Localization of orphanin FQ (nociceptin) peptide and messenger RNA in the central nervous system of the rat

Orphanin FQ (OFQ) is the endogenous agonist of the opioid receptor-like receptor (ORL-1). It and its precursor, prepro-OFQ, exhibit structural features suggestive of the opioid peptides. A cDNA encoding the OFQ precursor sequence in the rat recently has been cloned, and the authors recently generated a polyclonal antibody directed against the OFQ peptide. In the present study, the authors used in situ hybridization and immunohistochemistry to examine the distribution of OFQ peptide and mRNA in the central nervous system of the adult rat. OFQ immunoreactivity and prepro-OFQ mRNA expression correlated virtually in all brain areas studied. In the forebrain, OFQ peptide and mRNA were prominent in the neocortex endopiriform nucleus, claustrum, lateral septum, ventral forebrain, hypothalamus, mammillary bodies, central and medial nuclei of the amygdala, hippocampal formation, paratenial and reticular nuclei of the thalamus, medial habenula, and zona incerta. No OFQ was observed in the pineal or pituitary glands. In the brainstem, OFQ was prominent in the ventral tegmental area, substantia nigra, nucleus of the posterior commissure, central gray, nucleus of Darkschewitsch, peripeduncular nucleus, interpeduncular nucleus, tegmental nuclei, locus coeruleus, raphe complex, lateral parabrachial nucleus, inferior olivary complex, vestibular nuclear complex, prepositus hypoglossus, solitary nucleus, nucleus ambiguous, caudal spinal trigeminal nucleus, and reticular formation. In the spinal cord, OFQ was observed throughout the dorsal and ventral horns. The wide distribution of this peptide provides support for its role in a multitude of functions, including not only nociception but also motor and balance control, special sensory processing, and various autonomic and physiologic processes.

Serotonin 1A receptor messenger RNA regulation in the hippocampus after acute stress

BACKGROUND

When rats are subjected to chronic stress for 2 weeks, a significant decrease in hippocampal serotonin (5-HT)1A messenger RNA (mRNA) is observed. We wanted to investigate whether stress, administered for shorter periods of time, would result in decreases in 5-HT1A gene expression in hippocampus.

METHODS

In one experiment, rats were either stressed daily for 1 week or implanted with two corticosterone pellets to produce elevated corticosterone levels. In another experiment, rats were subjected to a severe acute stressor and sacrificed 1 day or 1 week after the stressor.

RESULTS

We found that 24 hours after the acute stress, rats showed a significant decrease in 5-HT1A mRNA levels in CA1 and the dentate gyrus compared to controls. No significant changes in 5-HT1A mRNA levels were detected in any of the other groups.

CONCLUSIONS

Although 1 week of chronic stress is not sufficient to cause significant decreases in hippocampal 5-HT1A mRNA levels, a severe and prolonged acute stress is capable of down-regulating, at least transiently, 5-HT1A mRNA gene expression in hippocampus.

Gene chips and arrays revealed: a primer on their power and their uses

This article provides an overview and general explanation of the rapidly developing area of gene chips and expression array technology. These are methods targeted at allowing the simultaneous study of thousands of genes or messenger RNAs under various physiological and pathological states. Their technical basis grows from the Human Genome Project. Both methods place DNA strands on glass computer chips (or microscope slides). Expression arrays start with complementary DNA (cDNA) clones derived from the EST data base, whereas Gene Chips synthesize oligonucleotides directly on the chip itself. Both are analyzed using image analysis systems, are capable of reading values from two different individuals at any one site, and can yield quantitative data for thousands of genes or mRNAs per slide. These methods promise to revolutionize molecular biology, cell biology, neuroscience and psychiatry. It is likely that this technology will radically open up our ability to study the actions and structure of the multiple genes involved in the complex genetics of brain disorders.

