Testing the role of preBötzinger Complex somatostatin neurons in respiratory and vocal behaviors

Abstract

Identifying neurons essential for the generation of breathing and related behaviors such as vocalization is an important question for human health. The targeted loss of preBötzinger complex (preBötC) glutamatergic neurons, including those that express high levels of somatostatin protein (SST neurons), eliminates normal breathing in adult rats. Whether preBötC SST neurons represent a functionally specialized population is unknown. We tested the effects on respiratory and vocal behaviors of eliminating SST neuron glutamate release by Cre-Lox-mediated genetic ablation of the vesicular glutamate transporter 2 (VGlut2). We found the targeted loss of VGlut2 in SST neurons had no effect on viability in vivo, or on respiratory period or responses to neurokinin 1 or µ-opioid receptor agonists in vitro. We then compared medullary SST peptide expression in mice with that of two species that share extreme respiratory environments but produce either high or low frequency vocalizations. In the Mexican free-tailed bat, SST peptide-expressing neurons extended beyond the preBötC to the caudal pole of the VII motor nucleus. In the naked mole-rat, however, SST-positive neurons were absent from the ventrolateral medulla. We then analyzed isolation vocalizations from SST-Cre;VGlut2F/F mice and found a significant prolongation of the pauses between syllables during vocalization but no change in vocalization number. These data suggest that glutamate release from preBötC SST neurons is not essential for breathing but play a species- and behavior-dependent role in modulating respiratory networks. They further suggest that the neural network generating respiration is capable of extensive plasticity given sufficient time.

Somatostatin 2a receptors are not expressed on functionally identified respiratory neurons in the ventral respiratory column of the rat

“…Alternatively, it may be that input from this group is not required by rhythm generating core of the preBötC, but instead represents a peripheral component of the rhythm generating network. This view is supported by recent work by Tupal et al (), who found that elimination of glutamate release from SSTergic preBötC neurons is not associated with any respiratory phenotype, as would be predicted if this population contained the pacemaking kernel.…”

The RNA-binding protein Celf6 is highly expressed in diencephalic nuclei and neuromodulatory cell populations of the mouse brain

“…Of these areas, Amb, a motor nucleus, showed high expression of Celf6 protein, yet the decrease in overall vocalization amount seen in the Celf6 mutants did not in any way alter the temporal or spectral features of the remaining calls. This is in contrast to mutations specifically disrupting a brainstem motor circuit (Tupal et al 2014), which resulted in perturbed temporal structure of call phrasing, but a normal overall amount of calls. This argues against the Celf6 −/− phenotype being primarily a result of motoric deficits, and suggests there may be some upstream motivational deficit, despite a loss of the protein in the Amb.…”

Testing the evolutionary conservation of vocal motoneurons in vertebrates

“…Mammalian vocalization, it should be pointed out, also clearly involves non-Phox2b expressing neurons from XII and phrenic motor pools. Whether the pattern generating premotoneuron populations involved in vocalization are similarly developmentally flexible is an interesting question for future analysis (Bass and Baker, 1997; Bass et al, 2008; Bouvier et al, 2010; Gray et al, 2010; Sweeney and Kelley, 2014; Tupal et al, 2014b). …”