Evidence for bilateral vagal innervation of postganglionic parasympathetic neurons in chicken heart

Summary

Stimulation of the cervical vagus nerves caused an output of acetylcholine (ACh) from the isolated chicken heart, which almost exclusively was released from the postganglionic neurons: (+)-tubocurarine (3×10⁻⁴ M) reduced the output to 12±6% (n=7) of the control. Stimulation of the two nerve trunks was equally effective in releasing ACh.-Evidence that a large number of postganglionic neurons receives bilateral innervation was based on two experimental series. (1.) The sum of the ACh outputs evoked by unilateral (separate) nerve stimulation of the right and the left vagus was higher than the bilaterally evoked output (100%) and increased with increasing frequencies (10, 20 and 40 Hz) from 115±13% to 131±9% (n=13). In the presence of 10⁻⁴ M 4-aminopyridine, unilaterally evoked output (40 Hz) was further increased from 131 to 176±5% (n=21).-(2.) In the presence of 4-aminopyridine plus hemicholinium-3 (2×10⁻⁵ M), unilateral nerve stimulation at 40 Hz evoked an output of ACh that decreased from 477 to 79 pmol g⁻¹min⁻¹ during a 20 min-period of stimulation due to transmitter depletion. Thereafter output of ACh evoked by stimulation of the contralateral nerve was reduced by 73% as compared to the control value (475 pmol g⁻¹min⁻¹; output without the preceding 20 min-stimulation).-It is concluded that a large number of parasympathetic postganglionic neurons of the chicken heart receives a dual excitatory input from both right and left vagus nerve.