Antigen-induced synaptic plasticity in sympathetic ganglia from actively and passively sensitized guinea-pigs

Alterations in synaptic efficacy induced by antigen challenge to isolated superior cervical ganglia (SCG) were monitored by measuring the magnitude of the postganglionic compound action potential (CAP) elicited by electrical stimulation of the cervical sympathetic nerve trunk. Antigen-induced changes in the CAP were measured in SCG removed from actively and from passively sensitized guinea-pigs. Additionally, some SCG were sensitized in vitro by incubating naive ganglia 24 h in serum obtained from actively sensitized animals. Histamine released from SCG upon specific antigenic challenge was measured to assess the effectiveness of the two forms of sensitization. Challenging SCG isolated from passively or actively sensitized animals with the sensitizing antigen, ovalbumin (OVA), produced a sustained potentiation of the CAP lasting longer than 30 min (antigen-induced long-term potentiation, A-LTP) and a net increase in histamine release. Neither the magnitude nor duration of A-LTP induced by passive sensitization differed significantly (p < 0.05) from results after active sensitization. The existence of A-LTP in SCG following passive sensitization indicates that the afferent limb of the immune system is not required for the development of this phenomenon and that the immune cells and the mediators responsible for A-LTP are resident to sympathetic ganglia.