Estrogen-induced memory enhancements are blocked by acute bisphenol A in adult female rats: role of dendritic spines

Acute effects of bisphenol (BPA), an environmental chemical, on estradiol (17α or β-E2)-dependent recognition memory and dendritic spines in the medial prefrontal cortex and hippocampus were investigated in adult female rats. Ovariectomized rats received BPA 30 min before or immediately after a sample trial (viewing objects), and retention trials were performed 4 h later. Retention trials tested discrimination between old and new objects (visual memory) or locations (place memory). When given immediately after the sample trial, BPA, 1-400 μg/kg, did not alter recognition memory, but 1 and 40 μg/kg BPA, respectively, blocked 17β-E2-dependent increases in place and visual memory. When ovariectomized rats were tested with 17α-E2, 1 μg/kg BPA blocked place memory, but up to 40 μg did not block visual memory. BPA, given to cycling rats at 40 μg/kg, blocked visual, but not place, memory during proestrus when 2 h intertrial delays were given. Spine density was assessed at times of memory consolidation (30 min) and retention (4 h) after 17β-E2 or BPA + 17β-E2. In prefrontal cortex, BPA did not alter E2-dependent increases. In the hippocampus, BPA blocked E2 increases in basal spines at 4 h and was additive with E2 at 30 min. Thus, these novel data show that doses of BPA, below the current Environmental Protection Agency safe limit of 50 μg/kg, rapidly alter neural functions dependent on E2 in adult female rats.

Bisphenol-A impairs memory and reduces dendritic spine density in adult male rats

Exposure to Bisphenol-A (BPA), an endocrine disruptor used in plastics, occurs in the United States on a daily basis. Recent studies suggest exposure during development causes memory deficits later in life; however, the ramifications of exposure in adulthood are unclear. We examined the effects of acute BPA administration (40 μg/kg) on memory and synaptic plasticity in adult male rats. BPA significantly impaired both visual and spatial memory and decreased dendritic spine density on pyramidal cells in CA1 and the medial prefrontal cortex (mPFC). Additionally, BPA significantly decreased PSD-95, a synaptic marker, in the hippocampus and increased cytosolic pCREB, a transcription factor, in mPFC. Together, these findings show that a single dose of BPA, below the USEPA reference safe daily limit of 50 μg/kg/day, may block the formation of new memories by interfering with neural plasticity processes in the adult brain.

Cocaine alters dendritic spine density in cortical and subcortical brain regions of the postpartum and virgin female rat

Cocaine use during pregnancy induces profound neural and behavioral deficits in both mother and offspring. The present study was designed to compare the effects of cocaine exposure on spine density of postpartum and virgin female rat brains. Timed, pregnant, primiparous rats were injected with either cocaine (30 mg/kg) or saline, once daily, from gestational day 8 to 20. Twenty-four hours after giving birth, dam brains were processed for Golgi-impregnation. Virgin females were also injected with the same dose of cocaine or saline for 12 days and sacrificed 24 h after the last injection for comparison. Pregnant rats had significantly greater spine density in the medial amygdala (MeA) and medial preoptic area (MPOA) and lower spine density in CA1 than virgin females independent of cocaine treatment. Cocaine significantly increased dendritic spine density on the apical branch of pyramidal cells in the prefrontal cortex (PFC, 15%), both apical (13%) and basal (14.8%) branches of CA1 and cells in the MeA (28%) of pregnant rats. In the MPOA, cocaine administration resulted in a decrease in dendritic spine density (14%) in pregnant rats. In virgin females, cocaine had fewer effects but did increase dendritic spine density on both branches of CA1 neurons and in the MeA. The present study is the first to demonstrate that spine density differs between pregnant and virgin females and that pregnancy makes the brain more vulnerable to cocaine, which has important clinical implications.

