Innervation of the feline eustachian tube

Functional study of mucus secretion of the eustachian tube in Guinea pigs

OBJECTIVES

Our aim was to verify neural regulation of submucous gland mucus secretions in the Eustachian tubes of guinea pigs.

STUDY DESIGN

Prospective animal study.

METHODS

Eustachian tubes harvested from 12 guinea pigs were used for this study. For real-time resolution of pure glandular secretion, we used a modified method of single-gland optical measurement. Secretory monitoring was undertaken after each preparation with phenylephrine, isoproterenol, forskolin, and substance P. To confirm the viability of each tissue, we examined glandular secretion after treatment with carbachol. Secretory effects of each agonist were evaluated by comparing with basal secretion using a Student's t test (p < 0.01).

RESULTS

The Ca-elevating agonists carbachol and substance P showed greater effects on submucous gland secretions of the Eustachian tube than the cyclic adenosine monophosphate (cAMP)-elevating agonists forskolin and isoproterenol. However, phenylephrine, although it belongs to the Ca-elevating agonist group, did not show any significant secretory effect.

CONCLUSION

The optical measurement method used in this study had the merit of real-time resolution of submucous glandular secretion. Submucous glandular secretion in the Eustachian tube was regulated by both Ca- and cAMP-elevating agonists, and Ca-elevating agonists seemed to be more potent than cAMP-elevating agonists except phenylephrine. Our results suggest that not only the autonomic nerve system but also the neuropeptides such as substance P are closely related to glandular secretion in the Eustachian tube, and beta-adrenergic receptors seem to be more related to submucous glandular secretion of the Eustachian tube in guinea pig than alpha-adrenergic receptors.

A model of active Eustachian tube function in the rat: effect of modulating parasympathetic innervation

The effect of altering secretion into the Eustachian tube by modulating cholinergic innervation was studied in the anaesthetized rat. Active properties of the Eustachian tube were determined by measuring the ability of reflex-induced swallowing to equalize against an increased pressure level in the bulla. Reflex-induced swallowing was initiated by electrically stimulating the superior laryngeal nerve. Passive properties of the Eustachian tube were determined by increasing middle ear pressure until the Eustachian tube spontaneously opened. Blocking cholinergic neurotransmission with atropine had no effect on active or passive properties of the Eustachian tube. Potentiating cholinergic neurotransmission with neostigmine significantly impaired the ability of active swallowing to equilibrate middle ear pressure, but had no effect on passive properties of the Eustachian tube. The findings show that cholinergic nerve transmission, most likely from the parasympathetic division of the autonomic nervous system, can influence Eustachian tube function. We hypothesize that this effect is due to changes in surface tension in the Eustachian tube as a result of changes in secretion.

Electron-microscopic observation of adrenergic innervation in guinea pig Eustachian tube

The precise locations of adrenergic nerve terminals in the Eustachian tube of guinea pigs have, for the first time, been demonstrated by electron microscopy, with application of a false transmitter (5-OHDA). Adrenergic nerve terminals were found in abundance near the arteries in each area of the Eustachian tube. In particular, these terminals were observed just beneath the smooth muscle layer of the arteries. The exact locations of adrenergic nerve terminals in the submucous and gland region are also discussed.

Origin and distribution of VIP (vasoactive intestinal polypeptide)-nerves in the genito-urinary tract

VIP (Vasoactive Intestinal Polypeptide)-immunoreactive nerves were found throughout the genito-urinary tract of the cat; they were less numerous in the guinea pig and in the rat. In the cat, VIP nerves were particularly numerous in the neck of the urinary bladder and proximal urethra, in the uterine cervix and in the prostate gland. The nerves were found in smooth muscle, around blood vessels and in the connective tissue immediately beneath the epithelium. Ganglia were found below the trigonum area of the bladder, in the wall of the proximal urethra, and in paracervical tissue. VIP-immunoreactive nerve cell bodies occurred in all these ganglionic formations. These ganglia probably represent the origin of the VIP nerves of the genital tract since their removal in the female cat greatly reduced the VIP nerve supply. Transection of the hypogastric nerves had no overt effect. Transection of the cervix eliminated the VIP nerves above the level of the lesion, except those in the ovaries, supporting the view that the VIP nerves of the uterus and the oviduct are derived from a paracervical source.