Physostigmine induced reversal of ischemia following acute middle cerebral artery occlusion in the rat

Therapeutic effects of physostigmine during systemic inflammation

Introduction

Usually, physostigmine is used as antidote for anticholinergic poisons in order to improve hemodynamics and cardiac output. In addition, it causes beneficial effects during sepsis when added timely. Here, we studied whether physostigmine improves hemodynamics when treatment during systemic inflammation was delayed.

Methods

Two series of randomized studies with overall 44 rats were conducted. Systemic inflammation was induced by lipopolysaccharide (LPS) infusion (0.5 mg LPS/kg×h). Physostigmine (PHY) was intravenously applied after an LPS infusion period of 90 minutes (50 µg PHY/kg within 10 minutes) with (series 1) and without (series 2) additional volume loading. Hemodynamic parameters, blood gases, and parameters for tissue damage were periodically determined for up to 180 minutes.

Results

Even though volume was additionally administered (series 1), LPS caused a reduction of peripheral blood flow. Treatment with PHY improved hemodynamics in macrocirculation (mean arterial blood pressure) and microcirculation (peripheral blood flow). PHY neither affected alterations in blood gases, electrolyte homeostasis, and glucose metabolism nor prevented intestinal damage induced by LPS. In series 2, without any additional volume loading, PHY likewise resulted in an improvement of the LPS-induced alterations in macro- and microcirculation, but finally worsened the LPS-mediated effects on plasma parameters for tissue damage such as creatine kinase, probably due to the lack of volume and a further damage to the heart.

Conclusion

The present results demonstrated that hemodynamic responses to PHY may not only be visible in patients with anticholinergic drug overdose but also be visible in septic patients, provided that fluid intake of these patients is adequate.

Blockade of central histaminergic H2 receptors facilitates catecholaminergic metabolism and aggravates ischemic brain damage in the rat telencephalon

Blockade of central H(2) receptors aggravates ischemic neuronal damage. Since changes in the activity of the monoaminergic system are contributing factors in the development of ischemic neuronal damage, the authors evaluated the effects of ranitidine on the monoaminergic system and ischemic neuronal damage in the middle cerebral artery (MCA) occlusion model of rats. Wistar rats pretreated with saline or ranitidine (3 and 30 nmol, i.c.v.) were subjected to reversible occlusion of MCA for 2 h. The total infarct volume was determined 24 h after reperfusion. The relationship between dopaminergic activity and the histologic outcome was estimated by lesioning the substantia nigra 2 days before MCA occlusion. In a second experiment, the animals were subjected to 15 min of MCA occlusion, and the effects of ranitidine on the histologic outcome was evaluated 7 days after ischemia. In a third experiment, the tissue concentrations of monoamines and their metabolites were determined in the cerebral cortex and striatum 2 h after reperfusion following MCA occlusion for 2 h. The turnover of norepinephrine and dopamine was compared between animals treated with saline and those treated with ranitidine by estimating the alpha-methyl-p-tyrosine-induced depletion of norepinephrine and dopamine, respectively. The turnover of 5-hydroxytryptamine was evaluated by the probenecid-induced accumulation of 5-hydroxyindoleacetic acid. Treatments with ranitidine markedly increased the infarct volume 24 h after reperfusion. Ranitidine also aggravated delayed neuronal death 7 days after ischemia. The aggravation was abolished by the lesion of the substantia nigra before MCA occlusion. The MCA occlusion increased the turnover of cortical norepinephrine and striatal dopamine. The turnover was further facilitated by ranitidine. Although ranitidine suppressed the 5-hydroxytryptamine turnover in the cerebral cortex, the extent of this effect was similar in both the ischemic and non-ischemic sides. These results suggest that facilitation of the catecholaminergic systems is involved in the aggravation of ischemic neuronal damage by H(2) blockade.

