THE ORIGIN OF ACETYLCHOLINE APPEARING IN THE EFFLUENT OF PERFUSED CEREBRAL VENTRICLES OF THE CAT

Acetylcholine determination of cerebrospinal fluid in aneurysmal subarachnoid hemorrhage

Acetylcholine (ACh) concentrations were determined serially in cerebrospinal fluid (CSF) obtained from 23 patients with aneurysmal subarachnoid hemorrhage (SAH) by high-performance liquid chromatography (HPLC) with electrochemical detection (ED). The values of CSF ACh were significantly low in the initial stage of SAH, and increased subsequently but they did not return to control values within 3 weeks. In addition, serial measurements of CSF butyrylcholinesterase (BChE) activity in 12 SAH patients showed that the activity was elevated significantly in the initial stage of SAH and returned to control levels within a week. This discrepancy in the recovery period between the ACh levels and the BChE activity in CSF indicated that significantly lower CSF ACh levels after SAH could not be attributed to plasma BChE contamination of CSF. These results suggested central cholinergic dysfunction after SAH, especially in the initial stage.

Changes of acetylcholine and choline concentrations in cerebrospinal fluids of normal subjects and patients with dementia of Alzheimer-type

Acetylcholine (ACh) and choline (Ch) in cerebrospinal fluid from 29 normal volunteers and 7 patients with Alzheimer-type dementia (DAT) were examined using high-performance liquid chromatography with electrochemical detector coupled with liquid cation-exchange method. In normal volunteers, ACh concentration was decreased significantly from 40-50 years and Ch concentration was increased significantly from 50-60 years. CSF from patients with DAT revealed high Ch concentration and the increase was statistically significant while ACh concentration in CSF of DAT did not show a significant difference with that of normal volunteers. This Ch augmentation may suggest a disturbance in utilization of Ch for ACh synthesis and may become an useful indicator for organic changes in central cholinergic system.

In vivo voltammetry: promise and perspective

Dopamine, 5-hydroxytryptamine and noradrenaline are electroactive (oxidisable) neurotransmitters in the mammalian brain. Voltammetry, a technique which can measure the concentration of such compounds by their oxidation at an inert electrode, has been applied in vivo in the hope of measuring the release of these neurotransmitters without recourse to perfusion-based or post-mortem analyses. The measurement of neurotransmitter release is, however, complicated by the presence of high concentrations of other electroactive species (ascorbic and uric acids). Nevertheless, when used properly, with due emphasis on pharmacological identification of electrochemical signals, the technique can measure catechol and indole metabolites in vivo. Under certain circumstances the release of the catecholamines and 5-hydroxytryptamine themselves can be measured. The advantages and drawbacks of the voltammetric methodology are discussed.

Microelectrophoresis of biogenic amines on hypothalamic thermosensitive cells

The rat hypothalamus contains thermally insensitive, normally sensisitive, and highly thermosensitive cells. The responses of thermosensitive neurons to microelectrophoretically applied acetylcholine, norepinephrine, and 5-hydroxy-tryptamine were the same in both rats and cats. The firing rate of warm-sensitive interneurons was accelerated by acetylcholine and inhibited by norepinephrine. The firing rate of cool-sensitive interneurons was accelerated by norepinephrine and, in one case, was inhibited by 5-hydroxytryptamine. Thermodetector cells were relatively insensitive to these amines, but were sensitive to current flow. These results from the rat, but not from the cat, agree with the data for thermoregulatory responses following microinjection of these amines into the hypothalamus.

Appearance of 5-hydroxytryptamine and an unidentified pharmacologically active lipid acid in effluent from perfused cerebral ventricles

1. In cats anaesthetized with intraperitoneal pentobarbitone sodium, three regions of the cerebral ventricles, the third ventricle, the inferior or the anterior horn, were perfused with artificial c.s.f. and the effluent was tested on the fundus strip of the rat's stomach.2. Effluent from all three regions contracted the fundus strip. The contractions were due to at least two substances as revealed by treatment of the strip with 2-bromolysergic acid diethylamide (BOL). The contractions that were sensitive to BOL are attributed to 5-hydroxytryptamine (5-HT) whereas the BOL resistant contractions appear to be due to an unknown hydroxy acid related to irin or the prostaglandins.3. The contractions produced by effluent collected from the third ventricle were due wholly or mainly to 5-HT, those from the inferior horn to the unknown hydroxy acid, and those from the anterior horn to both substances in varying proportions. In addition, some samples of effluent from the third ventricle seemed to contain catecholamines as well.4. The 5-HT in the effluent from the third ventricle is thought to be derived from the hypothalamus. The amounts assayed in 1 ml. effluent-the volume collected during 10 or 20 min perfusion-varied between 0.4 and 12 ng 5-HT. Output of 5-HT was initially high, then usually decreased but sometimes increased again during prolonged perfusion when temperature began to rise as anaesthesia lightened or when additional pentobarbitone sodium was given intravenously.5. When perfusion of the third ventricle was continued after death the 5-HT content in the effluent increased 3 to 24-fold during the first hour and then gradually declined. This post mortem rise in 5-HT output suggests an abnormal state of release of 5-HT from the hypothalamus. The theory is discussed that the same may happen in certain cases of brain injury and that the abnormal release of 5-HT would explain the pyrexia and shivering seen in such cases.6. The intraperitoneal injection of 5-hydroxytryptophan greatly increased the output of 5-HT in the effluent from the perfused third ventricle but only when this precursor of 5-HT was injected in large doses which caused respiratory arrest thus necessitating artificial ventilation. Upon the injection of 150 mg/kg the output of 5-HT rose to 90 ng/ml. and a further rise to 180 ng/ml. occurred when perfusion was continued after death.7. It was not possible to establish a relation between the presence of the hydroxy acid in the effluent from the inferior horn and neuronal activity.8. The 5-HT detected in the effluent from the anterior horn is assumed to have been released from the caudate nucleus.