Comparison of the effects of benzodiazepine and nonbenzodiazepine anxiolytics on mouse-killing behavior in rats

DSP-1053, a novel serotonin reuptake inhibitor with 5-HT1A partial agonistic activity, displays fast antidepressant effect with minimal undesirable effects in juvenile rats

Enhancement of serotonergic neurotransmission has been the main stream of treatment for patients with depression. However, delayed therapeutic onset and undesirable side effects are major drawbacks for conventional serotonin reuptake inhibitors. Here, we show that DSP-1053, a novel serotonin reuptake inhibitor with 5-HT_1A partial agonistic activity, displays fast antidepressant efficacy with minimal undesirable effects, especially nausea and emesis in animal models. DSP-1053 bound human serotonin transporter and 5-HT_1A receptor with the K_i values of 1.02 ± 0.06 and 5.05 ± 1.07 nmol/L, respectively. This compound inhibited the serotonin transporter with an IC₅₀ value of 2.74 ± 0.41 nmol/L and had an intrinsic activity for 5-HT_1A receptors of 70.0 ± 6.3%. In rat microdialysis, DSP-1053, given once at 3 and 10 mg kg⁻¹, dose-dependently increased extracellular 5-HT levels. In the rat forced swimming test, 2-week administration of DSR-1053 (1 mg kg⁻¹) significantly reduced rats immobility time after treatment, whereas paroxetine (3 and 10 mg kg⁻¹) required 3-week administration to reduce rats immobility time. In olfactory bulbectomy model, 1- and 2-week administration of DSP-1053 reduced both of emotional scores and activity in the open field, whereas paroxetine required 2 weeks to show similar beneficial effects. Although single administration of DSP-1053-induced emesis and vomiting in the rat and Suncus murinus, multiple treatment with this compound, but not with paroxetine, decreased the number of vomiting episodes. These results highlight the important role of 5-HT_1A receptors in both the efficacy and tolerability of DSP-1053 as a new therapeutic option for the treatment of depression.

The olfactory bulbectomized rat as a model of depression: an update

The olfactory bulbectomized (OB) rat has been proposed as an animal model of depression. The following behavioural changes have been observed following bilateral olfactory bulbectomy: hyperactivity in an enclosed arena, such as the open-field; enhanced nocturnal hyperactivity in a 24-hr home cage activity monitor; deficits in memory, as shown by passive avoidance behaviour and in the Morris maze and the 8-arm radial maze; increased open arm entries in the elevated plus-maze; and changes in food motivated and conditioned taste aversion behaviour. Alterations in the noradrenergic, serotonergic, cholinergic, gamma-aminobutyric acid (GABA)ergic and glutamatergic neurotransmitter systems are also associated with olfactory bulbectomy. The variety of immune changes following olfactory bulbectomy includes reduced neutrophil phagocytosis, lymphocyte mitogenesis, lymphocyte number and negative acute phase proteins, increased leucocyte adhesiveness/aggregation, monocyte phagocytosis, neutrophil number and positive acute phase proteins. An enhanced nocturnal secretion of corticosterone is observed in OB rats, which is normally suppressed by dexamethasone. The most commonly employed behavioural indicator of antidepressant activity is attenuation of the OB-related hyperactivity in the open-field. However, many of the other behavioural, neurotransmitter and immune changes have been shown to be attenuated by chronic (but not acute) antidepressant treatment. Tricyclic antidepressants (amitriptyline, desipramine), atypical agents (mianserin), selective serotonin reuptake inhibitors (paroxetine, sertraline, fluvoxamine), reversible inhibitors of monoamine oxidase A (moclobemide), as well as putative antidepressants such as 5-hydroxytryptamine1A agonists (zalospirone, ipsapirone), noncompetitive N-methyl-D-aspartate antagonists (MK-801) and triazolobenzodiazepines (alprazolam, adinazolam), have demonstrated antidepressant-like activity in this model. As many of the changes exhibited by the OB rat are qualitatively similar to those observed in depressed patients, it may be concluded that the OB rat is a model of depression and not just a means whereby putative antidepressants may be tested.

Effects of psychotropic drugs on the behavior and neurochemistry of olfactory bulbectomized rats

Since its first characterization as a model for the detection of antidepressant drugs (van Riezen et al., 1976) a large body of data now supports the view that olfactory bulbectomy produces changes in animal behavior that are reversed by chronic treatment with antidepressants. The behavioral deficits seen in olfactory bulbectomized rats (such as irritability, deficits in acquisition of avoidance and of appetitive motivated conditioning and hyperactivity in a new environment) are probably the results of a reduced ability to adapt to environmental changes. These behavioral changes, their biochemical consequences and the effects of treatments with psychotropic drugs are reviewed. These studies suggest that the olfactory bulbectomized rat is a model of depression useful to detect antidepressant drugs.