Receptors In Specific Brain Regions Research Articles

Characterization of oxytocin and vasopressin receptors in the Southern giant pouched rat and comparison to other rodents.

Vasopressin and oxytocin are well known and evolutionarily ancient modulators of social behavior. The distribution and relative densities of vasopressin and oxytocin receptors are known to modulate the sensitivity to these signaling molecules. Comparative work is needed to determine which neural networks have been conserved and modified over evolutionary time, and which social behaviors are commonly modulated by nonapeptide signaling. To this end, we used receptor autoradiography to determine the distribution of vasopressin 1a and oxytocin receptors in the Southern giant pouched rat (Cricetomys ansorgei) brain, and to assess the relative densities of these receptors in specific brain regions. We then compared the relative receptor pattern to 23 other species of rodents using a multivariate ANOVA. Pouched rat receptor patterns were strikingly similar to hamsters and voles overall, despite the variation in social organization among species. Uniquely, the pouched rat had dense vasopressin 1a receptor binding in the caudate-putamen (i.e., striatum), an area that might impact affiliative behavior in this species. In contrast, the pouched rat had relatively little oxytocin receptor binding in much of the anterior forebrain. Notably, however, oxytocin receptor binding demonstrated extremely dense binding in the bed nucleus of the stria terminalis, which is associated with the modulation of several social behaviors and a central hub of the social decision-making network. Examination of the nonapeptide system has the potential to reveal insights into species-specific behaviors and general themes in the modulation of social behavior.

Providing or receiving alloparental care promote partner preference and alter central oxytocin and dopamine systems in adult mandarin voles

Juveniles of cooperative breeding species usually remain in the natal area and provide care to younger siblings, a behavior considered one form of alloparenting in the natural condition. Previous studies have demonstrated the effects of providing or receiving alloparental care on adult behaviors, including anxiety-like behavior, social interaction, and parental behavior, but little is known about the influences on species-typical bonding behaviors, such as pair-bond formation. In this study, we explored this concept using socially monogamous mandarin voles (Lasiopodomys mandarinus). As the oxytocin (OT) and dopamine systems are involved in alloparental and pair-bonding behaviors, we also examined the levels of central OT and tyrosine hydroxylase (TH), as well as OT receptor (OTR) and dopamine D1-type and D2-type receptors (D1R and D2R) mRNA expression in the nucleus accumbens (NAcc) and amygdala to investigate the underlying mechanisms. Our results show that mandarin voles providing alloparental care to younger siblings displayed facilitation of partner preference formation, lower levels of OT expression in the paraventricular nucleus of the hypothalamus (PVN) and lateral hypothalamus (LH), and increased OTR and D2R mRNA expression in the NAcc compared to controls. Individuals receiving alloparental care also demonstrated facilitation of partner preference formation in adult voles. Additionally, alloparental care enhanced OT expression in the PVN, anterior medial preoptic nucleus (MPOAa), medial amygdala (MeA), and TH expression in the ventral tegmental area (VTA) and zona incerta (ZI). Furthermore, males displayed decreased D1R mRNA expression in the NAcc, whereas females showed slightly increased D2R expression in the amygdala. These results demonstrate that providing or received alloparental care can promote partner preference formation in monogamous species and that these changes are associated with altered OT and dopamine levels and their receptors in specific brain regions.

Dysphoric Milk Ejection Reflex: The Psychoneurobiology of the Breastfeeding Experience.

Breastfeeding, given its biochemical and physiological basis, is known for its many benefits for both the lactating mother and the infant. Among the many challenges new breastfeeding mothers experience is the feeling of aversion in response to their newborn's suckling which has been termed dysphoric milk-ejection reflex (D-MER). Characterized by intense feelings of dysphoria which may eventually interfere with the mother's ability to breastfeed regularly, evidence suggests both the neurobiological and psychological basis of D-MER in an attempt to explain its complexity. Biologically, breastfeeding is expressed by the intracerebral release of oxytocin, an increased expression of oxytocin receptors in specific brain regions, increased mesocorticolimbic reward region activation, the secretion of prolactin and possibly the inhibition of dopamine. Hence, different theories explain D-MER in terms of disrupted neurotransmitter and hormonal activity. Breastfeeding has also proven to influence mood and stress reactivity in nursing mothers with a potential link with postpartum depression. Psychological theories attempt to explain D-MER from a sociopsychosexual lense shedding light on the significance of mother-infant attachment, the sexualization of the female body and the motherhood experience as a developmental stage in a woman's lifespan. The aim of this review is to provide a literature update of D-MER incorporating both neurobiological and psychological theories calling for raising awareness about the complexity of breastfeeding and for the need for mother-centered interventions for the management of D-MER and other postpartum-specific conditions.

