Sex differences in pain-induced modulation of corticotropin-releasing hormone neurons in the dorsolateral part of the stria terminalis in mice

We earlier reported female-biased, sex-specific involvement of the dorsolateral bed nucleus of the stria terminalis (dl BST) in the formalin-induced pain response in rats. The present study investigated pain effects on mice behaviors. Because the dl BST is densely populated with corticotropin-releasing hormone (CRH) neurons, we examined sex differences in these parameters for the dl BST CRH neurons in male and female mice of a mouse line for which the CRH gene promoter (corticotropin-releasing factor [CRF]-Venus ΔNeo) controls the expression of the modified yellow fluorescent protein (Venus). Approximately 92% of Venus-positive cells in the dl BST were also CRH mRNA-positive, irrespective of sex. Therefore, the cells identified using Venus fluorescence were regarded as CRH neurons. A female-biased sex difference was observed in pain-induced behaviors during the interphase (5-15 min after formalin injection) but not during the later phase (phase 2, 15-60 min) in wild-type mice. In CRF-Venus ΔNeo mice, a female-biased difference was observed in either the earlier phase (phase 1, 0-5 min) or the interphase, but not in phase 2. Patch-clamp recordings taken using an acute BST slice obtained from a CRF-Venus ΔNeo mouse after formalin injection showed miniature excitatory postsynaptic currents (mEPSCs) and miniature inhibitory postsynaptic currents (mIPSCs). Remarkably, the mEPSCs frequency was higher in the Venus-expressing cells of formalin-injected female mice than in vehicle-treated female mice. Male mice showed no increase in mEPSC frequency by formalin injection. Formalin injection had no effect on mEPSC or mIPSC amplitudes in either sex. Pain-induced changes in mEPSC frequency in putative CRH neurons were phase-dependent. Results show that excitatory synaptic inputs to BST CRH neurons are temporally enhanced along with behavioral sex differences in pain response, suggesting that pain signals alter the BST CRH neurons excitability in a sex-dependent manner.

Transcription factor signal transducer and activator of transcription 6 (STAT6) is an inhibitory factor for adult myogenesis

Background

The signal transducer and activator of transcription 6 (STAT6) transcription factor plays a vitally important role in immune cells, where it is activated mainly by interleukin-4 (IL-4). Because IL-4 is an essential cytokine for myotube formation, STAT6 might also be involved in myogenesis as part of IL-4 signaling. This study was conducted to elucidate the role of STAT6 in adult myogenesis in vitro and in vivo.

Methods

Myoblasts were isolated from male mice and were differentiated on a culture dish to evaluate the change in STAT6 during myotube formation. Then, the effects of STAT6 overexpression and inhibition on proliferation, differentiation, and fusion in those cells were studied. Additionally, to elucidate the myogenic role of STAT6 in vivo, muscle regeneration after injury was evaluated in STAT6 knockout mice.

Results

IL-4 can increase STAT6 phosphorylation, but STAT6 phosphorylation decreased during myotube formation in culture. STAT6 overexpression decreased, but STAT6 knockdown increased the differentiation index and the fusion index. Results indicate that STAT6 inhibited myogenin protein expression. Results of in vivo experiments show that STAT6 knockout mice exhibited better regeneration than wild-type mice 5 days after cardiotoxin-induced injury. It is particularly interesting that results obtained using cells from STAT6 knockout mice suggest that this STAT6 inhibitory action for myogenesis was not mediated by IL-4 but might instead be associated with p38 mitogen-activated protein kinase phosphorylation. However, STAT6 was not involved in the proliferation of myogenic cells in vitro and in vivo.

Conclusion

Results suggest that STAT6 functions as an inhibitor of adult myogenesis. Moreover, results suggest that the IL-4-STAT6 signaling axis is unlikely to be responsible for myotube formation.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13395-021-00271-8.

Ketogenic diet feeding improves aerobic metabolism property in extensor digitorum longus muscle of sedentary male rats

Recent studies of the ketogenic diet, an extremely high-fat diet with extremely low carbohydrates, suggest that it changes the energy metabolism properties of skeletal muscle. However, ketogenic diet effects on muscle metabolic characteristics are diverse and sometimes countervailing. Furthermore, ketogenic diet effects on skeletal muscle performance are unknown. After male Wistar rats (8 weeks of age) were assigned randomly to a control group (CON) and a ketogenic diet group (KD), they were fed for 4 weeks respectively with a control diet (10% fat, 10% protein, 80% carbohydrate) and a ketogenic diet (90% fat, 10% protein, 0% carbohydrate). After the 4-week feeding period, the extensor digitorum longus (EDL) muscle was evaluated ex vivo for twitch force, tetanic force, and fatigue. We also analyzed the myosin heavy chain composition, protein expression of metabolic enzymes and regulatory factors, and citrate synthase activity. No significant difference was found between CON and KD in twitch or tetanic forces or muscle fatigue. However, the KD citrate synthase activity and the protein expression of Sema3A, citrate synthase, succinate dehydrogenase, cytochrome c oxidase subunit 4, and 3-hydroxyacyl-CoA dehydrogenase were significantly higher than those of CON. Moreover, a myosin heavy chain shift occurred from type IIb to IIx in KD. These results demonstrated that the 4-week ketogenic diet improves skeletal muscle aerobic capacity without obstructing muscle contractile function in sedentary male rats and suggest involvement of Sema3A in the myosin heavy chain shift of EDL muscle.

Age-related decrease in muscle satellite cells is accompanied with diminished expression of early growth response 3 in mice

Skeletal muscle regeneration is mostly dependent on muscle satellite cells. Proper muscle regeneration requires enough number of satellite cells. Recent studies have suggested that the number of satellite cells in skeletal muscle declines as we age, leading to the impairment of muscle regeneration in older population. Our earlier study demonstrated that zinc finger transcription factor early growth response 3 (Egr3) plays an important role for maintaining the number of myoblasts, suggesting that age-related decrease in muscle satellite cell should be associated with the expression levels of Egr3. The aim of this study was to investigate whether aging would alter the Egr3 expression in satellite cells. A couple groups of male C57BL/6J mice were examined in this study: young (3 Mo) and old (17 Mo). Immunohistochemical staining showed that the satellite cell number decreased in normal and injured muscles of old mice. In fluorescence-activated cell sorting-isolated muscle satellite cells from normal and injured muscles, the mRNA expression of Egr3 was significantly decreased with age regardless of injury. In harmony with these results, Pax7 mRNA levels also decreased in the satellite cells from old mice. Alternatively, inhibition of Egr3 expression by shRNA decreased Pax7 protein expression in cultured myoblasts. These results suggest that Egr3 is associated with the age-related decline of muscle satellite cells in older population. Also, Egr3 might be implicated in the regulation of Pax7. Therefore, the loss of Egr3 expression may elucidate attenuated MSCs function and muscle regeneration in older age.