Prenatal cocaine exposure increases anxiety, impairs cognitive function and increases dendritic spine density in adult rats: influence of sex

Cocaine exposure during pregnancy can impact brain development and have long-term behavioral consequences. The present study examined the lasting consequences of prenatal cocaine (PN-COC) exposure on the performance of cognitive tasks and dendritic spine density in adult male and female rats. From gestational day 8 to 20, dams were treated daily with 30 mg/kg (ip) of cocaine HCl or saline. At 62 days of age, offspring were tested consecutively for anxiety, locomotion, visual memory and spatial memory. PN-COC exposure significantly increased anxiety in both sexes. Object recognition (OR) and placement (OP) tasks were used to assess cognitive function. Behavioral tests consisted of an exploration trial (T1) and a recognition trial (T2) that were separated by an inter-trial delay of varying lengths. Male PN-COC subjects displayed significantly less time investigating new objects or object locations during T2 in both OR and OP tasks. By contrast, female PN-COC subjects exhibited impairments only in OR and only at the longest inter-trial delay interval. In addition, gestational cocaine increased dendritic spine density in the prefrontal cortex and nucleus accumbens in both genders, but only females had increased spine density in the CA1 region of the hippocampus. These data reveal that in-utero exposure to cocaine results in enduring alterations in anxiety, cognitive function and spine density in adulthood. Moreover, cognitive deficits were more profound in males than in females.

S 24795 limits beta-amyloid-alpha7 nicotinic receptor interaction and reduces Alzheimer's disease-like pathologies

BACKGROUND

Beta-amyloid (Abeta) enables Alzheimer's disease (AD) plaque and neurofibrillary pathogenesis. Soluble Abeta promotes intraneuronal Abeta aggregates and tau phosphorylation by interacting with alpha7 nicotinic receptors (alpha7nAChRs). The current study assessed whether the novel alpha7nAChR partial agonist 2-(2-(4-bromophenyl)-2-oxoethyl)-1-methyl pyridinium (S 24795) could reduce AD-like pathologies by interfering with Abeta-alpha7nAChR interaction.

METHODS

We compared the in vitro effect of S 24795, memantine, galantamine, and Abeta(12-28) on Abeta(42)-alpha7nAChR interaction in rat hippocampal synaptosomes. We further evaluated the effect of S 24795 on Abeta(42)-induced tau phosphorylation with rat hippocampal synaptosomes in vitro. Effects of S 24795 on Abeta(42) immunostaining, Abeta(42)-alpha7nAChR interaction, and/or Abeta(42)-mediated reduction of calcium (Ca(2+)) influx through alpha7nAChR and N-methyl-d-aspartate receptor (NMDAR) were assessed in Abeta(42)-incubated organotypic brain slices and intracerebroventricularly (ICV) Abeta(42)-injected mouse brain.

RESULTS

Preincubation with S 24795 in vitro reduces Abeta(42)-alpha7nAChR interaction and Abeta(42)-induced tau phosphorylation. In organotypic brain slice cultures and in an ICV Abeta(42) injection in vivo model, S 24795 reduces Abeta(42)-alpha7nAChR association and Abeta(42) immunostaining. S 24795 also normalizes Ca(2+) fluxes through both alpha7nAChR and NMDAR channels in Abeta(42)-infused mouse brains and Abeta(42)-exposed organotypic cortical slices. Unlike S 24795 and Abeta(12-28), galantamine or memantine minimally affect Abeta(42)-alpha7nAChR coupling and Abeta(42)-mediated reduction of alpha7nAChR- and NMDAR-mediated Ca(2+) influx.

INTERPRETATION

Drugs like S 24795 that disrupt Abeta(42)-alpha7nAChR interaction might alleviate Abeta(42)-mediated synaptic dysfunction and block AD-like pathologies.

