Bistability and its regulation by serotonin in the endogenously bursting neuron R15 in Aplysia

Abstract

1. Previous computational studies of models of neuron R15 in Aplysia have indicated that several distinct modes of electrical activity may coexist at a given set of parameters, that this multistability can be modulated by transmitters such as serotonin (5-HT) and that brief perturbations of the membrane potential can induce persistent changes in the mode of electrical activity. To test these predictions, the responses of R15 neurons to injections of brief (1.5 s) current pulses were recorded intracellularly in the absence and presence of 5-HT. 2. In the absence of 5-HT, brief perturbations induced abrupt transitions in the electrical activity from bursting to beating. Such transitions were observed in approximately 20% of the cases. The duration of beating activity varied from several seconds to tens of minutes. In the presence of low concentrations (1 microM) of 5-HT, both the probability of mode transitions and the duration of induced beating activity increased significantly. 3. These results indicate that at least two stable modes of electrical activity can coexist in R15 neurons and that this bistability can be regulated by 5-HT. In general, these conclusions agree with the results from analyses of mathematical models of R15. Although the function of these dynamic properties in R15 is speculative, our results, interpreted on the background of the model, support the notion that nonlinear dynamical properties of individual neurons can endow them with richer forms of information processing than has generally been appreciated.

Memory from the dynamics of intrinsic membrane currents

“…Therefore the demonstration that these are seen in biological neurons under modulatory control is quite significant. Lechner et al (18) showed that the R15 neuron of Aplysia exhibited this behavior (Fig. 3B).…”

“…Another very interesting bistability is seen in theoretical and experimental work on the R15 neuron of Aplysia (16)(17)(18)(19). R15 is a prototypic bursting neuron, an extensive biophysical literature on its membrane currents and their modulation has been gathered (19), and a detailed model of this neuron and its modulation has been developed (16,17).…”

Behavioral andIn VitroCorrelates of Compulsive-Like Food Seeking Induced by Operant Conditioning inAplysia

“…Indeed, it is well known that individual neurons can express either irregular or regular forms of burst firing as a result of specific sets of voltage-dependent conductances and intracellular signal cascades that can be activated and modified by neuromodulatory transmitters (Canavier et al, 1994;Turrigiano et al, 1994;Lechner et al, 1996;Falcke et al, 2000). Although in the context of the present study the pattern-initiating B63 neurons themselves are obvious candidates for such modulatory control, the possible contribution of modifications to the burst-generating properties of other buccal Conversely, continuous hyperpolarizing current (Ϫ2 nA) injected into the B63 neurons of contingent preparations (middle gray bar) significantly decreased the rate of motor patterns compared with that occurring spontaneously (middle black bar; W ϭ 21).…”

Slow State Transitions of Sustained Neural Oscillations by Activity-Dependent Modulation of Intrinsic Excitability

“…Slow transitions between a slow-wave state and a fast-wave state were also observed in the olfactory cortex (Murakami et al, 2005). Coexistence of bursting and tonic spiking regimens is not limited to vertebrates (Lechner et al, 1996;Turrigiano et al, 1996;Shilnikov et al, 2005). Different levels of synaptic excitatory drive, activation of intrinsic conductances by neuromodulation, and changes in the extracellular ionic environment control the state-dependent oscillatory regimen (McCormick, 1992;Gil et al, 1997;Steriade and McCarley, 2005).…”