Functional autonomic neuromuscular junctions in tissue culture

Stages of neurotransmitter development in autonomic neurons

The ontogeny of neurotransmitters in autonomic neurons proceeds through the successive stages of early expression, definitive expression, modulation, and regulation, extending from embryonic life to maturity. Although different extracellular signals influence development at different stages, a number of signals that influence development continue to govern transmitter function during maturity. The sequential ontogenetic stages parallel the progressive restriction of mutability of phenotypic expression; however, some degree of neuronal mutability appears to persist through maturity.

Smooth muscle from aganglionic bowel in Hirschsprung's disease impairs neuronal development in vitro

Hirschsprung's disease results from the congenital absence of enteric neurons in human distal colon. The reason for aganglionosis is unknown but may reflect an unfavourable microenvironment for neuronal development. We asked if smooth muscle cells from the anganglionic region could affect neuronal development in vitro. Neurons from neonatal mouse superior cervical ganglia were added to cultures of smooth muscle obtained from normal or aganglionic regions of five patients with Hirschsprung's disease. Although neurons initially showed more rapid attachment to aganglionic smooth muscle, this was equal by 60 min and thereafter. Progressive increase in the diameter of the nerve cell body was characteristic of normal maturation in vitro. This was consistently inhibited by 15-22% in neurons grown on aganglionic muscle compared with normal controls over the 6-day test period (P < 0.05). This phenomenon was preserved when the smooth muscle cells were lysed by brief exposure to distilled water before initiation of co-culture (16-18% inhibition; P < 0.05). These data imply that smooth muscle of the aganglionic colon is less favourable for neuronal development than the normally innervated region and suggest a membrane-linked factor. Clearly, this persists in postnatal life and in vitro and may reflect an abnormality of cellular interaction causing Hirschsprung's disease.

The use of cell and tissue culture techniques in the study of regulatory peptides

Cell and tissue culture preparations have a number of general advantages for the study of biological processes: cells are more accessible for study, diffusion delays and barriers to applied substances are minimised, the humoral and cellular components of the culture environment can be controlled and progressive changes in intracellular and intercellular events can be directly monitored. These significant advantages mean that culture preparations can provide unique opportunities for investigation of the properties and functions of regulatory peptides. Culture preparations also have disadvantages and not all cultures are suitable for use in all types of experiments; therefore, the choice of preparation must be made accordingly. Here we describe different types of culture preparation and give examples where cultures have been used to examine peptide synthesis, storage, secretion and receptor localisation, as well as the short-term and trophic actions of regulatory peptides.

Electrical activity and contraction in cells isolated from rat and guinea-pig ventricular muscle: a comparative study

1. Contraction in single ventricular muscle cells from rat and guinea-pig heart was measured using an optical technique, while at the same time either action potentials were recorded or transmembrane currents were measured under voltage-clamp conditions. 2. When the membrane was depolarized to 0 mV, there was a phasic and a tonic component of the contraction in guinea-pig cells, whereas in rat cells only the phasic component was obvious. In both species the depolarizations evoked the second inward current (Isi). 3. In rat cells, when the membrane potential during a depolarization was varied over the range -40 to +60 mV, the amplitude of contraction first increased to a peak at a potential close to 0 mV, and then declined as the membrane potential became more positive. In contrast, contraction in guinea-pig cells measured under similar conditions continued to increase as the depolarization was increased, and the tonic component of contraction became more obvious at more positive potentials. Contraction amplitude in guinea-pig cells could also be increased by increasing pulse duration under conditions where the tonic component of contraction was prominent. 4. Contraction during depolarization was suppressed by ryanodine in rat cells, whereas in guinea-pig cells contraction persisted, but with a modified time course. Ryanodine did inhibit spontaneous contractions of guinea-pig cells during exposure to low extracellular sodium. 5. Nifedipine suppressed Isi and phasic contraction in both rat and guinea-pig cells. In guinea-pig cells these effects developed contemporaneously, but in rat cells substantial reduction of Isi occurred before marked suppression of contraction. 6. In rat cells exposed to strontium in place of external calcium, inactivation of Isi was slowed and contraction was prolonged, with a slower time-to-peak and relaxation. The time course of the action potential was modified and ryanodine no longer inhibited contraction of rat cells in the presence of strontium. 7. It is concluded that the amplitude of contraction in rat and guinea-pig ventricular cells is determined by calcium both entering through the surface membrane and released from internal stores, and that under normal conditions the balance is towards release from stores in rat cells, and towards entry through the surface in guinea-pig cells.

