Cerebrovascular responses to pathophysiological insult in diabetic rats.

Diabetes mellitus is associated with altered cerebrovascular responsiveness and this could contribute to the pathology of stroke in diabetic patients. In these studies, we used a model of haemorrhagic stroke (intrastriatal injection of 50 microl blood) to examine subacute perilesional perfusion and blood-brain barrier (BBB) integrity in spontaneously diabetic rats. Volumes of striatal oligaemia (blood flow < 35 ml 100 g(-1) min(-1)) were significantly increased (>300%) in diabetic rats with intrastriatal blood, compared to either non-diabetic rats with blood or control diabetic rats with striatal injection of silicon oil. However, the increase in BBB permeability was both qualitatively and quantitatively similar in diabetic and control rats. Poorer outcomes following haemorrhagic stroke in diabetic patients may thus result from dysfunctional cerebrovascular control, and particularly decreased dilatatory reserve.

7-nitroindazole reduces cerebral blood flow following chronic nitric oxide synthase inhibition.

Blood flow and glucose utilization were measured in rat brain after chronic L-NAME treatment followed by acute 7-nitroindazole. Following chronic L-NAME, blood flow was not significantly different from control. Treatment with acute 7-nitroindazole reduced blood flow to the same extent in both chronic saline and L-NAME groups. Glucose utilization was unaffected. These results suggest that residual NOS activity in brain is sufficient to provide tonic, NO-dependent cerebrovascular dilator tone.

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.

Intracerebral fetal raphé implants normalize hippocampal function but not cerebrovascular control in serotonin-depleted adult rat brain.

The effects of hypercapnia upon local cerebral blood flow and local cerebral glucose utilization were measured by quantitative autoradiography in parallel groups of rats (six per group) which 14-16 weeks previously had been treated with the serotonergic neurotoxin, methylenedioxymethamphetamine, followed by implantation of fetal raphé or basal forebrain tissues. Following the experiments, transplants were visualized by acetylcholinesterase histochemistry, and serotonergic reinnervation assessed using [3H]paroxetine binding to serotonin reuptake sites. In methylenedioxymethamphetamine-treated rats, contralateral to the implants, [3H]paroxetine binding was reduced by between 50 and 90% in the neocortex and hippocampus. Hippocampal glucose utilization was significantly increased in these rats, and the normal increase in flow which accompanies hypercapnia was also significantly enhanced. High levels of [3H]paroxetine binding were found within the raphé transplants (308 +/- 13 fmol/mg tissue). In host brain adjacent to the implant, binding levels were normalized, and in these same areas glucose utilization was also normalized. Basal forebrain implants had no effect upon either [3H]paroxetine binding or glucose utilization. Raphé transplants did not, however, alter the enhanced cerebrovascular response to hypercapnia induced by methylenedioxymethamphetamine, even in those areas where there was evidence of serotonergic reinnervation. The transplants also showed the same enhanced response. In conclusion, intracerebral fetal raphé implants normalize hippocampal function but not cerebrovascular control in serotonin-depleted adult rat brain, and despite not sharing the serotonergic deficit, blood flow in the implants follows that of the dysfunctional host.

Possible role for nitric oxide releasing nerves in the regulation of ocular blood flow in the rat.

AIM: To investigate the role of nitrergic nerves in the regulation of ocular blood flow. METHODS: Conscious, lightly restrained rats were treated with either the neuronal nitric oxide synthase inhibitor 7-nitroindazole (7-NI), or the nonselective inhibitor, NG-nitro-L-arginine methyl ester (L-NAME), and ocular blood flow was measured ex vivo from tissue samples, using the fully quantitative [14C]-iodoantipyrine technique. RESULTS: In the peripheral circulation, L-NAME produced an increase in arterial blood pressure (+22%) while 7-NI had no effect. In contrast, both 7-NI and L-NAME produced significant decreases in ocular blood flow (-31% and -59% respectively). The ocular vascular resistance calculated from ocular blood flow and mean arterial blood pressure increased by 29% following 7-NI, but by 130% following L-NAME. CONCLUSIONS: Nitric oxide releasing neurons may play an important contributory role in regulating ocular blood flow.

Cerebrovascular effects of nitric oxide manipulation in spontaneously hypertensive rats.