Reduced Luteinizing Hormone Induction Following Estrogen and Progesterone Priming in Female-to-Male Transsexuals

Anatomical studies have suggested that one of the brain structures involved in gender identity is the bed nucleus of the stria terminalis, though this brain structure is probably not the only one to control gender identity. We hypothesized that, if this brain area also affected gonadotropin secretion in humans, transsexual individuals might produce different gonadotropin levels in response to exogenous stimulation. In the present study, we examined whether estrogen combined with progesterone might lead to a change in luteinizing hormone (LH) secretion in female-to-male (FTM) transsexual individuals. We studied female control subjects (n = 9), FTM transsexual subjects (n = 12), and male-to-female (MTF) transsexual subjects (n = 8). Ethinyl estradiol (50 μg/tablet) was administered orally, twice a day, for five consecutive days. After the first blood sampling, progesterone (12.5 mg) was injected intramuscularly. Plasma LH was measured with an immunoradiometric assay. The combination of estrogen and progesterone resulted in increased LH secretion in female control subjects and in MTF subjects, but this increase appeared to be attenuated in FTM transsexual subjects. In fact, the %LH response was significantly reduced in FTM subjects (P < 0.05), but not in MTF subjects (P > 0.5), compared to female control subjects. In addition, the peak time after progesterone injection was significantly delayed in FTM subjects (P < 0.05), but not in MTF subjects (P > 0.5), compared to female control subjects. We then compared subjects according to whether the combination of estrogen and progesterone had a positive (more than 200% increase) or negative (less than 200% increase) effect on LH secretion. A χ² analysis revealed significantly different (P < 0.05) effects on LH secretion between female controls (positive n = 7, negative n = 2) and FTM transsexual subjects (positive n = 4, negative n = 8), but not between female controls and MTF transsexual subjects (positive n = 7, negative n = 1). Thus, LH secretion in response to estrogen- and progesterone priming was attenuated in FTM subjects, but not in MTF subjects, compared to control females. This finding suggested that the brain area related to gender identity in morphological studies might also be involved in the LH secretory response in humans. Thus, altered brain morphology might be correlated to altered function in FTM transsexuals.

Prostaglandin E2 modulates presynaptic regulation of GnRH neurons via EP4 receptors in accordance with estrogen milieu

Prostaglandin E2 (PGE2) promotes gonadotropin secretion by regulating the activity of neurons that release gonadotropin-releasing hormone (GnRH) in the hypothalamus. However, the mechanisms of action of PGE2 at these neurons have yet to be fully explored. We examined the effects of PGE2 on the generation of miniature excitatory postsynaptic currents (mEPSCs) at GnRH neurons as measured by whole-cell, patch-clamp recordings. GnRH neurons were identified in slices prepared from the preoptic areas of female GnRH-EGFP rats. Exposure to PGE2 significantly increased the frequency, but not the amplitude, of the mEPSCs generated on the day of proestrus, but neither frequency nor amplitude was altered on day 1 of diestrus. These data suggest that the action of PGE2 on mEPSC frequency varies depending on the stage of estrous. An estrogen-dependence of PGE2's action was further supported by the increased frequency, but not amplitude, of mEPSCs generated at GnRH neurons prepared from estrogen-primed ovariectomized rats. Conversely, PGE2 had no effect on mEPSC frequency or amplitude at GnRH neurons in cholesterol-treated rats. Subsequent experiments to identify candidate receptors for PG2E's action revealed that exposure to a PGE2 receptor 4 (EP4) agonist, but not EP1 or EP2 agonists, mimicked the effects achieved by PGE2 exposure. These effects of mEPSCs could be reversed using an EP4 antagonist, illustrating the specificity of the effect. Collectively, these data demonstrate that PGE2 can alter excitatory synaptic neurotransmission at GnRH neurons via EP4 signaling at presynaptic site(s) in an estrogen-dependent fashion during proestrus.

Early Growth Response 3 (Egr3) Contributes a Maintenance of C2C12 Myoblast Proliferation

Satellite cell proliferation is a crucially important process for adult myogenesis. However, its regulatory mechanisms remain unknown. Early growth response 3 (Egr3) is a zinc-finger transcription factor that regulates different cellular functions. Reportedly, Egr3 interacts with multiple signaling molecules that are also known to regulate satellite cell proliferation. Therefore, it is possible that Egr3 is involved in satellite cell proliferation. Results of this study have demonstrated that Egr3 transcript levels are upregulated in regenerating mouse skeletal muscle after cardiotoxin injury. Using C2C12 myoblast culture (a model of activated satellite cells), results show that inhibition of Egr3 by shRNA impairs the myoblast proliferation rate. Results also show reduction of NF-кB transcriptional activity in Egr3-inhibited cells. Inhibition of Egr3 is associated with an increase in annexin V⁺ cell fraction and apoptotic protein activity including caspase-3 and caspase-7, and Poly-ADP ribose polymerase. By contrast, the reduction of cellular proliferation by inhibition of Egr3 was partially recovered by treatment of pan-caspase inhibitor Z-VAD-FMK. Collectively, these results suggest that Egr3 is involved in myoblast proliferation by interaction with survival signaling. J. Cell. Physiol. 232: 1114-1122, 2017. © 2016 Wiley Periodicals, Inc.

Involvement of Transient Receptor Potential Cation Channel Vanilloid 1 (TRPV1) in Myoblast Fusion

The mechanisms that underlie the complex process of muscle regeneration after injury remain unknown. Transient receptor potential cation channel vanilloid 1 (TRPV1) is expressed in several cell types, including skeletal muscle, and is activated by high temperature and by certain molecules secreted during tissue inflammation. Severe inflammation and local temperature perturbations are induced during muscle regeneration, which suggests that TRPV1 might be activated and involved in the process. The aim of this study, was to clarify the role of TRPV1 in the myogenic potential of satellite cells responsible for muscle regeneration. We found that mRNA and protein levels of TRPV1 increased during regeneration after cardiotoxin (CTX)-induced muscle injury in mice. Using isolated mouse satellite cells (i.e., myoblasts), we observed that activation of TRPV1 by its agonist capsaicin (CAP) augmented myogenin protein levels. Whereas CAP did not alter myoblast proliferation, it facilitated myoblast fusion (evaluated using myonucleii number per myotube and fusion index). In contrast, suppression of TRPV1 by siRNA impaired myoblast fusion. Using mice, we also demonstrated that intramuscular injection of CAP facilitated muscle repair after CTX-induced muscle injury. Moreover, we showed that these roles of TRPV1 might be mediated by interleukin-4 and calcium signaling during myoblast fusion. Collectively, these results suggest that TRPV1 underlies normal myogenesis through promotion of myoblast fusion. J. Cell. Physiol. 231: 2275-2285, 2016. © 2016 Wiley Periodicals, Inc.

