K252a Prevents Microglial Activation Induced by Anoxic Stimulation of Carotid Bodies in Rats

Inducing carotid body anoxia through the administration of cyanide can result in oxygen deprivation. The lack of oxygen activates cellular responses in specific regions of the central nervous system, including the Nucleus Tractus Solitarius, hypothalamus, hippocampus, and amygdala, which are regulated by afferent pathways from chemosensitive receptors. These receptors are modulated by the brain-derived neurotrophic factor receptor TrkB. Oxygen deprivation can cause neuroinflammation in the brain regions that are activated by the afferent pathways from the chemosensitive carotid body. To investigate how microglia, a type of immune cell in the brain, respond to an anoxic environment resulting from the administration of NaCN, we studied the effects of blocking the TrkB receptor on this cell-type response. Male Wistar rats were anesthetized, and a dose of NaCN was injected into their carotid sinus to induce anoxia. Prior to the anoxic stimulus, the rats were given an intracerebroventricular (icv) infusion of either K252a, a TrkB receptor inhibitor, BDNF, or an artificial cerebrospinal fluid (aCSF). After the anoxic stimulus, the rats were perfused with paraformaldehyde, and their brains were processed for microglia immunohistochemistry. The results indicated that the anoxic stimulation caused an increase in the number of reactive microglial cells in the hypothalamic arcuate, basolateral amygdala, and dentate gyrus of the hippocampus. However, the infusion of the K252a TrkB receptor inhibitor prevented microglial activation in these regions.

Vitamin D Receptor (VDR) Genetic Variants: Relationship of FokI Genotypes with VDR Expression and Clinical Disease Activity in Systemic Lupus Erythematosus Patients

Vitamin D (VD) deficiency is more frequent in systemic lupus erythematosus (SLE) patients than in control subjects (CS); genetic variants in the VD receptor (VDR) could contribute to the clinical disease activity. This study was aimed to determine the association of the VDR variants FokI (rs2228570), BsmI (rs1544410), ApaI (rs7975232), and TaqI (rs731236) with susceptibility to the disease, VD status, VDR mRNA expression, and clinical disease activity in SLE patients. A cross-sectional study was conducted in 194 SLE and 196 CS Mexican women. Immunoassays quantified serum calcidiol and calcitriol. Genotyping was performed by allelic discrimination assays and mRNA VDR expression by qPCR. The FokI variant was not in linkage disequilibrium with BsmI, ApaI, and TaqI VDR variants. SLE patient carriers of the TT FokI genotype showed higher clinical disease activity scores. Notably, the mRNA VDR expression was higher in SLE patients vs. CS, in active vs. inactive SLE patients, and in participants of both study groups with vitamin D deficiency, higher calcitriol levels, and TT FokI genotype carriers. In conclusion, the TT FokI VDR genotype was related to high VDR expression and clinical disease activity in systemic lupus erythematosus patients.

Presence of Adenovirus-36 DNA in Adipose Tissue of Women: Relationship with Adipocyte Morphology and the Expression of C/EBPβ and HIF-1α

BACKGROUND

Human adenovirus 36 (HAd36) infection has been associated with obesity. Experiments using 3T3-L1 adipocyte cultured cells and human adipose stem cells (hASCc) have shown that HAd36 stimulates the expression of genes implicated in cell differentiation and increased lipid accumulation. The presence of HAd36 in adipose tissue of overweight and obese women has also been confirmed. This study aims to analyze the presence of HAd36 DNA in the adipose tissue of women undergoing surgery for weight reduction and its relationship with obesity through changes in adipocyte morphology as well as the expression of C/EBPβ and HIF-1α.

METHODS

Fifty-two subcutaneous adipose tissue biopsies were collected. The anthropometric parameters measured were weight, height, skin folds, body circumferences, and body fat percentage. Biochemical measures were performed for glucose, cholesterol, triglycerides, cholesterol HDL-c, and LDL-c. The presence of HAd36 DNA was performed by conventional PCR. Adipocyte morphology was analyzed in H&E-stained sections using ImageJ/Fiji software. The expression of genes C/EBPβ, HIF-1α and β-actin was determined using TaqMan probes.

