Newly discovered neuron circuit shows gut is directly connected to the brain

The video explores how gut cells with neuron-like protrusions may communicate with the brain via the vagus nerve. An experiment using a fluorescent rabies virus demonstrated a direct connection from the gut to the brainstem. Enteroendocrine cells, when grown with vagal neurons, form connections and release glutamate, a neurotransmitter involved in sensory perception, which neurons detect rapidly.

What neurotransmitter do the gut cells release, and what senses is it involved in conveying?

How quickly do neurons pick up on signals related to taste or smell?