Expression of amyloid precursor protein, tau and presenilin RNAs in rat hippocampus following deafferentation lesions.

In this study, entorhinal cortex lesions and/or medial septal area cholinergic lesions were used in the rat to mimic some of the principal and earliest affects in Alzheimer's disease, namely hippocampal deafferentation. We wished to test the hypothesis that deafferentation lesions cause changes in the regulation of three proteins that are known to be important in Alzheimer's disease pathology, namely amyloid precursor protein, presenilin and tau. Expression of amyloid precursor protein mRNA was increased in several subfields of hippocampus when examined 1 week after entorhinal cortex lesion, but was reduced, compared to sham operated controls, after medial septal area cholinergic lesions. Cholinergic lesions were combined with entorhinal cortex lesions and produced no change in APP mRNA levels compared to controls. No significant changes were observed in the parietal cortex after entorhinal cortex or cholinergic lesions either alone or in combination. Tau mRNA level in hippocampus was unchanged after lesions. Presenilin-1 mRNA was expressed in the hippocampus at very low levels, and appeared to be increased following entorhinal cortex lesion. Our results support the hypothesis that amyloid precursor protein expression in hippocampal neurons is differentially affected by glutamatergic and cholinergic afferent input, and that presenilin-1, but not tau, may be subject to the same type of control in vivo.

Effect of reserpine on behavioural responses to agonists at 5-HT1A, 5-HT1B, 5-HT2A, and 5-HT2C receptor subtypes.

Rats were given a single dose of reserpine (5 mg/kg s.c.) and behavioural responses to agonists at 5-HT receptor subtypes compared with those of control animals 21 days later. The following effects of activating postsynaptic 5-HT1A receptors by the agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) were significantly increased: tail-flick, reciprocal forepaw treading, flat body posture. The hyperphagic effect of activating presynaptic 5-HT1A receptors by 8-OH-DPAT tended to increase and hypothermia on activating postsynaptic 5-HT1A sites tended to decrease. The hyperlocomotor effect of activating 5-HT1A sites also tended to decrease possibly as a result of a dependence of this response on the known depletion of catecholamines by reserpine. Head shakes on activating 5-HT2A receptors by 1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and two effects of activating 5-HT2C receptors by 1-(3-chlorophenyl) piperazine (mCPP) were significantly increased (hypophagia, anxiety) and a third effect, hypolocomotion tended to increase but hypophagia on activating postsynaptic 5-HT1B receptors by CP-94, 253 was significantly attenuated. The results are discussed with particular reference to altered 5-HT function in depression.

Serotonin metabolism and release in frontal cortex of rats on a vitamin E-deficient diet.

Rats were fed a control or vitamin E (all-rac-alpha-tocopheryl acetate)-deficient diet for 3 or 12 weeks. Serotonin (5-HT), 5-hydroxyindoleacetic acid (5-HIAA), tryptophan, and alpha-tocopherol concentrations were determined in the frontal cortex using HPLC, alpha-Tocopherol concentrations fell significantly to 27% of control values at 12 weeks. Tissue 5-HT, 5-HIAA, and tryptophan concentrations were not significantly altered by the vitamin E-deficient diet at either time point. In vivo microdialysis revealed normal basal and K(+)-stimulated concentrations of 5-HT and 5-HIAA, but extracellular concentrations of tryptophan were significantly decreased after 3 weeks on the vitamin E-deficient diet, which resulted in an increase in the tissue/extracellular ratio and suggested a change in compartmentation. However, after 12 weeks on the deficient diet these values had returned to normal. Results in general indicate that a prolonged and substantial depletion of brain vitamin E can occur without major disturbance of serotonergic function.

Depletion and repletion of cortical tissue and dialysate 5-HT after reserpine.

