Anatomical and functional connections between the locus coeruleus (LC) and the nucleus of the solitary tract (NTS) in neonatal rats

Abstract

To study the communication among chemosensitive brainstem areas, we injected rhodamine beads into the LC in rat pups (P7–P10). After 8–10 days, retrograde labeling was seen in the brainstem, including neurons from many chemosensitive regions, such as contralateral LC, caudal NTS (cNTS), retrotrapezoid nucleus, medullary raphé and periaqueductal gray. Similar connections were seen with cNTS injection, although less labeling was seen in each area. We patched cNTS neurons that project to the LC and found that 4 of 5 retrogradely‐labeled cNTS neurons had increased firing rate (FR) in response to hypercapnic acidosis (HA‐15% CO2), even in synaptic blockade medium (SNB—high Mg2+/low Ca2+). In contrast, 2 of 3 retrogradely‐labeled LC neurons that project to the cNTS had reduced FR in response to HA both in the presence and absence of SNB. We loaded the patched neuron with Lucifer Yellow (LY) from the pipette and verified that the neuron was labeled for both rhodamine and LY. Our studies show: extensive connections among chemosensitive brainstem regions; HA‐induced increased FR of cNTS neurons results in increased action potentials (APs) to the LC; and HA‐induced decreased FR of LC neurons results in reduced APs to cNTS neurons. Complex interactions clearly exist among chemosensitive regions within the central respiratory control network.Supported by FAPESP, CAPES, CNPq, NIH R01‐HL‐56683 and WSU Research Incentive Grant