Somatostatin receptors in the ventral pallidum/substantia innominata modulate rat locomotor activity

Characterization of the somatostatin system in tilapia: implications for growth and reproduction

Somatostatin (SST) plays diverse physiological roles in vertebrates, particularly in regulating growth hormone secretion from the pituitary. While the function of SST as a neuromodulator has been studied extensively, its role in fish and mammalian reproduction remains poorly understood. To address this gap, we investigated the involvement of the somatostatin system in the regulation of growth and reproductive hormones in tilapia. RNA sequencing of mature tilapia brain tissue revealed the presence of three SST peptides: SST6, SST3, and low levels of SST1. Four different isoforms of the somatostatin receptor (SSTR) subfamily were also identified in the tilapia genome. Phylogenetic and synteny analysis identified tiSSTR2-like as the root of the tree, forming two mega clades, with SSTR1 and SSTR4 in one and SSTR2a, SSTR3a, and SSTR5b in the other. Interestingly, the tiSSTR-5 isoforms 5x1, 5x2, and 5x3 were encoded in the sstr3b gene and were an artifact of misperception in the nomenclature in the database. RNA-seq of separated pituitary cell populations showed that SSTRs were expressed in gonadotrophs, with sstr3a enriched in luteinizing hormone (LH) cells and sstr3b significantly enriched in follicle-stimulating hormone (FSH) cells. Notably, cyclosomatostatin, an SSTR antagonist, induced cAMP activity in all SSTRs, with SSTR3a displaying the highest response, whereas octreotide, an SSTR agonist, showed a binding profile like that observed in human receptors. Binding site analysis of tiSSTRs from tilapia pituitary cells revealed the presence of canonical binding sites characteristic of peptide-binding class A G-protein-coupled receptors. Based on these findings, we explored the effect of somatostatin on gonadotropin release from the pituitary in vivo. Whereas cyclosomatostatin increased LH and FSH plasma levels at 2 h post-injection, octreotide decreased FSH levels after 2 h, but the LH levels remained unaffected. Overall, our findings provide important insights into the somatostatin system and its mechanisms of action, indicating a potential role in regulating growth and reproductive hormones. Further studies of the complex interplay between SST, its receptors, and reproductive hormones may advance reproductive control and management in cultured populations.

Immunoregulatory role of hesperidin against ovalbumin (OVA)-induced bronchial asthma and depression in rats

Links between bronchial asthma and depression have recently become a great subject of interest. The present study was carried out to assess the protective role of hesperidin against ovalbumin (OVA)-induced bronchial asthma that is associated with depression in rats, for this purpose, four groups. Rats were sensitized with intraperitoneal administration of 200 μg OVA/10 mg aluminum hydroxide (Al (OH) 3 for 3 consecutive days then at day 11 followed by intranasal challenge with OVA (1.5 mg/kg) at days 19, 20, and 21. Rats were pretreated with hesperidin (100 & 200 mg/kg) 1h before OVA challenge. At the end of the study, behavioral tests, biochemical indices, and histopathological architectures of lung and brain tissues were evaluated. Our findings showed that hesperidin significantly ameliorated the reduction in motor activity, motor coordination, forced swimming, CD4, CD25 and foxp3, interleukin-10 (IL-10), dopamine, serotonin, and neurotrophin-3 (NT3) as well as alleviated the elevation in transforming growth factor-beta (TGF-β), tumor necrosis factor-alpha (TNF-α), iL-5, and immunoglobulin E (IgE). In addition, hesperidin reduced cellular infiltration, alveolar sacs damage, the bronchioles wall disruption, and nuclei pyknosis in neuron cells. Finally, hesperidin may provide protection against OVA-induced asthma and depression. This impact could be mediated in part by its anti-inflammatory and immunoregulatory properties.

