The octadecaneuropeptide ODN induces anxiety in rodents: possible involvement of a shorter biologically active fragment

Multi-omics insight into the molecular networks of mental disorder related genetic pathways in the pathogenesis of inflammatory bowel disease

Mental disorders are associated with inflammatory bowel disease (IBD), but the genetic pathophysiology is not fully understood. We obtained data on mental disorder-related gene methylation, expression, protein levels, and summary statistics of IBD, and performed Summary data-based Mendelian randomization and colocalization analyses to explore the causal associations and shared causal genetic variants between multiple molecular traits and IBD. Integrating multi-omics data, we found QDPR, DBI and MAX are associated with ulcerative colitis (UC) risk, while HP is linked to IBD risk. Inverse associations between gene methylation (cg0880851 and cg26689483) and expression are observed in QDPR, consistent with their detrimental role in UC. Methylation of DBI (cg11066750) protects against UC by enhancing expression. Higher levels of DBI (OR = 0.79, 95%CI = 0.69-0.90) and MAX (OR = 0.74, 95%CI = 0.62-0.90) encoded proteins are inversely associated with UC risk, while higher QDPR (OR = 1.17, 95%CI = 1.07-1.28) and HP (OR = 1.09, 95%CI = 1.04-1.14) levels increase UC and IBD risk. Our findings advance the understanding of IBD's pathogenic mechanisms and gut-brain interaction.

Acyl-CoA binding protein for the experimental treatment of anorexia

Extracellular acyl-coenzyme A binding protein [ACBP encoded by diazepam binding inhibitor (DBI)] is a phylogenetically ancient appetite stimulator that is secreted in a nonconventional, autophagy-dependent fashion. Here, we show that low ACBP/DBI plasma concentrations are associated with poor prognosis in patients with anorexia nervosa, a frequent and often intractable eating disorder. In mice, anorexia induced by chronic restraint stress (CRS) is accompanied by a reduction in circulating ACBP/DBI concentrations. We engineered a chemical-genetic system for the secretion of ACBP/DBI through a biotin-activatable, autophagy-independent pathway. In transgenic mice expressing this system in hepatocytes, biotin-induced elevations in plasma ACBP/DBI concentrations prevented anorexia induced by CRS or chemotherapeutic agents including cisplatin, doxorubicin, and paclitaxel. ACBP/DBI reversed the CRS or cisplatin-induced increase in plasma lipocalin-2 concentrations and the hypothalamic activation of anorexigenic melanocortin 4 receptors, for which lipocalin-2 is an agonist. Daily intravenous injections of recombinant ACBP/DBI protein or subcutaneous implantation of osmotic pumps releasing recombinant ACBP/DBI mimicked the orexigenic effects of the chemical-genetic system. In conclusion, the supplementation of extracellular and peripheral ACBP/DBI might constitute a viable strategy for treating anorexia.

Acyl coenzyme A binding protein (ACBP): An aging- and disease-relevant "autophagy checkpoint"

Acyl coenzyme A binding protein (ACBP), also known as diazepam-binding inhibitor (DBI), is a phylogenetically ancient protein present in some eubacteria and the entire eukaryotic radiation. In several eukaryotic phyla, ACBP/DBI transcends its intracellular function in fatty acid metabolism because it can be released into the extracellular space. This ACBP/DBI secretion usually occurs in response to nutrient scarcity through an autophagy-dependent pathway. ACBP/DBI and its peptide fragments then act on a range of distinct receptors that diverge among phyla, namely metabotropic G protein-coupled receptor in yeast (and likely in the mammalian central nervous system), a histidine receptor kinase in slime molds, and ionotropic gamma-aminobutyric acid (GABA)A receptors in mammals. Genetic or antibody-mediated inhibition of ACBP/DBI orthologs interferes with nutrient stress-induced adaptations such as sporulation or increased food intake in multiple species, as it enhances lifespan or healthspan in yeast, plant leaves, nematodes, and multiple mouse models. These lifespan and healthspan-extending effects of ACBP/DBI suppression are coupled to the induction of autophagy. Altogether, it appears that neutralization of extracellular ACBP/DBI results in "autophagy checkpoint inhibition" to unleash the anti-aging potential of autophagy. Of note, in humans, ACBP/DBI levels increase in various tissues, as well as in the plasma, in the context of aging, obesity, uncontrolled infection or cardiovascular, inflammatory, neurodegenerative, and malignant diseases.

Astrocytes: GABAceptive and GABAergic Cells in the Brain

Astrocytes, the most numerous glial cells in the brain, play an important role in preserving normal neural functions and mediating the pathogenesis of neurological disorders. Recent studies have shown that astrocytes are GABAceptive and GABAergic astrocytes express GABA_A receptors, GABA_B receptors, and GABA transporter proteins to capture and internalize GABA. GABAceptive astrocytes thus influence both inhibitory and excitatory neurotransmission by controlling the levels of extracellular GABA. Furthermore, astrocytes synthesize and release GABA to directly regulate brain functions. In this review, we highlight recent research progresses that support astrocytes as GABAceptive and GABAergic cells. We also summarize the roles of GABAceptive and GABAergic astrocytes that serve as an inhibitory node in the intercellular communication in the brain. Besides, we discuss future directions for further expanding our knowledge on the GABAceptive and GABAergic astrocyte signaling.

Metabolic and psychiatric effects of acyl coenzyme A binding protein (ACBP)/diazepam binding inhibitor (DBI)

Acyl coenzyme A binding protein (ACBP), also known as diazepam binding inhibitor (DBI) is a multifunctional protein with an intracellular action (as ACBP), as well as with an extracellular role (as DBI). The plasma levels of soluble ACBP/DBI are elevated in human obesity and reduced in anorexia nervosa. Accumulating evidence indicates that genetic or antibody-mediated neutralization of ACBP/DBI has anorexigenic effects, thus inhibiting food intake and inducing lipo-catabolic reactions in mice. A number of anorexiants have been withdrawn from clinical development because of their side effects including an increase in depression and suicide. For this reason, we investigated the psychiatric impact of ACBP/DBI in mouse models and patient cohorts. Intravenously (i.v.) injected ACBP/DBI protein conserved its orexigenic function when the protein was mutated to abolish acyl coenzyme A binding, but lost its appetite-stimulatory effect in mice bearing a mutation in the γ2 subunit of the γ-aminobutyric acid (GABA) A receptor (GABA_AR). ACBP/DBI neutralization by intraperitoneal (i.p.) injection of a specific mAb blunted excessive food intake in starved and leptin-deficient mice, but not in ghrelin-treated animals. Neither i.v. nor i.p. injected anti-ACBP/DBI antibody affected the behavior of mice in the dark–light box and open-field test. In contrast, ACBP/DBI increased immobility in the forced swim test, while anti-ACBP/DBI antibody counteracted this sign of depression. In patients diagnosed with therapy-resistant bipolar disorder or schizophrenia, ACBP/DBI similarly correlated with body mass index (BMI), not with the psychiatric diagnosis. Patients with high levels of ACBP/DBI were at risk of dyslipidemia and this effect was independent from BMI, as indicated by multivariate analysis. In summary, it appears that ACBP/DBI neutralization has no negative impact on mood and that human depression is not associated with alterations in ACBP/DBI concentrations.