1. Evidence that nitric oxide (NO) bioactivity is altered in chronic hypertension is conflicting, possibly as a result of heterogeneity in both the nature of the dysfunction and in the disease process itself. The brain is particularly vulnerable to the vascular complications of chronic hypertension, and the aim of this study was to assess whether differences in the cerebrovascular responsiveness to the NO synthase (NOS) inhibitors, NG-nitro-L-arginine methyl ester (L-NAME) and 7-nitroindazole (7-NI), and to the NO donor 3-morpholinosydnonimine (SIN-1) might indicate one possible source of these complications. 2. Conscious spontaneously hypertensive (SHR) and WKY rats, were treated with L-NAME (30 mg kg-1, i.v.), 7-NI (25 mg kg-1, i.p.), (0.54 or 1.8 mg kg-1 h-1, continuous i.v. infusion) or saline (i.v.), 20 min before the measurement of local cerebral blood flow (LCBF) by the fully quantitative [14C]-iodoantipyrine autoradiographic technique. 3. With the exception of mean arterial blood pressure (MABP), there were no significant differences in physiological parameters between SHR and WKY rats within any of the treatment groups, or between treatment groups. L-NAME treatment increased MABP by 27% in WKY and 18% in SHR groups, whilst 7-NI had no significant effect in either group. Following the lower dose of SIN-1 infusion, MABP was decreased to a similar extent in both groups (around -20%). There was no significant difference in MABP between groups following the higher dose of SIN-1, but this represented a decrease of -41% in SHR and -21% in WKY rats. 4. With the exception of one brain region (nucleus accumbens), there were no significant differences in basal LCBF between WKY and SHR. L-NAME produced similar decreases in LCBF in both groups, ranging between -10 and -40%. The effect of 7-NI upon LCBF was more pronounced in the SHR (ranging from -34 to -57%) compared with the WKY (ranging from -14 to -43%), and in seven out of the thirteen brain areas examined there were significant differences in LCBF. 5. Following the lower dose of SIN-1, in the WKY 8 out of the 13 brain areas examined showed significant increases in blood flow compared to the saline treated animals. In contrast, only 2 brain areas showed significant increases in flow in the SHR. In the rest of the brain areas examined the effects of SIN-1 upon LCBF were less marked than in the WKY. 6. Infusion of the higher dose of SIN-1 resulted in further significant increases in LCBF in the WKY group (ranging between +30% and +74% compared to saline-treated animals), but no significant effects upon LCBF were found in the SHR. As a result, there were significant differences in LCBF between SIN-1-treated WKY and SHR in six brain areas. In most brain areas examined, cerebral blood flow in SHR following the higher dose of SIN-1 was less than that measured with the lower dose of SIN-1. 7. Despite comparable reductions in MABP (approximately 20%) in both groups, calculated cerebrovascular resistance (CVR) confirmed that the vasodilator effects of the lower dose of SIN-1 were significantly more pronounced throughout the brain in the WKY (ranging between -3% and -50%; median = -38%) when compared to the SHR (ranging between -10% and -36%; median = -26%). In the animals treated with the higher dose of SIN-1, CVR changes were broadly similar in both groups (median = -45% in WKY and -42% in SHR), but with the reduction in MABP in SHR being twice that found in WKY, this is in keeping with an attenuated blood flow response to SIN-1 in the SHR. 8. The results of this study indicate that NO-dependent vasodilator capacity is reduced in the cerebrovasculature of SHR. In addition, the equal responsiveness to a non-specific NOS inhibitor but an enhanced effectiveness of a specific neuronal NO inhibitor upon LCBF in the SHR could be consistent with an upregulation of the neuronal NO system.

Effect of chronic inhibition of nitric oxide synthase on ocular blood flow and glucose metabolism in the rat.

