Carl E. Aronson

Quantitative autoradiography of serotonin uptake sites in rat brain using [3H]cyanoimipramine

The binding of [3H]cyanoimipramine to serotonin uptake sites in rat brain slices was studied using quantitative autoradiography. Binding was of high affinity and was to a single class of binding site. This is in contrast to results previously obtained by others with [3H]imipramine where two binding sites were observed. The sites labeled by [3H]cyanoimipramine had properties consistent with this ligand labeling serotonin uptake sites, as: (1) binding is displaced by drugs which are potent inhibitors of serotonin uptake but not by drugs which are weak inhibitors of uptake; (2) binding is dependent on the presence of sodium ions as is the uptake of serotonin; (3) binding is almost completely eliminated in the brains of rats lesioned by the serotonin neurotoxin 5,7-dihydroxytryptamine; (4) the distribution of binding sites throughout the rat brain is highly correlated with that found previously for [3H]indalpine, a potent serotonin uptake inhibitor, and for [3H]imipramine. The properties of binding of [3H]cyanoimipramine make it an ideal ligand for the quantitative autoradiography of serotonin uptake sites.

Effects of high-dose methamphetamine administration on serotonin uptake sites in rat brain measured using [3H]cyanoimipramine autoradiography.

Repeated administration of high doses of methamphetamine (15 mg/kg given for 5 doses over 24 h) resulted in long-term decreases in the binding of [3H]cyanoimipramine ([3H]CN-IMI) to serotonin uptake sites measured using quantitative autoradiography. Seven days after termination of drug administration decreases were seen in 23 of 28 regions examined. This is consistent with previous studies indicating that methamphetamine and related amphetamines are neurotoxic to serotonin neurons. Significant decreases were still present in many brain areas on the same dosage schedule 30 days after drug administration. However, the number of areas affected was considerably less, consistent with some regrowth of serotonin neurons. At a lower dosage (7.5 mg/kg on the same schedule) no effects on [3H]CN-IMI binding were seen. The results of this study provide support for the serotonergic neurotoxicity of repeated methamphetamine administration in rats. They also show that the neurotoxicity is highly regional and dose dependent.

Effect of chronic administration of antidepressants on α2-adrenoceptors in the locus coeruleus and its projection fields in rat brain determined by quantitative autoradiography

The density of α2-adrenoceptors, using 3H-idazoxan as the radioligand, was determined by quantitative autoradiography in the locus coeruleus and in 13 noradrenergic projection fields following chronic administration of drugs acting on noradrenergic and/or serotonergic neurons. Protriptyline, an inhibitor of the uptake of norepinephrine, and mianserin, an α2-adrenoceptor antagonist, reduced the binding of 3H-idazoxan only in the locus coeruleus. Phenelzine, an inhibitor of both type A and type B monoamine oxidase (MAO), reduced the binding of 3H-idazoxan in the locus coeruleus and in several areas with noradrenergic innervation from tegmental cell bodies. Clorgyline, a selective inhibitor of type A MAO, had no effect. Of the two selective inhibitors of serotonin uptake, citalopram caused a modest increase in binding only in one terminal field area, whereas sertraline had no effect. Although these antidepressants did not produce consistent effects on α2-adrenoceptors, protriptyline, mianserin, and phenelzine were similar in that they all decreased the binding of 3H-idazoxan in the locus coeruleus without widely affecting its binding in the coerulean terminal fields. Deprenyl, a selective inhibitor of type B MAO, the only drug in this study without proven antidepressant efficacy, differed from all other drugs in that it decreased the binding of 3H-idazoxan both in the locus coeruleus as well as in most terminal fields with primarily coerulean noradrenergic innervation.

Effects of prolonged perfusion time on the isolated perfused rat heart

Abstract Hearts from normal male rats were perfused with Krebs-Ringer bicarbonate buffer by the Langendorff method for periods ranging from 0–4 hr following an initial 15-min equilibration period. Spontaneous heart rate began to decrease by 30 min, whereas changes in coronary flow were not evident until after approximately 2 hr of perfusion. A reduction in isometric systolic tension was evident by 1 hr; after 4 hr of perfusion, tension was 35% of control. Cardiac glycogen concentrations became significantly different from control after 3 hr of perfusion, and at the end of 4 hr had decreased to 33% of control. Adenosine-5′-triphosphate content of hearts was not significantly different from control until perfused for 4 hr. In contrast, creatine phosphate concentrations decreased approximately 50% during the first hour of perfusion but remained constant thereafter. Prolonged perfusion (4 hr) caused no alteration in cardiac phosphorylase activity nor was there evidence of gross or microscopic lesions in the heart.