The diversity of ACBD proteins - From lipid binding to protein modulators and organelle tethers

Members of the large multigene family of acyl-CoA binding domain containing proteins (ACBDs) share a conserved motif required for binding of Coenzyme A esterified fatty acids of various chain length. These proteins are present in the three kingdoms of life, and despite their predicted roles in cellular lipid metabolism, knowledge about the precise functions of many ACBD proteins remains scarce. Interestingly, several ACBD proteins are now suggested to function at organelle contact sites, and are recognized as host interaction proteins for different pathogens including viruses and bacteria. Here, we present a thorough phylogenetic analysis of the ACBD family and discuss their structure and evolution. We summarize recent findings on the various functions of animal and fungal ACBDs with particular focus on peroxisomes, the role of ACBD proteins at organelle membranes, and their increasing recognition as targets for pathogens.

FGIN-1-27, an agonist at translocator protein 18 kDa (TSPO), produces anti-anxiety and anti-panic effects in non-mammalian models

FGIN-1-27 is an agonist at the translocator protein 18 kDa (TSPO), a cholesterol transporter that is associated with neurosteroidogenesis. This protein has been identified as a peripheral binding site for benzodiazepines; in anamniotes, however, a second TSPO isoform that is absent in amniotes has been implicated in erythropoiesis. Functional conservation of the central benzodiazepine-binding site located in the GABA_A receptors has been demonstrated in anamniotes and amniotes alike; however, it was not previously demonstrated for TSPO. The present investigation explored the behavioral effects of FGIN-1-27 on an anxiety test in zebrafish (Danio rerio, Family: Cyprinide) and on a mixed anxiety/panic test on wall lizards (Tropidurus oreadicus, Family: Tropiduridae). Results showed that FGIN-1-27 reduced anxiety-like behavior in the zebrafish light/dark preference test similar to diazepam, but with fewer sedative effects. Similarly, FGIN-1-27 also reduced anxiety- and fear-like behaviors in the defense test battery in wall lizards, again producing fewer sedative-like effects than diazepam; the benzodiazepine was also unable to reduce fear-like behaviors in this species. These results A) underline the functional conservation of TSPO in defensive behavior in anamniotes; B) strengthen the proposal of using anamniote behavior as models in behavioral pharmacology; and C) suggest TSPO/neurosteroidogenesis as a target in treating anxiety disorders.

Genetic loss of diazepam binding inhibitor in mice impairs social interest

Neuropsychiatric disorders in which reduced social interest is a common symptom, such as autism, depression, and anxiety, are frequently associated with genetic mutations affecting γ-aminobutyric acid (GABA)ergic transmission. Benzodiazepine treatment, acting via GABA type-A receptors, improves social interaction in male mouse models with autism-like features. The protein diazepam binding inhibitor (DBI) can act as an endogenous benzodiazepine, but a role for DBI in social behavior has not been described. Here, we investigated the role of DBI in the social interest and recognition behavior of mice. The responses of DBI wild-type and knockout male and female mice to ovariectomized female wild-type mice (a neutral social stimulus) were evaluated in a habituation/dishabituation task. Both male and female knockout mice exhibited reduced social interest, and DBI knockout mice lacked the sex difference in social interest levels observed in wild-type mice, in which males showed higher social interest levels than females. The ability to discriminate between familiar and novel stimulus mice (social recognition) was not impaired in DBI-deficient mice of either sex. DBI knockouts could learn a rotarod motor task, and could discriminate between social and nonsocial odors. Both sexes of DBI knockout mice showed increased repetitive grooming behavior, but not in a manner that would account for the decrease in social investigation time. Genetic loss of DBI did not alter seminal vesicle weight, indicating that the social interest phenotype of males lacking DBI is not due to reduced circulating testosterone. Together, these studies show a novel role of DBI in driving social interest and motivation.

DBI/ACBP loss-of-function does not affect anxiety-like behaviour but reduces anxiolytic responses to diazepam in mice

Diazepam is well known for its anxiolytic properties, which are mediated via activation of the GABAA receptor. Diazepam Binding Inhibitor (DBI), also called acyl-CoA binding protein (ACBP), is a ubiquitously expressed protein originally identified based on its ability to displace diazepam from its binding site on the GABAA receptor. Central administration of ACBP or its cleaved fragment, commonly referred to as endozepines, induces proconflict and anxiety-like behaviour in rodents. For this reason, ACBP is known as an anxiogenic peptide. However, the role of endogenous ACBP in anxiety-like behaviour and anxiolytic responses to diazepam has not been investigated. To address this question, we assessed anxiety behaviour and anxiolytic responses to diazepam in two complementary loss-of-function mouse models including astrocyte-specific ACBP KO (ACBP(GFAP) KO) and whole-body KO (ACBP KO) mice. Male and female ACBP(GFAP) KO and ACBP KO mice do not show significant changes in anxiety-like behaviour compared to control littermates during elevated plus maze (EPM) and open field (OF) tests. Surprisingly, ACBP(GFAP) KO and ACBP KO mice were unresponsive to the anxiolytic effect of a low dose of diazepam during EPM tests. In conclusion, our experiments using genetic ACBP loss-of-function models suggest that endozepines deficiency does not affect anxiety-like behaviour in mice and impairs the anxiolytic action of diazepam.

