Autoradiographical analysis of excitatory amino acid binding sites in rat hippocampus during the development of hippocampal kindling

Binding sites for excitatory amino acids have been determined by autoradiographical procedures in the rat hippocampus and striatum during hippocampal kindling. The binding sites measured were the N-methyl-D-aspartate (NMDA)-sensitive sites for L-[3H]glutamate and [3H]MK-801 sites (transmitter recognition site and ion channel of the NMDA receptor, respectively), [3H]alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionate (AMPA) sites (quisqualate receptor), [3H]kainate sites (kainate receptor) and NMDA-insensitive sites for L-[3H]glutamate. In general, little change was apparent in the hippocampus or striatum for any of these binding sites when assessed 48 h after attaining stages 1/2, 3 or 5 of kindling. These results suggest that hippocampal kindling does not bring about a change in the excitatory amino acid receptor binding sites examined, and that the appearance of an NMDA receptor-mediated component to synaptic responses in the hippocampus produced by kindling, cannot be explained on this basis.

[Clinical evaluation of atracurium besylate in patients at risk: major burns]

Atracurium besylate 0.5 mg/kg-1, an intermediate-duration non-depolarizing neuromuscular relaxant, was administered slowly (over 75 sec) in anesthesia induction of 61 patients with major thermal injury undergoing surgical excision and immediate skin-grafting procedures. Patients' mean +/- SD age was 40 +/- 9, body weight 64 +/- 2, burn size ranging from 20% to 90% of body surface area (BSA), postburn day of surgery 5th and more. Induction of anesthesia was carried out with sodium thiopental 2-5 mg/kg-1 plus fentanyl 2.8 micrograms/kg-1 e.v. and after few minutes atracurium 0.5 mg/kg-1 e.v. Anesthesia was maintained with N2O/O2 (70%/30%), isoflurane and small amounts of fentanyl. The mean arterial pressure and heart rate were recorded at I, II, III, IV, V min post atracurium administration. The endotracheal intubation conditions were assessed by a "IOT score". Results are expressed as mean value +/- standard deviation. The significance of the difference in mean values was analysed by t-test. Little haemodynamic changes occurred; intubating conditions showed a relative hyposensitivity of burn patients to atracurium, more severely burned patients (greater than 50-60%) exhibiting greater resistance.

Hypophosphatemia in course of chronic obstructive pulmonary disease. Prevalence, mechanisms, and relationships with skeletal muscle phosphorus content

Serum phosphorus levels (Ps), dietary intake of phosphorus, and renal phosphate handling indexes were evaluated in 158 patients with chronic obstructive pulmonary disease (COPD) of varying degrees of severity; moreover, skeletal muscle phosphorus content (Pm) was measured in muscle samples obtained by quadriceps femoris needle biopsy in 14 of the same patients. Hypophosphatemia (Ps less than or equal to 2.5 mg/dl) was found in 34 (21.5 percent) of 158 patients without differences between groups of COPD patients presenting increasing severity of respiratory illness. No relationship was found between serum levels and dietary intake of phosphorus; hypophosphatemia was associated with low renal phosphate threshold (TmPO4/GFR) values in 31 (91 percent) of 34 patients. The prevalence of hypophosphatemia was significantly higher among COPD patients taking one or more drugs commonly used in COPD and known as negatively influencing renal phosphate handling: xanthine derivatives, corticosteroids, loop diuretics, and beta 2-adrenergic bronchodilators. Short-term administration of therapeutic doses of these drugs in COPD patients previously not taking any drug reduced TmPO4/GFR values; phosphaturic effect of short-term theophylline administration on renal phosphate handling was additive to that of long-term assumption of the drug. Muscle phosphorus content was both reduced in COPD patients as compared with control subjects and significantly correlated to serum phosphorus levels and to TmPO4/GFR values. The present investigation revealed a high prevalence of hypophosphatemia among COPD patients as well as a defect in renal phosphate reabsorption secondary, at least in part, to pharmacologic therapy. Moreover, it also suggests that in COPD patients muscle phosphorus content is likely to be reduced in presence of hypophosphatemia.

