Presynaptic actions of propofol enhance inhibitory synaptic transmission in isolated solitary tract nucleus neurons

Cranial nerve visceral afferents enter the brain stem to synapse on neurons within the solitary tract nucleus (NTS). The broad heterogeneity of both visceral afferents and NTS neurons makes understanding afferent synaptic transmission particularly challenging. To study a specific subgroup of second-order neurons in medial NTS, we anterogradely labeled arterial baroreceptor afferents of the aortic depressor nerve (ADN) with lipophilic fluorescent tracer (i.e., ADN+) and measured synaptic responses to solitary tract (ST) activation recorded from dye-identified neurons in medial NTS in horizontal brain stem slices. Every ADN+ NTS neuron received constant-latency ST-evoked excitatory postsynaptic currents (EPSCs) (jitter <192 μs, SD of latency). Stimulus-recruitment profiles showed single thresholds and no suprathreshold recruitment, findings consistent with EPSCs arising from a single, branched afferent axon. Frequency-dependent depression of ADN+ EPSCs averaged ∼70% for five shocks at 50 Hz, but single-shock failure rates did not exceed 4%. Whether adjacent ADN− or those from unlabeled animals, other second-order NTS neurons (jitters <200 μs) had ST transmission properties indistinguishable from ADN+. Capsaicin (CAP; 100 nM) blocked ST transmission in some neurons. CAP-sensitive ST-EPSCs were smaller and failed over five times more frequently than CAP-resistant responses, whether ADN+ or from unlabeled animals. Variance-mean analysis of ST-EPSCs suggested uniformly high probabilities for quantal glutamate release across second-order neurons. While amplitude differences may reflect different numbers of contacts, higher frequency-dependent failure rates in CAP-sensitive ST-EPSCs may arise from subtype-specific differences in afferent axon properties. Thus afferent transmission within medial NTS differed by axon class (e.g., CAP sensitive) but was indistinguishable by source of axon (e.g., baroreceptor vs. nonbaroreceptor).

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Angiotensin potentiates excitatory sensory synaptic transmission to medial solitary tract nucleus neurons

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00505.2002 ◽

2003 ◽

Vol 284 (5) ◽

pp. R1340-R1353 ◽

Cited By ~ 33

Author(s):

Karen L. Barnes ◽

Dannette M. DeWeese ◽

Michael C. Andresen

Keyword(s):

Substance P ◽

Synaptic Transmission ◽

Solitary Tract Nucleus ◽

Ang Ii ◽

Intracellular Recordings ◽

Solitary Tract ◽

Sensory Transmission ◽

Group A ◽

Group B ◽

Higher Doses

Femtomole doses of angiotensin (ANG) II microinjected into nucleus tractus solitarii (nTS) decrease blood pressure and heart rate, mimicking activation of the baroreflex, whereas higher doses depress this reflex. ANG II might generate cardioinhibitory responses by augmenting cardiovascular afferent synaptic transmission onto nTS neurons. Intracellular recordings were obtained from 99 dorsal medial nTS region neurons in rat medulla horizontal slices to investigate whether ANG II modulated short-latency excitatory postsynaptic potentials (EPSPs) evoked by solitary tract (TS) stimulation. ANG II (200 fmol) increased TS-evoked EPSP amplitudes 20–200% with minimal membrane depolarization in 12 neurons excited by ANG II and glutamate, but not substance P ( group A). Blockade of non- N-methyl-d-aspartate receptors eliminated TS-evoked EPSPs and responses to ANG II. ANG II did not alter TS-evoked EPSPs in 14 other neurons depolarized substantially by ANG II and substance P ( group B). ANG II appeared to selectively augment presynaptic sensory transmission in one class of nTS neurons but had only postsynaptic effects on another group of cells. Thus ANG II is likely to modulate cardiovascular function by more than one nTS neuronal pathway.

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Postnatal Development of Inhibitory Synaptic Transmission in the Rostral Nucleus of the Solitary Tract

Journal of Neurophysiology ◽

10.1152/jn.2001.85.5.2203 ◽

2001 ◽

Vol 85 (5) ◽

pp. 2203-2212 ◽

Cited By ~ 21

Author(s):

Gintautas Grabauskas ◽

Robert M. Bradley

Keyword(s):

Synaptic Transmission ◽

Postnatal Development ◽

Age Groups ◽

Brain Slices ◽

Single Stimulus ◽

Synaptic Activity ◽

Membrane Properties ◽

Tetanic Stimulation ◽

Solitary Tract ◽

Inhibitory Synaptic Transmission

To explore the postnatal development of inhibitory synaptic activity in the rostral (gustatory) nucleus of the solitary tract (rNST), whole cell and gramicidin perforated patch-clamp recordings were made in five age groups of rats [ postnatal day 0–7 ( P0–7), P8–14, P15–21, P22–30, and P > 55]. The passive membrane properties of the developing rNST neurons as well as the electrophysiological and pharmacological characteristics of single and tetanic stimulus-evoked inhibitory postsynaptic potentials (IPSPs) were studied in brain slices under glutamate receptor blockade. During the first postnatal weeks, significant changes in resting membrane potential, spontaneous activity, input resistance, and neuron membrane time constant of the rNST neurons occurred. Although all the IPSPs recorded were hyperpolarizing, the rise and decay time constants of the single stimulus shock-evoked IPSPs decreased, and the inhibition response–concentration function to the γ-aminobutyric acid (GABA) receptor antagonist bicuculline methiodide (BMI) shifted to the left during development. In P0–7 and P8–14, but not in older animals, the IPSPs had a BMI-insensitive component that was sensitive to block by picrotoxin, suggesting a transient expression of GABAC receptors. Tetanic stimulation resulted in both short- and long-term changes of inhibitory synaptic transmission in the rNST. For P0–7 and P8–14 animals tetanic stimulation resulted in a sustained hyperpolarization that was maintained for some time after termination of the tetanic stimulation. In contrast, tetanic stimulation of neurons in P15–21 and older animals resulted in hyperpolarization that was not sustained but decayed back to a more positive level with an exponential time course. Tetanic stimulation resulted in potentiation of single stimulus shock-evoked IPSPs in ∼50% of neurons in all age groups. These developmental changes in inhibitory synaptic transmission in the rNST may play an important role in shaping synaptic activity in early development of the rat gustatory system during a time of maturation of taste preferences and aversions.

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