The development of oxidative metabolism in diencephalic structures of the rat: a quantitative study

Akkermansia muciniphila and environmental enrichment reverse cognitive impairment associated with high-fat high-cholesterol consumption in rats

Nonalcoholic steatohepatitis (NASH) is one of the most prevalent diseases globally. A high-fat, high-cholesterol (HFHC) diet leads to an early NASH model. It has been suggested that gut microbiota mediates the effects of diet through the microbiota-gut-brain axis, modifying the host's brain metabolism and disrupting cognition. Here, we target NASH-induced cognitive damage by testing the impact of environmental enrichment (EE) and the administration of either Lacticaseibacillus rhamnosus GG (LGG) or Akkermansia muciniphila CIP107961 (AKK). EE and AKK, but not LGG, reverse the HFHC-induced cognitive dysfunction, including impaired spatial working memory and novel object recognition; however, whereas AKK restores brain metabolism, EE results in an overall decrease. Moreover, AKK and LGG did not induce major rearrangements in the intestinal microbiota, with only slight changes in bacterial composition and diversity, whereas EE led to an increase in Firmicutes and Verrucomicrobia members. Our findings illustrate the interplay between gut microbiota, the host's brain energy metabolism, and cognition. In addition, the findings suggest intervention strategies, such as the administration of AKK, for the management of the cognitive dysfunction related to NASH.

Neurobehavioral dysfunction in non-alcoholic steatohepatitis is associated with hyperammonemia, gut dysbiosis, and metabolic and functional brain regional deficits

Non-alcoholic steatohepatitis (NASH) is one of the most prevalent diseases worldwide. While it has been suggested to cause nervous impairment, its neurophysiological basis remains unknown. Therefore, the aim of this study is to unravel the effects of NASH, through the interrelationship of liver, gut microbiota, and nervous system, on the brain and human behavior. To this end, 40 Sprague-Dawley rats were divided into a control group that received normal chow and a NASH group that received a high-fat, high-cholesterol diet. Our results show that 14 weeks of the high-fat, high-cholesterol diet induced clinical conditions such as NASH, including steatosis and increased levels of ammonia. Rats in the NASH group also demonstrated evidence of gut dysbiosis and decreased levels of short-chain fatty acids in the gut. This may explain the deficits in cognitive ability observed in the NASH group, including their depressive-like behavior and short-term memory impairment characterized in part by deficits in social recognition and prefrontal cortex-dependent spatial working memory. We also reported the impact of this NASH-like condition on metabolic and functional processes. Brain tissue demonstrated lower levels of metabolic brain activity in the prefrontal cortex, thalamus, hippocampus, amygdala, and mammillary bodies, accompanied by a decrease in dopamine levels in the prefrontal cortex and cerebellum and a decrease in noradrenalin in the striatum. In this article, we emphasize the important role of ammonia and gut-derived bacterial toxins in liver-gut-brain neurodegeneration and discuss the metabolic and functional brain regional deficits and behavioral impairments in NASH.

Altered metabolic activity in the developing brain of rats predisposed to high versus low depression-like behavior

Individual differences in human temperament can increase the risk of psychiatric disorders like depression and anxiety. Our laboratory utilized a rat model of temperamental differences to assess neurodevelopmental factors underlying emotional behavior differences. Rats selectively bred for low novelty exploration (Low Responders, LR) display high levels of anxiety- and depression-like behavior compared to High Novelty Responder (HR) rats. Using transcriptome profiling, the present study uncovered vast gene expression differences in the early postnatal HR versus LR limbic brain, including changes in genes involved in cellular metabolism. These data led us to hypothesize that rats prone to high (versus low) anxiety/depression-like behavior exhibit distinct patterns of brain metabolism during the first weeks of life, which may reflect disparate patterns of synaptogenesis and brain circuit development. Thus, in a second experiment we examined activity of cytochrome C oxidase (COX), an enzyme responsible for ATP production and a correlate of metabolic activity, to explore functional energetic differences in the HR/LR early postnatal brain. We found that HR rats display higher COX activity in the amygdala and specific hippocampal subregions compared to LRs during the first 2 weeks of life. Correlational analysis examining COX levels across several brain regions and multiple early postnatal time points suggested desynchronization in the developmental timeline of the limbic HR versus LR brain during the first two postnatal weeks. These early divergent COX activity levels may reflect altered circuitry or synaptic activity in the early postnatal HR/LR brain, which could contribute to the emergence of their distinct behavioral phenotypes.

Prehepatic portal hypertension induces alterations in cytochrome oxidase activity in the rat adrenal gland

One approach to assess neuroendocrine response to portal hypertension in short-term portal vein-stenosed rats consists in studying metabolic and functional activity patterns in adrenal glands using mitochondrial enzyme cytochrome c oxidase (COX) as a histochemical marker. Male Wistar rats were divided into two groups: a control group (Group I; n = 8), in which the animals did not undergo any operative intervention, and a triple calibrated portal vein stenosis group (TPVS) (Group II; n = 7). The sections of suprarenal glands were histochemically stained for COX and the optical densitometry was measured by a computer image analyzer attached to a microscope. In TPVS rats, COX activity in the adrenal gland cortex is lower than in control rats and affects the fascicular (52.30, 47.16-60.98, vs. 67.12, 60.31-73.89, p = .002), glomerular (49.68, 46.19-53.56 vs. 70.47, 64.64-73.51, p < .001), and reticular (47.35, 35.63-54.39, vs. 55.37, 49.76-58.97; p < .05) layers. In contrast, COX activity in the adrenal gland medulla is similar in TPVS rats and in control rats (29.91, 29.54-31.18, vs. 29.67, 28.95-30.23). The changes in adrenocortical COX activity in short-term-TPVS rats could constitute a pathogenic factor for both splanchnic and systemic hyperdynamic circulations, described in this experimental model of prehepatic portal hypertension.

