Nicotinic stimulation of catecholamine synthesis and tyrosine hydroxylase phosphorylation in cervine adrenal medullary chromaffin cells.

The synthesis and secretion of catecholamines by the adrenal medulla is of major importance in the stress response. Tyrosine hydroxylase, the rate-limiting enzyme for catecholamine biosynthesis, has been extensively studied in adrenal medullary chromaffin cells from a number of species. Cervine chromaffin cells are of interest because the deer is known to be a relatively stress-prone reactive species. We report the first characterisation of tyrosine hydroxylase regulation in cervine chromaffin cells. Nicotinic receptor activation resulted in a time- and concentration-dependent increase in catecholamine synthesis, which was significantly reduced by the extracellular signal-regulated kinase (ERK)1/2 signalling pathway inhibitor PD98059 and the calcium/calmodulin protein kinase II inhibitor KN-93, but not by H89 or bisindolylmaleimide I, inhibitors of protein kinase A and C, respectively. Nicotinic stimulation also increased the phosphorylation of ERK1/2 and tyrosine hydroxylase. This latter response occurred on serine residues 19, 31 and 40 of the enzyme. The nicotinic-induced phosphorylation of ERK1/2 and serine 31 of tyrosine hydroxylase was suppressed by PD98059 but not bisindolylmaleimide I. These data indicate that nicotinic stimulation of tyrosine hydroxylase involves the phosphorylation of serine 31 via an ERK1/2-dependent, protein kinase C-independent pathway. Protein kinase C activation by phorbol 12-myristate 13-acetate also caused an ERK1/2-dependent increase in the serine 31 phosphorylation of tyrosine hydroxylase but, in contrast to the nicotinic response, was not accompanied by an increase in enzyme activity. Thus, ERK1/2-mediated serine 31 phosphorylation of tyrosine hydroxylase appears necessary but not sufficient for nicotinic activation of catecholamine synthesis in cervine chromaffin cells. These data present potentially important similarities and differences between the regulation of catecholamine synthesis in cervine and the more widely studied bovine adrenal medulla.

Poisson equation in the Kohn-Sham Coulomb problem.

We apply the Poisson equation to the quantum mechanical Coulomb problem for many-particle systems. By introducing a suitable basis set, the two-electron Coulomb integrals become simple overlaps. This offers the possibility of very rapid linear-scaling treatment of the Coulomb contribution to Kohn-Sham theory.

Insertion and abstraction pathways in the reaction O(1D2) + H2-->OH+H.

Rigorous quantum dynamical calculations have been performed on the ground 1 1A' and first excited 1 1A" electronic states of the title reaction, employing the most accurate potential energy surfaces available. Product rovibrational quantum state populations and rotational angular momentum alignment parameters are reported, and are compared with new experimental, and quasiclassical trajectory calculated results. The quantum calculations agree quantitatively with experiment, and reveal unequivocally that the 1 1A" excited state participates in the reaction.

Chromatic-contrast threshold impairment in diabetes.

A prospective study was carried out to investigate acquired colour-vision deficits in diabetics using an automated, computer-controlled, cathode-ray-tube based test of chromatic contrast. Chromatic-contrast thresholds estimates were measured along both a red/ green (constant S-cone) confusion axis and a tritan (constant M/L-cone) confusion axis for 305 eyes of 305 diabetics. The diabetic data were partitioned into groups based on a clinical categorisation of retinopathy. The diabetic data were compared with both age-matched and 'lens-equated' control data obtained from a bank of 347 normal subjects. Further analysis of differences between diabetic-status groups was performed. Associations between chromatic contrast threshold estimates and age, duration of disease, and severity of both macular oedema and ischaemia were investigated. The diabetic group was found to have significantly reduced chromatic-contrast threshold estimates when compared with normal controls, even in the absence of retinopathy. This reduction in chromatic contrast was predominantly tritanopic in nature. Interestingly, no reduction in red/green chromatic-contrast threshold estimate was found in diabetics without retinopathy. The tritan deficit seen in diabetics without retinopathy was strongly correlated with duration of disease, but when adjustments were made to account for the effects of duration-dependent lens yellowing, the tritan deficit was no longer apparent. A correlation between both the severity of macular oedema and severity of ischaemia with chromatic-contrast loss was established. Acquired reductions in both red/green and tritan chromatic-contrast threshold estimates seen in diabetics are strongly correlated with the severity of retinopathy. The results provide evidence that the specific tritan deficits seen in diabetics can be explained by the effects of lens yellowing rather than by selective damage of the blue cone system as has been hypothesised by other groups. The results provide support for the potential use of automated CRT-based tests of colour vision in diabetic retinopathy screening protocols.

Radiotherapy treatment of age-related subfoveal neovascular membranes in patients with good vision.

