two-bottle free-choice model (ethanol 10% (v/v)+glucose 3% (w/v), and glucose 3% (w/v)) for 15days. Ventral striatum samples were obtained to determine monoamine levels. Results revealed that neonatal finasteride increased both ethanol and glucose consumption, and AlloP increased alcohol intake compared with neonatal vehicle-injected animals. The differences between neonatal groups in alcohol consumption were not found in EMS animals. In accordance, both finasteride and AlloP animals that did not suffer EMS showed lower levels of dopamine and serotonin in ventral striatum. Taken together, these results reveal that neonatal neurosteroids alterations affect alcohol intake; an effect which can be modified by subsequent EMS. Thus, these data corroborate the importance of the relationship between neonatal neurosteroids and neonatal stress for the correct CNS development.

Programming the brain and behaviour by early-life stress: a focus on neuroactive steroids

Animal studies have amply demonstrated that stress exposure during pregnancy or in early postnatal life can adversely influence brain development and have long-term 'programming' effects on future brain function and behaviour. Furthermore, a growing body of evidence from human studies supports the hypothesis that some psychiatric disorders may have developmental origins. Here, the focus is on three adverse consequences of early-life stress: dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis, heightened anxiety behaviour and cognitive impairments, with review of what is known about the underlying central mechanisms. Neuroactive steroids modulate neuronal activity and play a key role in neurodevelopment. Moreover they can negatively modulate activity of the HPA axis, exert anxiolytic actions and influence cognitive performance. Thus, neuroactive steroids may provide a link between early-life stress and the resultant adverse effects on the brain and behaviour. Here, a role for neuroactive steroids, in particular the 5α-reduced/3α-hydroxylated metabolites of progesterone, testosterone and deoxycorticosterone, is discussed in the context of early-life stress. Furthermore, the impact of early-life stress on the brain's capacity to generate neurosteroids is considered and the evidence for an ability of neuroactive steroids to over-write the negative effects of early-life stress on the brain and behaviour is examined. An enhanced understanding of the influence of early-life stress on brain neurosteroid systems could aid the identification of new targets for developing treatments for stress-related conditions in humans.

Sex-related differences in effects of progesterone following neonatal hypoxic brain injury

There is no satisfactory therapeutic intervention for neonatal hypoxic-ischemic (HI) encephalopathy. Progesterone is known to be effective in treating traumatic brain injury in adult animals but its effects in neonatal brains have not been reported. Brain injuries were induced by a unilateral common carotid artery ligation plus hypoxia exposure. Progesterone was administered immediately after hypoxia and daily for 5 days at 8 mg/kg, followed by a tapered dose for two days. At six weeks post-injury, lesion size and inflammatory factors were evaluated. Progesterone-treated, HI-injured male animals, but not females, showed significant long-term tissue protection compared to vehicle, suggesting an important sex difference in neuroprotection. Progesterone-treated, HI-injured male rats had fewer activated microglia in the cortex and hippocampus compared to controls. The rats were tested for neurological reflexes, motor asymmetry, and cognitive performance at multiple time points. The injured animals exhibited few detectable motor deficits, suggesting a high level of age- and injury-related neuroplasticity. There were substantial sex differences on several behavioral tests, indicating that immature males and females should be analyzed separately. Progesterone-treated animals showed modest beneficial effects in both sexes compared to vehicle-treated injured animals. Sham animals given progesterone did not behave differently from vehicle-treated sham animals on any measures.

GABAA receptor-acting neurosteroids: a role in the development and regulation of the stress response

Regulation of hypothalamic-pituitary-adrenocortical (HPA) axis activity by stress is a fundamental survival mechanism and HPA-dysfunction is implicated in psychiatric disorders. Adverse early life experiences, e.g. poor maternal care, negatively influence brain development and programs an abnormal stress response by encoding long-lasting molecular changes, which may extend to the next generation. How HPA-dysfunction leads to the development of affective disorders is complex, but may involve GABAA receptors (GABAARs), as they curtail stress-induced HPA axis activation. Of particular interest are endogenous neurosteroids that potently modulate the function of GABAARs and exhibit stress-protective properties. Importantly, neurosteroid levels rise rapidly during acute stress, are perturbed in chronic stress and are implicated in the behavioural changes associated with early-life adversity. We will appraise how GABAAR-active neurosteroids may impact on HPA axis development and the orchestration of the stress-evoked response. The significance of these actions will be discussed in the context of stress-associated mood disorders.

Neonatal exposure to estradiol decreases hypothalamic allopregnanolone concentrations and alters agonistic and sexual but not affective behavior in adult female rats

Exposure of developing female rats to estradiol during the perinatal period induced long-lasting dysregulation of gonadal axis and decreased cerebrocortical and plasma concentrations of allopregnanolone. We have now examined the effects of neonatal estradiol administration in female rats on hypothalamic allopregnanolone concentrations and on exploratory, affective, agonistic and sexual behaviors as well as social learning. A single administration of β-estradiol 3-benzoate (EB, 10μg) on the day of birth resulted in a delay of vaginal opening, acyclicity and ovarian failure. These alterations were associated with a significant decrease in the concentrations of allopregnanolone in the hypothalamus at 21 and 60days, but not at 7days, after birth. Neonatal administration of EB also increased agonistic behaviors in adult rats, such as dominant behaviors and following of an ovariectomized intruder, while living attacks unaffected. EB-treated rats showed also an increase in anogenital investigation, associated with a drastic reduction in spontaneous and induced female sexual behaviors (receptivity and proceptivity). In contrast, neonatal administration of EB did not affect locomotor activity, anxiety- and mood-related behaviors, the social transmission of flavor preferences, and seizures sensitivity. These effects of estradiol suggest that it plays a major role in regulation of both the abundance of allopregnanolone and the expression of agonistic and sexual behaviors, while failing to influence affective behaviors and social learning. Thus, the pronounced and persistent decrease in hypothalamic allopregnanolone concentration may be related to the manifestation of agonistic and sexual behaviors.