Neuromodulatory role of L-arginine: nitric oxide precursor against thioacetamide-induced-hepatic encephalopathy in rats via downregulation of NF-κB-mediated apoptosis

The aim of the present study was to investigate the impact of arginine (ARG), a nitric oxide (NO) precursor, on thioacetamide (TAA)-induced hepatic encephalopathy (HE) in rats by injection of TAA (100 mg/kg, i.p) three times per week for six consecutive weeks. TAA-injected rats were administered ARG (100 mg/kg; p.o.) concurrently with TAA for the six consecutive weeks. Blood samples were withdrawn, and rats were sacrificed; liver and brain tissues were isolated. Results of the present study demonstrated that ARG administration to TAA-injected rats revealed a restoration in the serum and brain ammonia levels as well as serum aspartate transaminase, alanine transaminase, and alkaline phosphatase and total bilirubin levels as well as behavioral alterations evidenced by restoration in locomotor activity, motor skill performance, and memory impairment. ARG showed also improvement in the hepatic and neuro-biochemical values, pro-inflammatory cytokines, and oxidative stress biomarkers. All these results were confirmed by histopathological evaluation as well as ultrastructural imaging of the cerebellum using a transmission electron microscope. Furthermore, treatment with ARG could ameliorate the immunological reactivity of nuclear factor erythroid-2-related factor 2 (Nrf2) and cleaved caspase-3 proteins in the cerebellum and hepatic tissues. From all the previous results, it can be fulfilled that ARG showed a beneficial role in modulating the adverse complications associated with TAA-induced HE in rats via reducing hyperammonemia and downregulating nuclear factor kappa B (NF-κB)-mediated apoptosis.

Flavonoids from Barnebydendron riedelii leaf extract mitigate thioacetamide-induced hepatic encephalopathy in rats: The interplay of NF-κB/IL-6 and Nrf2/HO-1 signaling pathways

Phytochemical investigation of the butanol fraction (BUF) derived from the 70% aqueous methanolic leaf extract of Barnebydendron riedelii led to the isolation of three flavonoid glycosides; kaempferol-3-O-α-l-rhamnopyranosyl-(1 → 6)-β-d-glucopyranoside, quercetin-3-O-α-l-rhamnopyranosyl-(1 → 6)-β-d-galactopyranoside and quercetin-3-O-α-l-rhamnopyranosyl-(1 → 6)-β-d-glucopyranoside. Docking studies were fulfilled to validate the possible bio-properties of BUF toward nuclear factorkappa B (NF-κB) and nuclear factor erythroid 2-related factor 2 (Nrf2). The protective role of BUF against behavioral, biochemical, molecular, histopathological and immunohistochemical alterations in thioacetamide (TAA)-induced hepatic encephalopathy in rats was investigated. The toxicological studies indicated that BUF was safe up to 2000 mg/kg bw. Prior to TAA intoxication, rats were orally treated with either BUF at multiple doses (70, 140 and 280 mg/kg bw) or lactulose (8 mL/kg bw) for 14 consecutive days. On the 13th and the 14th day, TAA (200 mg/kg bw/day) was intraperitoneally injected. The BUF significantly improved motor impairment, ameliorated cognitive deficits and attenuated TAA-induced hepatotoxicity. Moreover, BUF controlled the inflammatory processes by suppressing the hepatic inflammatory cytokine; interleukin-6 (IL-6) as well as its pro-inflammatory mediator; NF-κB supporting the molecular docking assessment. The brain neurotransmitters; dopamine, serotonin and noradrenaline, as well as ammonia levels were improved in BUF-treated TAA-intoxicated animals in a dose-dependent manner. Furthermore, BUF administration to TAA-intoxicated rats modulated the Nrf2 and heme oxygenase 1 (HO-1) genes expression in liver and brain tissues. The histological evaluation showed that pretreatment of TAA-intoxicated rats with BUF ameliorated the degenerative effects of TAA on liver and brain tissues as well as reduced the activation of cellular apoptotic marker; caspase-3 and glial fibrillary acidic protein (GFAP⁺) astrocytes. In conclusion, the observed hepato-neuroprotective effect of BUF is attributed to its flavonoidal content through its modulatory effects on of NF-κB/IL-6 and Nrf2/HO-1 signaling pathways.