Molecular analysis of the X11-mLin-2/CASK complex in brain

A heterotrimeric complex containing Lin-10/X11alpha, Lin-2/CASK, and Lin-7 is evolutionarily conserved from worms to mammals. In Caenorhabditis elegans, it localizes Let-23, a receptor tyrosine kinase, to the basolateral side of vulval epithelium, a step crucial for proper vulva development. In mammals, the complex may also participate in receptor targeting in neurons. Accordingly, phosphotyrosine binding (PTB) and postsynaptic density-95/Discs large/Zona Occludens-1 domains found in X11alpha and mLin-2/CASK bind to cell-surface proteins, including amyloid precursor protein, neurexins, and syndecans. In this paper, we have further analyzed the X11alpha-mLin-2/CASK association that is mediated by a novel protein-protein interaction. We show that the mLin-2/CASK calmodulin kinase II (CKII) domain directly binds to a 63 amino acids peptide located between the Munc-18-1 binding site and the PTB domain in X11alpha. Ca2+/calmodulin association with mLin-2/CASK does not modify the X11alpha-mLin-2 interaction. A region containing the mLin-2/CASK guanylate kinase domain also interacts with X11alpha but with a lower affinity than the CKII domain. Immunostaining of X11alpha in the brain shows that the protein is expressed in areas shown previously to be positive for mLin-2/CASK staining. Together, our data demonstrate that the X11alpha-mLin-2 complex contacts many partners, creating a macrocomplex suitable for receptor targeting at the neuronal plasma membrane.

The effect of stressor controllability on stress-induced neuropeptide mRNA expression within the paraventricular nucleus of the hypothalamus

Many stressors elicit changes in corticotrophin (CRH), enkephalin (ENK), and neurotensin (NT) mRNA levels within the medial parvocellular region of the paraventricular nucleus of the hypothalamus (mpPVN), and the pattern of changes in mRNA levels appears to depend on the physical characteristics of the stressor. We questioned whether psychologically distinct stressors would cause different patterns of neuropeptide mRNA expression within the PVN. Psychologically distinct stressors were created by employing a paradigm of escapable (controllable) vs. non-escapable (yoked) tail shock. An adult male rats could terminate the stress stimulus by performing wheel-turning behaviour; his behaviour also terminated the stress for his yoked partner, who had no control over the termination of the shock. Four h post-stress, brains were collected and processed for in-situ hybridization histochemistry. Tail-shock stress stimulated a significant increase in CRH, ENK, and NT mRNA levels within the mpPVN. The number of CRH identified neurones coexpressing AVP mRNA was also significantly elevated in both stress groups. Moreover, the pattern and magnitude of the stress-induced increases in mRNA was similar in both stress groups. Additionally, no stress-induced changes in CRH mRNA levels were observed in the central nucleus of the amygdala. In sum, two psychologically distinct stressors, escapable vs. yoked tail shock stress, stimulated similar increases in CRH, NT, ENK, and AVP mRNA levels within the mpPVN. These results suggest that physical attributes of a stress, rather than psychological, may be the more important factors in determining the PVN mRNA response.

Functional significance of a newly discovered neuropeptide, orphanin FQ, in rat gastrointestinal motility

BACKGROUND & AIMS

Orphanin FQ (OFQ) is a recently discovered neuropeptide that structurally resembles an opioid peptide. However, the functional role of OFQ in rat gastrointestinal tract remains unknown.

METHODS

We investigated the effects of OFQ on contractions of muscle strips obtained from different regions of the gastrointestinal tract. Immunohistochemical studies were performed on rat colonic tissue using OFQ antibody.

RESULTS

OFQ (10(-9) to 10(-7) mol/L) caused significant contractions in the rat colon but not in the stomach or small intestine. Tetrodotoxin, veratridine, and long-term serosal application of benzalkonium chloride completely abolished OFQ-induced colonic contractions without affecting myogenic contractions in response to carbachol. OFQ-induced contractions were not affected by naloxone, atropine, phentolamine, propranolol, methysergide, substance P antagonist, vasoactive intestinal polypeptide antagonist, apamin, and NG-nitro-L-arginine methyl ester. OFQ (10(-9) to 10(-7) mol/L) significantly reduced muscle contractions and 3H-acetylcholine release in response to electrical field stimulation in both the stomach and small intestine but not in the colon. OFQ-immunopositive neuronal fibers were found in the colonic myenteric plexus.

