ACETYLCHOLINE METABOLISM IN SALIVARY GLANDS DURING THE "DEGENERATION SECRETION"

Salivatory neurons in the brainstem nucleus parvocellularis of the rat: effects of electrolytic lesions

This study was based on several recent anatomical studies suggesting that the superior salivatory nucleus is located within the area parvocellularis of the brainstem reticular formation. The aforementioned zone was lesioned in order to observe the alterations produced in salivary secretion. Electrolytic lesion of the area parvocellularis was followed by salivary hypersecretion as an immediate and transitory effect of the stimulatory capacity of the electrolytic lesioning method. Some days later the animals presented a markedly impaired salivary secretion as shown by the appearance of inefficient feeding behavior and the development of a prandial drinking pattern. The prandial behavior, which was characterized by numerous drinking episodes during dry food intake, was reversed when wet food was offered, suggesting a true deficit in salivary secretion caused by the parvocellularis lesion. Following the administration of pilocarpine, the submandibular and sublingual salivary glands of experimental animals showed an increased capacity for response (postsynaptic supersensitivity) in comparison to the control group.

Disappearance of noradrenaline from different parts of the rabbit external ear following superior cervical ganglionectomy

Following superior cervical ganglionectomy the noradrenaline tissue levels in the base of the rabbit external ear started to decrease after about 12 hours. About 4 hours later noradrenaline started to decrease about simultaneously in the middle piece and the tip. Within 24 hours after ganglionectomy the noradrenaline decreased rapidly in all three pieces. Thereafter the noradrenaline of the base piece was levelling off at about 15% of the normal whereas the noradrenaline in the two other pieces remained at about 40% of the normal. The results indicate that the adrenergic innervation of the ear is complex, but that the base piece is supplied with adrenergic axons that are shorter than those of the middle and tip pieces. Based on 1: the delay of 4 hours observed in the pattern of the noradrenaline disappearance between the base and the two other pieces, and II: the difference in distance between the three pieces of the ear and the superior cervical ganglion, a transport rate of a "protecting factor" could be discussed to be about 1-2 cm/h. The rate of axonal transport of dopamine-beta-hydroxylase in the rabbit sciatic nerve, was found to be within the same range, being about 2 cm/h.

Acetylcholine synthesis and its dependence on nervous activity

The findings discussed in this paper mainly derived from studies on salivary glands, serving as model organs, indicate that the capacity to form the neurotransmitter acetylcholine, as judged by the activity of choline acetyltransferase, is influenced by the traffic of nerve impulses, as a long term effect. In the glands, choline acetyltransferase seems to be exclusively localized to the cholinergic nerves. In the postganglionic parasympathetic nerves of the glands, the activity of choline acetyltransferase decreases when the flow of secretory impulses in these nerves is abolished or reduced either by isolating the nerves from the central nervous system, surgically or pharmacologically, or by diminishing the reflex activation of the glands from the mouth. The opposite occurs when the reflex activation of the salivary glands is enhanced, i.e. the activity of choline acetyltransferase increases. Observations on various other organs are quoted in support of the view that the traffic of nerve impulses is of importance for the activity of the enzyme. An increase in choline acetyltransferase activity also occurs in some salivary glands after sympathetic denervation. This puzzling observation is discussed in relation to impulse traffic. Increased nerve impulse traffic and collateral sprouting seem to be responsible for the rapid restitution of choline acetyltransferase activity from a low level in an organ partially deprived of its cholinergic nerve supply.

Movement of choline acetyltransferase in axons disconnected from their cell bodies

1. Phrenic nerves of rats were cut out and divided into two parts of equal length, one proximal and one distal. The activity of choline acetyltransferase of the two pieces was estimated. Four groups of rats were studied: (1) normal rats, and rats in which 3 days earlier, (2) the right nerve had been cut in the uppermost part of the thorax, (3) a ligature had been tied round the right nerve just above the diaphragm, and (4) these two procedures had been combined.2. In normal rats the activity of the enzyme was about the same in proximal and distal pieces. Ligation of the nerve caused an increase of the activity, of about 50%, in the distal but not in the proximal segment.3. After section of the nerve the activity below the section was 18% of normal in the proximal, and 9% in the distal piece.4. When the nerve was both cut and tied the activity decreased to the same level in both pieces, and this was about the level of the proximal piece after mere section of the nerve.5. It is concluded that choline acetyltransferase can move for some time along the axons to the nerve terminals even when the connexion with the soma has been interrupted.

Degeneration secretion from parotid glands after section of the auriculotemporal nerves at different levels

1. In cats under ether or hexobarbitone anaesthesia the auriculotemporal nerve was cut near the parotid gland on one side and 12-20 mm more proximally on the other. After 22-64(1/2) hr the cats were anaesthetized with chloralose and the parotid ducts cannulated. Degeneration secretion of saliva which appears after post-ganglionic parasympathetic denervation was found to start 2-5(1/2) hr later in the gland denervated proximally than in that denervated distally. It ceased, on the other hand, later in the former than in the latter gland.2. Before degeneration secretion had started spontaneously it could be provoked by intravenous injection of acetylcholine, methacholine, carbachol or eserine and the effect was more pronounced on the gland denervated distally. When it had ceased spontaneously it could also be provoked, and the effect on the other gland was now more marked.3. Earlier it has been assumed that while a nerve is degenerating there is a period when the nerve endings are unable to retain in a normal way acetylcholine still being synthesized. It is now suggested that this period starts later after proximal than after distal denervation because more of the material required for the normal function of the endings is available in a long piece than in a short piece of nerve.