Expression of classical mitochondrial respiratory responses in homogenates of rat forebrain

Colloid osmotic pressure of cat brain homogenate separated from autogenous CSF by a copper ferrocyanide membrane

The colloid osmotic pressure (oncotic pressure) of cat brain homogenate against cerebrospinal fluid (CSF) was determined using an electronic osmometer with a rigid selectively permeable copper ferrocyanide membrane. First, the basic characteristics of the membrane were examined. The relative value of the reflexion coefficient (sigma) for polyethylene glycol (PEG) became rather stable above a molecular weight of 6000 Da, below which sigma declined. The osmometer showed a linear response to sucrose concentration, whereas it revealed a non-idealistic change with respect to concentration of high molecules (PEG). The temperature effect on sigma for albumin solution was found to be large. The membrane could thus be used for measuring the relative value of the colloid osmotic pressure of protein solutions without dilution and at the same temperature as the calibrating solution. Samples of CSF and brain cortex were freshly obtained from 5 cats. The cortex was immediately homogenized and the colloid osmotic pressure of the homogenate against the CSF was measured at room temperature within 3 min after cortex removal. The mean value was 213 +/- 11 (S.D.) mm Hg with the osmometer calibrated with respect to the colloid osmotic pressure of autogenous plasma.

Mitochondrial function in brain tissue in primary degenerative dementia

Previous in vitro and in vivo studies of the brain in Alzheimer's disease indicated alterations in metabolism related to energy production although the relationships between these changes remains obscure. To help resolve this issue, in vitro oxygen uptake by homogenates of fresh samples of frontal neocortex from patients with dementia and neurosurgical controls has been examined as a measure of energy-related metabolism and mitochondrial function. Maximal respiratory rates (measured in the presence of an uncoupling agent) were similar for samples from 7 controls, 5 patients with Alzheimer's disease and two patients diagnosed clinically as Pick's disease, suggesting that there was little or no effect of these dementias on the maximal metabolic capacity of the tissue. However, under some conditions producing sub-maximal metabolic activity (which are of potentially greater physiological relevance) oxygen uptake rates were significantly elevated in the dementia group. The ratio of oxygen uptake rates in the presence and absence of ADP was significantly reduced (to 58% of control; P less than 0.02) for the dementia patients compared with controls, possibly indicative of partial mitochondrial uncoupling. These results indicate metabolic changes expressed in vitro which may be relevant to the pathogenesis of Alzheimer's disease and some related dementias.

Altered mitochondrial respiration in selectively vulnerable brain subregions following transient forebrain ischemia in the rat

Mitochondrial respiratory function, assessed from the rate of oxygen uptake by homogenates of rat brain subregions, was examined after 30 min of forebrain ischemia and at recirculation periods of up to 48 h. Ischemia-sensitive regions which develop extensive neuronal loss during the recirculation period (dorsal-lateral striatum, CA1 hippocampus) were compared with ischemia-resistant areas (paramedian neocortex, CA3 plus CA4 hippocampus). All areas showed reductions (to 53-69% of control) during ischemia for oxygen uptake rates determined in the presence of ADP or an uncoupling agent, which then recovered within 1 h of cerebral recirculation. In the ischemia-resistant regions, oxygen uptake rates remained similar to control values for at least 48 h of recirculation. After 3 h of recirculation, a significant decrease in respiratory activity (measured in the presence of ADP or uncoupling agent) was observed in the dorsal-lateral striatum which progressed to reductions of greater than 65% of the initial activity by 24 h. In the CA1 hippocampus, oxygen uptake rates were unchanged for 24 h, but were significantly reduced (by 30% in the presence of uncoupling agent) at 48 h. These alterations parallel the development of histological evidence of ischemic cell change determined previously and apparently precede the appearance of differential changes between sensitive and resistant regions in the content of high-energy phosphate compounds. These results suggest that alterations of mitochondrial activity are a relatively early change in the development of ischemic cell death and provide a sensitive biochemical marker for this process.

Effects of postdecapitative ischemia on mitochondrial respiration in brain tissue homogenates

Mitochondria isolated from ischemic brain characteristically show changes in respiratory function. As conventional procedures for mitochondrial isolation yield a subpopulation of the total population and require extensive manipulation, it is unclear to what extent these changes are representative of mitochondria in the unfractionated tissue. We previously showed that the oxygen uptake by unfractionated forebrain homogenates, measured under two different sets of incubation conditions, provided information on some aspects of the respiratory activity of both the free and synaptosomal pools of mitochondria. Forebrain homogenates from animals subjected to 30 min of postdecapitative ischemia exhibited large reductions in oxygen uptake rates measured in a high K+ (mitochondrial) buffer in the presence of either ADP (44% of control values) or an uncoupling agent (45% of control values). These reductions in respiratory activity were comparable to alterations observed under the same conditions for mitochondria isolated from the ischemic brains. Similar alterations were seen in homogenates from three subregions: neocortex, hippocampus, and striatum. In a physiological buffer, in which oxygen uptake by homogenates largely resulted from activity of mitochondria within synaptosomes, there was little or no change in basal glucose-supported rates (79-96% of control values) and small reductions in maximal rates (63-81% of control values) measured in the presence of an uncoupling agent. These results suggest that alterations of respiratory function seen in isolated free mitochondria provide appropriate estimates of the dysfunction in the total free mitochondrial pool but that synaptosomal mitochondria may be less affected. Measurements of respiratory function of isolated synaptosomes from ischemic tissue provided further support for the relative preservation of synaptosomal mitochondria during ischemic insult.