Effects of di-2-ethylhexyl phthalate on the isolated perfused rat heart☆

Abstract Perfusion of hearts by the Langendorff method with di-2-ethylhexyl phthalate (DEHP, 100 μl/liter, 2.5 × 10 −4 m ), a plasticizer reported to leach from plastics utilized for biomedical applications, significantly decreased spontaneous heart rate, coronary flow, and isometric systolic tension, but elevated diastolic tension. Tissue concentrations of glycogen, adenosine 5′-triphosphate, total adenine nucleotides, and creatine phosphate decreased 40 to 50%, while d -glucose 6-phosphate, l -(−)-glycerol 1-phosphate, adenosine 5′-monophosphate, and lactate values increased 50 to 300% after 60 min of perfusion with DEHP-containing buffer. Lactate in the coronary effluent of DEHP-perfused hearts was 400% greater than control values after 60 min, and phosphorylase a activity was also significantly enhanced. PR and QT intervals in electrical recordings were prolonged by DEHP.

Effects of chlorpromazine on the isolated perfused rat heart

Abstract Perfusion of hearts with chlorpromazine · HCl (50–5000 ng/ml) caused significant changes in heart rate, coronary flow, isometric systolic tension, certain metabolite concentrations, and electrical activity. Phosphorylase a activity remained normal. Chlorpromazine (50 ng/ml) decreased isometric systolic tension and prolonged QT interval in the electrocardiogram. Fructose 1,6-diphosphate and pyruvate concentrations were elevated, suggesting aldolase inhibition and decreased pyruvate utilization. Similar results were obtained at 500 ng/ml. At 5000 ng/ml, heart rate and isometric systolic tension were markedly diminished. Coronary flow increased briefly but returned to normal. PR, QT a , and QT intervals were prolonged. Fructose 1,6-diphosphate, glyceraldehyde-3-phosphate, and pyruvate concentrations in the tissue increased, while the amount of dihydroxyacetone phosphate and l -(−)-glycerol-1-phosphate decreased. No chlorpromazine-induced lesions, gross or microscopic, were found.

The effect of metabolic inhibitors on the response of the perfused rat heart to epinephrine

Abstract The effects of epinephrine on contractility and metabolism were measured in the isolated, perfused rat heart. Epinephrine produced an initial increase in force of contraction followed by a lowering of tension and finally a sustained increase in contractility. When fluoroacetate or iodoacetate was present in the perfusion fluid, the mechanical response to epinephrine was markedly altered. The initial response to epinephrine was depressed in the presence of either inhibitor and the final increase in force of contraction was poorly maintained during metabolic blockade. When the perfusion fluid contained both pyruvate and iodoacetate, the mechanical response of the heart to epinephrine was restored. Results of determinations of metabolites in the myocardium demonstrated that stimulation of glycogenolysis is not essential for the contractile response to epinephrine when adequate substrate is provided for the reactions of the tricarboxylic acid cycle.

Effects of ketamine on the isolated perfused rat heart

Abstract 1. 1. Ketamine caused decreases in spontaneous heart rate and isometric systolic tension whereas its effects on coronary flow and diastolic tension were variable. 2. 2. Ketamine altered electrical activity by prolonging PR and QT intervals, but it produced no major changes in the characteristic pattern of the electrocardiographic recordings. 3. 3. Ketamine produced a dose dependent decrease in the tissue content of glycogen and enhanced the conversion of phosphorylase b to a at the highest concentration (10,000 ng/ml) studied.

Metabolic effects of bretylium and phentolamine in euthyroid and thyrotoxic rats

Abstract In rats chronic administration of thyroid hormone produced an increase in cardiac phosphorylase a activity. Intravenous injection of bretylium or phentolamine into normal and thyrotoxic rats caused an acute elevation of heart phosphorylase a ; the increase in enzyme activity greater when bretylium was administered to thyrotoxic animals. When propranolol was given prior to bretylium, the increase in phosphorylase a was completely prevented. Reserpine alone did not alter cardiac phosphorylase a but prevented the rise in enzyme activity observed after injection of bretylium or phentolamine. In adrenal demedullated rats hearts phosphorylase a was below control levels but the metabolic response to bretylium and phentolamine could still be elicited. Stimulation of cardiac phosphorylase a activity by thyroxine was diminished in adrenal demedullated rats and was completely absent in demedullated rats with adrenergic blockade.

Effects of promethazine on the isolated perfused rat heart

Abstract 1. 1. Perfusion of hearts from normal male rats with promethazine (50–5000 ng) containing Krebs-Ringer bicarbonate buffer caused a profound bradycardia at each dose studied, and at the highest concentration, cardiac arrest occurred between 15 and 30 min after exposure to the drug. 2. 2. Coronary flow showed either a slight increase or no change as a consequence of perfusion with promethazine-containing medium. 3. 3. Promethazine (5000 ng/ml) decreased isometric systolic tension to 37% of control by 15 min, after which cardiac arrest occurred. Diastolic tension increased simultaneously at 5000 ng/ml whereas at lower concentrations, it decreased over the 60 min perfusion period. 4. 4. PR and QT intervals increased following perfusion with promethazine, and its effects were greatest at 1000 and 5000 ng/ml respectively. 5. 5. Although promethazine caused pronounced alterations in mechanical and electrical activity, it had no effect, on the biochemical functions which we measured. 6. 6. There was no evidence of promethazine-induced early myocardial ischemia, as determined by histochemical methods, and no drug-induced lesions, gross or microscopic, were found in any of the hearts studied.