RESULTS

HAd36 DNA was detected in 31% of adipose tissue samples. The presence of viral DNA was not significantly associated with anthropometric, clinical, or metabolic measurements, or with changes in adipose tissue morphology. The levels of mRNA expression for C/EBPβ and HIF-1α did not show significant differences between positive and negative samples for HAd36 (p>0.05).

CONCLUSION

The presence of HAd36 DNA in adipose tissue was identified, but it was not related to morphological changes of adipocytes, or the expression of C/EBPβ and HIF-1α. Further studies are needed to confirm these findings.

Male rats exhibit higher pro-BDNF, c-Fos and dendritic tree changes after chronic acoustic stress

Prolonged or intense exposure to environmental noise (EN) has been associated with a number of changes in auditory organs as well as other brain structures. Notably, males and females have shown different susceptibilities to acoustic damage as well as different responses to environmental stressors. Rodent models have evidence of sex-specific changes in brain structures involved in noise and sound processing. As a common effect, experimental models have demonstrated that dendrite arborizations reconfigure in response to aversive conditions in several brain regions. Here, we examined the effect of chronic noise on dendritic reorganization and c-Fos expression patterns of both sexes. During 21 days male and female rats were exposed to a rats' audiogram-fitted adaptation of a noisy environment. Golgi-Cox and c-Fos staining were performed at auditory cortices (AC) and hippocampal regions. Sholl analysis and c-Fos counts were conducted for evidence of intersex differences. In addition, pro-BDNF serum levels were also measured. We found different patterns of c-Fos expression in hippocampus and AC. While in AC expression levels showed rapid and intense increases starting at 2 h, hippocampal areas showed slower rises that reached the highest levels at 21 days. Sholl analysis also evidenced regional differences in response to noise. Dendritic trees were reduced after 21 days in hippocampus but not in AC. Meanwhile, pro-BDNF levels augmented after EN exposure. In all analyzed variables, exposed males were the most affected. These findings suggest that noise may exert differential effects on male and female brains and that males could be more vulnerable to the chronic effects of noise.

Melatonin modifies SOX2+ cell proliferation in dentate gyrus and modulates SIRT1 and MECP2 in long-term sleep deprivation

Melatonin is a pleiotropic molecule that, after a short-term sleep deprivation, promotes the proliferation of neural stem cells in the adult hippocampus. However, this effect has not been observed in long-term sleep deprivation. The precise mechanism exerted by melatonin on the modulation of neural stem cells is not entirely elucidated, but evidence indicates that epigenetic regulators may be involved in this process. In this study, we investigated the effect of melatonin treatment during a 96-hour sleep deprivation and analyzed the expression of epigenetic modulators predicted by computational text mining and keyword clusterization. Our results showed that the administration of melatonin under sleep-deprived conditions increased the MECP2 expression and reduced the SIRT1 expression in the dentate gyrus. We observed that let-7b, mir-132, and mir-124 were highly expressed in the dentate gyrus after melatonin administration, but they were not modified by sleep deprivation. In addition, we found more Sox2⁺/5-bromo-2′-deoxyuridine (BrdU)⁺ cells in the subgranular zone of the sleep-deprived group treated with melatonin than in the untreated group. These findings may support the notion that melatonin modifies the expression of epigenetic mediators that, in turn, regulate the proliferation of neural progenitor cells in the adult dentate gyrus under long-term sleep-deprived conditions. All procedures performed in this study were approved by the Animal Ethics Committee of the University of Guadalajara, Mexico (approval No. CI-16610) on January 2, 2016.

