Central Gustatory Neurons Integrate Taste Quality Information From Four Appendages in the Moth Heliothis virescens

Discrimination between edible and noxious food, crucial for animal survival, is based on separate gustatory receptors for phagostimulants and deterrents. In the moth Heliothis virescens , gustatory receptor neurons (GRNs) tuned to phagostimulants like sucrose and deterrents like quinine, respectively, have indicated a labeled line mechanism for mediating appetitive and aversive information to the CNS. In the present study, we have investigated the central gustatory neurons (CGNs) in this moth as an approach to understand how gustatory information is coded in the CNS. Intracellular recordings from CGNs in the suboesophageal ganglion (SOG) combined with fluorescent staining revealed a large diversity of CGN types responding to sucrose, quinine, water, and mechanosensory stimuli applied to the antennae, the proboscis, and the right tarsus. The CGNs responded with varying tuning breadth to tastants applied to more than one appendage. This integration of information across stimuli and appendages, contradict a simple labeled line mechanism in the CNS for coding identity and location of taste stimuli. Instead the distinct pattern of activity found in an ensemble of CGNs, suggests a population coding mechanism. Staining revealed that the majority of the CGNs were confined locally within the SOG/tritocerebrum, whereas others projected to the deutocerebrum, protocerebrum, frontal ganglion, and thoracic ganglia. Some CGNs were reconstructed and registered into the H. virescens standard brain atlas, showing dendritic overlap with the previously described GRN projections. In general, the physiology and morphology of the CGNs suggested multifunctional properties, where a single CGN might belong to several networks executing different functions.

Neuromuscular systems in the fifth instar larva of silkworm Bombyx mori (Lepidoptera: Bombycidae): I-Cephalothoracic musculature and its innervation

The cephalo-thoracic musculature of the fifth instar larva of Bombyx mori comprises distinct groups of segmental muscle bands arranged in a stereotyped pattern. It includes dorsal, ventral, tergopleural, tergocoxal, lateral intersegmental, pleurosternal, sternocoxal, pleurocoxal and spiracular muscles. The cephalothoracic segments are innervated by the nerves of brain, suboesophageal ganglion (SG) and three thoracic ganglia (TG1, TG2, TG3).The brain gives nerves for compound eyes, antennae, labrum, frontal ganglion and the integument in the head. The SG, TG1,TG2,and TG3 give out a pair of lateral segmental nerves each, called the dorsal (DN) and ventral (VN) nerves. The DN of SG innervates muscles in the cephalic region, while its VN innervates muscles in the prothorax. The DN of thoracic ganglia innervates muscles in the dorsal, lateral and ventral regions of the hemi-segment while the VN innervates muscles in the ventral region. The innervation pattern indicates the presence of mixed nerves and multiple innervations that facilitate coordinated body movements and locomotion.