Detection, characterization and biological activities of [bisphospho-thr3,9]ODN, an endogenous molecular form of ODN released by astrocytes

Astrocytes synthesize and release endozepines, a family of regulatory neuropeptides, including diazepam-binding inhibitor (DBI) and its processing fragments such as the octadecaneuropeptide (ODN). At the molecular level, ODN interacts with two types of receptors, i.e. it acts as an inverse agonist of the central-type benzodiazepine receptor (CBR), and as an agonist of a G protein-coupled receptor (GPCR). ODN exerts a wide range of biological effects mediated through these two receptors and, in particular, it regulates astrocyte activity through an autocrine/paracrine mechanism involving the metabotropic receptor. More recently, it has been shown that Müller glial cells secrete phosphorylated DBI and that bisphosphorylated ODN ([bisphospho-Thr(3,9)]ODN, bpODN) has a stronger affinity for CBR than ODN. The aim of the present study was thus to investigate whether bpODN is released by mouse cortical astrocytes and to compare its potency to ODN. Using a radioimmunoassay and mass spectrometry analysis we have shown that bpODN as well as ODN were released in cultured astrocyte supernatants. Both bpODN and ODN increased astrocyte calcium event frequency but in a very different range of concentration. Indeed, ODN stimulatory effect decreased at concentrations over 10(-10)M whereas bpODN increased the calcium event frequency at similar doses. In vivo effects of bpODN and ODN were analyzed in two behavioral paradigms involving either the metabotropic receptor (anorexia) or the CBR (anxiety). As previously described, ODN (100ng, icv) induced a significant reduction of food intake. Similar effect was achieved with bpODN but at a 10 times higher dose (1000 ng, icv). Similarly, and contrasting with our hypothesis, bpODN was also 10 times less potent than ODN to induce anxiety-related behavior in the elevated zero maze test. Thus, the present data do not support that phosphorylation of ODN is involved in receptor selectivity but indicate that it rather weakens ODN activity.

Macroglia-microglia interactions via TSPO signaling regulates microglial activation in the mouse retina

Chronic retinal inflammation in the form of activated microglia and macrophages are implicated in the etiology of neurodegenerative diseases of the retina, including age-related macular degeneration, diabetic retinopathy, and glaucoma. However, molecular biomarkers and targeted therapies for immune cell activation in these disorders are currently lacking. To address this, we investigated the involvement and role of translocator protein (TSPO), a biomarker of microglial and astrocyte gliosis in brain degeneration, in the context of retinal inflammation. Here, we find that TSPO is acutely and specifically upregulated in retinal microglia in separate mouse models of retinal inflammation and injury. Concomitantly, its endogenous ligand, diazepam-binding inhibitor (DBI), is upregulated in the macroglia of the mouse retina such as astrocytes and Müller cells. In addition, we discover that TSPO-mediated signaling in microglia via DBI-derived ligands negatively regulates features of microglial activation, including reactive oxygen species production, TNF-α expression and secretion, and microglial proliferation. The inducibility and effects of DBI-TSPO signaling in the retina reveal a mechanism of coordinated macroglia-microglia interactions, the function of which is to limit the magnitude of inflammatory responses after their initiation, facilitating a return to baseline quiescence. Our results indicate that TSPO is a promising molecular marker for imaging inflammatory cell activation in the retina and highlight DBI-TSPO signaling as a potential target for immodulatory therapies.

Endogenous positive allosteric modulation of GABA(A) receptors by diazepam binding inhibitor

Benzodiazepines (BZs) allosterically modulate γ-aminobutyric acid type-A receptors (GABAARs) to increase inhibitory synaptic strength. Diazepam binding inhibitor (DBI) protein is a BZ site ligand expressed endogenously in the brain, but functional evidence for BZ-mimicking positive modulatory actions has been elusive. We demonstrate an endogenous potentiation of GABAergic synaptic transmission and responses to GABA uncaging in the thalamic reticular nucleus (nRT) that is absent in both nm1054 mice, in which the Dbi gene is deleted, and mice in which BZ binding to α3 subunit-containing GABAARs is disrupted. Viral transduction of DBI into nRT is sufficient to rescue the endogenous potentiation of GABAergic transmission in nm1054 mice. Both mutations enhance thalamocortical spike-and-wave discharges characteristic of absence epilepsy. Together, these results indicate that DBI mediates endogenous nucleus-specific BZ-mimicking ("endozepine") roles to modulate nRT function and suppress thalamocortical oscillations. Enhanced DBI signaling might serve as a therapy for epilepsy and other neurological disorders.

The octadecaneuropeptide stimulates somatolactin release from cultured goldfish pituitary cells

The present study aimed to investigate the distribution of the octadecaneuropeptide (ODN) in the goldfish brain and to look for a possible effect of ODN on somatolactin (SL) release from pituitary cells. A discrete population of ODN-immunoreactive neurones was localised in the lateral part of the nucleus lateralis tuberis. These neurones sent projections through the neurohypophyseal tract towards the neurohypophysis, and nerve fibres were seen in the close vicinity of SL-producing cells in the pars intermedia. Incubation of cultured goldfish pituitary cells with graded concentrations of ODN (10(-9) -10(-5 ) m) induced a dose-dependent stimulation of SL-β, but not SL-α, release. ODN-evoked SL release was blocked by the metabotrophic endozepine receptor antagonist cyclo(1-8) [DLeu(5) ]OP but was not affected by the central-type benzodiazepine receptor antagonist flumazenil. ODN-induced SL release was suppressed by treatment with the phospholipase C (PLC) inhibitor U-73122 but not with the protein kinase A (PKA) inhibitor H-89. These results indicate that, in fish, ODN produced by hypothalamic neurones acts as a hypophysiotrophic neuropeptide stimulating SL release. The effect of ODN is mediated through a metabotrophic endozepine receptor positively coupled to the PLC/inositol 1,4,5-trisphosphate/protein kinase C-signalling pathway.

Repeated administration of an aqueous spray-dried extract of the leaves of Passiflora alata Curtis (Passifloraceae) inhibits body weight gain without altering mice behavior

ETHNOPHARMACOLOGICAL RELEVANCE

Passiflora alata is a Southern American species that constitutes many traditional remedies as well as phytomedicines used for sedative and anxiolytic purposes in Brazil. However studies on repeated treatment effects are scarce.

AIM OF THE STUDY

To evaluate behavioral, physiological and biochemical effects of the repeated treatment with an aqueous spray-dried extract of Passiflora alata leaves containing 2.5% (w/v) of flavonoids (PA) in mice.

MATERIAL AND METHODS

Male adult CF1 mice were treated (p.o.) for 14 days with PA (2.5; 25 or 250 mg/kg). The feeding behavior was evaluated at the beginning (1h after the first administration) and at the end of the treatment (15th day). The body weight gain and food consumption were monitored along the days. On day 15 mice were evaluated on plus maze, spontaneous locomotor activity, catalepsy and barbiturate sleeping time tests. Serum glucose, lipids, ALT and AST enzymes were determined. Liver, kidney, perirenal fat, epididymal and peritoneal fat were analyzed.

