Stromal cell-derived factor-1alpha directly modulates voltage-dependent currents of the action potential in mammalian neuronal cells.

Stromal cell-derived factor-1alpha (SDF-1alpha) is a chemokine whose receptor, CXCR4, is distributed in specific brain areas including hypothalamus. SDF-1alpha has recently been found to play important roles in neurons, although direct modulation of voltage-gated ionic channels has never been shown. In order to clarify this issue, we performed patch-clamp experiments in fetal mouse hypothalamic neurons in culture. SDF-1alpha (10 nm) decreased the peak and rising slope of the action potentials and spike discharge frequency in 22% of hypothalamic neurons tested. This effect was blocked by the CXCR4 antagonist AMD 3100 (1 microm) but not by the metabotropic glutamate receptor antagonist MCPG (500 microm), indicating a direct action of SDF-1alpha on its cognate receptor. This effect involved a depression of both inward and outward voltage-dependent currents of the action potential. We confirmed these effects in the human neuroblastoma cell line SH-SY5Y, which endogenously expresses CXCR4. Voltage-clamp experiments revealed that SDF-1alpha induced a 20% decrease in the peak of the tetrodotoxin-sensitive sodium current and tetraethylammonium-sensitive delayed rectifier potassium current, respectively. Both effects were concentration dependent, and blocked by AMD 3100 (200 nm). This dual effect was reduced or blocked by 0.4 mm GTPgammaS G-protein pre-activation or by pre-treatment with the G-protein inhibitor pertussis toxin (200 ng/mL), suggesting that it is mediated via activation of a G(i/o) protein. This study extends the functions of SDF-1alpha to a direct modulation of voltage-dependent membrane currents of neuronal cells.

Differential neuronal expression and projections of melanin-concentrating hormone (MCH) and MCH-gene-overprinted-polypeptide (MGOP) in the rat brain.

The rat melanin-concentrating hormone (MCH) gene may produce, through alternative splicing, either the precursor of MCH and neuropeptide EI, two neuropeptides coexpressed in the zona incerta (ZI) and lateral hypothalamus (LHA), or a putative protein we named previously MCH-gene-overprinted-polypeptide (MGOP). First, we investigated the distribution and relative expression of MCH and MGOP mRNA in the rat brain by Northern blotting, RT-PCR and in situ hybridization. MGOP gene transcripts were detected mainly in the hypothalamus only by RT-PCR. Second, different antisera were raised toward the C-terminus of MGOP and used to identify the translational products. In the rat brain, no MGOP-processed peptide could be detected based on RP-HPLC coupled to specific RIA. A polypeptide of 14 kDa was found in the secretory pathway of transfected monkey COS7 cells expressing recombinant MGOP. In the rat hypothalamus, a specific protein of 12 kDa was identified by Western blot analysis. Finally, distribution of MGOP-immunoreactivity (IR) was investigated in the rat brain. Colocalization studies demonstrated that 98% of the MGOP-expressing perikarya in ZI/LHA also synthesized MCH. In addition, numerous, strongly stained MGOP-containing neurons were encountered in the hypothalamic periventricular nucleus. Perikarya labelled with MGOP antiserum were also found scattered in the cortex, caudate putamen, amygdala and lateral septal nucleus. MCH was not detected in these MGOP-containing neurons. Strikingly, dense staining of terminals was observed with MGOP antiserum but not with MCH antibodies in the suprachiasmatic, ventromedial and arcuate nuclei, and also in the external layer of the median eminence. These results demonstrated that MGOP and MCH-IR overlapped in LHA/ZI but displayed a differential distribution in other areas. Based on this cerebral distribution, MGOP may act as a new secreted protein in regulating many neuroendocrine functions, such as nursing, feeding and growth control in associated behavioural components.