Microbiota regulate social behaviour via stress response neurons in the brain.

Social interactions among animals mediate essential behaviours, including mating, nurturing, and defence1,2. The gut microbiota contribute to social activity in mice3,4, but the gut-brain connections that regulate this complex behaviour and its underlying neural basis are unclear5,6. Here we show that the microbiome modulates neuronal activity in specific brain regions of male mice to regulate canonical stress responses and social behaviours. Social deviation in germ-free and antibiotic-treated mice is associated with elevated levels of the stress hormone corticosterone, which is primarily produced by activation of the hypothalamus-pituitary-adrenal (HPA) axis. Adrenalectomy, antagonism of glucocorticoid receptors, or pharmacological inhibition of corticosterone synthesis effectively corrects social deficits following microbiome depletion. Genetic ablation of glucocorticoid receptors in specific brain regions or chemogenetic inactivation of neurons in the paraventricular nucleus of the hypothalamus that produce corticotrophin-releasing hormone (CRH) reverse social impairments in antibiotic-treated mice. Conversely, specific activation of CRH-expressing neurons in the paraventricular nucleus induces social deficits in mice with a normal microbiome. Via microbiome profiling and in vivo selection, we identify a bacterial species, Enterococcus faecalis, that promotes social activity and reduces corticosterone levels in mice following social stress. These studies suggest that specific gut bacteria can restrain the activation of the HPA axis, and show that the microbiome can affect social behaviours through discrete neuronal circuits that mediate stress responses in the brain.

The Effect of Perinatal Blockade of Androgen Receptors on Adult Rat Behaviors and the Expression of Estrogen and Androgen Receptors in specific brain regions

The brain, by default, differentiates into a female brain unless testosterone (T) is present during a critical window of time. In rats, there is a surge of T around the time of birth, more specifically four days prior to and four days after birth, referred to as the perinatal period. The purpose of this study was to examine the effects of blockade of androgen receptors (AR) during the perinatal period using flutamide (F) on sexual motivation (SM) and an open field (OF) test as well as the expression of AR and estrogen receptors (ER)‐alpha and ER‐beta in the hypothalamus, hippocampus, and amygdala. Four timed‐pregnant rats were divided into two groups: one group (N=2) received F during perinatal period whereas the other group (N=2) served as the control group receiving vehicle (95% Olive oil‐5% ethanol). Once the pups reached adulthood, the male rats underwent SM testing where they were exposed to either an estrus or an ovariectomized rat. Both F and control groups of male rats spent more time with the estrus rat compared to the ovariectomized rat suggesting that SM was not affected by their AR blockade during perinatal period. Open field testing recorded animal movements between the two zones, the center and the periphery, within an open arena. Male rats moved between the two zones more than the female rats did. At the end of the behavioral study, animals were sacrificed and the brains were harvested to isolate the hippocampus, hypothalamus, and amygdala. Real time PCR testing was carried out to quantify the levels of AR, ER alpha, and ER beta using B‐Actin as an internal control. Perinatal blockade of AR had no effect on the expression of any of the receptors in the three regions tested in the adult rats. Thus, the increased movement by the male rats in the OF testing is not associated with changes in the expression of AR, ER‐alpha, or ER‐beta.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Selective serotonin 5-HT1A receptor biased agonists elicitdistinct brain activation patterns: a pharmacoMRI study.

Serotonin 1A (5-HT1A) receptors are involved in several physiological and pathological processes and constitute therefore an important therapeutic target. The recent pharmacological concept of biased agonism asserts that highly selective agonists can preferentially direct receptor signaling to specific intracellular responses, opening the possibility of drugs targeting a receptor subtype in specific brain regions. The present study brings additional support to this concept thanks to functional magnetic resonance imaging (7 Tesla-fMRI) in anaesthetized rats. Three 5-HT1A receptor agonists (8-OH-DPAT, F13714 and F15599) and one 5-HT1A receptor antagonist (MPPF) were compared in terms of influence on the brain blood oxygen level-dependent (BOLD) signal. Our study revealed for the first time contrasting BOLD signal patterns of biased agonists in comparison to a classical agonist and a silent antagonist. By providing functional information on the influence of pharmacological activation of 5-HT1A receptors in specific brain regions, this neuroimaging approach, translatable to the clinic, promises to be useful in exploring the new concept of biased agonism in neuropsychopharmacology.

