Kazuyo Muramoto

Frequency of synchronous oscillations of neuronal activity increases during development and is correlated to the number of synapses in cultured cortical neuron networks.

It has been proposed that synchronous oscillations of groups of neurons corresponding to sensory information and changes in temporal pattern of oscillations are important for processing of the information in the cortex. However, it has not been determined yet how the temporal or spatial pattern of such oscillations are regulated. We observed spontaneous synchronous oscillations of Ca2+ transients, which were caused by bursts of action potentials of neurons, even in cultured cortical neurons. The frequency of synchronous Ca2+ oscillations increased with development of synapses in cultured neurons and was highly correlated to the number of synapses formed in the same culture.

A primary culture system of rat olfactory bulb forming many synapses similar to intact ones and spontaneously generating synchronous intracellular calcium oscillations

Previously, several studies attempting to analyze olfactory functions using dissociated culture systems of the olfactory bulb (OB) have been reported. Reciprocal dendrodendritic synapses between secondary neurons (mitral/tufted cells) and interneurons (periglomerular/granule cells) are considered to play the most important role in signal processing in the OB. However, it is unclear whether these reciprocal synapses are formed in vitro in the same way as they are in the intact OB. Thus, we synaptologically investigated the nature of cultured OB neurons. These neurons from embryonic rats were classified into four groups based on the size of their somata and their glutamic acid decarboxylase (GAD) immunoreactivity. At 14 days in vitro, most of the neurons synchronously showed spontaneous intracellular Ca2+ oscillations that were reversibly inhibited by application of d-APV and CNQX. Moreover, the frequency of the oscillations decreased and their amplitude became larger following application of bicuculline. These results suggest functional glutamatergic synaptic coupling and inhibitory GABAergic synaptic modulation. Immunocytochemical staining revealed many dot-like products (puncta) that were immunoreactive to GAD as well as to synaptophysin surrounding the cultured neurons. These results strongly indicate the presence of GABAergic synapses. The existence of synaptic contacts in OB neuron cultures was also confirmed by electron microscopy. Two types of synapses, symmetrical and asymmetrical, were morphologically recognizable. Moreover, we could also identify peculiar synapses resembling the in vivo reciprocal dendrodendritic synapses. The use of these primary culture systems will facilitate the elucidation of mechanisms underlying olfactory functions.

Assay System for Neurotoxicants Causing Parkinson’s Disease: 1-Methyl-4-Phenylpyridinium Ion (MPP+) Inhibits Survival of Cultured Neurons from Substantia Nigra of Fetal Monkey(Macaca fascicularis)

Most neurotoxicological research is carried out using living rodents (mice and rats). This has three main drawbacks. The first is the fundamental difficulty of extrapolating these results to human toxicity. However, obtaining statistical data on living non-human primates is practically impossible because of its high cost. The second is the killing of a great number of living animals in opposition to recent animal protection movements. The third is the difficulty of molecular and cellular studies in vivo. To avoid or decrease these scientific and social problems, it is worthwhile exploring the possibility of using in vitro preparations such as brain slices1 or cultured neurons2.