Synaptic interaction between ghrelin- and ghrelin-containing neurons in the rat hypothalamus

Synaptic relationships between ghrelin-like immunoreactive axon terminals and other neurons in the hypothalamic arcuate nucleus (ARC) were studied using immunostaining methods at the light and electron microscope levels. Many ghrelin-like immunoreactive axon terminals were found to be in apposition to ghrelin-like immunoreactive neurons at the light microscopic level. At the electron microscopic level, ghrelin-like immunoreactive axon terminals were found to make synapses on ghrelin-like immunoreactive cell bodies and dendrites in the ARC. While the axo-dendritic synapses between ghrelin- and ghrelin-like immunoreactive neurons were mostly the asymmetric type, the axo-somatic synapses were both asymmetric and symmetric type of synapses. Ghrelin at 10(-10) M increased cytosolic Ca(2+) concentration ([Ca(2+)](i)) in the neurons isolated from the ARC, some of which were immunocytochemically identified as ghrelin-positive. Ghrelin at 10(-10) M also increased [Ca(2+)](i) in 12% of ghrelin-like immunoreactive neurons in the ARC. These findings suggest that ghrelin serves as a transmitter and/or modulator that stimulates [Ca(2+)](i) signaling in ghrelin neurons of the ARC, which may participate in the orexigenic action of ghrelin. Our data suggests a possibility of existing a novel circuit implicating regulation of feeding and/or energy metabolism.     

Neuronal interactions between neuropeptide W- and orexin- or melanin-concentrating hormone-containing neurons in the rat hypothalamus

Neuropeptide W (NPW) was recently discovered as the endogenous ligand for GPR7 and GPR8, which are orphan G protein-coupled receptors isolated from the porcine brain. These receptors are assumed to be involved in feeding regulation and/or energy homeostasis. Recent anatomical studies have revealed that high levels of GPR7 mRNA are distributed in the brain, including the hypothalamus and amygdala. However immunohistochemical studies on the distribution and localization of NPW have revealed differing results concerning whether or not NPW-containing cell bodies and their processes are present in the hypothalamus. Only a few immunohistochemical reports have been published concerning the presence of NPW-containing neurons in the brains of rodents, while there have been no anatomical studies of the co-localization of this neuropeptide with other transmitters. On this basis, we used a specific antiserum against NPW to determine immunohistochemically the presence of NPW-containing neurons in the rat hypothalamus. Many NPW-like immunoreactive cell bodies and their processes could be detected in the caudal region of the lateral hypothalamus but not in its anterior or middle regions. Given this positive identification of NPW-containing neurons in the lateral hypothalamus, we further studied the nature of interaction between NPW-containing neurons and neurons containing feeding regulating peptides such as orexin- and melanin-concentrating hormone (MCH). Very close interactions between NPW-containing nerve processes and orexin- and MCH-containing neuronal cell bodies and processes could be observed. These morphological findings strongly suggest that NPW is involved in the regulation of feeding and/or sleep/arousal behavior through orexin- and/or MCH-mediated neuronal pathways.     

Lilliputians get into the limelight: Novel class of small peptide genes in morphogenesis

Generally, bioactive small peptides are derived from precursors with signal sequences at their N-terminal ends, which undergo modification and proteolysis through a secretory pathway. By contrast, small peptides encoded in short open reading frames (sORF) lack signaling sequences and therefore are released into the cytoplasm, which may result in their having functions distinct from those of secreted peptides. Several small peptides encoded by sORF are involved in the morphogenesis of multicellular organisms. POLARIS, ROTUNDIFOLIA4, and Enod40 are plant peptides that are involved, respectively, in root formation, leaf shape control, and cortical cell division during nodule formation. Brick1 / HSPC300 is an evolutionarily conserved component of the actin reorganization complex. polished rice / tarsal-less and mille-pattes encode related small peptides that are required for epithelial morphogenesis in Drosophila and segmentation in Tribolium . There are only a few known examples of small peptides encoded by sORF, and their molecular functions are still largely obscure. Nevertheless, an increasing number of sORF genes is being identified, and further research should reveal their roles in novel molecular mechanisms underlying developmental events.     

Negative Effects of Low Temperatures on the Vertical Transmission and Infection Density of a Spiroplasma Endosymbiont in <Emphasis Type="Italic">Drosophila hydei</Emphasis>

Maternally transmitted endosymbionts of the genus Spiroplasma infecting several species of Drosophila are known to cause selective death of male offspring (male killing). The male-killing trait is considered to be advantageous for maternally transmitted endosymbionts. However, a non-male-killing spiroplasma is present in Japanese populations of Drosophila hydei at high frequencies (23-66%). This spiroplasma is phylogenetically closely related to the male-killing spiroplasma infecting other Drosophila species. It is unknown why this spiroplasma is maintained in its host populations despite its inability to cause male killing. We examined the susceptibilities of the spiroplasma in D. hydei to four different temperatures (28, 25, 18, and 15 degrees C). Diagnostic PCR revealed that vertical transmission of the spiroplasma was nearly perfect at 28 and 25 degrees C, partially suppressed at 18 degrees C, and completely blocked at 15 degrees C. Furthermore, quantitative PCR demonstrated that offspring treated at 18 degrees C exhibited dramatically lower densities of spiroplasma (i.e., approximately one-tenth) compared to offspring treated at 28 and 25 degrees C. Considering the low temperatures during winter in Japan, some unknown advantageous effects of the spiroplasma that compensate for the failure of vertical transmission are suggested to act in natural populations of D. hydei.     

Effect of atrial natriuretic peptide on renin release in rat isolated glomeruli

Effects of atrial natriuretic peptide (ANP) on renin release in isolated rat glomeruli were investigated. ANP suppressed renin release by 25% at 5 x 10(-8) M when glomeruli were incubated in a medium containing 1.26 mM calcium (p = 0.0019). When glomeruli were incubated in a calcium free medium containing 2 mM EGTA, ANP suppressed stimulated renin release significantly at 5 x 10(-8) and 5 x 10(-9) M by 25% (p = 0.0204, and p = 0.0101, respectively). These results indicate that ANP suppresses renin release in a dose dependent manner, probably through a calcium independent process.