Synergistic effect of aminoguanidine and l-carnosine against thioacetamide-induced hepatic encephalopathy in rats: behavioral, biochemical, and ultrastructural evidence

Hepatic encephalopathy depicts the cluster of neurological alterations that occur during acute or chronic hepatic injury. Hyperammonemia, inflammatory injury, and oxidative stress are the main predisposing factors for the direct and indirect changes in cerebral metabolism causing encephalopathy. The aim of this study was to evaluate the possible synergistic effect between aminoguanidine (AG; 100 mg/kg, p.o.) and l-carnosine (CAR; 200 mg/kg, p.o.) on hepatic encephalopathy that was induced by thioacetamide (TAA; 100 mg/kg, i.p.) administered three times weekly for six weeks. Behavioral changes, biochemical parameters, histopathological analysis, and immunohistochemical and ultrastructural studies were conducted 24 h after the last treatment. Combining AG with CAR improved TAA-induced locomotor impairment and motor incoordination evidenced by reduced locomotor activity and decline in motor skill performance, as well as ameliorated cognitive deficits. Moreover, both drugs restored the levels of serum hepatic enzymes and serum and brain levels of ammonia. In addition, the combination significantly modulated hepatic and brain oxidative stress biomarkers, inflammatory cytokines, and cleaved caspase-3 expression. Furthermore, they succeeded in activating nuclear erythroid 2-related factor 2 (Nrf2) expression and heme oxygenase-1 (HO-1) activity and ameliorating markers of hepatic encephalopathy, including hepatic necrosis and brain astrocyte swelling. This study shows that combining AG with CAR exerted a new intervention for hepatic and brain damage in hepatic encephalopathy due to their complementary antioxidant, anti-inflammatory effects and hypoammonemic effects via Nrf2/HO-1 activation and NO inhibition.

Neural Circuits for Sleep-Wake Regulation

The neural mechanisms of sleep, a fundamental biological behavior from invertebrates to humans, have been a long-standing mystery and present an enormous challenge. Gradually, perspectives on the neurobiology of sleep have been more various with the technical innovations over the recent decades, and studies have now identified many specific neural circuits that selectively regulate the initiation and maintenance of wake, rapid eye movement (REM) sleep, and non-REM (NREM) sleep. The cholinergic system in basal forebrain (BF) that fire maximally during waking and REM sleep is one of the key neuromodulation systems related to waking and REM sleep. Here we outline the recent progress of the BF cholinergic system in sleep-wake cycle. The intricate local connectivity and multiple projections to other cortical and subcortical regions of the BF cholinergic system elaborately presented here form a conceptual framework for understanding the coordinating effects with the dissecting regions. This framework also provides evidences regarding the relationships between the general anesthesia and wakefulness/sleep cycle focusing on the neural circuitry of unconsciousness induced by anesthetic drugs.

Brain sites mediating cyclosomatostatin-induced catalepsy in Wistar rats: A specific role for the nigrostriatal system and locus coeruleus

A decrease in somatostatin activity is observed in the Parkinsonian brain. In recent experiments on rats, we simulated this abnormality by intracerebroventricular injections of a somatostatin antagonist, cyclosomatostatin. The treated animals displayed catalepsy, a state that resembles the extrapyramidal signs of Parkinson's disease. The neuroanatomical substrates mediating the catalepsy-inducing effect of cyclosomatostatin are unknown. To clarify this issue, we assessed here the action of cyclosomatostatin injected into the substantia nigra pars compacta (SNc), dorsal striatum (DS), locus coeruleus (LC), pedunculopontine tegmental nucleus (PPTg), and inferior colliculus (IC). The experiments were conducted with male Wistar rats of 270-290 g bw, catalepsy was evaluated by using the bar test. The injections into the PPTg and IC were without effect whereas the intra-SNc, intra-DS, and intra-LC administrations produced distinct cataleptic response. Thus, it was shown for the first time that the LC is a brain center capable of causing catalepsy. These data provide new insights into the neuroanatomical organization of the catalepsy-initiating mechanism and suggest the LC representing a potential target for therapeutic manipulations of extrapyramidal dysfunctions.