AIMS: To investigate the effects of chronic administration of nitric oxide synthase inhibition on ocular blood flow and metabolic demand in the rat and to compare these effects with changes in the cerebral and peripheral circulation. METHODS: Male Sprague-Dawley rats were injected with the nitric oxide synthase inhibitor L-NAME (75 mg/kg i.p.), either on a single occasion only or once daily for 10 consecutive days. Controls were injected with saline. Regional blood flow and glucose metabolism were measured from tissue samples, using [14C]-iodoantipyrine and [14C]-2-deoxyglucose respectively, 1 hour after either acute L-NAME injection or 1 hour after the last injection of the chronic treatment protocol. RESULTS: Mean arterial pressure was significantly increased (+31%) following the acute injection (indicating peripheral vasoconstriction) and this effect was enhanced (+50%) following chronic treatment. In both the ocular and cerebral circulation, blood flow was decreased following acute treatment (-48% and -43% respectively). However, while this response was totally attenuated in the cerebral circulation following chronic L-NAME treatment (-4%), the ocular circulation remained responsive (-57%). Metabolic demand in brain and eye tissue, as reflected in the accumulation of 2-deoxyglucose, was unaffected by either acute or chronic treatment with L-NAME. CONCLUSION: Homeostatic mechanisms appear to be activated in the cerebral circulation which re-establish flow metabolism homeostasis, and the effect of L-NAME on cerebral blood flow is attenuated following repeated exposure. This process does not seem to happen in the ocular circulation and, thus, the ocular vasculature appears to behave more like those blood vessels which determine total peripheral resistance than the cerebral circulation. It remains to be seen whether the sustained decrease in blood flow in the eye is sufficient to compromise ocular function and render the eye susceptible to damage from chronic L-NAME induced oligaemia.

Comparison of the patterns of altered cerebral glucose utilisation produced by competitive and non-competitive NMDA receptor antagonists.

Recent studies indicate that competitive and non-competitive NMDA receptor antagonists can be readily distinguished by their effects on local cerebral glucose utilisation (1CGU). In the present study we compare the effects of the novel NMDA antagonist, (+)-1-methyl-1phenyl-1,2,3,4-tetrahydroisoquinoline (FR115427) on 1CGU, comparing its metabolic profile with that of the non-competitive NMDA receptor antagonist, dizocilpine (MK801) and of the competitive NMDA receptor antagonist CGS19755, using the 2-deoxyglucose metabolic mapping approach. Local cerebral glucose utilisation was measured in 80 anatomically discrete regions of the conscious rat brain using [14C]2-deoxyglucose quantitative autoradiography. Studies were initiated 10 min after the administration of FR115427 (0.1-3 mg/kg i.v.; n = 20), dizocilpine (0.03-0.3 mg/kg; n = 15), CGS19755 (1-30 mg/kg; n = 15) or saline (2 ml/kg; n = 5). Dizocilpine produced characteristic alterations in 1CGU with widespread increases in 1CGU in primary olfactory and limbic areas while reducing 1CGU in somatosensory and motor cortex. FR115427 produced a pattern of altered 1CGU which was broadly similar to that elicited by dizocilpine with increases in 1CGU in the pontine nuclei, presubiculum and hippocampus and reductions in somatosensory and motor cortex and within components of the auditory system. However, FR115427 was approximately 30-fold less potent than dizocilpine in this regard. In limbic structures, the effects of FR115427 were less pronounced than those produced by dizocilpine. Increases in 1CGU of 62-98% were found in retrosplenial, piriform and entorhinal cortex of dizocilpine-treated rats whereas these areas appeared relatively unaffected following FR115427 administration. A comparison of the pattern of metabolic response produced by each of these agents was performed by constructing a hierarchy of regional responsiveness using the f statistic: while focal differences in the metabolic profiles of dizocilpine and FR115427 were evident, a plot of the regional f values for dizocilpine and FR115427 revealed a strong overall relationship between the metabolic responses with a Pearson's product moment correlation of 0.78. In contrast, the correlation between the patterns produced by CGS19755 and that for dizocilpine or FR115427 was poor (r = 0.28 and 0.5 respectively).

Cerebrovascular responsiveness to NG-nitro-L-arginine methyl ester in spontaneously diabetic rats.