Neonatal finasteride administration alters hippocampal α4 and δ GABAAR subunits expression and behavioural responses to progesterone in adult rats

Allopregnanolone is a neurosteroid that has been reported to fluctuate during early developmental stages. Previous experiments reported the importance of neonatal endogenous allopregnanolone levels for the maturation of the central nervous system and particularly for the hippocampus. Changes in neonatal allopregnanolone levels have been related to altered adult behaviour and with psychopathological susceptibility, including anxiety disorders, schizophrenia and drug abuse. However, the mechanism underlying these changes remains to be elucidated. In the present study we assessed changes in hippocampal expression of α4 and δ GABAA receptor (GABAAR) subunits as a consequence of neonatal finasteride (a 5-α reductase inhibitor) administration during early development (PD6 to PD15) in male rats. We observed that the treatment altered the temporal window of the natural peak in the expression of these subunits during development. Additionally, the level of these subunits were higher than in non-handled and control animals in the adult hippocampus. We observed that in adulthood, neonatal finasteride-treated animals presented an anxiogenic-like profile in response to progesterone administration which was absent in the rest of the groups. In conclusion, these results corroborate the relevance of neonatal maintenance of neurosteroid levels for behavioural anxiety responses in the adult, and point to some of the mechanisms involved in this alterations.

Revisiting the roles of progesterone and allopregnanolone in the nervous system: resurgence of the progesterone receptors

Progesterone is commonly considered as a female reproductive hormone and is well-known for its role in pregnancy. It is less well appreciated that progesterone and its metabolite allopregnanolone are also male hormones, as they are produced in both sexes by the adrenal glands. In addition, they are synthesized within the nervous system. Progesterone and allopregnanolone are associated with adaptation to stress, and increased production of progesterone within the brain may be part of the response of neural cells to injury. Progesterone receptors (PR) are widely distributed throughout the brain, but their study has been mainly limited to the hypothalamus and reproductive functions, and the extra-hypothalamic receptors have been neglected. This lack of information about brain functions of PR is unexpected, as the protective and trophic effects of progesterone are much investigated, and as the therapeutic potential of progesterone as a neuroprotective and promyelinating agent is currently being assessed in clinical trials. The little attention devoted to the brain functions of PR may relate to the widely accepted assumption that non-reproductive actions of progesterone may be mainly mediated by allopregnanolone, which does not bind to PR, but acts as a potent positive modulator of γ-aminobutyric acid type A (GABA(A) receptors. The aim of this review is to critically discuss effects of progesterone on the nervous system via PR, and of allopregnanolone via its modulation of GABA(A) receptors, with main focus on the brain.

Time-dependent modulation of GABA(A)-ergic synaptic transmission by allopregnanolone in locus coeruleus neurons of Mecp2-null mice

Rett syndrome (RTT) is a neurodevelopmental disorder with symptoms starting 6-18 mo after birth, while what underlies the delayed onset is unclear. Allopregnanolone (Allop) is a metabolite of progesterone and a potent modulator of GABAA-ergic currents whose defects are seen in RTT. Allop changes its concentration during the perinatal period, which may affect central neurons via the GABAA-ergic synaptic transmission, contributing to the onset of the disease. To determine whether Mecp2 disruption affects Allop modulation, we performed studies in brain slices obtained from wild-type (WT) and Mecp2(-/Y) mice. Allop dose dependently suppressed locus coeruleus (LC) neuronal excitability in WT mice, while Mecp2-null neurons showed significant defects. Using optogenetic approaches, channelrhodopsin was specifically expressed in GABA-ergic neurons in which optical stimulation evoked action potentials. In LC neurons of WT mice, Allop exposure increased the amplitude of GABAA-ergic inhibitory postsynaptic currents (IPSCs) evoked by optical stimulation and prolonged the IPSC decay time. Consistently, Allop augmented both frequency and amplitude of GABAA-ergic spontaneous IPSCs (sIPSCs) and extended the decay time of sIPSCs. The Allop-induced potentiation of sIPSCs was deficient in Mecp2(-/Y) mice. Surprisingly, the impairment occurred at 3 wk postnatal age, while no significant difference in Allop modulation was observed in 1-2 wk between WT and Mecp2(-/Y) mice. These results indicate that the modulation of GABAA-ergic synaptic transmission by Allop is impaired in LC neurons of Mecp2-null mice at a time when RTT-like symptoms manifest, suggesting a potential mechanism for the delayed onset of the disease.

Neonatal allopregnanolone levels alteration: effects on behavior and role of the hippocampus

Several works have pointed out the importance of the neurosteroid allopregnanolone for the maturation of the central nervous system and for adult behavior. The alteration of neonatal allopregnanolone levels in the first weeks of life alters emotional adult behavior and sensory gating processes. Without ruling out brain structures, some of these behavioral alterations seem to be related to a different functioning of the hippocampus in adult age. We focus here on the different behavioral studies that have revealed the importance of neonatal allopregnanolone levels for the adult response to novel environmental stimuli, anxiety-related behaviors and processing of sensory inputs (prepulse inhibition). An increase in neonatal physiological allopregnanolone levels decreases anxiety and increases novelty responses in adult age, thus affecting the individual response to environmental cues. These effects are also accompanied by a decrease in prepulse inhibition, indicating alterations in sensory gating that have been related to that present in disorders, such as schizophrenia. Moreover, behavioral studies have shown that some of these effects are related to a different functioning of the dorsal hippocampus, as the behavioral effects (decrease in anxiety and locomotion or increase in prepulse inhibition) of intrahippocampal allopregnanolone infusions in adult age are not present in those subjects in whom neonatal allopregnanolone levels were altered. Recent data indicated that this hippocampal involvement may be related to alterations in the expression of gamma-aminobutyric-acid receptors containing α4 and δ subunits, molecular alterations that can persist into adult age and that can, in part, explain the reported behavioral disturbances.

Neonatal neurosteroid levels are determinant in shaping adult prepulse inhibition response to hippocampal allopregnanolone in rats

Diverse studies indicate that the alteration of the physiological levels of neurosteroids in early neonatal phases provokes alterations in the maturation of certain cerebral structures. Allopregnanolone (ALLO) has important modulatory effects in the hippocampus during the postnatal period where the adult pattern of inhibitory transmission is being established. In order to study whether endogenous neonatal ALLO levels would be a determinant parameter involved in mediating adult hippocampal GABAA system maturation, we investigated the effects of neonatal finasteride (50mg/kg, SC) treatment and ALLO (ALLO; 20mg/kg, SC) supplementation on an animal behavioural model with relevance to neurodevelopmental disorder, such as schizophrenia. Two sets of experiments were conducted. Neonatal treatment (from postnatal day (pnd) 5 to pnd9) was performed in 23 male Wistar rats and steroid quantification was performed in hippocampal homogenates at pnd9. A second group (n=127) underwent neonatal treatment (pnd5-pnd9) and were submitted to hippocampal surgery at 80d. The behavioural response to bilateral intrahippocampal neurosteroid administration (ALLO, 0.2μg/0.5μl per side or pregnenolone sulphate 5ng/0.5μl per side) on novelty-induced exploration activity and prepulse inhibition (PPI) was assessed at 95d. Results showed that neonatal ALLO and finasteride administration decreased novelty directed exploratory behaviour and impaired the prepulse inhibition of the acoustic startle response at 95 days of age. Moreover, intrahippocampal ALLO increased head-dipping behaviour independently of the neonatal treatment, while intrahippocampal ALLO decreased PPI only in finasteride and ALLO groups. The results obtained in the present study indicate the importance of neonatal neurosteroid levels in the development of hippocampal function and their relevance in a behavioural phenotype that some have likened to that present in schizophrenia.

