TROPHIC FACTORS FROM CHROMAFFIN GRANULES PROMOTE SURVIVAL OF PERIPHERAL AND CENTRAL-NERVOUS-SYSTEM NEURONS

Chromaffin cells of the adrenal medulla were used to study the release of neurotrophic factors operationally defined by their capacity to pr omote the in vitro survival of embryonic neurons from the peripheral a nd central nervous system. Chromaffin cells are closely related to sym pathetic neurons in terms of their transmitters and specific proteins and, like sympathetic neurons, receive preganglionic cholinergic, amin ergic and peptidergic neuronal inputs. The issue of whether chromaffin cells store and secrete neurotrophic factors is therefore pertinent t o the question whether trophic mechanisms may be involved in neuronal interactions and what modes of secretion are employed to liberate neur otrophic factors from neurons. Cell culture media conditioned by purif ied bovine chromaffin cells supported several neuron populations in vi tro. Stimulation of the chromaffin cells with the cholinergic agonist carbachol (10(-4) M) increased in parallel the output of neurotrophic factor activity (assayed on chick ciliary ganglionic neurons) as well as two components specifically located in chromaffin granules, chromog ranin A and catecholamines. The release of all three components was pa rtially blocked by the Ca2+ channel blocker verapamil (10(-5) M), sugg esting co-storage and -release of neurotrophic factors, chromogranin A and catecholamines in/from chromaffin granules. Neurotrophic factor a ctivity for ciliary ganglionic neurons accumulating in the medium of u nstimulated chromaffin cells decreased with time, and so did catechola mines. In contrast, amounts of neurotrophic factors and catecholamines released by challenging cells with carbachol did not significantly de cline up to 62 h. The neurotrophic factor activity tested on chick cil iary, sensory and spinal cord neurons as well as on rat hippocampal ne urons was heat- and trypsin-labile and could not be blocked by polyclo nal antibodies against bovine nerve growth factor and the chromogranin A, B, and C. Defined fragments of chromogranin A and pancreastatin we re devoid of neurotrophic activity. Our results suggest the presence o f one or several neurotrophic factors in chromaffin granules, which ca n be released by exocytosis and may be potentially relevant for the ma intenance of neurons innervating the adrenal medulla.