A comparative clinical study on the effects of cardiopulmonary bypass with different flows and pressures on skeletal muscle cell metabolism in patients undergoing coronary bypass grafting

This study compares the effects of cardiopulmonary bypass with different flows and pressures on intracellular energy metabolism, acid-base equilibrium, and muscle water compartments in two groups of patients undergoing coronary artery bypass grafting. Eighteen patients (16 men and two women aged 54 +/- 7 years, New York Heart Association class I-II) undergoing low flow (flow rate 1.5 L/min/m2 at 26 degrees C), low pressure (mean arterial pressure 40 to 60 mm Hg) cardiopulmonary bypass, as well as 10 age-matched and sex-matched patients undergoing normal flow (flow rate 2.2 L/min/m2 at 26 degrees C), normal pressure (mean arterial pressure 60 to 80 mm Hg) bypass were studied. Intracellular acid-base equilibrium (intracellular pH and intracellular bicarbonate), cell energetics (adenosine triphosphate, diphosphate, and monophosphate, phosphocreatine, and lactate), and muscle water compartments were evaluated in specimens of the quadriceps femoris muscle obtained by needle biopsy before and at the end of cardiopulmonary bypass. In both the low flow-low pressure and normal flow-normal pressure groups, adenosine triphosphate levels were unchanged at the end of bypass, whereas phosphocreatine concentration was decreased; muscle total water and extracellular water increased without variations of intracellular water; muscle and plasma lactate increased as intracellular bicarbonate decreased; intracellular pH values remained unchanged. The present study suggests the following: (1) Cardiopulmonary bypass is associated with the overall preservation of intracellular compartment metabolism in skeletal muscle (about 40% of body cell mass) of patients undergoing coronary bypass grafting, even though low phosphocreatine values and increased plasma and muscle lactate values found at the end of bypass could be an expression of cell functional reserve exhaustion; (2) the effects of cardiopulmonary bypass on cell metabolism are comparable, regardless of the flows and pressures used.

[Cerebral perfusion pressure in endocranial hypertension in comatose head-injured patients]

The aim of the intensive care of the injured is the coupling of the availability and the requirement of the cerebral metabolic substates. The measurement of the cerebral blood flow is not currently available at the bedside and less direct monitoring is required. The cerebral perfusion can be estimated looking at the cerebral perfusion pressure (CPP), that can be easily measured using intracranial pressure (ICP) and the systemic arterial pressure (MAP) monitoring. Hundred-twenty-one consecutive head injured admitted to an Intensive Care Unit were studied assessing the severity of the neurological injury, the CT-Scan diagnosis of the intracranial lesion, the Trauma Score and the behavior of the ICP and MAP. The outcome was classified according to a modified version of the Glasgow Outcome Scale. More than 77% of the patients suffered raised intracranial pressure above 20 mmHg and 16 of them had a CPP less than 60 mmHg for more than 5 minutes. The outcome was directly related to the degree of intracranial hypertension and to the severity of insufficient CPP. The treatment of the severe head injured must be aimed at maintaining a good CPP, because of the close relationships between this value and the prognostic result. The monitoring of the ICP is a reliable and relatively safe procedure in this series, where the rate of infections complicating the intracranial recording is less than 3%.

Cell metabolism in patients undergoing major valvular heart surgery: relationship with intra and postoperative hemodynamics, oxygen transport, and oxygen utilization patterns

The relationships between cell metabolism and both hemodynamics and oxygen transport/utilization (VO2/DO2) pattern were evaluated intra and postoperatively in eight patients undergoing major valvular heart surgery with the aid of moderately hypothermic cardiopulmonary bypass (CPB). Quadriceps femoris specimens were obtained by the needle biopsy technique for muscle ATP, ADP, AMP, phosphocreatine (PCr), creatine and lactate determination at anesthesia induction, after CPB, as well as in the ICU 18 h after surgery. Moreover, hemodynamic variables, oxygen transport and utilization indices, and plasma lactate were measured at the same intervals and throughout the CPB period. After CPB, muscle ATP and PCr contents were reduced (p less than .05) as compared to those of both pre-CPB patients and healthy control subjects; muscle and plasma lactate levels were increased (p less than .05). Mean VO2 and DO2 values measured during CPB significantly decreased (p less than .05), but VO2 reduction was proportionally greater than that of DO2 (-62% vs. -41%). No correlation was found between VO2 and DO2 at that time, but a significant relationship (p less than .05) was found at the end of CPB. A further decrease in muscle ATP and PCr levels was measured in the ICU, as muscle and plasma lactate levels were still elevated. At that time, VO2 and DO2 were not significantly different from pre-CPB values, but were significantly (p less than .05) correlated with each other.(ABSTRACT TRUNCATED AT 250 WORDS)

