Kenji Mitsuhashi

Androgen rapidly increases dendritic thorns of CA3 neurons in male rat hippocampus.

Modulation of hippocampal synaptic plasticity by androgen has been attracting much attention. Thorns of thorny excrescences of CA3 hippocampal neurons are post-synaptic regions whose presynaptic partners are mossy fiber terminals. Here we demonstrated rapid effects of dihydrotestosterone (DHT) and testosterone (T) on the density of thorns, by imaging Lucifer Yellow-injected neurons in adult male rat hippocampal slices. The application of 10nM DHT or T induced rapid increase in the density of thorns within 2h. The androgen-mediated increase was suppressed by blocking several kinases, such as Erk MAPK, p38 MAPK, PKC, and CaMKII. On the other hand, PKA, PI3K were not involved in the signaling of thorn-genesis. The increase in the thorn density by androgen was also blocked by the inhibitor of classical androgen receptor. Almost no difference was observed between DHT and T in the effect on the thorn density. We observed that the androgen-induced thorn-genesis is opposite to estrogen-induced thorn-degeneration.

Automated Analysis of Spines from Confocal Laser Microscopy Images: Application to the Discrimination of Androgen and Estrogen Effects on Spinogenesis

Accurate 3D determination of postsynaptic structures is essential to our understanding memory-related function and pathology in neurons. However, current methods of spine analysis require time-consuming and labor-intensive manual spine identification in large image data sets. Therefore, a realistic implementation of algorithm is necessary to replace manual identification. Here, we describe a new method for the automated detection of spines and dendrites based on analysis of geometrical features. Our “Spiso-3D” software carries out automated dendrite reconstruction and spine detection using both eigenvalue images and information of brightness, avoiding detection of pseudo-spines. To demonstrate the potential application of Spiso-3D automated analysis, we distinguished the rapid effects of androgen and estrogen on rapid modulation of spine head diameter in the hippocampus. These findings advance our understanding of neurotrophic function of brain sex steroids. Our method is expected to be valuable to analyze vast amounts of dendritic spines in neurons in the mammalian cerebral cortex.

Automated analysis of spines from confocal laser microscopy images: Application to the discrimination of androgen and estrogen effects on hippocampal neurons

pyramidal and PV neurons, we found distinct differences in dependency of excitatory input density on dendritic diameter and distance from soma. Further, in pyramidal cells we found these two types of excitatory boutons to have differential distribution pattern on spine and shaft, the densities of which also depended upon the subtype of target neuron (L5b CPn or CCS cells). In PV neurons, we found differences in the proportion of thalamic inputs. Our results suggest glutamatergic inputs are highly selective in finding targets, both in terms of cell-type specificity, but also in choosing appropriate target domains. Research fund: KAKENHI (20700320).