CONCLUSIONS

These studies indicate that the mechanisms and sites of action of OFQ are region specific. OFQ inhibits cholinergic transmission in the stomach and small intestine, whereas OFQ stimulates colonic contraction possibly by inhibiting an inhibitory neural pathway within the myenteric plexus.

Amphetamine-induced behavior, dopamine release, and c-fos mRNA expression: modulation by environmental novelty

We have shown recently that the psychomotor activating effects of amphetamine in the rat are much greater when this drug is administered in association with environmental novelty than when it is given in a home environment. The main purpose of the present study was to explore the neural basis of this phenomenon. We found, using in situ hybridization of c-fos mRNA, that the pattern of neuronal activation in the cortex, in the caudate, in the shell and core of the nucleus accumbens, and in other subcortical structures was markedly different when amphetamine (2.0 mg/kg, i.p.) was given in association with exposure to environmental novelty relative to when it was given at home. In most brain regions the magnitude of c-fos expression was over two times greater in rats given amphetamine plus novelty than in rats given amphetamine alone. In contrast, an in vivo microdialysis study indicated that environmental novelty did not affect amphetamine-induced dopamine release in either caudate or nucleus accumbens. Furthermore, a unilateral 6-hydroxydopamine lesion of the mesostriatal dopamine system reduced amphetamine- but not novelty-induced c-fos expression. Finally, we found no differences in the amount of corticosterone secreted after exposure to novelty, amphetamine, or both, suggesting that corticosterone does not play a critical role in the ability of novelty to modulate amphetamine-induced psychomotor activation. In conclusion, it seems that environmental novelty alters the neurobiological effects of amphetamine independently of the primary neuropharmacological actions of this drug in the striatum.

Regulation of nitric oxide synthase messenger RNA expression in the rat hippocampus by glucocorticoids

Nitric oxide and glucocorticoids have been implicated in learning and memory, as well as in regulation of the stress response. By use of the in situ hybridization technique, we examined the role of glucocorticoids in the regulation of nitric oxide synthase messenger RNA in the hippocampus. In control animals, nitric oxide synthase subtype I (neuronal) messenger RNA was expressed in the CA1, CA3 and dentate gyrus of the hippocampus. Nitric oxide synthase subtype I expression was almost absent in CA2 pyramidal neurons. Neither subtype II (immunological) nor subtype III (endothelial) nitric oxide synthase messenger RNAs were observed in neurons of the hippocampal subfields. Bilateral removal of the adrenal glands resulted in a significant increase in nitric oxide synthase subtype I messenger RNA expression in the CA1 and CA3 pyramidal neurons and in granular cells of the dentate gyrus. To a lesser degree, the nitric oxide synthase subtype I messenger RNA signal was increased in CA2 pyramidal neurons. Daily administration of glucocorticoids for one week attenuated the adrenalectomy-induced increased level of expression of the messenger RNA encoding nitric oxide synthase subtype I in all areas studied. Because adrenalectomy, which suppresses the production of glucocorticoids, increases nitric oxide synthase expression, and replacement of adrenalectomized animals with glucocorticoids restores the basal levels of nitric oxide synthase subtype I expression, our results demonstrate an up-regulation of nitric oxide synthase subtype I messenger RNA in the absence of glucocorticoids in the hippocampus. The present findings suggest an involvement of the stress axis in the regulation of the synaptic plasticity process mediated by nitric oxide in the hippocampus.

