Anxiolytic-like effects observed in rats exposed to the elevated zero-maze following treatment with 5-HT₂/5-HT₃/5-HT₄ ligands

The present study examined the effects of administering selective 5-HT antagonists and agonists to rats tested in the elevated zero-maze (EZM) model of anxiety. The EZM paradigm has advantages over the elevated plus-maze (EPM) paradigm with respect to measuring anxiety, yet has been utilized less frequently. Three experiments were conducted each with a diazepam control (0.25, 0.5 and 0.75 mg/kg). In the first experiment, we administered the 5-HT(2C) antagonist RS 102221 (0.5, 1.0, and 2.0 mg/kg) and 5-HT(2C) agonist MK-212 (0.25, 0.5 and 0.75 mg/kg); in the second experiment, we administered the 5-HT(3) antagonist Y-25130 (0.1, 1.0 and 3.0 mg/kg) and 5-HT(3) agonist SR 57227A (0.1, 1.0 and 3.0 mg/kg), and in the third experiment, we administered the 5-HT(4) antagonist RS 39604 (0.01, 0.1, 1.0 mg/kg) and 5-HT(4) agonist RS 67333 (0.01, 0.1 and 0.5 mg/kg). The administration of 5-HT(2/3/4) subtype antagonists all generated behavioral profiles indicative of anxiolytic-like effects in the EZM, which was apparent from examination of both traditional and ethological measures. While little effect was observed from 5-HT(2) and 5-HT(3) agonists, the 5-HT(4) agonist RS 67333 was found to produce a paradoxical anxiolytic-like effect similar to that produced by the 5-HT(4) antagonist RS 39604. We conclude by discussing the implications of these findings

Acute SSRI administration affects the processing of social cues in healthy volunteers.

Enhancement of serotonin neurotransmission plays an important role in the antidepressant response to agents presently available to treat depression. This response forms the major evidence for the role of serotonin in affective and social behaviour in humans. The present study investigated the effects of acute administration of the selective serotonin reuptake inhibitor (SSR1), citalopram (10 mg, i.v.) upon a measure of emotional processing in healthy female volunteers. Subjects completed a facial expression recognition task following infusion of citalopram or saline (between-subjects design, double-blind). Facial expressions associated with five basic emotions--happiness, sadness, fearfulness, anger and disgust--were displayed. Each face had been 'morphed' between neutral (0%) and each emotional standard (100%) in 10% steps, leading to a range of emotional intensities. Mood and subjective experience were also monitored throughout the testing session. Volunteers receiving citalopram detected a higher number of facial expressions of fear and happiness, with reduced response times, relative to those given the placebo. By contrast, changes in the recognition of other basic emotions were not observed following citalopram. Notable differences in mood were also not apparent in these volunteers. These results suggest that acute administration of antidepressant drugs may affect neural processes involved in the processing of social information. This effect may represent an early acute effect of SSRIs on social and emotional processing that is relevant to their therapeutic actions

Color vision in animals

BackgroundThe colors in which we see an object are not only dependent on the spectral composition of the reflected light but also represent an interpretation by our eyes and the trichromatic visual system.ObjectiveHow do animals of other species see the world?ResultsThe majority of mammals do not have three but only two types of cones and therefore have dichromatic color vision. Marine mammals and some nocturnally active mammals even have only one type of cone and are completely color blind. In contrast, birds as well as many fish and reptiles see in the world in more color hues and with four types of cones. Many vertebrates, insects and crustaceans can see not only the spectrum perceived by us but also ultraviolet radiation as light.ConclusionIn order to understand how animals of other species see the world, their visual systems must be understood and the animals must be tested in behavioral investigations