Exposure to social defeat stress in adolescence improves the working memory and anxiety-like behavior of adult female rats with intrauterine growth restriction, independently of hippocampal neurogenesis

Intrauterine growth restriction (IUGR) is a risk factor for memory impairment and emotional disturbance during growth and adulthood. However, this risk might be modulated by environmental factors during development. Here we examined whether exposing adolescent male and female rats with thromboxane A2-induced IUGR to social defeat stress (SDS) affected their working memory and anxiety-like behavior in adulthood. We also used BrdU staining to investigate hippocampal cellular proliferation and BrdU and NeuN double staining to investigate neural differentiation in female IUGR rats. In the absence of adolescent stress, IUGR female rats, but not male rats, scored significantly lower in the T-maze test of working memory and exhibited higher anxiety-like behavior in the elevated-plus maze test compared with controls. Adolescent exposure to SDS abolished these behavioral impairments in IUGR females. In the absence of adolescent stress, hippocampal cellular proliferation was significantly higher in IUGR females than in non-IUGR female controls and was not influenced by adolescent exposure to SDS. Hippocampal neural differentiation was equivalent in non-stressed control and IUGR females. Neural differentiation was significantly increased by adolescent exposure to SDS in controls but not in IUGR females. There was no significant difference in the serum corticosterone concentrations between non-stressed control and IUGR females; however, adolescent exposure to SDS significantly increased serum corticosterone concentration in control females but not in IUGR females. These results demonstrate that adolescent exposure to SDS improves behavioral impairment independent of hippocampal neurogenesis in adult rats with IUGR.

Sex differences in feeding behavior in rats: the relationship with neuronal activation in the hypothalamus

There is general agreement that the central nervous system in rodents differs between sexes due to the presence of gonadal steroid hormone during differentiation. Sex differences in feeding seem to occur among species, and responses to fasting (i.e., starvation), gonadal steroids (i.e., testosterone and estradiol), and diet (i.e., western-style diet) vary significantly between sexes. The hypothalamus is the center for controlling feeding behavior. We examined the activation of feeding-related peptides in neurons in the hypothalamus. Phosphorylation of cyclic AMP response element-binding protein (CREB) is a good marker for neural activation, as is the Fos antigen. Therefore, we predicted that sex differences in the activity of melanin-concentrating hormone (MCH) neurons would be associated with feeding behavior. We determined the response of MCH neurons to glucose in the lateral hypothalamic area (LHA) and our results suggested MCH neurons play an important role in sex differences in feeding behavior. In addition, fasting increased the number of orexin neurons harboring phosphorylated CREB in female rats (regardless of the estrous day), but not male rats. Glucose injection decreased the number of these neurons with phosphorylated CREB in fasted female rats. Finally, under normal spontaneous food intake, MCH neurons, but not orexin neurons, expressed phosphorylated CREB. These sex differences in response to fasting and glucose, as well as under normal conditions, suggest a vulnerability to metabolic challenges in females.

Phasic synaptic incorporation of GluR2-lacking AMPA receptors at gonadotropin-releasing hormone neurons is involved in the generation of the luteinizing hormone surge in female rats

Reproductive success depends on a robust and appropriately timed preovulatory luteinizing hormone (LH) surge, which is induced by the activation of gonadotropin-releasing hormone (GnRH) neurons in response to positive feedback from increasing estrogen levels. Here we document an increase in postsynaptic GluR2-lacking Ca2+ -permeable AMPA-type glutamate receptors (CP-AMPARs) at synapses on GnRH neurons on the day of proestrus in rats, coincident with the increase in estrogen levels. Functional blockade of CP-AMPARs depressed the synaptic responses only on the day of proestrus and concomitantly attenuated the LH surge. Thus, the phasic synaptic incorporation of postsynaptic CP-AMPARs on GnRH neurons is involved in the generation of the LH surge.

Immunohistochemical evidence for the relationship between microglia and GnRH neurons in the preoptic area of ovariectomized rats with and without steroid replacement

Prostaglandins (PGs), whose synthesis is catalyzed by the rate-limiting enzyme cyclooxygenase (COX) including COX-1 and COX-2, are among the important mediators involved in the regulation of gonadotropin-releasing hormone (GnRH) secretion. However, the cellular origin of PGs remains obscure in terms of its relationship to GnRH neurons. The present study was therefore aimed to clarify the anatomical relationship between COX-1-producing microglia and GnRH neurons in the preoptic area (POA), and to examine possible influence of ovarian steroids. We performed a triple labeled immunofluorescent histochemistry of COX-1, CD11b (a specific marker for microglia) and GnRH in the POA of ovarian steroid-primed and non-primed ovariectomized rats. The result confirmed our previous study suggesting COX-1 immunoreactivity in the vicinity of, but not within, GnRH neurons in the POA. COX-1 around GnRH cells was entirely (100%) localized in cells containing CD11b regardless of steroid replacement in ovariectomized rats. These CD11b-immunoreactive cells had small cell bodies and highly branched fibers characteristic of ramified microglia. Three-dimensional reconstruction of confocal images revealed close proximity of some COX-1-containing microglia and GnRH neurons. These results showed selective and constitutive expression of COX-1 in ramified microglia in the vicinity of GnRH neurons, providing evidence for intercellular communication, mediated by PGs, from microglia to GnRH cells.

Phosphorylation of cAMP response element-binding protein in the extended amygdala of male rats is induced by novel environment and attenuated by estrous female-bedding

OBJECTIVE

We examined whether female pheromone, which would be contained in female-soiled bedding, affected the expression of phosphorylated cAMP response element-binding protein-like (pCREB) immunoreactive cells in the extended amygdala.

METHODS

Male rats were exposed to following conditions: maintained in their home cage (home cage group), or relocated to a cage containing clean bedding (clean-bedding exposed group), ovariectomized (OVX) rat-soiled bedding (OVX-bedding exposed group) or estrogen-treated OVX rat-soiled bedding (OVX+E2-bedding exposed group). Rats were sacrificed 10-20 min after exposure and brain sections were subject to immunocytochemical processing.

RESULTS

In the medial subdivision of the bed nucleus of the stria terminalis (BST) and the central amygdala (CeA), the number of pCREB immunoreactive (pCREB-ir) cells in the clean-bedding exposed group was significantly larger than in the home cage group, while the number of pCREB-ir cells in the OVX+E2-bedding exposed group did not differ from that in the home cage group. The bedding soiled by OVX rats was less effective. No significant difference in the number of pCREB-ir cells was detected in the other regions of the extended amygdala among all groups.

CONCLUSIONS

The present study suggests that the exposure of clean bedding to male rats induces the expression of pCREB-ir in the medial BST and the CeA; exposure to female pheromone attenuates this expression.

