P.2.d.015 Effects of antidepressants on behavioural despair in olfactory bulbectomized rats

P.2.d Affective disorders and antidepressants – Antidepressants (basic) vation distinct from that of reference agonists and that it favours activity in prefrontal cortex, a region associated with control of mood and cognitive function. This profile likely underlies the favourable influence of F15599 in models of depression and cognition (Depoortere et al., this meeting). P.2.d.014 F15599, a post-synaptic cortical preferential 5-HT1A agonist: II) Effect in rodent models of cognition/memory deficits R. Depoortere1 ° , A. Auclair1 , L. Bardin1 , A. Newman-Tancredi1 . 1 Institut de Recherche Pierre Fabre, Neurobiology 2, Castres, France Cognitive deficits are a core feature of numerous psychiatric/neurological disorders, most prominently schizophrenia, Alzheimer’s disease and depression. Activation of 5-HT1A receptors has been suggested to constitute a new therapeutic approach to not only treat the latter, but also to alleviate co-morbid cognitive deficits. Likewise, association of 5-HT1A receptor agonism with blockade of dopamine D2 receptors has been proposed to form the basis for third generation antipsychotics, free from extrapyramidal signs, and capable of countering cognitive impairment. In a companion poster (Newman-Tancredi et al., this meeting), we report on the binding and in-vitro functional profile of F15599, a selective 5-HT1A receptor agonist that preferentially targets postsynaptic receptors in the frontal cortex. Here, we investigated its efficacy in three models of pharmacologically-induced cognition/memory deficits. The first model was a scopolamine-induced deficit of working memory (WM) in an operant conditioningbased delayed non matching to position (DNMTP) task. In this model, rats were trained to press on the lever opposite to the one that was previously presented, in order to obtain food reinforcement The other two tests relied on NMDA/glutamatergic interference, using phencyclidine (PCP) to produce impairments. In the holeboard (HB) model, the efficiency to retrieve 4 food pellets placed at the bottom of 4/16 holes in the floor of an arena serves to calculate WM and reference memory (RM) indexes. The second test was an operant conditioning model of “cognitive flexibility”, the reversal learning task (RLT), in which rats were required to reverse a previously-learnt (initial) lever/light-tone association rule for food reinforcement. In the DNMTP model, F15599 (0.04 and 0.16 mg/kg ip), like the anticholinesterase agent tacrine (0.63 mg/kg ip), attenuated the decrease in correct responding induced by scopolamine (0.08 mg/kg sc). F15599 (0.16 mg/kg ip) partially opposed PCP (2.5 mg/kg sc)-induced deficits of WM and RM in the HB test, without deleterious effects of its own. Two other 5-HT1A receptor agonists, F13714 (0.04 mg/kg ip) and 8-OH-DPAT (0.16 mg/kg sc), that do not show a post- versus pre-synaptic preference, were inactive against PCP, and worsened basal performances in this model. In the RLT, F15599 (0.16 mg/kg ip) selectively diminished ‘cognitive inflexibility’ that resulted from protracted treatment with phencyclidine (PCP, 2.5 mg/kg sc, 14 days). In contrast, F13714 (0.04 mg/kg ip) worsened PCP-induced deficit. Taken together, these data indicate that selectively activating post-synaptic 5-HT1A receptors confers a promising profile of action in models of mnesic deficits induced by cholinergic and glutamatergic/NMDA interference. As such, drugs with postsynaptic preferential 5-HT1A receptor agonism, such as F15999, might be of benefit in pathologies with a high burden of cognitive/memory impairment such as depression, Alzheimer’s disease and schizophrenia.