Age-related and laminar-specific dendritic changes in the medial frontal cortex of the rat

Early hypotheses that normal brain aging involves widespread loss of neurons have been revised in light of accumulating evidence that, in most regions of the brain, the number of neurons is stable throughout adulthood and senescence. It is not clear, however, that all aspects of neuronal structure are similarly maintained, and anatomical changes are likely to contribute to age-related declines in cognitive function. The extent and pattern of dendritic branches is one likely target for age-dependent regulation since dendrites remain plastic into adulthood and since dendrites, as the site of most synapses, critically regulate neuronal function. This study quantified the dendritic extent and geometry of superficial and deep pyramidal neurons in the medial frontal cortex of Brown Norway rats from young adulthood through senescence. This region of cortex is of specific interest given its involvement in a variety of cognitive functions that change with age. In the present study, age-related changes in dendritic extent were found to occur with remarkable specificity. Superficial, but not deep, pyramidal neurons exhibited ongoing dendritic growth after 2 months-of-age and then dendritic regression after 18 months-of-age. Apical and basal dendrites were similarly regulated; in each arbor adult growth and regression were limited to terminal dendritic segments. The focal specificity of age-related changes suggests several possible regulatory mechanisms, including regional changes in trophic support and in neuronal activity. Although restricted to specific neuronal populations, dendritic regression in aged animals is likely to contribute to cognitive changes associated with senescence.

Cytochrome oxidase activity of the suprachiasmatic nucleus and pineal gland in rats with portacaval shunt

Rhythmic behavioral and biochemical changes have been observed in both human and animal models with hepatic insufficiency. The basis of all these alterations is the principal endogenous pacemaker, the suprachiasmatic nucleus. The aim of this work, therefore, is to determine cytochrome c oxidase activity, a marker of neuronal activity and oxidative metabolism, in this nucleus in rats with portacaval shunt. In order to do this, this enzyme was histochemically marked and quantified by computer-assisted optical densitometry. Results show a reduced cytochrome oxidase activity in the suprachiasmatic nucleus in animals with portacaval shunts and, inversely, an increase in oxidative metabolism in the pineal gland, another circadian structure. However, the activity measured in a noncircadian brain structure, the hippocampus, which served as a control, showed no changes with surgery. Additionally, locomotor activity was assessed by actimeters and revealed a clearly reduced activity in animals with portacaval shunt. We conclude that the suprachiasmatic nucleus is possibly involved in the rhythmic changes associated with hepatic insufficiency.

Undernutrition and Postnatal Development of Brain Oxidative Metabolism in Limbic Structures: A Quantitative Study

The effects of food restriction during gestation, lactation and post-weaning were studied in rat brain structures (14,21 and 30 days). Oxidative metabolism was quantified in neurons from the anterior thalamus and mammillary bodies using a quantitative histochemical method for cytochrome c oxidase (CO). In all the rat brains studied, a significant increase in activity occurred in the control group from 14 to 21 days after birth which then remained constant up to 30 days. A similar pattern was observed in the undernourished group, although in the anterodorsal and anteromedial thalamic nuclei the rise in CO only occurred between day 14 and 30 and there were no significant age-related changes in the lateral mammillary nucleus. Undernutrition produced a significant drop in CO activity after 21 days in all the nuclei except the lateral mammillary nucleus. In the latter nucleus and also in the pars medialis of the medial mammillary nucleus this parameter decreased at 30 days. Our results suggest that undernutrition and nutritional rehabilitation have different effects on the diencephalic regions studied, which depends on age and region.

Glial and neuronal cell numbers and cytochrome oxidase activity in CA1 and CA3 during postnatal development and aging of the rat

Stereological methods (neuron and glial cell numbers) and histochemical methods (cytochrome c oxidase) were used to study postnatal development and aging of the CA1 and CA3 hippocampal areas in male rats. No changes were observed in 10 microns sections in the neuronal population of areas CA1 and CA3 in any of the groups (14 days, 21 days, adult-90 days and elderly-22 months). Statistical differences were found in the number of glial cells in both the CA1 and CA3 areas. An increase was observed in cytochrome oxidase (CO) activity in the CA1 area in the 14 day old rats compared to the other groups while in area CA3 this parameter increased in the 14 and 21 day old groups and the group of adult rats. No significant changes in CO activity were found in the elderly rats in both areas. These results are discussed in the light of those recorded in other areas of the limbic system.

Changes of cytochrome oxidase activity in rat suprachiasmatic nucleus

This paper evaluates the changes of cytochrome oxidase (CO) activity that take place in the suprachiasmatic nucleus (SCN) during the light-dark cycle. CO is a mitochondrial energy-generating enzyme used as a marker of neural oxidative metabolism. We measured CO activity using quantitative histochemistry calibrated with brain tissue standards and a computerized analysis image system. The results indicate that the CO enzyme activity changes on the basis of a circadian pattern, with the higher levels during the light phase (P < 0.0001). These changes are detected over a period of hours, in accordance with other studies on the possible short-term regulation of CO activity in the nervous system. It is, therefore, possible to apply this methodology to the study of the SCN and other brain areas which show functional rhythmicity.