NEUROMODULATION OF TRANSDUCTION AND SIGNAL-PROCESSING IN THE END ORGANS OF TASTE

Chemical synapses transmit gustatory signals from taste receptor cells to sensory afferent axons. Chemical (and electrical) synapses also pr ovide a lateral pathway for cells within the taste bud to communicate. Lateral synaptic pathways may represent some form of signal processin g in the peripheral end organs of taste. Efferent synaptic input may a lso regulate sensory transduction in taste buds. To date, the synaptic neurotransmitter(s) or neuromodulator(s) released at chemical synapse s in taste buds have not been identified unambiguously. This paper sum marizes the attempts that have been made over the past 40 years to ide ntify the neuroactive substances acting at taste bud synapses. We revi ew the four traditional criteria for identifying chemical transmitters elsewhere in the nervous system-localization, uptake/degradation, rel ease and physiological actions-and apply these criteria to neuroactive substances in taste buds. The most complete evidence to date implicat es serotonin as a neuromodulator of taste transduction in the end orga ns. However, studies also suggest that adrenergic, cholinergic and pep tidergic neurotransmission may be involved in taste buds.