S353

P.2.d.015 Effects of antidepressants on behavioural despair in olfactory bulbectomized rats V. Roman1 ° , R. Kedves1 , I. Gyertyan1 . 1 Gedeon Richter Plc., Behavioral Pharmacology, Budapest, Hungary Olfactory bulbectomy (OBX) is a model of depression [1]. Surgical removal of the olfactory bulbs has been shown to induce behavioural changes that can be reversed by chronic treatment with antidepressants. The OBX-induced behavioural changes include irritability, deficits in acquisition of avoidance responses and hyperactivity in a novel environment. Since these behaviours are not essentially depressive-like, we explored the effect of OBX and chronic antidepressants in a more relevant test; the forced swim test. This test is highly accepted in depression research however, it has not been used extensively in the OBX paradigm [2,3]. Young male Sprague-Dawley rats were olfactory bulbectomized according to procedures described in the literature. After two weeks of recovery, rats received daily intraperitoneal injections of fluoxetine and desipramine (10 mg/kg; 2 ml/kg) for 14 days in 2 separate experiments. When the antidepressant treatment had been completed, rats were tested in the forced swim test (cylinder width, 20 cm; water depth, 30 cm; water temperature, 23−25 ºC), which included a 15-min pre-test swimming session and the day after a 5-min test swim. During the test swim, time spent swimming, climbing and immobile were measured. At the end of experiments, rats were sacrificed and olfactory bulbectomy was verified by gross anatomical observation. One-way ANOVA and the post hoc Tukey HSD test was used for statistical analysis (level of significance: p < 0.05). Results of the experiment with fluoxetine show that vehicletreated OBX rats swam significantly less than sham controls (Table 1). Fluoxetine-treated OBX animals significantly swam more than vehicle-treated OBX rats and were significantly less immobile compared to the vehicle treated sham and OBX groups. In the experiment with the tricyclic desipramine, vehicle-treated OBX rats swam less and were more immobile than sham controls (Table 1). Desipramine-treated OBX animals spent signifcantly less time immobile than vehicle-treated OBX rats. Desipramine also produced a non-significant decrease in immobility (and increase in swimming) in sham animals. Based on the results, we conclude that OBX may lead to behavioural despair in the forced swim test indicating a depressivelike state. Furthermore, both the selective serotonin reuptake inhibitor fluoxetine and the tricyclic desipramine affected OBX-induced despair. These results suggest that the forced swim test could be integrated into the behavioural OBX test battery. Table 1. surgery treatment

N

swimming (s) climbing (s) immobility (s)

sham

8 8 5 5 10 9 6 9

136.3±16.1 139.5±16.8 89.3±17.7# 201.9±14.3* 156.5±20.6 191.5±5.9 126.4±9.8# 179.0±6.7

OBX sham OBX

vehicle fluoxetine vehicle fluoxetine vehicle desipramine vehicle desipramine

58.8±12.1 60.5±10.9 48.8±19.4 48.9±12.5 53.5±12.7 54.7±7.4 48.9±10.0 77.6±5.0

103.2±17.0 98.9±16.2 160.1±29.6# 47.7±8.4* 87.8±16.5 52.0±9.0 122.3±8.6# 41.2±6.0# *

Data are mean±SEM. # p < 0.05 vs. sham+veh; *p < 0.05 vs. OBX+veh.

S354

P.2.d Affective disorders and antidepressants – Antidepressants (basic)

References [1] Song, C., Leonard, B.E., 2005, The olfactory bulbectomized rat as a model of depression. Neurosci Biobehav Rev 29, 627–647. [2] Gorka, Z., Earley, B., Leonard, B.E., 1985, Effect of bilateral olfactory bulbectomy in the rat, alone or in combination with antidepressants, on the learned immobility model of depression. Neuropsychobiology 13, 26−30. [3] Kelly, J.P., Leonard, B.E., 1999, An investigation of the antidepressant properties of lofepramine and its desmethylated metabolites in the forced swim and olfactory bulbectomized rat models of depression. Eur Neuropsychopharmacol 9, 101–105.

P.2.d.016 Depressive-resistant behavioural phenotype in mice overexpressing cannabinoid CB2 receptors M.S. Garc´ıa-Guti´errez1 ° , J. Manzanares1 . 1 Universidad Miguel Hern´andez, Instituto de Neurociencias, San Juan de Alicante, Spain Purpose of the study: The purpose of this study was to examine the role of the cannabinoid CB2 receptor in the regulation of depressive-like behaviours and in the actions of antidepressant drugs such as selective serotonin reuptake inhibitors. To this aim, transgenic mice overexpressing the cannabinoid CB2 receptor (CB2xP; developed in our laboratory) were challenged against different types of experimental paradigms to evaluate its response to depressive-like behaviours. Methods: CB2 gene expression in CB2xP and wild-type (WT) mice was assessed by quantitative real time PCR (RT-PCR) in microdissected brain nuclei. The role of the cannabinoid CB2 receptor in depression-like behaviours (tail-suspension test, novelty suppressed feeding test) was evaluated in CB2xP and WT mice. CB2xP and WT mice were exposed to the weekly chronic mild stress (CMS) regime for 6 weeks. The CMS procedure consisted of a variety of unpredictable mild stressors including periods of food deprivation (14 h), noise (2 h), restraint stress (1 h), intermittent lighting (3 h), continuous light (36 h), wet cage (12 h) and tilted cage (14 h). Once every week, the anxiolytic (light-dark box and elevated plus-maze test) and depressive-like behaviours (tail suspension test) of non-stressed and stressed groups were evaluated. The sucrose intake was measured at the end of the CMS. In addition, the behavioural effects of the antidepressant fluoxetine (10 mg/kg and 30 mg/kg, p.o.) were evaluated in CB2xP and WT mice using the tail suspension paradigm. Results: Mice CB2xP showed a significantly reduced time of immobility compared to WT in the tail suspension test (p < 0.002, t-test followed by Student Newman Keul’s test). The time of latency to initiate consumption is lower and the amount of consumption is significantly higher in CB2Xp compared to WT mice in the novelty-suppressed feeding test (p < 0.042, t-test followed by Student Newman Keul’s test). CMS procedure significantly decreases the time spent in the lighted box (p < 0.005, Two Way ANOVA followed by Student Newman Keul’s test), the time visiting the open arms (p < 0.004, Two Way ANOVA followed by Student Newman Keul’s test) and the time of immobility in WT mice. In contrast, CMS failed to alter these measurements in CB2xP mice. The sucrose intake decreased significantly in WT mice after CMS (p < 0.015, t-test followed by Student Newman Keul’s test) but did not change in CB2xP mice. Under basal conditions, the acute administration of fluoxetine decreased the immobility time in WT mice (p<0.05, One Way ANOVA followed by Student Newman Keul’s test) but was without effects at any of the doses tested in CB2xP mice.

