Heekyung Ahn

Age-related change in the neuropeptide Y and NADPH-diaphorase-positive neurons in the cerebral cortex and striatum of aged rats

Age-related changes of neuropeptide Y (NPY) and nicotinamide adenine dinucleotide phosphate-diaphorase (NADPH-d) were examined in the rat cerebral cortex and striatum by immunohistochemical and histochemical methods. Double labeling for NPY and NADPH-d showed that about 30-70% of NPY-immunoreactive (NPY-IR) neurons in the cerebral cortex of the control (4-month-old) rats contained NADPH-d and that 50-75% in the aged (24-month-old) rats. The aged rats showed a significant increase in percentage of colocalization of NPY and NADPH-d in comparison with the control rats in the temporal cortex, occipital cortex, cingulate cortex, insular cortex, retrosplenial cortex and caudatoputamen. However, colocalization percentage between control and aged rats in the frontal cortex, parietal cortex, perirhinal cortex, entorhinal cortex and nucleus accumbens were practically identical. In the aged group, the number of NPY-IR/NADPH-d-positive neurons was not significantly decreased in the cerebral cortex and striatum compared to the control group. However, the number of NPY-IR/NADPH-d-negative neurons was significantly decreased in all cerebral cortical areas and caudatoputamen in the aged group except in the nucleus accumbens. Major loss of NPY-IR/NADPH-d-negative neurons in the aged group were observed in the neurons of layer II/III and V/VI. These results demonstrate that the NADPH-d containing NPY-IR neurons are less influenced by aging than the control group in the cerebral cortex and striatum of rats.

Inhibition of neuronal nitric oxide synthase enhances cell proliferation in the dentate gyrus of the adrenalectomized rat

Recent studies have demonstrated that the elimination of adrenal steroids by an adrenalectomy (ADX) increases the expression of neuronal nitric oxide synthase (NOS), and that it increases cell proliferation in the rat dentate gyrus. However, no evidence has been presented to date which indicates that NO regulates cell proliferation in the dentate gyrus of the adult rats. In this study, the effect of blocking NO production on ADX-induced increase of cell proliferation and serotonergic innervation was examined in the rat dentate gyrus. 7-nitroindazole (7-NI; 30 mg/kg, intraperitoneally), a selective inhibitor of neuronal NOS, was injected 1 day before an ADX and then once every 24 h for 4 days after the ADX subsequently. The proliferating cells were identified with 5-bromo-2-deoxyuridine (BrdU) immunostaining. Long-term inhibition of the neuronal NOS by 7-NI markedly increased the BrdU-labeled cell population density 4-18-fold in the dentate gyrus of the adrenalectomized rats compared to that in the vehicle-injected adrenalectomized rats. Immunoreactivity of serotonin, known as a mediator of granule cell genesis, was detected only in the dentate gyrus of 7-NI-injected adrenalectomized rats. These results indicate that NO may be involved in the cell proliferation in the dentate gyrus of the adrenalecomized rat and that serotonin may mediate the regulatory effect of NO on the cell proliferation in rat dentate gyrus.

The chronic inhibition of nitric oxide synthase enhances cell proliferation in the adult rat hippocampus

We investigated the effect of chronic blocking nitric oxide synthase (NOS), an enzyme producing NO from L-arginine, on granule cell proliferation in the dentate gyrus of adult rats under normal conditions. We treated 7-nitroindazole (7-NI) for 5, 15, and 25 days or N-nitro-L-arginine-methyl ester (L-NAME) for 25 days to block NOS activity and subsequently injected 5-bromo-2-deoxyuridine (BrdU) to detect proliferating cells. The BrdU-immunoreactive (IR) cell number was significantly increased in the 7-NI 15 and 25 day treated group, but not in the control or in the 7-NI 5 day treated group. L-NAME treatment for 25 days significantly increased BrdU-IR cells versus the control and 7-NI 25 day treated group. In addition, nissl staining showed no cell death occurred in the dentate gyrus after 7-NI or L-NAME 25 day treatments. Our results demonstrate that chronic inhibition of NOS increases cell proliferation and has no effect on cell death in the dentate gyrus of the rat hippocampus, which suggests that NO may regulate cell proliferation in the dentate gyrus.

The inhibition of nitric oxide synthase enhances PSA-NCAM expression and CREB phosphorylation in the rat hippocampus.

It is well known that nitric oxide (NO) acts downstream of NMDA receptor activation, which regulates the neural plasticity in the brain. In the present study, the effect of L-NAME, a non-selective nitric oxide synthase (NOS) inhibitor, on neural plasticity in the hippocampus was investigated. L-NAME increased the expression of PSA-NCAM and pCREB in the adult rat hippocampus. The co-localization of PSA-NCAM and pCREB indicates a possible relationship between the two in the granule cell layer in the dentate gyrus. Our results demonstrate that NO, as a subsignal of NMDA receptors, could be involved in the structural plasticity of the granule cell layer in the dentate gyrus by regulating the expression of PSA-NCAM and pCREB in the hippocampus.

Transient induction of neuronal nitric oxide synthase in neurons of rat cerebral cortex after status epilepticus.

