The carotid body's physiological role is to sense arterial oxygen, CO 2 and pH. It is however, also powerfully excited by inhibitors of oxidative phosphorylation. This latter observation is the cornerstone of the mitochondrial hypothesis which proposes that oxygen is sensed through changes in energy metabolism. All of these stimuli act in a similar manner, i.e. by inhibiting a background TASK-like potassium channel (K B ) they induce membrane depolarization and thus neurosecretion. In this study we have evaluated the role of ATP in modulating K B channels. We find that K B channels are strongly activated by MgATP (but not ATP 4 − ) within the physiological range (K 1/2 = 2.3 mM). This effect was mimicked by other Mg-nucleotides including GTP, UTP, AMP-PCP and ATP-γ-S, but not by PP i or AMP, suggesting that channel activity is regulated by a Mg-nucleotide sensor. Channel activation by MgATP was not antagonized by either 1 mM AMP or 500 μM ADP. Thus MgATP is probably the principal nucleotide regulating channel activity in the intact cell. We therefore investigated the effects of metabolic inhibition upon both [ The carotid body is a peripheral arterial chemoreceptor which senses oxygen, carbon dioxide and arterial pH. In response to hypoxia, hypercapnia or acidosis it evokes an increase in neural discharge within afferent fibres of the carotid sinus nerve which project to cardiovascular and respiratory control centres in the brain stem. This results in increased ventilation, stimulation of the sympathetic nervous system and modulation of blood flow and cardiac output (Daly, 1997). The primary sensory element within the carotid body is the type-1 or glomus cell (Fidone & Gonzalez, 1986;Gonzalez et al. 1994).Type-1 cells express a background potassium channel (K B channel) with biophysical and pharmacological properties similar to those of the TASK group of tandem-pdomain K + channels, including weak rectification (similar to that predicted by the Goldman-Hodgkin-Katz constant field equation); inhibition by acidosis, quinidine and bupivacaine; activation by halothane; and insensitivity to TEA and 4-AP (Buckler et al. 2000). These channels are active over a wide range of membrane potentials and are the predominant K + conductance at the resting membrane potential (Buckler, 1997;Williams & Buckler, 2004). As a consequence modulation of these channels has a marked influence upon the type-1 cell. Their inhibition by either hypoxia or acidosis, the two main physiological stimuli of arterial chemoreceptors, causes destabilization of the resting membrane potential resulting in a depolarizing receptor potential which then initiates electrical activity and voltage-gated calcium entry (Buckler & Vaughan-Jones, 1994a, 1994bBuckler, 1997;Buckler et al. 2000). Inhibition of other K + channels, particularly the large-conductance Ca 2+ -activated K + channels by hypoxia and other chemostimuli (Peers, 1990;Peers & O'Donnell, 1990;Peers & Green, 1991) may facilitate some aspects of this electrical signalling process although their ...

Drosophila melanogaster has been successfully used as a simple model to study the cellular and molecular mechanisms underlying behaviors, including the generation of motor programs. Thus, it has been shown that, as in vertebrates, CNS biogenic amines (BA) including serotonin (5HT) participate in motor control in Drosophila. Several evidence show that BA systems innervate an important association area in the insect brain previously associated to the planning and/or execution of motor programs, the Mushroom Bodies (MB). The main objective of this work is to evaluate the contribution of 5HT and its receptors expressed in MB to motor behavior in fly larva. Locomotion was evaluated using an automated tracking system, in Drosophila larvae (3rd-instar) exposed to drugs that affect the serotonergic neuronal transmission: alpha-methyl-L-dopa, MDMA and fluoxetine. In addition, animals expressing mutations in the 5HT biosynthetic enzymes or in any of the previously identified receptors for this amine (5HT1AR, 5HT1BR, 5HT2R and 5HT7R) were evaluated in their locomotion. Finally, RNAi directed to the Drosophila 5HT receptor transcripts were expressed in MB and the effect of this manipulation on motor behavior was assessed. Data obtained in the mutants and in animals exposed to the serotonergic drugs, suggest that 5HT systems are important regulators of motor programs in fly larvae. Studies carried out in animals pan-neuronally expressing the RNAi for each of the serotonergic receptors, support this idea and further suggest that CNS 5HT pathways play a role in motor control. Moreover, animals expressing an RNAi for 5HT1BR, 5HT2R and 5HT7R in MB show increased motor behavior, while no effect is observed when the RNAi for 5HT1AR is expressed in this region. Thus, our data suggest that CNS 5HT systems are involved in motor control, and that 5HT receptors expressed in MB differentially modulate motor programs in fly larvae.

Biogenic amines (BAs) play a central role in the generation of complex behaviors in vertebrates and invertebrates, including the fly Drosophila melanogaster. The comparative advantages of Drosophila as a genetic model to study the contribution of BAs to behaviors stumble upon the difficulty to access the fly brain to ask relevant physiological questions. For instance, it is not known whether the activation of nicotinic acetylcholine receptors (nAChRs) induces the release of BAs in fly brain, a phenomenon associated to several behaviors in vertebrates. Here, we describe a new preparation to study the efflux of BAs in the adult fly brain by in vitro chronoamperometry. Using this preparation we show that nAChR agonists including nicotine induce a fast, transient, dosedependent efflux of endogenous BAs, an effect mediated by a-bungarotoxin-sensitive nAChRs. By using different genetic tools we demonstrate that the BA whose efflux is induced by nAChR activation is octopamine (Oct). Furthermore, we show that the impairment of a mechanically induced startle response after nicotine exposure is not observed in flies deficient in Oct transmission. Thus, our data show that the efflux of BAs in Drosophila brain is increased by nAChR activation as in vertebrates, and that then AChR-induced Oct release could have implications in a nicotine-induced behavioral response.

A better comprehension on how different molecular components of the serotonergic system contribute to the adequate regulation of behaviors in animals is essential in the interpretation on how they are involved in neuropsychiatric and pathological disorders. It is possible to study these components in "simpler" animal models including the fly Drosophila melanogaster, given that most of the components of the serotonergic system are conserved between vertebrates and invertebrates. Here we decided to advance our understanding on how the serotonin plasma membrane transporter (SERT) contributes to serotonergic neurotransmission and behaviors in Drosophila. In doing this, we characterized for the first time a mutant for Drosophila SERT (dSERT) and additionally used a highly selective serotonin-releasing drug, 4-methylthioamphetamine (4-MTA), whose mechanism of action involves the SERT protein. Our results show that dSERT mutant animals exhibit an increased survival rate in stress conditions, increased basal motor behavior, and decreased levels in an anxiety-related parameter, centrophobism. We also show that 4-MTA increases the negative chemotaxis toward a strong aversive odorant, benzaldehyde. Our neurochemical data suggest that this effect is mediated by dSERT and depends on the 4-MTA-increased release of serotonin in the fly brain. Our in silico data support the idea that these effects are explained by specific interactions between 4-MTA and dSERT. In sum, our neurochemical, in silico, and behavioral analyses demonstrate the critical importance of the serotonergic system and particularly dSERT functioning in modulating several behaviors in Drosophila.