Decreased alcohol consumption among former male users of finasteride with persistent sexual side effects: a preliminary report

BACKGROUND

There is a robust literature in rodents, but not in humans, on the interaction between finasteride and alcohol, particularly as it relates to neurosteroids. Finasteride has been shown to reduce alcohol intake and suppress alcohol preference in male mice. This study examines the role of finasteride in alcohol consumption in humans with male pattern hair loss.

METHODS

The subjects were 83 otherwise healthy men who developed persistent sexual side effects associated with finasteride, despite the cessation of this medication for at least 3 months. Information from standardized interviews was collected regarding medical histories, sexual function, and alcohol consumption before and after finasteride use.

RESULTS

Of the 63 men who consumed at least 1 alcoholic beverage/wk prior to starting finasteride, 41 (65%) noted a decrease in their alcohol consumption after stopping finasteride. This reduction typically began before discontinuing finasteride. Twenty men (32%) reported no change in their alcohol consumption, and 2 men (3%) reported an increase in their alcohol consumption. For the 63 consumers of alcohol, the mean number (± SE) of alcoholic beverages/wk declined from 5.2 ± 0.7 before finasteride to 2.0 ± 0.3 after finasteride (p < 0.0001). A major study limitation is the lack of a comparison group.

CONCLUSIONS

In former male users of finasteride who developed persistent sexual side effects, 65% noticed a decline in their alcohol consumption as compared to baseline. This finding is consistent with finasteride's ability to modulate alcohol intake in rodents. Further research is needed on the central nervous system effects of finasteride in humans.

Alteration of neonatal Allopregnanolone levels affects exploration, anxiety, aversive learning and adult behavioural response to intrahippocampal neurosteroids

Neurosteroids (NS) are well known to exert modulatory effects on ionotropic receptors. Recent findings indicate that NS could also act as important factors during development. In this sense, neonatal modifications of Allopregnanolone (Allop) levels during critical periods have been demonstrate to alter the morphology of the hippocampus but also other brain structures. The aim of the present work is to screen whether the alterations of Allop levels modify adult CA1 hippocampal response to NS administration. For this purpose, pups were injected with Allop (20 mg/kg s.c.), Finasteride (5α-reductase inhibitor that impedes Allop synthesis) (50 mg/kg s.c.) or Vehicle from postnatal day 5 (P5) to postnatal day 9 (P9). NS levels were tested at P5. To test the behavioural hippocampal response to NS in adulthood, animals were implanted with a bilateral cannula into the CA1 hippocampus at 80 days old and injected with Allop (0.2 μg/0.5 μl), Pregnenolone sulphate (5 ng/0.5 μl) or Vehicle in each hippocampus. After injections animals were tested in the Boisser test to assess exploratory behaviour, the elevated plus maze to assess anxiety and the passive avoidance to test aversive learning. Results indicate that alteration of neonatal Allop or pregnenolone levels (by Allop and Finasteride administration, respectively) suppressed intrahippocampal Allop anxiolytic effect in the EPM. Moreover our results also indicate that manipulation of neonatal Allop levels (Allop and Finast administration) alters exploratory and anxiety-like behaviour and impairs aversive learning in the adulthood. These data point out the role of Allop in the maturation of hippocampal function and behaviour.

Postnatal day 7 ethanol treatment causes persistent reductions in adult mouse brain volume and cortical neurons with sex specific effects on neurogenesis

Ethanol treatment on postnatal day seven (P7) causes robust brain cell death and is a model of late gestational alcohol exposure (Ikonomidou et al., 2000). To investigate the long-term effects of P7 ethanol treatment on adult brain, mice received either two doses of saline or ethanol on P7 (2.5 g/kg, s.c., 2 h apart) and were assessed as adults (P82) for brain volume (using postmortem MRI) and cellular architecture (using immunohistochemistry). Adult mice that received P7 ethanol had reduced MRI total brain volume (4%) with multiple brain regions being reduced in both males and females. Immunohistochemistry indicated reduced frontal cortical parvalbumin immunoreactive (PV + IR) interneurons (18-33%) and reduced Cux1+IR layer II pyramidal neurons (15%) in both sexes. Interestingly, markers of adult hippocampal neurogenesis differed between sexes, with only ethanol treated males showing increased doublecortin and Ki67 expression (52 and 57% respectively) in the dentate gyrus, consistent with increased neurogenesis compared to controls. These findings suggest that P7 ethanol treatment causes persistent reductions in adult brain volume and frontal cortical neurons in both males and females. Increased adult neurogenesis in males, but not females, is consistent with differential adaptive responses to P7 ethanol toxicity between the sexes. One day of ethanol exposure, e.g. P7, causes persistent adult brain dysmorphology.

Activation of thalamocortical networks by the N-methyl-D-aspartate receptor antagonist phencyclidine: reversal by clozapine

BACKGROUND

Noncompetitive N-methyl-D-aspartate receptor antagonists are widely used as pharmacological models of schizophrenia. Their neurobiological actions are still poorly understood, although the prefrontal cortex (PFC) appears as a key target area.

METHODS

We examined the effect of phencyclidine (PCP) on neuronal activity of the mediodorsal (MD) and centromedial (CM) thalamic nuclei, reciprocally connected with the PFC, using extracellular recordings (n = 50 neurons from 35 Wistar rats) and c-fos expression.