Huperzine A improves cognitive deficits caused by chronic cerebral hypoperfusion in rats

The effects of (-)-huperzine A, a promising therapeutic agent for Alzheimer's disease, on learning behavior and on alterations of the cholinergic system, the oxygen free radicals and energy metabolites induced by permanent bilateral ligation of the common carotid arteries were investigated in rats. Daily oral administration of huperzine A produced a significant improvement of the deficit in the learning of the water maze task, beginning 28 days after ischemia, correlating to about 33-40% inhibition of acetylcholinesterase activity in cortex and hippocampus. Huperzine A significantly restored the decrease in choline acetyltransferase activity in hippocampus and significantly reduced the increases in superoxide dismutase, lipid peroxide, lactate and glucose to their normal levels. The present findings demonstrate that the improvement by huperzine A of the cognitive dysfunction in the late phase in chronically hypoperfused rats is due to its effects, not only on the cholinergic system, but also on the oxygen free radical system and energy metabolism. Our results strongly suggest that huperzine A has therapeutic potential for the treatment of dementia caused by cholinergic dysfunction and/or decrease of cerebral blood flow.

Cholinesterase inhibition improves blood flow in the ischemic cerebral cortex

The ability of central cholinesterase inhibition to improve cerebral blood flow in the ischemic brain was tested in Sprague-Dawley rats with tandem occlusion of left middle cerebral and common carotid arteries. Cerebral blood flow was measured with lodo- 14C-antipyrine autoradiography in 170 regions of cerebral cortex. The regional distribution of blood flow was characterized in normal animals by cerebral blood flow maxima in the temporal regions. After 2 h ischemia, minimum cerebral blood flow values were found in the lateral frontal and parietal areas on the left hemisphere, and a new maximum was found in the right hemisphere in an area approximately symmetrical to the ischemic focus. Heptyl-physostigmine (eptastigmine), a carbamate cholinesterase inhibitor with prolonged time of action improved cerebral blood flow in most regions, with the exception of the ischemic core. The drug also enhanced the ischemia-induced rostral shift of cerebral blood flow maxima in the right hemisphere. The effects of eptastigmine were more marked 24 h after ischemia. Discriminant analysis showed that data from only 22 regions was sufficient to achieve 100% accuracy in classifying all cases into the various experimental conditions. The redistribution of cerebral blood flow to the sensorimotor area of the right hemisphere of animals with cerebral ischemia, a phenomenon possibly related to recovery of function, was also enhanced by eptastigmine.

YM796, a novel muscarinic agonist, improves the impairment of learning behavior in a rat model of chronic focal cerebral ischemia

We studied effects of YM796, a novel muscarinic agonist, on behavioral, histological and regional cerebral blood flow changes in the chronic phase after focal cerebral ischemia in rats. YM796 (0.03, 0.1, 0.3 and 1 mg/kg) was administered orally once a day from the 7th to the 13th day after the permanent occlusion of left middle cerebral artery. On the 7th day, rats were trained in one-trial step-through passive avoidance task 45 min after drug administration. Test trials were carried out on the 8th and 14th days. Neurological deficits, including hemiplegia and abnormal posture, were observed on the 7th and 14th days. After the completion of behavioral studies, the rats were decapitated and cerebral infarction was measured. Regional cerebral blood flow was also measured by the hydrogen clearance technique 7 days after MCA occlusion. YM796 (0.1-1 mg/kg) significantly (P < 0.05) attenuated the impairment of learning behavior in a dose-dependent manner without affecting spontaneous locomotor activity. The ameliorating effect of YM796 (0.3 mg/kg) on the impaired learning behavior was significantly (P < 0.05) suppressed by intracerebroventricular injection of pirenzepine (10 micrograms/rat), an M1 antagonist. No significant difference in either neurological deficits or cerebral infarction was found between the vehicle- and YM796-treated groups. Further, YM796 (0.3 mg/kg) had little effect on the reduced blood flow in the ipsilateral frontal cortex 7 days after occlusion. These results suggest that YM796 improves the impaired learning behavior probably by activating central M1 receptors in a rat model of chronic focal cerebral ischemia.