Reserpine (5 mg/kg s.c.) was given to rats kept under a reversed light-dark cycle and 5-hydroxytryptamine (5-HT) and 5-hydroxyindole acetic acid (5-HIAA) determined in frontal cortex tissue and dialysate at various times after drug treatment. The decline and return of spontaneous locomotor activity was also measured. Tissue 5-HT was depleted to 16% of control values 24 hr after drug administration and had recovered to 61% of control after 21 days. Locomotion was profoundly reduced by 7 hr after reserpine but had returned to normal at 4 days. Dialysate 5-HT, both basal and its rise on potassium (K+) stimulation, was reduced at 1, 7 and 21 days after reserpine but the K+ stimulated increases (as % of control) did not rise above % tissue repletion, thus providing evidence against increased mobilization of the transmitter from the partially repleted vesicular stores. However, at 1 day after reserpine, basal dialysate 5-HT was proportionately less reduced than tissue 5-HT suggesting that release from a reserpine insensitive (extravesicular) pool was more effective than from the vesicular pool. At this time, the K(+)-stimulated rise of dialysate 5-HT was proportionately more reduced than tissue 5-HT. By 21 days, values converged so that % changes of the 3 compartments were the same suggesting that at this time both basal and K+ stimulated dialysate 5-HT was essentially all derived from the vesicular pool.

Decrease in erythrocyte glycophorin sialic acid content is associated with increased erythrocyte aggregation in human diabetes.

1. Sialic acid moieties of erythrocyte membrane glycoproteins are the principal determinants of the negative charge on the cell surface. The resultant electrostatic repulsion between the cells reduces erythrocyte aggregation and hence the low shear rate viscosity and yield stress of blood. 2. Using g.c.-m.s., a decrease in sialic acid content has been observed in the major erythrocyte membrane glycoprotein, glycophorin A, obtained from nine diabetic patients compared with that from seven normal control subjects [median (range): 3.30 (0.01-11.90) versus 18.60 (3.20-32.60) micrograms/100 micrograms of protein, P less than 0.02]. 3. Erythrocyte aggregation, measured by viscometry as the ratio of suspension viscosity to supernatant viscosity (LS/S) in fibrinogen solution, was increased in ten diabetic patients compared with ten normal control subjects (mean +/- SEM, 37.6 +/- 1.3 versus 33.8 +/- 0.6, P less than 0.02). 4. In the patients in whom both viscometry and carbohydrate analysis were performed, the decrease in erythrocyte glycophorin sialylation and the increase in erythrocyte aggregation in fibrinogen solution were related statistically (LS/S correlated negatively with glycophorin sialic acid content, r = 0.73, P less than 0.05). 5. Decreased glycophorin sialylation provides an explanation at the molecular level for increased erythrocyte aggregation and it may be important in the pathogenesis of vascular disease in diabetes.

A defect in insulin release in women at risk of future non-insulin-dependent diabetes.

1. A study on seven Caucasian glucose-tolerant women with previous gestational diabetes and seven matched control subjects is presented. The insulin response to oral glucose, insulin sensitivity and fasting glucose production rates were measured by using a 75 g oral glucose tolerance test, an insulin tolerance test and a non-radioactive tracer, [6,6-2H]glucose, respectively. 2. Fasting plasma glucose levels were similar between the women with previous gestational diabetes and the control subjects (4.8 +/- 0.3 versus 4.7 +/- 0.2 mmol/l), as were fasting plasma insulin levels (median 4 m-units/l, range 1-13 m-units/l versus median 4 m-units/l, range 1-24 m-units/l). After oral glucose the 60 min plasma glucose levels in the women with previous gestational diabetes were significantly higher (8.5 +/- 0.6 versus 6.7 +/- 0.8 mmol/l, P less than 0.05), whereas the plasma insulin level was significantly lower at both 30 min (median 23 m-units/l, range 4-47 m-units/l versus median 55 m-units/l, range 23-100 m-units/l, P less than 0.02) and at 60 min (median 23 m-units/l, range 4-43 m-units/l versus median 60 m-units/l, range 16-126 m-units/l, P less than 0.02). 3. Insulin sensitivity, expressed as the slope of the regression line of plasma glucose level against time after intravenous infusion of insulin (0.05 unit/kg), was similar in the women with previous gestational diabetes and the control subjects (mean slope, -0.17 +/- 0.01 versus -0.17 +/- 0.01). 4. Fasting glucose production rates were similar in the women with previous gestational diabetes and the control subjects (2.2 +/- 0.3 versus 1.9 +/- 0.1 mg min-1 kg-1).(ABSTRACT TRUNCATED AT 250 WORDS)

Metabolic effects of pharmacological adrenergic blockade in phaeochromocytoma.