Nitric oxide in the nucleus of the tractus solitarius is involved in hypoglycemic conditioned response

The repeated injection of insulin (unconditioned stimulus, UCS) immediately followed by exposure to sensory stimulation (e.g. sound or odor; conditioned stimulus, CS) results in a learned conditioned reflex in which the exposure to the CS alone lowers blood glucose. The brain regions participating in this hypoglycemic Pavlovian response remain unknown. Here we investigate if nitric oxide (NO) in the nucleus tractus solitarius (NTS), a nucleus known to be involved in glucose homeostasis, participates in this hypoglycemic reflex. Insulin injections (UCS) were paired with exposure to menthol odor (CS). After 8-10 reinforcements (4-5days training), rats acquire the learned hypoglycemic response. An increase in c-Fos expression was observed in the NTS, the ventrolateral hypothalamic nucleus (VLH) and other brain regions of conditioned rats. Microinjections of 3-(5'-hydroxymethyl-2'furyl)-1-benzyl indazole (YC-1) a stimulator of soluble guanylate cyclase (sGC) into NTS before the UCS accelerated the acquisition of the learned hypoglycemic response; 5-6 reinforcement produced pronounced glucose drop when exposed to the CS. In contrast, an inhibitor of NO synthase (NOS) N^ω-Nitro-l-arginine methyl ester (L-NAME) in the NTS prolonged the required training period (11-15 reinforcements) to obtain the hypoglycemic reflex, and reduced the glycemic response. The number of c-Fos expressing cells in the NTS and VLH in rats receiving YC-1was significantly higher than that observed in rats receiving L-NAME. These findings suggest that NO-cGMP-PKG signaling in the NTS can modify the acquisition of conditioned hypoglycemia, and suggests that this nucleus directly participates in this reflex.

BDNF and AMPA receptors in the cNTS modulate the hyperglycemic reflex after local carotid body NaCN stimulation

The application of sodium cyanide (NaCN) to the carotid body receptors (CBR) (CBR stimulation) induces rapid blood hyperglycemia and an increase in brain glucose retention. The commissural nucleus tractus solitarius (cNTS) is an essential relay nucleus in this hyperglycemic reflex; it receives glutamatergic afferents (that also release brain derived neurotrophic factor, BDNF) from the nodose-petrosal ganglia that relays CBR information. Previous work showed that AMPA in NTS blocks hyperglycemia and brain glucose retention after CBR stimulation. In contrast, BDNF, which attenuates glutamatergic AMPA currents in NTS, enhances these glycemic responses. Here we investigated the combined effects of BDNF and AMPA (and their antagonists) in NTS on the glycemic responses to CBR stimulation. Microinjections of BDNF plus AMPA into the cNTS before CBR stimulation in anesthetized rats, induced blood hyperglycemia and an increase in brain arteriovenous (a-v) of blood glucose concentration difference, which we infer is due to increased brain glucose retention. By contrast, the microinjection of the TrkB antagonist K252a plus AMPA abolished the glycemic responses to CBR stimulation similar to what is observed after AMPA pretreatments. In BDNF plus AMPA microinjections preceding CBR stimulation, the number of c-fos immunoreactive cNTS neurons increased. In contrast, in the rats microinjected with K252a plus AMPA in NTS, before CBR stimulation, c-fos expression in cNTS decreased. The expression of AMPA receptors GluR2/3 did not change in any of the studied groups. These results indicate that BDNF in cNTS plays a key role in the modulation of the hyperglycemic reflex initiated by CBR stimulation.

Hippocampal cytogenesis and spatial learning in senile rats exposed to chronic variable stress: effects of previous early life exposure to mild stress

