Effects of dopamine on the superior cervical ganglion of the rabbit

1. The effects of dopamine on isolated rabbit superior cervical ganglion were investigated with intracellular recording techniques.2. Dopamine (10(-5)-10(-3)M) depressed the amplitude of the excitatory post-synaptic potential (e.p.s.p.) and blocked impulse transmission.3. Dopamine (10(-4)M) induced a slight (2-5 mV) post-synaptic hyperpolarization without altering membrane conductance.4. The post-synaptic membrane sensitivity to acetylcholine (ACh) applied iontophoretically was not affected by dopamine.5. Dopamine decreased the frequency of miniature excitatory post-synaptic potentials (m.e.p.s.p.s) in a high K(+) solution, with no change in the amplitude of m.e.p.s.p.s.6. Dopamine reduced the quantal content of the e.p.s.p. in a low Ca(2+) and high Mg(2+) solution, but had no effect on the quantal size.7. The ganglionic blocking effect of dopamine was antagonized by phenoxybenzamine, but not by propranolol.8. The results show that the ganglionic depressant effect of dopamine is exerted primarily through an alpha-adrenoceptive site at the presynaptic nerve terminal.     

Effects of guanethidine on paraganglionic cells in the superior cervical ganglion of the rat.

Paraganglionic cells in the rat superior cervical ganglion were investigated by fluorescence and electron microscopy following treatment with guanethidine for 5-30 days. Control animals received saline and guanidine. Fluorescence cytophotometric measurements revealed a general decrease in the catecholamine content of paraganglionic cells in guanethidine-treated animals. However a few cell clusters showed focal increases. Similarly by electron microscopy there was a general decrease of cell clusters showing increases. -- guanethidine -- as well as guanidine--treated animals showed non-specific cytological alterations such as mitochondrial swelling and increase of cytoplasmic glycogen. However no changes of catecholamine contents and of dense core vesicles were noted in control animals. These results confirm the conception that in rat paraganglionic cells the dense core vesicles are the main storage site of catecholamines. The marked difference in the response of some cell culsters to the experimental treatment can be considered as evidence of functional heterogeneity of this cell population in the rat superior cervical ganglion.     

Noradrenergic synaptic transmission in the superior cervical ganglion.

Morphology of dendrites of principal neurons in the rat superior cervical ganglion (SCG) was re-examined by an intracellular staining method followed by electron microscopic analysis. They exhibit a varying complexity in their morphology and arborization. Some dendrites show specializations such as a glomerular plexus, where extensively branched dendritic collaterals form synaptic connections comprising not only axodendritic synapses between preganglionic axons and principal cell dendrites, but also dendrodendritic synapses between principal cell dendrites. Most presynaptic elements of adrenergic synapses observed by conventional methods appear to represent these specialized dendritic collaterals of principal neurons. In denervated SCG, focal stimulation revoked an inhibitory postsynaptic potential in some principal neurons. The response was completely blocked by yohimbine, an alpha 2-adrenoceptor antagonist. The inhibitory synaptic connection between principal neurons via dendrodendritic synapses may be an important addition to the conventional scheme of intraganglionic synaptic transmission. Sympathetic ganglia may thus function as more than a simple relay station, with specialized neuronal circuitry that may be involved in the modulation of cholinergic transmission.     

Age-related structural and neurochemical changes of the human superior cervical ganglion.

The aim of this study was to investigate age-related morphological and neurochemical changes in the human superior cervical ganglion (SCG). Thirty-seven superior sympathetic human cervical ganglia of young, adult, and aged subjects were examined using morphometric analysis, biotin-streptavidin immunohistochemistry for detecting neurofilament, myelin protein, protein gene product 9.5, nerve growth factor receptor p75 in sympathetic neurons and nerve fibers. Morphometric parameters of neurons (area, long and short axis, shape factor of the neuron body, nucleus, cytoplasm, and lipofuscin) were investigated in every sixth serial section of the ganglion. Seven hundred neurons with clearly visible nuclei were measured in each studied group. The present study showed that human SCG of older subjects had larger areas of neuron body, cytoplasm and nucleus, a lower shape factor, an increased amount of lipofuscin, and a greater number of large-size neurons, as compared to SCG obtained from young subjects. Neuronal cytoskeletal alterations manifested themselves through a decreased number of neurofilament-positive neurons were detected in old human SCG. The amount of myelinated fibers decreased with age, although the amount of myelinated fibers in the young and the adult subjects varied from few to a moderate number. PGP 9.5 immunoreactivity varied in different age groups. A marked reduction of nerve growth factor receptor p75 in old human sympathetic neurons was detected. In conclusion, the findings of this study confirm age-related morphological changes in the human SCG. Structural neuronal changes may influence the deterioration of neuronal functional capacity, neuronal plasticity, and regenerative characteristics.     

