Toshiyuki Fujisaki

Deficient cerebellar long-term depression, impaired eyeblink conditioning, and normal motor coordination in GFAP mutant mice.

Mice devoid of glial fibrillary acidic protein (GFAP), an intermediate filament protein specifically expressed in astrocytes, develop normally and do not show any detectable abnormalities in the anatomy of the brain. In the cerebellum, excitatory synaptic transmission from parallel fibers (PFs) or climbing fibers (CFs) to Purkinje cells is unaltered, and these synapses display normal short-term synaptic plasticity to paired stimuli in GFAP mutant mice. In contrast, long-term depression (LTD) at PF-Purkinje cell synapses is clearly deficient. Furthermore, GFAP mutant mice exhibited a significant impairment of eyeblink conditioning without any detectable deficits in motor coordination tasks. These results suggest that GFAP is required for communications between Bergmann glia and Purkinje cells during LTD induction and maintenance. The data support the notion that cerebellar LTD is a cellular mechanism closely associated with eyeblink conditioning, but is not essential for motor coordination tasks tested.

Functional brain block preparation of the rat auditory cortex

To maintain neural functions in brain block preparations of the rat auditory cortex in vitro, a pressurized oxygenated medium was injected into the blocks. Distribution of indigo carmine contained in the injection medium indicated that a columnar region of 1-2 mm in diameter was homogeneously perfused from the white matter to the pial surface. Stimulation of cortical layers just above the white matter produced supragranular field potentials of two negative peaks. They represented antidromic and postsynaptic activities, of which only the latter was blocked by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX, 10 microM). The depth profile and temperature-dependency of field potentials in the blocks were very similar to those recorded in usual slice preparations. The responses in blocks were recorded stably for several hours. The functional brain block preparation may be a useful tool for analyses of neocortical neural networks in vitro.

Irreversible impairment of inhibitory neurons and nitric oxide release in the neocortex produced by low temperature and hypoxia in vitro

Brain ischemia causes irreversible hyperexcitability, which may be attributed to irreversible impairment of inhibitory neurons. However, the conditions required for selective and irreversible impairment of inhibitory interneurons in vitro are unknown. In this study, we found that a combination of low temperature and hypoxia produced hyperexcitability in the neocortex. Neocortical tissue blocks isolated from rats were exposed to low temperature (1-3 degrees C) for 45 min and subsequently to room temperature (21-23 degrees C) for 60 min in the non-oxygenated medium. In experimental slices prepared from the processed blocks, hyperexcitability, similar to that elicited by an antagonist of GABA(A) receptors, was observed. Exposure of the neocortical tissue blocks to low temperature alone or room temperature alone did not elicit hyperexcitability. The excitability of pyramidal neurons, excitatory synaptic transmission and inhibitory effects of an agonist of GABA(A) receptors were normal in experimental slices. However, excitation of pyramidal neurons was inhibited after local stimulation of inhibitory neurons in control slices, but not in experimental slices. Nitric oxide (NO) release from cortical interneurons was also markedly reduced in experimental slices. These results indicate that irreversible impairment of neocortical inhibitory neurons was produced by low temperature combined with hypoxia produced in vitro.

Acute neural damage in the rat neocortex in vitro induced by a combination of anoxia and mechanical stress.

To elucidate the mechanisms of neural damage after brain ischemia, rat neocortical slices were exposed to anoxia at room temperature for 1 h, and other slices were prepared from the neocortical blocks exposed to anoxia at room temperature for 1 h. Field potentials elicited by the stimulation of layer IV were recorded in supragranular layers in these slices. No clear damage was observed electrophysiologically or morphologically in these slices. In contrast, a complete loss of the trans-synaptic field potentials and a decrease in the density of the cells stained with Neutral Red were elicited by injecting an anoxic medium into the neocortical blocks at room temperature for 1 h. In the slice preparations, the injection of the anoxic medium failed to reproduce clear neural damage, while a combination of mechanical stress and anoxia elicited a complete loss of trans-synaptic potentials; this was alleviated by Gd3+ (50 microM) and D(-)-2-amino-5-phosphonovaleric acid (100 microM). These results indicate that a combination of mechanical stress and anoxia produces acute and severe neural damage even at room temperature in vitro. The mechanism of the damage and the relationship between the neural damage in vitro and in vivo are discussed.

A Case of Large Preauricular Epidermoid Cyst Expanded into the Skull Base

The patient was a 73-year-old male, complaining of progressive right otalgia and right facial palsy. A radical mastoidectomy on the right ear was performed, and the histopathological diagnosis was only granulous tissue. A small subcutaneous mass at the right preauricle appeared just after the operation, and an open biopsy was performed. The histopathological diagnosis was epidermoid cyst.MRI showed a high intensity area from the right preauricle to around the medial pterygoid muscle. The symptoms were not improved by the administration of antibiotics and drainage. CT and MRI after about two months revealed that the epidermoid cyst and its infection had expanded from the infratemporal fossa to the pterygopalatine fossa, but they were not detected as an apparent invading lesion of the skull base, so surgical treatment was selected. Although skull base surgery was performed, the cyst and its infection could not be extirpated completely, because they had expanded deeply into the skull base beyond the clivus, against preoperative assessment. Disturbances of the central nervous system appeared and gradually increased. Finally, the patient died of respiratory failure.We treated a rare case of preauricular epidermoid cyst invading the skull base. It was considered that the lesion was possibly more enlarged than was detected in the CT and MRI findings, due to the skull base infection.

1348 ACute neural necrosis induced by anoxic perfusion in the neocortical block preparation

Insults of transient cerebral ischemia to dopamine and hrstamine neuron systems were examtned in rats using immunohistochemistry andautoradiography in order to reveal the vulnerability of these neurons to ischemia. Male Wistar rats weresubjectedto 60-min or90-min occlusion of the unilateral middlecerebral artery (MCA)followedby recirculation Two weeks after MCA occlusion, the rats were perfused tntra-cardially with Ca” -free Tyrode’s solution and a fixative. Tyrosine hydroxylase (TH)and L-histidinedecarboxylase (HDC) immunostaining methods wereused to define theextent of ischemia-induced dopamtnergic and histaminergic neuronal lesions, respectively. TH-tmmunoreacttvtty was slightly decreased in the pars compacta of substantia nigra at the ischemic side to approximately SO-90 % of that at the intact side. Coincidentally, GFAP-immunoreactivity tn the substantia nigra was increasedat the ischemic stde. HDC-positive neurons were also damaged by transient MCA occlusion, but the extent of insults was less than 20 %. The bindings of [‘HIYM-09151-2 to D2 receptors in the striatum and [‘Hlpyrilamine to HI receptors tn the hypothalamus were not significantly changedby the transient MCAocclusion. These data indicatedthat dopamine and histamine neuron systems were relattvely resistant to transtent ischemta Induced by MCA occlusion when compared to leston induced in cerebral cortex and striatum.