摘要:

WE studied the effects of estradiol (E2) and progesterone (P4) on expression of genes coding for PR isoforms in the forebrain of ovariectomized rats by RT-PCR analysis. In the hypothalamus the expression of both PR isoforms was induced by E2 and down-regulated by P4. In the preoptic area these changes were only observed in the PR-B isoform. In contrast, in the hippocampus PR induction by E2 was only observed for PR-A. In this region P4 did not modify the expression of any PR isoform. These results indicate that PR isoforms expression is differentially regulated by sex steroid hormones in distinct forebrain regions and suggest that the tissue-specific regulation of either PR-A or PR-B may be involved in the physiological actions of P4 upon the rat brain.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

ABOUT 90% of neurons in dorsal root ganglia (DRGs) of rats 2–5 weeks of age are depolarized and excited by impulse activity in neighboring neurons that share the same DRG. Synaptic contacts are extremely rare in DRGs, but instances of close membrane apposition between pairs of neuronal somata are not uncommon, especially in prenatal rats. Close membrane apposition could permit electrotonic interactions among neighboring DRG neurons. We carried out an ultrastructural examination of DRGs taken from rats 2–5 weeks of age and found that by this age <2% of cells remain in close apposition with neighbors. The remainder are separated by one or two layers of satellite glial cytoplasm. It is, therefore, unlikely that close apposition between adjacent neurons contributes significantly to functional cross-excitation in the DRG.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

A psychophysical method was used to estimate the timing of perception of kinesthetic stimuli with different velocities in normal volunteers. A 1 ms auditory click occurred randomly before or after an imposed flexion movement at either 20, 40 or 60 deg/s of the meta-carpophalangeal joint. Subjects reported whether the click was perceived before or after the movement onset (experiment 1) or perception of movement velocity (experiment 2). The time at which there was a 50% chance that subjects reported movement or velocity perception after the click was taken as an estimate of the time subjects perceived the stimuli. The difference in time of perceived movement velocity discrimination and movement onset was only significant when the velocity was 20 deg/s (52 ms). This suggests that movement onset and identification of the velocity of the faster movements are perceived nearly simultaneously.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

DIPOLE source localization of ictal epileptiform activity recorded by scalp EEG was performed in patients prior to surgical treatment. The dipole tracing method combined with the scalp—skull—brain head model was used to locate epileptogenic foci. A digital EEG system was used for data collection. The accuracy of dipole source localization was evaluated by comparing the focus location with that obtained by chronic subdural electrocorticography. In a case of frontal lobe epilepsy with epileptogenic focus in the frontoparietal convexity, the results of dipole source localization agreed well with those obtained with chronic subdural electrocorticography. In a case of lateral temporal lobe epilepsy, the results of dipole source localization were consistent with those obtained with chronic subdural electrocorticography, but a small localization error was observed. The clinical usefulness of and suggestions for improving this method are discussed.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

CEREBRAL ischemia and the aftermath of reperfusion form a hypoxic/hyperoxic sequence of events that can trigger oxidative stress response cascades in neurons of the central nervous system. After transient ischemia there is an increase in intracellular Ca2+release, extra-cellular glutamate, reactive oxygen species (ROS) and nitric oxide, genotoxic events that stimulate DNA repair. Increased oxidative stress and interrupted blood flow in ischemia, like DNA repair, also deplete cellular ATP and commit neurons to apoptosis. We report that levels of the DNA repair enzyme apurinic/apyrimidinic endonuclease (APE/Ref-1) decreased significantly in the hippocampus but not other brain areas after 6h of reperfusion following an induced ischemic insult. This specific inhibition of APE/Ref-1 expression may affect the extent of apoptosis after ischemia