Formalin-induced nociceptive behavior and c-Fos expression in middle-aged female rats

The impact of the estrous cycle on the nociceptive response in middle-aged female rats was assessed using the formalin test and c-Fos immunoreactivity as a marker of neural activation. Young (2-month-old) and middle-aged (11-month-old) rats were examined, dividing the middle-aged rats into two groups based on their estrous cycle: regular 4-day estrous cycle and irregular estrous cycle. The right hind paw was subcutaneously injected with 50microl of 2% formalin or saline as a control. Behavioral changes were observed for 1h. Cycling rats were used during proestrus. Middle-aged female rats had a significantly higher score for nociceptive behavior compared to young rats, irrespective of estrous cyclicity, which suggests that aging, not the ability to maintain estrous cyclicity, causes hypersensitivity to the formalin injection. Immunohistochemical analysis found that the brain response to formalin injection was also more sensitive in middle-aged rats than young rats; a significant increase in the number of c-Fos immunoreactive cells was found in the ventral portion of the lateral septum of middle-aged rats injected with formalin compared to young and middle-aged rats injected with saline, irrespective of estrous cyclicity. Based on these results, we conclude that the sensitivity to painful stimuli in middle-aged female rats, which are in a neuroendocrine state similar to pre- and peri-menopausal women, is associated with age and not affected by reproductive ability.

Food availability affects orexin a/ hypocretin-1-induced inhibition of pulsatile luteinizing hormone secretion in female rats

Orexin A/hypocretin-1 inhibits pulsatile luteinizing hormone (LH) secretion in female rats. In this study, we investigated whether this inhibition was tied to the fasting state, as suggested by our previous study. We first examined whether orexin A inhibited pulsatile LH secretion when food was available ad libitumduring blood sampling. Next, we investigated the effect of intravenous administration of glucose (400 mg/kg) or lactic acid (negative control; 400 mg/kg) on orexin A-induced inhibition of pulsatile LH secretion. We found that orexin A did not affect pulsatile LH secretion in the presence of food, although it increased feeding behavior. Injection of orexin A significantly inhibited pulsatile LH secretion when food was withheld during blood sampling (p < 0.05); this inhibitory effect was rapidly reversed by intravenous injection of glucose but not lactic acid. Because orexin A did not seem to affect pulsatile LH secretion when food was available ad libitum, we speculate that orexin A has an effect on LH secretion when orexin A-induced hunger is accompanied by stress, such as the absence of food. Furthermore, glucose as well as food may act as a satiety factor in gonadotropin-releasing hormone pulse generation.

Extracellular glutamate level and NMDA receptor subunit expression in mouse olfactory bulb following nanoparticle-rich diesel exhaust exposure

In this present study, we aimed to investigate the extracellular glutamate level and memory function-related gene expression in the mouse olfactory bulb after exposure of the animals to nanoparticle-rich diesel exhaust (NRDE) with or without bacterial cell wall component. Lipoteichoic acid (LTA), a cell wall component derived from Staphylococcus aureus, was used to induce systemic inflammation. Male BALB/c mice were exposed to clean air (particle concentration, 4.58 microg/m(3)) or NRDE (148.86 microg/m(3)) 5 h per day on 5 consecutive days of the week for 4 wk with or without weekly intraperitoneal injection of LTA. We examined the extracellular glutamate levels in the olfactory bulb using in vivo microdialysis and high-performance liquid chromatography assay. Then, we collected the olfactory bulb to examine the expression of N-methyl-D-aspartate (NMDA) receptor subunits (NR1, NR2A, and NR2B) and calcium/calmodulin-dependent protein kinase (CaMK) IV and cyclic AMP response element binding protein (CREB)-1 using real-time reverse-transcription polymerase chain reaction (RT-PCR). NRDE and/or LTA caused significantly increased extracellular glutamate levels in the olfactory bulb of mice. Moreover, the exposure of mice to NRDE upregulates NR1, NR2A, NR2B, and CaMKIV mRNAs in the olfactory bulb, while LTA upregulates only NR2B and CREB1 mRNAs. These findings suggest that NRDE and LTA cause glutamate-induced neurotoxicity separately and accompanied by changes in the expression of NMDA receptor subunits and related kinase and transcription factor in the mouse olfactory bulb. This is the first study to show the correlation between glutamate toxicity and memory function-related gene expressions in the mouse olfactory bulb following exposure to NRDE.

The cAMP response element-binding protein in the bed nucleus of the stria terminalis modulates the formalin-induced pain behavior in the female rat

Abstract Differences in male and female responses to pain are widely recognized in many species, including humans, but the cerebral mechanisms that generate these responses are unknown. Using the formalin test, we confirmed that proestrus female rats showed nociceptive behavior, modulated by estrogen that was distinct from male rats, particularly during the interphase period. We then explored the brain areas, which were involved in the female pattern of nociceptive behavior. We found that, after a formalin injection and at the time corresponding to the behavioral interphase, the number of phosphorylated cAMP response element-binding protein (pCREB)-immunoreactive neurons observed by immunocytochemistry increased in the dorsolateral division of the bed nucleus of the stria terminalis (BSTLD) in female but not male rats. There were no significant sex differences in pCREB expression following formalin in any region other than the BSTLD. The increased pCREB in female rats was eliminated after an ovariectomy and restored with 17beta-estradiol treatment. Neither an orchidectomy nor 17beta-estradiol treatment affected the pCREB response in male rats. The increase in pCREB expression in the BSTLD in female rats after formalin injection was confirmed with immunoblotting. To determine the role of CREB in the BSTLD, adenovirus-mediated expression of a dominant-negative form of CREB (mCREB) was carried out. The nociceptive behavior during interphase was significantly attenuated by injection of virus carrying mCREB into the BSTLD in female rats but not in male rats. These results suggest a novel role for CREB in the BSTLD as a modulator of the pain response in a female-specific, estrogen-dependent manner.

Strain differences in extracellular amino acid neurotransmitter levels in the hippocampi of major histocompatibility complex congenic mice in response to toluene exposure

OBJECTIVE

The aim of the present study was to investigate the possible role of the major histocompatibility complex locus in neurotransmitter systems in the mouse hippocampus following toluene exposure.

METHODS

We compared the changes in toluene-induced extracellular amino acid neurotransmitter levels in the hippocampi of 2 strains of male congenic mice, C57BL/10 (H-2(b)) and B10.BR/Sg (H-2(k)). In vivo microdialysis was performed in each freely moving mouse after a single intraperitoneal injection of toluene (300 mg/kg), and neurotransmitters in the hippocampal microdialysates were measured using high-performance liquid chromatography.