Prolonged effects of cholinesterase inhibition with eptastigmine on the cerebral blood flow-metabolism ratio of normal rats

The cerebrovascular and metabolic effects of the novel cholinesterase inhibitor eptastigmine were tested in conscious rats. The drug was administered by single intravenous injection, and blood flow or glucose utilization were assessed in 38 brain regions by quantitative autoradiographic techniques. A dose-dependent increase in regional cerebral blood flow (rCBF) was obtained for i.v. doses ranging from 0.5 to 3 mg kg-1. Forty minutes after the dose of 1.5 mg kg-1, average rCBF of the 38 regions studied was (mean +/- SD) 2.62 +/- 0.62 ml g-1 min-1, a value significantly higher than that of saline-injected controls (1.46 +/- 0.26; p < 0.005). In contrast, a similar dose of eptastigmine did not significantly alter regional cerebral glucose utilization (rCGU) (0.90 +/- 0.21 mumol g-1 min-1) when compared with saline-injected controls (0.99 +/- 0.08 mumol g-1 min-1). A linear correlation between rCBF and rCGU was observed both in saline (r = 0.871) and eptastigmine (r = 0.873)-injected animals but the slope of the regression line of rCBF on rCGU was significantly higher (p < 0.01) in the eptastigmine group (2.863 +/- 0.266) than in the controls that received saline (1.00 +/- 0.094). The cerebral vasodilatation induced by eptastigmine peaked at 40 min after drug administration. No toxic signs were observed at the doses used. Mean arterial blood pressure decreased after 0.5 mg kg-1 (control = 109.3 +/- 10.56 mm Hg; eptastigmine = 96.6 +/- 8.10 mm Hg) but did not differ from control at the higher doses. It is concluded that eptastigmine induces a long-lasting increase in rCBF and a significant enhancement of the rCBF:rCGU ratio in most regions. The results suggest an important role of endogenous acetylcholine in the control of cerebral perfusion.

Stimulation of the fastigial nucleus enhances EEG recovery and reduces tissue damage after focal cerebral ischemia

Stimulation of the cerebellar fastigial nucleus (FN) increases CBF but not metabolism and reduces the tissue damage resulting from focal cerebral ischemia. This effect may result from enhancing CBF in the ischemic tissue without increasing local metabolic demands. To test this hypothesis, we studied whether the reduction in tissue damage is restricted to the neocortex, a region in which the CBF increase is independent of metabolism, and whether stimulation of the dorsal medullary reticular formation (DMRF), a treatment that increases both cerebral metabolism and CBF, also protects the brain from ischemia. In halothane-anesthetized Sprague-Dawley rats, the middle cerebral artery (MCA) was occluded either proximally or distally to the lenticulostriate branches. The FN or DMRF were then stimulated for 1 h (50-100 microA; 50 Hz; 1 s on/l s off). Twenty-four hours later, the infarct volume was determined. FN stimulation substantially reduced the size of the infarct, an effect that was greater with distal (-69 +/- 8%; n = 6; p < 0.001; mean +/- SD) than with proximal (-38 +/- 8%; n = 8; p < 0.001) MCA occlusion. The reduction occurred only in neocortex (-43 +/- 9%; p < 0.001) and not in striatum (-16 +/- 21%; p > 0.05). Stimulation of the FN also enhanced recovery of EEG amplitude in the ischemic cortex (+48%; p < 0.003). DMRF stimulation (n = 7) did not affect the stroke size or EEG recovery (p > 0.05). Thus, stimulation of the FN, but not the DMRF, attenuates the damage resulting from focal ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

The cellular basis of delirium and its relevance to age-related disorders including Alzheimer's disease

A wide variety of conditions lead to delirium (i.e., metabolic encephalopathies) in human beings and animals. Despite the varied etiology the clinical consequences are relatively stereotyped which suggests that the diverse insults that cause delirium may act by common metabolic and cellular "final pathways." Related molecular and cellular mechanisms may be involved in aging and Alzheimer's disease, conditions that predispose to the development of delirium. Animal models of delirium better reflect age-related disorders such as Alzheimer's disease than those that impair a single neurotransmitter system such as the cholinergic system; the metabolic encephalopathies produce global cognitive disturbance, which is more typical of these disorders. Thus, research related to delirium has far-reaching implications for normal and abnormal brain function.