Novel effect of Daflon and low-dose γ-radiation in modulation of thioacetamide-induced hepatic encephalopathy in male albino rats

This study was designed to evaluate the hepato and neuroprotective activity of Daflon and low-dose γ radiation on thioacetamide (TAA)-induced liver damage and hepatic encephalopathy (HE) in rats. Effect of daily Daflon treatment (100 mg/kg body weight, Per OS (p.o.) for consecutive 3 days) and/or fractionated low-dose γ-radiation (LDR; 0.25 Gy, twice the total dose of 0.5 Gy at the 1st and 3rd day, respectively) was evaluated against TAA (300 mg/kg, intraperitoneal × 3) induced liver damage and HE in rats. Serum aspartate transaminase, alanine transaminase, γ-glutamyltransferase, total bilirubin, ammonia, and manganese were estimated to evaluate liver function. In addition, malondialdehyde (MDA) as well as reduced glutathione (GSH), glutathione peroxidase (GPX), superoxide dismutase (SOD), and catalase (CAT) were determined to assess antioxidant capacity in liver tissue. Moreover, hepatic apoptotic markers (cysteine-dependent aspartate-directed proteases 3, 8 (caspase-3, 8) and cytochrome C) were estimated to indicate hepatic apoptosis. HE was evaluated through the determination of whole brain ammonia, manganese, MDA, GSH, GPX, SOD, CAT, and caspase-3. The cognitive and locomotor deficits were assessed via step through passive avoidance test, activity cage (actophotometer), γ-aminobutyric acid, and N-methyl-d-aspartate/adenosine triphosphate-neuronal nitric oxide synthase/nitric oxide-cyclic guanosine monophosphate axis in rats' cerebella and hippocampi. The involvement of hypoxia inducible factor-1α, aquaporine-4, and matrix metalloproteinase 9 in association with the brain water content (%) in the whole brain as an index for brain edema was also evaluated. The obtained results showed a marked amelioration of the aforementioned biochemical parameters and behavioral tasks which is supported by histopathological and immunohistochemical examination. It could be concluded that Daflon and LDR afforded hepatoprotection and neuroprotection against TAA-induced acute liver damage and HE.

Somatostatin-immunoreactive senile plaque-like structures in the frontal cortex and nucleus accumbens of aged tree shrews and Japanese macaques

BACKGROUND

Previously, we demonstrated decreased expression of somatostatin mRNA in aged macaque brain, particularly in the prefrontal cortex. To investigate whether or not this age-dependent decrease in mRNA is related to morphological changes, we analyzed somatostatin cells in the cerebra of aged Japanese macaques and compared them with those in rats and tree shrews, the latter of which are closely related to primates.

METHODS

Brains of aged macaques, tree shrews, and rats were investigated by immunohistochemistry with special emphasis on somatostatin.

RESULTS

We observed degenerating somatostatin-immunoreactive cells in the cortices of aged macaques and tree shrews. Somatostatin-immunoreactive senile plaque-like structures were found in areas 6 and 8 and in the nucleus accumbens of macaques, as well as in the nucleus accumbens and the cortex of aged tree shrews, where amyloid accumulations were observed.

CONCLUSIONS

Somatostatin degenerations may be related to amyloid accumulations and may play roles in impairments of cognitive functions during aging.

Somatostatin-28 modulates prepulse inhibition of the acoustic startle response, reward processes and spontaneous locomotor activity in rats

Somatostatins have been shown to be involved in the pathophysiology of motor and affective disorders, as well as psychiatric disorders, including schizophrenia. We hypothesized that in addition to motor function, somatostatin may be involved in somatosensory gating and reward processes that have been shown to be dysregulated in schizophrenia. Accordingly, we evaluated the effects of intracerebroventricular administration of somatostatin-28 on spontaneous locomotor and exploratory behavior measured in a behavioral pattern monitor, sensorimotor gating, prepulse inhibition (PPI) of the acoustic startle reflex, and brain reward function (measured in a discrete trial intracranial self-stimulation procedure) in rats. Somatostatin-28 decreased spontaneous locomotor activity during the first 10 min of a 60 min testing session with no apparent changes in the exploratory activity of rats. The highest somatostatin-28 dose (10 microg/5 microl/side) induced PPI deficits with no effect on the acoustic startle response or startle response habituation. The somatostatin-induced PPI deficit was partially reversed by administration of SRA-880, a selective somatostatin 1 (sst(1)) receptor antagonist. Somatostatin-28 also induced elevations in brain reward thresholds, reflecting an anhedonic-like state. The non-peptide sst(1) receptor antagonist SRA-880 had no effect on brain reward function under baseline conditions. Altogether these findings suggest that somatostatin-28 modulates PPI and brain reward function but does not have a robust effect on spontaneous exploratory activity. Thus, increases in somatostatin transmission may represent one of the neurochemical mechanisms underlying anhedonia, one of the negative symptoms of schizophrenia, and sensorimotor gating deficits associated with cognitive impairments in schizophrenia patients.