RESULTS

The basal extracelluar glutamate and glycine levels in the hippocampi of the C57BL mice were significantly higher than those in the B10.BR mice. However, the basal extracellular taurine levels in the hippocampi of the C57BL mice were significantly lower than those in the B10.BR mice. Although no changes in the glutamate levels were observed after toluene injection in either strain, the glycine levels increased significantly after toluene injection in the C57BL mice. On the other hand, significantly lower taurine levels were observed after toluene injection in both strains of mice.

CONCLUSIONS

Our data demonstrate the existence of a relationship between H-2 haplotypes and hippocampal neurotransmitter levels in mice.

DOPA cyclohexyl ester, a DOPA antagonist, blocks the depressor responses elicited by microinjections of nicotine into the nucleus tractus solitarii of rats

Nicotinic cholinergic receptors play a role in cardiovascular regulation in the lower brain stem. Herein, we present evidence that l-3,4-dihydroxyphenylalanine (DOPA), a putative neurotransmitter in the central nervous system, is involved in the depressor response to microinjection of nicotine into the nucleus tractus solitarii (NTS). Microinjection of nicotine into the medial area of the NTS led to decreases in arterial blood pressure and heart rate in anesthetized rats. Mecamylamine, a nicotinic receptor antagonist, microinjected into NTS, blocked the depressor and bradycardic responses to nicotine. Nicotine-induced depressor and bradycardic responses were blocked by DOPA cyclohexyl ester (DOPA CHE), an antagonist for DOPA. DOPA CHE did not modify the action of carbachol on excitatory postsynaptic potential in rat cortical slices. These results suggest that endogenous DOPA is involved in nicotine-induced depressor responses in the NTS of anesthetized rats.

Gonadal steroid hormones maintain the stress-induced acetylcholine release in the hippocampus: simultaneous measurements of the extracellular acetylcholine and serum corticosterone levels in the same subjects

To examine the role of gonadal steroid hormones in the stress responses of acetylcholine (ACh) levels in the hippocampus and serum corticosterone levels, we observed these parameters simultaneously in intact, gonadectomized, or gonadectomized steroid-primed rats. In both sexes of rats, neither gonadectomy nor the replacement of gonadal steroid hormone affected the baseline levels of ACh. However, gonadectomy severely attenuated the stress response of ACh, whereas the replacement of corresponding gonadal hormone successfully restored the response to intact levels. The gonadal hormones affected the serum corticosterone levels in a different manner; the testosterone replacement in orchidectomized rats suppressed the baseline and the stress response of corticosterone levels, whereas the 17beta-estradiol replacement in ovariectomized rats increased the levels. We further found that letrozole or flutamide administration in intact male rats attenuated the stress response of ACh. In addition, flutamide treatment increased the baseline levels of corticosterone, whereas letrozole treatment attenuated the stress response of corticosterone. Moreover, we found a low positive correlation between the ACh levels and corticosterone levels, depending on the presence of gonadal steroid hormone. We conclude that: 1) gonadal steroid hormones maintain the stress response of ACh levels in the hippocampus, 2) the gonadal steroid hormone independently regulates the stress response of ACh in the hippocampus and serum corticosterone, and 3) the sex-specific action of gonadal hormone on the cholinergic stress response may suggest a neonatal sexual differentiation of the septohippocampal cholinergic system in rats.

Gene memory in neuroendocrine and behavioural systems

Several examples of sex steroid hormone actions on rat brain and behaviour show that initial hormone exposures may be followed by enduring neuronal alterations, apparent long after the hormone itself has disappeared. Precedents from non-neuronal systems led to the concept of 'gene memory'. We are studying genomic structural alterations in rat hypothalamic neurons to account for these effects. The preproenkephalin gene is turned on by oestradiol in rat brain neurons in a tissue-specific and genetic sex-specific manner. Levels of preproenkephalin mRNA in the ventromedial hypothalamus correlate tightly with oestradiol-dependent reproductive behaviour. Our results indicate a tissue-specific pattern of DNA methylation in the enkephalin promoter. Putative binding sites for several transcription factors have been described in the preproenkephalin gene promoter; a role for some of these factors in regulating expression of the gene has been demonstrated.

Effects of tributyltin on the emotional behavior of C57BL/6 mice and the development of atopic dermatitis-like lesions in DS-Nh mice

BACKGROUND

Tributyltin (TBT) compounds have been widely used as antifouling biocides on ships and are known to be endocrine disrupters. However, little is known about the influence of TBT on emotion and atopic dermatitis.

OBJECTIVE

We evaluated the effects of TBT on the emotional behavior of C57BL/6 mice and on development of AD-like skin lesions in DS-Nh mice, which develop dermatitis spontaneously under conventional conditions.

METHODS

Five-week-old C57BL/6 mice were fed 0, 50, 100, 200, 300, 400 or 500 ppm TBT diet for 2 weeks. At the end of the exposure period, an open-field test was performed. Six-week-old DS-Nh mice were fed 200 ppm TBT for 14 weeks. Skin eruption scores were checked every week. Skin biopsy was performed from ears.

RESULTS

No significant difference was found in mortality or body weight among the groups receiving 0-200 ppm TBT diet during the course of the study. In the open-field test, mice fed 200 ppm TBT showed lower activity and higher frequency of defecation than did controls. These figures represent a high level of anxiety and fear and were significant in male mice compared with control mice. The skin eruption score was significantly higher in the DS-Nh mice fed TBT than in control mice. In the DS-Nh mice fed TBT, acanthosis of epidermis and infiltration of inflammatory cells in the dermis were more severe than those in controls.

CONCLUSION

TBT diet induced alterations in emotional behavior in C57BL/6 mice, and also induced early onset and deterioration of AD-like lesions in DS-Nh mice.

[Strategies and methods for research on sex- and gender-differences in the rat and human brain]

Strategies and methods for experiments on sex and gender-differences in the rat and human brain are discussed taking our experiments as examples. As sex differences that should be biologically present in "the old brain", control mechanism for the GnRH secretion in the rat, nicotine effects on pulsatile LH secretion in the human and feeding behavior in the rat are mentioned. Then, the absence of sex-difference in the spatial learning memory in the rat that has been fed soft diet, instead of ordinary hard diet, and also the absence of sex-difference in the overall cognitive function in the aged human, in accordance with our concept that gender-differences are produced in response to environmental stimuli in "the new brain", are mentioned.

