(K-435) Development of Bioelectronic Implants for In Vivo Recordings of the Enteric Nervous System

The gut-brain axis plays a major role in our behavior. Information transfer between the gut to the brain occurs along various routes, including hormonal changes, vascular pathways, immune alterations, and neural communication.¹ This final pathway is largely driven in the gut at the local level by the enteric nervous system (ENS). The ENS is an extensive sub-portion of the autonomic nervous system that runs along the entirety of the gut, wrapping circumferentially around the gastrointestinal (GI) tract. In the distal regions of the gut, the ENS consists of two nested sets of ganglionated plexi, where it plays a role in gut motility, mucous secretion and other factors relating to gut function.² The positioning of the ENS inside the walls of the GI tract have made neural recordings in live animals very difficult with traditional technologies. Flexible bioelectronic devices provide high compliance, providing a means to access highly mobile portions of the body, such as the gut. Here, we present the production of a chronic neural recording system for accessing the ENS in awake and freely-moving rodents.

We constructed flexible bioelectronic implants using photolithographic techniques.³ Briefly, gold tracks were patterned via a lift-off technique onto a silicon wafer coated with parylene-C, an insulating polymer. These tracks were insulated with a second layer of parylene-C, and the outline of the device was patterned and etched using a reactive ion etcher. Electrodes were etched and coated with PEDOT:PSS, a conducting polymer, using a peel-off technique. Devices were removed from the silicon wafer and bonded to a custom flat cable, designed for accessing the enteric nervous system. Acute recordings were performed on anesthetized rodents (n = 10 female, Sprague-Dawley rats). For these surgeries, an implant was inserted into the wall of the colon, and a neural response was elicited by injecting saline into the colon, causing the gut to distend. These recordings were also performed under a heightened anesthetic concentration to initiate silencing. Lastly, a small pilot study (n = 3 female, Sprague-Dawley rats) was conducted to determine the feasibility of wiring neural electrodes from the colon out of rodents through a transcutaneous connector port. For these surgeries, a transcutaneous connector port was sutured into sub-dermal space between the shoulder blades. The implant flat cable was wired subcutaneously and sutured into an opening to the peritoneal cavity for gut recordings. Animals were sacrificed after one week.

Custom, implantable bioelectronics were constructed for accessing the enteric nervous system in rodents (Figure 1a). These devices were used to perform neural recordings on anesthetized rodents. Histological analysis indicated successful device placement into the vicinity of the ENS. After implant placement, the colon was distended through an injection of saline into the lumen. During distension an increase in firing is notable, which ceases as the colon relaxes back to its initial state (Figure 1b). To confirm that this signal originates from a bioelectric phenomenon, we also performed the distension under an increased anesthetic concentration, finding no measurable increase in signal (Figure 1b). These data, in conjunction with previous ex vivo work, indicate the origin of this signal as the ENS. We now move to chronic surgeries, were we developed backend wiring and connectors for placement of wired implants into the peritoneal cavity (Figure 1c). Implantation surgeries from this pilot study were successful, showing healing around the wired crossing, laying out the next steps for chronic recordings. Overall, we have shown in this work that we can access and record from the ENS in live rodents, and we have developed an implant system for performing these recordings in awake and freely moving animals. Our next steps will involve recording and analysis of signals in animals as they eat and digest food and in response to changes in diet. These data lay the framework for generating a greater understanding of the ENS and its relevance to the gut-brain axis.

1.        Cryan, J. F. et al. The Microbiota-Gut-Brain Axis. Physiol. Rev. 99, 1877–2013 (2019).

2.        Furness, J. B. The enteric nervous system and neurogastroenterology. Nat. Rev. Gastroenterol. Hepatol. 9, 286–294 (2012).

3.        Boys, A. J. et al. 3D Bioelectronics with a Remodellable Matrix for Long‐Term Tissue Integration and Recording. Adv. Mater. 35, 2207847 (2023).