Isobel M. Ritchie

Catecholamines and cholinergic enzymes in pre-senile and senile Alzheimer-type dementia and down's syndrome

Noradrenaline, dopamine, homovanillic acid (HVA), choline acetyltransferase (ChAT) and acetylcholinesterase (AChE) levels were measured in post-mortem brains from 8 cases of pre-senile Alzheimer-type dementia (ATD), 5 cases of senile ATD, 4 cases of Downs syndrome aged 53-57 years, one 27-year-old case of Downs syndrome and 13 controls. In the controls, the concentration of noradrenaline in hypothalamus (P less than 0.05) and mamillary body (P less than 0.02) decreased with age. Compared with age-matched controls, noradrenaline levels in these areas were more markedly reduced in pre-senile ATD (P less than 0.01), the 53-57-year-old cases of Downs syndrome (P less than 0.001) and in the 27-year-old Downs, than in senile ATD (hypothalamus P less than 0.05, mamillary body, n.s.). Dopamine and HVA concentrations in caudate nucleus were unaltered in pre-senile or senile ATD but dopamine was decreased (P less than 0.01) in the older cases, although not in the 27-year-old case, of Downs syndrome. In the olfactory tubercle in ATD the level of HVA was unaltered but the activity of ChAT was decreased (P less than 0.01). ChAT activity was reduced in pre-senile ATD (P less than 0.001), the older Downs cases (P less than 0.01) but not the young Downs case, and senile ATD (P less than 0.001) in the temporal cortex and in pre-senile ATD (P less than 0.001) and the older Downs cases (P less than 0.001) but not senile ATD in the caudate nucleus.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibition of neuronal nitric oxide synthase by 7-nitroindazole : effects upon local cerebral blood flow and glucose use in the rat

The novel nitric oxide synthase inhibitor 7-nitroindazole (7-NI) is relatively specific for the neuronal isoform of the enzyme and in this study we have used this compound to investigate the physiological role of perivascular nitric oxide-containing nerves in the cerebrovascular bed. Following injection of 7-NI (25 or 50 mg/kg, i.p.), cerebral blood flow and glucose utilization were measured in the conscious rat using the fully quantitative [14C]iodoantipyrine and 2-[14C]deoxyglucose techniques, respectively. Neither dose of the drug produced any change in arterial blood pressure, confirming a lack of effect upon the endothelial isoform of the enzyme, although there was a pronounced decrease in heart rate (−28% by 10 min postinjection). Throughout the brain 25 mg/kg 7-NI i.p. resulted in decreases in blood flow of between −20% in the hippocampus and −58% in the substantia nigra. Increasing the dose to 50 mg/kg resulted in a further generalized decrease, to almost −60% in parts of the thalamus and hippocampus, but in every animal this higher dose of 7-NI also produced randomly distributed areas of relative hyperaemia, which were most commonly found in those areas where the most intense hypoperfusion was otherwise in evidence. Despite these changes in blood flow, in all but a very few areas of the brain no significant decrease in glucose use was measured at either of the two doses of 7-NI. Thus despite the greater specificity of 7-NI for neuronal nitric oxide synthase, the cerebrovascular effects of the drug in vivo are very similar to that reported for the arginine analogues. However, these data do suggest that nitric oxide-releasing neurones in the brain may have an important role to play in the regulation of cerebral blood flow.

Functional consequences of perinatal exposure to3,4-methylenedioxymethamphetamine in rat brain

