Comparative actions of gaba and acetylcholine on the Xenopus laevis lateral line

1. The effects of GABA, acetylcholine and carbachol on the spontaneous activity of afferent nerve fibers in the lateral line of Xenopus laevis are characterized.2. Atropine and bicuculline were also tested on drug- and water motion-evoked activity.3. GABA (0.019-1.25 mM) suppressed and both acetylcholine (1.25-80 [mu]M) and carbachol (1.25-40 [mu]M) increased spontaneous activity. These actions were blocked by bicuculline (100 [mu]M) and atropine (4 [mu]M) respectively.4. Atropine (20 [mu]M) and bicuculline (100 [mu]M) had no effect on water motion-evoked activity.5. The results characterize actions of GABA and acetylcholine not previously described and provide evidence that does not support the hypothesis that GABA or acetylcholine are the afferent transmitter.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25886/1/0000449.pd

Comparative actions of salicylate on the amphibian lateral line and guinea pig cochlea

1. 1. Salicylate actions on afferent nerve activity in the Xenopus lateral line and on cochlear potentials in guinea pig were investigated.2. 2. In the lateral line, salicylate (0.3-2.5 mM) suppressed spontaneous activity, water motion evoked excitation and responses to -glutamate (1-2 mM) and kainate (10-20[mu]M).3. 3. In the guinea pig, salicylate (0.6-10 mM) suppressed the compound action potential (CAP) and increased N1 latency at low but not high sound intensities.4. 4. In the lateral line salicylate action may involve an antagonism of the hair-cell transmitter on the afferent nerve.5. 5. In the cochlea salicylate may suppress the active process or cochlear amplifier.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28123/1/0000573.pd

Effects of -[alpha]-aminoadipate on excitation of afferent fibers in the lateral line of Xenopus laevis

The effects of -[alpha]-aminoadipate (D[alpha]AA) on excitation of afferent nerve fibers in the Xenopus laevis lateral line were studied in vitro. D[alpha]AA reversibly suppressed spontaneous activity and excitation induced by water motion at concentrations as low as 0.25-0.5 mM. Higher concentrations (up to 10 mM) caused a greater suppression that was rapidly and fully reversible. -[alpha]-Aminoadipate at 0.25-1.0 mM had no suppressive effects. Responses elicited by NMDA (1.0-2.0 mM) were the most sensitive to D[alpha]AA (0.25-0.5 mM), those elicited by -aspartate and -glutamate (1.0-2.0 mM) were less sensitive and similar, and those elicited by kainate (5-15 [mu]M) were the least sensitive. The results provide evidence that the transmitter released by hair cells in the Xenopus lateral line interacts postsynaptically with NMDA-preferring receptors and that the transmitter is an excitatory amino acid, possibly -glutamate of -aspartate.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/23828/1/0000067.pd

Acetylcholine, carbachol, and GABA induce no detectable change in the length of isolated outer hair cells

The mechanical and electrical properties of cochlear outer hair cells (OHCs) are suggested to modulate transduction by inner hair cells. These properties of OHCs are presumably regulated by efferent neurons which use several transmitters including acetylcholine (Ach) and gamma aminobutyric acid (GABA). Since it had been suggested that Ach causes isolated OHCs to shorten visibly, this study was designed to investigate whether GABA also alters the length of OHCs. OHCs were isolated from the guinea pig cochlea by mechanical dispersion after collagenase treatment. Cells were initially selected by strict morphological criteria. In addition they were only included in further studies if they attained a constant length during 10 min of superfusion with buffer solution. Neither GABA (20 [mu]M; 100 [mu]M), Ach (5 mM; 10 [mu]M with 10 [mu]M eserine) or carbachol (10 [mu]M; 100 [mu]M) altered OHC length when applied in iso-osmotic Hank's balanced salt solution (total number of cells tested, 72). If a change in length occurred it must have been smaller than 0.3 [mu]m, our detection ability. In contrast, high potassium and variations in osmolarity changed hair cell length by 3-10% in agreement with other reports.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/28432/1/0000219.pd

P2X receptors in cochlear Deiters' cells

1. The ionotropic purinoceptors in isolated Deiters' cells of guinea-pig cochlea were characterized by use of the whole-cell variant of the patch-clamp technique. 2. Extracellular application of adenosine 5′-triphosphate (ATP) induced a dose-dependent inward current when the cells were voltage-clamped at −80 mV. The ATP-induced current showed desensitization and had a reversal potential around −4 mV. 3. Increasing intracellular free Ca(2+) by decreasing the concentration of EGTA in the pipette solution reduced the amplitude of the ATP-gated current. 4. The order of agonist potency was: 2-methylthioATP (2-meSATP)>ATP>benzoylbenzoyl-ATP (BzATP)>α,β-methyleneATP (α,β,meATP>adenosine 5′-diphosphate (ADP)>uridine 5′-triphosphate (UTP)>adenosine 5′-monophosphate (AMP)=adenosine (Ad). 5. Pretreatment with forskolin (10 μM), 8-bromoadenosine-3′,5′-cyclophosphate (8-Br-cyclic AMP, 1 mM), 3-isobutyl-1-methylxanthine (IBMX, 1 mM) or phorbol-12-myristate-13-acetate (PMA, 1 μM) reversibly reduced the ATP-induced peak current. 6. The results are consistent with molecular biological data which indicate that P2X(2) purinoceptors are present in Deiters' cells. In addition, the reduction of the ATP-gated current by activators of protein kinase A and protein kinase C indicates that these P2X(2) purinoceptors can be functionally modulated by receptor phosphorylation