Discovery of the First α-Amino-3-hydroxy-5-methyl-4-isoxazolepropionic Acid (AMPA) Receptor Antagonist Dependent upon Transmembrane AMPA Receptor Regulatory Protein (TARP) γ-8

Transmembrane AMPA receptor regulatory proteins (TARPs) are a family of scaffolding proteins that regulate AMPA receptor trafficking and function. TARP γ-8 is one member of this family and is highly expressed within the hippocampus relative to the cerebellum. A selective TARP γ-8-dependent AMPA receptor antagonist (TDAA) is an innovative approach to modulate AMPA receptors in specific brain regions to potentially increase the therapeutic index relative to known non-TARP-dependent AMPA antagonists. We describe here, for the first time, the discovery of a noncompetitive AMPA receptor antagonist that is dependent on the presence of TARP γ-8. Three major iteration cycles were employed to improve upon potency, CYP1A2-dependent challenges, and in vivo clearance. An optimized molecule, compound (-)-25 (LY3130481), was fully protective against pentylenetetrazole-induced convulsions in rats without the motor impairment associated with non-TARP-dependent AMPA receptor antagonists. Compound (-)-25 could be utilized to provide proof of concept for antiepileptic efficacy with reduced motor side effects in patients.

Behavioral responses to pups in males with different reproductive experiences are associated with changes in central OT, TH and OTR, D1R, D2R mRNA expression in mandarin voles

Male rodents behave differently toward pups because of different sexual and/or paternal experiences; however, the mechanisms underlying these responses are not well understood. Using socially monogamous mandarin voles (Microtus mandarinus) we investigated the behavioral responses of males with different reproductive experiences (virgin males, paired males and new fathers) to new born pups. Central levels of neuropeptide oxytocin (OT), tyrosine hydroxylase (TH), as well as oxytocin receptor (OTR), dopamine 1-type receptor (D1R) and dopamine 2-type receptor (D2R) mRNA expression in the nucleus accumbens and medial amygdala were also measured in these males. Our data showed that new fathers exhibited more approaching behavior and contained more OT-immunoreactive and TH-immunoreactive neurons. In addition to increased OTR mRNA expression in the nucleus accumbens and medial amygdala, new fathers had higher D1R and D2R mRNA expression in the nucleus accumbens, and less D1R and D2R mRNA expression in the medial amygdala than paired males. These results demonstrate that males with different reproductive experiences display different behavioral responses to pups and that these differences are associated with altered OT and dopamine, and their receptors in specific brain regions.

Aldosterone synergizes with peripheral inflammation to induce brain IL-1β expression and depressive-like effects

Recent findings have shown that the physiological functions of the hormone aldosterone go far beyond its well-known role in blood-pressure regulation and salt/water homeostasis. Aldosterone is for example involved in the regulation of inflammation, and also binds directly to mineralocorticoid receptors in specific brain regions. Interestingly, depressive symptoms appear to correlate with alterations of the aldosterone system but the underlying mechanisms have not been elucidated.In this study aldosterone (2μg/100g body weight/day) was continuously administered via osmotic minipumps for 5days. Lipopolysaccharide (LPS) was administered once a day for 5days in a dose of 1mg/kg ip. The rats were tested for depressive-like behavior 24h after the last LPS injection. Protein levels of cytokines were measured in serum and cerebrospinal fluid (CSF). mRNA expression of interleukin (IL)-1β and IL-6 in the prefrontal cortex (PFC) was analyzed using reverse transcriptase qPCR.We found that aldosterone treatment increased LPS-induced IL-1β mRNA expression in the PFC and CSF. Moreover, there was a positive correlation between IL-1β in CSF and depressive-like behaviors. These findings suggest that IL-1β is affected by the renin–aldosterone–angiotensin system (RAAS) activity and connected to symptoms of depression.

