In vivo activity of B‐ and C‐neurones in the paravertebral sympathetic ganglia of the bullfrog.

Abstract

1. Spontaneous, in vivo synaptic activity was recorded from 146 B‐cells and 60 C‐cells in the IXth and Xth paravertebral sympathetic ganglia of the urethane‐anaesthetized bullfrog. Sympathetic outflow to the blood vessels, which are innervated by C‐cells, is different from that received by targets in the skin, which are innervated by B‐cells. 2. B‐cells were divided into three groups: the first (61 cells) exhibited only action potentials (APs) at 0.01‐0.3 s‐1; the second (59 cells) exhibited APs and EPSPs and the third (26 cells) were silent. In addition to their usual suprathreshold input from the ipsilateral sympathetic chain, 53% of B‐cells received subthreshold input which probably arose from fibres in the contralateral chain. ‘Slow’ B‐cells exhibited less subthreshold activity and a slightly higher AP frequency than ‘fast’ B‐cells. All B‐cells are involved in a sympathetic reflex which is activated by tactile stimulation of the skin of the hindlimb. Activation of this reflex increased AP frequency without promoting long‐lasting depolarization. 3. Sixty‐seven per cent of C‐cells exhibited rhythmic bursting activity with or without small intraburst EPSPs. Bursts tended to correlate with electrocardiographic (ECG) activity. The remainder exhibited an irregular pattern of activity which was not correlated with ECG activity and which included one to three APs and EPSPs interspersed between the bursts. Activity of both types of C‐cell was inhibited following stimulation of the skin. 4. An average of twenty‐three B‐cells and twenty‐one C‐cells discharge simultaneously in vivo. This reflects branching of preganglionic fibres and results in synchrony of discharge in both postganglionic B‐ and C‐fibres.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro relation between preganglionic sympathetic stimulation and activity of cutaneous glands in the bullfrog.

“…Depolarizations were half-maximal at -0-2 Hz and saturated at 1-2 Hz. This resembles observations in vivo in which B neurones normally fire at rates of 0-1-0-3 Hz, and can be driven to fire at >1 Hz by mechanical stimulation of the skin (Ivanoff & Smith, 1995). The similarity between frequency tuning of the isolated circuit and firing rates observed in anaesthetized bullfrogs suggests that glands are tonically active in vivo.…”

“…In this study, we have focused primarily upon simple depolarizations produced by single shocks or short trains of preganglionic stimuli. Based on observations of mucous secretion and B cell firing in vivo (Lillywhite, 1971;Ivanoff & Smith, 1995), the weaker stimuli employed in the present experiments appear more relevant to physiological activation of glandular secretion.…”

“…Based on intracellular recordings in vivo, it has been suggested that about half of B neurones receive subthreshold nicotinic synapses (Ivanoff & Smith, 1995). Interaction between subthreshold nicotinic EPSPs and slow peptidergic EPSPs could enhance postganglionic firing in B neurones (Schulman & Weight, 1977) and thereby increase cutaneous depolarization.…”

Reinnervation of frog sympathetic ganglia after selective denervation of B or C neurons

“…The lack of significant intraganglionic sprouting in totally denervated frog ganglia has already been noted in other experiments (Eug6ne & Taxi, 1995); (3) if they were not of intraganglionic origin, it seems likely that the few synapses were due to some preganglionic fibres having escaped sectioning because they followed a route different from that of the bulk of the preganglionic fibres. They could arise from the contralateral chain, as has recently been reported in R. catesbeiana by Ivanov and Smith (1995). However, anatomical evidence of the existence of connections between the right and left sympathetic chains is still lacking in R. esculenta.…”

Presynaptic muscarinic inhibition in bullfrog sympathetic ganglia.

“…Bullfrog sympathetic neurones are each innervated by a primary preganglionic fibre that produces a strong suprathreshold nicotinic EPSP, and in addition, some receive secondary subthreshold inputs (Dodd & Horn, 1983a;Ivanoff & Smith, 1995 (Shen & Horn, 1995a). Figure 1A The maximal effect of muscarine upon EPSC amplitude in B cells was determined by constructing a dose-response relation (Fig.…”