Patch-clamp analysis of voltage- and ligand-activated whole-cell currents in freshly dissociated neurons of the locust optic lobe |
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Authors: | M Schmidt C Benkenstein M Gewecke |
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Institution: | Universit?t Hamburg, Zoologisches Institut und Zoologisches Museum, Neurophysiologie, Martin-Luther-King-Platz 3, D-20146 Hamburg, Germany, DE
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Abstract: | Whole-cell patch-clamp recordings were obtained from 116 freshly dissociated neuronal somata from the optic lobe of adult
locusts (Schistocerca gregaria). Prerequisites were a papain treatment and the directed transfer of somata to the recording chamber by dabbing. Of the recorded
somata, 65 were from lamina and 51 from other optic lobe neurons. All somata supported voltage-activated outward currents
and some (24% of optic lobe, 3% of lamina neurons) also fast inward currents. Most lamina neurons supported an outward current
that activated (V
1/2=−8.5 mV) and inactivated rapidly and a sustained outward current. Some lamina and most optic lobe neurons expressed only
a sustained outward current (V
1/2=−9.4 mV). GABA and histamine elicited inward currents at negative holding potentials. Most optic lobe (95%) but only 18%
of lamina neurons showed a γ-aminobutyric acid (GABA) current, whereas a similar percentage of optic lobe (50%) and lamina
neurons (67%) expressed a histamine current. Both currents reversed near the chloride equilibrium potential, were reversibly
reduced by picrotoxin, and did not show rundown. Thus, they likely represent chloride currents mediated by ionotropic receptors.
Our data indicate that the lamina neurons recorded mainly represent monopolar cells postsynaptic to histaminergic photoreceptors.
The optic lobe neurons, on which GABA and histamine apparently act as inhibitory neurotransmitters, are more heterogeneous.
Accepted: 30 November 1997 |
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Keywords: | Electrophysiology Brain Insect Histamine GABA |
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