Small reduction of neurokinin-1 receptor-expressing neurons in the pre-Bötzinger complex area induces abnormal breathing periods in awake goats

Abstract

In awake rats, >80% bilateral reduction of neurokinin-1 receptor (NK1R)-expressing neurons in the pre-Bötzinger complex (pre-BötzC) resulted in hypoventilation and an "ataxic" breathing pattern (Gray PA, Rekling JC, Bocchiaro CM, Feldman JL, Science 286: 1566-1568, 1999). Accordingly, the present study was designed to gain further insight into the role of the pre-BötzC area NK1R-expressing neurons in the control of breathing during physiological conditions. Microtubules were chronically implanted bilaterally into the medulla of adult goats. After recovery from surgery, the neurotoxin saporin conjugated to substance P, specific for NK1R-expressing neurons, was bilaterally injected (50 pM in 10 microl) into the pre-BötzC area during the awake state (n = 8). In unoperated goats, 34 +/- 0.01% of the pre-BötzC area neurons are immunoreactive for the NK1R, but, in goats after bilateral injection of SP-SAP into the pre-BötzC area, NK1R immunoreactivity was reduced to 22.5 +/- 2.5% (29% decrease, P < 0.01). Ten to fourteen days after the injection, the frequency of abnormal breathing periods was sixfold greater than before injection (107.8 +/- 21.8/h, P < 0.001). Fifty-six percent of these periods were breaths of varying duration and volume with an altered respiratory muscle activation pattern, whereas the remaining were rapid, complete breaths with coordinated inspiratory-expiratory cycles. The rate of occurrence and characteristics of abnormal breathing periods were not altered during a CO2 inhalation-induced hyperpnea. Pathological breathing patterns were eliminated during non-rapid eye movement sleep in seven of eight goats, but they frequently occurred on arousal from non-rapid eye movement sleep. We conclude that a moderate reduction in pre-BötzC NK1R-expressing neurons results in state-dependent transient changes in respiratory rhythm and/or eupneic respiratory muscle activation patterns.

Focal acidosis in the pre-Bötzinger complex area of awake goats induces a mild tachypnea

“…2). This location of all of the MTs was consistent with the previously reported stereotaxic definition of the preBötzC in goats (36). Physiological confirmation of correct MT placement in the goats studied herein is provided by the characteristic tachypnea (Fig.…”

“…Previously reported data from our laboratory (36), together with data shown in Fig. 1 of this paper, establish that, in goats, there is a high density of neurokinin-1-positive neurons in an area that is just ventral to NA and medial to the spinal Fig.…”

“…An occipital craniotomy was created, and the dura mater was excised to expose the posterior cerebellum and the dorsal aspect of the medulla for visualization of obex. Using previously delineated coordinates of the preBötzC in goats (36,37), the MTs were implanted 2.5-3.5 mm rostral to obex, 4 -5 mm lateral to the midline, and extending 5-7 mm from the dorsal surface of the medulla.…”

“…Electrophysiological recordings of in vitro preparations have shown that neurons in the retrotrapezoid nucleus, nucleus of the solitary tract, the medullary raphe nucleus (MRN), locus coeruleus, and the pre-Bötzinger complex (preBötzC) increase discharge frequency when the pH in the bathing solution is reduced (3,5,8,14,22,24). Studies in anesthetized preparations that either created a focal acidosis (FA) or assessed the effects of lesions on the hypercapnic ventilatory response also support the concept of widespread chemosensitivity in the medulla, pons, and cerebellum (11,18,32,33,35,36,37).While the in vivo data, under physiological conditions, suggest that chemoreceptors at multiple sites influence breathing, the observed ventilatory effects are not uniform, and the hyperpnea is small, with FA at a single site compared with the hyperpnea observed during a global brain acidosis. In the awake goat, microdialyzing (MD) hypercapnic mock cerebral spinal fluid (mCSF), which decreases extracellular fluid (ECF) pH by 0.018 in one area of the MRN, increases pulmonary ventilation (V I) by 12% (10), while a comparable global brain acidosis resulting from 2.5% inspired CO 2 increases breathing by 100% (10).…”

“…Electrophysiological recordings of in vitro preparations have shown that neurons in the retrotrapezoid nucleus, nucleus of the solitary tract, the medullary raphe nucleus (MRN), locus coeruleus, and the pre-Bötzinger complex (preBötzC) increase discharge frequency when the pH in the bathing solution is reduced (3,5,8,14,22,24). Studies in anesthetized preparations that either created a focal acidosis (FA) or assessed the effects of lesions on the hypercapnic ventilatory response also support the concept of widespread chemosensitivity in the medulla, pons, and cerebellum (11,18,32,33,35,36,37).…”