Chronic haloperidol-induced spatial memory deficits accompany the upregulation of D1 and D2 receptors in the caudate putamen of C57BL/6 mouse

AimsHaloperidol (HAL) is an antipsychotic drug that has high affinities to the dopamine D2, but low affinities to D1 receptors in the brain. Of brain regions, caudate putamen (CP) has the highest levels of the D1 and D2 receptors. In this study we evaluated the spatial memory of C57BL/6 mice following chronic administration of HAL and measured levels of D1 and D2 receptors in specific brain regions, with the hypothesis that the D1 and D2 receptors in CP are important players in spatial memory function of the brain. Main methodsC57BL/6 mice received daily intraperitoneal injections of saline or HAL at 1.0 or 2.0mg/kg/day for 3 or 6weeks. Two days after the last injection, spontaneous alternation of mice in a Y-maze was evaluated to measure their exploratory behavior and spatial working memory. The Morris water maze test was performed to measure their spatial learning and memory. D1 and D2 receptors in specific brain regions were measured by Western-blot analysis. Key findingsHAL treatment for 6weeks decreased the spontaneous alternation of mice in Y-maze, altered the acquisition process and impaired spatial memory in Morris water maze. The same treatment increased levels of D1 and D2 receptors in CP and up-regulated D2 receptors in the hippocampus, but did not change the receptors in the prefrontal cortex. SignificanceThese results suggest that the D1 and D2 receptors in CP are among the main targets of HAL and the receptors in CP play an important role in spatial learning and memory.

GABA: A Cotransmitter Linking Leptin to Obesity Prevention

The recent surge of obesity, type II diabetes, and other obesity-relateddiseaseshasfocusedattentiononbrain mechanisms underlying the regulation of body weight. Leptinisakeyfactorlinkingbodyfattobrainmechanisms controlling food intake and energy expenditure. This hormoneisreleasedfromadipocytestocirculateatlevelsthat are approximately proportional to the levels of body fat (1).Highlevelsofleptinactonbrainfeedingcontrolmechanismsasanegativefeedbacksignaltoproducesatiety,an action produced when leptin binds to isoform B leptin receptors in specific brain regions (2). Consequently, subjects overeat and become massively obese if either endogenous leptin or its receptors are absent or ineffective. A question that has generated much interest and research is: What classes of neurons and neurotransmitters mediate leptin’s antiobesity actions? Significant insight into this question is provided by Xu et al. (3) in this issue. Their work suggests that a portion of leptin’s antiobesity effectsaremediatedbysynapticreleaseofaminobutyric acid (GABA) from the specific subset of hypothalamic GABAergic neurons that also express leptin receptors. To explore this question, they generated mice in which the vesicular GABA transporter (Vgat) gene was specifically deleted within leptin receptor-expressing neurons (i.e. LepR-Ires-Cre:Vgat flox/flox mice). The cellular impact of thismanipulationisthattheGABAergicneuronswithleptin receptors lose their ability to secrete GABA. However, they retain the ability to secrete their cotransmitters and respond to leptin. Given this manipulation, Xu et al. evaluated the impact of abolishing GABA release specifically from the subset of GABAergic neurons that also express leptin receptors. Controls for effectiveness and specificity of the gene deletions included evidence that deletion of Vgat in leptin receptor neurons: dramatically reduced Vgat mRNA expression in the arcuate nucleus, dorsomedial hypothalamus, and lateral hypothalamus (LH), the only brain regions with GABAergic neurons that express leptin receptors (4); produced little apparent change in Vgat expression in other brain regions (e.g. cortex); reduced vesicular GABA transporter immunoreactivity but left intact the leptin receptor p-STAT3 response to leptin application. The key behavioral findings were that the experimental mice exhibited mild but significant overeating, obesity, and had reduced energy expenditure as suggestedbythemildreductioninO2consumptionduringthe night phase of the light-dark cycle. The satiating effect of peripherallyinjectedleptinwasalsoblunted.Collectively,

Decreased expression of mineralocorticoid receptor mRNA and its splice variants in postmortem brain regions of patients with major depressive disorder