Prenatal cocaine increases dendritic spine density in cortical and subcortical brain regions of the rat

Alterations in dendritic spine density following prenatal cocaine exposure were examined in the present study. Timed pregnant rats were injected daily with 30 mg/kg cocaine or saline during gestation. At postnatal day 21, male and female animals were separated and spine density was assessed following Golgi impregnation. In prenatal cocaine-exposed rats, significant increases in dendritic spine density were observed on pyramidal cells in the CA1 region of the hippocampus, basal dendrites of layer II/III of the medial prefrontal cortex, medium spiny neurons of the striatum and the core of the nucleus accumbens, as well as in neurons of the ventromedial hypothalamic nucleus. No differences were observed in either apical or basal dendrites of pyramidal cells in layer III of the sensory cortex or layer V of the medial prefrontal cortex, or in apical dendrites of layer II/III pyramidal cells of the medial prefrontal cortex. Moreover, there were no sex differences in any region examined. These results demonstrate that prenatal cocaine exposure increases spine density in many brain regions at postnatal day 21, and this effect is independent of sex.

High-affinity naloxone binding to filamin a prevents mu opioid receptor-Gs coupling underlying opioid tolerance and dependence

Ultra-low-dose opioid antagonists enhance opioid analgesia and reduce analgesic tolerance and dependence by preventing a G protein coupling switch (Gi/o to Gs) by the mu opioid receptor (MOR), although the binding site of such ultra-low-dose opioid antagonists was previously unknown. Here we show that with approximately 200-fold higher affinity than for the mu opioid receptor, naloxone binds a pentapeptide segment of the scaffolding protein filamin A, known to interact with the mu opioid receptor, to disrupt its chronic opioid-induced Gs coupling. Naloxone binding to filamin A is demonstrated by the absence of [³H]-and FITC-naloxone binding in the melanoma M2 cell line that does not contain filamin or MOR, contrasting with strong [³H]naloxone binding to its filamin A-transfected subclone A7 or to immunopurified filamin A. Naloxone binding to A7 cells was displaced by naltrexone but not by morphine, indicating a target distinct from opioid receptors and perhaps unique to naloxone and its analogs. The intracellular location of this binding site was confirmed by FITC-NLX binding in intact A7 cells. Overlapping peptide fragments from c-terminal filamin A revealed filamin A_2561-2565 as the binding site, and an alanine scan of this pentapeptide revealed an essential mid-point lysine. Finally, in organotypic striatal slice cultures, peptide fragments containing filamin A_2561-2565 abolished the prevention by 10 pM naloxone of both the chronic morphine-induced mu opioid receptor–Gs coupling and the downstream cAMP excitatory signal. These results establish filamin A as the target for ultra-low-dose opioid antagonists previously shown to enhance opioid analgesia and to prevent opioid tolerance and dependence.

Chronic stress and neural function: accounting for sex and age

Cognitive responses to stress follow the temporally dependent pattern originally established by Selye (1) wherein short-term stressors elicit adaptive responses whereas continued stress (chronic) results in maladaptive changes--deleterious effects on physiological systems and impaired cognition. However, this pattern for cognitive effects appears to apply to only half the population (males) and, more specifically, to young, adult males. Females show different cognitive responses to stress. In contrast to impaired cognition in males after chronic stress, female rodents show enhanced performance on the same memory tasks after the same stress. Not only cognition, but anxiety, shows sex-dependent changes following chronic stress--stress is anxiolytic in males and anxiogenic in females. Moreover, behavioral responses to chronic stress are different in developing as well as aging subjects (both sexes) as compared to adults. In aged rats, chronic stress enhances recognition memory in both sexes, does not alter spatial memory, and anxiety effects are opposite to young adults. When pregnant dams are exposed to chronic stress, at adulthood the offspring display yet different consequences of stress on anxiety and cognition, and, in contrast to adulthood when the behavioral effects of stress are reversible, prenatal stress effects appear enduring. Changing levels of estradiol in the sexes over the lifespan appear to contribute to the differences in response to stress. Thus, theories of stress dependent modulations in CNS function--developed solely in male models, focused on peripheral physiological processes and tested in adults--may require revision when applied to a more diverse population (age- and sex-wise) at least in relation to the neural functions of cognition and anxiety. Moreover, these results suggest that other stressors and neural functions should be investigated to determine whether age, sex and gonadal hormones also have an impact.

