Plateau Potentials in Developing Antennal-Lobe Neurons of the Moth,Manduca sexta

Abstract

. Using whole cell recordings from antennal-lobe (AL) neurons in vitro and in situ, in semi-intact brain preparations, we examined membrane properties that contribute to electrical activity exhibited by developing neurons in primary olfactory centers of the brain of the sphinx moth, Manduca sexta. This activity is characterized by prolonged periods of membrane depolarization that resemble plateau potentials. The presence of plateau potential-generating mechanisms was confirmed using a series of tests established earlier. Brief depolarizing current pulses could be used to trigger a plateau state. Once triggered, plateau potentials could be terminated by brief pulses of hyperpolarizing current. Both triggering and terminating of firing states were threshold phenomena, and both conditions resulted in all-or-none responses. Rebound excitation from prolonged hyperpolarizing pulses could also be used to generate plateau potentials in some cells. These neurons were found to express a hyperpolarization-activated inward current. Neither the generation nor the maintenance of plateau potentials was affected by removal of Na ϩ ions from the extracellular medium or by blockade of Na ϩ currents with TTX. However, blocking of Ca 2ϩ currents with Cd 2ϩ (5 ϫ 10 Ϫ4 M) inhibited the generation of plateau potentials, indicating that, in Manduca AL neurons, plateau potentials depend on Ca 2ϩ . Examining Ca 2ϩ currents in isolation revealed that activation of these currents occurs in the absence of experimentally applied depolarizing stimuli. Our results suggest that this activity underlies the generation of plateau potentials and characteristic bursts of electrical activity in developing AL neurons of M. sexta.

Sequential acquisition of cacophony calcium currents, sodium channels and voltage‐dependent potassium currents affects spike shape and dendrite growth during postembryonic maturation of an identified Drosophila motoneuron

“…One striking feature in Manduca and Xenopus is the combination of calcium conductances with low expression levels of potassium channels during specific stages of development. This results in the generation of calcium‐dependent action potentials, which can also cause plateau potentials (Spitzer & Lamborghini, ; Holliday & Spitzer, ; Lockery & Spitzer, ; Gu & Spitzer, ; Duch & Levine, , ; Mercer & Hildebrand, ; Mercer et al ., ). By contrast, calcium‐dependent action potentials were not observed in Drosophila embryonic development (Baines & Bate, ).…”

Acetylcholine‐mediated axon‐glia signaling in the developing insect olfactory system

“…Injection of TTX into pupae, which blocks sodium‐driven action potentials, had no significant impact on antennal lobe development, suggesting normal development in the absence of neuronal activity (Oland et al ., 1996b). It should be noted, however, that Manduca antennal lobe neurons and motoneurons express Ca 2+ ‐driven action potentials around stage 6, before they switch to sodium‐driven activity (Duch & Levine, 2000; Mercer & Hildebrand, 2002; Mercer et al ., 2005). Ca 2+ ‐driven action potentials could also occur in olfactory receptor neurons during development and, because they are not blocked by TTX, could trigger glial Ca 2+ signaling and antennal lobe development in the presence of TTX.…”

The quest for action potentials in C. elegans neurons hits a plateau

“…Plateau potentials are the biological equivalents of Schmitt triggers which have many interesting applications including oscillators, timers, and flip-flop elements. Thus, it is not surprising that plateau potentials have been reported in a wide range of vertebrate and invertebrate organisms 29–35 , where they have been implicated in such functions as pattern generation and short-term memory. At present, almost nothing is known about either function in C. elegans , despite long-standingt behavioral evidence of multiple pattern generators 36–38 and several forms of associative and nonassociative learning 39 .…”