Neuronal architecture and functional mapping of the taste center of larval Helicoverpa armigera (Lepidoptera: Noctuidae)

Abstract

The sense of taste plays a crucial role in herbivorous insects by discriminating nutrients from complex plant metabolic compounds. The peripheral coding of taste has been thoroughly studied in many insect species, but the central gustatory pathways are poorly described. In the present study, we characterized single neurons in the gnathal ganglion of Helicoverpa armigera larvae using the intracellular recording/staining technique. We identified different types of neurons, including sensory neurons, interneurons, and motor neurons. The morphologies of these neurons were largely diverse and their arborizations seemingly covered the whole gnathal ganglion. The representation of the single neurons responding to the relevant stimuli of sweet and bitter cues showed no distinct patterns in the gnathal ganglion. We postulate that taste signals may be processed in a manner consistent with the principle of population coding in the gnathal ganglion of H. armigera larvae.

Gustation in insects: taste qualities and types of evidence used to show taste function of specific body parts

“…Hence the ALs have been called the primary olfactory center ( Gao et al 2000 , Rybak et al 2016 ). The subesophageal ganglion or zone (SOG or SEZ or gnathal ganglion) has been called the primary gustatory center (e.g., Maeda et al 2014 , Sun et al 2021b ); and consistent with this, axons from many mouthpart gustatory sensilla project to the SOG/SEZ or SOG/tritocerebrum, e.g., in various fly larvae and caterpillars ( Kvello et al 2010 , Tang et al 2014 , Kendroud et al 2018 , and references therein). However, some axons of some gustatory sensilla also project to other parts of the CNS.…”

Functional map of the macroglomerular complex of male Helicoverpa armigera

“…Intracellular recording and staining experiments were referred to as intracellular recording and retrograde filling, which is opposite of the single sensillum recording and anterograde filling experiments mentioned above, and were performed following previously described procedures (Zhao & Berg, 2010;Kymre et al, 2021;Sun et al, 2022). Briefly, H. armigera was restrained in a plastic pipette with the head exposed.…”

“…To visualize the glomerular units of the AL, immunostaining with anti-synapsin antibody was performed on brains with stained neurons according to previously described procedures (Zhao et al, 2016;Sun et al, 2022). After fixation in 4% paraformaldehyde, the brains were rinsed in PBS 4 times (each rinse 15 min) at room temperature, followed by preincubation in 5% normal goat serum (NGS, Sigma, St. Louis, MO, USA) and PBS containing 0.5% Triton X-100 (PBST; pH 7.4) for 3-5 h at room temperature to block nonspecific staining.…”