In this study we have examined methylenedioxymethamphetamine (MDMA)‐induced toxicity in perinatal rat brain, related this to normal development of serotonin transporter sites (SERT), and determined whether early exposure to MDMA subsequently alters cerebral function in adults. Perinatal development of SERT was visualized and quantified using [3H]‐paroxetine binding autoradiography in embryonic and neonatal rat brain from embryonic day 15 (E15) to postnatal day 30 (P30). Cerebral glucose utilization (lCMRglu) was measured by 2‐deoxyglucose autoradiography in adult rats. [3H]‐Paroxetine binding was observed in forebrain from E18. From birth (P0), binding was organized into neocortical columns (75% higher at P10 than in adult) which declined toward adult levels between P20 and P25. MDMA treatment (20 mg kg−1 s.c. twice daily for four days) commencing at developmental stages from E15 (treatment given to dams) to P20, had no effect upon [3H]‐paroxetine binding measured at P40. Treatments started on P25 or later resulted in significant decreases in [3H]‐paroxetine binding (46%). This was coincident with the development of adult patterns of binding in forebrain. Despite the lack of MDMA‐induced neurotoxicity, rats treated in utero (E15) showed increased lCMRglu in locus coeruleus (+37%), and in areas receiving ascending noradrenergic innervation, such as anterior thalamus (+44%) and septal nucleus (+24%). These studies confirm that the susceptibility of serotonergic terminals to the neurotoxic properties of MDMA is absent in the immediate perinatal period, but also suggests that in utero MDMA exposure produces significant long‐term effects on cerebral function by a mechanism as yet unknown.

Cerebrovascular autoregulation in response to hypertension induced by NG-nitro-l-arginine methyl ester

Local neocortical blood flow and glucose utilization were measured in conscious rats using [14C]iodoantipyrine and [14C]2-deoxyglucose quantitative autoradiography, respectively, following intravenous injection of the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (30 mg/kg). The dose of NG-nitro-L-arginine methyl ester was chosen so as to produce a level of hypertension equivalent to that produced in a parallel group of rats by the infusion of angiotensin-II (5 micrograms/ml at 0.5-2.0 ml/h). In those animals in which angiotensin-induced hypertension did not exceed 150 mmHg (mean arterial blood pressure), there were no significant effects upon cortical blood flow when compared to controls, but at higher pressures (157 +/- 1 mmHg), blood flow was significantly increased in circumscribed areas of cortex, most notably in parietal (from 204 +/- 10 to 780 +/- 44 ml/100 g per min) and occipital cortex (from 175 +/- 5 to 600 +/- 46 ml/100 g per min), whilst other cortical areas (e.g. temporal and frontal areas) were unchanged. Despite the fact that NG-nitro-L-arginine methyl ester increased blood pressure to levels (164 +/- 1 mmHg) which were in excess of the highest produced by angiotensin, there was no evidence of focal hyperaemia; indeed blood flow was significantly reduced in every cortical region except parietal area 1. No significant differences in glucose use were evident between any of the groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Cerebrovascular and functional consequences of 5-HT1A receptor activation

Cerebral glucose utilization and blood flow were measured in rats using 2-deoxy-D-[14C]glucose and [14C]iodoantipyrine quantitative autoradiography, respectively, following treatment with the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT). In control and 8-OH-DPAT-treated animals blood flow and glucose use were similarly correlated, but the ratio was increased following 8-OH-DPAT treatment. Since 5-HT1A receptor activation is known to reduce neuronal 5-HT release, these results are consistent with a vasoconstrictor role for endogenous serotonin.

Evidence for a possible role for serotonergic systems in the control of cerebral blood flow

Cerebral blood flow and glucose utilisation were measured in rats using [14C]iodoantipyrine and [14C]2-deoxyglucose quantitative autoradiography respectively following repeated exposure to the serotonergic neurotoxin methylenedioxyamphetamine. In both control and treated animals blood flow and glucose use were similarly correlated but the ratio was increased following lesion. Some focal increases in flow were greatly in excess of metabolic demand. These results are consistent with a cerebrovascular vasoconstrictor role for serotonin.

Nitric oxide synthase is expressed in experimental malignant glioma and influences tumour blood flow