1. There is evidence that endothelial dysfunction is associated with diabetes mellitus. The purpose of the present study was to assess local cerebral blood flow (LCBF) and cerebrovascular responsiveness to the NOS inhibitor NG-nitro-L-arginine methyl ester (L-NAME) in spontaneously diabetic insulin-dependent BioBred (BB) rats. 2. Diabetic rats, and non-diabetic controls, were treated with L-NAME (30 mg kg-1, i.v.) or saline, 20 min prior to the measurement of LCBF by the fully quantitative [14C]-iodoantipyrine autoradiographic technique. 3. There were no significant differences in physiological parameters (blood pH, PCO2, and PO2, rectal temperature, arterial blood pressure, or plasma glucose) between any of the groups of rats, and no difference in either the extent or the temporal characteristics of the hypertensive response to L-NAME between diabetic and non-diabetic rats. 4. In diabetic rats, a global reduction in basal LCBF was observed, although significant reductions (between -20 and -30%) were found in only 5 (mainly subcortical) out of the 13 brain regions measured. Following L-NAME injection, significant reductions in LCBF (between -20 and -40%) were found in the non-diabetic animals. In diabetic animals treated with L-NAME, a significant reduction in LCBF was measured only in the hypothalamus (-33%). 5. The cerebrovascular response to acute L-NAME is attenuated in spontaneously diabetic insulin-dependent BB rats. This would be consistent with the endothelial dysfunction in cerebral vessels, known to be associated with diabetes mellitus and it is possible that a loss of NO-induced dilator tone, amongst other factors, may underlie the observed reductions of basal LCBF in these animals.

Cerebrovascular consequences of repeated exposure to NG-nitro-L-arginine methyl ester.

1. Acute treatment with the nitric oxide synthase (NOS) inhibitor NG-nitro-L-arginine methyl ester (L-NAME) produces cerebral oligaemia. The effects of repeated exposure to L-NAME upon cerebral blood flow were examined to determine whether the enhanced NOS inhibition reported following chronic treatment might reduce cerebral perfusion to ischaemic levels. 2. Rats were treated with L-NAME (75 mg kg-1, i.p.) once daily for 10 days. Local cerebral blood flow and glucose utilization were measured by [14C]-iodoantipyrine and [14C]-2-deoxyglucose quantitative autoradiography respectively, either 1 h or 15 h after the last injection. A second group of rats was injected (i.p.) only once with L-NAME, either 1 h or 15 h prior to the measurement procedures. 3. Mean arterial blood pressure (MABP) was significantly increased (+35%) 1 h after a single injection of L-NAME. Although the hypertension was reduced 15 h after the injection (+13%), MABP remained significantly higher than control. 4. Local cerebral blood flow was significantly decreased 1 h after a single injection of L-NAME (ranging from -45% to -54%), and remained so even after 15 h (-39% to -48%). At neither time-point was there any change in glucose utilization. 5. At 15 h after the final injection of the chronic L-NAME treatment protocol, MABP was significantly elevated from control (+58%) and was also significantly higher than at 1 h following a single injection (+20%). There was no effect upon the established hypertension when rats treated chronically with L-NAME were challenged with a further injection of the drug and MABP was measured 1 h later, suggesting saturation of NOS inhibition. 6. Although reduced, cerebral blood flow was not significantly different from control when measured 15 h after the last injection of the chronic L-NAME treatment. When rats treated chronically with L-NAME were subjected to a further challenge with the drug, cerebral blood flow was reduced when measured 1 h after the acute injection (ranging from -34% to -41%). There was however evidence of some attenuation in the response when compared to that measured 1 h after a single injection of L-NAME (ranging from -45% to -54%). Thus, the cerebral circulation shows no evidence of either sustained L-NAME-induced vasoconstriction or saturated NOS inhibition following 10 daily injections of L-NAME. Chronic L-NAME treatment had no effect upon cerebral glucose use. 7. The trend towards re-establishment of cerebrovascular dilator tone and the normalization of cerebral flow-metabolism relationships could explain the lack of any ischaemic damage found in chronically treated rats, but the loss of an extended autoregulatory range afforded by acute L-NAME treatment may be responsible for an increased incidence of stroke.

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.

Enhanced cerebrovascular responsiveness to hypercapnia following depletion of central serotonergic terminals.