Estrogen-modulated frontal cortical CaMKII activity and behavioral supersensitization induced by prolonged cocaine treatment in female rats

RATIONALE

Females have been demonstrated repeatedly to be more sensitive to cocaine. The role of the frontal cortex (FCX) in mediating behavioral sensitization and the underlying signaling pathways are unclear.

OBJECTIVE

The study was designed to characterize the role of FCX calcium/calmodulin-dependent protein kinase II (CaMKII) activity in the behavioral supersensitization observed in female rats after prolonged cocaine exposure.

MATERIALS AND METHODS

Intact female rats that received cocaine for 9 days followed by 7 days of drug withdrawal constituted the model used for studying the mechanism of supersensitization.

RESULTS

This cocaine withdrawal treatment resulted in behavioral supersensitization in intact female rats as indicated by an enhanced behavioral response to cocaine challenge assessed on day 16 (7-day withdrawal) and compared to the response on day 9 of cocaine treatment. This treatment regimen did not lead to supersensitization in male or in ovariectomized (OVX) rats. Administration of estrogen to OVX rats restored behavioral supersensitivity to repeated cocaine. FCX CaMKII activity was significantly altered by cocaine in females, and this effect was related to estrogen's presence; cocaine-induced changes in striatal CaMKII activity were, however, less estrogen-sensitive. Furthermore, estrogen-modulated FCX CaMKII activity in cocaine-supersensitized rats was dependent on D(1) dopamine receptor activation.

CONCLUSION

Estrogen-modulated D(1) dopamine receptor activity mediates the effects of prolonged cocaine exposure on FCX CaMKII, and this, in turn, may contribute to the development of behavioral supersensitivity to repeated cocaine treatment in intact female rats.

Impaired Recognition Memory and Decreased Prefrontal Cortex Spine Density in Aged Female Rats

Aged F344 female rats (21 months) showed decreased performance, as compared to young rats (4 months), on an object recognition memory task. Golgi impregnation measured dendritic spine density of pyramidal neurons in the prefrontal cortex (layer II-III), a brain area important for recognition memory. Densities of spines in aged rats were 16% lower in tertiary, apical dendrites, but not significantly different in secondary basal dendrites. Concurrent measures of memory and spine density in the young and aged subjects show that age-related declines in recognition memory are associated with decreased cortical spine density.

Ovariectomized rats show decreased recognition memory and spine density in the hippocampus and prefrontal cortex

Effects of ovariectomy (OVX) on performance of the memory tasks, Object Recognition (OR) and Object Placement (OP), and on dendritic spine density in pyramidal neurons in layer II/III of the prefrontal cortex and the CA1 and CA3 regions of the hippocampus were determined. OVX was associated with a significant decline in performance of the memory tasks as compared to intact rats beginning at 1 week post OVX for OR and 4 weeks post OVX for OP. Golgi impregnation at 7 weeks post OVX showed significantly lower spine densities (17-53%) in the pyramidal neurons of the medial prefrontal cortex and the CA1, but not the CA3, region of the hippocampus in OVX compared to intact rats. These results suggest that cognitive impairments observed in OVX rats may be associated with morphological changes in brain areas mediating memory.

Dietary phytoestrogens enhance spatial memory and spine density in the hippocampus and prefrontal cortex of ovariectomized rats

Long-term maintenance of ovariectomized rats (9 weeks) on chow containing high phytoestrogen levels (Purina LabDiet 5001) as compared to chow with minimal phytoestrogens (Harlan 2016 Teklad) was associated with better performance of the spatial memory task, object placement, increased dendritic spine density in CA1 and prefrontal cortex pyramidal neurons, and higher uterine weights. Object recognition memory, anxiety on an elevated plus maze and body weight were unaffected by phytoestrogen levels in the diet.