In this study, we exposed adult rats to chronic variable stress (CVS) and tested the hypothesis that previous early-life exposure to stress changes the manner in which older subjects respond to aversive conditions. To this end, we analyzed the cytogenic changes in the hippocampus and hippocampal-dependent spatial learning performance. The experiments were performed on 18-month-old male rats divided into four groups as follows: Control (old rats under standard laboratory conditions), Early-life stress (ELS; old rats who were exposed to environmental noise from postnatal days, PNDs 21–35), CVS + ELS (old rats exposed to a chronic stress protocol who were previously exposed to the early-life noise stress) and CVS (old rats who were exposed only to the chronic stress protocol). The Morris Water Maze (MWM) was employed to evaluate the spatial learning abilities of the rats at the end of the experiment. Immunohistochemistry against 5′Bromodeoxyuridine (BrdU) and glial fibrillar acidic protein (GFAP) was also conducted in the DG, CA1, CA2 and CA3 regions of the hippocampus. We confocally analyzed the cytogenic (BrdU-labeled cells) and astrogenic (BrdU + GFAP-labeled cells) changes produced by these conditions. Using this procedure, we found that stress diminished the total number of BrdU+ cells over the main proliferative area of the hippocampus (i.e., the dentate gyrus, DG) but increased the astrocyte phenotypes (GFAP + BrdU). The depleted BrdU+ cells were restored when the senile rats also experienced stress at the early stages of life. The MWM assessment demonstrated that stress also impairs the ability of the rats to learn the task. This impairment was not present when the stressful experience was preceded by the early-life exposure. Thus, our results support the idea that previous exposure to mild stressing agents may have beneficial effects on aged subjects.

Early-life exposure to noise reduces mPFC astrocyte numbers and T-maze alternation/discrimination task performance in adult male rats

In this experiment, we evaluated the long-term effects of noise by assessing both astrocyte changes in medial prefrontal cortex (mPFC) and mPFC-related alternation/discrimination tasks. Twenty-one-day-old male rats were exposed during a period of 15 days to a standardized rats' audiogram-fitted adaptation of a human noisy environment. We measured serum corticosterone (CORT) levels at the end of the exposure and periodically registered body weight gain. In order to evaluate the long-term effects of this exposure, we assessed the rats' performance on the T-maze apparatus 3 months later. Astrocyte numbers and proliferative changes in mPFC were also evaluated at this stage. We found that environmental noise (EN) exposure significantly increased serum CORT levels and negatively affected the body weight gain curve. Accordingly, enduring effects of noise were demonstrated on mPFC. The ability to solve alternation/discrimination tasks was reduced, as well as the number of astroglial cells. We also found reduced cytogenesis among the mPFC areas evaluated. Our results support the idea that early exposure to environmental stressors may have long-lasting consequences affecting complex cognitive processes. These results also suggest that glial changes may become an important element behind the cognitive and morphological alterations accompanying the PFC changes seen in some stress-related pathologies.

Neurogenesis in Alzheimer´s disease: a realistic alternative to neuronal degeneration?

Neural stem cells (NSC) are cells that have the capacity to generate multiple types of differentiated brain cells. In conditions in which there is a loss of key functional cell groups, such as neurons, inducing or introducing neural stem cells to replace the function of those cells that were lost during the disease has the greatest potential therapeutic applications. Indeed, the achievement of one of the main objectives of various investigations is already on the horizon for some conditions, such as Alzheimer's disease. It is not known whether impaired neurogenesis contributes to neuronal depletion and cognitive dysfunction in Alzheimer's disease (AD). The results of the different investigations are controversial; some studies have found that neurogenesis is increased in AD brains, but others have not.

Progesterone regulates corticosterone elevation and alterations in spatial memory and exploratory behavior induced by stress in Wistar rats

The hippocampus is sensitive to high levels of glucocorticoids. During stress response, it suffers biochemical and cellular changes that affect functions such as spatial memory and exploratory behavior. In this study, we analyzed the influence of the neurosteroid progesterone (PROG), on stress-induced changes in urinary corticosterone (CORT) levels, spatial memory and exploratory behavior. Castrated adult male rats were implanted with PROG or vehicle (VEHI), and then exposed to chronic stress by overcrowding or ultrasonic noise for ten days. PROG and CORT levels were assessed in urine using high-performance liquid chromatography (HPLC). Implanted PROG inhibited stress-induced CORT raise, prevented spatial memory impairment in the Morris water maze, and eliminated increased exploratory behavior in the hole-board test. These results suggest protective effects of PROG against the corticosteroids raise and behavioral deficit generated by both stressful situations, possibly mediated by its anxiolytic mechanisms.