Cooperation between hippocampal somatostatin receptor subtypes 4 and 2: functional relevance in interactive memory systems

The hippocampal somatostatin (sst) receptor subtype 4 (sst(4)) modulates memory formation by diminishing hippocampus-based spatial function while enhancing striatum-dependent behaviors. sst(4)-mediated regulations on neuronal activity in the hippocampus appear to depend on both competitive and cooperative interactions with sst receptor subtype 2 (sst(2)). Here, we investigated whether interactions with sst(2) receptors are required for sst(4)-mediated effects on hippocampus-dependent spatial memory and striatum-dependent cued memory in a water maze paradigm. Competition was assessed in mice by intrahippocampal injections of the sst(4) agonist L-803,087 alone or combined with sst(2) agonists (L-779,976 or octreotide). Effects of L-803,087 were also tested in sst(2) knockout mice to assess for receptor cooperation. Finally, sst(2a) and sst(4) localizations within hippocampal subregions were analyzed by immunohistochemistry and expression levels of sst(2a) and sst(2b) were quantified by real-time qPCR. Hippocampal injections of L-803,087 impaired spatial memory but enhanced cued memory. The latter effect was lost not only in sst(2) knockout mice but also in the presence of sst(2) agonists, whereas the former effect remained unaffected by sst(2) agonists or gene deletion. Octreotide and L-779,976 did not yield memory effects but reduced swim velocity throughout the acquisition trials suggesting that stimulation of sst(2) affected motivation and/or anxiety. sst(2a) and sst(4) were respectively detected in the dentate gyrus (DG) and the CA1 subfield suggesting that their functional interactions are not mediated by direct receptor coupling. Hippocampus sst(2a) expression was 36-fold higher than sst(2b). Possible neural mechanisms and functional significances for interaction between memory systems in relationship with stress-induced changes in hippocampal functions are discussed.

Anxiolytic and antidepressant actions of somatostatin: the role of sst2 and sst3 receptors

RATIONALE AND OBJECTIVES

Somatostatin is a cyclic polypeptide that inhibits the release of a variety of regulatory hormones (e.g., growth hormone, insulin, glucagon, and thyrotropin). Somatostatin is also widely distributed within the central nervous system (CNS), acting both as a neurotransmitter and as a neuromodulator. Recently, we showed that intracerebroventricular (i.c.v.) administration of somatostatin reduced anxiety-like and depression-like behaviors in animal models. The somatostatin receptor subtypes that are involved in these behavioral effects, however, have not been investigated. In the CNS, the neurotransmitter actions of somatostatin are mediated through five G-protein coupled receptors (sst1 to sst5).

MATERIALS AND METHODS

We examined the behavioral effects of i.c.v. microinfusions of different doses of selective agonists of each of the five somatostatin receptor subtypes. Their behavioral effects were assessed in the elevated plus-maze and the forced swim apparatus, rodent models of anxiolytic and antidepressant drug effects, respectively.

RESULTS

Anxiety-like behavior was reduced following i.c.v. infusions of a selective sst2 receptor agonist, but not after infusions of the other four receptor agonists. An antidepressant-like effect was observed following infusions of either sst2 or sst3 agonists.

CONCLUSIONS

The results add to our nascent understanding of the role of somatostatin in anxiety- and depression-like behavior and suggest a clinical role for somatostatin agonists for the simultaneous treatment of anxiety and depression, which are often comorbid.