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

THIS study was performed to test the hypothesis that diminution in the preovulatory luteinizing hormone (LH) surge in middle-aged (MA) rats may be related to altered activity in nitric oxide (NO)ergic neurons. To begin to test the hypothesis, gene expression of hypothalamic NO synthase (NOS), the enzyme that catalyzes NO production, was examined on the day of proestrus in young (2–3 months old) and middle-aged (MA, 8–10 months old) rats. Compared with those at 10.00 h, NOS mRNA levels were increased significantly at 12.00 h and the LH surge occurred at 16.00 h in young rats. In MA rats, in contrast, there was no change in NOS mRNA levels between morning and afternoon hours in association with a delayed and attenuated LH surge. These results show that hypothalamic NOS gene expression increases long before the LH surge in young rats and that this antecedent increase in NOS gene expression does not occur in MA regularly cycling rats. Since hypothalamic NOergic neurons participate in induction of LH-releasing hormone (LHRH) and LH surges, our results suggest that reduced LH surges in MA rats may, in part, be due to altered NOS neuronal activity in these animals.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

THE present study was designed to investigate the effects of learning-dependent enlargement of cortical representation of a row of vibrissae upon the appearance of adjacent cortical representations. We have found previously that three sessions of classical conditioning, during which stimulation of row B of vibrissae is paired with a tail shock, result in an increase of cortical representation of the trained row, as visualized with 2-deoxyglucose (2DG) metabolic functional mapping. In the present experiment, after the training in which row B was stimulated, we mapped with 2DG the cortical representations of rows A and C, not stimulated during the training. We found that these representations do not differ from normal. Because of expansion of cortical representation of the trained row, the overlap between representations of neighboring rows of vibrissae became greater and the two maps co-existed within the same cortical space.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

THE excitatory amino acid glutamate, acting via ionotropic and metabotropic glutamate receptors, appears to play an important role in the control of neuroendocrine functions. The aim of the present investigations was to determine whether hypothalamic neurones which synthesize arginin-vasopressin (AVP), CRF and VIP express metabotropic glutamate receptor (mGluR). Double-label immunocytochemistry and the mirror technique were used. We found that AVP immunoreactive neurones of the paraventricular, supraoptic and suprachiasmatic nuclei contain mGluR1a, but the number of double-labelled neurones was different in the three cell groups. mGluR1a was present in a significant number of paraventricular CRF nerve cells, and in almost all VIP neurones of the SCHN. These results support the view that the excitatory transmitter glutamate may directly influence AVP, CRF and VIP neurones of the three hypothalamic cell groups.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

To assess the possible role of urocortin, a recently identified neuropeptide related to corticotropin-releasing factor (CRF), in modulation of peripheral immune functions, the effects of intracranially administrated urocortin on the proliferative activity of splenic lymphocytes were examined in rats. Intracerebroventricular (i.c.v.) injection of urocortin (1 ng) produced a marked decrease in the proliferative response of splenocytes to a mitogen. The suppressive effect of urocortin was abolished by pretreatment with a ganglionic blocking agent (chlorisondamine) or β-adrenergic receptor antagonist (propranolol), but not by adrenalectomy. These results suggest that urocortin is an important neuropeptide involved in the brain control of peripheral immune functions such as stress-induced immunosuppression, and that the suppressive effect of urocortin is mediated by the sympathetic nervous system.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID

摘要:

MELATONIN is synthesized in the chicken retina under the influence of a circadian clock, which also regulates the expression of tryptophan hydroxylase (TPH) and serotonin N-acetyltransferase (AA-NAT). In order to examine the role of substrate supply in the rhythmic synthesis of melatonin in chicken retina, tryptophan and 5-hydroxytryptophan were administered day and night in light or darkness. When administered systemically at night in darkness, 5-hydroxytryptophan, but not tryptophan, dramatically stimulates melatonin levels in the chick retina in a dose-dependent manner. Intraocular administration of 5-hydroxytryptophan also increases melatonin levels locally, indicating a retinal site of action of the serotonin precursor. The effect of 5-hydroxytryptophan is much greater at night, when TPH and AA-NAT activities are high, than during the day, when the enzyme activities are low. Similarly, unexpected light exposure at night, which inactivates AA-NAT, significantly reduces the ability of 5-hydroxytryptophan to increase retinal melatonin levels. The results suggest that TPH, but not AA-NAT or other enzymes in the melatonin biosynthetic pathway, is saturated with substratein sit u. The rate of melatonin production appears to be a function of the concentration of serotonin, which is regulated by TPH, and by the level of activity of AA-NAT.

ISSN:0959-4965    

出版商:OVID    

年代:1998

数据来源: OVID