AMPA receptor binding and subunit mRNA expression in prefrontal cortex and striatum of elderly schizophrenics

The dopamine hypothesis of schizophrenia has recently evolved into a model of dysfunctional integration between cortical and subcortical dopaminergic activity. Anatomical data suggest that regional alterations in dopaminergic activity may be linked by means of the rich glutamatergic innervation of the striatum by corticostriatal projections, suggesting a potential role for glutamatergic dysfunction in schizophrenia. Although pharmacological data have implicated the NMDA subtype of glutamate receptor in this illness, disturbance in AMPA receptor expression could potentially lead to the NMDA receptor hypoactivity hypothesized in schizophrenia. To address this possibility, we examined AMPA receptor binding and subunit mRNA levels in prefrontal cortex and striatum of schizophrenics and matched controls. There were no significant differences in AMPA receptor binding or subunit mRNA levels in either prefrontal cortical or striatal regions of schizophrenics. Furthermore, AMPA receptor expression did not seem to be regulated by chronic antipsychotic drug exposure, when neuroleptic treated and drug-free schizophrenics were analyzed separately. These data do not support a role for altered AMPA receptor expression in cortex and striatum in schizophrenia.

Nitric oxide in the stress axis

In recent years nitric oxide (NO) has emerged as a unique biological messenger. NO is a highly diffusible gas, synthesized from L-arginine by the enzyme nitric oxide synthase (NOS). Three unique subtypes of NOS have been described, each with a specific distribution profile in the brain and periphery. NOS subtype I is present, among other areas, in the hippocampus, hypothalamus, pituitary and adrenal gland. Together these structures form the limbic-hypothalamic-pituitary-adrenal (LHPA) or stress axis, activation of which is one of the defining features of a stress response. Evidence suggests that NO may modulate the release of the stress hormones ACTH and corticosterone, and NOS activity and transcription is increased in the LHPA axis following various stressful stimuli. Furthermore, following activation of the stress axis, glucocorticoids are thought to down-regulate the transcription and activity of NOS via a feedback mechanism. Taken together, current data indicate a role for NO in the regulation of the LHPA axis, although at present this role is not well defined. It has been suggested that NO may act as a cellular communicator in plasticity and development, to facilitate the activation or the release of other neurotransmitters, to mediate immune responses, and/or as a vasodilator in the regulation of blood flow. In the following review we summarize some of the latest insights into the function of NO, with special attention to its relationship with the LHPA axis.

Brain dopamine transporter messenger RNA and binding sites in cocaine users: a postmortem study

BACKGROUND

Results of recent radioligand binding experiments suggest that chronic cocaine exposure increases dopamine transporter (DAT) synthesis throughout the striatum of humans. However, detection of cocaine binding site increases in animals and humans has varied depending on the radioligand used. The present experiment tested the hypothesis in cocaine-using humans that synthesis of midbrain DAT messenger RNA increases parallel with increased striatal DAT binding sites.

METHODS

Striatal and midbrain samples were collected during autopsy examination from human cocaine users (n = 34) and from age-, sex-, and race-matched control subjects (n = 36). Levels of DAT messenger RNA were quantified in the medial and lateral midbrain regions using in situ hybridization, and striatal DAT binding sites were assessed by quantitative autoradiography using the DAT-specific radioligand [3H]WIN 35428.

RESULTS

Striatal DAT binding sites were markedly increased in cocaine users, but, paradoxically, medial DAT messenger RNA levels were decreased.

CONCLUSION

Cocaine exposure has a marked effect on DAT function, but the mechanisms involved may be complex.

The role of mineralocorticoid receptors in hypothalamic-pituitary-adrenal axis regulation in humans

In rodents, two types of glucocorticoid receptors, the mineralocorticoid (MR; type I) and the glucocorticoid (type II) receptors, have been demonstrated to play a role in hypothalamic-pituitary-adrenal (HPA) axis regulation. Because MR shows a very high affinity for cortisol, it has been suggested that MR plays an important role in restraint of CRH and ACTH secretion during the nadir of the circadian rhythm. Although a number of studies have established the importance of MR in rodents, the functional role of MR in humans has not been determined. These studies evaluated whether spironolactone, an MR antagonist, had a detectable effect on HPA axis regulation in humans, and whether the effect was greatest during the evening, when plasma cortisol concentrations are in the MR range. Compared to the placebo day, after a single dose of spironolactone at either 0800 or 1600 h, there is a significant increase in plasma cortisol, which is preceded by a rise in ACTH and beta-endorphin. A significant effect of spironolactone on cortisol secretion was demonstrated with no differences between the morning and evening. Because the effect of spironolactone on cortisol was short lived, a second experiment was conducted using two doses of spironolactone, again sampling in the morning and evening. After two doses of spironolactone, plasma cortisol levels showed a significant and sustained spironolactone-induced elevation for the entire sampling period. However, neither plasma beta-endorphin nor ACTH was increased compared to levels on the placebo day. These data suggest that MR appear to play a clear role in HPA axis regulation during the time of the circadian peak as well as the trough. Furthermore, MR blockade may affect the sensitivity of the adrenal to ACTH.

