Dopamine Modulates Synaptic Transmission in the Nucleus of the Solitary Tract

Abstract

10.1152/jn.00224.2002. Dopamine (DA) modulates the cardiorespiratory reflex by peripheral and central mechanisms. The aim of this study was to examine the role of DA in synaptic transmission of the nucleus tractus solitarius (NTS), the major integration site for cardiopulmonary reflexes. To examine DA's role, we used whole cell, voltage-clamp recordings in a rat horizontal brain stem slice. Solitary tract stimulation evoked excitatory postsynaptic currents (EPSCs) that were reduced to 70 +/- 5% of control by DA (100 microM). The reduction in EPSCs by DA was accompanied by a decrease in the paired pulse depression ratio with little or no change in input resistance or EPSC decay, suggesting a presynaptic mechanism. The D1-like agonist SKF 38393 Br (30 microM) did not alter EPSC amplitude, whereas the D2-like agonist, quinpirole HCl (30 microM), depressed EPSCs to 73 +/- 4% of control. The D2-like receptor antagonist, sulpiride (20 microM), abolished DA modulation of EPSCs. Most importantly, sulpiride alone increased EPSCs to 131 +/- 10% of control, suggesting a tonic D2-like modulation of synaptic transmission in the NTS. Examination of spontaneous EPSCs revealed DA reversibly decreased the frequency of events from 9.4 +/- 2.2 to 6.2 +/- 1.4 Hz. Sulpiride, however, did not alter spontaneous events. Immunohistochemistry of NTS slices demonstrated that D2 receptors colocalized with synaptophysin and substance P, confirming a presynaptic distribution. D2 receptors also localized to cultured petrosal neurons, the soma of presynaptic afferent fibers. In the petrosal neurons, D2 was found in cells that were TH-immunopositive, suggesting they were chemoreceptor afferent fibers. These results demonstrate that DA tonically modulates synaptic activity between afferent sensory fibers and secondary relay neurons in the NTS via a presynaptic D2-like mechanism.

Prostaglandin E2 depresses solitary tract-mediated synaptic transmission in the nucleus tractus solitarius

“…Thus, it is not too surprising that these synapses would also be regulated by lipid mediators such as PGE 2 . Our results reveal that PGE 2 , like GABA (Brooks et al 1992), glutamate (Chen et al 2002), dopamine (Kline et al 2002), and Substance P (Sekizawa et al 2003), also depressed synaptic transmission. By producing synaptic depression PGE 2 may convert vagal synapses from a lowpass filter function to a band-pass filter, potentially reducing spike failure in second-order NTS neurons.…”

Adaptive Depression in Synaptic Transmission in the Nucleus of the Solitary Tract afterIn VivoChronic Intermittent Hypoxia: Evidence for Homeostatic Plasticity

“…The submerged sections were secured with a nylon mesh and superfused at a flow rate of 3-4 ml/min with ACSF at 31-33°C. All recordings were made from cells in the caudal NTS (medial and commissural subnuclei) that receives a high density of carotid body afferent fiber termination and cardiorespiratory innervation (Andresen and Kunze, 1994;Kline et al, 2002).…”

Kv1.1 Deletion Augments the Afferent Hypoxic Chemosensory Pathway and Respiration

“…To characterize synaptic transmission in more detail, whole-cell voltage-clamp recordings were used to examine the effect of Kv1.1 deletion on stimulus-evoked EPSCs of caudal NTS relay neurons in brainstem slices, as previously described (Kline et al, 2002b). Electrical shocks to the TS at 0.5 Hz evoked EPSCs that were abolished by the non-N-methyl-D-aspartate glutamate receptor antagonist CNQX (10 M; n ϭ 2) (data not shown).…”