Potentiation of the effects of GABA by pentobarbitone

Pentobarbitone (50 microM) has been shown to potentiate GABA-induced responses in rat isolated superior cervical ganglia and in dorsal or ventral root fibres of immature rat isolated spinal cords. Measurements of dose ratios for the antagonism of GABA-induced responses of dorsal root fibres by bicuculline showed that pentobarbitone (50 microM) did not significantly alter this antagonism. This result indicates that the antagonism of GABA by bucuculline at dorsal root fibres is not reversed by pentobarbitone. Ventral root responses to GABA (but not glycine) were also potentiated by pentobarbitone (+/-)-Nipecotic acid (300 microM) potentiated responses to GABA much more than those to 3-aminopropane-sulphonic acid.

Norepinephrine inhibits calcium-dependent potentials in rat sympathetic neurons

Norepinephrine reversibly antagonizes three calcium-dependent potentials recorded from rat postganglionic neurons. Norepinephrine inhibits the development of a shoulder on the aciton potential, the magnitude of the hyperpolarizing afterpotential, and the rate of rise and amplitude of the calcium spike. The action of norepinephrine is antagonized by the alpha-adrenergic antagonist phentolamine, but not by MJ 1999, a beta-adrenergic antagonist. These results suggest that activation of an alpha-adrenergic receptor may antagonize a voltage-sensitive calcium current.

Relation between catecholamine-induced cyclic AMP changes and hyperpolarization in isolated rat sympathetic ganglia

1. The effect of catecholamines on cyclic adenosine 3'5'-monophosphate (cyclic AMP) production in isolated rat superior cervical ganglia has been measured under experimental conditions in which they also produce ganglion hyperpolarization.2. (+/-)Isoprenaline (1 muM) increased cyclic AMP levels by 8-100 times after 15 min incubation at 25 degrees C. Half-maximal stimulation occurred at about 0.03 muM. This was due to stimulation of beta-receptors, since it was prevented by 1 muM-propranolol but not by 1 muM-phentolamine.3. The alpha-agonists phenylephrine (100 muM), dopamine (100 muM) and clonidine (1 muM) did not produce a detectable increase in ganglionic cyclic AMP. Dopamine (100 muM) was also ineffective at 37 degrees C in the presence of 10 mM-theophylline.4. Exogenous cyclic AMP (0.01-1 mM) hyperpolarized the ganglion. This effect was replicated by other adenosine compounds, most effectively by adenosine and by adenosine 5'-monophosphate, and was antagonized by theophylline. Dibutyryl cyclic AMP was weaker than cyclic AMP.5. Neither theophylline nor the non-xanthine phosphodiesterase inhibitor, Ro 20-1724, enhanced the hyperpolarizing actions of noradrenaline or dopamine.6. Since catecholamine-induced hyperpolarization of the isolated rat ganglion is induced via alpha-receptors, whereas cyclic AMP-production is induced via beta-receptors, it is concluded that cyclic AMP is unlikely to mediate the hyperpolarization. The effect of exogenous cyclic AMP may be due to an action on external adenosine-receptors.

Autonomic block, cardiovascular depression and histamine release produced by polymyxin B in the cat

The present study quantifies the autonomic block, the cardiovascular depression and the histamine releasing effects of polymyxin B in nine anaesthetized cats. The dose requirements for 50 per cent depression of the mean arterial blood pressure, the bradycardiac response to vagal stimulation, and the contraction of the nictitating membrane elicited by pre-ganglionic and post-ganglionic stimulation of the cervical sympathetic trunk have a narrow range of scatter, being of the order of 6--12 mg.kg-1 of the polymycin B base. The neuromuscular blocking dose (ED50), previously determined and hereby confired, also falls in the same range. Bradycardia and possibly histamine release are also observable. The relatively unremarkable effect of polymyxin B on the heart rate can be attributed to the balance between the vagal, sympathetic and ganglionic blocks, as well as the possible histamine release. All effects are long-lasting. Thus lack of tissue specificity makes it implausible to explain the neuromuscular and the cardiovascular effects of polymyxin B solely by the cholinergic mechanism of action. Ganglionic block and histamine release do not completely explain hypotension induced by polymyxin B. We propose that all biological effects of polymyxin B derive from a common mechanism of action, which may be its antimembrane antibacterial action. We would like to alert anaesthetists to the possiblity that polymyxin B may cause severe multiple organ system depression, in addition to neuromuscular block.