The effects of ryanodine, EGTA and low-sodium on action potentials in rat and guinea-pig ventricular myocytes: evidence for two inward currents during the plateau

Action potentials were recorded from single cells isolated from rat and guinea-pig ventricular muscle. In rat cells the repolarization showed two distinct phases, referred to as the early and late phases. In guinea-pig cells there was a maintained plateau. Reducing external sodium by replacement with lithium or choline suppressed the late phase of the action potential in rat cells, and shortened the plateau of the action potential in guinea-pig cells. Intracellular EGTA abolished contraction while suppressing the late phase of the action potential in rat cells, and shortening the plateau in guinea-pig cells. Ryanodine (1 microM), which is thought to inhibit the release of calcium from internal stores, suppressed contraction and the late phase of the action potential in rat cells. In guinea-pig cells, there was no substantial effect of ryanodine (1 microM) on either contraction or the time course of the action potential. The late phase of the action potential in rat cells was suppressed by increasing the external potassium concentration to 12 mM, and enhanced by reducing external potassium to 1.2 mM. It is concluded that an inward current activated by internal calcium contributes to the late phase of the action potential in rat cells, and to the plateau in guinea-pig cells. Two possibilities are a current arising from electrogenic sodium-calcium exchange, and a current through ion channels activated by calcium. The effects of reducing external sodium would be consistent with either mechanism. The contribution of such an inward current would be expected to be modified by outward currents through a rectifying potassium conductance which varies with external potassium concentration. In the rat, but not the guinea-pig, the rise in internal calcium which activates the inward current seems to be largely dependent on ryanodine-sensitive release of calcium from internal stores.

Characteristics of the second inward current in cells isolated from rat ventricular muscle

The second inward current (Isi) in single cells isolated from ventricular muscle of adult rat hearts was measured in response to step depolarizations under voltage-clamp conditions. The major ion carrying this current was Ca, and Isi was reduced or abolished by Mn, Ni, Cd, nifedipine, nimodipine and D600. Sr and B could substitute for Ca as charge carriers, and reduced the rate of apparent inactivation of Isi. These effects of Sr and Ba, together with the relation between the steady level of apparent inactivation and membrane potential in Ca containing solution, were taken as evidence that inactivation was at least in part dependent on internal Ca. The reduction of external Na to 11% of normal caused a reduction in peak Isi when Ca was present in the external solution, but did not reduce Isi when Ca was replaced by Sr. It therefore seems unlikely that Na is a major charge carrier for Isi under the conditions of our experiments. The time-to-peak and rate of apparent inactivation of Isi were faster than in previous studies that used multicellular preparations. Both the kinetics and peak amplitude of Isi were markedly dependent on temperature (Q10 close to 3). Contraction of the cells, which was monitored optically, was initiated within 3 ms of the peak Isi, reached a maximum level after approximately 40-50 ms, and was about 100 ms in duration.

Review lecture. Neurotransmitters and trophic factors in the autonomic nervous system

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The development and ultrastructure of previously dissociated embryonic chick corpus striatum cultured on feeder layers of liver cells

Embryonic chick corpus striatum neurons were dissociated and maintained on liver feeder layers in culture. Although some large dark-cored vesicles were present in many nerve processes and presynaptic boutons they were substantially less numerous than chick spinal cord neurons grown under identical conditions. Paraformaldehyde-induced fluorescence, although observed in a few culture batches in aggregates of corpus striatum neurons, was otherwise absent and no decisive evidence was obtained to suggest that fluorescent corpus striatum neurons were commonly developed on liver feeder layers in culture. Microtubules filled most cell bodies and nerve processes, and extended well into synaptic boutons often approaching the active zones. They were much more abundant in cultures of corpus striatum than in comparable spinal cord preparations and formed the principal organelle of many nerve fibres. These differences between chick spinal cord and corpus striatum neurons are both interesting and difficult to interpret. It is possible that fewer appropriate cholinergic neurons are available for transformation into adrenergic neurons within the corpus striatum, and that excessive numbers of dark-cored vesicles indicate only a greatly increased rate of acetylcholine production and storage.