Sexually dimorphic effects of prenatal stress on cognition, hormonal responses, and central neurotransmitters

Exposure to stress during gestation results in physiological and behavioral alterations that persist into adulthood. This study examined the effects of prenatal stress on the postnatal expression of sexually differentiated cognitive, hormonal, and neurochemical profiles in male and female rats. Pregnant dams were subjected to restraint stress three times daily for 45 min during d 14-21 of pregnancy. The offspring of control and prenatally stressed dams were tested for anxiety-related and cognitive behaviors, stress and gonadal steroid hormone levels, as well as monoamines and metabolite levels in selected brain regions. Postnatal testosterone levels (measured at 1 and 5 d) did not differ between controls and prenatally stressed animals. In adulthood, the serum corticosterone response to stress was attenuated in prenatally stressed females, eliminating the sex difference normally observed in this parameter. Prenatally stressed females exhibited higher anxiety levels, evidenced by longer open field entry latencies. Prenatal stress had no effect on object recognition memory, but eliminated the advantage normally seen in the male performance of a spatial memory task. Neurochemical profiles of prenatally stressed females were altered toward the masculine phenotype in the prefrontal cortex, amygdala, and hippocampus. Thus, prenatal stress altered subsequent cognitive, endocrine, and neurochemical responses in a sex-specific manner. These data reinforce the view that prenatal stress affects multiple aspects of brain development, interfering with the expression of normal behavioral, neuroendocrine, and neurochemical sex differences. These data have implications for the effects of prenatal stress on the development of sexually dimorphic endocrine and neurological disorders.

Prevention of stress-induced morphological and cognitive consequences

Atrophy and dysfunction of the human hippocampus is a feature of aging in some individuals, and this dysfunction predicts later dementia. There is reason to believe that adrenal glucocorticoids may contribute to these changes, since the elevations of glucocorticoids in Cushing's syndrome and during normal aging are associated with atrophy of the entire hippocampal formation in humans and are linked to deficits in short-term verbal memory. We have developed a model of stress-induced atrophy of the hippocampus of rats at the cellular level, and we have been investigating underlying mechanisms in search of agents that will block the atrophy. Repeated restraint stress in rats for 3 weeks causes changes in the hippocampal formation that include suppression of 5-HT1A receptor binding and atrophy of dendrites of CA3 pyramidal neurons, as well as impairment of initial learning of a radial arm maze task. Because serotonin is released by stressors and may play a role in the actions of stress on nerve cells, we investigated the actions of agents that facilitate or inhibit serotonin reuptake. Tianeptine is known to enhance serotonin uptake, and we compared it with fluoxetine, an inhibitor of 5-HT reuptake, as well as with desipramine. Tianeptine treatment (10 mg/kg/day) prevented the stress-induced atrophy of dendrites of CA3 pycamidal neurons, whereas neither fluoxetine (10 mg/kg/day) nor desipramine (10 mg/kg/day) had any effect. Tianeptine treatment also prevented the stress-induced impairment of radial maze learning. Because corticosterone- and stress-induced atrophy of CA3 dendrites is also blocked by phenytoin, an inhibitor of excitatory amino acid release and actions, these results suggest that serotonin released by stress or corticosterone may interact pre- or post-synaptically with glutamate released by stress or corticosterone, and that the final common path may involve interactive effects between serotonin and glutamate receptors on the dendrites of CA3 neurons innervated by mossy fibers from the dentate gyrus. We discuss the implications of these findings for treating cognitive impairments and the risk for dementia in the elderly.

Tianeptine treatment induces regionally specific changes in monoamines

Tianeptine is an atypical tricyclic antidepressant that facilitates serotonin (5-HT) reuptake. Tianeptine (10 mg/kg) or saline was administered intraperitoneally to male rats daily for 4 days. Monoamine levels were measured in micropunches of discrete brain nuclei that are implicated in mood and cognition. In addition, the rates of 5-HT and norepinephrine (NE) accumulation were determined by the pargyline method. Few changes were noted in the 5-HT system. 5-HT levels were increased by short-term tianeptine in the CA3 region of hippocampus, and 5-hydroxyindoleacetic acid (5-HIAA) was increased in the ventromedial nucleus of hypothalamus, while 5-HT turnover was decreased in preoptic area (POA). In addition, short-term tianeptine treatment increased NE levels in POA, parietal sensory cortex (SCTX) and dorsal raphe (DR), and decreased NE in dentate gyrus. NE turnover was also decreased in DR, SCTX and parietal motor cortex. These data suggest that the short-term neural and behavioral actions of tianeptine may be attributable, in part, to alterations of the norepinephrine system.

