Dynamics of neurotensin stores in the stellate ganglion of the cat

Neurotensin (NT) within the stellate ganglion (SG) of the cat is present in axon terminals of extrinsic, presumably preganglionic, neurons and may play a role in ganglionic transmission. NT content of the SG, and of the preganglionic axons which innervate it, was determined by radioimmunoassay in the anesthetized cat under various experimental conditions in order to understand the factors determining the size of the ganglionic NT stores. The immunoreactive NT (iNT) from extracts of SG and its preganglionic inputs (white rami T₂ and T₃, sympathetic trunk between SG and T₄ white ramus) coeluted with synaptic NT(1-13) on RP-HPLC. NT accumulated proximal to ligatures on the preganglionic inputs of the SG. The daily rate of axonal transport of NT, estimated from the accumulation, represents 28.7% of the ganglionic stores of NT. Preganglionic stimulation at 2 Hz for 100 min did not change ganglionic NT content. Preganglionic stimulation at 40 Hz reduced the NT content to 70.4 ± 1.8% of control in 10 min and to 34.7 ± 4.2% of control in 20 min. Additional 100 min of 40 Hz stimulation produced no further depletion. The residual iNT, which coeluted with NT^1-13, presumably represents a pool of unreleasable NT. Post-depletion recovery was complete in 7 days and showed an initial rapid phase over the first 24 h followed by a shower phase over the remaining 6 days. Pepsin treatment, which has previously been shown to generate iNT from NT precursor in liver and other tissues, provided no evidence of the NT precursor in extracts of SG and its preganglionic input. This suggests that NT undergoes complete maturation in the preganglionic neuron soma. Therefore, axonal transport seems the only mechanism available for replenishment of stimulus-depleted ganglionic stores of NT.