Twelve-hour hormonal and metabolic profiles were performed in a 68-year-old woman with a benign adrenal phaeochromocytoma (a) prior to adrenergic blockade, (b) after the establishment of pharmacological alpha-blockade with phenoxybenzamine, (c) after combined alpha and beta-blockade with phenoxybenzamine and propranolol, and (d) after successful surgery and withdrawal of medication. Pretreatment, (a) vs (d), significant elevations (12-h mean +/- SD) were observed in the concentrations of noradrenaline (44.9 +/- 14.4 vs 2.3 +/- 0.7 nmol/l, P less than 0.01), glucose (6.9 +/- 1.9 vs 5.0 +/- 1.0 mmol/l, P less than 0.05), glycerol (0.22 +/- 0.02 vs 0.07 +/- 0.01 mmol/l, P less than 0.01), non-esterified fatty acids (0.71 +/- 0.28 vs 0.34 +/- 0.08 mmol/l, P less than 0.01), and total ketone bodies (0.08 +/- 0.03 vs 0.03 +/- 0.02 mmol/l, P less than 0.01). Alpha-blockade, (b) vs (a), was associated with an increase in noradrenaline levels (P less than 0.01) but not with any significant alterations in intermediary metabolite concentrations. Following the establishment of combined alpha and beta-blockade, (c) vs (b), plasma noradrenaline returned to its pretreatment level while the concentrations of glycerol, fatty acids and ketone bodies were normalized. A completely physiological 12-h blood glucose profile, however, was observed only post-operatively. No significant differences were observed in mean plasma insulin levels between the four studies. These results indicate impaired regulation of multiple aspects of carbohydrate, lipid and ketone body metabolism in our patient.(ABSTRACT TRUNCATED AT 250 WORDS)

Evidence that intravenous morphine stimulates central opiate receptors to increase sympatho-adrenal outflow and cause hypertension in conscious rabbits.

1. In conscious rabbits, intravenous morphine caused hypertension, bradycardia, hyperglycaemia and increased plasma adrenaline and noradrenaline. These effects were prevented by ganglionic blockade with pentolinium. 2. The cardiovascular responses to morphine were not altered by pretreatment with a vasopressin V1-receptor antagonist. 3. After bilateral adrenalectomy morphine caused a similar rise in noradrenaline but no increase in adrenaline. The rise in blood pressure was attenuated and the hyperglycaemia was abolished. 4. Adrenaline infused intravenously to mimic the levels that occurred after morphine caused a similar degree of hyperglycaemia but only a small increase in blood pressure. 5. Pretreatment with intracerebroventricular naloxone prevented the morphine-induced hypertension, hyperglycaemia, increase in plasma catecholamines, respiratory depression and sedation. 6. These results demonstrate that, in conscious rabbits, intravenous morphine causes hypertension by increasing sympathetic vasoconstrictor nerve activity and elevating plasma adrenaline levels; the latter alone produces the hyperglycaemia. Vasopressin release is not involved in the hypertensive response to morphine. The effects of morphine appear to result from stimulation of central opiate receptors leading to enhanced sympathoadrenal outflow.

Intravenous morphine causes hypertension, hyperglycaemia and increases sympatho-adrenal outflow in conscious rabbits.

1. In conscious rabbits, intravenous morphine (3 mg/kg) caused hypertension, bradycardia, hyperglycaemia and sedation. These changes were accompanied by large increases in plasma adrenaline and smaller increases in plasma noradrenaline. 2. These effects of morphine were prevented by intravenous naloxone, demonstrating their dependence on stimulation of opiate receptors. 3. Pretreatment with the antihistamines cimetidine and chlorpheniramine enhanced the morphine-induced rise in blood pressure, excluding a role for histamine release in the hypertensive action of morphine. 4. The centrally acting alpha 2-adrenergic agonist clonidine prevented the morphine-induced hypertension and rise in plasma catecholamines, suggesting that these effects are exerted via central pathways. Clonidine alone reduced blood pressure and heart rate and produced hyperglycaemia. 5. alpha-Adrenergic blockade with phenoxybenzamine reduced the increase in blood pressure after morphine, although the increase in plasma catecholamines was augmented. 6. Pentobarbitone anaesthesia prevented the morphine-induced cardiovascular changes, the increase in plasma catecholamines and the hyperglycaemia. 7. These findings indicate, that in conscious rabbits, morphine induces hypertension by stimulation of opiate receptors leading to increased sympatho-adrenal activity. The hyperglycaemia appears to be in response to secretion of adrenaline. These effects probably result from a central action of morphine.