RESULTS

The repeated treatment with the highest dose tested (250 mg/kg) did not alter the mice behavior on open field, elevated plus maze, catalepsy and barbiturate sleeping time tests. Repeated administration of PA 250 decreased mice feeding behavior and weight gain. PA 25 and PA 250 reduced mice relative liver weight and caused mild hepatic hydropic degeneration as well as a decrease in alanine aminotransferase (ALT) serum level.

CONCLUSIONS

These results indicate that Passiflora alata does not present central cumulative effects and point to the needs of further studies searching for its hepatotoxicity as well as potential anorexigenic.

The octadecaneuropeptide ODN protects astrocytes against hydrogen peroxide-induced apoptosis via a PKA/MAPK-dependent mechanism

Astrocytes synthesize and release endozepines, a family of regulatory peptides, including the octadecaneuropeptide (ODN) an endogenous ligand of both central-type benzodiazepine (CBR) and metabotropic receptors. We have recently shown that ODN exerts a protective effect against hydrogen peroxide (H₂O₂)-induced oxidative stress in astrocytes. The purpose of the present study was to determine the type of receptor and the transduction pathways involved in the protective effect of ODN in cultured rat astrocytes. We have first observed a protective activity of ODN at very low concentrations that was abrogated by the metabotropic ODN receptor antagonist cyclo_1–8[DLeu⁵]OP, but not by the CBR antagonist flumazenil. We have also found that the metabotropic ODN receptor is positively coupled to adenylyl cyclase in astrocytes and that the glioprotective action of ODN upon H₂O₂-induced astrocyte death is PKA- and MEK-dependent, but PLC/PKC-independent. Downstream of PKA, ODN induced ERK phosphorylation, which in turn activated the expression of the anti-apoptotic gene Bcl-2 and blocked the stimulation by H₂O₂ of the pro-apoptotic gene Bax. The effect of ODN on the Bax/Bcl-2 balance contributed to abolish the deleterious action of H₂O₂ on mitochondrial membrane integrity and caspase-3 activation. Finally, the inhibitory effect of ODN on caspase-3 activity was shown to be PKA and MEK-dependent. In conclusion, the present results demonstrate that the potent glioprotective action of ODN against oxidative stress involves the metabotropic ODN receptor coupled to the PKA/ERK-kinase pathway to inhibit caspase-3 activation.

The stimulatory effect of the octadecaneuropeptide ODN on astroglial antioxidant enzyme systems is mediated through a GPCR

Astroglial cells possess an array of cellular defense systems, including superoxide dismutase (SOD) and catalase antioxidant enzymes, to prevent damage caused by oxidative stress on the central nervous system. Astrocytes specifically synthesize and release endozepines, a family of regulatory peptides including the octadecaneuropeptide (ODN). ODN is the ligand of both central-type benzodiazepine receptors (CBR), and an adenylyl cyclase- and phospholipase C-coupled receptor. We have recently shown that ODN is a potent protective agent that prevents hydrogen peroxide (H(2)O(2))-induced inhibition of SOD and catalase activities and stimulation of cell apoptosis in astrocytes. The purpose of the present study was to investigate the type of receptor involved in ODN-induced inhibition of SOD and catalase in cultured rat astrocytes. We found that ODN induced a rapid stimulation of SOD and catalase gene transcription in a concentration-dependent manner. In addition, 0.1 nM ODN blocked H(2)O(2)-evoked reduction of both mRNA levels and activities of SOD and catalase. Furthermore, the inhibitory actions of ODN on the deleterious effects of H(2)O(2) on SOD and catalase were abrogated by the metabotropic ODN receptor antagonist cyclo(1-8)[Dleu(5)]OP, but not by the CBR antagonist flumazenil. Finally, the protective action of ODN against H(2)O(2)-evoked inhibition of endogenous antioxidant systems in astrocytes was protein kinase A (PKA)-dependent, but protein kinase C-independent. Taken together, these data demonstrate for the first time that ODN, acting through its metabotropic receptor coupled to the PKA pathway, prevents oxidative stress-induced alteration of antioxidant enzyme expression and activities. The peptide ODN is thus a potential candidate for the development of specific agonists that would selectively mimic its protective activity.

Neurosteroid biosynthesis: enzymatic pathways and neuroendocrine regulation by neurotransmitters and neuropeptides

Neuroactive steroids synthesized in neuronal tissue, referred to as neurosteroids, are implicated in proliferation, differentiation, activity and survival of nerve cells. Neurosteroids are also involved in the control of a number of behavioral, neuroendocrine and metabolic processes such as regulation of food intake, locomotor activity, sexual activity, aggressiveness, anxiety, depression, body temperature and blood pressure. In this article, we summarize the current knowledge regarding the existence, neuroanatomical distribution and biological activity of the enzymes responsible for the biosynthesis of neurosteroids in the brain of vertebrates, and we review the neuronal mechanisms that control the activity of these enzymes. The observation that the activity of key steroidogenic enzymes is finely tuned by various neurotransmitters and neuropeptides strongly suggests that some of the central effects of these neuromodulators may be mediated via the regulation of neurosteroid production.

Pharmacological characterization of the receptor mediating the anorexigenic action of the octadecaneuropeptide: evidence for an endozepinergic tone regulating food intake

Peptides of the endozepine family, including diazepam-binding inhibitor, the triakontatetraneuropeptide, and the octadecaneuropeptide (ODN), act through three types of receptors, that is, central-type benzodiazepine receptors (CBR), peripheral-type (mitochondrial) benzodiazepine receptors (PBR) and a metabotropic receptor positively coupled to phospholipase C via a pertussis toxin-sensitive G protein. We have previously reported that ODN exerts a potent anorexigenic effect in rat and we have found that the action of ODN is not affected by the mixed CBR/PBR agonist diazepam. In the present report, we have tested the possible involvement of the metabotropic receptor in the anorexigenic activity of ODN. Intracerebroventricular administration of the C-terminal octapeptide (OP) and its head-to-tail cyclic analog cyclo(1-8)OP (cOP) at a dose of 100 ng mimicked the inhibitory effect of ODN on food intake in food-deprived mice. The specific CBR antagonist flumazenil and the PBR antagonist PK11195 did not prevent the effect of ODN, OP, and cOP on food consumption. In contrast, the selective metabotropic endozepine receptor antagonist cyclo(1-8)[DLeu(5)]OP (100-1000 ng; cDLOP) suppressed the anorexigenic effect of ODN, OP, and cOP. At the highest concentration tested (1000 ng), cDLOP provoked by itself a significant increase in food intake. Taken together, the present results indicate that the anorexigenic effect of ODN and OP is mediated through activation of the metabotropic receptor recently characterized in astrocytes. The data also suggest that endogenous ODN, acting via this receptor, exerts an inhibitory tone on feeding behavior.

