Ultrastructure of the carotid body

Fine structure of the chemoreceptor cell in the amphibian carotid labyrinth

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The response of isolated cat muscle spindles to passive stretch

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Rhythmical and non-rhythmical spontaneous activity recorded from the central cut end of the sinus nerve

1. Two types of spontaneous nervous activities have been recorded from the central cut end of the carotid sinus nerve of the cat.2. One type was composed of nerve potentials that exhibited a respiratory or cardiac rhythm, whose rate of firing was depressed by the pressor response to adrenaline, and that were found to arise from post-ganglionic fibres of the superior cervical ganglion.3. The other type of activity consisted of non-rhythmical nerve potentials whose rate of discharge increased 10-30 sec after the injection of adrenaline. The activity of these fibres also increased when the arterial oxygen tension was lowered or when the arterial carbon dioxide tension was raised.4. It is conceivable that either of these two groups of fibres, rather than the chemoreceptor afferent fibres, could provide the source of the microvesicle-containing nerve endings on the type 1 cells of the carotid body.5. A nerve was also described coursing from the sinus nerve to the hypoglossal nerve; the activity in it was sympathetic in origin.

The release of acetylcholine from carotid body tissues. Further study on the effects of acetylcholine and cholinergic blocking agents on the chemosensory discharge

1. Both carotid bodies were removed from cats and placed in a small Perspex channel through which Locke solution was allowed to flow under a layer of paraffin oil. Stimulation of the upstream (;donor') organ elicited an increased sensory discharge in the downstream (;detector') preparation (Loewi effect).2. This effect was enhanced by eserine, depressed by hexamethonium and blocked by either mecamylamine or acetylcholinesterase. The Loewi effect did not disappear when chronically denervated (4 days) ;donor' carotid bodies were stimulated.3. These experiments led to the conclusion that ACh is released by the carotid body tissues (probably from the glomus cells) during stimulation and that this substance is responsible for the initiation of the chemosensory discharges.4. In single preparations the chemosensory endings proved to be very sensitive to ACh especially in the presence of eserine which, in all probability, inactivated the tissue cholinesterase. Curarizing agents such as mecamylamine, hexamethonium, (+)-tubocurarine and atropine blocked the response of the sensory endings to applied ACh in what appeared to be ;surmountable' antagonism.

Pharmacology of pH effects on carotid body chemoreceptors in vitro

1. The carotid body and the carotid nerve were removed from anaesthetized cats and placed in a small Perspex channel through which Locke solution (at various pH values and usually equilibrated with 50% O(2) in N(2)) was allowed to flow. The glomus was immersed in the flowing solution while the nerve was lifted into oil covering the saline. Sensory discharges were recorded from the nerve and their frequency was used as an index of receptor activity. At times, a small segment of carotid artery, containing pressoreceptor endings, was removed together with the glomus. In this case, pressoreceptor discharges were recorded from the nerve.2. The amplitude of either chemo- or pressoreceptor discharges was not changed by strong acid solutions. Acid decreased the frequency of the baroreceptor discharges only when pH fell to less than 4.0. Solutions at low pH increased the chemosensory discharge, but acid depressed the increased chemoreceptor discharge elicited by KCl. These experiments indicated that H(+) ions probably acted as membrane ;stabilizers' without depolarizing either the nerve fibres or endings.3. Acid solutions increased the action of acetylcholine chloride (AChCl) (100-200 mug) on chemoreceptors. This effect probably was due either to inactivation of tissue cholinesterase or to enhanced sensitivity of the sensory endings to ACh.4. Choline chloride (10(-3)M), which favours ACh synthesis, protected the preparation against decay during prolonged experimentation. Hemicholinium-3 (HC-3), which blocks ACh synthesis in low concentrations (10(-5)M), depressed the chemosensory response to acid and to hypoxia when such stimuli were applied repeatedly. This concentration of HC-3 did not change effects of applied ACh.5. Substances which affect ACh release markedly changed the chemoreceptor discharge increase induced by acidity and other forms of stimulation. In the absence of Ca(2+), acid, anoxia, and interruption of flow provoked receptor depression while receptor excitation induced by ACh and KCl persisted. All stimuli excited and showed increased effectiveness as the Ca(2+) concentration was raised, but their effects declined as Ca(2+) was increased above normal values. Mg(2+) ions depressed the chemoreceptor effects induced by all these stimuli. The action of Mg(2+) was not due entirely to nerve ending block. Morphine sulphate (which decreases ACh release in other structures) also depressed the receptor response to acid and flow interruption.6. Cholinergic blocking agents such as mecamylamine, hexamethonium, atropine, dihydro-beta-erithroidine (DHE), HC-3 (10(-4)M), choline and acetylcholine (in combination with choline) depressed the effects of acid and ACh on the chemoreceptors. The effect induced by interruption of flow was depressed only by mecamylamine and DHE.7. Agents which affect the fate of released ACh, such as acetylcholinesterase and eserine salicylate, did not affect clearly the response of chemoreceptors to acid.8. The results suggest that acid stimulates chemoreceptor fibres through an indirect mechanism, viz. through increased release and/or decreased destruction of a presynaptic transmitter from the glomus cell. This transmitter is probably ACh (see following paper, Eyzaguirre & Zapata, 1968).

Ultrastructure of the human carotid body. A perspective on the mode of chemoreception

Surgically excised human carotid bodies have been analyzed by electron microscopy. Several ultrastructural features suggest that they are closely related to sympathetic neuroendocrine glands and autonomic ganglia: the chief cells synthesize intensely osmiophilic cytoplasmic granules, occasionally develop neuroid processes, and are intimately associated with neurilemmal sustentacular cells. Other lines of evidence indicate that secretion of the chief cell is norepinephrine or a closely related bioamine-neurotransmitter. The role of chief cells in mediating chemosensation may be explained by modulated release of the bioamine in response to local metabolic conditions. Human chief cells are richly innervated. Recognizable zones of synapse display an efferent type of polarity and sometimes appear adrenergic. Thus, reflexive sympathetic excitation of chief cells may be physiologically significant in man. The anatomic compartmentalization characteristic of carotid body chief cells is discussed in relation to a possible functional significance.

The ultrastructure of early platelet aggregation in vivo

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