GABA antagonists reverse the somatostatin dependent attenuation of rat locomotor activity

Somatostatin infusion in rat ventral pallidum (VP) led to the attenuation of locomotor activity (Marazioti, A., Kastellakis, A., Antoniou, K., Papasava, D., Thermos, K., 2005. Somatostatin receptors in the ventral pallidum/substantia innominata modulate rat locomotor activity. Psychopharmacology 181, 319-326). In the present study, we investigated the putative circuitry involved in somatostatin's actions by examining the involvement of GABAergic neurotransmission in locomotor activity subsequent to somatostatin's infusion into the VP. Male Sprague-Dawley rats, 300-350 g, were used for all experiments. Saline or somatostatin (240 ng/0.5 microl/side) in the absence or presence of bicuculline (GABA-A antagonist; 5 mg/kg/ml, i.p.; 120 ng/side nucleus accumbens (NAc)) or phaclofen (GABA-B antagonist; 10 mg/kg/ml, i.p.; 120 ng/side NAc) were infused bilaterally, and the locomotor activity measured for 60 min using a rectangular activity cage. Somatostatin infused in the VP decreased the locomotor activity of the rat in a statistically significant manner. Bicuculline (i.p., and in the NAc) and phaclofen (only i.p.) reversed SRIF's actions, when administered prior to somatostatin's infusion in the VP. The present study provides further information on somatostatin's involvement in the VP-NAc circuitry, and implicates the GABAergic system in somatostatin's actions in the VP.

Activation of somatostatin receptors in the globus pallidus increases rat locomotor activity and dopamine release in the striatum

RATIONALE

Somatostatin and its receptors have been localized in brain nuclei implicated in motor control, such as the striatum, nucleus accumbens, ventral pallidum, and globus pallidus (GP).

OBJECTIVES

The objective of this study was to investigate the role of somatostatin receptors (sst(1,2,4)) in the GP on dopamine (DA)-mediated behaviors, such as locomotor activity, and to examine the GP-striatum circuitry by correlating the effect of somatostatin in the GP with the release of DA in the striatum.

MATERIALS AND METHODS

Animals received saline, somatostatin (60, 120, 240 ng/0.5 microl per side) or the following selective ligands: L-797,591 (sst(1) analog, 60, 120, 240 ng/0.5 microl per side), L-779,976 (sst(2) analog, 120, 240, 480 ng/0.5 microl per side), L-803,087 (sst(4) analog; 120, 240, 480 ng/0.5 microl per side), L-796,778 (sst(3) analog, 240 ng/0.5 microl per side), SRA-880 (sst(1) selective antagonist + somatostatin, 120 ng/0.5 microl per side), CYN154806 (sst(2) selective antagonist + somatostatin, 120 ng/0.5 microl per side) bilaterally in the GP of the rat. Locomotor activity was measured for 60 min. The effect of somatostatin, administered intrapallidally, on the extracellular concentrations of DA, 3,4-dihydroxyphenylacetic acid, and homovanillic acid in the striatum was also studied in the behaving rat using in vivo microdialysis methodology.

RESULTS

Somatostatin increased the locomotor activity of the rat in a dose-dependent manner. This effect was mediated by activation of the sst(1), sst(2), and sst(4) receptors. Selective sst agonists increased locomotor activity in a statistical significant manner, while selective sst(1) and sst(2) antagonists reversed the somatostatin-mediated locomotor activity to control levels. DA levels increased in the striatum after intrapallidal infusion of somatostatin (240 ng/side).

CONCLUSIONS

These data provide behavioral and neurochemical evidence of the functional role of somatostatin receptors in the GP-striatum circuitry.

