Transcriptional cascades are required for specification of 5-HT neurons and 5-HT modulated behaviors. Expression of several cascade factors extends across lifespan suggesting their control of behavior may not be temporally restricted to programming normal numbers of 5-HT neurons. We applied new mouse conditional targeting approaches to investigate ongoing requirements for Pet-1, a cascade factor required for the initiation of 5-HT synthesis but whose expression persists into adulthood. We found that Pet-1 was required after 5-HT neuron generation, for multiple steps in 5-HT neuron maturation including axonal innervation to the somatosensory cortex, firing properties, and 5-HT1A and 5-HT1B autoreceptor expression. Targeting Pet-1 in adult 5-HT neurons showed that it was still needed to preserve normal anxiety-related behaviors through direct autoregulated control of serotonergic gene expression. These findings show that Pet-1 is required across lifespan and therefore behavioral pathogenesis can result from both developmental and adult-onset alterations in serotonergic transcription.

No abstract

Serotonin (5-hydroxytryptamine (5-HT) 2 ) has been demonstrated to play important roles in regulating various physiological functions and modulating numerous disease processes. The 5-HT 1A receptor regulates 5-HT neuron firing by auto-regulating the release of 5-HT. Receptor activation leads to a decrease in firing via hyperpolarization of the cell membrane (1). In the dorsal raphe, the largest serotonergic nucleus, 5-HT 1A is found in cell bodies and dendrites of neurons (2, 3). 5-HT 1A receptors have been implicated in a wide variety of physiological and behavioral functions including learning and memory, sexual behavior, and aggression (4 -6). Furthermore, 5-HT 1A has been implicated in the pathogenesis of anxiety and depression and is thought to be a physiologic target for selective serotonin reuptake inhibitor treatment (7).Although to date it has been one of the most extensively studied of the serotonin receptors, there is still ambiguity about the normal in vivo function of 5-HT 1A , dysfunction in the context of disease, and role in therapeutic response. Studies using pharmacologic and genetic manipulations have been enormously useful in defining in vivo 5-HT 1A function, but of course both approaches have their limitations. Drugs can be applied focally but not spatially contained or targeted to specific cell populations; they also include side effects that can confound analysis. Genetic mutations have the power to be targeted to specific cell types but are constitutionally lost or gained with KOs or transgenics or imprecisely controlled with conditional strategies. Neither approach can be controlled on a second time scale. The ability to modulate 5-HT 1A activity in intact, behaving animals with non-invasive techniques would, thus, prove to be a significant advance to a clearer understanding of the role of 5-HT 1A and the serotonergic system.Light-activated G protein-coupled receptors (GPCRs) couple to intracellular signaling pathways in a receptor-specific manner (8). We previously demonstrated that the GPCR, vertebrate rhodopsin (Rh), can be functionally expressed in nonvisual cell types to activate downstream targets of G i/o signaling (9). Furthermore, we have shown that Rh can be exogenously expressed in neurons both in primary culture and in intact animals to inhibit neuronal and neural network excitability (9). Based on these findings, we aimed to tailor the properties of Rh to manipulate other GPCR signaling pathways, namely, the 5-HT 1A . Here we describe the development of a chimeric lightsensitive GPCR that mimics the intracellular targeting and functional G i/o -linked signaling of wild type 5-HT 1A . This receptor, which we call Rh-CT 5-HT1A , is able to functionally substitute for endogenous 5-HT 1A receptors by exploiting the intracellular trafficking mechanisms used by the endogenous receptors. We show that Rh-CT 5-HT1A distributes intra-neuronally to cell membrane sites normally occupied by 5-HT 1A ,

Leptin is critical for energy balance, glucose homeostasis, and for metabolic and neuroendocrine adaptations to starvation. A prevalent model predicts that leptin’s actions are mediated through pro-opiomelanocortin (POMC) neurons that express leptin receptors (LEPRs). However, previous studies have used prenatal genetic manipulations, which may be subject to developmental compensation. Here, we tested the direct contribution of POMC neurons expressing LEPRs in regulating energy balance, glucose homeostasis and leptin secretion during fasting using a spatiotemporally controlled Lepr expression mouse model. We report a dissociation between leptin’s effects on glucose homeostasis versus energy balance in POMC neurons. We show that these neurons are dispensable for regulating food intake, but are required for coordinating hepatic glucose production and for the fasting-induced fall in leptin levels, independent of changes in fat mass. We also identify a role for sympathetic nervous system regulation of the inhibitory adrenergic receptor (ADRA2A) in regulating leptin production. Collectively, our findings highlight a previously unrecognized role of POMC neurons in regulating leptin levels.