Higher Cytochrome Oxidase Activity Research Articles

Different brain networks underlying the acquisition and expression of contextual fear conditioning: a metabolic mapping study

The specific brain regions and circuits involved in the acquisition and expression of contextual fear conditioning are still a matter of debate. To address this issue, regional changes in brain metabolic capacity were mapped during the acquisition and expression of contextual fear conditioning using cytochrome oxidase (CO) quantitative histochemistry. In comparison with a group briefly exposed to a conditioning chamber, rats that received a series of randomly presented footshocks in the same conditioning chamber (fear acquisition group) showed increased CO activity in anxiety-related brain regions like the ventral periaqueductal gray, the ventral hippocampus, the lateral habenula, the mammillary bodies, and the laterodorsal thalamic nucleus. Another group received randomly presented footshocks, and it was re-exposed to the same conditioning chamber one week later (fear expression group). The conditioned group had significantly higher CO activity as compared with the matched control group in the following brain regions: the ventral periaqueductal gray, the central and lateral nuclei of the amygdala, and the bed nucleus of the stria terminalis. In addition, analysis of functional brain networks using interregional CO activity correlations revealed different patterns of functional connectivity between fear acquisition and fear expression groups. In particular, a network comprising the ventral hippocampus and amygdala nuclei was found in the fear acquisition group, whereas a closed reciprocal dorsal hippocampal network was detected in the fear expression group. These results suggest that contextual fear acquisition and expression differ as regards to the brain networks involved, although they share common brain regions involved in fear, anxiety, and defensive behavior.

Low-Intensity Exercise Training Delays Heart Failure and Improves Survival in Female Hypertensive Heart Failure Rats

Exercise training improves functional capacity and quality of life in patients with heart failure. However, the long-term effects of exercise on mortality associated with hypertensive heart disease have not been well defined. In the present study, we investigated the effect of low-intensity exercise training on disease progression and survival in female spontaneously hypertensive heart failure rats. Animals with severe hypertension (16 months old) were treadmill trained (14.5 m/min, 45 min/d, 3 d/wk) until they developed terminal heart failure or were euthanized because of age-related complications. Exercise delayed mortality resulting from heart failure (P<0.001) and all causes (P<0.05) and transiently attenuated the systolic hypertension and contractile dysfunction observed in the sedentary animals but had no effect on cardiac morphology or contractile function in end-stage heart failure. Training had no effect on terminal myocardial protein expression of antioxidant enzymes, calcium handling proteins, or myosin heavy chain isoforms but was associated with higher cytochrome oxidase activity in cardiac mitochondria (P<0.05) and a greater mitochondrial content of cardiolipin, a phospholipid that is essential for optimal mitochondrial energy metabolism. In conclusion, low-intensity exercise training significantly delays the onset of heart failure and improves survival in female hypertensive heart failure rats without eliciting sustained improvements in blood pressure, cardiac function, or expression of several myocardial proteins associated with the cardiovascular benefits of exercise. The effects of exercise on cytochrome oxidase and cardiolipin provide novel evidence that training may improve prognosis in hypertensive heart disease by preserving mitochondrial energy metabolism.

Enhanced metabolic capacity of the frontal cerebral cortex after Pavlovian conditioning

While Pavlovian conditioning alters stimulus-evoked metabolic activity in the cerebral cortex, less is known about the effects of Pavlovian conditioning on neuronal metabolic capacity. Pavlovian conditioning may increase prefrontal cortical metabolic capacity, as suggested by evidence of changes in cortical synaptic strengths, and evidence for a shift in memory initially processed in subcortical regions to more distributed prefrontal cortical circuits. Quantitative cytochrome oxidase histochemistry was used to measure cumulative changes in brain metabolic capacity associated with both cued and contextual Pavlovian conditioning in rats. The cued conditioned group received tone–foot-shock pairings to elicit a conditioned freezing response to the tone conditioned stimulus, while the contextually conditioned group received pseudorandom tone–foot-shock pairings in an excitatory context. Untrained control group was handled daily, but did not receive any tone presentations or foot shocks. The cued conditioned group had higher cytochrome oxidase activity in the infralimbic and anterior cingulate cortex, and lower cytochrome oxidase activity in dorsal hippocampus than the other two groups. A significant increase in cytochrome oxidase activity was found in anterior cortical areas (medial, dorsal and lateral frontal cortex; agranular insular cortex; lateral and medial orbital cortex and prelimbic cortex) in both conditioned groups, as compared with the untrained control group. In addition, no differences in cytochrome oxidase activity in the somatosensory regions and the amygdala were detected among all groups. The findings indicate that cued and contextual Pavlovian conditioning induces sustained increases in frontal cortical neuronal metabolic demand resulting in regional enhancement in the metabolic capacity of anterior cortical regions. Enhanced metabolic capacity of these anterior cortical areas after Pavlovian conditioning suggests that the frontal cortex may play a role in the retention and regulation of learned associations.

