Paul S. Guth - US grants

human therapy evaluation; ear disorder chemotherapy; tinnitus; hearing disorders; drug metabolism; drug administration rate /duration; dosage; pharmacokinetics; questionnaires; blood chemistry; human subject; audiometry;

DESCRIPTION: The proposed studies are a logical continuation of previous work by these investigators which have sought to identify and characterize transmitter/modulators of the vestibular periphery. The present proposal will focus specifically on acetylcholine (ACh) receptor subtypes. The questions to be addressed are: 1) What are the characteristics of the ACh receptors involved?; 2) What are the interactions between ACh and other transmitters and modulators?; 3) How do interactions between these agents influence vestibular physiology?; 4) Is there a correlation between hair cells shape and/or placement (location) in the vestibular organ and the nature of that hair cells response to ACh? A number of methods will be used to record bioelectric activity from the semi-circular canals and compare these with responses from the saccule. Bioelectric activity will be recorded using voltage and current clamping of hair cells isolated from the saccule and the semicircular canals. In addition to recording techniques, in situ hybridization and immunocytochemistry will be used to characterize and hopefully identify the location of the different ACh receptors and their subunits. The identity and distribution of other receptors will be mapped using these same techniques. A new preparation employing slices of semicircular canals (ampullae) will be used to study hair cells in situ. This technique in addition to the previously utilized techniques will be used to compare responses to ACh related compounds and other selective ligands. Thus these studies will use identification techniques of immunocytochemistry and in situ hybridization in conjunction with physiology and pharmacology to assess the functional role of acetylcholine and other neurotransmitter/modulators of the vestibular periphery. These studies have practical health related implications in terms of the future development of vestibular suppressants for treatment of vestibular pathologies and motion sickness. A clear understanding of the agents involved in normal vestibular function may lead to the development of a practical and safe vestibular suppressant. Also, while vestibular physiology is of interest in its own right, the process of the vestibular periphery are sufficiently similar to those of a cochlea that knowledge gained may be applied to hearing disorders.

The long term objectives of our research are the establishment and elucidation of the role of histamine (Hist) or a related imidazole- containing compound, in neurotransmission in acousticolateralis organs especially the semicircular canal (SCC). Specifically, the establishment of Hist's role requires fulfillment of several criteria including those of synthesis, presence and release. Whether the criterion of presence is fulfilled or not will be tested by the use of immunocytochemical techniques designed to detect histamine. Some evidence for the presence of the synthesizing enzyme histidine decarboxylase in the SCC has already been recorded. The fulfillment of the release criterion will be tested by stimulating the isolated SCC electrically and determining the presence of Hist (or congeners) by high performance liquid chromatography. The H1 and H2 antagonists have previously been shown to suppress afferent firing in the SCC. A role for Hist in neurotransmission in the SCC may also underlie the still-enigmatic finding that reserpine and other amine-depleting drugs cause a loss of electron-opacity in the synaptic bodies of vestibular hair cells. According to most authorities neither catecholamines nor indolamines are involved in hair cell recepto-neural transmission. Less well-known that the ability of reserpine to release and deplete catecholamines nor indolamines is its ability to release and deplete Hist. It is therefore proposed that we investigate whether the electron opacity of the synaptic body may be due to Hist storage. This will be done in two ways: 1) by collecting the fluid bathing the SCC following reserpine treatment and analyzing it for Hist and cogeners and 2) by determining whether repletion f electron opacity is hastened by treatment with the Hist precursor histidine. This research may provide evidence for the role of the synaptic body in hair cell receptoneural transmission; the role of Hist in hair cell transmission and finally provide a definite mechanism for the well-known suppressive effect of antihistamines in vestibular disorders.