How neurons make specific synaptic connections is a central question in neurobiology. The targeting of the Drosophila R7 and R8 photoreceptor axons to different synaptic layers in the brain provides a model with which to explore the genetic programs regulating target specificity. In principle this can be accomplished by cell-type-specific molecules mediating the recognition between synaptic partners 1 . Alternatively, specificity could also be achieved through cell-type-specific repression of particular targeting molecules. Here we show that a key step in the targeting of the R7 neuron is the active repression of the R8 targeting program. Repression is dependent on NF-YC, a subunit of the NF-Y (nuclear factor Y) transcription factor 2 . In the absence of NF-YC, R7 axons terminate in the same layer as R8 axons. Genetic experiments indicate that this is due solely to the derepression of the R8-specific transcription factor Senseless 3 (Sens) late in R7 differentiation. Sens is sufficient to control R8 targeting specificity and we demonstrate that Sens directly binds to an evolutionarily conserved DNA sequence upstream of the start of transcription of an R8-specific cell-surface protein, Capricious (Caps) that regulates R8 target specificity. We show that R7 targeting requires the R7-specific transcription factor Prospero 4,5 (Pros) in parallel to repression of the R8targetingpathway by NF-YC. Previous studies demonstrated that Sens 6,7 and Pros 8 directly regulate the expression of specific rhodopsins in R8 and R7. We propose that the use of the same transcription factors to promote the cell-type-specific expression of sensory receptors and cell-surface proteins regulating synaptic target specificity provides a simple and general mechanism for ensuring that transmission of sensory information is processed by the appropriate specialized neural circuits.The compound eye comprises about 750 simple eyes (ommatidia), each containing a cluster of eight photoreceptor neurons (R1-R8). These neurons form synaptic connections in two regions of the optic lobe, the lamina and the medulla (Fig. 1a). The R1-R6 neurons innervate the lamina; the R7 and R8 neurons form connections in the M6 and M3 medulla layers, respectively. Genetic studies have led to the identification of cell-surface proteins regulating R7 and R8 target specificity [9][10][11][12][13][14][15][16][17][18] (refs 9-14 ), the layer in which wild-type R8 axons terminate, suggesting a close relationship between the genetic programs controlling R7 and R8 target specificity. Here we describe transcriptional regulatory pathways that control the differential targeting specificity of these neurons.In a screen for R7 targeting mutants 10 , we identified a strong loss of function mutation in the NF-YC gene ( Supplementary Fig. 1), which encodes a subunit of NF-Y, an evolutionarily conserved heterotrimeric transcription factor. Although NF-Y function has not been studied extensively in the fly 19,20 , it has been shown to act as both an activator 21 and a repress...

Unlike other monoamine neurotransmitters, the mechanism by which the brain's histamine content is regulated remains unclear. In mammals, vesicular monoamine transporters (VMATs) are expressed exclusively in neurons and mediate the storage of histamine and other monoamines. We have studied the visual system of Drosophila melanogaster in which histamine is the primary neurotransmitter released from photoreceptor cells. We report here that a novel mRNA splice variant of Drosophila VMAT (DVMAT-B) is expressed not in neurons but rather in a small subset of glia in the lamina of the fly's optic lobe. Histamine contents are reduced by mutation of dVMAT, but can be partially restored by specifically expressing DVMAT-B in glia. Our results suggest a novel role for a monoamine transporter in glia that may be relevant to histamine homeostasis in other systems.