[Structure and biometric indices of the lumbar ganglia of the sympathetic trunk of normal cats and cats subjected to hormonal stimulation]

The structure of different components from lumbar ganglia of the cat sympathetic trunk were studied in norm and 6h after intramuscular administration of prednisolone (5 mg/kg). Paraffin sections were stained with azocramine after Heidenhain, Wallart and Houette, azure II -- eosin. Biometry of different ganglial structures was performed by G.G. Avtandilov's dotted method. It was demonstrated that as a response to prednisolone administration, certain morphological changes appeared in all ganglial components. The walls of capillaries grew thicker, endothelial nuclei protruded into their lumen. Collagenous fibres of the connective tissue capsule and ganglial stroma grew thicker and acquired twisted appearance, the amount of the basilar substance increased. Simultaneously, there was a sharp increase of the nuclear section area in perineuronal ganglia. The total area of neuronal sections in the ganglia also increased at the expense of both increasing area of neuronal cytoplasm and hypertrophy of their nuclei.

Reduction of bladder contractility after alpha-adrenergic blockade and after ganglionic blockade

Seven spinal cord injured patients were evaluated with cystometry bladder, electromyography, and pressure profiles of the external urethral sphincter before and after phenoxybenzamine administration. Seven more patients were evaluated before and after mecamylamine administration. Both drugs reduced the contractility of the bladder. The reduction of bladder contractility may reflect decreased sympathetic stimulation to the bladder. Bladder electric potentials reflect the intrinsic tone of the detrusor muscle.

A peptide as a possible transmitter in sympathetic ganglia of the frog

A search was made in sympathetic ganglia of the bullfrog for a noncholinergic, nonaminergic transmitter that is released by a distinct group of preganglionic axons. These initiate a late slow excitatory postsynaptic potential which lasts for many minutes. The most promising candidate for the role of transmitter is a peptide that resembles luteinizing hormone-releasing hormone (LHRH; luliberin). The reasons are: (i) LHRH (1 muM) and some of its analogs cause a slow depolarization of ganglion cells. (ii) Radioimmunoassays established that 100-800 pg of a LHRH-like substance is contained in the lumbar chain of sympathetic ganglia. (iii) The LHRH-like material is specifically distributed in those spinal nerves that contain axons that initiate the slow noncholinergic synaptic responses. (iv) Five days after ipsilateral preganglionic axons are cut, 95% of the LHRH-like substance disappears from ganglia, while the LHRH immunoreactivity triples in the spinal nerves proximal to the cut region. (v) About 0.6% of the LHRH-like material within ganglia can be collected from the perfusate after 30 min of incubation in isotonic KC1; this release is Ca dependent. (vi) The candidate for transmitter has several chemical characteristics of a peptide and has a Mr near 1000.

Activation of rat sympathetic ganglia SIF cell dopamine metabolism by muscarinic agonists

The biochemical responsiveness of the dopamine-containing small intensely fluorescent (SIF) cells to cholinoceptive drugs was evaluated in rat superior cervical ganglion (SCG), middle-inferior cervical ganglion and celiac ganglion. Amines and metabolites were analyzed by mass fragmentography. The major metabolite of dopamine (DA) in all ganglia was 3,4-dihydroxyphenylacetic acid (DOPAC). Stimulation of muscarinic receptors with carbachol induced a 3-10 fold increase of DOPAC concentration in the ganglia, the celiac ganglion being the most responsive and the SCG being the least. Pretreatment with atropine blocked the rise of DOPAC. The rise of DOPAC after activation of muscarinic receptors was not the consequence of blocking the removal of this acid from the ganglion. We concluded that DA metabolism in SIF cells is enhanced by stimulation of muscarinic receptors and that the magnitude of the DOPAC increase in a ganglion may reflect the importance of DA in ganglionic transmission.

Characteristics of fast excitatory postsynaptic current in bullfrog sympathetic ganglion cells. Effects of membrane potential, temperature and Ca ions

The membrane current underlying the fast excitatory postsynaptic potential (EPSC) of bullfrog sympathetic ganglion cells was studied. The relationship between the EPSC amplitude and membrane potential was linear at negative levels of membrane potential, but deviated from the linearity toward a smaller amplitude at positive levels. The falling phase of EPSC almost followed a single exponential decay. The half-decay time (HDT) of EPSC's increased exponentially with an increase in the negativity of membrane potential. The rise time (RT) was also prolonged slightly with membrane hyperpolarization. Lowering of temperature decreased the EPSC amplitude, lengthened markedly the HDT and increased the slope relating the logarithm of the HDT to membrane potential. Neostigmine (1 x 10(-5) M) prolonged both the RT and HDT. A decrease in Ca2+ concentration caused a marked reduction in the EPSC amplitude, and a slight shortening in the RT and HDT. An increase in Ca2+ concentration significantly prolonged the RT and HDT without altering the slope of the relationship between the HDT and membrane potential, while the amplitude of EPSC was increased slightly. The HDT was independent of EPSC amplitude. It is suggested that the mechanism responsible for closing the ion channels of the nicotinic receptor at the subsynaptic membrane is regulated by membrane potential. The possible mechanisms of the action of Ca2+ on the decay phase of EPSC were discussed.

