Drosophila Cbp53E Regulates Axon Growth at the Neuromuscular Junction.

Calcium is a primary second messenger in all cells that functions in processes ranging from cellular proliferation to synaptic transmission. Proper regulation of calcium is achieved through numerous mechanisms involving channels, sensors, and buffers notably containing one or more EF-hand calcium binding domains. The Drosophila genome encodes only a single 6 EF-hand domain containing protein, Cbp53E, which is likely the prototypic member of a small family of related mammalian proteins that act as calcium buffers and calcium sensors. Like the mammalian homologs, Cbp53E is broadly though discretely expressed throughout the nervous system. Despite the importance of calcium in neuronal function and growth, nothing is known about Cbp53E's function in neuronal development. To address this deficiency, we generated novel null alleles of Drosophila Cbp53E and examined neuronal development at the well-characterized larval neuromuscular junction. Loss of Cbp53E resulted in increases in axonal branching at both peptidergic and glutamatergic neuronal terminals. This overgrowth could be completely rescued by expression of exogenous Cbp53E. Overexpression of Cbp53E, however, only affected the growth of peptidergic neuronal processes. These findings indicate that Cbp53E plays a significant role in neuronal growth and suggest that it may function in both local synaptic and global cellular mechanisms.

CYP7B1 Enzyme Deletion Impairs Reproductive Behaviors in Male Mice.

In addition to androgenic properties mediated via androgen receptors, dihydrotestosterone (DHT) also regulates estrogenic functions via an alternate pathway. These estrogenic functions of DHT are mediated by its metabolite 5α-androstane-3ß, 17ß-diol (3ß-diol) binding to estrogen receptor ß (ERß). CYP7B1 enzyme converts 3ß-diol to inactive 6α- or 7α-triols and plays an important role as a regulator of estrogenic functions mediated by 3ß-diol. Using a mutant mouse carrying a null mutation for the CYP7B1 gene (CYP7B1KO), we examined the contribution of CYP7B1 on physiology and behavior. Male, gonadectomized (GDX) CYP7B1KO and their wild type (WT) littermates were assessed for their behavioral phenotype, anxiety-related behavioral measures, and hypothalamic pituitary adrenal axis reactivity. No significant effects of genotype were evident in anxiety-like behaviors in open field (OFA), light-dark (L/D) exploration, and elevated plus maze (EPM). T significantly reduced open arm time on the EPM while not affecting L/D exploratory and OFA behaviors in CYP7B1KO and WT littermates. T also attenuated the corticosterone response to EPM in both genotypes. In GDX animals, T was able to reinstate male-specific reproductive behaviors (latencies and number of mounts, intromission, and ejaculations) in the WT but not in the CYP7B1KO mice. The male reproductive behavior defect in CYP7B1KO seems to be due to their inability to distinguish olfactory cues from a behavioral estrus female. CYP7B1KO mice also showed a reduction in androgen receptor mRNA expression in the olfactory bulb. Our findings suggest a novel role for the CYP7B1 enzyme in the regulation of male reproductive behaviors.

An isomorphic mapping hypothesis of the grid representation.

We introduce a grid cell microcircuit hypothesis. We propose the 'grid in the world' (evident in grid cell discharges) is generated by a 'grid in the cortex'. This cortical grid is formed by patches of calbindin-positive pyramidal neurons in layer 2 of medial entorhinal cortex (MEC). Our isomorphic mapping hypothesis assumes three types of isomorphism: (i) metric correspondence of neural space (the two-dimensional cortical sheet) and the external two-dimensional space within patches; (ii) isomorphism between cellular connectivity matrix and firing field; (iii) isomorphism between single cell and population activity. Each patch is a grid cell lattice arranged in a two-dimensional map of space with a neural : external scale of approximately 1 : 2000 in the dorsal part of rat MEC. The lattice behaves like an excitable medium with neighbouring grid cells exciting each other. Spatial scale is implemented as an intrinsic scaling factor for neural propagation speed. This factor varies along the dorsoventral cortical axis. A connectivity scheme of the grid system is described. Head direction input specifies the direction of activity propagation. We extend the theory to neurons between grid patches and predict a rare discharge pattern (inverted grid cells) and the relative location and proportion of grid cells and spatial band cells.

Effects of maternal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin on parvalbumin- and calbindin-immunoreactive neurons in the limbic system and superior colliculus in rat offspring.

Previous studies have reported that maternal exposure to 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) induces socioemotional and cognitive disturbances in rat offspring. In the present study, the effects of maternal TCDD exposure on putative inhibitory interneurons were investigated in the medial prefrontal cortex (mPFC), basolateral amygdala (BLA), hippocampus (HP), and superior colliculus (SC) in rat offspring. Dams were given TCDD (1.0µg/kg) on gestational day 15. When offspring rats reached adulthood (14 weeks old), parvalbumin (PV)- and calbindin (Calb)-immunoreactive neurons were immunohistochemically investigated. The histological investigations indicated that the mean area of the mPFC had increased, whereas the mean area of the SC decreased in the exposed male rats. In the exposed female rats, the mean SC area increased. Furthermore, the number and area of PV-immunoreactive neurons increased in the mPFC of the female exposed rats. In contrast, the number of PV-immunoreactive neurons in the BLA, HP, and SC decreased in the male and female exposed rats. The number of Calb-immunoreactive neurons decreased in the HP of the male and female exposed rats and the SC of the female exposed rats. Because PV- and Calb-immunoreactive neurons, which are putatively GABAergic, have been implicated in various higher brain functions, the effects of TCDD on socioemotional and cognitive functions might be mediated partly through these alterations in PV- and Calb-immunoreactive neurons in these areas.

Paired-pulse facilitation at recurrent Purkinje neuron synapses is independent of calbindin and parvalbumin during high-frequency activation.

Paired-pulse facilitation (PPF) is a dynamic enhancement of transmitter release considered crucial in CNS information processing. The mechanisms of PPF remain controversial and may differ between synapses. Endogenous Ca(2+) buffers such as parvalbumin (PV) and calbindin-D28k (CB) are regarded as important modulators of PPF, with PV acting as an anti-facilitating buffer while saturation of CB can promote PPF. We analysed transmitter release and PPF at intracortical, recurrent Purkinje neuron (PN) to PN synapses, which show PPF during high-frequency activation (200 Hz) and strongly express both PV and CB. We quantified presynaptic Ca(2+) dynamics and quantal release parameters in wild-type (WT), and CB and PV deficient mice. Lack of CB resulted in increased volume averaged presynaptic Ca(2+) amplitudes and in increased release probability, while loss of PV had no significant effect on these parameters. Unexpectedly, none of the buffers significantly influenced PPF, indicating that neither CB saturation nor residual free Ca(2+) ([Ca(2+)]res) was the main determinant of PPF. Experimentally constrained, numerical simulations of Ca(2+)-dependent release were used to estimate the contributions of [Ca(2+)]res, CB, PV, calmodulin (CaM), immobile buffer fractions and Ca(2+) remaining bound to the release sensor after the first of two action potentials ('active Ca(2+)') to PPF. This analysis indicates that PPF at PN-PN synapses does not result from either buffer saturation or [Ca(2+)]res but rather from slow Ca(2+) unbinding from the release sensor.