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F15599 is a novel agonist with high selectivity and efficacy at serotonin 5-HT(1A) receptors (5-HT(1A)Rs). In signal transduction, electrophysiological and neurochemical tests, F15599 preferentially activates post-synaptic 5-HT(1A)Rs in rat frontal cortex. Such a profile may translate to an improved profile of therapeutic activity for mood disorders. The in-vivo effects of F15599 were therefore compared with those of a related compound, F13714, in rat models of antidepressant activity and 5-HT(1A)R activation: forced swimming test (FST), conditioned stress-induced ultrasonic vocalization, 5-HT syndrome, plasma corticosterone and body temperature. Acute administration of F15599 or F13714 reduced immobility in the FST at low doses; these effects were long lasting and the effects of F15599 were maintained after repeated (5 d, p.o.) administration. Both compounds decreased ultrasonic vocalization duration at low doses. In contrast, higher doses of F15599 were required to induce lower lip retraction, elements of the 5-HT behavioural syndrome, hypothermia and to increase plasma corticosterone levels. Notably, there was a greater separation of ED50 between FST and other effects for F15599 than for F13714. Thus, the in-vivo potency of F15599 in models of antidepressant/anti-stress activity is similar to that of F13714, despite the fact that the latter has an in-vitro potency two orders of magnitude greater. In contrast F15599 has a lower propensity than F13714 to induce other serotonergic signs. The distinctive pharmacological profile of F15599 suggests that preferential targeting of post-synaptic 5-HT(1A)Rs constitutes a promising strategy for improved antidepressant therapy.

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To better understand the neurotrophic function of the neurotransmitter noradrenaline, we have developed a model of mesencephalic cultures in which we ®nd low concentrations (0.3±10 mM) of noradrenaline to be remarkably effective in promoting long-term survival and function of dopaminergic neurons. This protective action reproduced the effect of caspase inhibition. It was atypical in that it occurred independently of adrenoceptor activation and was mimicked by some antioxidants, redox metal chelators and the hydroxyl radical detoxifying enzyme catalase. Interestingly, intracellular reactive oxygen species (ROS) were drastically reduced by treatment with noradrenaline, indicating that the neurotransmitter itself acted as an antioxidant. Prevention of oxidative stress was, however, independent of the glutathione antioxidant defense system. Chemical analogues of noradrenaline bearing two free hydroxyl groups in the ortho position of the aromatic ring (o-catechols), as well as o-catechol itself, mimicked the survival promoting effects of the neurotransmitter, suggesting that this diphenolic structure was critical for both neuroprotection and reduction of ROS production. Paradoxically, the autoxidation of noradrenaline and the ensuing production of quinone metabolites may be required for both effects, as the neurotransmitter was spontaneously and rapidly degraded over time in the culture medium. These results support the concept that central noradrenergic mechanisms have a neuroprotective role, perhaps in part by reducing oxidative stress.

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