Astrocytes have glutamate-induced rhythmic fluctuation of Ca2+ in their cytosol. The pituicyte, an astrocytic cell in the pituitary gland's neural lobe , is bathed by neurosecretory peptides:vasopressin, dynorphin and oxytocin, released from axon terminals. Is there a release of Ca2+ into the cytosol of pituicytes in response to stimulation with these peptides? Shifts in the compartmentalization of Ca2+, which fluoresces when it form a complex with fluo-3, is monitored by fluorescence changes detected with video enhanced microscopy. In pilot experiments, 100 micromoles or more of arginine vasopressin, added to pituicytes pre-loaded with fluo-3 and maintained at room temperature, results in the release of Ca2+ which pulses only once. Glutamate (100 micromoles) or unphysiological amounts (e.g., 1 mM) of dynorphin do not trigger Ca2+ release in pituicytes. Do pituicytes respond to osmolarity change, a stimulus for the neurons with which they are associated? The addition of 0.5 g % sucrose to the cells had no effect on Ca2+ release. Repetition of the experiments at 37 degrees C may yield different results. Exposure of pituicytes to 10 micromoles dynorphin for 5 m induces the expression of the proto-oncogene c-fos. The response is diminished by 30 m and disappears over 3 hours. The other peptides and neurotransmitters are to be used as well. Whether pituicytes have a trophic effect on neurosecretory axons is to be tested in vitro.