Purinergic innervation of the guinea-pig urinary bladder

1 A number of criteria for considering adenosine 5'-triphosphate (ATP) as a neurotransmitter in the guinea-pig urinary bladder have been examined. In addition, the effect of tachyphylaxis to ATP on the response to non-adrenergic, non-cholinergic nerve stimulation has been re-examined.2 Quinacrine fluorescence histochemistry revealed a population of nerve fibres, ganglion cells, and nerve bundles in the bladder which were not seen in either the iris or vas deferens, where adrenergic and cholinergic nerves predominate. The distribution and morphology of the quinacrine-positive nerves in the bladder were different from those observed with catecholamine fluorescence and cholinesterase histochemistry, and were unaffected by chemical sympathectomy.3 Release of ATP from the bladder during stimulation of intramural excitatory nerves, in the presence of atropine and guanethidine increased to 3-12 times prestimulation levels. Tetrodotoxin abolished both the contractile response and the increase in ATP release resulting from intramural nerve stimulation. There was no increase in ATP release during contraction resulting from direct muscle stimulation following nerve paralysis with tetrodotoxin.4 Sympathectomy with 6-hydroxydopamine did not affect release of ATP in response to intramural nerve stimulation.5 Release of ATP was dependent on the concentration of calcium ion in the medium.6 Contractions in response to non-adrenergic, non-cholinergic intramural nerve stimulation were closely mimicked by ATP, but not by acetylcholine or histamine.7 Adenosine and dipyridamole reduced the contractions to both ATP and non-cholinergic nerve stimulation.8 2-2'-Pyridylisatogen was not a specific blocker of either ATP or intramural nerve stimulation in the guinea-pig bladder. 2-Substituted imidazolines initiated spontaneous activity making it impossible to assess any blocking action that they may have had.9 Prostaglandins (E(1), E(2) and F(2alpha)) gave weak, slow contractions and an increase in spontaneous activity. Both the response to ATP and non-adrenergic, non-cholinergic nerve stimulation were greatly potentiated in the presence of prostaglandins.10 In the presence of indomethacin the response to non-adrenergic, non-cholinergic nerve stimulation was virtually abolished following desensitization to ATP.

Neurotransmitter synthesis and uptake by isolated sympathetic neurones in microcultures

Assays of isolated single sympathetic neurones show that their transmitter functions can be either adrenergic or cholinergic depending on growth conditions. The data suggest that the number of transmitters made by most mature individual neurones is restricted.

Innervation of heart cells in culture by an endogenous source of cholinergic neurons

Hearts of embryonic mice 9 days in utero were found to have an endogenous source of cholinergic neurons which can survive in dispersed cell cultures. These neurons are electrically excitable, have ultrastructural characteristics of cholinergic embryonic neurons, and functionally innervate heart cells in culture. The nature of the innervation described is muscarinic cholinergic.

Specificity of innervation of iris musculature by sympathetic nerve fibres in tissue culture

Irides from 3-5 day old rats have been grown 1-3 mm from superior cervical or lumbar paravertebral sympathetic ganglia in modified Rose chambers. The two muscles of the iris received distinctly different innervation patterns in vitro, and these were similar to those seen in vivo. Varicose, adrenergic fibres were consistently associated with the dilator pupillae rather than with the sphincter pupillae while excitatory, cholinergic junctions developed between the nerve fibres and the muscle cells of the spincter but not the dilator. There was a lack of specificity shown by the sympathetic neurons during this innervation. Fibres from lumbar ganglia formed plexuses within the dilator similar to those formed by superior cervical fibres, and sympathetic, cholinergic fibres were able to substitute for the normal parasympathetic, cholinergic fibres in the sphincter.