GAD67-GFP+ Neurons in the Nucleus of Roller: A Possible Source of Inhibitory Input to Hypoglossal Motoneurons. I. Morphology and Firing Properties

Abstract

van Brederode JFM, Yanagawa Y, Berger AJ. GAD67-GFPϩ neurons in the Nucleus of Roller: a possible source of inhibitory input to hypoglossal motoneurons. I. Morphology and firing properties. J Neurophysiol 105: 235-248, 2011. First published November 3, 2010 doi:10.1152/jn.00493.2010. In this study we examined the electrophysiological and morphological properties of inhibitory neurons located just ventrolateral to the hypoglossal motor (XII) nucleus in the Nucleus of Roller (NR). In vitro experiments were performed on medullary slices derived from postnatal day 5 (P5) to P15 GAD67-GFP knock-in mouse pups. ON cell recordings from GFPϩ cells in NR in rhythmic slices revealed that these neurons are spontaneously active, although their spiking activity does not exhibit inspiratory phase modulation. Morphologically, GFPϩ cells were bi-or multipolar cells with small-to medium-sized cell bodies and small dendritic trees that were often oriented parallel to the border of the XII nucleus. GFPϩ cells were classified as either tonic or phasic based on their firing responses to depolarizing step current stimulation in whole cell current clamp. Tonic GFPϩ cells fired a regular train of action potentials (APs) throughout the duration of the pulse and often showed rebound spikes after a hyperpolarizing step. In contrast, phasic GFPϩ neurons did not fire throughout the depolarizing current step but instead fired fewer than four APs at the onset of the pulse or fired multiple APs, but only after a marked delay. Phasic cells had a significantly smaller input resistance and shorter membrane time constant than tonic GFPϩ cells. In addition, phasic GFPϩ cells differed from tonic cells in the shape and time course of their spike afterpotentials, the minimum firing frequency at threshold current amplitude, and the slope of their current-frequency relationship. These results suggest that GABAergic neurons in the NR are morphologically and electrophysiologically heterogeneous cells that could provide tonic inhibitory synaptic input to HMs.

Structural-Functional Properties of Identified Excitatory and Inhibitory Interneurons within Pre-Bötzinger Complex Respiratory Microcircuits

“…As a further negative control, we also confirmed the absence of glycine or GABA immunolabeling in motoneurons exhibiting ChAT immunolabeling in the regions of nucleus ambiguus (NA) and XII nucleus. As a positive control, immunoreactivity of neurons located in the spinal trigeminal nucleus known to contain glycinergic and GABAergic neurons (Kuwana et al, 2006; Winter et al, 2009) or immunoreactivity of neurons located in the nucleus of Roller known to be GABAergic (van Brederode et al, 2011) was corroborated (data not shown) in every experiment. Overall, these immunolabeling results are consistent with our findings from scmRT-PCR experiments showing that pre-BötC intrinsic bursters with contralateral axonal projections are generally not inhibitory neurons, and that intrinsic nonbursters with such axonal projections consisted of a heterogeneous population of neurons with a small percentage (19%) of inhibitory neurons.…”

Altered neurobiological function of brainstem hypoglossal neurons in DiGeorge/22q11.2 Deletion Syndrome

“…Although the origins of GABAergic and glutamatergic synaptic inputs were not identified in this study, previous work by others has provided some potential sources of origin for these inputs (Ugolini, 1995). Neurons in the Nucleus of Roller may be the source of GABAergic neurotransmission to hypoglossal motor neurons, but this has not yet been tested directly (van Brederode et al , 2011). There is a glutamatergic input to hypoglossal neurons from the raphe pallidus which is primarily mediated by both NMDA and non-NMDA glutamate receptors (Bouryi and Lewis, 2003).…”

KCC2-mediated regulation of respiration-related rhythmic activity during postnatal development in mouse medulla oblongata

“…Cl À -dependent inhibition is critical in burst pattern formation, but is not necessary for rhythm generation itself (Ballanyi et al, 1999;Feldman and Smith, 1989). Here, GABAergic neurons may innervate to the motor neurons in 12 N from pre-BötC and/or premotorneurons (Koizumi et al, 2008(Koizumi et al, , 2013 because of an absence of GAD67-GFP positive cells within the 12 N (van Brederode et al, 2011). It might depend on the specific character of 12 N which does not include GABAergic interneurons.…”