Metabolic activity of the thalamic and telencephalic auditory centers of reptiles

329 The lemniscal (classical projection) and extralemniscal parts of mammalian sensory systems, including the auditory system have different levels of metabolic activity. The lemniscal parts have a higher activity of cytochrome oxidase (CO) and an increased ability to accumulate 2-deoxyglucose (2-DG), whereas the extralemniscal parts are characterized by a lower level of metabolic activity [1]. A similar distribution of metabolic activity was observed in the auditory system of birds (in the mesencephalic, thalamic, and telencephalic auditory centers) [2‐4]. Earlier, we showed that the mesencephalic auditory center, torus semicircularis (TS), of some reptiles, such as turtles and lizards, has a higher CO activity in the central nucleus of the lemniscal pathway than in the peripheral extralemniscal part [5]. However, it is not clear whether the metabolic activity in the rostral centers of reptilian auditory system, viz. the auditory relay thalamic nucleus (n. reuniens, Re) and its projection zone in the telencephalon (the ventromedial part of anterior dorsal ventricular ridge, Advr), have selective distribution. In this work, we studied the distribution of the activity of the mitochondrial oxidative enzyme CO in the rostral auditory centers of two turtle species, Testudo horsfieldi and Emys orbicularis. The experiments were performed with four T. horsfieldi and four E. orbicularis. The CO activity was measured by the standard histochemical method [6] with the use of bovine heart cytochrome Σ (Sigma). The CO activity was estimated by the density of histochemical staining of frozen frontal brain slices with a thickness of 50 µ m. Thalamus. The distribution of the CO activity in the Re in both turtle species was similar and heterogeneous. In the rostral level of the thalamus, we found a CO-active band-shaped structure that continuously spread from the ventricle in the lateral direction below the ventral border of the thalamic center of the tectofugal visual system (Rot) and coincided with the location of the n. anterior (nA). The medial part of this structure is a rostral pole of Re (Figs. 1a and 2a). The middle Re level had two areas with a high CO activity. The larger dorsocentral area occupied almost the entire nucleus except for a small ventrolateral part and extended to the somatic nucleus n. ventralis (nV) below the Rot. This area was continuously connected with the rostral bandshaped structure (Figs. 1b and 2b). Like the rostral part of the Re, this area was filled with stained punctuate terminals with sparse CO-positive cells located in the lat

Freewheel running selectively prevents mouse CD4 + intestinal lymphocyte death produced after a bout of acute strenuous exercise

Aerobic exercise increases oxidant stress and leads to apoptosis of mouse intestinal lymphocytes (IL). The purpose of this study was to determine whether freewheel running prevents IL loss 24 h after a bout of strenuous exercise. Mice were randomly assigned to in-cage running wheels with 24 h access (WR) or individual cages without running wheels (NR) for 4 months. WR mice accumulated 364 km over 4 months and had higher cytochrome oxidase activity in the plantaris ( p < .05), indicative of training. Total intestinal, CD3αβ, CD3γδ, CD8α, and CD8β lymphocytes and intracellular glutathione were significantly lower in WR and NR mice 24 h post-exercise. The number of CD4 IL decreased 24 h after exercise in NR ( p < .01) but not in WR mice relative to their respective no exercise controls. Thus, freewheel running in mice for 4 months prevented CD4 IL loss after acute exercise.

