Mitotic activity of the pars intermedia in the female mouse: age-associated variations in proliferation rate and circadian periodicity

We previously reported daily variations in the mitotic activity of the endocrine cells in the pars intermedia of 21- and 28-day-old male mice. Since cellular proliferation might be affected by factors such as sex and age, we undertook the present experiments to study the mitotic activity of the pars intermedia from 14-, 28-, and 150-day-old female mice. Inbred C3H/S mice, grouped according to age, were housed under standard conditions (12h each of light and dark [LD 12:12]) for periodicity analysis and were killed in lots of 5-11 animals every 4h over a single 24h cycle, with each mouse receiving 2 μg/g of colchicine 4h before decapitation. Pituitaries were excised, extracted, fixed in buffered formaldehyde, embedded in celloidin-paraffin, sectioned at 5 μm, and stained with hematoxylin and eosin. We counted the total number of nuclei to estimate the total number of cells monitored and then calculated the mitotic index (metaphases/1000 nuclei). Differences were analyzed for statistical significance by the Student t test. While the 14-day-old animals manifested no significant changes in mitotic activity during the 24h cycle, the 28- and 150-day-old mice showed higher mitotic indices during the period of darkness. The average mitotic activity over the entire cycle, however, was higher in the two groups of younger animals than in the 150-day-old mice. Moreover, the averages for the 28-day-old females were higher than the corresponding values previously reported by us for male mice of the same age. (Chronobiology International, 17(6), 751-756, 2000)     

The circadian clock in the brain: a structural and functional comparison between mammals and insects

The circadian master clocks in the brains of mammals and insects are compared in respect to location, organization and function. They show astonishing similarities. Both clocks are anatomically and functionally connected to the optic system and possess multiple output pathways allowing synchronization with the environmental light-dark cycles as well as the control of diverse endocrine, autonomic and behavioral functions. Both circadian master clocks are composed of multiple neurons, which are organized in populations with different morphology, physiology and neurotransmitter content and appear to subserve different functions. In the hamster and in the cockroach, the master clock consists of a core region that gets input from the eyes, and a shell region from which the majority of output projections originate. Communication between core and shell, between all other populations of clock neurons as well as between the master clocks of both brain hemispheres is a prerequisite of normal rhythmic function. Phenomena like rhythm splitting and internal desynchronization can be observed under constant light conditions and are caused by the uncoupling of the master clocks of both brain hemispheres.     

Internal desynchronization of the circadian activity and feeding rhythm in an owl monkey (Aotus lemurinus griseimembra): a case study

In the free-running circadian locomotor activity rhythm of a 7-year-old male owl monkey (Aotus lemurinus griseimembra) kept under constant light and climatic conditions (LL 0.2 lux, 25°C ± 1°C, 60 ± 5% relative humidity [RH]), a second rhythm component developed that showed strong relative coordination with the free-running activity rhythm of 24.4h and a 24h rhythm. The simultaneously recorded feeding activity rhythm strongly resembled this rhythm component. Therefore, it seems justified to infer that there was an internal desynchronization between the two behavioral rhythms or their circadian pacemakers, that is, between the light-entrainable oscillator located in the suprachiasmatic nuclei (SCN) and a food-entrainable oscillator located outside the SCN. This internal desynchronization may have been induced and/or maintained by a zeitgeber effect of the (irregular) 24h feeding schedule on the food-entrainable oscillator. The weak relative coordination shown by the activity rhythm indicates a much weaker coupling of the light-entrainable oscillator to the food-entrainable oscillator than vice versa. (Chronobiology International, 17(2), 147-153, 2000)     

The macrophage system in the intestinal muscularis externa during inflammation: an immunohistochemical and quantitative study of osteopetrotic mice

Intestinal inflammation results in disturbed intestinal motility in humans as well as in animal models. This altered function of smooth muscle cells and/or the enteric nervous system may be caused by activation of macrophages in muscularis externa and a thereby following release of cytokines and chemokines that causes influx of mononuclear cells and neutrophilic granulocytes. We subjected osteopetrotic (op/op) mice that lack certain macrophage subtypes, e.g. macrophages in the muscularis externa and +/+ mice to LPS to induce inflammatory cell influx. The densities of F4/80⁺, MHCII⁺, and myeloperoxidase⁺ cells were quantified using stereological sampling. In +/+ mice we found that MHCII⁺ cells outnumber F4/80⁺ cells and that LPS injection increased the density of MHCII⁺ cells temporarily but not that of F4/80⁺ cells. This indicates that an upregulation of MHCII antigen takes place and that two or more macrophage subtypes with comparable morphologies exist. Osteopetrotic mice lacked MHCII⁺, CD169⁺, and F4/80⁺ cells after either treatment, which indicate that these cells are CSF-1-dependent. LPS induced VCAM-1 activation of the vessels, modest influx of granulocytes, as well as an iNOS-activation in a cell type different from macrophages in both +/+ and op/op mice.