RESULTS

Phencyclidine (.25 mg/kg intravenous [IV]) markedly disorganized the activity of MD/CM neurons, increasing (424%) and decreasing (41%) the activity of 57% and 20% of the recorded neurons, respectively (23% remained unaffected). Phencyclidine reduced delta oscillations (.15-4 Hz) as assessed by recording local field potentials. The subsequent clozapine administration (1 mg/kg IV) reversed PCP effects on neuronal discharge and delta oscillations. Double in situ hybridization experiments revealed that PCP (10 mg/kg intraperitoneal [IP]) markedly increased c-fos expression in glutamatergic neurons of several cortical areas (prefrontal, somatosensory, retrosplenial, entorhinal) and in thalamic nuclei, including MD/CM. Phencyclidine also increased c-fos expression in the amygdala; yet, it had a small effect in the hippocampus. Phencyclidine did not increase c-fos expression in gamma-aminobutyric acidergic cells except in hippocampus, amygdala, somatosensory, and retrosplenial cortices. Clozapine (5 mg/kg IP) had no effect by itself but significantly prevented PCP-induced c-fos expression.

CONCLUSIONS

Phencyclidine likely exerts its psychotomimetic action by increasing excitatory neurotransmission in thalamo-cortico-thalamic networks involving, among others, PFC, retrosplenial, and somatosensory cortices. The antipsychotic action of clozapine includes, among other actions, an attenuation of the neuronal hyperactivity in thalamocortical networks.

Alterations in neonatal neurosteroids affect exploration during adolescence and prepulse inhibition in adulthood

Allopregnanolone (AlloP) is a neurosteroid that plays an important role during neural development. Alterations of endogenous neonatal allopregnanolone levels alter the localisation and function of GABA neurons in the adult brain and affect behaviour in adulthood. We have carried out research into the effects of an increase (AlloP administration) or a decrease (administration of finasteride, inhibitor of the AlloP synthesis) of neonatal AlloP levels during the fifth to ninth postnatal days in male Wistar rats on the novelty exploration (Boissier test) at adolescent ages (40 and 60 days old), and on the prepulse inhibition achievement in adulthood (85 days). We also investigated the role of a GABA(A) modulator (midazolam, 1, 1.75 or 2.5mg/kg body weight) in the long-lasting behavioural changes in adulthood (85 days). Results indicate that neonatal finasteride decreases both novelty-exploration (head-dipping and locomotion) and anxiety-relevant scores (the distance travelled in and the number of entries into the central zone) at adolescent age, along with a reduction in body weight and general locomotion. Also, neonatal AlloP administration decreases prepulse inhibition in adulthood. Prepulse inhibition disruption was only partially reproduced decreasing the neonatal AlloP levels by means of finasteride administration. Although there was no interaction between neonatal neurosteroid manipulation and adult benzodiazepine treatments, the effects of midazolam were dose-dependent: the lowest dose of midazolam increased whereas the highest disrupted the expected progressive reduction of the startle response (and the consequent improvement of the PPI percentage) after the gradual increase in prepulse intensity. Reduced prepulse inhibition of startle provides evidence of deficient sensorimotor gating in several disorders, including schizophrenia. Alterations of AlloP levels during maturation could partly explain the inter-individual differences shown by adult subjects in response to novelty (exploration) and in the sensorimotor gating and prepulse inhibition. Also, abrupt changes in neonatal levels of AlloP could be related to a susceptibility to neurodevelopmental disorders.

Neonatal exposure to estradiol in rats influences neuroactive steroid concentrations, GABAA receptor expression, and behavioral sensitivity to anxiolytic drugs

Gonadal steroids, in particular estradiol, exert important actions during pre- and perinatal periods in the regulation of sexual dimorphism and development of the nervous system. We have now examined the effects of neonatal estradiol administration in female rats on brain concentrations of the neuroactive steroids allopregnanolone and tetrahydrodeoxycorticosterone, expression of GABA(A) receptor subunits, and behavioral sensitivity to benzodiazepines and allopregnanolone. Administration of beta-estradiol 3-benzoate on the day of birth resulted in marked decreases in the concentrations of progesterone and allopregnanolone in the cerebral cortex at 21, 60, and 180 days after birth. The concentrations of tetrahydrodeoxycorticosterone, 17beta-estradiol, and dehydroepiandrosterone in the brain at 60 days were not affected by such treatment. Neonatal administration of beta-estradiol 3-benzoate also increased the cerebrocortical abundance of alpha(1), alpha(2), and gamma(2) subunits of the GABA(A) receptor without affecting that of alpha(3), alpha(4), alpha(5), or delta subunits. Diazepam induced a greater reduction in locomotor activity as well as a more pronounced anxiolytic-like effect in the elevated plus-maze test in rats subjected to neonatal treatment with beta-estradiol 3-benzoate than in vehicle-treated controls, while allopregnanolone induced a similar effect in both groups. These effects of estradiol suggest that it plays a major role in regulation both of GABAergic transmission and of the abundance of endogenous modulators of such transmission during development of the central nervous system.

Deficits in adult prefrontal cortex neurons and behavior following early post-natal NMDA antagonist treatment

The prefrontal cortex (PFC) is associated with higher cognitive functions including attention and working memory and has been implicated in the regulation of impulsivity as well as the pathology of complex mental illnesses. N-methyl D-aspartate (NMDA) antagonist treatment with dizocilpine induces cell death which is greatest in the frontal cortex on post-natal day seven (P7), however the long-term structural and behavioral effects of this treatment are unknown. This study investigates both the acute neurotoxicity of P7 dizocilpine and the persistent effects of this treatment on pyramidal cells and parvalbumin interneurons in the adult PFC, a brain region involved in the regulation of impulsivity. Dizocilpine treatment on P7 increased cleaved caspase-3 immunoreactivity (IR) in the PFC on P8. In adult mice (P82), P7 dizocilpine treatment resulted in 50% fewer parvalbumin-positive interneurons (p<0.01) and 42% fewer layer V pyramidal neurons (p<0.01) in the PFC. Double immunohistochemistry revealed cleaved caspase-3 IR in both GAD67 IR interneurons and GAD67 (-) neurons. Following dizocilpine treatment at P7, adults showed reduced time in the center of the open field suggesting increased anxiety-like behavior. These findings indicate that early brain insults affecting glutamatergic neurotransmission lead to persistent brain pathology that could contribute to impulsivity and cognitive dysfunction.

KCC2 expression promotes the termination of cortical interneuron migration in a voltage-sensitive calcium-dependent manner

The molecular mechanisms controlling the termination of cortical interneuron migration are unknown. Here, we demonstrate that, prior to synaptogenesis, migrating interneurons change their responsiveness to ambient GABA from a motogenic to a stop signal. We found that, during migration into the cortex, ambient GABA and glutamate initially stimulate the motility of interneurons through both GABA(A) and AMPA/NMDA receptor activation. Once in the cortex, upregulation of the potassium-chloride cotransporter KCC2 is both necessary and sufficient to reduce interneuron motility through its ability to reduce membrane potential upon GABA(A) receptor activation, which decreases the frequency of spontaneous intracellular calcium transients initiated by L-type voltage-sensitive calcium channel (VSCC) activation. Our results suggest a mechanism whereby migrating interneurons determine the relative density of surrounding interneurons and principal cells through their ability to sense the combined extracellular levels of ambient glutamate and GABA once GABA(A) receptor activation becomes hyperpolarizing.