Studies on the potential neurotoxic and convulsant effects of increased blood levels of quinolinic acid in rats with altered blood-brain barrier permeability

Intravenous injection of 450 mg/kg quinolinic acid (Quin), an endogenous kynurenine metabolite with excitotoxic properties, induced only minor electroencephalographic (EEG) modifications and no neurotoxicity in rats with a mature blood-brain barrier (BBB). BBB permeability was altered in rats by focal unilateral irradiation of the cortex (7 mm in diameter and 5 mm in depth) with protons (60 Gy, 9 Gy/min). Three days after irradiation, Evans blue dye staining showed BBB breakdown in the dorsal hippocampus of the irradiated hemisphere. No neurotoxic or convulsant effects were observed as a consequence of the radiation itself. When BBB-lesioned rats were challenged with 225 mg/kg Quin iv, epileptiform activity was observed on EEG analysis. Tonic-clonic seizures were induced by 225-450 mg/kg Quin. Light microscopic analysis showed a dose-related excitotoxic type of lesion restricted to the hippocampus ipsilateral to the irradiated side. Neuro-degeneration was prevented by local injection of 120 nmol D(-)2-amino-7-phosphonoheptanoic acid, a selective N-methyl-D-aspartate receptor antagonist. No lesions or EEG or behavioral modifications occurred after 450 mg/kg nicotinic acid, an inactive analog of Quin. The potential neurotoxic and convulsant effects of increased blood levels of Quin under conditions of altered BBB permeability are discussed.

Stimulation of [3H]norepinephrine release from hippocampal slices by excitatory amino acids

[3H]norepinephrine efflux from preloaded rat hippocampal slices was increased in a dose-dependent manner by excitatory amino acids (EAA) in the following potency order: N-methyl-D-aspartic acid (NMDA) greater than kainic acid greater than L-glutamic acid greater than or equal to D,L-homocysteic acid greater than L-aspartic acid greater than quinolinic acid greater than quisqualic acid. The effect of EAA was blocked by physiological concentration of Mg2+, with the exception of kainic acid. D,L-2-amino-7-phosphonoheptanoic acid (APH) dose-dependently inhibited NMDA effect (IC50 = 69 mumol/L), whereas at 1 mmol/L it was ineffective versus kainic acid. The release of [3H]norepinephrine induced by quinolinic acid was blocked by APH 0.1 mmol/L. gamma-D-glutamylglycine dose-dependently inhibited kainic acid effect with an IC50 = 1.15 mmol/L. Tetrodotoxin 2 mumol/L reduced NMDA and kainic acid effects by 40 and 20%, respectively. The data indicate a possible involvement of central noradrenergic system in the modulation of excitotoxic action of EAA and offer a reliable system for testing new compounds acting at EAA-receptors by measuring norepinephrine release in vitro.

Kinetics of MK-801 and its effect on quinolinic acid-induced seizures and neurotoxicity in rats