Structure−Activity Relationships of a Series of Analogs of the Endozepine Octadecaneuropeptide (ODN11-18) on Neurosteroid Biosynthesis by Hypothalamic Explants

We have previously shown that the endozepine octadecaneuropeptide (ODN) stimulates the biosynthesis of neurosteroids from frog hypothalamic explants. In the present study, we have investigated the structure-activity relationships of a series of analogs of the C-terminal octapeptide of ODN (OP) on neurosteroid formation. We found that OP and its cyclic analog cyclo1-8OP stimulate in a concentration-dependent manner the synthesis of various steroids including 17-hydroxypregnenolone, progesterone, 17-hydroxyprogesterone and dehydroepiandrosterone. Deletion or Ala-substitution of the Arg1 or Pro2 residues of OP did not affect the activity of the peptide. In contrast, deletion or replacement of any of the amino acids of the C-terminal hexapeptide fragment totally abolished the effect of OP on neurosteroid biosynthesis. The present study indicates that the C-terminal hexapeptide of ODN/OP is the minimal sequence retaining full biological activity on steroid-producing neurons.

Catabolism of the octadecaneuropeptide ODN by prolyl endopeptidase: identification of an unusual cleavage site

The octadecaneuropeptide ODN (QATVGDVNTDRPGLLDLK), a biologically active fragment of diazepam-binding inhibitor, exerts a number of behavioral and neurophysiological activities. The presence of a proline residue in the sequence of ODN led us to investigate the role of proline endopeptidase (PEP) in the catabolism of this neuropeptide. The effect of PEP on the breakdown of ODN and related analogs was studied by combining RP-HPLC analysis and MALDI-TOF MS characterization. Incubation of ODN with PEP generated two products, i.e. ODN3-18 and ODN5-18 which resulted from cleavage of the Ala-Thr and Val-Gly peptide bonds. S 17092, a specific PEP inhibitor, significantly reduced the PEP-induced cleavages of ODN. Similarly, [Ala2]OP showed S 17092-sensitive post-alanine cleavage, while [pGlu1]ODN and OP (ODN11-18) were not catabolized by the enzyme. For all these peptides, cleavage of the Pro-Gly peptide bond by PEP was never observed, even after prolonged incubation times. In contrast, PEP hydrolyzed human urotensin II at the canonical post-proline site. Collectively, these data suggest that the Ala2 residue is the preferential cleavage site of ODN and that the Pro-Gly bond of ODN is not hydrolyzed by PEP. In addition, this study reveals for the first time that the endoproteolytic activity of PEP can specifically take place after a valine moiety.

Abnormal benzodiazepine receptor function in the depressive-like behavior of diabetic mice

We previously reported that streptozotocin (STZ)-induced diabetic mice exhibited depressive-like behavior in the tail suspension test. In this study, we examined the involvement of benzodiazepine receptor functions in this diabetes-induced depressive-like behavior in mice. STZ-induced diabetes significantly increased the duration of immobility without affecting spontaneous locomotor activity. This increase was dose-dependently and significantly suppressed by a benzodiazepine receptor antagonist, flumazenil (0.1-1 mg/kg, i.v.). However, flumazenil (0.1-1 mg/kg, i.v.) did not affect the duration of immobility in non-diabetic mice. Furthermore, flumazenil (1 mg/kg, i.v.) had no significant effect on spontaneous locomotor activity in either non-diabetic or diabetic mice. The benzodiazepine receptor inverse agonist methyl beta-carboline-3-carboxylate (beta-CCM; 0.03-0.3 mg/kg, i.v.) dose-dependently and significantly increased the duration of immobility in non-diabetic mice, but not in diabetic mice. beta-CCM (0.3 mg/kg, i.v.) significantly suppressed spontaneous locomotor activity in non-diabetic mice, but not in diabetic mice. These results indicate that diabetic mice may have enhanced negative allosteric modulation by benzodiazepine receptor ligands, such as diazepam binding inhibitors, under stressful conditions, but not free-moving conditions, and this abnormal function of benzodiazepine receptors may cause, at least in part, the expression of depressive-like behavior in diabetic mice.

Somatostatin down-regulates the expression and release of endozepines from cultured rat astrocytes via distinct receptor subtypes

Endozepines, a family of regulatory peptides related to diazepam-binding inhibitor (DBI), are synthesized and released by astroglial cells. Because rat astrocytes express various subtypes of somatostatin receptors (sst), we have investigated the effect of somatostatin on DBI mRNA level and endozepine secretion in rat astrocytes in secondary culture. Somatostatin reduced in a concentration-dependent manner the level of DBI mRNA in cultured astrocytes. This inhibitory effect was mimicked by the selective sst4 receptor agonist L803-087 but not by the selective sst1, sst2 and sst3 receptor agonists L779-591, L779-976 and L797-778, respectively. Somatostatin was unable to further reduce DBI mRNA level in the presence of the MEK inhibitor U0126. Somatostatin and the sst1, sst2 and sst4 receptor agonists induced a concentration-dependent inhibition of endozepine release. Somatostatin and the sst1, sst2 and sst4 receptor agonists also inhibited cAMP formation dose-dependently. In addition, somatostatin reduced forskolin-induced endozepine release. H89 mimicked the inhibitory effect of somatostatin on endozepine secretion. In contrast the PLC inhibitor U73122, the PKC activator PMA and the PKC inhibitor calphostin C had no effect on somatostatin-induced inhibition of endozepine release. The present data demonstrate that somatostatin reduces DBI mRNA level mainly through activation of sst4 receptors negatively coupled to the MAPK pathway, and inhibits endozepine release through activation of sst1, sst2 and sst4 receptors negatively coupled to the adenylyl cyclase/PKA pathway.

Modulation of ethanol withdrawal-induced anxiety-like behavior during later withdrawals by treatment of early withdrawals with benzodiazepine/gamma-aminobutyric acid ligands

BACKGROUND

Anxiety states, including those arising during acute or protracted withdrawal periods, may be precipitating factors in alcoholic relapse. Given the cyclical nature of ethanol withdrawal associated with repeated cycles of ethanol intake and abstinence in a pattern that often spans years, meaningful attempts to model ethanol withdrawal-associated anxiety should incorporate cycled ethanol treatments. The studies reported herein examined the effects of gamma-aminobutyric acid-modulating drugs on social interaction behavior-an established model of anxiety-in rats exposed to repeated cycles of ethanol treatment and withdrawal.