Brain regional distribution of physostigmine and its relation to cerebral blood flow following intravenous administration in rats

3H-labeled physostigmine (50 micrograms.kg-1) was administered intravenously to rats, and its concentration in brain tissue and spinal cord was assessed by quantitative autoradiography. Regional cerebral blood flow (rCBF) was measured with iodo-14C-antipyrine autoradiography in control rats and in animals injected i.v. with a dose of physostigmine similar to that used for the distribution studies. Tissue concentration of 3H-physostigmine was correlated with rCBF for 37 brain regions. A high degree of correlation was found at 0.5 min after drug injection, r (correlation coefficient) = 0.87. This association decreased at later times (5 min r = 0.73, 12 min r = 0.24). Structures with high cholinesterase activity (caudate-putamen, amygdala, hippocampus) showed greater retention of physostigmine over time. The highest initial physostigmine concentrations were found in regions lacking a blood-brain barrier (pineal bland, median eminence, choroid plexus) (range = 10.4-23.8 nCi/mg) and the lowest in white matter (corpus callosum, internal capsule, hippocampus commisure, spinal cord dorsal column) (range = 1.2-2.6 nCi/mg). Initial concentrations of the drug in the areas in which physostigmine induced vasodilatation (motor, sensory, temporal and occipital cortex, claustrum, and superior collicullus) were not different from concentrations in areas of comparable basal rCBF in which no such effect was observed. Variations in drug access to brain regions, then, do not explain the topographical variations of the cerebrovascular action of physostigmine.

GM1 ganglioside treatment after global ischemia protects changes in membrane fatty acids and properties of Na+, K+-ATPase and Mg2+-ATPase

An examination was made of the effects of ganglioside GM1 (i.m.) on the losses of membrane fatty acids (palmitic, stearic, oleic, linoleic, and arachidonic), the plasma membrane enzyme Na+, K+-ATPase, and the mitochondrial membrane enzyme Mg2+-ATPase, associated with global ischemia 24 hr after permanent unilateral occlusion of the carotid artery in Mongolian gerbils. While there was a significant loss of fatty acids in saline controls, no loss was detected in membranes from GM1-injected gerbils. Rather, we found an increase in membrane fatty acid content, indicative of altered turnover. A 38% loss of Na+, K+-ATPase and a 36% loss of mitochondrial Mg2+-ATPase observed in membranes from saline controls was reduced in membranes from GM1-injected animals to losses of 15% and 8% respectively. These effects are further described by analyses of enzyme kinetics (apparent Vmax and apparent Km). After 1 week of storage, the activities of both membrane ATPases from saline controls decreased substantially more than from GM1-injected animals, suggesting that the GM1 membranes were better "preserved." Since there was a minimal loss in protein content after 24 hr of ischemia, these results indicate that systemically injected GM1 may protect structure and function of plama membranes during the acute phases of ischemic injury.

Distribution of physostigmine and metabolites in brain subcellular fractions of the rat

The distribution of 3H-physostigmine (Phy) has been studied in the rat brain subcellular fractions at various time intervals following i.v. injection. 3H-Phy or its metabolites rapidly accumulate into the cytoplasm of cells and penetrates the intracellular compartments. Kinetic studies of the subcellular distribution of radioactivity (RA) per gm of rat brain following i.v. injection of 3H-Phy show peak concentrations at 30 min in all subcellular fractions with the exception of mitochondria. In the mitochondrial fraction the RA levels continue to rise from 4682 +/- 875 DPM/gm at 5 min to 27474 +/- 2825 DPM/gm at 60 min (P less than .05). The cytosol contains the highest RA: 223341 +/- 21044 DPM/gm at 30 min which declined to 53475 +/- 3756 DPM/gm at 60 min. RA in synaptosome, microsomes and myelin increases from 5 to 30 min, and declines at 60 min. In vitro studies did not show a greater uptake of RA by the mitochondrial or synaptosomal fractions. The finding of relatively high concentrations of RA in the mitochondrial fraction at 60 min increases the likelihood that Phy or its metabolites could interfere with the physiological function of this organelle.