Effects of sertraline on regional neuropeptide concentrations in olfactory bulbectomized rats

Intranasal infusion of melanocortin receptor four (MC4R) antagonist to rats ameliorates development of depression and anxiety related symptoms induced by single prolonged stress

Brain melanocortinergic systems and specifically melanocortin receptor four (MC4R) are implicated in modulation of anxiety- and depressive-like behavior induced by mild or moderate stress. Here we examine whether blockage of central MC4Rs with HS014 before severe traumatic stress may protect against development of anxiety and depression co-morbid with post-traumatic stress disorder (PTSD). Male rats were treated intranasally (IN) with vehicle or varied doses of HS014, 30min prior to single prolonged stress (SPS) animal model of PTSD. IN administration of 100μg HS014 pre-SPS improved despair behavior in forced swim (FS) immediately after immobilization stress part of SPS protocol. During all 4 intervals of 20min FS these rats spent less time immobile than rats given vehicle or 3.5ng HS014. This dose of HS014 also had a long-term beneficial effect manifested as reduction of immobility time in forced swim test performed after SPS. However, both HS014 doses were effective in ameliorating development of anxiety-like behavior after traumatic stress. Thus, rats given IN HS014 prior to SPS exhibited less open arms (OA) visits in elevated plus maze (EPM), spent longer time in OA and less in closed arms, had lower anxiety index, higher risk assessment and more head dips over borders in OA. They also spent longer time in the center of the open field and defecated less. Reduced grooming behavior in EPM was observed with 100μg HS014. This is the first study revealing pronounced resilience effects of HS014 on development of behavioral symptoms co-morbid with PTSD.

Antidepressant-like effects of Δ⁹-tetrahydrocannabinol and rimonabant in the olfactory bulbectomised rat model of depression

The endocannabinoid signalling system is widely accepted to play a role in controlling the affective state. Plant cannabinoids are well known to have behavioural effects in animals and humans and the cannabinoid CB(1) receptor antagonist rimonabant has recently been shown to precipitate depression-like symptoms in clinical trial subjects. The aim of the present study was to investigate the behavioural and neurochemical effects of chronic administration of Δ⁹-tetrahydrocannabinol (THC) and rimonabant on intact and olfactory bulbectomised (OB) rats used as a model of depression. As expected, OB rats were hyperactive in the open field. Repeated THC (2 mg/kg, i.p. once every 48 h for 21 days) and rimonabant (5 mg/kg, i.p. once every 48 h for 21 days) reduced this hyperactivity, which is typical of clinically effective antidepressant drugs. In intact animals, chronic THC increased brain derived neurotrophic factor (BDNF) expression levels in the hippocampus and frontal cortex but rimonabant had no effect. Rimonabant increased the levels of phosphorylated extracellular signal regulated kinases (p-ERKs(1/2)) in the hippocampus and prefrontal cortex and THC also increased expression in frontal cortex. OB did not affect BDNF or p-ERK(1/2) expression in the hippocampus or frontal cortex and in, contrast to the intact animals, neither THC nor rimonabant altered expression in the OB rats. These findings indicate antidepressant-like behavioural properties of both THC and rimonabant in OB rats although additional studies are required to clarify the relationship between the chronic effects of cannabinoids in other pre-clinical models and in human depression.

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.

Behavioural signs of depression and apoptosis in the limbic system following myocardial infarction: effects of sertraline

Depression is diagnosed in 15-30% of patients following myocardial infarction (MI) and this may also be observed in the rat. We measured the effects of the antidepressant sertraline on behavioural and biochemical events following MI in a rat model. Following surgery, MI rats and sham controls were treated with sertraline (10 mg/kg, i.p.) or saline. Subgroups of rats were tested for behavioural depression 14 days after surgery. Apoptosis was estimated in other rats by measuring caspase-3 activity and TUNEL positive cells (3 days after surgery) in limbic structures (amygdale, hippocampus, hypothalamus, frontal and prefrontal cortices). Bax/Bcl-2 ratio was measured 14 days after surgery. Behavioural signs of depression (decreased sucrose intake and forced swimming time) were found in saline-treated MI rats but not in sertraline-treated rats. Compared with controls, caspase-3 activity and TUNEL positive cells were significantly increased in most limbic structures of MI rats. High prefrontal Bax/Bcl-2 ratio in MI rats correlated with low forced swimming time. Apoptosis was not found in sertraline-treated MI rats. These results establish the bases of a rat model of depression following MI and show for the first time that a selective serotonin reuptake inhibitor prevents both behavioural and biochemical markers in this model.

