Excitatory and inhibitory synaptic function in the rostral nucleus of the solitary tract in embryonic rat

Abstract

The embryonic development of synapses in the rostral nucleus of the solitary tract (rNST) was investigated in rat to determine when synapses begin to function. Using a brain slice preparation we studied appearance of synaptic receptors on second order rNST neurons and investigated the development of postsynaptic responses elicited by afferent nerve stimulation. Prenatal excitatory and inhibitory synaptic responses were recorded as early as E14. Glutamatergic and GABAergic postsynaptic responses were detected as early as E16. Both NMDA and AMPA receptors contributed to glutamatergic postsynaptic responses. GABAergic postsynaptic responses resulted primarily from activation of GABAA receptors. However, functional GABAC receptors were also demonstrated. A glycinergic postsynaptic response was not found although functional glycine receptors were demonstrated at E16. Solitary tract (ST) stimulation -evoked EPSCs, first detected at E16, were eliminated by glutamate receptor antagonists. ST-evoked IPSPs, also detected at E16, were eliminated by GABAA receptor antagonist. Thus, considerable prenatal development of rNST synaptic connections occurs and this will ensure postnatal function of central taste processing circuits.

Novel functions of GABA signaling in adult neurogenesis

“…Two general types of GABA receptors are identified: the ionotropic GABA A receptors (GABA A R) and the metabotropic GABA B receptors (GABA B R). Some of the differences between these receptors are reflected on variation in pharmacological sensitivity, ionic selectivity and kinetic properties (Owens and Kriegstein, 2002; Suwabe et al, 2013). …”

“…Inhibition in presynaptic sites occurs by a reduction in calcium flow in the axonal pole of the neuron, with a consequent reduction on neurotransmitter release. The postsynaptic inhibition is possibly due to the neuronal hyperpolarization generated by potassium currents mediated by GABA B Rs (Owens and Kriegstein, 2002; Suwabe et al, 2013). Since GABA is the principal neurotransmitter responsible for inhibition in the CNS, GABAergic dysfunctions have been suggested to play a pivotal role in mood disorders especially in major depression and anxiety (Cryan and Slattery, 2010).…”

Gustatory solitary tract development: A role for neuropilins

“…Embryonic synapse receptor expression and function have been reported recently in rat rNST (Suwabe et al, 2013). Synaptic receptor responses were recorded from E14, a stage before we first noted extensive collateral projections, at E16.…”

“…Synaptic receptor responses were recorded from E14, a stage before we first noted extensive collateral projections, at E16. On the other hand, solitary tract stimulation first elicited postsynaptic excitatory and inhibitory potentials from E16 (Suwabe et al, 2013). Overall, there is a period of days for development of prenatal synaptic connections, in concert with the timing of ST collateral extension.…”