Expression of multiple neurotransmitter receptors by sympathetic preganglionic neurons in vitro

Abstract

Neurons in the CNS generally receive inputs form multiple afferent sources. These afferent systems seldom all use the same neurotransmitter, so most central neurons are required to express multiple neurotransmitter receptors. This work addresses the issue of how multiple neurotransmitter receptors are regulated on the surface of individual neurons. We made whole-cell voltage-clamp recordings from identified chick sympathetic preganglionic neurons (SPNs) in dissociated cell cultures. The neurons were derived from stage 30-31 (7 d) chick embryos and were studied within the first week in vitro. We found that by 1 week in vitro, most SPNs responded to the application of GABA, glycine, and glutamate. The responses of SPNs to the amino acid neurotransmitters were similar to the responses of other CNS neurons to these 3 substances. SPNs became sensitive to these substances at different times in culture. At 1 d in vitro, most cells already responded to GABA, and about half of the cells also responded to glycine and kainate. In contrast, responses to NMDA and quisqualate were usually not seen until day 3-4 in vitro. Although there was a general trend for the amplitude of the responses of SPNs to each of the neurotransmitters to increase with time in vitro, there was an immense amount of cell-to-cell variability. By measuring the amplitudes of the responses of a series of SPNs to all 3 transmitters, we were able to test whether a common regulatory mechanism governed the level of responsiveness of SPNs to all 3 amino acid transmitters. We found no correlation between cells in the amplitudes of their responses to the 3 transmitters. Both the differences in time course of appearance of responsiveness and the lack of correlation in the amplitude of responses suggest that the multiple receptors on the surface of SPNs in vitro are independently regulated.

Synaptic‐ and agonist‐induced chloride currents in neonatal rat sympathetic preganglionic neurones in vitro.

“…We found no indication of a spontaneous GABAergic synaptic regulation of SPN activity in our preparation. This was not expected in view of the presence of GABAA receptor-gated chloride channels on the membranes of these neurones, as demonstrated by other authors (Yoshimura & Nishi, 1982;Backman & Henry, 1983;Clendening & Hume, 1990) and in this study. A possible explanation would be to postulate the presence of GABAergic interneurones in our preparation which form synaptic contacts with SPNs but are not spontaneously active.…”

“…Like the present study, both studies have been performed in NaHCO3-containing extracellular solutions. Also, a linear I-V relationship to exogenous application of glycine and GABA was reported for chicken embryonic SPNs (Clendening & Hume, 1990).…”

“…On the other hand, not only glycine, but also GABA have already been shown to inhibit SPN activity (Yoshimura & Nishi, 1982;Backman & Henry, 1983). Indeed, the presence of receptors of the glycine and the GABAA type has already been shown in dissociated chick embryonic SPNs in culture (Clendening & Hume, 1990). To test the hypothesis that the absence of a spontaneous GABAergic input in the transverse spinal cord slice preparation might be due to the cutting of GABAergic afferents during the slicing procedure, we assayed the activity of exogenously applied glycine and GABA on SPNs.…”

“…Morphological (Bogan et al 1986;Bacon & Smith, 1988;Cabot et al 1992) as well as electrophysiological data (Yoshimura & Nishi, 1982;Backman & Henry, 1983;Clendening & Hume, 1990) show that at least two different inhibitory neurotransmitters can modulate SPN activity. Our data support these findings.…”

Postsynaptic gephyrin immunoreactivity exhibits a nearly one‐to‐one correspondence with gamma‐aminobutyric acid‐like immunogold‐labeled synaptic inputs to sympathetic preganglionic neurons

“…GABAA receptor antagonist bicuculline (Clendening and Hume, 199Oa;Inokuchi et al, 1992). SPN membrane hyperpolarization following either synaptic release or cxogenous application of glycine is most often, but not always, abolished by the specific glycine receptor antagonist strychnine (Dun and Mo, 1989;Clendening and Hume, 1990a;Inokuchi et al, 1992).…”