Tomoo Ryushi

The effect of leptin on feeding-regulating neurons in the rat hypothalamus

Intense immunoreactivity for the leptin receptor was detected in the hypothalamic arcuate nucleus (ARC), ventromedial nucleus (VMH), and lateral hypothalamus (LH) by immunohistochemistry. Cytosolic Ca2+ concentration ([Ca2+]i) in single neurons isolated from the ARC, VMH and LH was measured with dual wavelength fura-2 fluorescence imaging. A reduction of the superfusate glucose concentration from 10 to 1 mM increased [Ca2+]i in 21% of ARC neurons and 22% of LH neurons. Leptin at 0.1 nM inhibited the [Ca2+]i increase in 66 and 64% of these glucose-sensitive ARC and LH neurons, respectively. Inversely, 10 mM glucose increased [Ca2+]i in 49% of the VMH neurons, and 0.1 nM leptin at 1 mM glucose also increased [Ca2+]i in 84% of these glucose-responsive neurons. These results reveal that leptin inhibits the ARC and LH neurons and stimulates the VMH neurons via the leptin receptor expressed in these cells.

Morphological evidence for neural interactions between leptin and orexin in the hypothalamus.

Both leptin and orexin have been recently discovered as peptides involved in feeding regulation. The morphological evidence of neural interaction between leptin and orexin, one considered to inhibit food intake and the other to stimulate it in the central nervous system (CNS), was studied by use of double immunostaining method. The leptin receptor-like immunoreactive (LR-LI) neurons in the hypothalamic arcuate nucleus and ventromedial nucleus were innervated by orexin-like immunoreactive (OX-LI) neurons. The distribution of LR-LI neurons in the hypothalamus was very similar to that of OX-LI neurons. These results may suggest that leptin and orexin are intimately correlated with each other and that they reciprocally regulate feeding at the hypothalamic level.

Ultrastructural localization of the receptor for leptin in the rat hypothalamus

Ultrastructural localization of the leptin receptor in the rat hypothalamus was studied by immunocytochemistry. The antiserum against the leptin receptor which was used specifically recognized the carboxy terminal of the cytoplasmic domain. Intense leptin receptor immunoreactivity was detected in the arcuate, paraventricular, and ventromedial nuclei of the hypothalamus and in the lateral hypothalamic area. At the ultrastructural level, leptin receptor-like immunoreactivity appeared to be concentrated predominantly in perikarya and dendrites of these areas and strong immunolabeling for the leptin receptor was detected in the plasma membrane, rough endoplasmic reticulum, Golgi apparatus, and cytoplasmic matrix. This study provides the first detailed fine structure of leptin receptor-immunoreactive neurons in the rat hypothalamus. It may help to provide better understanding of the functions of leptin in the rat hypothalamus.

Localization of the pituitary adenylate cyclase-activating polypeptide receptor and its mRNA in the rat adrenal medulla

We examined the localization of the pituitary adenylate cyclase-activating peptide (PACAP) receptor (PAC1-R) and its mRNA with immunocytochemistry and in situ hybridization, respectively. PAC1-R immunoreactivity and its transcript were detected in both chromaffin cells and ganglion cells but not detected in the adrenal cortex. In addition, strong PAC1-R immunoreactivity was found beneath the plasma membrane of the immunoreactive medullary cells. Electron microscopic immunocytochemistry revealed that PAC1-R was predominantly expressed in adrenaline-containing cells. This report supports the notion that PACAP is an activator and modulator of catecholamine secretion as well as synthesis in the adrenal medulla.

Dynamics of human cardiorespiratory responses to standing on one leg with eyes closed.

Abstract The postural control system has been extensively studied in terms of somatic motor function but little is known about its connection with human autonomic function. The purpose of this study was to determine the cardiorespiratory changes in response to the 1-min balance test that was performed by standing on one leg with eyes closed (SOLEC) or eyes open (SOLEO) in 12 healthy young women [mean age 20.7(SD 3.3) years]. Heart rate (HR), respiratory rate (RR), duration of inspiration and expiration, tidal volume (VT), and oxygen uptake (V˙O2) were measured during the test. The SOLEC test produced rapid increases in HR at the onset. There were significant increases in HR later during the test (P < 0.05). Metabolic rate (V˙O2) showed a gradual increase during the SOLEC test, indicating that the late responses could have been partly due to metabolic changes. The RR increased significantly at the onset of the test (P < 0.05), and remained elevated until the end of the test. The early responses were considered to be mediated neurally through the postural control system which receives the afferent inputs arising from the vestibular system and from muscle proprioceptors of the leg. In contrast, SOLEO caused small insignificant changes in HR, RR, VT and O2, suggesting that a visual input is essential for balancing a postural change. The SOLEC test may have potential as a test of autonomic function.