METHODS

Rats were exposed to 8 to 12 g/kg/day ethanol during three 7-day dietary cycles (5 days on ethanol diet followed by 2 days on control diet). Ethanol was administered either at hour 4 of withdrawal after cessation of each of the first 2 ethanol cycles or during the final withdrawal only. In other groups, the early withdrawals were treated with alphaxalone, diazepam, PK11159, or flumazenil to block anxiety-like behavior during an untreated later (third) withdrawal. The benzodiazepine inverse agonist DMCM (methyl-6, 7-dymerhoxy-4-ethyl-beta-carboline-3-carboxylate) was also given repeatedly to determine whether it would sensitize anxiety-like behavior during a future withdrawal. Finally, the effects of all drugs on deficits in locomotor behavior were assessed.

RESULTS

Pretreatment of earlier withdrawals with alphaxalone, diazepam, ethanol, or flumazenil reduced social interaction deficits during a later withdrawal, but pretreatment with PK11195 did not. In contrast, DMCM administered in lieu of early withdrawals increased social interaction deficits during an untreated later withdrawal. Locomotor deficits were significantly reversed only by the acute ethanol and diazepam treatment during the final withdrawal.

CONCLUSIONS

Single-dose administration of drugs that enhance or diminish activity at benzodiazepine-gamma-aminobutyric acid- receptors during earlier withdrawals reduced or potentiated, respectively, anxiety-like behavior during later, drug-free withdrawals. These results support the potential of the novel strategy of using prophylactic therapy administered during early withdrawals to ameliorate symptoms of later withdrawals.

Continuous exposure to nitric oxide enhances diazepam binding inhibitor mRNA expression in mouse cerebral cortical neurons

Effects of sustained exposure to nitric oxide (NO) formed by long-term activation of N-methyl-D-aspartate (NMDA) receptors and liberated from a long-lasting NO generator, DETA NONOate, on diazepam binding inhibitor (DBI) and its mRNA expressions were examined using mouse cerebral cortical neurons. Long-term exposure to NMDA increased DBI mRNA expression, and NO synthase inhibitors dose-dependently inhibited this increase. DETA NONOate dose-dependently increased DBI mRNA expression when exposing the neurons to this agent for 3 days and a maximal enhancement of the expression was found at 100 microM of the NO generator. In addition, a significant increase in DBI mRNA expression was observed 1 day after the exposure to 100 microM DETA NONOate, and the maximal expression was observed 2 days after the exposure, whereas transient exposure for less than 3 h to 100 microM DETA NONOate produced no changes in the expression. DETA NONOate (100 microM)-induced increase in DBI mRNA expression was completely abolished by concomitant exposure to hemoglobin. DBI content was also dose-dependently increased by DETA NONOate after the exposure for 3 days. The inhibition of cGMP formation by 1H-[1,2,4] oxadiazolo [4,3-alpha]quinoxalin-1-one (ODQ) showed no affects on the DETA NONOate-induced expression, suggesting that the increased expression of DBI mRNA is mediated via processes independent of cGMP. These results indicate that continuous exposure of the neurons to NO is an essential factor for increasing DBI mRNA expression in the neurons.

Behavioral effects of flumazenil in the social conflict test in mice

RATIONALE

Flumazenil, a competitive antagonist of benzodiazepine receptors (BZRs), has been used as a probe to detect effects of putative endogenous ligands for BZRs in anxiety. Flumazenil is renowned for its highly inconsistent behavioral effects.

OBJECTIVE

To ascertain effects of flumazenil in the social conflict test in mice, which provides complex measures for prediction of anxiolytic and anxiogenic activity of drugs in behaviorally different groups of animals.

METHODS

Singly housed male mice treated with flumazenil (5, 20 or 80 mg/kg i.p.) or vehicle were paired with untreated non-aggressive group-housed male mice in a novel cage. Behavior was analyzed from video tapes of the social interactions in three populations of mice: timid (n=21), aggressive (n=11), and sociable (n=7). Levels of gamma-aminobutyric acid (GABA) were measured in vivo in the prefrontal cortex.

RESULTS

Flumazenil reduced timid (defensive-escape) and increased locomotor activities in timid mice. The drug reduced aggressive and increased sociable (social investigation) activities in aggressive mice. These behavioral changes were produced at the lowest dose of flumazenil tested (5 mg/kg) and were not increased further by higher doses of the drug (20 mg/kg or 80 mg/kg). A tendency to increased timidity was found after flumazenil in sociable mice. Concentrations of GABA were markedly higher in the prefrontal cortex of sociable mice than in timid or aggressive mice.

CONCLUSIONS

Flumazenil produced moderate anxiolytic-like behavioural changes and a slight anxiogenic-like effect. The present data might be reflecting antagonism of corresponding endogenous BZR ligands. However, these putative ligands seem to exert only modest modulatory influence.

Polyunsaturated fatty acids in the blood of spontaneously or induced muricidal male Wistar rats

Serum levels of several n-6 and n-3 polyunsaturated fatty acids were compared in male Wistar muricidal (Mu) and non-Mu rats. The Mu behavior was either spontaneous or induced by long-term isolation, feeding with a starch-enriched polyunsaturated fatty acid diet (PUFA+S), water restriction, or adrenalectomy (ADX). Arachidonic acid (ARA) levels were lower in diet-induced (PUFA+S) Mu rats than in their non-Mu controls. Total n-6 fatty acid levels were also lower in spontaneously Mu rats than in spontaneously non-Mu rats. Docosahexaenoic acid (DHA) and total n-3 fatty acids levels were lower in rats with isolation-induced Mu behavior. The n-3/n-6 ratio was higher in spontaneously Mu rats than in spontaneously non-Mu rats. The changes in ARA levels were greater than those in DHA levels, possibly due to the higher blood-brain barrier passage of arachidonic acid. The results were analyzed in the light of recent results showing a role of PUFAs in human and animal behavior.