Quantitative immuno-electron microscopic analysis of nuclear respiratory factor 2 alpha and beta subunits: Normal distribution and activity-dependent regulation in mammalian visual cortex

The macaque visual cortex is exquisitely organized into columns, modules, and streams, much of which can be correlated with its metabolic organization revealed by cytochrome oxidase (CO). Plasticity in the adult primate visual system has also been documented by changes in CO activity. Yet, the molecular mechanism of regulating this enzyme remains not well understood. Being one of only four bigenomic enzymes in mammalian cells, the transcriptional regulation of this enzyme necessitates a potential bigenomic coordinator. Nuclear respiratory factor 2 (NRF-2) or GA-binding protein is a transcription factor that may serve such a critical role. The goal of the present study was to determine if the two major subunits of NRF-2, 2alpha and 2beta, had distinct subcellular distribution in neurons of the rat and monkey visual cortex, if major metabolic neuronal types in the macaque exhibited different levels of the two subunits, and if they would respond differently to monocular impulse blockade. Quantitative immuno-electron microscopy was used. In both rats and monkeys, nuclear labeling of alpha and beta subunits was mainly over euchromatin rather than heterochromatin, consistent with their active participation in transcriptional activity. Cytoplasmic labeling was over free ribosomes, the Golgi apparatus, and occasionally the nuclear envelope, signifying sites of synthesis and possible posttranslational modifications. The density of both subunits was much higher in the nucleus than in the cytoplasm for all neurons examined, again indicating that their major sites of cellular action is in the nucleus.

Regional brain cytochrome oxidase activity in β-amyloid precursor protein transgenic mice with the swedish mutation

Cytochrome oxidase activity was examined in a transgenic mouse model of Alzheimer’s disease with overexpression of the 751 amino acid isoform of β-amyloid precursor protein with the Swedish mutation under control of the murine thy-1 promoter. The neuritic plaques, abundantly localized in the hippocampus and anterior neocortical areas, showed a core devoid of enzymatic activity surrounded by higher cytochrome oxidase activity at the sites of the dystrophic neurites and activated glial cells. Quantitative measures, taken only in the healthy-appearing regional areas without neuritic plaques, were higher in numerous limbic and non-limbic regions of transgenic mice in comparison with controls. Enzymatic activity was higher in the dentate gyrus and CA2–CA3 region of the hippocampus, the anterior cingulate and primary visual cortex, two olfactory structures, the ventral part of the neostriatum, the parafascicularis nucleus of the thalamus, and the subthalamic nucleus. Brainstem regions anatomically related with altered forebrain regions were more heavily labeled as well, including the substantia nigra, the periaqueductal gray, the superior colliculus, the medial raphe, the locus coeruleus and the adjacent parabrachial nucleus, as well as the pontine nuclei, red nucleus, and trigeminal motor nucleus. Functional brain organization is discussed in the context of Alzheimer’s disease. Although hypometabolism is generally observed in this pathology, the increased cytochrome oxidase activity obtained in these transgenic mice can be the result of a functional compensation on the surviving neurons, or of an early mitochondrial alteration related to increased oxidative damage.

Transgenic mice expressing the human C99 terminal fragment of βAPP: effects on spatial learning, exploration, anxiety, and motor coordination

The functional consequence of beta-amyloid precursor protein (βAPP) manipulation on behavior was assessed in Tg13592 mice, characterized by transgene expression of the 99 amino acid C-terminal sequence of human βAPP in brain and skeletal muscle but with plaque formation only in muscle. By comparison to the C57BL/6 background strain controlled for age and gender, Tg13592 transgenic mice had fewer movements in an automated chamber and fewer enclosed arm entries in the elevated plus-maze. This hypoactivity was probably due to a loss in the motivation to explore novel environmental stimuli rather than motor weakness or anxiety. In addition, the acquisition of place learning in the Morris water maze task was impaired in Tg13592 mice. The transgenic mice were not impaired in a probe trial or while swimming toward a visible platform. These results are concordant with the hypothesis that transgene expression of the C-terminal sequence of human βAPP in brain is sufficient for causing behavioral abnormalities. The hypoactivity and the spatial learning deficit were associated with higher cytochrome oxidase activity seen in thalamic nuclei, indicating that altered regional brain metabolism caused by βAPP transgene expression may be responsible for the behavioral changes.

