Biomedical subjects

X N Nguyen

Publications and source records attributed to X N Nguyen.

4 recordsLinked to original sources

PubMed1997

Cyclic feeding behaviour and changes in hypothalamic galanin and neuropeptide Y gene expression induced by zinc deficiency in the rat.

Dietary zinc-deficiency induces a striking reduction and a cyclic pattern of food intake in rodents. To elucidate the mechanisms for these effects, we studied the hypothalamic content, synthesis, and distribution of galanin (GAL) and neuropeptide Y (NPY) during zinc deficiency and refeeding in the rat. In Wistar rats, three weeks of zinc-deprivation consistently induced a reduction and a cyclic pattern of night- and day-time food intake, as well as of water intake. This was accompanied in zinc-deficient (ZD) rats, and to a lesser extent in pair-fed (PF) rats, by a decrease of hypothalamic GAL mRNA concentration (CTR: 100 +/- 8, ZD: 61 +/- 4, PF: 78 +/- 2 arbitrary densitometric units, ADU, P < 0.01) and an increase of hypothalamic NPY (CTR: 100 +/- 11, ZD: 154 +/- 10, PF: 126 +/- 4 ADU, P < 0.05), without peptide modification. The two neuropeptidergic systems were not affected by the cycles of feeding, with the exception of the NPY-immunoreactivity in the suprachiasmatic nuclei (geniculo-hypothalamic tract), that was inversely correlated to the food intake in both ZD and PF animals. In a second experiment, we showed that zinc-repletion for 4 days suppressed the behaviour induced by a two-week zinc-deprivation, and reversed the increase of NPY mRNA in ZD animals. We finally demonstrated that zinc-deficiency induced a similar behaviour in Zucker rats. However, in these rats whose synthesis of NPY is constitutively up-regulated, no change of NPY synthesis was observed in ZD rats, suggesting that the increase observed in Wistar is adaptative rather than instrumental to the abnormal food intake. In conclusion, we have further characterized the cyclic feeding behaviour of the zinc-deficient Wistar rats, and shown in these animals a decreased activity of the GAL system and an increased activity of the NPY system, likely corresponding to a compensatory response of the two neuropeptidergic systems, as observed in food-deprived animals. As spontaneous food intake of ZD rats does not increase, a resistance to NPY could also be present. These behavioural and neuropeptidergic changes were partially reversed by reintroduction of zinc in the diet. In Zucker rats, the same behaviour occurred despite an insensitivity of the NPY system to the zinc-deficiency. In addition, we describe a nutritional regulation of the NPY-immunoreactivity in the geniculo-hypothalamic tract, that could constitute the substrate of circadian rhythm modulation by timed feeding.

Aging↗

PubMed1993

[Blue-sensitive mechanisms in pattern ERG and VEP].

Pattern onset-offset ERGs and VEPs in response to square-wave stripe patterns of different wavelengths and spatial frequencies under chromatic yellow adaptation (two-channel Maxwellian view) were studied in three subjects. One channel provided a steady homogeneous adapting field of 570 nm, while the other channel, containing the patterns, was superimposed on the adapting field (33 degrees). The spectral sensitivity curve of the ERG had a prominent peak in the blue (460 nm) and a shoulder in the red and green (above 500 nm). For wavelengths below 500 nm the shape of the psychophysically determined sensitivity curve to the onset and offset of the pattern was in close agreement with the electroretinal sensitivity curves determined for a low-amplitude criterion. With almost all wavelengths there were two components in the same VEP response at the same time: a slow negative wave with maximum sensitivity at 460 nm and an earlier fast positive component with maximum sensitivity in the red-green region. When the spatial frequency of a 460 nm test pattern was varied under yellow adaptation the onset response in the ERG showed only very slight spatial tuning. In the onset response of the VEP, however, the slow component showed prominent spatial tuning (around 2 c/deg) under the same conditions.

Adult↗

PubMed1989

Parapapillary chorioretinal atrophy in normal and glaucoma eyes. I. Morphometric data.

Glaucomatous optic nerve damage is associated with alterations of the intra- and parapapillary optic disc area. We measured and compared the parapapillary region in 582 eyes of 321 patients suffering from chronic primary open-angle glaucoma and in 390 eyes of 231 normal subjects. Only one randomly assessed eye per patient and subject was taken for statistical analysis. Highly mopic eyes with a myopic refractive error of more than -8.00 diopters had been excluded. The parapapillary chorioretinal atrophy was divided into a peripheral zone "Alpha" with irregular hyper- and hypopigmentation, and a more central zone "Beta" characterized by whitish colour, visible large choroidal vessels and visible sclera. In the normal eyes both zones were significantly (P less than 0.001) largest and most common in the temporal horizontal sector, followed by the inferior temporal sector, the superior temporal sector and finally the nasal sector. In the glaucoma group both zones were significantly larger (P less than 0.0001; Mann-Whitney test) and more frequent than in the normal eyes (0.40 +/- 0.32 mm2 versus 0.65 +/- 0.49 mm2 for zone Alpha, 0.13 +/- 0.42 mm2 versus 0.79 +/- 1.17 mm2 for zone Beta). The differences were significant also for the earliest glaucoma stage of this study. They were most marked for the nasal parapapillary sector. Significant differences (P less than 0.001) between the normal group and the earliest glaucoma stage were: zone Alpha larger than 0.20 mm2 or broader than 0.20 mm in the temporal horizontal sector, total area of zone Alpha larger than 0.30 mm2, occurrence of zone Alpha in the nasal sector, and occurrence of zone Beta anywhere.

Adolescent↗

PubMed1989

Parapapillary retinal vessel diameter in normal and glaucoma eyes. I. Morphometric data.

The retinal blood vessels serve for nutrition of the retinal ganglion cells and their axons. This study was undertaken to evaluate the vessel diameter in normal and glaucoma eyes. The calibers of the superior temporal and inferior temporal retinal artery and vein were measured at the optic disc border and at a distance of 2 mm from the optic disc center; 473 eyes of 281 patients suffering from chronic primary open-angle glaucoma and 275 eyes of 173 normal subjects were examined. Fifteen-degree, color stereo optic disc photographs were used. In the normal eyes the inferior temporal vessels were significantly larger than the superior temporal vessels. This corresponds with: (1) the configuration of the normal neuroretinal rim, which is significantly broader in the inferior disc region than in the superior disc area; (2) the visibility of the retinal nerve fibers, which are better detectable in the inferior temporal area than in the superior temporal one; and (3) the foveola location 0.53 +/- 0.34 mm inferior to the optic disc center. The retinal vessel diameter was independent of the patients' age and optic disc and parapapillary chorioretinal atrophy size. In the glaucoma group the vessel caliber was significantly smaller than in the normal eyes. The differences were more marked for the arteries and the inferior temporal vessels, respectively. The vessel diameters decreased significantly with increasing glaucoma stage independently of the patients' age. The parapapillary retinal vessel diameter may reflect the need of vascular supply in the corresponding superficial retinal area. It may be correlated with the local ganglion cell density and retinal nerve fiber layer thickness.

Adult↗