MK-801 [(+)-5-methyl-10,11-dihydro-5H-dibenzo(a,d)cyclo-hepten-5,10-imine maleate], a noncompetitive antagonist of the N-methyl-D-aspartate-type of excitatory aminoacid receptors, was measured in plasma and brain tissues after i.p. administration to rats by using a novel high-performance liquid chromatography assay. The drug reached maximal concentrations in plasma and brain within 10 to 30 min of injection (2 mg/kg) with an elimination half-life of 1.9 and 2.05 hr, respectively. Mean ratio of brain area concentration-time curve to plasma area concentration time curve was 12.5, referring to total plasma concentrations. MK-801 distributed almost equally between plasma and red cells (mean blood-to-plasma ratio averaged 1.2 +/- 0.2 when calculated 30 and 180 min from drug administration). Plasma and brain concentrations of MK-801 rose almost linearly from 0.5 to 4 mg/kg 30 min after injection and the brain-to-plasma ratio (12.9 +/- 2.8) was constant in the dose range studied. The distribution of the drug in various brain regions 30 and 180 min after 2 mg/kg i.p. showed no preferential concentration or retention in any of the areas studied. The anticonvulsant effect of MK-801 was evaluated against limbic seizures (measured by EEG) induced by intrahippocampal injection of 120 nmol of quinolinic acid, an agonist of the N-methyl-D-aspartate-type receptors, in freely moving rats. At 0.25 and 0.5 mg/kg, MK-801 significantly lowered by 71 to 77% the number of seizures and by 80% the total time spent in seizures (P less than .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of aspartame on seizures in various models of experimental epilepsy

We investigated in rats whether aspartame intake affected the susceptibility to seizures induced chemically (metrazol, quinolinic acid) or electrically (electroshock). Aspartame (0.75-1.0 g/kg), given orally as a single bolus to 16-hr fasted animals 60 min before metrazol, significantly increased the number of animals showing clonic-tonic seizures. At 1.0 g/kg the ED50 for clonic-tonic convulsions was lowered by 23%. A similar increase in seizure susceptibility was observed with 0.25-0.5 g/kg of the aspartame's metabolite phenylalanine. When aspartame was administered to fasted rats in three divided doses (0.33 g/kg) over 120 min or to fed animals after a meal, or overnight with the diet, no significant changes in the incidence of animals showing seizures was observed. One gram per kilogram aspartame and 0.5 g/kg phenylalanine did not modify the CC50 (mA) for tonic hindlimb extension induced by electroshock and the electroencephalographic seizures caused by intrahippocampal injection of 120 nmol quinolinic acid. Plasma and brain levels of phenylalanine and tyrosine significantly raised after both 1 g/kg aspartame as a single bolus (plasma: Phe 285%, Tyr 288%; brain: Phe 146%, Tyr 192%; above controls) or in three divided doses (plasma: Phe 207%, Tyr 315%; brain Phe 103%, Tyr 211%; above controls) and 0.5 g/kg phenylalanine (plasma: Phe 339%, Tyr 410%; brain: Phe 219%, Tyr 192%; above controls), but the ratio Phe/Tyr was not modified. Our data indicate that aspartame cannot be regarded as a general proconvulsant agent. The mechanisms of potentiation of seizures induced by metrazol after the administration of the sweetner in a single rapid intake will be discussed.

Effect of various calcium channel blockers on three different models of limbic seizures in rats

Voltage-dependent calcium channel-blockers were studied for their ability to modulate limbic seizures induced in rats by injection of quinolinic acid and kainic acid into the hippocampus or by hippocampal kindling. Flunarizine, at 40 mg/kg (but not 20 mg/kg), reduced the total number of seizures and total time spent in seizures induced by quinolinic acid by 75%; at 60 mg/kg, both parameters were reduced more than 90%, while at 80 mg/kg seizures induced by kainic acid were not affected. Forty and 60 mg/kg of flunarizine protected hippocampal-kindled rats from fully developed convulsions (Stage 5). Nifedipine, at 20 and 40 mg/kg, was ineffective on seizures induced by both quinolinate and kainate. However, at 20 mg/kg, 57% of the kindled animals were protected from Stage 5 and total protection was achieved at 40 mg/kg. Verapamil, at 40 mg/kg, reduced by respectively, 88% and 78%, the total number of seizures and the total time spent in seizures induced by quinolinic acid, but had no effect on seizures induced by kainate and Stage 5 seizures. The results suggest that, while seizures induced by kainic acid were refractory to all voltage-dependent calcium channel blockers, binding sites affected by flunarizine and verapamil in the brain may selectively facilitate ictal activity induced by quinolinic acid. Binding sites for dihydropyridine might contribute to the increased hippocampal excitability in kindled animals. The role of calcium entry through voltage-dependent calcium channels in the occurrence of seizures in these models of limbic epilepsy is discussed.