Serotonin-containing nerve fibres innervate cerebral blood vessels, but the source of this innervation and the physiological effects of perivascular serotonin release remain controversial. The purpose of the present study was to examine the effects of central serotonergic depletion upon the relationship between CBF and glucose utilization under both normo- and hypercapnic conditions. To induce the loss of serotonergic terminals, rats were injected twice daily for 4 consecutive days with 20 mg/kg of the specific serotonergic neurotoxin methylenedioxyamphetamine (MDA). Between 4 and 6 weeks later, local CBF and glucose utilization were measured using the fully quantitative [14C]iodoantipyrine and [14C]2-deoxyglucose autoradiographic techniques, respectively, and the efficacy of the lesioning protocol was assessed using [3H]paroxetine radioligand binding analysis. In all animals treated with MDA, there was a significant decrease in serotonin uptake sites throughout the brain, falling from 223 +/- 20 to 40 +/- 16 fmol/mg tissue in parietal cortex, for example, although the raphe nuclei themselves were unaffected (300 +/- 20 fmol/mg tissue in controls and 291 +/- 18 in MDA-treated rats). In normocapnic rats, the effects of MDA pretreatment upon blood flow and glucose use were slight and focally concentrated. However, when the animals were rendered hypercapnic, CBF was significantly higher in MDA-treated rats than in normal controls, for example, increasing from 356 +/- 22 ml 100 g-1 min-1 in frontal cortex of hypercapnic controls to 700 +/- 81 ml 100 g-1 min-1 in MDA-pretreated rats with similar levels of hypercapnia. In some brain areas of hypercapnic MDA-pretreated rats, blood flows were too high (> 800 ml 100 g-1 min-1) to be accurately quantified.(ABSTRACT TRUNCATED AT 250 WORDS)

Hyperaemia in rat neocortex produced by acute exposure to methylenedioxymethamphetamine.

Cerebral blood flow and glucose utilization were measured in rat neocortex, hippocampus and striatum following methylenedioxymethamphetamine injection (5 mg/kg, i.v.), using the tracers [14C]iodoantipyrine and [14C]2-deoxyglucose, respectively. In control rats, blood flow was coupled to glucose metabolism, but in methylenedioxymethamphetamine-treated rats, marked hyperperfusion was measured in frontal and parietal cortex with no change in glucose use. This suggests that methylenedioxymethamphetamine has the potential to disrupt cerebrovascular control.

Differential effects of competitive (CGS19755) and non-competitive (MK 801) NMDA receptor antagonists upon local cerebral blood flow and local cerebral glucose utilisation in the rat.

The effects of the selective non-competitive NMDA receptor antagonist dizocilpine (MK801) and the competitive NMDA receptor antagonist CGS19755 upon local blood flow (lCBF) and local glucose utilisation (lCGU) were examined in 81 neuroanatomically discrete regions of the conscious rat brain using the [14C]iodoantipyrine and [14C]2-deoxyglucose quantitative autoradiographic techniques, respectively. Animals received dizocilpine (0.3 mg/kg), CGS19755 (30 mg/kg) or saline vehicle (2 ml/kg) 10 min prior to the initiation of lCGU studies while blood flow determinations were performed in parallel groups of animals 20 min after drug administration. Dizocilpine significantly increased lCGU in 33 of the 81 regions measured (most notably in cortical and subcortical limbic structures and in the basal ganglia) while reducing glucose use in seven brain areas (frontoparietal and somatosensory cortex, and in areas subserving auditory function). In contrast, CGS19755 significantly reduced lCGU use in 39 of the 81 areas examined while increases were observed in only three areas (anterior piriform cortex, substantia nigra pars reticulata, and posterior thalamic nucleus). Following Dizocilpine administration, there was evidence of widespread (64 of the 81 areas studied) increases in lCBF, while blood flow was reduced in the inferior colliculus. Significant increases in lCBF were also noted in 26 brain areas of CGS19755-treated rats while in one area (flocculus) blood flow was reduced. In saline-treated rats there was a close correlation between lCBF and lCGU. Dizocilpine administration was associated with an increase in the overall lCBF:lCGU ratio from 1.56 ml/mumol (in saline-treated rats) to 2.34 ml/mumol. In some brain areas (CA1 subfield of the dorsal hippocampus, somatosensory cortex and nucleus accumbens) there was evidence of focal disturbances in flow-metabolism relationship. While a similar increase in the overall lCBF-lCGU use ratio was evident in CGS19755 treated animals, there was no evidence of focal uncoupling of the flow metabolism relationship in any of the 81 brain areas examined. These data show that whilst both competitive and non-competitive NMDA receptor antagonists increased cerebral tissue perfusion beyond that required to meet underlying metabolic demand, focal disturbances in the flow metabolism relationship were observed only in dizocilpine-treated rats.

Alterations in local cerebral blood flow in mature rats following prenatal exposure to cocaine.