SummaryThe distribution and function of nitric oxide synthase (NOS) was studied in the rodent C6 implantation glioma model. Using a histochemical stain for NADPH diaphorase, which colocalises with NOS, morphological studies revealed non homogenous staining of the constituent tumour cells and the neoplastic endothelium. Immunocytochemical staining for macrophages (ED1, ED2) showed dense positivity at the tumour brain interface with more patchy positivity within the tumour mass. This finding suggests that both macrophages, which are known to produce large amounts of NO, and the C6 cells contribute to the NADPH diaphorase positivity. Administration of the NOS inhibitor Ng-nitro-L-argine methyl ester (L-NAME) significantly reduced both tumour (40%) and contralateral local cerebral blood flow (20%) compared to control animals. These findings demonstrate that (i) NOS is present in experimental malignant glioma; (ii) NO mediated mechanisms contribute to tumour blood vessel dilatation and blood flow regulation; and (iii) using this model there is a significant differential sensitivity of the tumour and brain parenchymal vascular beds to a NOS inhibitor. Further investigations are required to determine the potential therapeutic and biological relevance of these findings and the relative contributions of tumour cells, neoplastic endothelium and reactive macrophages to NO mechanisms in gliomas.

Effects of nitric oxide modulation on tumour blood flow and microvascular permeability in C6 glioma

C6 glioma strongly express nitric oxide synthase. Rats bearing C6 tumours were pre-treated with i.v. Ng-nitro-L-arginine methyl ester (L-NAME), 3-morpholinosydnonimine (SIN-1) or saline before local cerebral blood flow (LCBF) or tumour capillary permeability (TCP) was measured by the [14C]iodoantipyrine autoradiographic or [14C]α-amino-isobutyric acid techniques. L-NAME and SIN-1 caused significant TBF alterations (−44% and +136%, respectively) with less marked (−15% and +33%) alterations in normal brain. Calculated cerebrovascular resistance changes within tumour were indeed selective. Baseline TCP was increased compared with normal brain (20-fold). L-NAME and SIN-1 administration did not alter TCP. These effects have significant implications for human malignant glioma management. Selective i.v. manipulation of LCBF, without significant changes in TCP, could increase the efficacy of chemotherapy, radiotherapy or provide better peritumoural oedema control.

Acute cocaine alters cerebrovascular autoregulation in the rat neocortex

Although cocaine abuse has been associated with an increased incidence of cerebrovascular accident, the underlying mechanisms are unknown. In this study we have investigated the effects of cocaine upon the autoregulation of local cortical blood flow (lCBF) during hypertension. Hypertension was induced in conscious rats by intravenous infusion of angiotensin-II (5 micrograms/ml; 0.5-2.5 ml/h), and animals were subsequently injected IV with either cocaine-HCl (5 mg/kg) or saline, prior to the measurement of lCBF of glucose utilization (lCGU) using [14C]-iodoantipyrine or [14C]-2-deoxyglucose quantitative autoradiography, respectively. Hypertension alone (< 155 mmHg) did not significantly alter lCBF in any cortical areas examined. However, at higher mean arterial blood pressure (MABP), lCBF increased focally (+265%) in parietal cortex. Cocaine did not alter lCBF in normotensive animals, but with increasing levels of hypertension (MABP > 145 mmHg), all cocaine-treated rats showed focal increases (200-400%) in lCBF in parietal cortex. Glucose use remained relatively unaffected in all treatment groups. This hyperaemia in cocaine-treated rats at MABP below the normal upper limit of autoregulation may provide a mechanism to explain haemorrhagic stroke in cocaine abusers.

Effects of the specific serotonin reuptake inhibitor, citalopram, upon local cerebral blood flow and glucose utilisation in the rat

The effects of the potent selective 5-HT reuptake blocking agent, citalopram (10 mg/kg, i.v.), on local cerebral blood flow (lCBF) and local cerebral metabolic rate of glucose (lCMRglu) were measured using [14C]iodoantipyrine (IAP) and [14C]2-deoxyglucose (2-DG) autoradiography, respectively. Significant decreases in lCBF were observed in nine of the 27 brain areas analysed, with significant decreases in lCMRglu observed in 17 areas. While decreases in blood flow were observed, it cannot be concluded that these were in fact the result of a direct action of 5-HT upon serotonergic receptors in cerebrovascular smooth muscle, since the dynamic relationship between flow and metabolism remains largely intact. The reductions in lCBF may be explained entirely by the secondary effects of depressed cerebral metabolic demand induced by citalopram which would, once again, question the role of specifically perivascular serotonergic nerve activity in the tonic control of cerebral blood flow.