The role of the frontal ganglion in foregut movements of the moth, Manduca sexta

Abstract

Two types of rhythmic foregut movements are described in fifth instar larvae of the moth, Manduca sexta. These consist of posteriorly-directed waves of peristalsis which move food toward the midgut, and synchronous constrictions of the esophageal region, which appear to retain food within the crop. We describe these movements and the muscles of the foregut that generate them.The firing patterns of a subset of these muscles, including a constrictor and dilator pair from both the esophageal and buccal regions of the foregut, are described for both types of foregut movement.The motor patterns for the foregut muscles require innervation by the frontal ganglion (FG), which lies anterior to the brain and contains about 35 neurons. Eliminating the ventral nerve cord, leaving the brain and FG intact, did not affect the muscle firing patterns in most cases. Eliminating both the brain and the ventral nerve cord, leaving only the FG to innervate the foregut, generally resulted in an increased period for both gut movements and muscle bursts. This manipulation also produced increases in burst durations for most muscles, and had variable effects on the phasing of muscle activity. Despite these changes, the foregut muscles still maintained a rhythmic firing pattern when innervated by the FG alone.Two nerves exit the FG to innervate the foregut musculature: the anteriorly-projecting frontal nerve, and the posteriorly-directed recurrent nerve. Cutting the frontal nerve immediately and irreversibly stopped all muscle activity in the buccal region, while cutting the recurrent nerve immediately stopped all muscle activity in the pharyngeal and esophageal regions. Recordings from the cut nerves leaving the FG showed that the ganglion was Abbreviations: BC, Buccal Constrictor; BC 1, buccal constrictor motoneuron 1; BC2, buccal constrictor motoneuron 2; BD, Buccal Dilator; BD1, buccal dilator motoneuron 1; EC, Esophageal Dilator; EC1, esophageal dilator motoneuron l; EC2, esophageal dilator motoneuron 2; EC3, esophageal dilator motoneuron 3; ejp, excitatory j unction potential; FG, frontal ganglion; psp, postsynaptic potential Correspondence to: C.I. Miles spontaneously active, with rhythmic activity continuing within the nerves. These observations indicate that all of the foregut muscle motoneurons are located within the FG, and the FG in isolation produces a rhythmic firing pattern in the motoneurons. We have identified several motoneurons within the FG, by cobalt backfills and/or simultaneous intracellular recordings and fills from putative motoneurons and their muscles.

Modulation of foregut synaptic activity controls resorption of molting fluid during larval molts of the mothManduca sexta

“…Preparations were bathed in physiological saline (140 mmol l -1 NaCl; 5 mmol l -1 KCl; 4 mmol l -1 CaCl2; 28 mmol l -1 dextrose; 5 mmol l -1 Hepes; 2 mmol l -1 MgCl2.6H2O; 5 mmol l -1 trehalose; modified from Trimmer and Weeks, 1989). Isolation of the foregut and FG has been shown to have little effect on the foregut motor pattern generated by the FG (Miles and Booker, 1994).…”

“…The gut also appears to be a major route used for the removal of MF during the pupal-adult molt of Manduca. Approximately 6-12 h before the emergence of the adult moth, the foregut swallowing motor pattern is activated, resulting in the ingestion of the MF (Miles and Booker, 1998). Moths whose foreguts were denervated failed to absorb their MF and often failed to emerge from their pupal cuticle.…”

Motor neurons controlling fluid ingestion in Drosophila

“…In Drosophila, ingestion is driven by a pump located in the proboscis (3,4). Although the mechanics of fluid ingestion have been examined in other insects, the neural circuits controlling ingestion have not been extensively characterized (5)(6)(7).…”

Know your insect: The structural backgrounds of regurgitation, a case study on Manduca sexta and Heliothis virescens (Lepidoptera: Sphingidae, Noctuidae)

“…The cleaned up alimentary canal was analyzed and imaged under a light microscope. For imaging with confocal laser scanning microscope (CLSM), foregut was isolated and fixed in between two coverslips spaced with a small amount of Blue-Tack (Mikó and Deans 2013). A small drop of 0.1M monobasic phosphate buffer was added to the specimen to prevent desiccation.…”