Time-mated female Sprague-Dawley rats were injected subcutaneously with either 40 mg/kg cocaine-HCl or saline once daily on gestational days 13 through to 16. Local cerebral blood flow and glucose use were measured in the mature male offspring from these dams using the fully quantitative [14C]2-deoxyglucose and [14C]iodoantipyrine autoradiographic techniques, respectively. The effects of the treatment upon the integrity of central serotonergic terminals was assessed using [3H]paroxetine radioligand binding autoradiography. There were no significant changes in glucose use in any of the 40 brain areas analysed in this study, and although there was a generalized tendency towards increases, these never exceeded +15% of control values. In contrast, significant increases in local cerebral blood flow were measured in more than one-third of the areas examined in cocaine-treated rats, ranging from +20% in dorsal raphe nucleus to +95% in some parts of the neocortex. In all but three brain areas, the ratio of cerebral blood flow to metabolic demand was found to increase following cocaine exposure, resetting the relationship from an overall ratio of 1.6 in controls to 2.5 in treated rats. This relative hyperaemia, which must result from excessive dilatation of the cerebrovascular bed under normal physiological conditions, could not be explained by a direct effect of the treatment on serotonergic constrictor neurons as there was no evidence for any changes in [3H]paroxetine binding. Whatever the underlying cause, we conclude that the effects upon cerebrovascular control mechanisms of prenatal exposure to cocaine identified here, might present a further source of difficulty in the management of "crack babies".

Sympathetic denervation and the cerebrovascular response to hypertension induced by NG-nitro-L-arginine methyl ester.

Cerebral blood flow and glucose utilization were measured in rat neocortex, using [14C]iodoantipyrine and 2-deoxy-D-[14C]glucose quantitative autoradiography, respectively, following nitric oxide synthesis inhibition with L-NAME. In intact animals cortical blood flow was decreased, despite increased arterial blood pressure above autoregulatory limits, whilst glucose use remained unaffected. Unilateral sympathectomy at the superior cervical ganglion had no effect, suggesting that the autoregulatory response to L-NAME-induced hypertension is independent of sympathetic activity.

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)

Perivascular microapplication of endothelin-1: a new model of focal cerebral ischaemia in the rat.

In the present study, we describe the effects of perivascular microapplication of the potent vasoconstrictor peptide endothelin-1 (ET-1; (120 pmol in 3 microliters), delivered via a guide cannula stereotaxically positioned above the left cerebral artery (MCA) of the conscious male Sprague-Dawley rat. Ten minutes after the administration of Et-1, mean arterial blood pressure had increased by 20% and profound reductions in local cerebral blood flow (up to 93%) were observed within those brain areas supplied by the MCA. In addition, significant increases in local cerebral blood flow were observed within the globus pallidus (100%), substantia nigra pars reticulata (48%), ventrolateral thalamus (65%), and dorsal hippocampus (74%) ipsilateral to the insult. Twenty-four hours following the insult, the pattern of ischaemic damage was similar to that reported previously following permanent occlusion of the rat MCA. It is suggested that perivascular microapplication of Et-1 may provide a useful model for the study of the functional disturbances associated with focal cerebral ischaemia in the conscious rat.

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.

Autoradiographic determination of glucose content and estimation of the lumped constant in intracerebral neuronal tissue transplants.

The quasi-steady-state distribution volume of brain glucose was measured using 3-O-[14C]methylglucose quantitative autoradiography in a group of rats (n = 5) which 12-15 weeks previously had undergone unilateral ibotenic acid-induced lesion of the nucleus basalis magnocellularis, followed by implantation into ipsilateral neocortex of primordial basal forebrain cell suspensions. The effects of the lesion and the presence of transplanted tissue in neocortex were visualized by acetylcholinesterase histochemistry. The 3-O-[14C]methylglucose tracer was distributed homogeneously throughout the host brain areas analysed, with no side-to-side differences, despite a marked unilateral depletion of acetylcholinesterase activity ipsilateral to the lesion site. Whilst the transplants were indistinguishable from the homogeneity of surrounding host frontal cortex, there was a 70% increase in the apparent distribution volume of methylglucose localized around the ibotenate injection site and associated needle tract. Brain glucose content is an important experimental variable affecting the lumped constant of the 2-deoxyglucose technique. There was no evidence of any significant difference in the lumped constant between transplant and host tissue which might compromise the validity of the 2-deoxyglucose technique when used together with intracerebral implantation of fetal neuronal cell suspensions.