Neonatal finasteride induces anxiogenic-like profile and deteriorates passive avoidance in adulthood after intrahippocampal neurosteroid administration

Recent findings indicate that neurosteroids could act as important keys during the brain development. Fluctuations in neonatal allopregnanolone (AlloP) could result in altered pharmacological properties of the GABA(A) receptor system in adulthood. Recent studies demonstrated that neurosteroids play a critical role in regulating normal neurodevelopment in the hippocampus. The aim of the present work is to screen whether developmentally altered neurosteroid levels influence the behavioral response to adult intrahippocampal administration of AlloP, a GABA(A) positive modulating neurosteroid, and pregnenolone sulfate (PregS), a GABA(A) negative modulator in rats. For this purpose, pups received AlloP (10 mg/kg, s.c.), a 5alpha-reductase inhibitor (finasteride, 50 mg/kg, s.c.) or vehicle from the fifth to the ninth postnatal day. At maturity (i.e. 90 days old) a bilateral cannula was implanted into the hippocampus. After recovery from surgery, animals received an administration of AlloP (0.2 microg/0.5 microl), PregS (5 ng/0.5 microl) or vehicle in each hippocampus 5 min before they were tested in the elevated plus maze (EPM) and immediately after the passive avoidance training session, and retention was tested 24 h later. Results indicated that neonatal finasteride treatment deteriorated passive avoidance retention and elicited an anxiogenic-like effect in the EPM test in adulthood, as seen by the reduction of open arm entries and in the time spent in the open arms. Intrahippocampal PregS administration also disrupted passive avoidance, possibly related to its anxiogenic profile. Fluctuations in neonatal AlloP affect the aversive learning and the anxiety-related behavior in adulthood, and this effect could be in part mediated by alterations of the mature functions of the hippocampus, possibly via the GABA(A) receptor. These data point to the role of GABAergic neurosteroids in critical periods of vulnerability that influence normal development of GABAergic pathways in the CNS.

Neurosteroid regulation of central nervous system development

Neurosteroids are a relatively new class of neuroactive compounds brought to prominence in the past 2 decades. Despite knowing of their presence in the nervous system of various species for over 20 years and knowing of their functions as GABA(A) and N-methyl-d-aspartate (NMDA) ligands, new and unexpected functions of these compounds are continuously being identified. Absence or reduced concentrations of neurosteroids during development and in adults may be associated with neurodevelopmental, psychiatric, or behavioral disorders. Treatment with physiologic or pharmacologic concentrations of these compounds may also promote neurogenesis, neuronal survival, myelination, increased memory, and reduced neurotoxicity. This review highlights what is currently known about the neurodevelopmental functions and mechanisms of action of 4 distinct neurosteroids: pregnenolone, progesterone, allopregnanolone, and dehydroepiandrosterone (DHEA).

Antipsychotic drugs reverse the disruption in prefrontal cortex function produced by NMDA receptor blockade with phencyclidine

NMDA receptor (NMDA-R) antagonists are extensively used as schizophrenia models because of their ability to evoke positive and negative symptoms as well as cognitive deficits similar to those of the illness. Cognitive deficits in schizophrenia are associated with prefrontal cortex (PFC) abnormalities. These deficits are of particular interest because an early improvement in cognitive performance predicts a better long-term clinical outcome. Here, we examined the effect of the noncompetitive NMDA-R antagonist phencyclidine (PCP) on PFC function to understand the cellular and network elements involved in its schizomimetic actions. PCP induces a marked disruption of the activity of the PFC in the rat, increasing and decreasing the activity of 45% and 33% of the pyramidal neurons recorded, respectively (22% of the neurons were unaffected). Concurrently, PCP markedly reduced cortical synchrony in the delta frequency range (0.3-4 Hz) as assessed by recording local field potentials. The subsequent administration of the antipsychotic drugs haloperidol and clozapine reversed PCP effects on pyramidal cell firing and cortical synchronization. PCP increased c-fos expression in PFC pyramidal neurons, an effect prevented by the administration of clozapine. PCP also enhanced c-fos expression in the centromedial and mediodorsal (but not reticular) nuclei of the thalamus, suggesting the participation of enhanced thalamocortical excitatory inputs. These results shed light on the involvement of PFC in the schizomimetic action of NMDA-R antagonists and show that antipsychotic drugs may partly exert their therapeutic effect by normalizing a disrupted PFC activity, an effect that may add to subcortical dopamine receptor blockade.

Acute effects of neurosteroids in a rodent model of primary paroxysmal dystonia

The pathophysiology of various types of dyskinesias, including dystonias, is poorly understood. Clinical and epidemiological studies in humans revealed that the severity of dyskinesias and the frequency of paroxysmal forms of the disease are altered by factors such as the onset of puberty, pregnancy, cyclical changes and stress, indicating an underlying hormonal component. The dystonic phenotype in the dt(sz) hamster, a genetic animal model of paroxysmal dystonia, has been suggested to be based on a deficit of striatal gamma-aminobutyric acid (GABA)ergic interneurons and changes in the GABA(A) receptor complex. In this animal model, hormonal influences seem to be also involved in the pathophysiology, but an influence of peripheral sex hormones has already been excluded. Possibly, neurosteroids as endogenous regulators of the GABA(A) receptor may be critically involved in the pathophysiology of dystonia in this animal model. Therefore, in the present study, the effects of the neurosteroids allopregnanolone acetate and allotetrahydrodeoxycorticosterone (THDOC), representing positive modulators of the GABA(A) receptor, as well as of the negative GABA(A) receptor modulators pregnenolone sulfate and dehydroepiandrosterone (DHEA), on severity of dystonia were examined in dt(sz) hamsters after acute intraperitoneal injections. Allopregnanolone acetate and THDOC exerted a moderate reduction of dystonia, whereas pregnenolone sulfate and DHEA had no significant effects. Although the effects of allopregnanolone acetate and THDOC were moderate and short-lasting, the present results suggest that changes in neurosteroid levels might be involved in the initiation of dystonic episodes. Future studies have to include measurements of brain neurosteroid levels as well as of chronic neurosteroid administrations to clarify the pathophysiological role and therapeutic potential of neurosteroids in dystonia.