Alpha, beta, and gamma mineralocorticoid receptor messenger ribonucleic acid splice variants: differential expression and rapid regulation in the developing hippocampus

Two different types of corticoid receptor molecules bind circulating corticosterone in brain: mineralocorticoid receptors (MR) and glucocorticoid receptors. MR exhibit the highest affinity for the endogenous glucocorticoid in the rat, corticosterone. During development, low corticosterone levels influence neurogenesis, and these effects are probably MR mediated. Three MR complementary DNA clones, alpha, beta, and gamma, have been identified in the rodent. All of these MR complementary DNA clones have identical coding regions, but differ significantly at the 5'-untranslated end. Although the functional significance of these three messenger RNA (mRNA) species remains unknown, one hypothesis is that they reflect the ability of the brain to regulate the expression of MR, allowing multiple factors to differentially control transcription in a tissue- and time-specific manner. To investigate this possibility, we examined the presence of these distinct mRNA forms in the developing rat hippocampus (HC). In situ hybridization with specific alpha, beta, and gamma complementary RNA probes was performed in the HC of 3-, 5-, 7-, 12-, 14-, 28-, 35-, and 65-day-old animals. We found that there is differential expression of these forms in each of the HC subfields from infancy to adulthood. y expression appears to be associated with periods of cell birth and increased axonal sprouting. beta expression, on the other hand, may be best linked to periods of synaptogenesis, growth of commissural and associative terminal fields, and possibly active pruning. To explore the possibility that the differential gene expression may be related to corticosterone environment, adrenalectomy was performed. A rapid modulation of the MR mRNA variants (14 h) in an age- and site-specific fashion was seen. These findings suggest that the variation in expression and regulation during development of the multiple MR transcripts could reflect a complex pattern of developmental regulation that may involve a multitude of factors unique to each postnatal age and to the different neuronal populations within the hippocampal formation.

Mu and kappa opioid receptors in periaqueductal gray and rostral ventromedial medulla

The periaqueductal gray (PAG) and rostral ventromedial medulla (RVM) are important brain stem pain modulating regions. Recent evidence suggests that kappa opioids antagonize the effects of mu opioids in the RVM. However, the anatomical relationship between mu and kappa opioid receptors in PAG and RVM is not well characterized. This study examined relationships between mu and kappa opioid receptor immunoreactivity (IR) and mRNA in PAG and RVM. Brain slices were processed for either immunocytochemistry or in situ hybridization. We found considerable anatomical overlap of mu and kappa opioid IR and mRNA in the RVM and PAG. These results provide an anatomical basis for recent behavioral and electrophysiological findings in RVM, and suggest modulatory interactions between mu and kappa opioids in PAG.

Principles of psychoneuroendocrinology

The goal of this article is to describe some of the central nervous system circuits involved in the regulation of the hypothalamopituitary-adrenocortical (HPA) axis, with an emphasis on animal models believed to mimic the human experience of emotional stress. First, the basic constitutive elements of the HPA axis that control glucocorticoid secretion are reviewed. A description of the neural systems assumed to regulate the activity of the HPA axis, both anatomically and functionally, follows. It is argued that hypothalamic, septal and bed nucleus of the stria terminalis neurons are involved in the regulation of the HPA axis by situations eliciting emotional responses.