The change in neuronal nitric oxide synthase (nNOS) expression after status epilepticus induced by kainate was examined in the rat cerebral cortex. Expressional change was assessed using nNOS immunohistochemistry and reverse transcription-polymerase chain reaction for nNOS mRNA. Constitutive nNOS-positive neurons was observed in the cerebral cortex of the control group. At 1 and 3 days after status epilepticus, nNOS-positive neurons were present in a deep layer of various cortical regions such as primary motor cortex, secondary motor cortex, primary somatosensory cortex, secondary somatosensory cortex, parietal association cortex, insular cortex, ectorhinal cortex, temporal association cortex, auditory cortex and visual cortex. The level of nNOS mRNA increased at 1, 3, 6 and 12 days after status epilepticus compared to controls. This report provides the first morphological evidence that nNOS are induced in neurons of the cerebral cortex following seizure.

Regional changes of NADPH-diaphorase and neuropeptide Y neurons in the cerebral cortex of aged Fischer 344 rats

This study examined the effects of aging on neuropeptide Y (NPY) and NADPH-diaphorase (NADPH-d)-positive neurons of the cerebral cortex in young (3 months) and aged (24 months) Fischer 344 rats by immunohistochemical and histochemical methods. In the aged group, the number of NPY-immunoreactive (IR)/NADPH-d-positive neurons was not significantly changed in all regions of the cerebral cortex compared to the control group. However, the number of NPY-IR/NADPH-d-negative neurons was significantly decreased in frontal association, primary motor, secondary somatosensory, insular, ectorhinal, perirhinal and auditory cortex in the aged group. In the aged rats, about 5-10% of NPY-IR/NADPH-d-positive neurons were dystrophic and scattered within the cerebral cortex. These results suggested that NPY-IR neurons that do not contain NADPH-d are affected by aging and that aging influences NPY-IR/NADPH-d-negative neurons in a region-specific pattern within the cerebral cortex of rats.

Superior aspect of the perirenal space: Anatomy and pathological correlation

To study the anatomy of the superior aspect of the perirenal space, we analysed 50 computed tomographic (CT) scans with reference to the anatomy of Gerotas fascia, and dissected five cadavers laying special emphasis on the ascent of Gerotas fascia. We also reviewed 10 scans of patients with a large lesion in the right upper abdomen regarding localisation of the lesion. We conclude that Gerotas fascia does not cover the upper portion of the kidney and adrenal gland so that the superior aspect of the perirenal space is open towards the upper abdominal extraperitoneal space. Thus, a large lesion arising from the right adrenal gland or kidney easily invaginates the liver through the bare area mimicking a hepatic lesion, and vice versa. This explains the difficulty in localising a large lesion in the right upper abdomen.

Inhibition of neuronal nitric oxide synthase increases adrenalectomy-induced granule cell death in the rat dentate gyrus

Recent studies have shown that the expression of neuronal nitric oxide synthase (NOS) mRNA is increased after adrenalectomy (ADX). However, the role of increased NO production after ADX in the dentate gyrus is unknown. In this study, the relationship between NO inhibition and apoptosis in the dentate gyrus after ADX was examined. 7-Nitroindazole (7-NI; 30 mg/kg, i.p.), a selective inhibitor of neuronal NOS, was injected 1 day before ADX and subsequently once every 24 h. Then 4 days after ADX, dentate granule cell death was evaluated using silver impregnation and Nissl staining methods. Inhibition of neuronal NOS by 7-NI increased the number of dying granule cells approximately 4-fold in the dentate gyrus of the ADX rats, compared to vehicle-injected ADX controls. These results suggest that increased NO production after ADX may play an endogenous neuroprotective role in the dentate gyrus.

Differential effects of aging on NADPH-diaphorase and VIP neurons in cerebral cortex of rats.

AGE-RELATED changes of NADPH-diaphorase (NADPH-d) and vasoactive intestinal polypeptide (VIP) were examined in the rat brain. Aged (24 months) rats showed a significant decrease in the number of VIP-immunoreactive (IR) neurons in the cerebral cortex when compared with control (4 months) rats. However, the number of NADPH-d-positive neurons was not significantly different in the two groups. Quantitative analysis of cell areas revealed a significant shrinkage of VIP-IR neurons in the aged group, whereas no further cell shrinkage was noted for NADPH-d-positive neurons compared with the control group. These morphometric results demonstrate that NADPH-d-containing neurons are more resistant to aging than the VIP-IR neurons in the cerebral cortex of rats.

Ectopic expression of serotonin-positive neurons in the hypothalamus associated with a significant serotonin decrease in the midbrain of food restricted rats.

The effects of food restriction on the serotonergic system were investigated immunohistochemically in both the midbrain and hypothalamic regions of rats. Rats were fed on a restricted feeding schedule consisting of half of the ad libitum quantity for 1, 2, 4 and 6 weeks and a free feeding schedule for 1 week. The optical density of serotonin-positive neurons in the raphe nuclei of the midbrain was found to be significantly lower in the 1 week-food restricted group than in the ad libitum fed control. In the hypothalamus, serotonin-positive neurons were observed in the 1 and 2 week food restricted groups but not in the 4 and 6 week-food restricted groups. This finding was confirmed by immunohistochemistry with tryptophan hydroxylase, a serotonin synthesizing enzyme. In this study, we provide morphological evidence that food restriction has a significant effect on the serotonergic system of the midbrain and hypothalamic regions and suggest some possibilities for the ectopic expression of serotonin-positive neurons after food restriction.