Somatostatin increases rat locomotor activity by activating sst(2) and sst (4) receptors in the striatum and via glutamatergic involvement

The involvement of striatal somatostatin receptors (sst(1), sst(2) and sst(4)) in locomotor activity was investigated. Male Sprague-Dawley rats, 280-350 g, received in the striatum bilateral infusions of saline, somatostatin, and selective sst(1), sst(2), and sst(4) ligands. Spontaneous locomotor activity was recorded for 60 min. The involvement of excitatory amino acid receptors (AMPA and NMDA) on somatostatin's actions was also examined. Western blot analysis was employed for the identification of somatostatin receptors in striatal membranes. Somatostatin, sst(2) and sst(4), but not sst(1), selective ligands increased rat locomotor activity in a dose-dependent manner. Blockade of AMPA and NMDA receptors reversed somatostatin's actions. In conclusion, striatal somatostatin receptor activation differentially influence rat locomotor activity, while glutamatergic actions underlie the behavioral actions of somatostatin.

The hyperactive syndrome: metanalysis of genetic alterations, pharmacological treatments and brain lesions which increase locomotor activity

The large number of transgenic mice realized thus far with different purposes allows addressing new questions, such as which animals, over the entire set of transgenic animals, show a specific behavioural abnormality. In the present study, we have used a metanalytical approach to organize a database of genetic modifications, brain lesions and pharmacological interventions that increase locomotor activity in animal models. To further understand the resulting data set, we have organized a second database of the alterations (genetic, pharmacological or brain lesions) that reduce locomotor activity. Using this approach, we estimated that 1.56% of the genes in the genome yield to hyperactivity and 0.75% of genes produce hypoactivity when altered. These genes have been classified into genes for neurotransmitter systems, hormonal, metabolic systems, ion channels, structural proteins, transcription factors, second messengers and growth factors. Finally, two additional classes included animals with neurodegeneration and inner ear abnormalities. The analysis of the database revealed several unexpected findings. First, the genes that, when mutated, induce hyperactive behaviour do not pertain to a single neurotransmitter system. In fact, alterations in most neurotransmitter systems can give rise to a hyperactive phenotype. In contrast, fewer changes can decrease locomotor activity. Specifically, genetic and pharmacological alterations that enhance the dopamine, orexin, histamine, cannabinoids systems or that antagonize the cholinergic system induce an increase in locomotor activity. Similarly, imbalances in the two main neurotransmitters of the nervous system, GABA and glutamate usually result in hyperactive behaviour. It is remarkable that no genetic alterations pertaining to the GABA system have been reported to reduce locomotor behaviour. Other neurotransmitters, such as norepinephrine and serotonin, have a more complex influence. For instance, a decrease in norepinephrine synthesis usually results in hypoactive behaviour. However, a chronic increase in norepinephrine may result in hypoactivity too. Similarly, changes in both directions of serotonin levels may reduce locomotor activity, whereas alterations in specific serotonin receptors can induce hyperactivity. The lesion of at least 12 different brain regions can increase locomotor activity too. Comparatively, few focal lesions decrease locomotor activity. Finally, a large number of toxic events can increase locomotor activity, particularly if delivered during the prepuberal time window. These data show that there is a net imbalance in the number of altered genes/brain lesions/toxics that induce hyperactivity versus hypoactive behaviour. Although some of these data may be explained in terms of the activating role of subcortical systems (such as catecholamines), the larger number of alterations that induce hyperactivity suggests a different scenario. Specifically, we hypothesize (i) the existence of a control system that continuously inhibit a basally hyperactive locomotor tone and (ii) that this control system is highly vulnerable (intrinsic fragility) to any change in the genetic asset or to any toxic/drug delivered during prepuberal stages. Brain lesion studies suggest that the putative control system is located along an axis that connects the olfactory bulb and the enthorhinal cortex (enthorhinal-hippocampal-septal-prefrontal cortex-olfactory bulb axis). We suggest that the increased locomotor activity in many psychiatric diseases may derive from the interference with the development of this brain axis during a specific postnatal time window.