Role of the N-methyl-D-aspartate-type receptors in the development and maintenance of hippocampal kindling in rats

The effect of intrahippocampal infusion of 70 nmol (1 microliter/2 min) D,L-2-amino-7-phosphonoheptanoic acid (APH), a selective antagonist of N-methyl-D-aspartate (NMDA)-type receptors, was studied on behavioral seizures and afterdischarge (AD) at different stages of hippocampal kindling in rats. After completion of kindling (3 consecutive stage 5 seizures) APH infusion at the site of stimulation (granule cells of dentate gyrus) 60 min before stimulus delivery (50 Hz, 2 ms monophasic rectangular wave pulses for 1 s, current intensity 60-200 microA) suppressed the behavioral convulsions and focal AD. Four stimulations were needed after drug injection to recover stage 5 seizures and AD. When similarly injected early in kindling (stage 1-2) APH had no effect on the AD duration but significantly increased (by 37% with respect to controls) the number of stimulations needed to reach the first stage 5 seizures. Thus, it appears that NMDA-type receptors at the site of stimulation become progressively involved during the development of kindling and mediate the behavioral convulsions and focal AD observed at stage 5.

Cell metabolism response to cardiopulmonary bypass in patients undergoing aorto-coronary grafting

The main parameters of muscle acid-base, water and energy metabolism were studied in ten patients undergoing low-flux (1.5 l/min/m2), low-pressure (40 to 60 mmHg) hypothermic (26 degrees C) cardiopulmonary bypass (CPB) for aortocoronary grafting; absolute gas exchange and haemodynamic data were also measured throughout the entire CPB period. At the end of CPB a substantial preservation of water and energy metabolic indexes was found; a condition of extracellular metabolic acidosis was apparently sustained by muscle cell anaerobic glycolysis enhancement with a consequent increase of both muscle and plasma lactate content. Subnormal cell phosphocreatine levels as well as reduced bicarbonate buffer stores and decreased intracellular pH, were detected. Direct limiting effects of hypothermia on tissue O2 delivery and muscle oxidative metabolism as well as vasoconstriction and arteriovenous shunting associated with CPB procedures are likely to be involved in the above mentioned alterations of cell metabolism.

[3H]norepinephrine release from hippocampal slices is an in vitro biochemical tool for investigating the pharmacological properties of excitatory amino acid receptors

[3H]Norepinephrine ([3H]NE) efflux from preloaded rat hippocampal slices was increased in a dose-dependent manner by excitatory amino acids, with the following order of potencies: N-methyl-D-aspartate (NMDA) greater than kainic acid (KA) greater than L-glutamate greater than or equal to D,L-homocysteate greater than L-aspartate greater than quinolinic acid greater than quisqualic acid. The effect of the excitatory amino acids was blocked by physiological concentrations of Mg2+, with the exception of KA. D,L-2-Amino-7-phosphonoheptanoic acid dose-dependently inhibited the NMDA effect (ID50 = 69 microM), whereas at 1 mM it was ineffective versus KA. The release of [3H]-NE induced by quinolinic acid was blocked by 0.1 mM D,L-2-amino-7-phosphonohepatanoic acid. gamma-D-Glutamylglycine dose-dependently inhibited the KA effect with an ID50 of 1.15 mM. Tetrodotoxin (2 microM) reduced by 40 and 20% the NMDA and KA effects, respectively. The data indicate that [3H]NE release from hippocampal slices can be used as a biochemical marker for pharmacological investigations of excitatory amino acid receptors and their putative agonists and antagonists.

ATP as a marker of excitotoxin-induced nerve cell death in vivo

In an attempt to find an marker for nerve cell death in vivo, the ATP content was measured in the rat dorsal hippocampus within hours or days following in the local injection of the excitotoxins quinolinic or kainic acid. Beginning or completed neuronal degeneration is accompanied by significant decreases in ATP levels. Selective blockade of the quinolinic acid-induced decrement in ATP content by D-(-) 2-amino-7-phosphonoheptanoic acid indicates that ATP measurements may of value for the rapid in vivo screening of the anti-neurotoxic properties of pharmacologically distinct excitatory amino acid receptor antagonists.