Sex difference in the 24-h acetylcholine release profile in the premotor/supplementary motor area of behaving rats

The sex differences in various motor functions suggest a sex-specific neural basis in the nonprimary or primary motor area. To examine the sex difference in the 24-h profile of acetylcholine (ACh) release in the rostral frontal cortex area 2 (rFr2), which is equivalent to the premotor/supplementary motor area in primates, we performed an in vivo microdialysis study in both sexes of rats fed pelleted or powdered diet. The dialysate was automatically collected from the rFr2 for 24 h under freely moving conditions. Moreover, the number of cholinergic neurons in the nucleus basalis magnocellularis (NBM) was examined. Further, to confirm the relation between ACh release in the rFr2 and motor function, the spontaneous locomotor activity was monitored for 24 h. Both sexes showed a distinct 24-h rhythm of ACh release, which was high during the dark phase and low during the light phase. Female rats, however, showed a greater ACh release and more cholinergic neurons in the NBM than male rats. Similarly, spontaneous locomotor activity also showed a 24-h rhythm, which paralleled the changes in ACh release in both sexes, and these changes were again greater in female rats than in male rats. In addition, feeding with powdered diet significantly increased the ACh release and spontaneous locomotor activity. The present study is the first to report the sex difference in the 24-h profile of ACh release in the rFr2 in rats. The sex specific ACh release in the rFr2 may partly contribute to the sex difference in motor function in rats.

Bisphenol A induces transforming growth factor-β3 mRNA in the preoptic area: A cDNA expression array and Northern blot study

To gain better understanding of the effects of bisphenol A (BPA) in the adult brain, a cDNA expression array was used to screen possible candidates for BPA-inducible genes in the medial preoptic area (MPOA). Adult ovariectomized rats were given a subcutaneous injection of 10 mg BPA or sesame oil alone as a control. Twenty-four hours after the injection, the MPOAs were dissected and total RNAs were extracted. When expression levels of cDNAs derived from pooled samples were compared to controls, the expression levels of some genes in BPA-injected rats appeared to be different from those in sesame oil-injected rats. Among the candidate genes, we focused on an increase in the expression of transforming growth factor (TGF)-beta3 mRNA. To quantify the change in TGF-beta3 mRNA by BPA, we examined the effects of 10 mg BPA (n=6), 1 microg 17beta-estradiol (n=6), or oil injection (n=6) on the expression of TGF-beta3 mRNA in the MPOA of ovariectomized rats by Northern blot. The TGF-beta3 mRNA level in the MPOA of BPA-injected rats was significantly increased compared to the level in oil-injected rats (p<0.05). Injection of 1 microg 17beta-estradiol did not have any significant effect. The results suggest that, in the adult female rat, BPA acts on the MPOA by altering the expression of the TGF-beta3 gene in a manner distinct from that of estrogen.

Effects of neonatal testosterone treatment on sex differences in formalin-induced nociceptive behavior in rats

There are sex differences in nociceptive behavior induced by formalin in rats. To determine whether these sex differences are the result of the sexual differentiation of the brain, that is masculinization and defeminization [A.P. Arnold, R.A. Gorski, Gonadal steroid induction of structural sex differences in the central nervous system, Annu. Rev. Neurosci. 7 (1984) 413-442; M.M. McCarthy, A.T.M. Konkle, When is a sex difference not a sex difference? Front Neuroendocrinol. 26 (2005) 85-102], some female rats were injected with testosterone propionate (TP, 100 microg/25 microl/rat) on the day of birth and on the following day. As controls, other female rats and all male rats were injected with the same volume of sesame oil. They were castrated at the age of 8 weeks, and implanted with a silicon tube containing 20% of 17beta-estradiol or cholesterol. Two weeks after the implantation, rats were injected with 50 microl of 2% formalin in the right hind paw and their behavioral changes were observed for 1h. In cholesterol-implanted rats, all rats exhibited three typical phases of pain response and there were no significant differences in the scores of nociceptive behavior. In 17beta-estradiol implanted rats, female and TP-treated female rats had a significantly higher score of nociceptive behavior than male rats. These results indicate that estrogen produces sex differences in nociceptive behavior induced by formalin, and suggest that these differences are not due to the sexual differentiation of the brain, since the dose and the timing of the TP treatment effectively defeminize and masculinize female rats. Alternatively, sexual differentiation of the brain response to formalin-induced nociceptive behavior may be different from ordinary sexual differentiation.

Sex differences in the basolateral amygdala: the extracellular levels of serotonin and dopamine, and their responses to restraint stress in rats

The sex difference in the emotional response to stress suggests a sex-specific stress response in the amygdala. To examine the sex difference in extracellular levels of serotonin (5HT) and dopamine (DA) in the basolateral amygdala (BLA) and their responses to restraint stress, in vivo microdialysis studies were performed in male and female rats. In experiment I, dialysates were collected from the BLA at 15-min intervals under the freely moving condition. Mean extracellular levels of 5HT or DA in the BLA were higher in male rats than in female rats. In experiment II, rats were subjected to restraint stress for 60 min to examine the stress response of 5HT or DA levels. Although restraint stress significantly increased extracellular 5HT levels in both sexes of rats, female rats showed a greater response than male rats. Moreover, restraint stress significantly increased extracellular DA levels in female rats, but not in male rats. In experiment III, rats were subjected to restraint stress for 30 min to examine behavioral responses to restraint stress. Although no sex difference was observed in the number of audible vocalizations, male rats defecated a larger number of fecal pellets than female rats. In experiment IV, rats were tested for freezing behavior to examine contextual fear responses. Conditioned male rats showed a longer freezing time than conditioned female rats. We found sex differences in the extracellular levels of 5HT and DA in the BLA and their responses to restraint stress, which may be involved in the sex-specific emotional response to stress in rats.

L-3,4-dihydroxyphenylalanine-induced c-Fos expression in the CNS under inhibition of central aromatic L-amino acid decarboxylase

L-3,4-dihydroxyphenylalanine (DOPA) is a neurotransmitter candidate. To map the DOPAergic system functionally, DOPA-induced c-Fos expression was detected under inhibition of central aromatic L-amino acid decarboxylase (AADC). In rats treated with a central AADC inhibitor, DOPA significantly increased the number of c-Fos-positive nuclei in the paraventricular nuclei (PVN) and the nucleus tractus solitarii (NTS), and showed a tendency to increase in the supraoptic nuclei (SON), but not in the striatum. On the other hand, DOPA with a peripheral AADC inhibitor elevated the level of c-Fos-positive nuclei in the four regions, suggesting that DOPA itself induces c-Fos expression in the SON, PVN and NTS. In rats treated with 6-hydroxydopamine (6-OHDA) to lesion the nigrostriatal dopamine (DA) pathway, DOPA significantly induced c-Fos expression in the four regions under the inhibition of peripheral AADC. However, under the inhibition of central AADC, DOPA did not significantly increase the number of c-Fos-positive nuclei in the four regions, suggesting that DOPA at least in part induces c-Fos expression through its conversion to DA. It was likely that the 6-OHDA lesion enhanced the response to DA, but attenuated that to DOPA itself. In conclusion, we proposed that the SON, PVN and NTS include target sites for DOPA itself.

