Masuhiro Ikeda

Apoptotic neurodegeneration following trauma is markedly enhanced in the immature brain

Age dependency of apoptotic neurodegeneration was studied in the developing rat brain after percussion head trauma. In 7‐day‐old rats, mechanical trauma, applied by means of a weight drop device, was shown to trigger widespread cell death in the hemisphere ipsilateral to the trauma site, which first appeared at 6 hours, peaked at 24 hours, and subsided by 5 days after trauma. Ultrastructurally, degenerating neurons displayed features consistent with apoptosis. A decrease of bcl‐2 in conjunction with an increase of c‐jun mRNA levels, which were evident at 1 hour after trauma and were accompanied by elevation of CPP 32‐like proteolytic activity and oligonucleosomes in vulnerable brain regions, confirmed the apoptotic nature of this process. Severity of trauma‐triggered apoptosis in the brains of 3‐ to 30‐day‐old rats was age dependent, was highest in 3‐ and 7‐day‐old animals, and demonstrated a subsequent rapid decline. Adjusting the mechanical force in accordance with age‐specific brain weights revealed a similar vulnerability profile. Thus, apoptotic neurodegeneration contributes in an age‐dependent fashion to neuropathological outcome after head trauma, with the immature brain being exceedingly vulnerable. These results help explain unfavorable outcomes of very young pediatric head trauma patients and imply that, in this group, an antiapoptotic regimen may constitute a successful neuroprotective approach. Ann Neurol 1999;45:724–735

Extracellular accumulation of glutamate in the hippocampus induced by ischemia is not calcium dependent — In vitro and in vivo evidence

Calcium dependency of ischemia-induced increase in extracellular glutamate in the hippocampus was studied in vitro and in vivo. Perfusion of a low pO2 medium without glucose (in vitro ischemia) induced an increase in extracellular glutamate in rat hippocampal slices. This increase did not depend on Ca2+, which is in contrast with the observation that about 40% of membrane depolarization (50 mM KCl)-evoked release was Ca2+-dependent. In vivo cerebral ischemia of 5 min duration in gerbils also caused Ca2+-independent increase in extracellular glutamate in the hippocampus. The data suggest that the increase in extracellular glutamate induced by ischemia is not due to the enhanced release of neurotransmitter glutamate.

Analgesic effects of dynorphin-A and morphine in mice

To investigate whether or not dynorphin-A is analgesic, the effect of this peptide was tested in comparison with that of morphine in mice. Dynorphin-A produced a potent analgesic effect in the acetic acid writhing and tail pinch tests, but a weak effect in the tail flick test when given by intracerebroventricular injection. In contrast, morphine caused a potent analgesia in all the tests. Dynorphin-A was more effective when given by intrathecal injection than by intracerebroventricular injection, whereas morphine was equipotent by both injection routes. The results suggest that dynorphin-A is analgesic and that its analgesia may be differentiated from that of morphine.

A high-performance liquid chromatographic method for the determination of polyphosphoinositides in brain

A simple high-performance liquid chromatographic method for the determination of endogenous phosphatidylinositol 4-phosphate (PIP) and phosphatidylinositol 4,5-bisphosphate (PIP2) in brain has been developed. PIP and PIP2 were derivatized with 9-anthryldiazomethane to yield (9-anthryl)PIP and di(9-anthryl)-PIP2. The derivatives were separated on a reversed-phase column using isocratic elution and detected with a uv detector. The detection limits of PIP and PIP2 were 0.25 micrograms. The method with uv detection was sufficiently sensitive to measure the concentrations of PIP and PIP2 in rat brain. The levels of PIP and PIP2 were increased in developing rat brain and were decreased after 10 min of ischemia.

Reduction of phosphoinositide hydrolysis by L−amino−3−phosphonopropionate may be caused by the inhibition of synthesis of phosphatidylinositols

L-Amino-3-phosphonopropionate (L-AP3), a putative antagonist of metabotropic glutamate receptors, inhibited the formation of [3H]inositol phosphates induced by (1S,3R)1-aminocyclopentane-1,3-dicarboxylic acid in rat hippocampal slices. The inhibition was accompanied by a decrease in the levels of [3H]phosphatidylinositols ([3H]PIs). Preincubation of slices with L-AP3 inhibited the incorporation of [3H]myo-inositol into PI fractions. The effects of L-AP3 was in contrast with those of a typical receptor antagonist, atropine; atropine inhibited carbachol-induced phosphoinositide hydrolysis, but the levels of [3H]PIs were not affected. These findings suggest that the inhibition of phosphoinositide hydrolysis by L-AP3 is not due to the receptor antagonism but may be caused by the inhibition of synthesis of PIs.

The Role of Glutamate Decarboxylase and GABA Transaminase in Post Mortem GABA Increases in Discrete Regions of Rat Brain

ABSTRACT Preliminary experiments were performed to establish the optimal microwave irradiation time required to protect the brain from post mortem metabolism of GABA. Following this study, the high-energy phosphates, which deplete rapidly during brain ischemia and/or anoxia, were measured along with GABA to further acertain the utilization of the proper irradiation time. The metabolic enzymes in the GABA system are known to be more rapidly destroyed by microwave treatment than those in the high-energy phosphate system. The regional distribution of GABA in discrete regions of the rat brain was then determined and compared for animals sacrificed by decapitation or microwave irradiation (5kW, 1 sec). As generally accepted, the GABA content found in most regions after decapitation was higher than that after microwave irradiation. However, the degree of post mortem GABA increase varied from region to region. For example, the GABA content in the substantia nigra, superior colliculus, inferior colliculus and hypothalamus increased by 86, 112, 119 and 37 percent, respectively, when compared to the control levels obtained with microwave irradiation. In other regions, such as the striatum and the thalamus, the post mortem GABA increase was not significant. The regional distribution of GAD activity paralleled that of the GABA concentration, whereas the regional distribution of GABA-T activity was not necessarily consistent with the GABA concentration and the GAD activity. The correlation between the regional post mortem GABA increase and the GAD and GABA-T activities in the present study, however, indicate that both enzymes may be involved in determining the degree of post mortem GABA increase in individual brain regions.