O. Stiedl et al., MORPHOLOGY AND PHYSIOLOGY OF LOCAL AUDITORY INTERNEURONS IN THE PROTHORACIC GANGLION OF THE CRICKET ACHETA-DOMESTICUS, The Journal of experimental zoology, 279(1), 1997, pp. 43-53
The omega-neuron 2 (ON2) is an auditory interneuron in Acheta domestic
us that could play an important role in prothoracic auditory informati
on processing. ON2 neurons were intracellularly recorded and iontophor
etically stained with lucifer-yellow. The morphology of ON2 is similar
to that described in other cricket species. Wholemounts and transvers
e sections of prothoracic ganglia show that ON2 branches cover the sam
e regions as the omega-neuron 1 (ON1) branches except that ON2 has cro
ssover branches in the anterior ring tract from both the ipsilateral a
nd contralateral side. Auditory responses of ON2 are measured with spi
king thresholds of about 60 dB SPL at 16 kHz (courtship song frequency
) and about 80 dB SPL at 5 kHz (calling song frequency) under open fie
ld and closed field (monaural) stimulation. Open and closed field stim
ulations show almost identical threshold curves and response magnitude
s to soma-ipsilateral and soma-contralateral stimulation. These data d
o not support a function of ON2 for directional hearing. In addition t
o excitation, ON2 receives inhibitory inputs from both ears at 5 and 1
6 kHz. Subthreshold inhibition is obvious in responses with open and c
losed field stimulation at 5 kHz. Responses show mixed excitation and
inhibition at intensities above 80 dB SPL at 5 and 16 kHz. These data
confirm previous immunohistochemical results showing GABAergic input t
o ON2 in Gryllus bimaculatus. Two newly described local neurons (''LN1
'', ''LN2''), which are probably nonspiking and have low 5-kHz thresho
lds, could be candidates for the inhibitory input to ON2. (C) 1997 Wil
ey-Liss, Inc.