Effects of extracellular calcium and other divalent cations on mechanical response of frog skeletal muscle

In order to investigate the mechanism by which elevated extracellular Ca ions decrease twitch and tetanus tension in frog skeletal muscle we made mechanical and electrophysiological measurements on single fibers or small bundles from twitch muscles. High concentration of Ca caused a hyperpolarization and an increase in the duration of action potential. The mechanical threshold, estimated by using the strength-duration curve, was shifted upward by adding Ca ions. These effects were fully reversible. Steady state twitch tension was slightly increased by replacing Mg and Ni with Ca and decreased by elevating their concentrations, although Ba resulted in a marked twitch augmentation and a positive correlation with the ion concentration. By contrast, the strength-duration curve was shifted upward by Ni while Mg and Ba showed no shift. These evidences point to a failure of the early step of excitation-contraction coupling, including the T-membrane depolarization, as the primary mechanism of action of high concentration of Ca, Mg, and Ni ions, whereas Ba ion has an additional intracellular potentiating effect.     

Peptide 19 in the rat superior cervical ganglion

Peptide 19 is a 7.6 kDa polypeptide which can bind to calmodulin and inhibit calcium-calmodulin signaling. In this study, peptide 19-immunoreactivity was examined in the rat superior cervical ganglion. In the ganglion, 54.8% of postganglionic sympathetic neuron profiles were immunoreactive for peptide 19. These neuron profiles were small- to medium-sized and measured 87–845 μm² (mean±SD=343±111 μm²). Double immunofluorescence method revealed that 99.9% of peptide 19–containing neurons had neuropeptide Y in the superior cervical ganglion. Retrograde neuronal tracing and immunohistochemical studies also demonstrated that peptide 19 was common in postganglionic sympathetic neurons which innervated the facial skin and masseter but not the submandibular gland; 55.6% and 75.2% of cutaneous and muscular neuron profiles, respectively, contained peptide 19. Only 9.8% of glandular neurons were immunoreactive for peptide 19. These findings indicate that the content of peptide 19 in superior cervical ganglion neurons depends on their cell sizes and peripheral projections. On the other hand, colchicine injection into the superior cervical ganglion decreased the number of peptide 19–positive neurons (30.7%) compared to saline injection (53.3%). In contrast, the treatment induced nicotine adenine dinucleotide phosphate diaphorase activity in 12.7% of postganglionic sympathetic neurons. Double stain demonstrated that 56.3% of nicotine adenine dinucleotide phosphate diaphorase–positive neurons co-expressed peptide 19. These findings indicate that colchicine treatment causes decrease of peptide 19 expression and increase of nitric oxide synthase activity.     

The influence of preganglionic nerves on the superior cervical ganglion of the rat.

Sympathetic neurones grown in tissue culture with non-neuronal cells become cholinergic. Such a change from an adrenergic to cholinergic character does not occur in vivo and it has been suggested that this may be due to the determination of the adrenergic character by electrical activity. Electrical activity in the superior cervical ganglion by young rats were prevented by transection of the preganglionic nerve trunk. In no case did this operation result in an increase in the intrinsic choline acetyltransferase (CAT) of the ganglion. We conclude that electrical activity is not the factor responsible for the difference between in vivo and in vitro results.     

Effects of ryanodine on the spike after-hyperpolarization in sympathetic neurones of the rat superior cervical ganglion

Effects of ryanodine on sympathetic neurones of the rat superior cervical ganglion were investigated by means of intracellular recording. Ryanodine (1 M) significantly shortened the after-hyperpolarization (AH) following the spike evoked by current injection or pre-ganglionic stimulation without affecting the configuration of the spikes. The shortening of AH caused by ryanodine was dose-dependent at concentrations between 0.1 and 1 M and was slowly recovered by washing the tissue over 1 h. A partial inhibition of the apamin-sensitive slow component of AH was the maximal effect obtained at 1 M. Although the input membrane resistance was not changed, ryanodine evoked repetitive discharges at long intervals in response to long depolarizing current pulses applied across the cell membrane. Ryanodine (5 M) did not depress the Ca-spike but shortened the following AH in a lesser degree than that following the normal spike. Spontaneous small fluctuations of the resting membrane potential were occasionally observed under normal conditions. They were facilitated by caffeine and abolished by ryanodine. Caffeine also enhanced the slow component of the AH but did not affect it in the presence of ryanodine. These results suggest that ryanodine inhibits Ca release from intracellular store sites. The released Ca may contribute to generating the long-lasting AH and to regulating the excitability of rat sympathetic neurones.     

Vasoactive intestinal polypeptide facilitates the late component of the 5-hydroxytryptamine-induced discharge in the cat superior cervical ganglion

The intra-arterial administration of vasoactive intestinal polypeptide (VIP, 1-10 micrograms, i.a.) to the cat superior cervical ganglion facilitated or unmasked the late component but not the early component of the 5-hydroxytryptamine (5-HT, 0.5-50 micrograms, i.a.)-induced postganglionic discharge. The facilitation occurred in acutely and chronically decentralized ganglia. The early and late 5-HT discharges were blocked by MDL-72222, a 5-HT antagonist, but not by cholinergic antagonists. These data together with previous observations indicate that VIP selectively facilitates slow cholinergic and non-cholinergic excitatory mechanisms in autonomic ganglia.