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Neuronal regulation of cochlear blood flow in the guinea-pig
Ist Teil von
The Journal of physiology, 1994-11, Vol.480 (Pt 3), p.563-573
Ort / Verlag
England: The Physiological Society
Erscheinungsjahr
1994
Quelle
Free E-Journal (出版社公開部分のみ)
Beschreibungen/Notizen
1. Previous studies have shown that electrical stimulation (ES) of the guinea-pig cochlea causes a neurally mediated increase
in cochlear blood flow (CBF). It is known that the centrifugal neuronal input to the cochlea comes through the perivascular
sympathetic plexus from the cervical sympathetic chain and along the vestibular nerve (VN) from the periolivary area of the
brainstem. Both of these neuronal systems are distributed topographically in the cochlea. 2. In order to study the neural
origins of ES-evoked CBF increase, laser Doppler flowmetry was used to test the following hypotheses. (a) The response is
regional, that is, limited to the area of the cochlea stimulated. To test this we performed differential ES of the cochlear
turns. CBF was measured from either the third or the first turn. (b) The response is mediated via autonomic receptors within
the cochlea. To study this, we applied atropine, succinylcholine and idazoxan locally to the cochlea. (c) The response is
influenced by neuronal input via the sympathetic cervical chain (SC) and components of the VN. We stimulated and sectioned
the SC, and sectioned the VN, to test this hypothesis. 3. We observed that the CBF response was topographically restricted
to the stimulated region. Locally applied muscarinic or nicotinic antagonists (atropine and succinylcholine respectively)
did not affect the response. However, local idazoxan (an alpha 2-blocker) eliminated the response. Locally applied adrenaline
and SC stimulation modified the dynamic range of the response. SC sectioning enhanced the responsiveness of the cochlear vasculature
to ES. The VN section caused a temporary decrease in CBF and elimination of the ES-evoked CBF response. 4. We conclude that
the release of dilating agents is topographical with respect to ES current flow, the ES-evoked CBF increase is peripherally
mediated via alpha 2-receptors, and the response is influenced by input via the SC. The elimination of the response by VN
sectioning proximal to the brainstem indicated that fibres of the VN mediate the CBF increase during direct cochlear ES. The
data suggest that these fibres may be the efferent limb of a neural loop involved with the regulation of CBF. Such a system
could provide a mechanism for the rapid increase in CBF with organ stress.