Action of Sympathomimetic and Allied Amines on the Central Nervous System of the Chicken

Abstract

The effects of the a-methyl derivatives of noradrenaline, phenethylamine and tryptamine on the central nervous system of the chicken have been described (Dewhurst & Marley, 1965a). In the present experiments a larger series of amines and of their amino acid precursors has been tested on the central nervous system and on blood pressure. In addition, factors potentiating activity such as monoamine oxidase inhibition or diminishing activity such as tachyphylaxis or pharmacological antagonism have been studied.Preliminary accounts of this work have been presented (Dewhurst & Marley, 1964, and communication to the British Pharmacological Society, January, 1964). METHODSThe methods used for implanting electrodes and cannulae and for measuring cheeping and electrocortical and electromyographic activity were the same as those described previously (Dewhurst & Marley, 1965a,b). In addition to 1-to 28-day-old chickens, fowls up to 1 year old were used.To record blood pressure in the conscious unrestrained chicken a polyethylene cannula sealed with a nylon spigot and containing heparin-saline (100 mg/ml.) was tied into the upper part of a carotid artery; the tubing was brought through the scalp incision and fixed to the skull and wound into the strand of electrodes and the venous cannula. In the experiments in which electrocortical activity and blood pressure were recorded, the cortical electrodes were implanted on the left cerebral hemisphere and the blood pressure cannula was tied into the right carotid artery. At the time of the experiment, the spigot was removed and the arterial catheter was connected via saline-filled polyethylene tubing to a tap unit and screening micrometer transducer. The signals were amplified and displayed on a D.E. potentiometric recorder (Cambridge Instruments).Other blood pressure experiments were made with spinal chickens. These were prepared with halothane and oxygen anaesthesia given by endotracheal tube. After destroying the brain through an occipital craniotomy, the animal was artificially ventilated with a Palmer Miniature Ideal respiration pump. Excess air was allowed to escape through an adjustable leak in the circuit and round the endotracheal cannula. Blood pressure was recorded with a transducer connected to a cannula in the carotid or the ischiadic artery.Chromatography was carried out with the apparatus and techniques devised by Smith (1960). Amines were applied as the salts (detailed below) dissolved in 50% methanol in water to give an amine concentration of 10 pmoles/ml. Spots (1 id.) were applied with a Hamilton syringe. The major component of the developing solvent was oleyl alcohol (B.D.H.) which had been washed successively with equal volumes of N-sodium hydroxide, de-ionized water, N-hydrochloric acid, further water until washings were neutral and then shaken with an equal volume of 0.1 N-ammonifm acetate buffer, pH 7.4, for 20 min. The two

Effect of Sympathomimetic and Allied Amines on Temperature and Oxygen Consumption in Chickens

“…From previous studies with young chickens it appeared that the central excitant sympathomimetic amines such as amphetamine, cyclopentamine, tuaminoheptane and a-methyltryptamine were a homogeneous group despite their variety of chemical structure (Dewhurst & Marley, 1965b). However, the present experiments indicate that amines have additional sites of action because of their effects on temperature and oxygen consumption.…”

“…The catecholamines adrenaline, noradrenaline and the a-methyl derivatives given intravenously lowered core and surface temperatures. These amines raise blood pressure in chickens (Dewhurst & Marley, 1965b) and the associated vasoconstriction would hinder heat loss. The effects of the a-methyl derivatives of adrenaline and noradrenaline were the most consistent, and were dose-dependent.…”

In vivo PHARMACOLOGICAL STUDIES ON THE INTERACTIONS BETWEEN TRYPTAMINE AND 5‐HYDROXYTRYPTAMINE

“…In contrast, NA exhibited no apparent excitatory actions but did cause behavioural depression. These observations agree with those of Dewhurst & Marley (1965) was greatly prolonged. At higher doses, which by themselves caused behavioural alerting, tryptamine reduced the duration of the 5-HT-induced depression.…”

“…(3) 5-HT-induced behavioural depression in young chicks. Since young chicks lack a mature blood-brain barrier (Lajtha, 1957), the behavioural effects seen following systemic administration of 5-HT are probably due to an action of the amine on central receptors (Dewhurst & Marley, 1965). The effects of tryptamine on these manifestations of the central actions of 5-HT have been studied.…”

“…It appears to be located subcellularly in nerve terminals (Boulton & Baker, 1975). Dewhurst (1968) suggested that tryptamine may be an excitatory transmitter in the CNS on the basis of behavioural evidence (Dewhurst & Marley, 1965). Martin and his colleagues have suggested that tryptamine may be a transmitter of certain descending spinal pathways (Martin, Sloan, Bell, Vaupel & Nozaki, 1976).…”