Effects of p-nonylphenol and 4-tert-octylphenol on the anterior pituitary functions in adult ovariectomized rats

p-Nonylphenol (NP) and 4-tert-octylphenol (OP) are known to mimic the action of estrogens as endocrine disruptors. However, their acute effects on the pituitary and the hypothalamus functions in vivo have been uncertain. We therefore determined their effects on the anterior pituitary, in particular, gonadotropin secretion. Two weeks after ovariectomy, the rats were given a subcutaneous injection of 10 mg NP, 10 mg OP, 10 mg bisphenol A, 1 microg 17beta-estradiol, or sesame oil alone as control. Twenty-four hours after the treatment, the expression of progesterone receptor mRNA in the anterior pituitary and the level of luteinizing hormone (LH), follicle-stimulating hormone, and prolactin were determined. The expression of progesterone receptor mRNA in the anterior pituitary was significantly increased by either NP, OP, bisphenol A, or estradiol, but bisphenol A was less effective. The level of LH was significantly decreased by either NP or OP, but not by bisphenol A and estradiol. Only estradiol significantly increased the level of prolactin. The level of follicle-stimulating hormone was unchanged by any of the treatments. To check the effects of NP and OP on pulsatile LH secretion, blood samplings were done at 6-min intervals for 3 h. Twenty-four hours after treatment in ovariectomized adult rats, we found that the injection of NP significantly decreased the amplitude of LH pulses and the mean LH concentrations, but not the frequency of LH pulses. The injection of OP significantly decreased the mean LH concentrations without affecting the frequency and amplitude of the LH pulses. Finally, the rats given an injection of NP or sesame oil were intravenously injected with 50 ng of gonadotropin-releasing hormone (GnRH) to check whether NP affected the LH secretory responsiveness of the anterior pituitary to GnRH. We found that the responsiveness to GnRH in NP-injected rats was significantly attenuated compared to the sesame oil-injected rats. The present study suggests that NP, even with a single injection, suppresses the pulsatile LH secretion in adult ovariectomized rats, probably by affecting the anterior pituitary level.

Feeding with powdered diet after weaning increases visuospatial ability in association with increases in the expression of N-methyl-d-aspartate receptors in the hippocampus of female rats

We determined whether feeding with powdered diet improved the visuospatial ability in female rats by checking the expression of N-methyl-D-aspartate receptor (NMDAR) subunit 1 (NR1) mRNA in the hippocampus. In rats fed standard pelleted diet, males performed better than females in a radial 8-arm maze task as we reported previously. We found that the expression of NR1 mRNA, which may be the key mediator in visuospatial ability in the hippocampus, was also higher in males than in females. However, in rats fed powdered diet, no sex difference was seen in the radial 8-arm maze task and the expression of NR1 mRNA in the hippocampus, since feeding with powdered diet improved the visuospatial ability with increases in the expression of NR1 mRNA in the hippocampus in females. We suggest that the sex difference in visuospatial ability is at least in part due to feeding conditions.

Sex difference in the response of melanin-concentrating hormone neurons in the lateral hypothalamic area to glucose, as revealed by the expression of phosphorylated cyclic adenosine 3',5'-monophosphate response element-binding protein

Because there are sex differences in feeding behavior in rats, we looked for a possible sex difference in the response to glucose of melanin-concentrating hormone (MCH) neurons in the lateral hypothalamic area using phosphorylated cAMP response element-binding protein (pCREB) as a marker of neural activity. Intact male rats and female rats at diestrus 2, proestrus, or estrus were fed normally or fasted for 48 h and injected with saline or glucose (400 mg/kg). Thereafter, preparations were subjected to immunohistochemical processing for the double staining of MCH and pCREB. Fasting increased the ratio of MCH neurons with pCREB (double-stained cells) in both male and female rats. In fasted rats, glucose injection decreased the ratio of double-stained cells more promptly in females than in males. The magnitude of decrease caused by glucose was greater at proestrus and estrus than at diestrus 2. Gonadectomy in males enhanced and in females attenuated the response of MCH neurons to glucose. Testosterone and estrogen replacement in males and females, respectively, restored the response of MCH neurons to glucose. The demonstrated sex differences in the response of MCH neurons to glucose correlated well with the gonadal steroid milieu; thus, MCH neurons may play an important role in sex differences in feeding behavior.

Nicotine inhibits pulsatile luteinizing hormone secretion in human males but not in human females, and tolerance to this nicotine effect is lost within one week of quitting smoking

CONTEXT AND OBJECTIVE

Despite having increased knowledge of the adverse reproductive effects of smoking, it is unclear whether nicotine affects the pulsatile LH secretion in humans. We addressed this issue in male and female smokers and nonsmokers.

SUBJECTS AND METHODS

Twenty-nine male and 16 female nonsmokers and smokers were recruited as volunteers. In male smokers, nicotine effect was also studied before and after quitting smoking. In females, cyclic ovulatory function was assessed by measuring basal body temperature, and sampling studies were performed during the follicular phase. In the morning of the sampling day, an iv catheter was inserted into an anterobrachial vein, and blood samples (1.0-1.5 ml each) were taken at 10-min intervals for 480 min, during which, at 240 min, nicotine was administered via a transdermal patch (Nicotinell transdermal therapeutic system) containing 17.5 mg nicotine. Plasma LH was measured by immunoradiometric assay kits.

RESULTS

Nicotine significantly lengthened the interpulse interval of pulsatile LH secretion in male nonsmokers but not in female nonsmokers. In male smokers, nicotine did not lengthen the interpulse interval, and in female smokers it was also ineffective. After quitting cigarette smoking in male smokers, the refractory to nicotine effect disappeared within 1 wk.

CONCLUSIONS

We conclude that nicotine inhibits pulsatile LH secretion only in males, and the tolerance developed to the nicotine effect disappears within 1 wk of quitting cigarette smoking. However, we cannot deny the possibility that nicotine effect would have been detected in females if more subjects had been studied.