Norepinephrine modulates seizures induced by quinolinic acid in rats: selective and distinct roles of alpha-adrenoceptor subtypes

We investigated in rats whether alterations in noradrenergic function caused by 6-hydroxydopamine or alpha- and beta-adrenoceptor agonists and antagonists would modify the susceptibility of the brain to electroencephalographic seizures induced by intrahippocampal infusion of quinolinic acid. 6-Hydroxydopamine depletion of norepinephrine facilitated the expression of seizures while alpha-adrenoceptor stimulation by clonidine had either proconvulsant (0.1 mg/kg) or anticonvulsant (from 0.5 to 2 mg/kg) effects. Clonidine's anticonvulsant activity (0.5 mg/kg) was mimicked by methoxamine given intrahippocampally (10 micrograms), and antagonized by prazosin (1 mg/kg), whereas both yohimbine (5 and 10 mg/kg) and piperoxane (5 mg/kg) had no significant effect. Seizure facilitation induced by clonidine (0.1 mg/kg) was blocked by yohimbine (10 mg/kg). Systemic (0.25 and 0.5 mg/kg) or intrahippocampal (10 and 20 micrograms) isoproterenol and propranolol (10 mg/kg) had no effect. Spiking activity and neurotoxicity induced by quinolinic acid were unaltered by treatments which protected against convulsions. Modulation of quinolinic acid-convulsive activity by alpha-adrenoceptor subtypes appears to be selective and complex, since alpha 1-type activation reduces seizures while alpha 2-type stimulation has proconvulsant effects.

Determination of endogenous acetylcholine release in freely moving rats by transstriatal dialysis coupled to a radioenzymatic assay: effect of drugs

The technique of intracerebral dialysis in combination with a sensitive and specific radioenzymatic method was used for recovery and quantification of endogenous extracellular acetylcholine from the striata of freely moving rats. A thin dialysis tube was inserted transversally through the caudate nuclei, and the tube was perfused with Ringer solution, pH 6.1, at a constant rate of 2 microliter min-1. The perfusates were collected at 10-min intervals. In the presence of 1 and 10 microM physostigmine, acetylcholine release was 4.5 +/- 0.02 and 7.3 +/- 0.3 pmol/10 min, respectively (not corrected for recovery). The latter concentration of the acetylcholinesterase inhibitor was used in all experiments. Under basal conditions, acetylcholine output was stable over at least 4 h. A depolarizing K+ concentration produced a sharp, reversible 87% increase in acetylcholine output. Both the basal and K+-stimulated release were Ca2+ dependent. The choline uptake inhibitor hemicholinium-3 (20 micrograms intracerebroventricularly) reduced striatal acetylcholine output to 35% of the basal value within 90 min. Scopolamine (0.34 mg/kg s.c.) provoked a sharp enhancement of acetylcholine release of approximately 63% over basal values, whereas oxotremorine (0.53 mg/kg i.p.) transiently reduced acetylcholine release by 54%. These results indicate the physiological and pharmacological suitability of transstriatal dialysis for monitoring endogenous acetylcholine release.

Anticonvulsant drugs effective against human temporal lobe epilepsy prevent seizures but not neurotoxicity induced in rats by quinolinic acid: electroencephalographic, behavioral and histological assessments

Intrahippocampal injection of quinolinic acid (QUIN) in rats caused an epileptic-like syndrome reminiscent of human temporal lobe epilepsy. By electroencephalographic (EEG) analysis, the authors assessed whether QUIN seizures were responsive to anticonvulsants effective in the treatment of the human disease. Anticonvulsants used in clinical practice to control partial seizures, such as carbamazepine, diphenylhydantoin, sodium phenobarbital, sodium valproate and diazepam, prevented QUIN-induced EEG seizures, whereas ethosuximide, which is specifically used to control absence attacks, and chlorpromazine, a sedative with no anticonvulsant properties, were ineffective. QUIN seizures showed particular sensitivity to carbamazepine (5 mg/kg) but were resistant to diphenylhydantoin unless a relatively high dose was used (100 mg/kg). None of the effective anticonvulsants completely suppressed EEG paroxysmal events like spikes and fast activity. Animals injected with QUIN displayed chewing, sniffing and rearing; no clear correlation was found between the ability of drugs to prevent QUIN-induced EEG seizures and effects on stereotypies, suggesting that these behavioral signs are not sensitive measures of anticonvulsant activity in this model. The anticonvulsants that protected animals from QUIN seizures did not prevent nerve cell degeneration induced by the excitotoxin, thus indicating that nerve cell death can occur even in the absence of sustained seizure activity. The data show that, in this animal model of epilepsy, the EEG seizure activity is specifically sensitive to anticonvulsants effective in partial epilepsy, thus suggesting that it could be used to test potential new drugs for this human disorder.

