Yuuta Hamasaki

Nitric Oxide-Mediated Modulation of Central Network Dynamics during Olfactory Perception

Nitric oxide (NO) modulates the dynamics of central olfactory networks and has been implicated in olfactory processing including learning. Land mollusks have a specialized olfactory lobe in the brain called the procerebral (PC) lobe. The PC lobe produces ongoing local field potential (LFP) oscillation, which is modulated by olfactory stimulation. We hypothesized that NO should be released in the PC lobe in response to olfactory stimulation, and to prove this, we applied an NO electrode to the PC lobe of the land slug Limax in an isolated tentacle-brain preparation. Olfactory stimulation applied to the olfactory epithelium transiently increased the NO concentration in the PC lobe, and this was blocked by the NO synthase inhibitor L-NAME at 3.7 mM. L-NAME at this concentration did not block the ongoing LFP oscillation, but did block the frequency increase during olfactory stimulation. Olfactory stimulation also enhanced spatial synchronicity of activity, and this response was also blocked by L-NAME. Single electrical stimulation of the superior tentacle nerve (STN) mimicked the effects of olfactory stimulation on LFP frequency and synchronicity, and both of these effects were blocked by L-NAME. L-NAME did not block synaptic transmission from the STN to the nonbursting (NB)-type PC lobe neurons, which presumably produce NO in an activity-dependent manner. Previous behavioral experiments have revealed impairment of olfactory discrimination after L-NAME injection. The recording conditions in the present work likely reproduce the in vivo brain state in those behavioral experiments. We speculate that the dynamical effects of NO released during olfactory perception underlie precise odor representation and memory formation in the brain, presumably through regulation of NB neuron activity.

Various Firing Patterns Found in a Giant Neuron of the Pond Snail Lymnaea stagnalis and Their Dynamics

In order to understand the function of the nervous system, it is important to elucidate the characteristics of complex activities of individual neurons. In the present study, we therefore examined firing patterns of the central giant neuron of the pond snail Lymnaea stagnalis by intracellular recording. Interestingly, they differed among individuals. In a series of firing patterns, the neuron revealed the transition from the beating discharge to the regular bursting discharges when the depolarizing current was injected. In another series of firing patterns, the neuron revealed quite different and more complex activities, in which a regular bursting switched irregularly to another bursting state. The Poincare map obtained from the reconstructed attractor showed the switching dynamics between two bursting states. The present results showed a variety of possible activities of the neuron and the different firing dynamics among individuals.