Age-related changes in parvalbumin-positive interneurons in the striatum, but not in the sensorimotor cortex in dystonic brains of the dt mutant hamster

In the dt(sz) hamster, a model of paroxysmal dystonia, an age-dependent increase in the activity of striatal projection neurons has been hypothesized to be based on a deficit of striatal parvalbumin-immunoreactive (PV(+)) interneurons at an age of most marked expression of dystonia (30-40 days of life). In the present study, the spontaneous age-dependent remission of paroxysmal dystonia in older dt(sz) hamsters (age>90 days) was found to coincide with a normalization of the density of striatal PV(+) interneurons. Furthermore, the arborization of these interneurons was lower in 31 day old dt(sz) hamsters, but was even higher in dt(sz) mutant at an age of >90 days than in control animals. Double-labeling with bromodeoxyuridine failed to show a retarded proliferation, while the number of interneurons with strong expression of PV mRNA was lower in young mutant hamsters. As shown by unaltered density of PV(+) interneurons in sensorimotor cortex of 31 day old dt(sz) hamsters, PV containing interneurons are not reduced throughout the whole brain at the sensitive age. The present data suggest that a retarded postnatal maturation of striatal PV(+) interneurons plays a critical role in paroxysmal dystonia.

Neonatal neurosteroid administration results in development-specific alterations in prepulse inhibition and locomotor activity: neurosteroids alter prepulse inhibition and locomotor activity

RATIONALE

Early life exposure to stress and to GABAA receptor modulators have well-defined and persistent behavioral effects. A single neonatal injection of the GABAergic neurosteroid allopregnanolone (3alpha-hydroxy,5alpha-pregnane-20-one, 10 mg/kg, i.p.) alters the localization of prefrontal cortex (PFC) interneurons in adulthood. Such displacement could result in disinhibited behavior associated with impaired development of the mesocortical dopamine system.

OBJECTIVES

To determine if there is a critical window in which allopregnanolone levels may impact the development and mature function of the mesocorticolimbic circuitry.

METHODS

Behavioral measures, including prepulse inhibition (PPI) and total locomotor activity, after amphetamine exposure were assessed at postnatal day 20 (P20) (prepuberty), P40 (puberty), P60 (postpuberty), and P80 (adulthood) in animals previously exposed to allopregnanolone (10 mg/kg) on P2 and P5. PFC tyrosine hydroxylase immunoreactivity was stereologically measured.

RESULTS

P2 administration of allopregnanolone resulted in an increased locomotor response to amphetamine (14, 28% on P20 and P80, respectively) and reduced PPI (28, 22% on P20 and P80, respectively) at P20 and P80, whereas allopregnanolone administration on P5 increased locomotor response to amphetamine (20%) and reduced PPI (37%) at P80. Clozapine (7.5 mg/kg) pretreatment reversed the PPI deficit in P2-exposed animals. The total length of tyrosine hydroxylase immunopositive fibers in PFC was not altered by neonatal neurosteroid exposure, but more fibers were located in layers V/VI vs I-III.

CONCLUSIONS

Altering neonatal allopregnanolone levels disrupts PFC-dependent behavior, indicating that allopregnanolone might be important for normal PFC circuitry development. The temporal exposure differences (P2 vs P5) and ontological-dependent effects (P20 and P80, but not P40 or P60) suggest critical windows of vulnerability to neurosteroid insult across development.

Neurosteroids, GABAA receptors, and ethanol dependence

RATIONALE

Changes in the expression of type A receptors for gamma-aminobutyric acid (GABA) represent one of the mechanisms implicated in the development of tolerance to and dependence on ethanol. The impact of such changes on the function and pharmacological sensitivity of GABAA receptors (GABAARs) has remained unclear, however. Certain behavioral and electrophysiological actions of ethanol are mediated by an increase in the concentration of neuroactive steroids in the brain that results from stimulation of the hypothalamic-pituitary-adrenal (HPA) axis. Such steroids include potent modulators of GABAAR function.

OBJECTIVES

We have investigated the effect of ethanol exposure and withdrawal on subunit expression and receptor function evaluated by subunit selective compounds, as well as the effects of short-term exposure to ethanol on both neurosteroid synthesis and GABAAR function, in isolated neurons and brain tissue.

RESULTS

Chronic treatment with and subsequent withdrawal from ethanol alter the expression of genes for specific GABAAR subunits in cultured rat neurons, and these changes are associated with alterations in receptor function and pharmacological sensitivity to neurosteroids, zaleplon, and flumazenil. Acute ethanol exposure increases the amount of 3alpha-hydroxy-5alpha-pregnan-20-one (allopregnanolone) in hippocampal slices by a local action independent of the activity of the HPA axis. This effect of ethanol was associated with an increased amplitude of GABAAR-mediated miniature inhibitory postsynaptic currents recorded from CA1 pyramidal neurons in such slices.

CONCLUSIONS

Chronic ethanol exposure elicits changes in the subunit composition of GABAARs, which, in turn, likely contribute to changes in receptor function associated with the altered pharmacological and behavioral sensitivity characteristic of ethanol tolerance and dependence. Ethanol may also modulate GABAAR function by increasing the de novo synthesis of neurosteroids in the brain in a manner independent of the HPA axis. This latter mechanism may play an important role in the central effects of ethanol.

Perinatal allopregnanolone influences prefrontal cortex structure, connectivity and behavior in adult rats

Cortical neurosteroid levels vary dramatically across development; during the second week of life elevated levels of allopregnanolone are associated with decreased GABA(A) receptor function. Since GABA(A) receptor modulation plays a role in proliferative regulation in developing neocortex, it is possible that endogenous neurosteroids such as allopregnanolone, acting through GABA(A) receptors, modulate cortical development. We augmented normally low levels with exogenous administration of allopregnanolone (10 mg/kg) during the first week of rodent life. The localization of parvalbumin-labeled cells was markedly altered; the ratio of cell number in the deep (layers V-VI) vs. superficial (layers I-III) layers of adult prefrontal cortex increased two-fold in rats administered allopregnanolone on postnatal day 1 or 5. The mechanism underlying these anatomical changes likely involves GABA(A) receptors because similar changes in interneuron placement were observed after neonatal benzodiazepine administration. Measures of mature cortical function were also altered after neonatal neurosteroid administration, including [(3)H]MK-801 binding, prepulse inhibition and amphetamine-induced locomotor activity. Moreover, neonatal allopregnanolone administration increases the number of parvalbumin-expressing neurons in medial dorsal nucleus of the thalamus while the total neuron number is decreased. These findings suggest that connectivity between the medial dorsal nucleus of the thalamus and prefrontal cortex is likely altered by neonatal neurosteroid administration and may result in a disinhibited frontal cortex. Disinhibition in the prefrontal cortex is associated with behavioral changes relevant to human psychosis and developmental disorders. If neurosteroids play a role in normal development of prefrontal/medial dorsal patency as suggested by these studies, then alterations in neurosteroid levels may contribute to abnormal neurodevelopment.