Appropriate signaling in the brain by the glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) is critical in regulation of the hypothalamic–pituitary–adrenal (HPA) axis, emotional arousal and cognitive performance. To date, few data exist on MR (and GR) expression in the brain of patients suffering from major depressive disorder (MDD). With the help of quantitative PCR we assessed MR and GR mRNA expression, including the splice variants MRα and MRβ, in tissue samples from the hippocampus, amygdala, inferior frontal gyrus, cingulate gyrus and nucleus accumbens. Expression levels were compared between tissue samples from six MDD patients and six non-depressed subjects. Relative to total GR, total MR mRNA expression was higher in hippocampus and lower in the amygdala, inferior frontal gyrus and nucleus accumbens. Both MRα and MRβ could be detected in all brain regions that were analyzed, although MRβ expression was low. Significantly lower expression levels (30–50%) were detected for MR or GR in hippocampal, inferior frontal gyrus and cingulate gyrus tissue from MDD patients ( p < .05), while no differences were found in the amygdala or nucleus accumbens. The data show that both MRα and MRβ mRNA are expressed throughout the human limbic brain with highest expressions in the hippocampus. A decreased expression of corticosteroid receptors in specific brain regions of MDD patients could underlie HPA hyperactivity, mood and cognitive disturbances often observed in patients suffering from stress-related psychopathologies.

Nuclear orphan receptor Nor-1 contributes to depressive behavior in the Wistar–Kyoto rat model of depression

The current study explored the effects of prolonged antidepressant treatment on mRNA levels of two nuclear receptors in specific brain regions of an animal model of depression, the Wistar–Kyoto (WKY) rat. Both nuclear receptors have been implicated in the development or treatment of depression. The expression of nuclear orphan receptor-1 (Nor-1), a member of the NR4A nuclear orphan receptor family, is induced by electroconvulsive shock, an effective treatment for depression. Deficit in the levels or function of the glucocorticoid receptor (GR) found in depressed patients has been causally implicated in depression, as this deficit is normalized by antidepressant treatments. Baseline levels of amygdalar Nor-1 and GR mRNA were higher in the WKYs compared to the comparison control Sprague–Dawley rats (SD). Prolonged treatment with the antidepressant desipramine (DMI) decreased the expression of both transcripts in the WKY strain concomitantly with decreased immobility in the forced swim test (FST) of depressive behavior. Using short hairpin RNA (shRNA) targeted against Nor-1, we investigated the direct contribution of elevated Nor-1 expression in the amygdala of WKY to their exaggerated depressive behavior in the FST. After validating the shRNA targeting of Nor-1 in vitro, Nor-1 shRNA containing vector was infused intracerebroventricularly, using a linear polyethylenimine (PEI)-containing in vivo gene delivery system. Repeated administration of Nor-1 shRNA ameliorated the depressive behavior of WKYs in the FST and decreased amygdalar Nor-1 mRNA levels without affecting GR mRNA levels. These data demonstrate that brain region-specific changes in GR expression in response to DMI are strain dependent and that elevated amygdalar Nor-1 expression can contribute to depressive behavior in the WKY model of depression.

Clinical Potential of Neuropeptide Y Receptor Ligands in the Treatment of Epilepsy

A substantial amount of experimental evidence implicates neuropeptide Y (NPY) in the pathophysiology of epilepsy. Over the past 20 years, remarkable progress has been made in unraveling the mechanisms and receptors involved in the anticonvulsant effect of this abundantly expressed neuropeptide. Activation of Y(2) and/or Y(5) receptors and blockade of Y(1) receptors in the central nervous system suppresses seizures in a variety of animal seizure models. Orally available, brain penetrating Y(2) and/or Y(5) agonists, and possibly Y(1) antagonists, may therefore constitute a novel class of antiepileptic drugs, which could greatly benefit patients with medically refractory epilepsy. Significant progress has been made in identifying non-peptidergic Y(1) antagonists that fulfill these criteria, but suitable Y(2) and/or Y(5) agonists have proven to be more elusive. Innovative oral and parental drug delivery strategies which are currently under development may offer a means of using the more readily available peptidergic NPY receptor ligands in a clinical setting. Finally, gene therapy, antisense probes or RNA interference strategies which alter the expression of NPY or its receptors in specific brain regions may also be of use in the treatment of epilepsy, but will probably benefit a smaller subgroup of epilepsy patients, since they typically require an invasive procedure.