Estrogen-induction of dendritic spines in ventromedial hypothalamus and hippocampus: effects of neonatal aromatase blockade and adult GDX

Treatment of male rats at birth with an aromatase inhibitor (Letrazole), followed by adult gonadectomy GDX, led to an increase in dendritic spine density on ventromedial hypothalamic neurons (VMN) when treated with estrogen as compared to a decrease when vehicle animals were given estrogen. In contrast, estrogen-treatment increased dendritic spine density on CA1 pyramidal neurons regardless of neonatal treatment. In addition, in CA1 there was a significant difference between the two estrogen groups. These results suggest that estrogen induction of dendritic spines in the VMN and CA1 is dependent on organizational effects of gonadal steroids.

Gonadal steroids and neuronal plasticity. Studies in the adult rat hypothalamus

In this chapter, recent studies on gonadal steroid-induced neural plasticity in the adult rat hypothalamus have been described. Neurons in the VMN and DMN are capable of rapid, reversible structural alterations in response to a changing hormonal environment. Given the importance of the VMN in mediating lordosis in female rats, the present studies suggest that hormonally induced morphological changes in the VMN may be necessary for the manifestation of lordosis. This possibility is supported by the 5,7-DHT studies which indicate that the induction of dendritic spines on VMN neurons may somehow decrease the threshold of E needed to elicit lordosis. Moreover, the sex differences in hormonal requirements for lordosis in 5,7-DHT-treated rats are probably the result of organizational effects of gonadal steroids. Our data support the idea that activational effects can only be superimposed on existing brain circuitry to a certain degree. Finally, the neuronal plasticity seen in the hypothalamus may be an important physiological mechanism by which gonadal steroid feedback mediates reproductive and behavioral function.

The effects of aging and hormonal manipulation on amyloid precursor protein APP695 mRNA expression in the rat hippocampus

In the rat hippocampus, neuronal morphology and survival are profoundly affected by adrenal steroids, and synaptic plasticity can be modulated by the ovarian sex steroids estrogen and progesterone. beta-amyloid peptides, which accumulate in neuritic plaques and are derived from the amyloid precursor protein (APP), have been shown to be both trophic and toxic for hippocampal neurons. Of the various APP isoforms, APP695 is the predominant form found in rat brain and the APP695 mRNA is abundantly expressed in the hippocampus. In order to investigate the hypothesis that APP may serve as a mediator of the steroid effects, we have monitored the hippocampal expression of APP695 mRNA by in situ hybridization, with aging and with steroid manipulation. In aged female rats we observed a decrease in the level of APP695 mRNA relative to young female rats, while no such age difference was evident in male rats. Physiological, surgical and pharmacological manipulation of glucocorticoids appeared to have no effect on APP695 mRNA levels in the hippocampus. Treatment of young, ovariectomized female rats with estrogen and progesterone, resulted in an increase in hippocampal APP695 expression compared to untreated, ovariectomized controls.

Creating a participant text: writing, multiple voices, narrative multiplicity

This article uses the ideas of social constructionism to explore how families change by investigating the way our perceptions of ourselves in relation to others are formed through language. The idea that language has the inherent potential to generate a reply has strongly influenced our thinking. We propose that the reply to others is shaped by our initial reply to ourselves in inner conversation. Interaction moves back and forth from inner conversation to conversation with others, from monologue to dialogue, becoming the "stuff" of new narratives. The particular focus on language in this article is on how adding writing to the session conversation produces a "participant text," a therapeutic narrative that is composed of the voices of the family and the therapists. These voices, often newly discovered or invented, allow our narrative discourse to expand and multiply. Using this approach with individuals, couples, and families from different socioeconomic levels, we have worked with mourning, divorcing couples, recovery from abuse, marital conflict, parenting dilemmas, and physical illness.