Executive functions in the heterozygous reeler mouse model of schizophrenia

Deficits in working memory and executive functions are now considered among the most reliable endophenotypes for schizophrenia. To determine whether cognitive deficits exist in mouse models of the disease, the authors trained heterozygous reeler (+/rl) mice on a series of visual discriminations similar to those used to test executive abilities in primates. These mice resemble schizophrenia patients in that both have reduced levels of reelin protein and altered gamma aminobutyric acid neurotransmission in the prefrontal cortex. The +/rl mice showed a selective deficit in reversal learning, with a pattern of errors that suggested impaired visual attention rather than a deficiency in perseveration and inhibitory control. These results show that cognitive dysfunction may serve as a useful biomarker in mouse models of neuropsychiatric disease.

Region-, age-, and sex-specific effects of fetal diazepam exposure on the postnatal development of neurosteroids

Fetal exposure to diazepam (DZ), a positive modulator of GABA(A) receptors and an agonist at mitochondrial benzodiazine receptors, induces long-term neural and behavioral effects. This study evaluated whether the early manipulation influenced the normal development of brain levels of neurosteroids or altered steroid action at GABA(A) receptors. Pregnant dams were injected over gestation days 14 through 20 with DZ (2.5 mg/kg) or the vehicle. Male and female offspring were analyzed at five postnatal ages. The levels of progesterone (P), dihydroprogesterone (DHP), 3alpha-hydroxy-5alpha-pregnan-20-one (3alpha,5alpha-THP), testosterone (T), dihydrotestosterone, and 5alpha-androstan-3alpha,17beta diol were measured in the cerebral cortex and diencephalon. The results indicated that development of brain steroid levels and the impact of fetal DZ exposure were region- and sex-specific. Age-related changes in brain steroids did not mirror associated changes in circulating P and T. Age regulated the levels of all 3 progestins in the cerebral cortex, and fetal DZ exposure interacted with the development of P and DHP. The development of 3alpha,5alpha-THP in the cortex was markedly influenced by sex, with levels in males decreasing over postnatal development whereas they increased over postpubertal development in females. An adolescent surge in T levels was observed in male cortex and fetal DZ exposure prevented that surge. Steroid levels in the diencephalon were altered by age mainly in females, and DZ exposure had little effect in this region. The data support region-specific regulation of brain steroid synthesis. Only in the cerebral cortex are relevant mechanisms readily modifiable by fetal DZ exposure. However, neither sex nor fetal DZ exposure altered the response of GABA(A) receptors in adult cortex to neurosteroid.

Allopregnanolone treatment, both as a single injection or repetitively, delays demyelination and enhances survival of Niemann-Pick C mice

Niemann-Pick C disease (NPC) is an irreversible neurodegenerative disorder without current treatment. It is thought to result from deficient intracellular cholesterol and/or ganglioside trafficking. We have investigated the effects of allopregnanolone treatments on survival, weight loss, motor function, magnetic resonance imaging (MRI), and neuropathology in the mouse model of NPC (Npc1(-/-) mice). We confirmed previous results showing that a single injection of 250 microg of allopregnanolone on postnatal day 7 significantly extended the life span of Npc1(-/-) mice. This caused a marked difference in the weight curves of the treated mice but no statistical difference in the Rota-Rod performance. T2-weighted MRI and diffusion tensor imaging (DTI) of treated mice showed values of signal intensity and fractional anisotropy closer to those of wild-type mice than those of untreated Npc1(-/-) mice. Neuropathology showed that day-7 treatment markedly suppressed astrocyte reaction and significantly reduced microglial activation. Furthermore, the steroid treatment also increased myelination in brains of Npc1(-/-) mice. Similar effects of allopregnanolone treatment were observed in Npc1(-/-), mdr1a(-/-) double-mutant mice, which have a deficient blood-brain barrier, resulting in increased steroid uptake. The effects on survival and weight loss of a single injection on day 7 followed by injections every 2 weeks were also evaluated in Npc1(-/-) mice, and the beneficial effects were found to be greater than with the single injection at day 7. We conclude that allopregnanolone treatment significantly ameliorates several symptoms of NPC in Npc1(-/-) mice, presumably by effects on myelination or neuronal connectivity.

Neuroactive steroids and inhibitory neurotransmission: mechanisms of action and physiological relevance

Dysfunction of GABA(A) receptor-mediated inhibition is implicated in a number of neurological and psychiatric conditions including epilepsy and affective disorders. Some of these conditions have been associated with abnormal levels of certain endogenously occurring neurosteroids, which potently and selectively enhance the function of the brain's major inhibitory receptor, the GABA(A) receptor. Consistent with their ability to enhance neuronal inhibition, such steroids exhibit in animals and humans anxiolytic, anticonvulsant and anesthetic actions. Neurosteroids, exemplified by the potent progesterone metabolite, 5alpha-pregnan-3alpha-ol-20-one can be synthesized de novo in the CNS both in neurones and glia in levels sufficient to modulate GABA(A) receptor function. Neurosteroid levels are not static, but are subject to dynamic fluctuations, for example during stress, or the later stages of pregnancy. These observations suggest that these endogenous modulators may refine the function of the brain's major inhibitory receptor and thus, play an important physiological and pathophysiological role. However, given the ubiquitous expression of GABA(A) receptors throughout the mammalian CNS, changes in neurosteroid levels should be widely experienced, causing a generalized enhancement of neuronal inhibition. Such a non-specific action would seem incompatible with a physiological role. However, neurosteroid action is both brain region and neurone selective. This specificity results from a variety of molecular mechanisms including receptor subunit composition, local steroid metabolism and phosphorylation. This paper will evaluate the relative contribution these mechanisms play in defining the interaction of neurosteroids with synaptic and extra-synaptic GABA(A) receptors.