Regional brain variations of cytochrome oxidase activity and motor coordination in hot-foot mutant mice.

Hot-foot mutant mice are characterized by defective arborization of Purkinje cell dendrites, resulting in ataxia of gait and deficits of equilibrium. Regional brain variations of cytochrome oxidase (CO) activity were analysed for the purpose of identifying those brain regions with abnormal metabolic activity as a secondary consequence to the cerebellar alteration. In addition, the possible relation between CO activity and motor deficits was evaluated. By comparison to normal littermate controls of the same background strain, hot-foot mutants had higher CO activity in the molecular layer of the cerebellum, the ventrolateral and midline thalamic nuclei, as well as in the frontal eye field. There was no other alteration of CO activity in the hot-foot brain. No linear correlation was discerned between CO activity in the molecular layer of the cerebellum and the ventrolateral and midline nuclei on one hand, and motor coordination performance on the other. These results indicate regionally selective abnormalities of metabolic activity in a cerebellar mutant with defective dendritic arborization of the Purkinje cell.

Regional brain variations of cytochrome oxidase activity and motor coordination in Lurcher mutant mice.

Lurcher mutant mice are characterized by massive degeneration of cerebellar Purkinje cells and granule cells and by deficits in motor coordination. Regional brain variations of cytochrome oxidase (CO) activity were analyzed to identify those brain regions with abnormal metabolic activity as a secondary consequence of the cerebellar atrophy and to establish the relationship between CO activity and motor deficits. Lurcher mutants had higher CO activity in all three cerebellar deep nuclei than normal littermate controls of the same background strain. Higher CO activity was also found in Lurcher mutants in brain regions directly connected to the cerebellum, such as the lateral vestibular nucleus, the cochlear nucleus, the red nucleus, the ventrolateral thalamus, the dorsal raphe, the interpeduncular nucleus, and the inferior colliculus. By contrast, there was a sharp decrease in CO activity in the inferior olive. As for brain regions not directly connected to the cerebellum, higher CO activity was observed in the trigeminal motor nucleus and the CA1 molecular layer of the hippocampus, which highlights probable transsynaptic alterations as a secondary consequence of cerebellar atrophy. A positive correlation between CO activity in the red nucleus and latencies before falling in two motor-coordination tests indicates that a compensatory increase of metabolic activity in a cerebellar efferent region is associated with improved behavior.

Laminar and columnar patterns of geniculocortical projections in the cat: Relationship to cytochrome oxidase

We examined the laminar and columnar arrangement of projections from different layers of the lateral geniculate nucleus (LGN) to the visual cortex in the cat. In light of recent reports that cytochrome oxidase blobs (which in primates receive specific geniculate inputs) are also found in the visual cortex of cats, the relationship between cytochrome oxidase staining and geniculate inputs in this species was studied. Injections of wheat germ agglutinin-conjugated horseradish peroxidase were made into the anterior "genu" of the LGN, where isoelevation contours of the geniculate layers are distorted due to the curvature of the nucleus. Consequently, anterograde labeling from the various LGN layers was topographically separated across the surface of the cortex, and labeling in a particular isoelevation representation of the cortex could be associated with a specific layer of the LGN. Labeling from the A layers, which contain X and Y cells, was coextensive with layers 4 and 6 in both area 17 and area 18, as previously reported. Labeling from the C layers, which contain Y and W cells, occupied a zone extending from the 4a/4b border to part way into layer 3 in area 17. The labeling extended throughout layer 4 in area 18. There was also labeling in layer 5a and layer 1 in both area 17 and area 18. Except in layer 1, labeling from the C layers was patchy. In the tangential plane, adjacent sections stained for cytochrome oxidase showed that the patches of labeling from the C laminae aligned with the cytochrome oxidase blobs. The cytochrome blobs were visible in layers 3 and 4a, but not in layer 4b in both areas 17 and 18. These results suggest that W cells project specifically to the layer 3 portion of the blobs, while Y cells, at least those of the C layers, project specifically to the layer 4a portion of the blobs in area 17. The heavy synaptic drive of the Y cells is probably the cause of the elevated metabolism, and thus, higher cytochrome oxidase activity, of the blobs.