Short-term fluoxetine treatment alters monoamine levels and turnover in discrete brain nuclei

The effects of short-term fluoxetine administration on monoamine levels and turnover were assessed in discrete brain nuclei. Adult male rats received fluoxetine HCl (10 mg/kg) or saline injections intraperitoneally for 4 days and monoamine levels determined by high performance liquid chromatography. The major metabolite of 5-HT, 5-hydroxyindoleacetic acid (5-HIAA), was decreased by fluoxetine treatment in the ventromedial hypothalamic nucleus (VMN), the lateral hypothalamic area and the CA1 region of the hippocampus. Fluoxetine treatment significantly increased serotonin (5-HT) levels in the VMN but did not change 5-HT levels in any other area examined. Norepinephrine (NE) levels were higher in fluoxetine-treated rats in the dorsomedial hypothalamic nucleus, dorsal raphe nucleus and parietal motor cortex (MCTX). 5-HT and NE turnover were also determined by the pargyline method. Fluoxetine treatment decreased 5-HT turnover in the VMN and increased 5-HT turnover in the median raphe. NE turnover was decreased in the preoptic area, the MCTX and parietal sensory cortex by fluoxetine administration. These results demonstrate that brain areas with similar 5-HT innervation respond differently to fluoxetine administration and fluoxetine, which selectively alters 5-HT uptake, also affects NE levels and turnover in several brain nuclei.

Effect of 5,7-dihydroxytryptamine, ovariectomy and gonadal steroids on serotonin receptor binding in rat brain

Quantitative autoradiography was used to assess alterations in serotonin (5-HT) receptor binding in the hypothalamus and hippocampus following denervation with 5,7-dihydroxytryptamine (5,7-DHT), ovariectomy (OVX) and gonadal steroid manipulation. Seven days after 5,7-DHT injection, 5-HT1a receptor density was significantly increased in the ventromedial hypothalamic nucleus (VMN) of intact but not OVX female rats. Under these conditions 5-HT1b receptor density was unchanged in any brain region examined and 5-HT transporter binding was decreased in all 5,7-DHT injected animals. In addition, there was a significant interaction between OVX and 5,7-DHT for both the 5-HT1a receptor and the 5-HT transporter in the VMN, such that OVX inhibited the 5,7-DHT-induced increase in 5-HT1a receptors and attenuated the 5,7-DHT-induced decrease in 5-HT transporter binding. In a separate experiment the effect of gonadal steroid manipulation on 5-HT receptor binding was assessed. In female OVX rats, 5-HT1a receptor density was unchanged by estrogen or estrogen and progesterone administration. In male rats, castration significantly decreased 5-HT1a receptor density in the medial preoptic area. Estrogen and progesterone administration to female OVX rats increased the density of 5-HT1b receptors in the VMN, as compared to estrogen alone. The relationship of these results to the role of 5-HT in mediating lordosis behavior is discussed.

Alterations of serotonin receptor binding in the hypothalamus following acute denervation

Quantitative autoradiography was used to determine the effect of acute serotonergic denervation with 5,7-dihydroxytryptamine (5,7-DHT) or serotonin 5HT1a and 5-HT1b receptors in male rats. Seven days after intrahypothalamic 5,7-DHT injection there was a significant increase in the density of 5HT1a receptors in the ventromedial and dorsomedial hypothalamic nuclei (VMN and DMN) of male rats. In adjacent sections. 5-HT1b receptors were significantly increased only in the VMN. No changes in receptor density were observed in the lateral hypothalamic area or hippocampus even though binding of [3H]paroxetine, which labels the presynaptic transporter site, was significantly decreased in all evaluated brain regions in 5,7-DHT-treated animals. In addition to demonstrating that 5-HT1a and 5-HT1b receptors are differentially regulated in different brain areas, these results show that in the brain regions examined both 5-HT1a and 5-HT1b receptors are primarily post-synaptic.