Organization of synaptic transmission in the mammalian solitary complex, studied in vitro.

Abstract

SUMMARY1. Synaptic transmission and neuronal morphology were studied in the nucleus tractus solitarius and in the dorsal vagal motor nucleus (solitary complex), in coronal brain-stem slices of rat or cat, superfused in vitro.2. Electrical stimulation of afferent fibres of the solitary tract evoked two different types of post-synaptic response recorded intracellularly in different solitary complex neurones. Labelling with horseradish peroxidase showed that these two sorts of orthodromically evoked responses were correlated with different post-synaptic neuronal morphologies.3. The majority of recorded neurones (n = 93) showed a prolonged reduction in excitability following the initial solitary-tract-evoked excitatory post-synaptic potential (e.p.s.p.). A smaller number of neurones (n = 53) showed a prolonged increase in excitability following solitary tract stimulation. In no case did the solitary tract stimulation induce a burst of action potentials at high frequency.4. The time-to-peak and the half-width of the initial solitary-tract-evoked e.p.s.p. were shorter in neurones with prolonged increased excitability than in those with prolonged reduced excitability. In neurones with prolonged reduced excitability, this e.p.s.p. was followed by a hyperpolarization lasting 60-100 ms. The latency of this inhibitory post-synaptic potential (i.p.s.p.) was 3-5 ms longer than that of the initial e.p.s.p. and its reversal potential was 10 mV more negative than the reversal potential of the response measured following application of y-aminobutyric acid or glycine. In neurones with prolonged increased excitability, at a membrane potential of -40 to -50 mV, the initial solitary tract e.p.s.p. was followed by a prolonged depolarization lasting 100-400 ms.5. Background synaptic activity was high in neurones with prolonged increased excitability, consisting of unitary e.p.s.p.s with an amplitude of more than 0-8 mV. This activity was increased for a period of 300-800 ms following solitary tract stimulation. Spontaneous excitatory potentials of more than 0-5 mV were not seen in neurones with prolonged reduced excitability. In these neurones, after intracellular injection of choride ions, reversed unitary i

Distinct target cell-dependent forms of short-term plasticity of the central visceral afferent synapses of the rat

“…Our data confirm neurophysiologically the previously published anatomical observations showing that the TS terminals make monosynaptic asymmetric contact with the dendrites of viscerally projecting DMX neurons in the cNTS regions [11,21,25]. Such a monosynaptic vago-vagal connection has also been functionally suggested by the authors of studies using slice preparations of rats and guinea pigs [16,22,24]. The novel finding of the present study is that, unlike the TS-NTS synapses that consistently exhibit strong short-term depression [13,26,36,37] and this study, the TS-DMX synapses show distinct types of short-term plasticity ranging from paired-pulse depression to facilitation, which results primarily from the distinct release properties of each afferent fiber.…”

Convergence properties of solitary tract neurones driven synaptically by cardiac vagal afferents in the mouse

“…The finding that the response of DS NTS neurones terminated abruptly during the pressure stimulus is indicative of a pressure threshold as reported for baroreceptive NTS neurones (Rogers et al 1993). In other DS neurones (and some baroreceptive cells), firing remained elevated after the pressure stimulus, which may reflect the in vitro findings of prolonged increased excitability of commissural NTS neurones following solitary tract stimulation (Champagnat, Denavit-Saubie, Grant & Shen, 1986). Indeed, the latter slice preparation and the WHBP share common features such as an absence of anaesthesia and descending inhibitory connections, which may both potentiate and prolong these excitatory responses.…”

Presynaptic Melanocortin-4 Receptors on Vagal Afferent Fibers Modulate the Excitability of Rat Nucleus Tractus Solitarius Neurons

“…Because the major source of glutamatergic input to neurons of the NTS originates from vagal afferent fibers (Champagnat et al, 1986;Mifflin and Felder, 1990;Andresen and Kunze, 1994;Smith et al, 1998;Hornby, 2001;Jean, 2001;Baptista et al, 2005b;Travagli et al, 2006), we hypothesized that the modulation of sEPSCs by ␣MSH and MTII may target vagal afferent (sensory) terminals preferentially. We thus conducted a series of experiments in animals in which the vagal afferent terminals were surgically removed.…”