Predator stress induces behavioral inhibition and amygdala somatostatin receptor 2 gene expression

Psychological stressors precipitate and maintain stress-induced psychopathology, and it is likely that altered amygdala function underlies some of the deleterious effects of psychological stress. To understand the mechanisms underlying the linkage between the response to psychological stressors and maladaptive or psychopathological responses, we have focused on amygdala responsivity in animal models employing species-specific psychological stressors. In the present study, we characterized the effects of a 15-min exposure to a natural predator, the ferret, on rat behavior and the expression of the somatostatin family of genes in the amygdala. We examined the somatostatin family of genes because substantial evidence shows that central somatostatin systems are altered in various neuropsychiatric illnesses. We report that rats respond to acute ferret exposure with a significant increase in fearful and anxious behaviors that is accompanied by robust amygdala activation and an increase in somatostatin receptor 2 (sst2) messenger RNA expression within the amygdala and anterior cingulate cortex. These studies are the first to show stress-induced changes in amygdala sst2 expression and may represent one mechanism by which psychological stress is linked to adaptive and maladaptive behavioral responses.

Somatostatin regulates aggressive behavior in an African cichlid fish

Animals respond to environmental and social change with plasticity in the neural substrates underlying particular behavioral states. In the African cichlid fish Astatotilapia burtoni, social dominance status in males is accompanied by reduced somatic growth rate as well as increased somatostatin neuron size in the preoptic area. Although somatostatin is commonly studied within the context of growth, we show here for the first time that this ancient neuropeptide also plays a role in controlling social behavior. Somatostatin antagonists increased aggressive behavior in a dose-dependent fashion and the potent somatostatin agonist octreotide decreased aggression. We cloned and sequenced the genes encoding two somatostatin receptor subtypes in this species to study transcription in the gonads. When we examined somatostatin receptor gene expression in testes, expression of the somatostatin type 3 receptor was negatively correlated with an aggressive display and androgen levels. However, octreotide treatment did not reduce plasma testosterone or 11-ketotestosterone levels, suggesting that the behavioral effects of somatostatin are not mediated by androgens. These results show that somatostatin has important effects on social behavior. In dominant male A. burtoni, somatostatin may function to contain energetically costly processes such as somatic growth and aggressive behavior.

Chronic antidepressant treatment modulates the release of somatostatin in the rat nucleus accumbens

This study investigated the in vivo neuronal release of somatostatin in the rat nucleus accumbens (NAc), and the effect of chronic administration of antidepressants. Microdialysis studies were performed on male Sprague-Dawley rats, in accordance with the EU guidelines (EEC Council 86/609). Somatostatin levels were quantified by radioimmunoassay (RIA) or enzyme linked immuno sorbent assay (ELISA). A high concentration of potassium ions (K(+), 100 mM) was used to ascertain the neuronal release of somatostatin. Antidepressant treatments involved the administration of citalopram (20 mg/2 ml/kg, i.p., once daily) or desipramine (DMI, 5 mg/2 ml/kg, i.p., twice daily) for 21 days. Control groups received saline (2 ml/kg for 21 days, i.p.) once or twice daily respective of the antidepressant treatment. Basal levels of somatostatin released were found to be 20.01+/-0.52 fmol/sample. K(+) (100 mM) increased somatostatin levels at 205% of basal. Chronic citalopram and desipramine treatments also increased the somatostatin levels by 83+/-32% and 40+/-6% of basal, respectively. These findings indicate that somatostatin is released neuronally in the NAc. Antidepressants influence its release in a positive manner, suggesting the necessity of further studies for the elucidation of the involvement of somatostatin in the putative therapeutic effects of these agents.

The somatostatin sst1 receptor: an autoreceptor for somatostatin in brain and retina?

The sst1 receptor was the first of the 5 somatostatin receptors to be cloned by homology with the glucagon receptor 13 years ago. It is a 7-transmembrane domain G-protein-coupled receptor that is negatively coupled to adenylyl cyclase, but can also trigger other transduction pathways. The distribution of sst1 mRNA, immunolabeling, and radioligand binding are not entirely overlapping, but the recent availability of knockout (KO) mice and a (still limited) number of selective agonists/antagonists has increased our knowledge about this receptor. These new tools have helped to reveal a role for the sst1 receptor in hippocampal, hypothalamic, basal ganglia, and retinal functions. In at least the latter 3 structures, the sst1 receptor appears to act as an inhibitory autoreceptor located on somatostatin neurons, whereas in the hippocampus such a role is still based on circumstantial evidence.