Pituitary adenylate cyclase-activating polypeptide (PACAP) stimulates endozepine release from cultured rat astrocytes via a PKA-dependent mechanism

Astroglial cells synthesize and release endozepines, neuropeptides that are related to the octadecaneuropeptide ODN. Glial cells also express PACAP/VIP receptors. We have investigated the possible effect of PACAP on the release of ODN-like immunoreactivity (ODN-LI) by cultured rat astrocytes. Administration of PACAP27 and PACAP38 induced a concentration-dependent increase in secretion of ODN-LI whereas VIP was approximately 1000-fold less potent. The maximum effect of PACAP38 occurred after 5 min, then gradually declined during the next 10 min. The stimulatory effects of PACAP and VIP were abrogated by the PACAP antagonist PACAP6-38. PACAP38 stimulated cAMP formation, activated polyphosphoinositide turnover, and provoked calcium mobilization from IP3-sensitive pools. The PKA inhibitor H89 suppressed PACAP-induced secretion of ODN-LI, whereas PLC inhibitor U73122 and the PKC inhibitor chelerythrine had no effect. In contrast, U73122 restored the stimulatory action of PACAP on ODN-LI release and cAMP formation during prolonged (15 min) incubation with the peptide, and this effect was prevented by PMA. The present results demonstrate that PACAP stimulates endozepine release through activation of PAC1 receptors coupled to the AC/PKA pathway. Our data also show that activation of the PLC/PKC pathway down-regulates the effect of PACAP on endozepine release.

Synthesis, conformational analysis and biological activity of cyclic analogs of the octadecaneuropeptide ODN. Design of a potent endozepine antagonist

The octadecaneuropeptide (ODN; QATVGDVNTDRPGLLDLK) and its C-terminal octapeptide (OP; RPGLLDLK), which exert anxiogenic activity, have been previously shown to increase intracellular calcium concentration ([Ca2+]i) in cultured rat astrocytes through activation of a metabotropic receptor positively coupled to phospholipase C. It has also been found that the [d-Leu5]OP analog possesses a weak antagonistic activity. The aim of the present study was to synthesize and characterize cyclic analogs of OP and [d-Leu5]OP. On-resin homodetic backbone cyclization of OP yielded an analog, cyclo1-8 OP, which was three times more potent and 1.4-times more efficacious than OP to increase [Ca2+]i in cultured rat astrocytes. Cyclo1-8 OP also mimicked the effect of both OP and ODN on polyphosphoinositide turnover. Conversely, the cyclo1-8 [d-Leu5]OP analog was totally devoid of agonistic activity but suppressed the effect of OP and ODN on [Ca2+]i and phosphoinositide metabolism in astrocytes. The structure of these cyclic analogs has been determined by two-dimensional 1H-NMR and molecular dynamics. Cyclo1-8 OP exhibited a single conformation characterized by a gamma turn comprising residues Pro2-Leu4 and a type III beta turn encompassing residues Leu5-Lys8. Cyclo1-8 [d-Leu5]OP was present as two equimolar conformers resulting from cis/trans isomerization of the Arg-Pro peptide bond. These pharmacological and structural data should prove useful for the rational design of non peptidic ODN analogs.

Anatomical and biochemical evidence for the synthesis of unconjugated and sulfated neurosteroids in amphibians

Various studies have shown that, in mammals, neurons and glial cells are capable of synthesizing bioactive steroids, or neurosteroids, which regulate the activity of the central nervous system (CNS). However, although steroid hormones are involved in the regulation of behavioral and neuroendocrine processes in amphibians, neurosteroid biosynthesis has never been studied in the CNS of non-mammalian vertebrates. Reviewed here are several data sets concerning the production of unconjugated and sulfated neurosteroids in amphibians. These data were obtained by investigating the immunohistochemical localization and activity of 3beta-hydroxysteroid dehydrogenase (3beta-HSD), 17beta-hydroxysteroid dehydrogenase (17beta-HSD) and hydroxysteroid sulfotransferase (HST), in the frog brain. Numerous 3beta-HSD-immunoreactive neurons were detected in the anterior preoptic area, nucleus of the periventricular organ, posterior tuberculum, ventral and dorsal hypothalamic nuclei. 17beta-HSD-like immunoreactivity was found in ependymal gliocytes bordering the lateral ventricles of the telencephalon. Two populations of HST-immunoreactive neurons were localized in the anterior preoptic area and the dorsal magnocellular nucleus of the hypothalamus. High amounts of progesterone (PROG), 17-hydroxyprogesterone (17OH-PROG), testosterone (T) and dehydroepiandrosterone sulfate (DHEAS) were measured in the frog brain by combining HPLC analysis of tissue extracts with radioimmunoassay detection. Incubation of telencephalic or hypothalamic explants with tritiated pregnenolone ([3H]PREG) yielded the synthesis of various metabolites including PROG, 17OH-PROG, DHEA and T. Incorporation of [35S]3'-phosphoadenosine 5'-phosphosulfate ([35S]PAPS) and [3H]PREG or [3H]DHEA into frog brain homogenates led to the formation of [3H,35S]pregnenolone sulfate ([3H,35S]PREGS) or [3H,35S]DHEAS, respectively. Altogether, these results demonstrate that the process of neurosteroid biosynthesis occurs in amphibians as previously seen in mammals.

The octadecaneuropeptide [diazepam-binding inhibitor (33-50)] exerts potent anorexigenic effects in rodents

The effects of intracerebroventricular administration of the octadecaneuropeptide ODN on food intake have been investigated in rat and mouse. In rats deprived of food from 9:00 a.m. to 7:00 p.m., i.c.v. injection of ODN (30 to 100 ng) provoked a dose-dependent reduction of food consumption during the following 12-h nocturnal period. At a dose of 100 ng, ODN almost completely suppressed food intake. Treatment of rats with diazepam (2 mg/kg s.c.; 15 min before ODN administration) did not affect the anorexigenic response evoked by 100 ng ODN. Continuous i.c.v. infusion of ODN (10 ng/h during 15 days) using osmotic minipumps, significantly reduced food intake during the 2nd, 3rd and 4th days of treatment. The decrease in food consumption was associated with a significant reduction in body weight, which persisted during the 15-day duration of the experiment. In mice deprived of food for 18 h, i.c.v. administration of a low dose of ODN (5 ng) significantly reduced food intake. Treatment of mice with diazepam (1 mg/kg s.c.; 10 min before ODN administration) did not prevent the inhibitory effect of ODN (100 ng) on food intake. The C-terminal octapeptide fragment of ODN mimicked the anorexigenic effect of the intact peptide. Taken together, the present data demonstrate that i.c.v. injection of ODN causes, in both rat and mouse, a long-lasting anorexigenic effect that is not mediated through central-type benzodiazepine receptors. The biologically active region of ODN appears to be located in the C-terminal domain of the peptide.

