ABSTRACT
Dispersed neurons from embryonic chicken sympathetic ganglia were innervated in vitro by explants of spinal cord containing the autonomic preganglionic nucleus or somatic motor nucleus. The maturation of postsynaptic acetylcholine (ACh) sensitivity and synaptic activity was evaluated from ACh and synaptically evoked currents in voltage-clamped neurons at several stages of innervation. All innervated cells are more sensitive to ACh than uninnervated neurons regardless of the source of cholinergic input. Similarly, medium conditioned by either dorsal or ventral explants mimics innervation by enhancing neuronal ACh sensitivity. This increase is due to changes in the rate of appearance of ACh receptors on the cell surface. There are also several changes in the nature of synaptic transmission with development in vitro, including an increased frequency of synaptic events and the appearance of larger amplitude synaptic currents. In addition, the mean amplitude of the unit synaptic current mode increases, as predicted from the observed changes in postsynaptic sensitivity. Although spontaneous synaptic current amplitude histograms with multimodal distributions are seen at all stages of development, histograms from early synapses are typically unimodal. Changes in the synaptic currents and ACh sensitivity between 1 and 4 days of innervation were paralleled by an increase in the number of synaptic events that evoked suprathreshold activity in the postsynaptic neurons. The early pre- and postsynaptic differentiation described here for interneuronal synapses formed in vitro may be responsible for increased efficacy of synaptic transmission during development in vivo.
Subject(s)
Acetylcholine/pharmacology , Ganglia, Sympathetic/physiology , Neurons/physiology , Spinal Cord/physiology , Synapses/physiology , Synaptic Transmission , Acetylcholine/analogs & derivatives , Acetylcholine/metabolism , Animals , Cells, Cultured , Chick Embryo , Electrophysiology/methods , Ganglia, Sympathetic/embryology , Motor Neurons/drug effects , Motor Neurons/physiology , Neurons/drug effects , Organ Culture Techniques , Spinal Cord/embryology , Synapses/drug effects , Synaptic Transmission/drug effects , Tetrodotoxin/pharmacologyABSTRACT
The levels of mRNA encoding hnRNP core protein A1 have been compared in quiescent and proliferating Rat-1 embryonic fibroblasts. Northern blot hybridization analyses using probes made from an A1 cDNA clone, lambda HDP-182, isolated by Cobianchi et al. (J. Biol. Chem. 261:3536-2543 (1986] indicated that three sizes of poly A + RNAs, 1.6, 2.0, & 4.0 kb, have extensive sequence homology. The levels of all three A1 RNA species are responsive to the proliferation state of the cells. Stimulation of quiescent Rat-1 cells with serum or epidermal growth factor resulted in a 2- to 5-fold increase in the levels of each of these three RNAs that was evident after 2 hours and reached a peak after about 8 hours. Addition of the protein synthesis inhibitor, cycloheximide, along with epidermal growth factor completely blocked the upsurge in A1 RNA levels. Thus, the A1 RNA species are not primary transcriptional targets of epidermal growth factor but do show an induction pattern similar to mRNAs encoding some glycolytic enzymes.
