Research in animals and humans has shown that mastication maintains cognitive function in the hippocampus, a brain area important for learning and memory. Reduced mastication, an epidemiological risk factor for the development of dementia in humans, attenuates spatial memory and causes hippocampal neurons to deteriorate morphologically and functionally, especially in aged animals. Active mastication rescues the stress-attenuated hippocampal memory process in animals and attenuates the perception of stress in humans by suppressing endocrinological and autonomic stress responses. Active mastication further improves the performance of sustained cognitive tasks by increasing the activation of the hippocampus and the prefrontal cortex, the brain regions that are essential for cognitive processing. Abnormal mastication caused by experimental occlusal disharmony in animals produces chronic stress, which in turn suppresses spatial learning ability. The negative correlation between mastication and corticosteroids has raised the hypothesis that the suppression of the hypothalamic-pituitary-adrenal (HPA) axis by masticatory stimulation contributes, in part, to preserving cognitive functions associated with mastication. In the present review, we examine research pertaining to the mastication-induced amelioration of deficits in cognitive function, its possible relationship with the HPA axis, and the neuronal mechanisms that may be involved in this process in the hippocampus.

Mitochondria are the principal producers of energy in higher cells. Mitochondrial dysfunction is implicated in a variety of human diseases, including cancer and neurodegenerative disorders. Effective medical therapies for such diseases will ultimately require targeted delivery of therapeutic proteins or nucleic acids to the mitochondria, which will be achieved through innovations in the nanotechnology of intracellular trafficking. Here we describe a liposome-based carrier that delivers its macromolecular cargo to the mitochondrial interior via membrane fusion. These liposome particles, which we call MITO-Porters, carry octaarginine surface modifications to stimulate their entry into cells as intact vesicles (via macropinocytosis). We identified lipid compositions for the MITO-Porter which promote both its fusion with the mitochondrial membrane and the release of its cargo to the intra-mitochondrial compartment in living cells. Thus, the MITO-Porter holds promise as an efficacious system for the delivery of both large and small therapeutic molecules into mitochondria.

Gap junctions and the intercellular communication syncytium they form between glial cells are thought to play a critical role in glial maintenance of appropriate metabolic environments in neural tissues. We have previously suggested (Yamamoto et al., Brain Res. 508:313-319, '90) that the vast majority of astrocytes in rat brain express connexin43, one of several recently identified gap junction proteins. Here, we confirm ultrastructurally that astrocytes in a number of brain regions of rat are immunolabelled with an antibody against connexin43 and that neurons and oligodendrocytes are devoid of labelling. The distribution of connexin43 immunoreactivity throughout the brain is presented at the light microscope (LM) level. By LM, immunoreactive structures consisted primarily of round or elongated puncta ranging from 0.3 microns to 4 microns in length and of annular profiles ranging from 1 to 10 microns in diameter. Immunolabelled fibrous processes were only occasionally seen and no labelling was observed in astrocytic cell bodies. Long, linear arrays of puncta were rare in gray matter but were common in white matter where they were arranged parallel to myelinated fibers. Puncta organized in a honeycomb pattern were seen near the cerebral cortical surface and frequently around blood vessels. Regional immunoreaction density, which was a reflection of either the concentration or staining intensity of immunoreactive elements, was remarkably heterogeneous; dramatic differences in labelling intensity frequently delineated anatomical boundaries between adjacent nuclei. Abrupt as well as graded fluctuations of immunoreaction intensity were also observed within nuclear structures. By electron microscopy (EM), gap junctions of fibrous and protoplasmic astrocytes were intensely stained and labelled organelles were often observed intracellularly in areas near gap junctions. These junctions and the spread of immunoreaction product to perijunctional organelles in their vicinity were considered to correspond to puncta seen by LM. Labelling within astrocytic cell bodies was seen in only a few instances. In some brain areas, astrocytic processes commonly gave rise to immunoreactive lamellae that partially ensheathed neuronal cell bodies, axon terminals, dendrites, and synaptic glomeruli. Such lamellae were considered to correspond to immunoreactive annular profiles seen by LM. Perivascular endfoot processes of astrocytes displayed intense staining of their gap junctions and portions of their apposing membranes.(ABSTRACT TRUNCATED AT 400 WORDS)

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Astronauts experience osteoporosis‐like loss of bone mass because of microgravity conditions during space flight. To prevent bone loss, they need a riskless and antiresorptive drug. Melatonin is reported to suppress osteoclast function. However, no studies have examined the effects of melatonin on bone metabolism under microgravity conditions. We used goldfish scales as a bone model of coexisting osteoclasts and osteoblasts and demonstrated that mRNA expression level of acetylserotonin O‐methyltransferase, an enzyme essential for melatonin synthesis, decreased significantly under microgravity. During space flight, microgravity stimulated osteoclastic activity and significantly increased gene expression for osteoclast differentiation and activation. Melatonin treatment significantly stimulated Calcitonin (an osteoclast‐inhibiting hormone) mRNA expression and decreased the mRNA expression of receptor activator of nuclear factor κB ligand (a promoter of osteoclastogenesis), which coincided with suppressed gene expression levels for osteoclast functions. This is the first study to report the inhibitory effect of melatonin on osteoclastic activation by microgravity. We also observed a novel action pathway of melatonin on osteoclasts via an increase in CALCITONIN secretion. Melatonin could be the source of a potential novel drug to prevent bone loss during space flight.