Nonradioactive in situ hybridization was used on sections of the prothoracic ganglion of the female cricket Acheta domesticus, to evaluate expression of an mRNA targeted by alkaline phosphatase-linked oligonucleotide probes based on the sequence of the α-L1 subunit of the locust nicotinic acetyl choline receptor. Somata for the L1 and L3 auditory interneurons (previously shown to be behaviorally important in the phonotactic response of females to the males' calls) in the prothoracic ganglion were stained with experimental probes for two different nucleotide sequences within this gene. Controls (heterologous probe targeting other mRNA, sense control probe, control probe for specific nucleotide sequences, competition control, and absence of probe) produced no evidence of hybridization in L1 or L3 neuron somata. The two experimental probes showed hybridization patterns in the L1 and L3 neurons that correlated well the neuron's level of excitation and with the female's phonotactic behavior. The hybridization signal is high in the L1 neuron somata of females at ages (4-28 days old) when phonotactic and L1 thresholds are low. Females (4-12 days old) that typically were selective for the syllable period of the male's calling song and showed higher levels of excitation in their L3 neurons demonstrated higher hybridization in the somata of these neurons.