Effects of Prenatal Stress on the Activity of an Enzyme Involved in Neurosteroid Synthesis During the “Critical Period” of Sexual Differentiation of the Brain in Male Rats

The effects of daily immobilization stress applied to female rats on days 15 to 18 of pregnancy on the activity of the enzyme 5 alpha-reductase (isoform I), involved in the synthesis of brain neurosteroids were studied in male offspring. The results demonstrated a decrease in enzyme activity in the cerebral cortex and hypothalamus of male fetuses one day after the last session of stress, while enzyme activity was elevated in the cortex of neonates. Increases in 5 alpha-reductase activity in the cortex, hippocampus, and hypothalamus were also seen in prenatally stressed males on day 5 of life. There were reductions in plasma testosterone and progesterone levels in experimental animals on day 19 of embryonic life and in neonatal rats, the blood progesterone level in prenatally stressed rats remaining decreased at age five days. The possible involvement of neurosteroids in the actions of prenatal stress on sexual differentiation of the brain is discussed.

Age-Dependent Alterations of Striatal Calretinin Interneuron Density in a Genetic Animal Model of Primary Paroxysmal Dystonia

Various types of hereditary dystonia are regarded as a basal ganglia disorder, but the underlying mechanisms are still unknown. In the dt hamster, a genetic animal model of age-dependent paroxysmal dystonia, recent studies demonstrated a reduced density of striatal parvalbumin-immunoreactive (PV) GABAergic interneurons at an age of maximum severity of dystonia in comparison with age-matched nondystonic controls. So far, alterations of other types of striatal interneurons in dt hamsters cannot be excluded. Therefore, we determined the density of calretinin-immunoreactive (CR) interneurons in the dt mutant at an age of maximum severity and after spontaneous remission of dystonia in comparison with age-matched nondystonic controls using an image analysis system and a stereologic counting method in a blinded fashion. At an age of maximum severity of dystonia, CR interneuron density was significantly lower in dt hamsters in comparison with controls (-20%), whereas no significant differences between the animal groups could be detected after spontaneous remission of dystonia. The comparison of CR interneuron density between young hamsters with those at an age of > 90 days revealed a significant ontogenetic decrease of CR interneurons in both animal groups (dt hamsters: -38%, controls: -54%). These results demonstrate that alterations of striatal interneuron density in dt mutants are not restricted to PV ones. A deficit of CR interneurons that coexpress GABA may contribute to previous findings of disinhibition of striatal projection neurons in the dt mutant at an age of maximum expression of dystonia.

Post-ictal circulating levels of allopregnanolone in children with partial or generalized seizures

INTRODUCTION

Allopregnanolone (3alpha-hydroxy-5alpha-pregnan-20-one) is a neurosteroid with a potent modulating activity on the gamma-aminobutyric acid (GABA)(a) receptor complex. It plays a key role in the epileptogenesis of partial seizures. Serum allopregnanolone concentrations significantly increase in the postcritical phase. In the present study we investigated the post-ictal serum allopregnanolone levels in children with partial seizures and generalized seizures, respectively.

PATIENTS AND METHODS

Three groups of subjects were included in the study. Group 1 consisted of 18 children affected by complex partial seizures. Group 2 consisted of 11 children presenting with generalized epilepsy. Group 3 consisted of 20 healthy age-matched subjects. Serum allopregnanolone levels were assayed in the inter-ictal phase and within 30 min after an epileptic event.

RESULTS

The data we obtained suggest that circulating allopregnanolone level significantly increases in the post-ictal phase. However, we found no significant differences in the post-ictal serum allopregnanolone concentrations between patients with partial seizures and those with generalized seizures.

CONCLUSIONS

Further studies are needed to establish if allopregnanolone is a reliable circulating marker of epileptic seizures. However, our observations seem to indicate that post-ictal circulating allopregnanolone level is not useful in differentiating focal and generalized epilepsy events.

Neurosteroids: endogenous regulators of the GABAA receptor

GABA(A) (gamma-aminobutyric acid type A) receptors mediate most of the 'fast' synaptic inhibition in the mammalian brain and are targeted by many clinically important drugs. Certain naturally occurring pregnane steroids can potently and specifically enhance GABA(A) receptor function in a nongenomic (direct) manner, and consequently have anxiolytic, analgesic, anticonvulsant, sedative, hypnotic and anaesthetic properties. These steroids not only act as remote endocrine messengers, but also can be synthesized in the brain, where they modify neuronal activity locally by modulating GABA(A) receptor function. Such 'neurosteroids' can influence mood and behaviour in various physiological and pathophysiological situations, and might contribute to the behavioural effects of psychoactive drugs.

3alpha,5alpha-Tetrahydroprogesterone (allopregnanolone) and gamma-aminobutyric acid: autocrine/paracrine interactions in the control of neonatal PSA-NCAM+ progenitor proliferation

The earliest identified neonatal neural progenitors are cells that express the polysialylated form of the neural cell adhesion molecule (PSA-NCAM). One of these progenitors is the early PSA-NCAM+ progenitor (ePSA-NCAM+ progenitor; Gago et al. [2003] Mol Cell Neurosci 22:162-178), which corresponds to a multipotential cell with a default differentiation through glial lineages. The ePSA-NCAM+ progenitor can synthesize the neurosteroid progesterone (PROG) and its reduced metabolite 3alpha,5alpha-tetrahydroprogesterone (3alpha,5alpha-THP, or allopregnanolone; Gago et al. [ 2001] Glia 36:295-308). The latter is a potent positive allosteric modulator of gamma-aminobutyric acid type A (GABAA) receptors. In the present work, we demonstrate that PROG and 3alpha,5alpha-THP both stimulate ePSA-NCAM+ progenitor proliferation. PROG exerted its mitogenic effect indirectly, through its conversion to 3alpha,5alpha-THP, since it could be abolished by an inhibitor of the 5alpha-reductase (L685-273) and mimicked by 3alpha,5alpha-THP. A dose-response curve revealed a bell-shaped effect of 3alpha,5alpha-THP on ePSA-NCAM+ progenitor proliferation, with greatest stimulation at nanomolar concentrations. The mitogenic effect of 3 alpha,5 alpha-THP was mediated by GABAA receptors, insofar as it could be blocked by the selective antagonist bicuculline. ePSA-NCAM+ progenitors indeed expressed mRNAs for GABAA receptor subunits, and GABA enhanced cell proliferation, an effect that was also bicuculline sensitive. Moreover, these cells synthesized GABA, which was involved in a tonic stimulation of their proliferation. These results reveal complex autocrine/paracrine loops in the control of ePSA-NCAM+ progenitor proliferation, involving both neurosteroid and GABA signaling, and suggest a novel key role for 3alpha,5alpha-THP in the development of the nervous system.