A.E. Bennett Research Award. Regulation of serotonin1A, glucocorticoid, and mineralocorticoid receptor in rat and human hippocampus: implications for the neurobiology of depression

BACKGROUND

Disturbances of the limbic-hypothalamic-pituitary-adrenal axis and the serotonin system are commonly found in depressive illness. Studying the effect of stress on these two neurobiological systems may give us important clues into the pathophysiology of affective illness and help us understand how stress and mood disorders are related.

METHODS

We studied the effect of chronic unpredictable stress and antidepressant treatment on serotonin 1A (5-HT1A), glucocorticoid (GR), anti mineralocorticoid (MR) receptor levels in rat hippocampus, using in situ hybridization and receptor autoradiography. We also used in situ hybridization to quantify hippocampal 5-HT1A, GR, and MR messenger (mRNA) levels in a small group of suicide victims with a history of depression, compared to matched controls (n = 6).

RESULTS

We found that rats subjected to chronic unpredictable stress showed a significant elevation of basal plasma corticosterone compared to nonstressed rats. Chronic stress also caused a decrease in 5-HT1A mRNA and binding in the hippocampus. In addition, chronic stress produced alterations on the MR/GR mRNA ratio in this same region. The decreases in 5-HT1A mRNA and binding, as well as the MR/GR alterations, were prevented in animals that received imipramine or desipramine antidepressant treatment. Zimelidine was unable to reverse stress-induced increases in corticosterone, and was only partially successful in preventing the stress-induced receptor changes in the hippocampus. Suicide victims with a history of depression showed changes that were very similar to the changes found in chronic stress.

CONCLUSIONS

Alterations in hippocampal 5-HT1A levels and in the MR/GR balance may be one of the mechanisms by which stress may trigger and/or maintain depressive episodes.

Creating a functional opioid alkaloid binding site in the orphanin FQ receptor through site-directed mutagenesis

Although much has been learned about the mechanisms of ligand selectivity between different opioid receptor subtypes, little is known about the common opioid binding pocket shared by all opioid receptors. The recently discovered orphanin system offers a good opportunity to study the mechanisms involved in the binding of opioid versus nonopioid ligands. In the current study, we adopt a "gain of function" approach aimed at shifting the binding profile of the orphanin FQ receptor toward that of the opioid receptors. After two rounds of mutagenesis, several orphanin FQ receptor mutants can be labeled with the opiate alkaloid [3H]naltrindole and show greatly increased affinities toward the opiate antagonists naltrexone, nor-binaltrophine HCl, and (-)-bremazocine. These orphanin FQ receptor mutants also display stereospecificity similar to that of opioid receptors. Furthermore, the orphanin FQ receptor mutant that has the best affinities toward the opioid alkaloids shows, in the presence of GTP and high salt concentration, an affinity-shift profile similar to that of the delta receptor. Most strikingly, the same mutant exhibits naltrindole-sensitive etorphine-stimulated [35S]guanosine-5'-O-(3-thio)triphosphate binding, whereas the effect of etorphine on GTP binding cannot be inhibited by naltrindole in the wild-type receptor. Our results indicate that 1) several residues in the orphanin FQ receptor are critical to its selectivity against the opiate alkaloids, particularly antagonists; and 2) mutating these residues to those of the opioid receptor at the corresponding position preserves the agonist/antagonist nature of opiate alkaloids as they interact with the mutant receptor. It is reasonable to hypothesize that the corresponding residues in the opioid receptors may form a functional common binding pocket for opiate alkaloids. These findings may be helpful to medicinal chemists in designing ligands for the orphanin FQ receptor based on the structure of the opiate alkaloids.