Antidepressants influence somatostatin levels and receptor pharmacology in brain

This study investigated how the administration (acute and chronic) of the antidepressants citalopram and desmethylimipramine (DMI) influences somatostatin (somatotropin release inhibitory factor, SRIF) levels and SRIF receptor density (sst(1-5)) in rat brain. Animals received either of the following treatments: (1) saline for 21 days (control group), (2) saline for 20 days and citalopram or DMI for 1 day (citalopram or DMI acute groups), (3) citalopram or DMI for 21 days (citalopram or DMI chronic groups). Somatostatin levels were determined by radioimmunoassay. [(125)I]LTT SRIF-28 binding in the absence (labeling of sst(1-5)) or presence of 3 nM MK678 (labeling of sst(1/4)) and [(125)I]Tyr(3) octreotide (labeling of sst(2/5)) binding with subsequent autoradiography was performed in brains of rats treated with both antidepressants. Somatostatin levels were increased after citalopram, but not DMI administration, in the caudate-putamen, hippocampus, nucleus accumbens, and prefrontal cortex. Autoradiography studies illustrated a significant decrease in receptor density in the superficial and deep layers of frontal cortex (sst(2)), as well as a significant increase in the CA1 (sst(1/4)) hippocampal field in brains of chronically citalopram-treated animals. DMI administration increased sst(1/4) receptors levels in the CA1 hippocampal region. These results suggest that citalopram and to a lesser extent DMI influence the function of the somatostatin system in brain regions involved in the emotional, motivational, and cognitive aspects of behavior.

Effect of olfactory bulbectomy on adenylyl cyclase activity in the limbic system

Monoaminergic neurotransmission is a key element in the physiopathology of depressive disorders, but information is still sparse on animal models of this disease. Here, we used the olfactory bulbectomy (OBX) model of depression to characterize cAMP-second messenger signaling pathways, i.e., adenylyl cyclase activity (basal, sodium fluoride (NaF)- and forskolin-stimulated conditions) as well as Gi and Gs protein levels in different regions of the limbic system. Two weeks after surgery and compared to sham controls, OBX rats displayed reduced NaF-stimulated adenylyl cyclase activity and increased Gi/Gs ratios in the hypothalamus, pre-frontal and cingulate cortices but not in the amygdala, hippocampus and caudate nucleus. No differences were found in basal or forskolin-stimulated conditions. The observed reduction of adenylyl cyclase activity induced by NaF and the increase in the Gi/Gs ratio could explain the changes in neurotransmission in OBX rats as well as in humans with depression.

An arginine vasopressin V1b antagonist, SSR149415 elicits antidepressant-like effects in an olfactory bulbectomy model

Olfactory bulbectomized (OB) rats have been considered to serve as a useful animal model of depression in terms of behavioral, neurochemical, and neuroendocrine alterations, which reflect symptoms of patients with major depression. These behavioral and neurochemical changes in OB rats are normalized by the chronic administration of antidepressants. Recently, it has been reported that the compounds acting on stress-related peptide receptors such as an arginine vasopressin 1b (V(1b)) receptor antagonist and corticotropin-releasing factor (CRF) 1 receptor antagonists have antidepressant-like effects in several animal models. Here, the effects of acute and chronic (14 days) treatment with a V(1b) receptor antagonist (SSR149415) and a CRF1 receptor antagonist (CP-154,526) were examined in olfactory bulbectomy-induced hyperemotionality. Oral acute treatment with SSR149415 or CP-154,526 did not affect olfactory bulbectomy-induced hyperemotionality. In contrast, oral chronic treatment with SSR149415 (10 and 30 mg/kg) or CP-154,526 (10 mg/kg) significantly reduced hyperemotionality. The present results suggest that stress-related peptides such as arginine vasopressin and CRF might be implicated in olfactory bulbectomy-induced hyperemotionality. Furthermore, blockade of the V(1b) receptor or the CRF1 receptor may be useful in treating subjects suffering from chronic stressful conditions.

MCL0042: a nonpeptidic MC4 receptor antagonist and serotonin reuptake inhibitor with anxiolytic- and antidepressant-like activity

In the present study, we examined the anxiolytic and antidepressant effects of MCL0042, a novel compound showing activity in both MC4 receptor antagonism and serotonin transporter inhibition. MCL0042 showed relatively high affinity for the MC4 receptor and serotonin reuptake site, as determined by receptor binding assays. MCL0042 attenuated [Nle(4),d-Phe(7)]alpha-MSH-increased cAMP formation in MC4 receptor expressing cells, and it inhibited [(3)H]serotonin uptake by rat brain synaptosomes; thus, MCL0042 is an MC4 receptor antagonist and serotonin transporter inhibitor. Subcutaneous administration of MCL0042 significantly increased the number of licks in a Vogel punished drinking test in rats, and it also significantly attenuated swim stress-induced reduction in time spent in open arms in an elevated plus-maze task in rats, showing the anxiolytic-like potential of MCL0042. Moreover, repeated administration of MCL0042 for 14 days attenuated olfactory bulbectomy-induced locomotor hyperactivity in rats, indicating antidepressant-like potential. These data show that MCL0042 has unique properties of both the MC4 receptor antagonist and serotonin transporter inhibitor, and produces anxiolytic and antidepressant activity in rats. Moreover, blockade of both the MC4 receptor and serotonin reuptake sites might represent a useful approach in the treatment of anxiety and depression.

Corticotropin-releasing factor type-1 receptor antagonists: the next class of antidepressants?