GnRH antagonist-induced down-regulation of the mRNA expression of pituitary receptors: comparisons with GnRH agonist effects

In order to compare the mechanism for the down regulation of the mRNA expression of pituitary receptors induced by GnRH antagonist (GnRHant) to that by GnRH agonist (GnRHa), we examined the effects of GnRHant (Cetrorelix, 333 mug/kg/day), GnRHa (leuprolide depot, 333 microg/kg), and GnRHant combined with GnRHa on LH response to exogenous GnRH, pituitary LH content, LH beta subunit mRNA, and GnRH receptor (GnRH-R) mRNA levels at 2, 5, 24, 72 hours, and 7 days after the treatment in ovariectomized rats. GnRHant significantly decreased serum LH, the LH response of the pituitary to exogenous GnRH, and the pituitary LH content compared to the control treatment, though GnRHa significantly increased serum LH. GnRHant with GnRHa significantly diminished the GnRHa-induced flare-up phenomenon. GnRHant significantly decreased LH beta mRNA and GnRH-R mRNA levels, but the magnitude of the decrease in these mRNA levels by GnRHant was significantly less than those by GnRHa until 72 hours following treatment. Prolonged treatment of GnRHant caused a marked inhibition of LH beta mRNA and GnRH-R mRNA expression, similar to that caused by GnRHa. Combination treatment with GnRHa and GnRHant was demonstrated to decrease LH beta mRNA and GnRH-R mRNA levels as much as GnRHa alone and GnRHant alone over 7 days of the treatment. The present study showed differences between GnRHant and GnRHa treatment in the reduction of GnRH-R mRNA levels up to 72 hours after the treatment, and indicated that the suppression of GnRH-R mRNA by GnRHant was the maximal by GnRHa 7 days after the treatment because more profound suppression was not observed upon additional treatment with GnRHa. The findings in the present study support the hypothesis that the mechanism by which GnRHant leads to down-regulation of the mRNA expression of pituitary receptors is similar to that of GnRHa.

Sex and housing conditions affect the 24-h acetylcholine release profile in the hippocampus in rats

To examine the sex difference in the 24-h profile of the acetylcholine (ACh) release in the hippocampus, in addition to the effects of housing conditions on this profile, we performed an in vivo microdialysis study in intact male and cycling female rats that had been living in large (diameter=35 cm) or small (diameter=19 cm) cylindrical cages. Each rat was individually housed in a cage for 4 days. On the day of the experiment, the dialysate was collected from the dorsal hippocampus at 20-min intervals and sequential blood samples were simultaneously obtained at 2-h intervals, under the freely moving condition for more than 24 h. ACh in the dialysates was measured by the high performance liquid chromatography system, while the corticosterone concentration in the serum was measured by radiostereoassay. Although the ACh release showed a clear daily rhythm in both sexes of rats, the amount of ACh released in female rats was significantly lower than that in males. Furthermore, the housing in the small cage significantly attenuated the ACh release during the dark phase in male rats, but not in female rats. Conversely, the serum corticosterone concentration showed a clear daily rhythm and the mean concentration of serum corticosterone in female rats was significantly higher than that in male rats. Housing in the small cage did not affect the corticosterone rhythm in either sex. These results reveal a sex difference in the 24-h profile of the ACh release, which suggests vulnerability of the cholinergic system in male rats depending on its housing conditions.

Feeding with powdered diet after weaning affects sex difference in acetylcholine release in the hippocampus in rats

We have reported in the past that female rats fed a powdered diet showed better spatial learning and memory functions than female rats a fed pelleted diet. In the present study, we examined the effects of feeding with powdered diet on acetylcholine release in the hippocampus in both sexes of rats. After weaning (3 weeks of age), rats were fed either standard pelleted diet or powdered diet, and after maturation (9-12 weeks of age), they were used in an in vivo microdialysis study, in which no eserine (a cholinesterase inhibitor) was added to the perfusate. The dialysate was collected from the dorsal hippocampus at 20-min intervals under freely moving conditions for more than 24 h. Acetylcholine in the dialysate was measured by high performance liquid chromatography. As we reported previously, the acetylcholine release showed a clear daily rhythm in both sexes, and males showed significantly greater acetylcholine release in the hippocampus than females in rats fed pelleted diet. Conversely, in rats fed powdered diet, no sex difference in the acetylcholine release was observed, since feeding with powdered diet significantly increased the acetylcholine release only in females. To further examine the number of cholinergic neurons in the medial septum and horizontal limb of the diagonal band of Broca, immunocytochemistry for choline acetyltransferase was performed in both sexes of rats fed either standard pelleted diet or powdered diet. However, neither sex nor feeding conditions affect the number of choline acetyltransferase immunoreactive cells in the areas. These results suggest that powdered diet after weaning enhances spontaneous acetylcholine release in the hippocampus in female rats without changes in the number of cholinergic neurons in the areas. It is possible that this effect of feeding contributes to improve the performance in spatial learning and memory functions in female rats fed powdered diet.

Intracerebroventricular injection of corticotropin-releasing hormone receptor antagonist blocks the suppression of pulsatile luteinizing hormone secretion induced by neuromedin U in ovariectomized rats after 48hours of fasting

We recently reported that neuromedin U (NMU) and fasting synergistically suppressed the pulsatile LH secretion, even though NMU has been shown to act as a satiety factor. In the present study, we examined whether this synergistic effect on the pulsatile LH secretion was mediated via corticotropin-releasing hormone (CRH) neurons. Adult ovariectomized (OVX) rats were stereotaxically implanted with a guide cannula into the third ventricle. After 2 weeks of recovery, blood samples were taken under freely-moving conditions at 6-min intervals for 180 min from 09:00 to 12:00 h in OVX rats that had been fasted for 48 h. After first 60 min of blood sampling, astressin (2 nmol/3 microl), a CRH receptor antagonist, dissolved in artificial cerebrospinal fluid (aCSF) or aCSF (3 microl) was injected as a control into the third ventricle. Thirty minutes after the first injection, the rats were injected with NMU (1 nmol/3 microl) into the third ventricle. We found that pre-treatment with astressin completely blocked the prolongation of the interpulse interval, which should be induced by NMU. We confirmed that a single intracerebroventricular injection of astressin per se did not affect the pulsatile LH secretion. The present study suggests that synergistic inhibitory effect of NMU and fasting on the pulsatile LH secretion is at least in part mediated via CRH neurons.

Nicotine inhibition of pulsatile GnRH secretion is mediated by GABAA receptor system in the cultured rat embryonic olfactory placode

In past work, we suggested that nicotine inhibition of in vivo pulsatile LH release is not mediated by opiate receptors known to be involved in the inhibition of LH release. In the present study, we examined whether nicotine inhibits the pulsatile gonadotropin-releasing hormone (GnRH) release, and whether this inhibition of GnRH release by nicotine is mediated by the GABA receptor system, by checking in vitro pulsatile GnRH release from cultured GnRH neurons obtained from olfactory placodes of rat embryos at E13.5. The mean interpulse interval of pulsatile GnRH release into the medium was 34.2+/-2.0 min in the control period and increased to 95.3+/-19.0 min (n=6) in the period of nicotine treatment at a concentration of 500 nM, showing an inhibitory effect of nicotine on pulsatile GnRH release. The GABA(A) receptor antagonist bicuculline used alone at a concentration of 20 microM caused no significant changes in the pulsatile GnRH release, but when used in combination with 500 nM of nicotine, bicuculline blocked the nicotine inhibition of GnRH release. In a separate experiment, nicotine treatment at a concentration of 500 nM significantly increased GABA release. These results suggest that, in the cultured embryonic olfactory placode, nicotine stimulates GABA release, which then inhibits GnRH release through GABA(A) receptor system.