Conclusions: The results revealed that overexpression of cannabinoid CB2 receptors induced a depressive-resistant behavioural phenotype and a lack of antidepressant activity after the administration of fluoxetine. These results point out the cannabinoid CB2 receptor as a potential target in the treatment of depression related disorders.

P.2.d.017 Ketanzerine modulates expression of 5-HT2A/2C- and 17b-estradiol receptors mRNAs in female rats in forced swim test J. Fedotova1 ° , N. Losev1 . 1 Institute for Experimental Medicine, Dept. of Neuropharmacology, St. Petersburg, Russia Most preclinical studies examining the mechanisms of action of antidepressants are carried out using male animals. The participation of 5-HT1A- and 5-HT2A receptor sybtypes is the initial event that triggers a not completely understood process that results in clinical improvement in depression. Estrogens (E2) influence cognition, mood, depression and anxiety, an effect presumably mediated by the serotonergic system. A key receptors in this interplay may be the 5-HT1A- and 5-HT2A receptor sybtypes. The aim of this work was to study the effects of chronic treatment with high-selective agonist of 5-HT2A/2C receptors – m-CPP or antagonist of 5-HT2A/2C receptors – ketanzerine alone or in a combination with low dose of 17b-E2 and its effects on depression-like behavior and expression of 5-HT2A-, 5-HT2C-, 17b-E2-receptors mRNAs in the different structures of the brain in ovariectomized (OVX) rats. The OVX females have been treated with m-CPP (0.5 mg/kg, i.p.) or ketanzerine (0.1 mg/kg, i.p.) alone or in a combination with low dose of 17b-E2 (0.5 mkg per rat, s.c.) during 14 days. The control group rats have been treated by saline. The behavior of animals was assessed in the forced swim test (FST). The measurement of expression of 5-HT2A-, 5-HT2C-, 17b-E2 – receptors mRNAs in the hippocampus, amygdala and cortex was performed by RT-PCR. Statistical processing of the data was carried out with use of one-way ANOVA test and post-hoc Tukey test at p < 0.05. In forced swim test OVX rats demonstrated the increased time immobility (p < 0.05) and decreased time mobility as compared to the intact rats. Administration of 17b-E2 in the OVX rats reduced the time immobility to some extent as compared to the OVX rats (p < 0.05). In FST ketanzerine administered alone significantly decreased time immobility in OVX rats as compared to the OVX rats without treatment. Combination ketanzerine with 17b-E2 in OVX females resulted in exaggerated antidepressant effect as compared to the OVX rats (p < 0.05). On the contrary, administration of m-CPP alone or in combination with 17b-E2 to OVX rats significantly increased (p < 0.05) time immobility as compared to the control rats. Simultaneously, administration of ketanzerine to OVX rats induced significant increase of 5-HT2A/2Creceptors mRNAs expression and decrease of 17b-E2-receptor mRNA expression in the investigated structures of the brain in OVX rats as compared to the control intact rats (p < 0.05). Thus, modulation of 5-HT2A/2C- and 17b-E2 – receptors genes expression may be of importance for agonists of 5-HT2A/2C receptors and estrogens effects on mood and depression at estrogen deficiency. The data indicate in a close interaction between ovary hormonal and serotonergic systems of the brain in mechanisms of depression. Although the reactivity of central serotonergic system