Nitric oxide in the solitary tract nucleus (STn) modulates glucose homeostasis and FOS-ir expression after carotid chemoreceptor stimulation

We evaluate in rats the role of NO in the solitary tract nucleus (STn) after an anoxic stimulus to carotid body chemoreceptor cells (CChrc) with cyanide (NaCN), on the hyperglycemic reflex with glucose retention by the brain (BGR) and FOS expression (FOS-ir) in the STn. The results suggest that nitroxidergic pathways in the STn may play an important role in glucose homeostasis. A NO donor such as sodium nitroprusside (NPS) in the STn before CChrc stimulation increased arterial glucose level and significantly decreased BGR. NPS also induced a higher FOS-ir expression in STn neurons when compared to neurons in control rats that only received artificial cerebrospinal fluid (aCSF) before CChrc stimulation. In contrast, a selective NOS inhibitor such as Nomega-nitro-L-arginine methyl ester (L-NAME) in the STn before CChrc stimulation resulted in an increase of both, systemic glucose and BGR above control values. In this case, the number of FOS-ir positive neurons in the STn decreased when compared to control or to NPS experiments. FOS-ir expression in brainstem cells suggests that CChrc stimulation activates nitroxidergic pathways in the STn to regulate peripheral and central glucose homeostasis. The study of these functionally defined cells will be important to understand brain glucose homeostasis.

[The effects of the social environment on the brain]

AIMS

This work analyses the main studies dealing with the mechanisms by which the brain is altered by chronic stress and the impact of social stimuli on the activation of these mechanisms, which can lead to behavioural disorders and cognitive impairment in communities of mammals.

DEVELOPMENT

The physiological and hormonal responses triggered as a response to stress are linked to alterations in certain areas of the brain and more particularly in the hippocampus. These mechanisms include hyperactivity of the hypothalamus-pituitary-adrenal axis, raised levels of corticosteroids and excitatory amino acids, neurotoxicity due to intracellular accumulation of calcium, apoptosis and a number of factors having to do with the immunological system. Most of these studies have involved the exogenous application of supraphysiological levels of corticosteroids or challenging the individual with stimuli that do not properly belong to their natural surroundings. Nevertheless, it is also possible that these mechanisms are triggered by aversive social stimuli from the natural environment, such as confrontation, establishing hierarchies, neglect and social evaluation. It has been proved that social stress has important effects on conduct and health, especially with regard to the structural and functional integrity of the brain.

CONCLUSIONS

Social stress can trigger important alterations in the nervous system of individuals exposed to it and these changes can manifest themselves as varying types of disorders affecting conduct and the cognitive skills. Nevertheless, not all natural surroundings give rise to these adverse effects, as balanced communities offer their members support, protection and a series of other advantages.

Astrocytic and microglia cells reactivity induced by neonatal administration of glutamate in cerebral cortex of the adult rats

Recent studies confirm that astrocytes and neurons are associated with the synaptic transmission, particularly with the regulation of glutamate (Glu) levels. Therefore, they have the capacity to modulate the Glu released from neurons into the extracellular space. It has also been demonstrated an intense astrocytic and microglia response to physical or chemical lesions of the central nervous system. However, the persistence of the response of the glial cells in adult brain had not been previously reported, after the excitotoxic damage caused by neonatal dosage of monosodium glutamate (MSG) to newborn rats. In this study, 4 mg/g body weight of MSG were administered to newborn rats at 1, 3, 5, and 7 days after birth, at the age of 60 days the astrocytes and the microglia cells were analyzed with immunohistochemical methods in the fronto-parietal cortex. Double labeling to glial fibrillary acidic protein (GFAP) and BrdU, or isolectin-B(4) and BrdU identified astrocytes or microglia cells that proliferated; immunoblotting and immunoreactivity to vimentin served for assess immaturity of astrocytic intermediate filaments. The results show that the neonatal administration of MSG-induced reactivity of astrocytes and microglia cells in the fronto-parietal cortex, which was characterized by hyperplasia; an increased number of astrocytes and microglia cells that proliferated, hypertrophy; increased complexity of the cytoplasm extension of both glial cells and expression of RNAm to vimentin, with the presence of vimentin-positive astrocytes. This glial response to neuroexcitotoxic stimulus of Glu on the immature brain, which persisted to adulthood, suggests that the neurotransmitter Glu could trigger neuro-degenerative illnesses.