Laminar and columnar patterns of geniculocortical projections in the cat: Relationship to cytochrome oxidase

We examined the laminar and columnar arrangement of projections from different layers of the lateral geniculate nucleus (LGN) to the visual cortex in the cat. In light of recent reports that cytochrome oxidase blobs (which in primates receive specific geniculate inputs) are also found in the visual cortex of cats, the relationship between cytochrome oxidase staining and geniculate inputs in this species was studied. Injections of wheat germ agglutinin-conjugated horseradish peroxidase were made into the anterior “genu” of the LGN, where isoelevation contours of the geniculate layers are distorted due to the curvature of the nucleus. Consequently, anterograde labeling from the various LGN layers was topographically separated across the surface of the cortex, and labeling in a particular isoelevation representation of the cortex could be associated with a specific layer of the LGN. Labeling from the A layers, which contain X and Y cells, was coextensive with layers 4 and 6 in both area 17 and area 18, as previously reported. Labeling from the C layers, which contain Y and W cells, occupied a zone extending from the 4a/4b border to part way into layer 3 in area 17. The labeling extended throughout layer 4 in area 18. There was also labeling in layer 5a and layer 1 in both area 17 and area 18. Except in layer 1, labeling from the C layers was patchy. In the tangential plane, adjacent sections stained for cytochrome oxidase showed that the patches of labeling from the C laminae aligned with the cytochrome oxidase blobs. The cytochrome blobs were visible in layers 3 and 4a, but not in layer 4b in both areas 17 and 18. These results suggest that W cells project specifically to the layer 3 portion of the blobs, while Y cells, at least those of the C layers, project specifically to the layer 4a portion of the blobs in area 17. The heavy synaptic drive of the Y cells is probably the cause of the elevated metabolism, and thus, higher cytochrome oxidase activity, of the blobs. © 1996 Wiley-Liss, Inc.

Cytochrome oxidase activity in brown fat varies with reproductive response and use of torpor in deer mice

Reproductive responses and thermogenic properties of brown adipose tissue (BAT) were evaluated in individuals from an outbred population of deer mice (Peromyscus maniculatus nebrascensis) after 10 weeks exposure to short photoperiod (8:16 light:dark) and cold ambient temperature (2°C). Deer mice populations are composed of phenotypes that differ in their reproductive response to environmental cues. These phenotypes also differ in body temperature regulation as indicated by their use of daily torpor. By comparing BAT responses among individuals of different phenotypes, we were able to assess the association between environmentally induced changes in reproduction and metabolism. Short/cold days caused increased proliferation of BAT and higher cytochrome oxidase activity. However, the magnitude of these changes varied with reproductive phenotype and use of daily torpor. BAT weight in short/cold day exposed males with normal sized testes more than doubled while total cytochrome oxidase activity increased by 30% as compared to controls. In contrast, short/cold day exposed deer mice with atrophic testes that employed daily torpor exhibited a 64% increase in BAT weight and 100% increase in total cytochrome oxidase activity, compared to control mice. Cytochrome oxidase activity in nontorpid deer mice with atrophic testes was intermediate to these two groups. Our results demonstrate a response of BAT to short/cold days that varies with individual reproductive response. This finding suggests that there exists a common integrative mechanism for temperature and photoperiod to regulate both seasonal reproductive and metabolic adjustments.

