Effects of pharmacological treatment and photoinactivation on the directional responses of an insect neuron

• Published in: Journal of experimental zoology. Part A, Comparative experimental biology Comparative experimental biology, 2005-12, Vol.303A (12), p.1085-1103
• Main Authors: Molina, Jorge, Stumpner, Andreas
• Format: Article
• Language: English
• Subjects: Acoustic Stimulation; Animals; Auditory Pathways - cytology; Excitatory Postsynaptic Potentials - drug effects; Excitatory Postsynaptic Potentials - physiology; Excitatory Postsynaptic Potentials - radiation effects; Greece; Gryllidae; Gryllidae - physiology; Interneurons - cytology; Interneurons - drug effects; Interneurons - physiology; Interneurons - radiation effects; Isoquinolines; Lasers; Neural Inhibition - drug effects; Neural Inhibition - physiology; Neural Inhibition - radiation effects; Picrotoxin - pharmacology
• ISSN: 1548-8969; 1932-5223; 1552-499X; 1932-5231
• DOI: 10.1002/jez.a.228

Soma‐ipsilateral branches of the large segmental omega neuron of the phaneropterid bush cricket Ancistrura nigrovittata have smooth endings, which extend through most of the auditory neuropile. Correspondingly, it shows a broad frequency tuning. Large excitatory postsynaptic potentials (EPSPs) and inhibitory postsynaptic potentials (IPSPs) are observed when recording from soma‐ipsilateral branches. Stimulation from the soma‐ipsilateral side leads to a strong excitation. Soma‐contralateral branches have a strong, beaded appearance. IPSPs, which seem to be of soma‐contralateral origin, can be recorded from these branches. Stimulation from the soma‐contralateral side leads to a strong inhibition of the omega neuron. Soma‐contralateral stimulation must be 30–40 dB more intense than soma‐ipsilateral stimulation to evoke similar spike numbers in the omega neuron. The side‐to‐side difference is reduced to 10–15 dB after cutting the input from the soma‐contralateral leg (tympanic nerve). The thresholds for eliciting IPSPs by soma‐contralateral stimulation correspond roughly to excitatory thresholds of the mirror‐image omega with the same stimuli. Pharmacological treatment with picrotoxin (PTX) or photoinactivation of the Lucifer Yellow filled mirror‐image omega neuron reduces contralateral inhibition considerably and eliminates all visible IPSPs. Nevertheless, an additional contralateral inhibition survives both procedures and is only eliminated after cutting the soma‐contralateral tympanic nerve. These results demonstrate that the mirror‐image partners of the omega neuron mutually inhibit each other in bush crickets—as in crickets. This mutual inhibition is PTX‐sensitive. At least one additional element exerts contralateral PTX‐insensitive inhibition on the omega neuron. J. Exp. Zool. 303A:1085–1103, 2005. © 2005 Wiley‐Liss, Inc.