Increased cyclic AMP in in vitro regenerating frog sciatic nerves inhibits Schwann cell proliferation but has no effect on axonal outgrowth

Further characterization of 5-HT1A receptors in the goldfish retina: role of cyclic AMP in the regulation of the in vitro outgrowth of retinal explants

The presence of serotonin 5-HT1A receptors and their physiological role were further characterized in the goldfish retina. The effects of the 5-HT6/7 receptor antagonists pimozide, fluphenazine and amoxapine, the 5-HT1A receptor antagonist WAY-100,135, and the alkylating agent N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline, on the 5-HT1A receptor agonist [3H]8-hydroxy-2-(di-n-propylamino)tetralin binding to retinal membranes, were evaluated. In addition, the effects of serotonin, 8-hydroxy-2-(di-n-propylamino)tetralin, WAY-100,135, the adenylate cyclase inhibitors SQ22536 and MDL12330A, and the cyclic AMP analog 8-bromoadenosine-3':5' cyclic monophosphate were also studied on neuritic outgrowth from retinal explants. WAY-100,135 but not 5-HT6/7 receptor antagonists inhibited [3H]8-hydroxy-2-(di-n-propylamino)tetralin binding to retinal membranes N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline decreased [3H]8-hydroxy-2-(di-n-propylamino)tetralin binding sites up to 70%, while receptor turnover was similar to that reported in other tissues. Serotonin and 8-hydroxy-2-(di-n-propylamino)tetralin stimulated cyclic AMP production, both ex vivo and in vitro, and these increases were related to inhibition of neuritic outgrowth. The inhibitory effect was reduced by SQ22536 and by WAY-100,135, and was mimicked by 8-bromoadenosine-3':5'cyclic monophosphate. This study supports previous findings about the role of serotonin as a regulator of axonal outgrowth during in vitro regeneration of the goldfish retina and demonstrates that this effect is mediated, at least in part, by 5-HT1A receptors through a mechanism which involves an increase of cyclic AMP levels.

Protein kinase C inhibition has only a transient growth arresting effect on in vitro regenerating mouse sensory neurons

Adult mice sensory ganglia were cultured in an extracellular matrix gel. Analyses of extending axons were made 48 h (long-term) or immediately (short-term) after addition of protein kinase inhibitors. Long- and short-term growth was insensitive to protein kinase A/G inhibition by HA-1004. Long-term protein kinase C inhibition by chelerythrine affected only certain, long axons. In the short-term virtually all axon growth was arrested, but largely recovered on the following day. When combined, the drugs inhibited all long- and short-term growth and largely prevented the recovery of the latter. The transient effect by chelerythrine, and the permanent inhibition after combination with HA-1004, suggests compensatory mechanisms, perhaps via other kinases.

In vitro central nervous system models of mechanically induced trauma: a review

Injury is one of the leading causes of death among all people below the age of 45 years. In the United States, traumatic brain injury (TBI) and spinal cord injury (SCI) together are responsible for an estimated 90,000 disabled persons annually. To improve treatment of the patient and thereby decrease the associated mortality, morbidity, and cost, several in vivo models of central nervous system (CNS) injury have been developed and characterized over the past two decades. To complement the ability of these in vivo models to reproduce the sequelae of human CNS injury, in vitro models of neuronal injury have also been developed. Despite the inherent simplifications of these in vitro systems, many aspects of the posttraumatic sequelae are faithfully reproduced in cultured cells, including ultrastructural changes, ionic derangements, alterations in electrophysiology, and free radical generation. This review presents a number of these in vitro systems, detailing the mechanical stimuli, the types of tissue injured, and the in vivo injury conditions most closely reproduced by the models. The data generated with these systems is then compared and contrasted with data from in vivo models of CNS injury. We believe that in vitro models of mechanical injury will continue to be a valuable tool to study the cellular consequences and evaluate the potential therapeutic strategies for the treatment of traumatic injury of the CNS.

Protein kinase C and mouse sciatic nerve regeneration

We have studied the role of protein kinase C (PKC) in peripheral nerve regeneration by using the cultured adult mouse sciatic nerve, which displays regrowth of sensory axons under serum-free conditions. By the use of immunohistochemistry we show that one of the isoforms of PKC, PKC beta, is present in the nerve cell bodies of normal nerves and is upregulated after injury. In spite of this, the specific PKC inhibitor chelerythrine at 5 microM, a concentration well above its IC50 value for PKC, failed to reduce the outgrowth distance of new axons. This was not due to impermeability of the drug, since the same concentration caused a clear reduction of the injury-induced proliferation of Schwann cells in the crush region. Likewise, HA-1004, an inhibitor of cyclic nucleotide-dependent protein kinases, also lacked effect on outgrowth when used on its own, even at very high concentrations (100 microM). In contrast, outgrowth was significantly reduced when 5 microM chelerythrine and 5 microM HA-1004 were used in combination. In conclusion, the present results suggest that PKC-activity is important but not indispensable for the regeneration process. Successful completion of the latter could be achieved by several, perhaps redundant, phosphorylation systems.