This prospective study investigated whether low-dose ionising radiotherapy preserved vision and caused membrane regression in patients with age-related subfoveal neovascular membranes (SFNVMs) or vascularised pigment epithelial detachments (PEDs) and relatively good initial visual acuities. Twenty-five patients with initial Snellen acuities of 6/24 or better were treated with low-dose external beam radiotherapy. Of the patients with SFNVMs, visual acuities were maintained or improved in 58% at 6 months and 53% at 1 year. Neovascular membrane size was assessed by image analysis and showed some regression in 47% and 41% at 6 and 12 months respectively. These results suggest that patients with SFNVMs and good vision may benefit from radiotherapy, faring better than previous reports of the natural history of this condition. Conversely, patients with vascularised PEDs did not appear to benefit from radiotherapy. Only 17% maintained their vision at 1 year and 33% suffered retinal pigment epithelial tears. The results from patients with SFNVMs and good initial vision, excluding those with vascularised PEDs, are encouraging however, any benefit from this treatment needs to be proven by controlled trials with long follow-up.

Colour vision in diabetic and normal pseudophakes is worse than expected.

Automated colour vision testing in pseudophakes showed unexpected results. Chromatic discrimination sensitivity was measured in 22 diabetic pseudophakes with no retinopathy, 23 diabetic pseudophakes with background retinopathy and 34 non-diabetic pseudophakes. These results were compared with those in age-matched normal and diabetic phakic subjects, all of whom had good vision. The diabetics were also matched for retinopathy grading and duration of diabetes. In all three groups, red-green discrimination sensitivity was worse in the pseudophakes when compared with the corresponding phakic subjects (normals, p < 0.001; no retinopathy, p = 0.467; background retinopathy, p = 0.057). However, tritan vision was marginally worse in the normal pseudophake group but was better in the two diabetic pseudophake groups, when compared with phakic controls. This may be due to a reduction in tritan sensitivity in age-matched phakic controls from the effects of increased lens yellowing with age.

Automated tritan discrimination sensitivity: a new clinical technique for the effective screening of severe diabetic retinopathy.

We have developed and extensively assessed an automated chromatic discrimination test which can be used to screen effectively a diabetic population for sight threatening diabetic eye disease. Equiluminant, sinusoidal, low spatial frequency, chromatic gratings are produced along a tritan confusion axis under computer software control on a high resolution CRT. The correct position of the tritan axis in colour space was calibrated using subjects whilst they were transiently tritanopic. The minimum amplitude about a neutral "grey point" along the tritan confusion axis at which a subject can just distinguish a grating is found using a double staircase reversal algorithm. This measure is taken as the Tritan Discrimination Sensitivity and it is this that we use to flag those diabetics with severe diabetic retinopathy. This computerised tritan discrimination test is quick, non-invasive, easy to operate, inexpensive and reliable. The test-retest reliability coefficient (rho) is 0.92. The tritan discrimination test effectively identifies those diabetics who have or are most at risk of developing severe diabetic retinopathy. The sensitivity of the test for the detection of maculopathy, ischaemic retinopathy (pre-proliferative), and proliferative retinopathy is 97%, 65%, and 93%, respectively. The corrected specificity of the test is 83%. We conclude that the tritan discrimination test has potential for use as a valuable screening tool for the early detection and treatment of severe diabetic retinopathy.

Measurement of visual evoked potential in the asphyctic fetus and during neonatal survival.

Visual evoked potentials were measured in eight exteriorized near-term fetal lambs prior to and during 8 minutes of asphyxia and during 1 hour of newborn survival. Four of the lambs were then extubated, and measurements were continued while the lambs were observed for behavior and gross motor function. Early in the asphyctic period, marked changes in the visual evoked potential occurred in association with a fall in Po2, whereas during the postexposure period the visual evoked potential appeared to recover independently of cardiovascular or arterial blood gas values. Moreover, early wave components of the visual evoked potentials were more resistant to asphyxia than were later components and responded more quickly to resuscitative efforts. During the survival period the visual evoked potential did not correlate with gross motor function when animals were exposed to moderate acidosis. After severe acidosis abnormal visual evoked potentials were seen during periods of clinical deterioration.

Birth asphyxia. I. Measurement of visual evoked potential (VEP) in the healthy fetus and newborn lamb.

The visual evoked potential (VEP) of five healthy, near-term exteriorized fetal lambs was compared with the VEP obtained from the same animals during the first hour after ventilation. Characteristics of the individual wave components and their relationship to blood pressure, heart rate, and arterial blood gas measurements concomitantly obtained were examined. Results show that the VEP of the healthy fetus is a stable, reproducible signal consisting of four basic components, and that the latencies (msec) and the amplitude (mu V) of the individual components of the VEP are similar to those of the newborn. In two related experiments, fetal asphyxia of unknown duration was encountered during fetal exteriorization an instrumentation. In the first case, neonatal, acidosis persisted despite aggressive resuscitation efforts and was accompanied by an atypical VEP. In the second case, the neonatal VEP obtained after 15 min of resuscitation was markedly depressed despite restoration of acid-base balance but gradually recovered during the remainder of the 1-hr newborn period. In conclusion, the VEP is a reproducible measure of cortical function in the healthy fetus and neonate and may reflect the acute status of cerebral function during fetal asphyxia and neonatal resuscitation.