Effects of early unilateral blur on the macaque's visual system. II. Anatomical observations

We studied the effects of early unilateral blur on the anatomical organization of the visual pathways in 8 macaque monkeys. Blur was induced in one eye, beginning 2-14 d after birth, by 0.5% atropine twice a day. Atropinization was stopped at 6-8 months of age, and the animals were studied for anatomy 3-24 months later. The retina and all other eye tissues showed normal histology. In the dorsal lateral geniculate nucleus (LGN), cells in parvocellular layers receiving input from the atropine-treated eye were 9-32% smaller and were more lightly stained than those in layers innervated by the untreated eye. These changes were generally larger in the LGN ipsilateral to the treated eye. LGN cell size changes were absent or much smaller in the magnocellular layers. In the striate cortex, the distribution of the oxidative enzyme cytochrome oxidase (CO) was markedly altered in layer 4C beta. Layer 4C beta is uniformly stained in normal animals, but showed a distinct pattern of alternating high and low CO bands in the atropine-treated animals; the bands of higher CO activity were narrower than the bands of lower activity and had a 857-1050 micron repeat. Fainter banding was seen in layers 4A, 4C alpha, and 6, but the density of the rows of dark CO-stained dots in layer 3 was unaffected. Double-labeling revealed that the narrow dark CO bands were associated with the centers of the ocular dominance columns devoted to the atropine-treated eye. The distribution of 14C-2-deoxyglucose uptake in visual cortex produced by 4.5-9 c/deg spatial frequency stimulation was strongly biased toward the untreated eye. The treated eye could, however, elicit reasonably strong uptake when stimulated with patterns containing lower spatial frequencies. These results suggest that unilateral neonatal blur preferentially affects the parvocellular layers of the LGN and layer 4C beta of striate cortex, which are the portions of the central visual system associated with the processing of information concerning fine spatial detail. These anatomical changes are consistent with the high spatial frequency loss of vision demonstrated behaviorally and electrophysiologically in the atropine eye-driven visual system of these same animals.

Comparative studies on mitochondria isolated from neuron-enriched and glia-enriched fractions of rabbit and beef brain.

Fractions enriched in neuronal and glial cells were obtained from dispersions of whole beef brain and rabbit cerebral cortex by large-scale density gradient centrifugation procedures. The fractions were characterized by appropriate microscopic observation. Mitochondria were then isolated from these fractions by differential centrifugation of their homogenates. The two different types of mitochondria were characterized with respect to certain enzyme activities, respiratory rate, rate of protein synthesis, and their buoyant density in sucrose gradients. The mitochondria from the neuron-enriched fraction were distinguished by a higher rate of incorporation of amino acids into protein, higher cytochrome oxidase activity, and a higher buoyant density in sucrose density gradients. Mitochondria from the glia-enriched fraction showed relatively high monoamine oxidase and Na(+)- and K(+)-stimulated ATPase activities. The rates of oxidation of various substrates and the acceptor control ratios did not differ appreciably between the two types of mitochondria. The difference in the buoyant density of mitochondria isolated from the neuron-enriched and glia-enriched cell fractions was utilized in attempts to separate neuronal and glial mitochondria from the mixed mitochondria obtained from whole brain homogenates in shallow sucrose gradients. The appearance of two peaks of cytochrome oxidase, monoamine oxidase, and protein concentration in such gradients shows the potential feasibility of such an approach.

Influence of Potassium Fertilization on Enzymatic Activity, Phenolic Content and Discoloration of Potatoes

SUMMARY— Ontario potatoes, representing a variety that is very susceptible to precooking blackening, were grown in each of two consecutive years at different levels of potassium fertilization. In each of the two years of the study, the discoloration and total phenolic content of tubers decreased as potash applications were increased from 140 to 400 or 540 lb. per acre. The differences in discoloration were significant at the 1% level and the differences in phenolic content at the 5% level. Potatoes grown at high levels of potassium fertilization had higher cytochrome oxidase activity than those grown at lower levels. Potassium fertilization had no significant effect on polyphenol oxidase activity. A positive correlation (0.830) was found between the phenolic content and discoloration of potatoes as affected by potassium fertilizer.

Cytochrome Oxidase in the Liver of the G3H Mouse with Carcinoma.

SummaryIn C3H female mice growing either spontaneous or transplanted breast carcinoma the cytochrome oxidase activity of liver homogenates decreased as the tumor attained an increasingly larger percentage of total body weight. On the other hand, confirming previous results with Rochester rats, an increase in the activity of this enzyme was found in liver homogenates from Sprague-Dawley rats bearing Walker carcinoma 256. In tumor-free animals, mice had significantly higher cytochrome oxidase activity than rats of either strain.