Dehydroepiandrosterone, pregnenolone and sex steroids down-regulate reactive astroglia in the male rat brain after a penetrating brain injury

Astrocytes are a target for steroid hormones and for steroids produced by the nervous system (neurosteroids). The effect of gonadal hormones and several neurosteroids in the formation of gliotic tissue has been assessed in adult male rats after a penetrating wound of the cerebral cortex and the hippocampal formation. The hormones testosterone, 17beta-estradiol and progesterone and the neurosteroids dehydroepiandrosterone, pregnenolone and pregnenolone sulfate resulted in a significant decrease in the accumulation of astrocytes in the proximity of the wound and in a decreased bromodeoxyuridine incorporation in reactive astrocytes. Of all steroids tested, dehydroepiandrosterone was the most potent inhibitor of gliotic tissue formation. These findings suggest that neurosteroids and sex steroids may affect brain repair by down-regulating gliotic tissue.

Expression of the beta 1 and beta 2(AMOG) subunits of the Na,K-ATPase in neural tissues: cellular and developmental distribution patterns

We have used isoform-specific antisera against the Na,K-ATPase beta 1 (SpETb1) and beta 2(AMOG) (SpETb2) subunit isoforms in order to establish their specific cellular and subcellular localization in several developmental stages of the rat central nervous system. Immunocytochemical preparations revealed beta 1 Isoform protein in most neural cells, being predominantly located in the soma of neurons and astrocytes, with no appreciable developmental variations. In the newborn rat, beta 2(AMOG) immunoreactivity was present in cellular processes of astroglia and in the somas of neurons and decreasing in intensity with maturation until adulthood, where no beta 2 isoform was detected in neurons. The differential location of these isoforms, both developmentally and at the cellular level suggest a complex regulation of their genes expression and mechanisms of subcellular distribution, as well as functional differences.

Gonadal hormone regulation of insulin-like growth factor-I-like immunoreactivity in hypothalamic astroglia of developing and adult rats

The influence of gonadal steroids on insulin-like growth factor I (IGF-I)-like immunoreactivity was assessed in the rat arcuate nucleus, an area of the hypothalamus that regulates pituitary secretion. IGF-I-like immunoreactivity was observed in hypothalamic cells with the morphological aspects of tanycytes and astrocytes. The surface density of IGF-I-like immunoreactive glia increased with puberty in the arcuate nucleus of male and female rats, while decreasing with age in other brain areas. Gender differences in the surface density of IGF-I-like immunoreactive glia were detected in adult animals, with males and androgenized females having significantly higher values than normal females. In the latter, the surface density of IGF-I-like immunoreactive glia was increased in the afternoon of proestrus and in the morning of estrus compared to the morning of proestrus, diestrus and metestrus. In addition, IGF-I-like immunoreactivity showed a dose-dependent increase in ovariectomized rats injected with 17 beta-estradiol, but not in those receiving 17 alpha-estradiol. The effect of 17 beta-estradiol was blocked by simultaneous administration of progesterone, while this hormone alone had no effect. These results indicate that IGF-I-like immunoreactivity in arcuate glial cells is affected by the hormonal environment and suggest that IGF-I-like immunoreactive glia may be involved in neuroendocrine events within the hypothalamus.

