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A Perez-Burgos1, B Wang1, B Mistry1, J Bienenstock1, W Kunze2

1McMaster Brain-Body Institute St Joseph's Healthcare; 2The Farncombe Family Digestive Health Research Institute, Hamilton, ON
Brain function may be altered by ingesting certain symbiotic microorganisms; an effect that may be very important therapeutically. Bravo et al (1) reported that ingestion of Lactobacillus rhamnosus (JB-1) induces alterations in mRNA expression of GABA A and B receptors in widespread regions of the mouse brain. JB-1 also reduced anxiety-like behaviour. Severing the vagus nerve subdiaphragmatically before feeding the probiotic eliminated the central actions of JB-11.
We have previously shown that when JB-1 is applied to the luminal epithelium jejunal motility is moderated within minutes (2); and this effect may be mediated by an increase in excitability of myenteric intrinsic primary afferent neurons. In contrast, L salivarius has no effect on motility or enteric neuron excitability. We postulated that JB-1 but not L salivarius would affect vagal nerve afferent firing and recorded from the mesenteric nerve bundles to elucidate the nature of this signal.
Methods: We recorded multi- and single-unit activity from the mesenteric afferent nerve bundles innervating ex vivo segments of mouse jejunum. Segments were cannulated at the oral and anal end, and serosal and luminal compartments separately perfused with carbogen gassed Krebs buffer. Recordings were made after drawing a single nerve bundle into a glass suction pipette. Probiotics were added to the Krebs perfusing the luminal compartment. Subdiaphragmatic vagotomies were carried out in some animals prior to the recording experiments.
Results: JB-1 increased the constitutive firing rate of the mesenteric afferent bundle at an effective concentration of 9 log cfu/ml. Average multiunit discharge increased from 10.82 to 14.23 Hz (n=7), but L salivarius (n=5) or medium alone (n=6) were ineffective. The increase in constitutive firing rate was also replicated with single unit analysis. In addition, we found that only JB-1 augmented multiunit discharge responses to distension evoked by applying 30 hPa intraluminally. With Krebs only in the lumen, distension increased the multiunit firing frequency by 22831% (n=7) above baseline; however, after the addition of the JB-1, distension further increased the firing frequency significantly by 31991% (n=7). Vagotomy abolished all of the JB-1 evoked effects.
Conclusions: Our results show that JB-1 affect vagal signalling by enhancing both constitutive and distension-evoked spike discharge. This work provides the first recordings of potentially anxiolytic and hedonic signals that are caused to be relayed toward the CNS via the vagus nerve by a psychoactive probiotic.
1. Bravo JA, et al. Proc Natl Acad Sci 2011;108:16050
2. Wang B, et al. FASEB J 2010;24:4078