Corticotropin-releasing factor (CRF) is a neuropeptide that plays a primary role in the neuroendocrine, autonomic, and behavioral responses to stressors. Numerous reports suggest that alterations in CRF function contribute to the pathogenesis of depression. Recently, selective nonpeptide CRF type 1 (CRF1) receptor antagonists have been discovered and several of these CRF1 receptor antagonists have demonstrated antidepressant-like efficacy in animals. The CRF1 receptor antagonists appear to be unique, as they exhibit antidepressant-like activity principally in animal models that are hyperresponsive to stress or under experimental conditions that alter endogenous stress-hormone activity. A nonpeptide CRF1 receptor antagonist has also been shown to reduce symptoms of major depression in an open-label clinical trial. Accumulating evidence supports a role for nonpeptide CRF1 receptor antagonists among the future pharmacotherapies for the treatment of depression.

Anxiolytic- and antidepressant-like profile of a new CRF1 receptor antagonist, R278995/CRA0450

1-[8-(2,4-dichlorophenyl)-2-methylquinolin-4-yl]-1,2,3,6-tetrahydropyridine-4-carboxamide benzenesulfonate (R278995/CRA0450) is a newly synthesized corticotropin-releasing factor subtype 1 (CRF(1)) receptor antagonist. In the present study, in vitro and in vivo pharmacological profiles of R278995/CRA0450 were investigated. R278995/CRA0450 showed high affinity for recombinant and native CRF(1) receptors without having affinity for the CRF(2) receptor. R278995/CRA0450 attenuated CRF-induced cyclic AMP formation in AtT-20 cells and CRF-induced forepaw treading in gerbils, indicating that R278995/CRA0450 is an antagonist of the CRF(1) receptor. In addition to CRF(1) receptor antagonism, R278995/CRA0450 showed high affinity for the sigma(1) receptor, and attenuated (+)-SKF10,047-induced head-weaving behavior, suggesting sigma(1) receptor antagonism. R278995/CRA0450 showed dose-dependent in vivo occupancy when assessed by ex vivo receptor binding, indicating good brain penetration. R278995/CRA0450 did not alter spontaneous anxiety when tested in the rat elevated plus maze (up to 3 mg/kg, p.o.) or lick suppression test (up to 10 mg/kg, i.p.). However, potent anxiolytic-like properties were observed in rats subjected to swim stress prior to testing on the elevated plus-maze, indicating activity primarily in tests taxing stress-induced anxiety. R278995/CRA0450 was inactive in mouse tail suspension, rat forced swim and rat differential-reinforcement-of-low-rate 72-s (DRL72), while it showed dose-dependent antidepressant-like effects in the rat learned helplessness paradigm and the olfactory bulbectomy model, demonstrating activity in a subset of animal models of depression associated with subchronic stress exposure. No or only mild effects were seen in tests of locomotor activity, motor coordination and sedation. These results indicate that R278995/CRA0450 is an orally active CRF(1) and sigma(1) receptor antagonist with potent anxiolytic-like and antidepressant-like activities.

Elevated concentrations of CRF in the locus coeruleus of depressed subjects

Research evidence that corticotropin-releasing factor (CRF) plays a role in the pathophysiology of major depressive disorder (MDD) has accumulated over the past 20 years. The elevation of lumbar cerebrospinal fluid (CSF) concentrations of CRF decreased responsiveness of pituitary CRF receptors to challenge with synthetic CRF, and increased levels of serum cortisol in MDD subjects support the hypothesis that CRF is chronically hypersecreted in at least the endocrine circuits of the hypothalamic-pituitary-adrenal (HPA) axis and may also involve other CRF brain circuits mediating emotional responses and/or arousal. One such circuit includes the excitatory CRF input to the locus coeruleus (LC), the major source of norepinephrine in the brain. Furthermore, there are now reports of decreased levels of CRF in lumbar CSF from MDD patients after symptom relief from chronic treatment with antidepressant drugs or electroconvulsive therapy. Whether this normalization reflects therapeutic effects on both endocrine- and limbic-associated CRF circuits has not yet been effectively addressed. In this brief report, we describe increased concentrations of CRF-like immunoreactivity in micropunches of post-mortem LC from subjects with MDD symptoms as established by retrospective psychiatric diagnosis compared to nondepressed subjects matched for age and sex.

Assessing antidepressant activity in rodents: recent developments and future needs

Animal models are indispensable tools in the search to identify new antidepressant drugs and to provide insights into the neuropathology that underlies the idiopathic disease state of depression. As new targets are developed, both serendipitously and through hypothesis-driven research, existing animal paradigms are being modified and new tests are being developed to detect antidepressant actions of compounds acting on a broad range of neural and genetic targets. This review focuses on recent findings regarding some of the most widely employed animal models used currently to predict antidepressant potential. Emphasis is placed on recent modifications to such paradigms that have increased their utility and reliability. Furthermore, some key issues that need to be addressed for future discovery of novel antidepressant agents are examined, and the available data on genetically altered mice that might lead to the discovery of novel targets for antidepressant action are collated.