Key result
Pulmonary stretch receptor afferents form monosynaptic connections with medial and ventrolateral tractus solitarius nuclei.
Pulmonary stretch receptors appear to have monosynaptic connections with neurons in specific regions of the tractus solitarius.
Hypothesis-generating for autonomic integration of pulmonary afferents in animals; leaves open translation to human cardiovascular reflexes.
Central projections of single slowly adapting pulmonary stretch receptors were mapped in the medulla by the technique of spike-triggered averaging of extracellular field potentials. Discharge of pulmonary stretch receptors was recorded in continuity from the nodose ganglion; this activity provided the trigger for an averaging computer. 2. These pulmonary stretch receptors were characterized by a linear increase in firing rate in response to increases in transpulmonary pressure, an adaptation index, and peripheral axonal and intramedullary conduction velocities. 3. In accordance with the terminology used by Munson and Sypert (21), three types of electrical potentials were observed for the projection of a pulmonary stretch receptor in the medulla. Axonal potentials were recorded when the brain stem electrode was in the vicinity of the afferent axon. Terminal potentials were recorded when the electrode was adjacent to terminations of the afferent axon. Focal synaptic potentials were recorded when the electrode was near postsynaptic units receiving input from the pulmonary stretch receptor. Maxima of terminal potentials were recorded in a region 1 mm rostral to the obex in the medial nucleus of the tractus solitarius (six cases), in the ventrolateral nucleus of the tractus solitarius (three cases), and in an area just dorsolateral to the tractus solitarius (two cases). Focal synaptic potentials for five pulmonary stretch receptors were observed in a region 1 mm rostral to obex. Maxima of these potentials were recorded in the medial nucleus of tractus solitarius (two cases), in the ventrolateral nucleus of tractus solitarius (two cases), and in an area just dorsolateral to the tractus solitarius (one case). 4. Occasionally both terminal and focal synaptic potentials were observed for the same pulmonary afferent. The difference in the latencies of these potentials fell within the range previously reported for monosynaptic connections of muscle spindle Ia and group II afferents for alpha-motoneurons. This suggests that the afferents of pulmonary stretch receptors have monosynaptic connections with neurons in the medial nucleus of the tractus solitarius, in the ventrolateral nucleus of the tractus solitarius, and in an area dorsolateral to the tractus solitarius.
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Berger et al. (1983) studied this question. Spike-triggered averaging of extracellular field potentials was evaluated on Central projections of single slowly adapting pulmonary stretch receptors. Pulmonary stretch receptor afferents have monosynaptic connections with neurons in the medial and ventrolateral nuclei of the tractus solitarius, and an area dorsolateral to it.