Cutaneous-evoked tinnitus. II. Review Of neuroanatomical, physiological and functional imaging studies.

Cutaneous-evoked tinnitus is a clinical entity that has not been reported previously in the neurootological literature. Herein, a neuroscience framework that encompasses several distinct areas of research is used to conceptualize and help understand this phenomenon. We review normal neuroanatomical and physiological interactions between auditory and somatosensory systems in mammals. Also considered are mechanistic accounts of lesion-induced changes in the CNS following deafferentation/deefferentation of peripheral sensory or motor structures that may have a relationship to this phenomenon, as well as the role of functional imaging modalities in studying various phantom perceptions.

Cutaneous-evoked tinnitus. I. Phenomenology, psychophysics and functional imaging.

DC00166e and acute unilateral deafferentation of the auditory periphery (auditory and vestibular afferents) can induce changes in the central nervous system that may result in unique forms of tinnitus. These tinnitus perceptions can be controlled (turned on and off) or modulated (changed in pitch or loudness) by performing certain overt behaviors in other sensory/motor systems. Clinical reports from our laboratory and several other independent sources indicate that static change in eye gaze, from a neutral head-referenced position, is one such behavior that can evoke, modulate and/or suppress these phantom auditory events. This report deals with a new clinical entity and a form of tinnitus that can be evoked directly by cutaneous stimulation of the upper hand and fingertip regions. In 2 adults, cutaneous-evoked tinnitus was reported following neurosurgery for space-occupying lesions at the base of the skull and posterior craniofossa, where hearing and vestibular functions were lost completely and acutely in one ear (unilateral deafferentation) and facial nerve paralysis (unilateral deefferentation) was present either immediately following neurosurgery or had occurred as a delayed-onset event. Herein, we focus on the phenomenology of this discovery, provide perceptual correlates using contemporary psychophysical methods and document in one individual cutaneous-evoked tinnitus-related neural activity using functional magnetic resonance imaging. In a companion paper, neuroanatomical and physiological interactions between auditory and somatosensory systems, possible mechanistic accounts and relevant functional neuroimaging studies are reviewed.

Autoradiography of high affinity uptake of catecholamines by primary astrocyte cultures.

Uptake of D.L-[3H]norepinephrine ([3H]NE) and [3H]dopamine ([3H]DA) by primary astrocyte cultures prepared from neonatal rat brains, which are greater than or equal to 95% glial fibrillary acidic protein (GFAP(+)), was studied by measuring accumulation of tritium label, and localizing such uptake at the cellular level by autoradiography. Uptake of [3H]NE was 95% Na+ dependent at 10(-7) M and 80% Na+ dependent at 7.5 X 10(-7) M [3H]NE. Uptake of [3H]DA at 7.5 X 10(-7) M was 58% Na+ dependent, but total uptake of [3H]DA was greater than uptake of [3H]NE. Autoradiography of cells incubated with 7.5 X 10(-7) M [3H]NE or [3H]DA showed that a high proportion of all the cells in these cultures had a grain density which was clearly above background. When Na+ was omitted from the medium, the temperature was lowered to 4 degrees C, or 10(-7) M desmethylimipramine or 10(-7) M amitryptyline were present, cellular grain density after exposure to both [3H]NE and [3H]DA was greatly reduced, to close to background levels. It also appeared necessary to have inhibitors of both monoamine oxidase (pargyline) and catecholamine-O-methyltransferase (tropolone) present to see clear cellular localization for [3H]DA. In the case of [3H]NE the presence of tropolone alone was adequate to observe cellular localization. These results confirm our previous findings of the existence of a high affinity uptake process for catecholamines in primary astrocyte cultures based on uptake properties, and in the present study also localizes such uptake to the major, astrocytic cell type.