Dean R. Haubrich

Increase in rat brain acetylcholine induced by choline or deanol

Abstract Administration of choline chloride, deanol, or Deaner ® to rats subsequently killed by microwave irradiation caused an increase in the concentration of both choline and acetylcholine in the corpus striatum, indicating that synthesis of brain acetylcholine can be stimulated in vivo by elevating the tissue concentration of its precursor. This finding suggests that the concentration of free choline in brain is below that necessary for a maximal rate of synthesis of acetylcholine, and raises the possibility that the availability of choline in brain may regulate the rate of synthesis of acetylcholine. These results also provide biochemical evidence for the view that the clinical effects of deanol result from its conversion to acetylcholine.

Serotonergic afferents to the dorsal raphe nucleus: Evidence from HRP and synaptosomal uptake studies

Afferent connections of the serotonin (5-HT)-containing dorsal raphe nucleus were investigated in the rat utilizing the horseradish peroxidase (HRP) retrograde cell labeling technique. Small quantities (0.1-0.5 mul) of HRP solutions were infused into the dorsal raphe, and the brains were examined 19-72 h later for retrograde transport of the enzyme. Intrinsic connections within the dorsal raphe nucleus were revealed by this mapping technique, as was an input to the dorsal raphe from another serotonergic cell group, the median raphe nucleus. Little evidence was found for projections from other, more remote, brain sites. A serotonergic innervation of the dorsal raphe was also demonstrated by the presence of high affinity uptake of [3H]5-HT (Km=0.17 muM) into synaptosomal suspensions of the dorsal raphe nucleus. Synaptosomal uptake of [3H]5-HT was blocked by selective destruction of serotonergic axon terminals induced by the intraventricular injection of 200 mug of 5,7-dihydroxytryptamine following desipramine HCl pretreatment, but not by destruction of catecholaminergic axon terminals induced by intraventricularly injected 6-hydroxydopamine (2 X 250 mug). The uptake of [3H]-5-HT by synaptosomes of the dorsal raphe was comparable to that of striatal and hypothalamic synaptosomes, and markedly greater than that of synaptosomes from the cerebellum or nearby dorsal central gray or midbrain reticular formation, indicating the presence of a relatively dense serotonergic innervation. These data together indicate that neurons in the dorsal raphe nucleus receive a prominent serotonergic input that is derived, at least in part, from other neurons within the dorsal nucleus and from a neighboring raphe nucleus.

Increase in tissue concentration of acetylcholine in guinea pigs in vivo induced by administration of choline

Abstract Administration of choline chloride (200 μmoles/kg) intravenously to guinea pigs caused an increase in the concentrations of choline and acetylcholine in adrenals, heart, kidneys, lungs, and liver within 2 min. These results suggest that raising the concentration of choline in plasma will accelerate the formation of acetylcholine in the organs cited. No significant increase in concentration of choline or acetylcholine occurred in brain.

A simple, sensitive, and specific assay for free choline in plasma

Abstract This paper describes a sensitive and specific enzymatic-radioisotopic method for determining plasma choline. Assays may be performed without prior extraction of the tissue. Plasma is first heated to destroy enzymes that would otherwise produce free choline from that which is normally bound. The free choline in plasma is then converted to phosphorylcholine [ 32 P], in the presence of ATP-γ- 32 P, in a reaction catalyzed by choline kinase. Phosphorylcholine [ 32 P], isolated by ion-exchange chromatography, is measured as an index of the concentration of free choline. The concentration of plasma choline in man and in several species of laboratory animals was determined, and found to range from 5.5 nmoles/ml in dogs to 15.4 nmoles/ml in guinea pigs. The concentration of free choline in plasma of adult rats raised on a choline-deficient diet was half that of littermate controls raised on a control diet supplemented with free choline.

Acetylcholine synthesis in rat brain: dissimilar effects of clozapine and chlorpromazine.

Abstract The rate of synthesis of acetylcholine, estimated from the rate of incorporation of intravenously administered choline (methyl- 3 H) into acetylcholine, was at least three times greater in the corpus striatum than in the cortex of rats killed by microwave irradiation. Administration of chlorpromazine (10 mg/kg) orally to rats induced a decrease in the concentration of acetylcholine in the corpus striatum, but did not affect either the concentration of acetylcholine in the cortex or its rate of synthesis in either brain region, as measured 3 hr after treatment. In contrast to the effect of chlorpromazine, however, treatment with clozapine (100 mg/kg, p.o.) lowered the level of acetylcholine in both the corpus striatum and cortex, and reduced its rate of synthesis in these regions of the brain. The doses of clozapine and chlorpromazine that produced these dissimilar effects on metabolism of acetylcholine did induce equivalent changes in both the rate of avoidance responding and the metabolism of striatal dopamine in rats. The results suggest that clozapine reduces cholinergic neuronal activity in brain. This effect of clozapine may explain the lack of extrapyramidal side effects in psychotic patients treated with the drug.

Inhibition of acetylcholine synthesis by juglone and 4-(1-naphthylvinyl) pyridine

Inhibition by juglone (5-hydroxy-l,4-naphthoquinone) of choline acetyltransferase [ChAt; acetyl-CoA: choline O-acetyltransferase (EC 2.3.1.6)] of rabbit brain was noncompetitive for choline and not reversible by dialysis. When acetyl-CoA and juglone were mixed together before the addition of ChAt, inhibition was competitive with respect to acetyl-CoA: when juglone was preincubated with the enzyme, inhibition was mixed competitive and noncompetitive. The effects in vivo of juglone and 4-(l-naphthylvinyl) pyridine (NVP) were determined in brains of mice sacrificed by microwave radiation. Changes in the rate of synthesis of acetylcholine were assessed by measuring the amount of choline-methyl[3H] converted to acetylcholine in the brains of mice 30 sec after the intravenous administration of the isotope. Administration of two doses of juglone (2 mg/kg. 1 hr apart) increased the concentrations of both endogenous and radioactive choline in brain, but had no effect on either the rate of synthesis or the concentration of acetylcholine. These results suggest that juglone, when administered to animals, does not inhibit brain ChAt. On the other hand, administration of two doses of 4-(1-naphthylvinyl) pyridine (100 mg/kg, i.p., 1 hr apart) did inhibit the synthesis of acetylcholine, but had no effect on the concentration of either choline or acetylcholine in brain. This latter finding indicates that inhibition of ChAt can occur in vivo without causing a reduction in the concentration of acetylcholine.

Increased susceptibility to seizures and decreased catecholamine turnover in spontaneously hypertensive rats

Spontaneously hypertensive rats (SHR) were compared with normotensive Wistar rats for their sensitivity to tonic extensor seizures. SHR were more sensitive to seizures and did not respond to the anticonvulsant effects of L-DOPA. SHR had a slower turnover rate of norepinephrine in brain stem and cortex and of dopamine in striatum. Steady-state levels of catecholamines were similar in both groups. These findings are consistent with earlier ones that reported an inverse relationship between central catecholamine activity and sensitivity to electroconvulsive seizures.

Chronic administration of electroconvulsive shock effects on mouse-killing activity and brain monoamines in rats

Abstract Mouse-killing by rats is blocked by chronic administration of electroconvulsive shock. Antidepressive drugs also block mouse-killing by rats. Thus, mouse-killing by rats may be under the control of mechanisms analogous to human depression. Whole brain concentrations of norepinephrine were higher in rats that received ECS.