Respiration related neurons in the region of the nucleus tractus solitarius of the rabbit.

Systematic mapping of respiration-related units (RRUs) in the region of the nucleus tractus solitarius (NTS) was performed on rabbits anesthetized with urethane. Of 523 RRUs 295 (56%) were inspiratory (I), 130 (25%) expiratory (E) and 98 (19%) phase-spanning (PS). Such a large number of E and PS RRUs in NTS have not been reported in the cat. Six out of 16 I RRUs 6 of 13 E RRUs, and 1 of 3 PS RRUs had projections to contralateral cervical spinal cord. The 'no I inflation' test was conducted on 76 I and 38 E RRUs, of which 29 I RRUs were identified as I alpha and 31 as I beta. Thirteen E RRUs were inhibited and 6 facilitated by preceding lung inflation. Almost all types of respiratory neurons so far reported from different nuclei of cat's brainstem have been located in the NTS region of the rabbit.