In vivo and in vitro studies on the regulation of cholinergic neurotransmission in striatum, hippocampus and cortex of aged rats

Young (3 months) and senescent (23 months) rats were challenged with oxotremorine both in vivo, to determine its effects on acetylcholine content in hemispheric regions, and in vitro, to assess its action on K+-evoked release of ACh from brain synaptosomes. The drug failed to inhibit KCl-induced [3H]ACh release from the P2 fraction of striatal and hippocampal homogenates of the senescent animals, whereas it was less efficient in increasing striatal ACh content. In contrast, oxotremorine was still able to stimulate an increase in ACh in the hippocampus and cerebral cortex of the aged rats to the same extent as it did in the young ones. The [3H]ACh output from striatal synaptosomes was lower in old rats with respect to young ones at low KCl depolarizing concentrations but was equal in the two groups at a high depolarizing concentration. In the hippocampus of the senescent rats, the release was significantly lower at each concentration of KCl used, resulting in a parallel downward-shift in the concentration-release plot. We also measured cholinergic muscarinic receptor binding in rat hemispheric regions using the radioligand [3H]dexetimide, a classical non-selective muscarinic receptor antagonist. It was found, in conformity with some of the literature, that receptor binding was decreased by about 32% in striatum of aged female rats as compared to younger rats. Changes were not observed in cortex and hippocampus. Analysis of the binding data indicated that the observed decrease in specific ligand binding was due to a decrease in the number of binding sites without a change in affinity. The results favor, once again, the cholinergic hypothesis for geriatric dysfunction.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of low flux-low pressure cardiopulmonary bypass on intracellular acid-base and water metabolism

In eight patients undergoing open heart surgery for elective myocardial revascularization, extra-intracellular acid-base and water metabolism parameters were studied before and after cardiopulmonary bypass procedures. All patients presented a different degree of metabolic acidosis related to plasma lactate increase. Intracellular acid-base indexes did not change significantly, though all but one patient showed an intracellular buffers consumption. Both total muscle and extracellular water increased, while intracellular water did not change. It was concluded that low flux-low pressure perfusion CPB was related to a substantial preservation of cell integrity.

A noradrenergic component of quinolinic acid-induced seizures

Unilateral application of the convulsant brain metabolite, quinolinic acid, to unanesthetized rats resulted in a transient dramatic decrease in norepinephrine levels (nadir -70% after 2 h) in both the injected and the contralateral hippocampus. Dose-response relationships and the temporal sequence of this effect indicated a close functional association between seizure events and the decrease in hippocampal norepinephrine content. Massive release of the inhibitory transmitter, norepinephrine, may thus constitute the brain's defensive response to quinolinic acid-induced seizures.

In vivo brain dialysis of amino acids and simultaneous EEG measurements following intrahippocampal quinolinic acid injection: evidence for a dissociation between neurochemical changes and seizures

The extracellular content of taurine, glutamate, glutamine, and glycine was measured by the novel method of brain dialysis in the acute phases following an intrahippocampal injection of the excitotoxic convulsant brain metabolite quinolinic acid (QUIN). Using bilaterally implanted depth electrodes physically combined with hollow fibers for dialysis, it was possible to collect continuously brain perfusates while simultaneously monitoring brain activity in the unanesthetized rat. In separate animals, hippocampal amino acid tissue levels were measured 2 h after an intracerebral injection of a convulsant dose (156 nmol) of QUIN. When compared with those in animals receiving the nonconvulsant decarboxylation product of QUIN, nicotinic acid, no differences in tissue levels were detected. In contrast, the same dose of QUIN caused a selective increase (2.24-fold) in taurine levels in perfusates from the injected hippocampus. These changes were apparent prior to the onset of electrographic seizures and did not occur in the contralateral hippocampus where seizure activity was equally severe. Thus, increases in extracellular taurine, triggered by the presence of QUIN in the hippocampus, may reflect a selective tissue response to the neurotoxic (rather than the convulsant) effects of this excitotoxin.