The octadecaneuropeptide ODN stimulates neurosteroid biosynthesis through activation of central-type benzodiazepine receptors

Neurosteroids may play a major role in the regulation of various neurophysiological and behavioural processes. However, while the biochemical pathways involved in the synthesis of neuroactive steroids in the central nervous system are now elucidated, the mechanisms controlling the activity of neurosteroid-producing cells remain almost completely unknown. In the present study, we have investigated the effect of the octadecaneuropeptide (ODN), an endogenous ligand of benzodiazepine receptors, in the control of steroid biosynthesis in the frog hypothalamus. Glial cells containing ODN-like immunoreactivity were found to send their thick processes in the close vicinity of neurones expressing the steroidogenic enzyme 3 beta-hydroxysteroid dehydrogenase. Exposure of frog hypothalamic explants to graded concentrations of ODN (10(-10)-10(-5) M) produced a dose-dependent increase in the conversion of tritiated pregnenolone into various radioactive steroids, including 17-hydroxypregnenolone, progesterone, 17-hydroxyprogesterone, dehydroepiandrosterone and dihydrotestosterone. The ODN-induced stimulation of neurosteroid biosynthesis was mimicked by the central-type benzodiazepine receptor (CBR) inverse agonists methyl beta-carboline-3-carboxylate (beta-CCM) and methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM). The stimulatory effects of ODN, beta-CCM and DMCM on steroid formation was markedly reduced by the CBR antagonist flumazenil. The ODN-evoked stimulation of neurosteroid production was also significantly attenuated by GABA. Collectively, these data indicate that the endozepine ODN, released by glial cell processes in the vicinity of 3 beta-hydroxysteroid dehydrogenase-containing neurones, stimulates the biosynthesis of neurosteroids through activation of central-type benzodiazepines receptors.

Reduction of pentylenetetrazol-induced convulsions by the octadecaneuropeptide ODN

Intracerebroventricular injection of the octadecaneuropeptide ODN in mouse, at doses of 12.5-1000 ng, reduced the percentage of convulsing animals and increased the latency of convulsions elicited by pentylenetetrazol (50 mg/kg, intraperitoneal [i.p.]). ODN also reduced the percentage of mortality induced by pentylenetetrazol (100 mg/kg, i.p.). The COOH-terminal octapeptide fragment of ODN was approximately equally effective but acted more rapidly than ODN to reverse the convulsant effect of pentylenetetrazol. ODN (100 ng, intracerebroventricular [i.c.v.]) increased the convulsion latency and reduced the percentage of animals that convulsed after the administration of the inverse agonist of benzodiazepine receptors DMCM (13 mg/kg, i.p.), whereas the benzodiazepine receptor antagonist flumazenil (1 mg/kg, subcutaneously) abrogated the protective effect of ODN (100 ng, i.c.v.) on pentylenetetrazol-induced convulsions. ODN (100 ng, i.c.v.) also reduced the percentage of DBA/2J mice displaying audiogenic convulsions. In contrast, ODN did not reduce the percentage of mice displaying tonic or clonic convulsions when electrical interauricular stimulations were applied. It is concluded that ODN, or more likely a proteolytic fragment derived from ODN, reduces pentylenetetrazol-induced convulsions through activation of central-type benzodiazepine receptors.

Effects of peptides: a cross-listing of peptides and their central actions published in the journal Peptides from 1994 through 1998

Effects of peptides on the central nervous system are presented in two ways so as to provide a cross-listing. In the first table, the peptides are listed alphabetically. In the second table, the central nervous system effects are arranged alphabetically. No longer can there be any doubt that peptides affect the central nervous system, sometimes in several ways.

Structure-activity relationships of a series of analogues of the octadecaneuropeptide ODN on calcium mobilization in rat astrocytes

The octadecaneuropeptide ODN (QATVGDVNTDRPGLLDLK), originally characterized as an endogenous ligand for central-type benzodiazepine receptors, increases intracellular calcium concentration ([Ca2+]i) in rat astroglial cells. A series of ODN analogues was synthesized, and each compound was studied for its ability to induce Ca2+ mobilization in cultured rat astrocytes. Replacement of each amino acid by an L-alanine residue (AlaScan) showed that the N-terminal region of the molecule was relatively tolerant to alanine substitution (2-8, 10), except for the Ala9-substituted analogue (9) which was totally devoid of activity. Pyroglutamization (21) and acetylation (22) of the Gln1 residue reduced the Ca2+ response suggesting that a free N-terminal amine function is required for full activity of ODN. Alanine substitution of the residues in the C-terminal region of the molecule (11-14, 16-18) significantly reduced the biological activity of ODN. In particular, modifications of the Leu15 residue (15, 20) abolished the Ca2+-mobilizing activity. The analogues [Ala9]ODN (9), [Ala15]ODN (15), [D-Thr9]ODN (19), and [D-Leu15]ODN (20) partially antagonized the Ca2+ response evoked by ODN. Most importantly, the octapeptide ODN11-18 (OP, 24) produced a dose-response curve that was superimposable to that obtained with ODN, indicating that the C-terminal region of the molecule possesses full biological activity. Finally, the AlaScan of OP revealed that replacement of the Leu5 residue by Ala (29) or D-Leu (33) totally suppressed the calcium response, confirming the crucial contribution of the Leu15 residue of ODN to the biological activity of the neuropeptide.

The octadecaneuropeptide ODN inhibits apomorphine-induced yawning in rats

High concentrations of diazepam-binding inhibitor (DBI) have been detected in brain areas containing dopaminergic cell bodies and nerve terminals. In the present study, we have investigated the effect of a proteolytic fragment of DBI, the octadecaneuropeptide ODN, on apomorphine-induced yawning in Sprague-Dawley rats. Injection of graded doses of ODN (12.5 to 100 ng i.c.v.) caused a dose-dependent inhibition of apomorphine-induced yawning and penile erections. At a dose of 100 ng, intracerebroventricularly administered ODN was able to inhibit, during more than 3 h, the apomorphine-evoked yawning. ODN also inhibited pilocarpine-induced yawning. Apomorphine induces a bell-shaped dose-dependent effect on yawning with a maximum response at the dose of 100 microg/kg and a much lower effect at a dose of 200 microg/kg. Injection (i.c.v.) of 100 ng ODN markedly attenuated the number of yawns induced by 100 microg/kg apomorphine but partially restored the yawning behavior in rats treated with a 200 microg/kg dose of apomorphine. At doses of 0.5 or 5 mg/kg s.c., diazepam did not modify the inhibitory effect of ODN on the apomorphine-induced yawning. Taken together, the present data suggest that ODN inhibits yawning downstream dopaminergic as well as cholinergic synapses involved in yawning. In addition, the effect of ODN cannot be ascribed to an inverse agonistic activity on central-type benzodiazepine receptors.