Pattern of c-fos mRNA induction in rat brain by acute morphine

Initially, opioid signaling had been thought to be mainly inhibitory in nature. However, it has been shown that opioids can activate specific signaling pathways and induce immediate early gene (IEG) transcription in brain. IEGs can then regulate the transcription of other genes, leading to changes in neuronal function in response to extracellular stimuli. This study was designed to identify brain regions that demonstrate specific induction of the IEG c-fos, a component of the AP-1 transcription factor, in response to acute morphine, and to contrast this induction with the stressful effects of the injection itself. Rats received either 10 mg/kg morphine or an equivalent volume of saline injected subcutaneously. Animals were then sacrificed 15, 30, or 60 min after injection. Specific induction of c-fos mRNA by morphine was seen in dorsomedial caudate-putamen, paraventricular nucleus of the thalamus, central and intralaminar thalamic nuclei, dorsal central grey, superior colliculus, lateral parabrachial nucleus, inferior olivary complex, and caudal nucleus tractus solitarius. These findings represent the first complete anatomical mapping of c-fos induction in rat brain, and show that acute morphine administration alters gene expression in several areas related to known functional properties of opioids. However, regions showing c-fos induction are not all classically associated with opioid receptors and opioid-mediated effects. These findings are considered in the context of the effects of opioids on neural circuitry as well as direct, receptor-mediated effects of morphine on neural cells.Key words: anatomy, immediate early genes, opioids, neural circuitry, nociception, transcriptional regulation.

Pattern of c-fos mRNA induction in rat brain by acute morphine

Initially, opioid signaling had been thought to be mainly inhibitory in nature. However, it has been shown that opioids can activate specific signaling pathways and induce immediate early gene (IEG) transcription in brain. IEGs can then regulate the transcription of other genes, leading to changes in neuronal function in response to extracellular stimuli. This study was designed to identify brain regions that demonstrate specific induction of the IEG c-fos, a component of the AP-1 transcription factor, in response to acute morphine, and to contrast this induction with the stressful effects of the injection itself. Rats received either 10 mg/kg morphine or an equivalent volume of saline injected subcutaneously. Animals were then sacrificed 15, 30, or 60 min after injection. Specific induction of c-fos mRNA by morphine was seen in dorsomedial caudate-putamen, paraventricular nucleus of the thalamus, central and intralaminar thalamic nuclei, dorsal central grey, superior colliculus, lateral parabrachial nucleus, inferior olivary complex, and caudal nucleus tractus solitarius. These findings represent the first complete anatomical mapping of c-fos induction in rat brain, and show that acute morphine administration alters gene expression in several areas related to known functional properties of opioids. However, regions showing c-fos induction are not all classically associated with opioid receptors and opioid-mediated effects. These findings are considered in the context of the effects of opioids on neural circuitry as well as direct, receptor-mediated effects of morphine on neural cells.

Cocaine, ethanol, and genotype effects on human midbrain serotonin transporter binding sites and mRNA levels

OBJECTIVE

Earlier platelet and postmortem brain studies have found alterations in serotonin transporter function in ethanol-abusing human subjects. The present investigation tested the hypothesis that brain serotonin transporter function is altered in chronic users of ethanol and cocaine, which might be related to a common serotonin transporter promoter polymorphism.

METHOD

Serotonin transporter binding sites, serotonin transporter mRNA levels, and serotonin transporter promoter variants were quantified in postmortem samples from a group of human subjects who had been ethanol users or cocaine users and then compared to those of a matched group of comparison subjects. Quantitative autoradiographic and in situ hybridization assays were performed in midbrain samples that contained the dorsal and median raphe nuclei (the location of serotonin cell bodies that innervate the forebrain).

RESULTS

There was a significant overall cocaine-by-ethanol-by-genotype interaction. Dorsal raphe [125I]CIT binding to the serotonin transporter was lower in cocaine users than in comparison subjects. In addition, serotonin transporter binding and serotonin transporter mRNA levels varied significantly by genotype. It was also found that serotonin transporter binding in subjects with either the short or heterozygote genotype was significantly higher in the ethanol-user subjects.

CONCLUSIONS

Serotonin transporter binding sites were regulated in a region-specific and substance-specific pattern, which was not simply a local response to functional blockade. Also, a reciprocal relationship appeared to exist between cocaine and ethanol effects in the dorsal raphe, which may have interesting clinical implications for dual-diagnosis patients. It is possible that serotonin transporter promoter genotype may play a complex role in chronic ethanol dependence.

