A divergent pattern of sensory axonal projections is rendered convergent by second-order neurons in the accessory olfactory bulb.

The mammalian vomeronasal system is specialized in pheromone detection. The neural circuitry of the accessory olfactory bulb (AOB) provides an anatomical substrate for the coding of pheromone information. Here, we describe the axonal projection pattern of vomeronasal sensory neurons to the AOB and the dendritic connectivity pattern of second-order neurons. Genetically traced sensory neurons expressing a given gene of the V2R class of vomeronasal receptors project their axons to six to ten glomeruli distributed in globally conserved areas of the AOB, a theme similar to V1R-expressing neurons. Surprisingly, second-order neurons tend to project their dendrites to glomeruli innervated by axons of sensory neurons expressing the same V1R or the same V2R gene. Convergence of receptor type information in the olfactory bulb may represent a common design in olfactory systems.

Multiple new and isolated families within the mouse superfamily of V1r vomeronasal receptors.

Seven-transmembrane-domain proteins encoded by the vomeronasal receptor V1r and V2r gene superfamilies, and expressed by vomeronasal sensory neurons, are believed to be pheromone receptors in rodents. Four V1r gene families have been described in the mouse (V1ra, V1rb, V1rc and V3r). Here we have screened near-complete mouse genomic databases to obtain a first global draft of the mouse V1r repertoire, including 104 new V1r genes. It comprises eight new and extremely isolated families in addition to the four families previously identified. Members of these new families were expressed in vomeronasal sensory neurons. The genome-wide view revealed great sequence diversity within the V1r superfamily. Phylogenetic analyses suggested an ancient original radiation, followed by the isolation, divergence and expansion of families by extensive gene duplications and frequent gene loss. The isolated nature of these gene families probably reflects a specialization of different receptor classes in the detection of specific types of chemicals.

Genetic address book for retinal cell types.

The mammalian brain is assembled from thousands of neuronal cell types that are organized in distinct circuits to perform behaviorally relevant computations. Transgenic mouse lines with selectively marked cell types would facilitate our ability to dissect functional components of complex circuits. We carried out a screen for cell type-specific green fluorescent protein expression in the retina using BAC transgenic mice from the GENSAT project. Among others, we identified mouse lines in which the inhibitory cell types of the night vision and directional selective circuit were selectively labeled. We quantified the stratification patterns to predict potential synaptic connectivity between marked cells of different lines and found that some of the lines enabled targeted recordings and imaging of cell types from developing or mature retinal circuits. Our results suggest the potential use of a stratification-based screening approach for characterizing neuronal circuitry in other layered brain structures, such as the neocortex.

Deficient pheromone responses in mice lacking a cluster of vomeronasal receptor genes.

The mammalian vomeronasal organ (VNO), a part of the olfactory system, detects pheromones--chemical signals that modulate social and reproductive behaviours. But the molecular receptors in the VNO that detect these chemosensory stimuli remain undefined. Candidate pheromone receptors are encoded by two distinct and complex superfamilies of genes, V1r and V2r (refs 3 and 4), which code for receptors with seven transmembrane domains. These genes are selectively expressed in sensory neurons of the VNO. However, there is at present no functional evidence for a role of these genes in pheromone responses. Here, using chromosome engineering technology, we delete in the germ line of mice an approximately 600-kilobase genomic region that contains a cluster of 16 intact V1r genes. These genes comprise two of the 12 described V1r gene families, and represent approximately 12% of the V1r repertoire. The mutant mice display deficits in a subset of VNO-dependent behaviours: the expression of male sexual behaviour and maternal aggression is substantially altered. Electrophysiologically, the epithelium of the VNO of such mice does not respond detectably to specific pheromonal ligands. The behavioural impairment and chemosensory deficit support a role of V1r receptors as pheromone receptors.

Regulacion de la esteroidogenesis testicular por oxido nitrico / Regulation of testicular steroidogenesis by nitric oxide

Los macrófagos testiculares y las células endoteliales, constituyen una fuente parácrina potencial de óxido nítrico (NO) en el testículo. En este trabajo, se investigó el efecto de liberadores de NO sobre la esteroidogénesis en una línea celular tumoral de Leydig murina y en células de Leydig de rata. Se observó que los liberadores de NO inhiben, de una manera reversible, la esteroidogénesis inducida por hCG en ambos tipos celulares. También se estudió el mecanismo de acción del NO. Contrariamente a lo observado en otros sistemas, los efectos inhibitorios del NO sobre la esteroidogénesis en células de Leydig no son mediados por GMPc, puesto que el NO no aumenta la producción de GMPc ni los análogos de GMPc reproducen los efectos del NO. El NO tampoco modifica la producción de AMPc, el segundo mensajero de la acción gonadotrófica. Cuando se evaluó el efecto del NO sobre el camino esteroidogénico en las células MA10, se encontró que el NO inhibe la conversión de colesterol a pregnenolona. En conjunto, estos resultados muestran un efecto inhibitorio de liberadores de NO sobre la esteroidogénesis en células de Leydig y sugieren que el NO puede inhibir en forma directa la enzima que escinde la cadena lateral del colesterol (citocromo P-450scc) como lo hace con otras hemo proteínas que incluyen diferentes citocromos P-450.