Oral haloperidol or risperidone treatment in rats: Temporal effects on nerve growth factor receptors, cholinergic neurons, and memory performance

First and second generation antipsychotics (FGAs and SGAs) ameliorate psychotic symptoms of schizophrenia, however, their chronic effects on information processing and memory function (i.e. key determinants of long term functional outcome) are largely unknown. In this rodent study the effects of different time periods (ranging from 2 weeks to 6 months) of oral treatment with the FGA, haloperidol (2.0 mg/kg/day), or the SGA, risperidone (2.5 mg/kg/day) on a water maze repeated acquisition procedure, the levels of nerve growth factor receptors, and two important cholinergic proteins, the vesicular acetylcholine transporter and the high affinity choline transporter were evaluated. The effects of the antipsychotics on a spontaneous novel object recognition procedure were also assessed during days 8–14 and 31–38 of treatment. Haloperidol (but not risperidone) was associated with impairments in water maze hidden platform trial performance at each of the time periods evaluated up to 45 days, but not when tested during days 83–90. In contrast, risperidone did not impair water maze task performance at the early time periods and it was actually associated with improved performance during the 83–90 day period. Both antipsychotics, however, were associated with significant water maze impairments during the 174–180 day period. Further, haloperidol was associated with decrements in short delay performance in the spontaneous novel object recognition task during both the 8–14 and 31–38 day periods of treatment, while risperidone was associated with short delay impairment during the 31–38 day time period. Both antipsychotics were also associated with time dependent alterations in the vesicular acetylcholine transporter, the high affinity choline transporter, as well as tyrosine kinase A, and p75 neurotrophin receptors in specific brain regions. These data from rats support the notion that while risperidone may hold some advantages over haloperidol, both antipsychotics can produce time-dependent alterations in neurotrophin receptors and cholinergic proteins as well as impairments in the performance of tasks designed to assess spatial learning and episodic memory.

Nuclear receptor coactivators function in estrogen receptor- and progestin receptor-dependent aspects of sexual behavior in female rats

The ovarian hormones, estradiol (E) and progesterone (P) facilitate the expression of sexual behavior in female rats. E and P mediate many of these behavioral effects by binding to their respective intracellular receptors in specific brain regions. Nuclear receptor coactivators, including Steroid Receptor Coactivator-1 (SRC-1) and CREB Binding Protein (CBP), dramatically enhance ligand-dependent steroid receptor transcriptional activity in vitro. Previously, our lab has shown that SRC-1 and CBP modulate estrogen receptor (ER)-mediated induction of progestin receptor (PR) gene expression in the ventromedial nucleus of the hypothalamus (VMN) and hormone-dependent sexual receptivity in female rats. Female sexual behaviors can be activated by high doses of E alone in ovariectomized rats, and thus are believed to be ER-dependent. However, the full repertoire of female sexual behavior, in particular, proceptive behaviors such as hopping, darting and ear wiggling, are considered to be PR-dependent. In the present experiments, the function of SRC-1 and CBP in distinct ER- (Exp. 1) and PR- (Exp. 2) dependent aspects of female sexual behavior was investigated. In Exp. 1, infusion of antisense oligodeoxynucleotides to SRC-1 and CBP mRNA into the VMN decreased lordosis intensity in rats treated with E alone, suggesting that these coactivators modulate ER-mediated female sexual behavior. In Exp. 2, antisense to SRC-1 and CBP mRNA around the time of P administration reduced PR-dependent ear wiggling and hopping and darting. Taken together, these data suggest that SRC-1 and CBP modulate ER and PR action in brain and influence distinct aspects of hormone-dependent sexual behaviors. These findings support our previous studies and provide further evidence that SRC-1 and CBP function together to regulate ovarian hormone action in behaviorally-relevant brain regions.

Targeting Brain AT 1 Receptors By RNA Interference

The dipsogenic and pressor actions of angiotensin II (Ang II) in the central nervous system (CNS) have been well documented in many species and are now accepted as dogma. The major central cardiovascular effects of Ang II are elicited by a complex receptor-dependent signaling cascade initiated by the detection of circulating Ang II in regions of the brain lacking a blood brain barrier (BBB) through local production of Ang II in regions outside and inside the BBB or through the neurotransmitter actions of Ang II. It is generally accepted that most of the central neurocardiovascular actions of Ang II occur through the activation of intracellular signaling cascades that originate at the Ang II type 1 (AT1) receptor. A second Ang II receptor, termed AT2, has been implicated in some cardiovascular and behavioral responses. However, the AT2 receptor is distantly related to AT1 and can be effectively distinguished from AT1 pharmacologically. In humans, a single gene encodes the AT1 Ang II receptor, whereas in rodents a duplication resulted in 2 AT1 receptor genes, located on different chromosomes, each known to encode 1 of 2 distinct subtypes of the receptor, AT1a and AT1b. Both receptors are highly homologous, use the same signaling mechanisms, and cannot be distinguished using currently available pharmacological reagents or antisera. Despite their high similarity at the protein level, sufficient divergence is present in the sequence of the mRNA that allows them to be distinguished by RT-PCR and in situ hybridization. Through