Kynurenic acid blocks neurotoxicity and seizures induced in rats by the related brain metabolite quinolinic acid

Kynurenic acid (KYNA) was tested as an antagonist of the neurotoxic and epileptogenic effects of the metabolically related brain constituent quinolinic acid (QUIN). In the rat striatum, KYNA blocked the neurotoxic effects of QUIN in preference to those of other excitotoxins. In the hippocampus, KYNA antagonized both the neurodegeneration and seizures caused by the local application of QUIN. These properties of KYNA raise the possibility of a functional link between KYNA and QUIN in the brain which may be of relevance for an understanding of human neurodegenerative disorders.

Mode of action of gamma-butyrolactone on the central cholinergic system

Gamma-butylactone (GBL), a drug depressing the central nervous system, produced marked increases in acetylcholine contents in rat brain hemispheric regions (striatum, hippocampus, cortex) and in striatal choline content without modifying choline acetyltransferase or acetylcholinesterase activities. In the hippocampus GBL also strongly decreased the acetylcholine turnover rate and inhibited the high affinity uptake of choline. Its increase in acetylcholine content was prevented by an acute electrolytic lesion of the medial septum but not by a wide array of drug treatments designed to interfere with neurotransmission in various pathways. The results are taken to indicate that GBL directly depresses the cholinergic septal-hippocampal afferents by interrupting impulse flow. In the striatum, too, GBL markedly depressed the acetylcholine synthesis rate but had no effect on the high affinity choline uptake process. Such dissociation of the two phenomena had previously been observed using other drugs and may denote that acetylcholine synthesis in this region is regulated differently from that in the hippocampus. By comparison, gamma-hydroxybutyric acid (GHBA), an active metabolite which shares with GBL the capacity to produce a somnolent state and depress impulse flow in the dopaminergic nigroneostriatal pathway, had no effect on either striatal acetylcholine content or on hippocampal high affinity choline uptake. The results suggest that GBL can be distinguished from GHBA in its neuropharmacological central cholinergic effects.

Effect of dimethylamino-2-ethoxyimino-2-adamantane (CM 54903), a non-polar dimethylaminoethanol analog, on brain regional cholinergic neurochemical parameters

CM 54903, a new psychotropic drug with a particular pharmacological profile, produced a widespread but short-lasting decrease in acetylcholine content in rat brain hemispheric regions but not in the midbrain-hindbrain or cerebellum at the dose of 40 mg/kg, i.p. The decrease was most conspicuous in the striatum. Brian regional choline contents were unaltered as were the acetylcholine turnover rates in the striatum and hippocampus. Neither choline acetyltransferase nor acetylcholinesterase activities were altered after the in vitro incubation or the in vivo administration of high amounts of the drug. CM 54903 was found to be a competitive, reversible inhibitor of the sodium-dependent high affinity uptake of choline by crude hippocampal and striatal synaptosomal preparations showing an IC50 of 10 microM in vitro. Despite the fact that the drug readily crosses the blood-brain barrier and achieves brain concentrations several-fold greater than its in vitro IC50, CM 54903 did not inhibit choline uptake in vivo although it was capable of preventing the pentylenetetrazol-stimulated choline uptake by hippocampal synaptosomes. The changes in striatal acetylcholine content induced by the blockade or the stimulation of muscarinic cholinergic receptors or dopaminergic receptors did not interfere with the effect of CM 54903 on striatal acetylcholine content while pentylenetetrazol completely prevented the decrease. The results taken together indicate that the major effect of CM 54903 on the cholinergic neurons is at the presynaptic level to compete with choline at its uptake sites.