Analysis of intestinal cell proliferation after guanethidine-induced sympathectomy. I. Stathmokinetic, labelling index, mitotic index, and cellular migration studies

Guanethidine-induced sympathectomy in the rat during the neonatal period (injection of 20 microgram/g body weight every 48 h from day of birth until day 14) produces an absolute reduction in the number of sympathetic ganglion cells, but no significant alteration of body weight. Superior cervical ganglia show 79.8% fewer cell bodies at 15 days and 92.3% at 45 days; coeliac ganglia exhibit an 81.0% reduction at 15 days and 89.6% at 45 days in guanethidine-treated rats as compared to normal controls. The sympathetic ganglion cells that remain after treatment have an abnormal morphological appearance with distended mitochondria and depletion of endoplasmic reticulum. Sympathectomy produces a prolongation of the generation cycle time (Tc) as measured by the colchicine-induced mitotic arrest technique, and a decrease in labelling, mitotic, and migration indices. In addition, sympathectomy suppresses the amplitude of the circadian rhythm in mitotic activity. The general suppression of this activity in the intestinal epithelium is more pronounced in the jejunum and ileum than in the duodenum. Variation in the effectiveness of sympathectomy on the inhibition of intestinal cell proliferation may be related to segmental differences in cell proliferation, to segmental differences in innervation, and/or to segmental variation in the effectiveness of guanethidine.

Regulation by histamine of cyclic nucleotide levels in sympathetic ganglia

An investigation has been carried out of the role of histamine H1- and H2-receptors in the control of cyclic guanosine 3':5'-monophosphate (cGMP) and cyclic adenosine 3':5'-monophosphate (cAMP) levels in blocks of bovine superior cervical ganglion. The data suggest that activation of H1-receptors is associated with cGMP accumulation and that activation of H2-receptors is associated with cGMP accumulation. Histamine increased both cGMP and cGMP levels with similar time course and concentration-response relationships. Low concentrations of the H1-receptor agonist 2-(2-aminoethyl)thiazole increased cGMP but not cAMP levels. Conversely low concentrations of the H2-receptor agonist 4-methylhistamine increased cAMP but not cGMP levels. H1-receptor antagonists blocked the histamine-induced increase in cGMP at low concentrations but blocked the cAMP increase only at substantially higher concentrations. Conversely, H2-receptor antagonists blocked the histamine-induced increased in cAMP but not cGMP. The effects of histamine on cyclic nucleotide levels did not appear to be mediated via the release of an endogenous neurotransmitter. The histamine-induced increase in cGMP appeared to be mediated through calcium: the increase in cGMP required the presence of calcium in the extracellular medium, and the calcium ionophore A23187 caused a calcium-dependent increase in cGMP. When considered with previous electrophysiological and biochemical findings in sympathetic ganglia, a correspondence can be seen: both histamine (at H1-receptors) and acetylcholine (at muscarinic receptors) raise cGMP levels and are associated with excitatory actions; both histamine (at H2- receptors) and dopamine raise cAMP levels and are associated with inhibitory actions.

Effect of tumor promoters on the response of cultured embryonic chick ganglia to nerve growth factor

The tumor-promoting plant diterpene 12-O-tetradecanoyl-phorbol-13-acetate (TPA) inhibits nerve growth factor (NGF)-provoked neurite outgrowth in cultured embryonic chick sensory and sympathetic ganglia. Other plant diterpenes that are tumor promoters on the mouse skin carcinogenesis system also inhibit ganglia response to NGF, but structurally related nonpromoting compounds are inactive. There is no evidence that the inhibitory effect of TPA is due to cytotoxicity. In fact, it appears that TPA can enhance the survival of neuronal and nonneuronal cells in culture. Although neurite outgrowth is prevented, established neurites do not retract in the presence of TPA. After 24 hr, ganglia can slowly overcome the block, even in the presence of fresh TPA; thus, inhibition is transient. The concentration of NGF that does induce a half-maximal neurite outgrowth response in sensory ganglia is approximately 0.6 X 10(-11) M. The antagonism of NGF by TPA is dose dependent and apparently noncompetitive. TPA concentrations that extensively inhibit neurite outgrowth do not affect the amount of 125I-labeled NGF bound to specific sites on dissociated dorsal root ganglion cells, which supports the contention that TPA acts at a stage beyond the initial interaction of the factor with its receptive site.