Increased brain dopamine D4-like binding after chronic ethanol is not associated with behavioral sensitization in mice

Dopaminergic D4 receptors have been hypothesized to be involved in neuropsychiatric disorders and substance abuse. In mice, repeated ethanol administration may induce behavioral sensitization, a phenomenon of increased sensitivity to the drug's stimulant properties. This study aimed to analyze brain D4 receptors binding in mice with different levels of behavioral sensitization to ethanol. Male Swiss mice received 2.2 g/kg ethanol ( n = 64) or saline ( n = 16) intraperitoneally daily for 21 days and were weekly tested for locomotor activity and for blood ethanol levels. According to the locomotor scores presented across test days, ethanol-treated mice were classified as “sensitized” or “nonsensitized.” Twenty-four hours after the last administration, mice were sacrificed and brains were processed for autoradiography. Brain D4 binding was assessed by quantitative autoradiography using [ 3H]nemonapride + raclopride in three groups: saline-treated controls ( n = 10), ethanol-sensitized ( n = 11), and ethanol-nonsensitized ( n = 9) mice. Both sensitized and nonsensitized mice showed higher D4 binding densities than saline-treated controls in the posterior caudate–putamen and the olfactory tubercle ( p < .02), but only sensitized mice presented higher D4 binding than controls at the lateral septal nucleus ( p < .02). However, there were no differences between sensitized and nonsensitized mice in any of the brain regions analyzed. Furthermore, sensitized and nonsensitized mice presented similar blood ethanol levels during the treatment. The higher D4 binding levels observed in both ethanol-treated subgroups (sensitized and nonsensitized) suggest that chronic ethanol treatment may induce upregulation of D4 receptors in specific brain regions. However, this mechanism does not seem to be associated with the differential ability to develop behavioral sensitization to ethanol in mice.

Expression and distribution of kinin B1 receptor in the rat brain and alterations induced by diabetes in the model of streptozotocin

A role for kinin B1 receptors was suggested in the spinal cord and peripheral organs of streptozotocin (STZ)-diabetic rats. The present study aims at determining whether B1 receptors are also induced and over-expressed in the brain of STZ-rats at 2, 7, and 21 days post-treatment. This was addressed by in situ hybridization using the [35S]-UTPalphaS-labeled riboprobe and by in vitro autoradiography with the radioligand [125I]-HPP-des-Arg10-Hoe 140. In control rats, B1 receptor mRNA was found widely distributed in many brain regions. Low mRNA levels were found in thalamus and hypothalamus (7-12 nCi/g) while high mRNA signals were detected in cortical regions and hippocampus (18-29 nCi/g). In diabetic rats, B1 receptor mRNA was markedly increased in hippocampus, temporal/parietal cortices and amygdala at 2 and 7 days (+88 to +150%). Low densities of B1 receptor binding sites were detected in all analyzed regions in control rats (0.18-0.37 fmol/mg tissue). In diabetic rats, B1 receptor binding sites were significantly increased in hippocampus, amygdala, temporal/parietal, and perhinal/piriform cortices (+ 55 to + 165 %) at 7 days only. Results highlight an early but transient and reversible up-regulation of B1 receptors in specific brain regions of STZ-diabetic rats. This may offer the advantage of reducing putative central side effects with B1 receptor antagonists if used for the treatment of diabetic complications in the periphery.

Serotonin-Transporter Binding of Antidepressants at Therapeutic Doses

Studies examining the extent to which specific medications bind to specific receptors in specific brain regions aid our understanding of the pathophysiology of psychiatric disorders and the mechanisms of treatment. Researchers have shown that minimal therapeutic doses of paroxetine and citalopram result in approximately 80% occupancy …