Local and systemic autonomic nervous effects on cell migration to the spleen.

This work is based on the hypothesis that sympathetic nerves regulate the uptake of circulating cells by the spleen by affecting splenic blood flow and that the quantity of cells sequestered depends on whether changes in noradrenergic transmission occur at local or systemic levels. Fluorescently labeled lymphoid cells were injected into rats, and organ blood flow was measured by the microsphere method. Increased retention of cells in the spleen paralleled by increased blood flow was detected after local denervation of this organ or administration of bacterial endotoxin. A comparable enhanced splenic blood flow was observed after general sympathectomy. However, the redistribution of blood perfusion during general vasodilatation resulted in deviation of leukocyte flow from the spleen, thus resulting in reduced uptake of cells by this organ. These results indicate that, although the uptake of cells by the spleen depends on arterial blood supply, enhanced perfusion does not always result in increased cell sequestration because general vasodilatation reduces cell uptake by this organ and even overrides stimulatory effects of endotoxin.

Interactions of temperature and angiotensin II in paraventricular neurons of rats in vitro.

We recorded extracellular impulse activity of hypothalamic paraventricular neurons ( n=75) in rat brain slices during application of angiotensin II (ANG II, 10(-9)-10(-6) M) and/or temperature changes (32-42 degrees C). ANG II, with a threshold concentration of 10(-8) M, increased the firing rate in more than 80% of the neurons with strongest excitations occurring in bursting neurons. Increasing the temperature also raised the discharge rate in the majority of the neurons, often together with enhanced burst discharges. When ANG II was applied during ongoing sinusoidal temperature changes, its effects were more pronounced at elevated temperatures. These electrophysiological data illustrate that stimulus-encoding properties at the neuronal level can contribute to the interactions between osmoregulatory and thermoregulatory mechanisms including mutual sensitization when different stimuli (here: ANG II and temperature changes) are applied simultaneously.