Yukifumi Shigematsu

Duality of conduction mechanism in bipolar cells of the frog retina

Abstract After impulse activity in the frog retina was suppressed by tetrodotoxin, the graded postsynaptic potentials were still observed inside the ganglion cells. Impulse activity, therefore, may be dispensable for information transmission in the bipolar cells. In short-axon neurons such as the bipolar cells, the postsynaptic potentials arising at the receptor-bipolar synapses appears to spread electrotonically over the whole distance of the cells and, in this manner, transmit information to the ganglion cells. Based on the above observation, electrophysiological properties of the bipolar cells are discussed and compared with those of the multipolar neurons in the central nervous system.

Dopamine decreases receptive field size of rod-driven horizontal cells in carp retina.

Receptive field size of rod-driven horizontal cells (HCs) in the carp retina was measured by the spread of responses to the slit of light stimulus with changing the distance from the recording electrode and it was found to decay with a single exponential function. By perfusing 10 microM dopamine (DA) the length constant of rod-driven HCs was reduced to half and the response amplitude in the centre increased approximately two-fold, and the input resistance was markedly increased. This suggests that DA as a neuromodulator released from interplexiform cells could decouple the rod-driven HCs which had no direct synaptic contact with the interplexiform cells.

Latency of horizontal cell response in the carp retina

The response latency of horizontal cells in the carp retina was investigated by means of the stimulus-response crosscorrelation using a randomly modulated light of various wavelengths. R/G type cells produced two response components with some difference in latency; short-latency hyperpolarising response to green light and long-latency depolarising one to red light. The latency difference could not be made smaller than 14 ms by increasing the intensity of test light. These results were reconciled with similar measurements under selective chromatic adaptation. The latency difference revealed here supports the current view of neural circuitry that accounts for spectral response characteristics of horizontal cell subtypes.

Brain learning control representation in nucleus accumbens

Brain information processing is supported by the dual architecture of the cortical and limbic systems for the knowledge-based and emotional information, respectively. We hypothesize this dual architecture of the brain contributes to brain learning control. In order to examine the role of emotion in forming memory that is, automatic algorithm acquisition, solidification and retrieval, single unit recording was executed to nucleus accumbens of the rat. The rat was trained in a circular open field to develop its learning ability for food and water reward. After this reward acquisition task was trained, electrical activities were recorded in nucleus accumbens neurons of the in vivo brain while the rat continued the originally-trained reward acquisition task or executed some other combinations of food and water reward task. In nucleus accumbens, some neurons were found to respond to anticipation of reward. Some other neurons changed their activities while the rat continued to perform its training. These results suggest that activities of nucleus accumbens are learning-controlled by the reward value evaluated possibly by both amygdala and ventral tegmental area.

A multimicroelectrode system composed of independent glass micropipettes with an eccentric tip structure for simultaneous intracellular recording

A glass multimicroelectrode system for simultaneous intracellular recordings in which four pieces of micropipettes with rectangular cross section are arranged in a square compartment is described. Techniques are outlined for fabricating such an eccentric micropipette. An example of simultaneous recordings of intracellular membrane potentials in the carp retina is demonstrated. A technique which would allow researchers to record from three or four neurons simultaneously is presented.<<ETX>>

Temporal learning rule and dynamic neural network model

The central nervous system is a highly dynamic network which is constantly being changed by a learning process. A new temporal learning rule, the revised Hebbian rule with synaptic history, was proposed in order to organize the dynamic associative memory. The learning rule was applied to a pulse-driven neural network model, and a temporal associative memory was self-organized by input temporal signals. This result leads to a new concept that the temporal sequence of events is memorized among the asymmetric connections in the network. It was also shown that dynamic neural networks were effectively organized using temporal information. Grouping or isolation for the multi-modal information was performed well by temporal learning processing. These results suggest that temporal information may be an important factor for organizing information processing circuits in the nervous system in addition to spatial information.