Regulation of 5-HT receptors and the hypothalamic-pituitary-adrenal axis. Implications for the neurobiology of suicide

Disturbances in the serotonin (5-HT) system is the neurobiological abnormality most consistently associated with suicide. Hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis is also described in suicide victims. The HPA axis is the classical neuroendocrine system that responds to stress and whose final product, corticosteroids, targets components of the limbic system, particularly the hippocampus. We will review results from animal studies that point to the possibility that many of the 5-HT receptor changes observed in suicide brains may be a result of, or may be worsened by, the HPA overactivity that may be present in some suicide victims. The results of these studies can be summarized as follows: (1) chronic unpredictable stress produces high corticosteroid levels in rats; (2) chronic stress also results in changes in specific 5-HT receptors (increases in cortical 5-HT2A and decreases in hipocampal 5-HT1A and 5-HT1B); (3) chronic antidepressant administration prevents many of the 5-HT receptor changes observed after stress; and (4) chronic antidepressant administration reverses the overactivity of the HPA axis. If indeed 5-HT receptors have a partial role in controlling affective states, then their modulation by corticosteroids provides a potential mechanism by which these hormones may regulate mood. These data may also provide a biological understanding of how stressful events may increase the risk for suicide in vulnerable individuals and may help us elucidate the neurobiological underpinnings of treatment resistance.

Dopamine receptor transcript expression in striatum and prefrontal and occipital cortex. Focal abnormalities in orbitofrontal cortex in schizophrenia

BACKGROUND

The identification of novel subtypes of the dopamine receptors has renewed interest in the involvement of dopaminergic mechanisms in schizophrenia. We determined the expression of transcripts encoding the dopamine receptors in the brains of schizophrenic patients.

METHODS

The levels of the messenger RNA molecules encoding the 5 dopamine receptors were quantified in postmortem brain samples from 16 schizophrenic patients and 9 control subjects. Samples from multiple regions of the prefrontal cortex, primary visual cortex, and striatum were subjected to in situ hybridization followed by quantitative image analysis.

RESULTS

Expression of dopamine receptor transcripts did not differ between schizophrenic patients and controls in striatum or visual cortex. Dramatic decreases of dopamine receptor transcripts were found in the prefrontal cortex, but these changes were restricted to the D3 and D4 receptors, and localized to Brodmann area 11 (orbitofrontal cortex).

CONCLUSIONS

Cortical dopaminergic neurotransmission may be disrupted in schizophrenia at the level of receptor expression. There appears to be a focal abnormality of D3 and D4 messenger RNA expression in the prefrontal cortex, with down-regulation of both, consistent with prefrontal cortical hypodopaminergia in schizophrenia.

Correlation between Changes in Stress-Induced Corticosterone Secretion and GR mRNA Levels

The current study was conducted to determine the potential relationship between stress-induced corticosterone secretion and corticosteroid receptor mRNA levels after 5 days of intermittent stress. In particular, we were interested in the rate at which animals terminate a stress response, and how this termination may be altered by repeated stress. Adult male Sprague-Dawley rats were subjected to either 5 days of restraint stress or 5 days of an unpredictable stress paradigm. Restraint-stress induced corticosterone secretion was measured on Days 1 and 5 in both groups, and animals were killed on Day 6. Glucocorticoid receptor (GR), and mineralocorticoid (MR) mRNA levels were determined using in-situ hybridization techniques. Five days of restraint stress caused an habituation of the plasma corticosterone response to stress measured 60 and 90 min post-stress initiation; this pattern of corticosterone secretion was not observed in the animals subjected to unpredictable stress. Five days of either stress paradigm did not alter MR mRNA levels measured within the hippocampus or GR mRNA levels within the hippocampus or the medial parvocellular division of the paraventricular nucleus of the hypothalamus (mpPVN). However, an individual's GR mRNA levels measured within the CA1/2 region of the hippocampus and the mpPVN were significantly correlated with the degree of habituation of the corticosterone response to stress measured on Day 5. This suggests that an increase in the rate of termination of the stress response and levels of GR within the hippocampus and mpPVN may be functionally related.