Alzheimer’s disease (AD) is the most common cause of dementia and is hallmarked by the presence of amyloid beta (Aβ) plaques and neurofibrillary tangles which cause memory deficits and gradual cognitive decline. Studies looking at AD typically focus on central nervous system dysfunction, however, there has been an increasing number of studies that suggest the gut is involved in AD pathology. The enteric nervous system is a division of the autonomic nervous system that contains specific neural networks to control important gastrointestinal tract function such as digestion, motility, nutrient absorption, blood flow, and secretion. Intestinal motility is regulated through the synchronized activity of enteric neurons, interstitial cells of Cajal, and smooth muscle cells which lie within the musculature of the gastrointestinal (GI) tract. Acetylcholine is released from excitatory motor neurons to contract smooth muscle while nitric oxide and ATP—or a similar purine—are released from inhibitory motor neurons to relax smooth muscle. Disruption in these signaling mechanisms which mediate the peristaltic reflex could lead to GI dysfunction in AD. Electrochemical tools are incredibly useful for studying neurotransmission events owed to their spatial and temporal resolution. To determine if nitric oxide or acetylcholine release is altered in AD, we measured the real time release of nitric oxide and acetylcholine from mouse myenteric ganglia in vitro using electrochemical sensors and pharmacological tools. Nitric oxide was detected directly as oxidation current using continuous amperometry along with a boron-doped diamond microelectrode modified with platinum (Pt) nanoparticles and a Nafion coating. Acetylcholine/choline was detected using an enzyme-based sensor which consisted of a platinized-Pt microelectrode modified with a permselective poly(m-phenylenediamine) coating and multienzyme film consisting of choline oxidase and acetylcholinesterase immobilized using inert protein bovine serum albumin and glutaraldehyde to cross-link the amino groups of the enzymes together. We applied these sensors in vitro to determine if nitrergic or cholinergic neuromuscular signaling are altered in a 5xFAD and APP/PS1 transgenic mouse model, which mimic major AD pathology. This work focuses primarily on the development, characterization, and application of these sensors in vitro. We also report on the development and characterization of an enzyme-based ATP biosensor and preliminary data using optogenetics and blue light stimulation for the selective stimulation of nitrergic neurons from a NOS1cre/ROSA transgenic mouse and electrochemical detection of nitric oxide using the modified BDD microelectrodes. This work is foundational is better understanding the neural circuitry which mediates GI motility.
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