Gonadal hormone regulation of glial fibrillary acidic protein immunoreactivity and glial ultrastructure in the rat neuroendocrine hypothalamus

The influence of gonadal steroids on the ultrastructure of glial cells and on the immunoreactivity for the specific astrocytic marker glial fibrillary acidic protein (GFAP) has been assessed in the neuroendocrine hypothalamus. The following parameters were analyzed in the arcuate nucleus of adult female rats: the number and the surface density of cells immunoreactive for GFAP, the number of glial profiles showing bundles of glial filaments, the size of the bundles of glial filaments, and the proportion of neuronal perikaryal membrane apposed by glial processes. These parameters were studied during the different phases of the estrous cycle, after ovariectomy, and after the administration of estradiol or progesterone to ovariectomized rats. No significant differences were detected in the number of GFAP-immunoreactive cells among the different experimental groups. The surface density of GFAP-immunoreactive material, the number of glial profiles in the neuropil, and the proportion of neuronal perikaryal membrane covered by glia were increased in the afternoon of proestrus and in the morning of estrus compared with other phases of the estrous cycle or to ovariectomized rats and showed a rapid (5 h) and reversible increase in ovariectomized rats injected with 17 beta estradiol, with a maximal effect by 24 h after the administration of the hormone. In contrast, the size of the bundles of glial filaments was decreased in the afternoon of proestrus, in the morning of estrus, and by the administration of estradiol to ovariectomized rats. The parameters studied were not affected by the administration of progesterone. However, progesterone (300 micrograms/rat) blocked the effects of 17 beta estradiol (1, 10, and 300 micrograms). The results suggest that glial cells may be actively involved in the modulation of neuroendocrine events by the hypothalamus.

Differential expression and gonadal hormone regulation of histone H1(0) in the developing and adult rat brain

The cellular distribution of histone H1(0) has been examined immunohistochemically in the rat brain. H1(0) accumulates in neurons and glial cells during postnatal development. In neurons, immunoreactivity increases progressively from about postnatal day 10, and reaches a distribution pattern similar to that of adult rats by postnatal day 20. Immunoreactivity in glial cells shows a prominent increase from postnatal day 20 to adult age. The accumulation of H1(0) during postnatal development appears to be correlated with terminal differentiation and maturation. Although immunoreactive neurons are widely distributed in all areas of the central nervous system, many neurons do not express immunoreactivity. For instance in the cerebellum, Purkinje neurons are negative. In females, the number of immunoreactive neurons in the arcuate area of the hypothalamus increases during postnatal development. In contrast, the percentage of immunoreactive neurons in males is low at all ages studied. The expression of H1(0) in the ventromedial part of the arcuate is reversibly and negatively regulated during the estrous cycle by the level of plasma estradiol. Ovariectomy increases the number of immunoreactive neurons while the restoration of the physiological levels of estradiol results in the opposite effect. Early postnatal androgenization of females suppresses the increment in the number of immunoreactive neurons in both the dorsolateral and the ventromedial parts of the arcuate during postnatal development, thus leading to permanently decreased levels of H1(0) immunoreactivity in postpuberal females.

The role of estradiol and progesterone in phased synaptic remodelling of the rat arcuate nucleus

During the estrous cycle there is a phasic synaptic remodelling in the hypothalamic arcuate nucleus, consisting in a loss and regain of axo-somatic synapses during the 48 h period between the morning of proestrus and the morning of metestrus. Synaptic changes are accompanied by cyclic modifications in the number of intramembrane particles in the plasma membrane of arcuate neuronal somas. To test the effect of the ovarian steroids on arcuate axo-somatic synapses we treated castrated females either with oil vehicle, 17 beta-estradiol, progesterone, or a combination of estradiol and progesterone, and observed them for 48 h. The number of axo-somatic synaptic profiles showed a 33% fall by 24 h after estradiol treatment and returned to control levels by 48 h. The effect of estradiol on axo-somatic synapses was accompanied by a marked and reversible modification of the number of intramembrane particles in the plasma membrane of arcuate neuronal somas. Progesterone alone did not affect the number of axo-somatic synaptic profiles nor the number of intramembrane particles, but when administered together with estradiol, blocked the effects of estradiol on neuronal membrane and synapses.