Mecamylamine, a noncompetitive nicotinic cholinergic antagonist, inhibits nicotine self-administration in animals and may attenuate tobacco smoking in humans trying to quit. Our preliminary data suggested that this agent, at a dose of 2 mg/kg (subcutaneous (s.c.)), also attenuates cue-induced relapse to nicotine-seeking behavior in rats. This study determined whether mecamylamine-induced attenuation can be obtained at doses lower than the high 2 mg/kg dose used in the first study, and whether it is specific to nicotine-associated cues. Male Sprague-Dawley rats were trained to intravenously self-administer nicotine (0.03 mg/kg/infusion) on a fixed-ratio 5 schedule. Each infusion was accompanied by a visual cue (1 s onset of a lever light followed by offset of a house light for 20 s during which time no infusions could be obtained). After the nicotine-maintained responding was extinguished by withholding the delivery of nicotine (saline substitution) and its associated cue, reinstatement tests were conducted. Response-contingent re-presentation of the cue without further availability of nicotine significantly reinstated extinguished responding at the previously nicotine-reinforced lever. Pretreatment with mecamylamine (0.5, 1, and 2 mg/kg, s.c.) dose-dependently attenuated the cue-induced reinstatement of lever responding. Mecamylamine did not change food-taking and -seeking responses, whereas the highest dose (2 mg/kg) decreased nicotine selfadministration behavior. The results confirm previous findings that stimuli conditioned to nicotine self-administration effectively elicit reinstatement of nicotine-seeking behavior after extinction and demonstrate that mecamylamine, besides suppressing self-administration of nicotine, effectively attenuates cue-induced nicotine-seeking behavior. These findings suggest that the response-reinstatement procedures used in this study may be useful for studying neurobiological mechanisms of nicotine-seeking behavior and that mecamylamine-like drugs may be potential candidates for pharmacological treatment and prevention of relapse to tobacco smoking in abstinent smokers.

Rationale-Smoking-related environmental stimuli have been implicated as an important factor in triggering relapse in abstinent tobacco smokers, and recent evidence indicates that drug-associated stimuli can reinstate nicotine-seeking in rats. However, there is little investigation on the factors that contribute to the latter effect.Objective-This study examined whether a nicotine-associated visual stimulus (VS) can reinstate nicotine-seeking after extinction in a response-reinstatement model of relapse, and whether the behavioral effects of the VS are sensitive to pharmacological blockade of nicotinic neurotransmission. It also determined whether active lever reassignment after food training influences nicotine self-administration and the VS-induced reinstatement.Methods-Male Sprague-Dawley rats were trained to self-administer nicotine (0.03 mg/kg/ infusion, IV) and associate a VS with each nicotine infusion in 30 daily 1-h sessions. Half of the animals received nicotine infusions for responding at the same lever that previously delivered food; for the other half, infusions resulted from pressing the previously inactive lever during food training. Then, the nicotine-maintained response was extinguished by saline substitution and withholding the VS. One day after rats reached extinction criterion, the reinstatement tests were conducted where the VS was response-contingent represented without further delivery of nicotine. In pharmacological tests, a nicotinic antagonist, mecamylamine, was subcutaneously administered 30 min before reinstatement sessions. © Springer-Verlag 2005Correspondence to: Xiu Liu. NIH Public AccessAuthor Manuscript Psychopharmacology (Berl). Author manuscript; available in PMC 2010 January 24. NIH-PA Author ManuscriptNIH-PA Author Manuscript NIH-PA Author ManuscriptResults-Presentation of the nicotine-associated VS significantly reinstated responding at the previously drug-reinforced lever and pretreatment with mecamylamine effectively attenuated the response-reinstating effect of the VS. Additionally, animals showed similar profiles of nicotinetaking and nicotine-seeking behavior regardless of reassignment of the active lever after food training.Conclusions-Nicotine self-administration and the VS-induced reinstatement of nicotine-seeking do not result from a lever bias due to prior experience for food reinforcement. Significantly, these results suggest that environmental stimuli associated with nicotine self-administration can effectively elicit nicotine-seeking behavior in abstinent subjects, that this effect is blocked by nicotine antagonism, and that the present procedures may be useful for studying neurobiological mechanisms of nicotine-seeking behavior and relapse.

It is widely accepted that nicotine is the active ingredient of tobacco smoke that promotes tobacco dependence. Nicotine interacts with several subtypes of nicotinic acetylcholine receptors (nAChRs). In brain, it primarily targets nAChRs that contain beta2 and alpha4 subunits in combination and those composed of solely alpha7 subunits. The present study tested whether operantly trained rats would self-administer a ligand active at beta2-containing (i.e. not alpha7) nAChRs. Male Sprague-Dawley rats were trained to lever press for i.v. cocaine self-administration. After 2 weeks of cocaine washout, rats were given operant access to 5-iodo-A-85380 (5IA), a beta2-selective nAChR ligand, in daily 1 h sessions. The rats rapidly developed a stable level of 5IA self-administration behavior (unit dose = 5 nmol/kg/infusion). This finding suggests that interaction with beta2-containing nAChRs, without direct involvement of alpha7 receptors, can produce reinforcement and thereby can support self-administration behavior.