Proceedings of The Physiological Society

University College London 2006 (2006) Proc Physiol Soc 3, PC212

Poster Communications

Unilateral ablation of neurokinin-1 receptor-expressing (NK1R) neurones within the pre-Bötzinger complex (preBötC) in adult rats disrupts breathing during sleep but not during wakefulness

Leanne Campbell McKay1, Jack L Feldman1

1. Neurobiology, UCLA, Los Angeles, CA, USA.

In adult rats, as the number of ablated preBötC NK1R neurones increases, breathing becomes increasingly disrupted during sleep [1], eventually resulting in an ataxic breathing pattern during wakefulness when cell loss is >80% [2]. Here we determine whether ablation of fewer preBötC NKIR neurones leads to sleep-disordered breathing (SDB). Adult male Sprague Dawley rats (n=8) were anaesthetised (100mg/kg ketamine, 10mg/kg xylazine i.p.) and instrumented to record diaphragmatic, abdominal and neck EMG, ECG, and EEG. Fourteen days post-implantation a second surgery was performed (anaesthesia as before) to stereotaxically inject unilaterally into the preBötC, either the toxin saporin conjugated to substance P (SP-SAP), which selectively ablates NK1R neurones (n=4) or as a control, SP mixed with SAP (unconjugated) that does not ablate NK1R neurones (n=4). Rats were kept on a 12-hour light/dark cycle and monitored within a plethysmograph from day 1 post-injection until they were humanely killed (days 21-50). Post SP-SAP injection, respiratory pattern remained unchanged during wakefulness. During sleep, particularly REM sleep, respiratory pattern became increasingly disordered at ~day 9 post SP-SAP injection, compared to pre-injection control. The disruptions in breathing pattern were characterised by an increase in frequency of apnoeas and hypopnea (~4-6/hour of sleep vs <3 control; p<0.05). To test responses to respiratory challenges, rats were exposed to hypercapnia (5% CO2) and hypoxia (8% O2) during wakefulness. All SP-SAP injected rats responded by increasing ventilation in a manner similar to pre-injection control until ~day 12 post-injection. Beyond this point SP-SAP injected rats were unable to increase ventilation appropriately (breaths/min: 120±15 vs 150±11 in 5% CO2; 136±12 vs 180±8 in 8% O2, p<0.05 post-injection vs pre-injection; mean±S.E.M.). Statistical analysis was performed using ANOVA. Rats that were monitored up to 50 days post SP-SAP injection continued to have SDB, while breathing during resting wakefulness remained normal. Unlike bilateral SP-SAP injected rats, an ataxic breathing pattern [1,2] did not develop during wakefulness. Histological analysis of the ventrolateral medulla confirmed that only NKIR neurones within the preBötC on one side of the medulla were ablated. There are ~300 preBötC NK1R neurones/side in the adult rat. Ablation of half of these neurones by unilateral SP-SAP injection results in SDB, while breathing during resting wakefulness appears normal, however, when the respiratory system is challenged during wakefulness it does not respond appropriately. We have previously proposed that in the elderly and in individuals who suffer from various neurodegenerative diseases, loss of preBötC NK1R neurones over time may explain why SDB is highly prevalent in these populations.

Where applicable, experiments conform with Society ethical requirements