Vesicular Glutamate Transporter 2 Is Required for Central Respiratory Rhythm Generation But Not for Locomotor Central Pattern Generation

Abstract

Glutamatergic excitatory neurotransmission is dependent on glutamate release from presynaptic vesicles loaded by three members of the solute carrier family, Slc17a6 -8, which function as vesicular glutamate transporters (VGLUTs). Here, we show that VGLUT2 (Slc17a6) is required for life ex utero. Vglut2 null mutant mice die immediately after birth because of the absence of respiratory behavior. Investigations at embryonic stages revealed that neural circuits in the location of the pre-Bötzinger (PBC) inspiratory rhythm generator failed to become active. However, neurons with bursting pacemaker properties and anatomical integrity of the PBC area were preserved. Vesicles at asymmetric synapses were fewer and malformed in the Vglut2 null mutant hindbrain, probably causing the complete disruption of AMPA/kainate receptor-mediated synaptic activity in mutant PBC cells. The functional deficit results from an inability of PBC neurons to achieve synchronous activation. In contrast to respiratory rhythm generation, the locomotor central pattern generator of Vglut2 null mutant mice displayed normal rhythmic and coordinated activity, suggesting differences in their operating principles. Hence, the present study identifies VGLUT2-mediated signaling as an obligatory component of the developing respiratory rhythm generator.

VGLUT2 in dopamine neurons is required for psychostimulant-induced behavioral activation

“…Briefly, this mouse line carries LoxP sites surrounding exons four to six in the genomic Vglut2 sequence that encode three transmembrane domains. The presence of Cre protein in Vglut2-expressing cells in these mice has been shown previously to result in synaptic vesicle malformation and loss of miniature excitatory postsynaptic potentials (10,18). Thus, the presence of Cre in DAT-expressing mDA neurons is expected to produce dysfunctional VGLUT2 protein, abrogating VGLUT2-mediated glutamatergic neurotransmission.…”

“…We next bred the DAT-Cre mouse line into our conditional Vglut2 f/f mouse line, which has been validated and described elsewhere (10,12). Briefly, this mouse line carries LoxP sites surrounding exons four to six in the genomic Vglut2 sequence that encode three transmembrane domains.…”

“…VGLUT2-mediated neurotransmission has been shown to be absolutely critical for respiration, and thus VGLUT2-null mutant mice die from asphyxia (10). VGLUT2 also has been shown to play a role in the hypothalamic neurocircuitry that prevents hypoglycemia (11).…”

Cumulative lesioning of respiratory interneurons disrupts and precludes motor rhythms in vitro

“…An important consideration is that neuroanatomical evidence shows that approximately one-half of the neurons in the preBötC are inhibitory, either glycinergic or GABAergic, and one-half are glutamatergic (13,25). Glutamatergic transmission is obligatory for rhythmogenesis in vitro (26,27), whereas inhibitory transmission is not (28,29). Synaptic inhibition nonetheless regulates the amplitude of XII motor output (10,11).…”

Complexe de pré-Bötzinger et automatisme respiratoire

“…Cette population de neurones et son phénotype excitateur glutamatergique sont essentiels pour l'activité rythmique du CPB. Ainsi, les souris transgéniques déficientes pour le gène Vglut2 ne survivent pas à la naissance et leur CPB est inactif in vitro [35]. L'ablation génétique d'une sous-population de ces neurones (les neurones V2a) n'abolit pas le rythme du CPB, mais le rend irrégulier [36].…”