Histochemical study of the cholinesterase activity in cat myenteric ganglia during postnatal development

Postnatal development of methionine-enkephalin modulation of cholinergic transmission in cat ileum

The age-dependent effects of methionine-enkephalin (Met-enk) on contractions and [3H]-acetylcholine ([3H]-ACh) release evoked by electrical field stimulation (EFS) were studied in vitro on cat terminal ileum of young (2-month old) and adult cats. Radioactivity was measured by liquid scintillation spectrometry and the effect of Met-enk was evaluated by the FrS2/FrS1 ratio. Scopolamine, 1 microM, abolished the EFS-induced contractions. Met-enk dose dependently (0.01-1 microM) decreased the EFS-induced contractions. The inhibitory effect of Met-enk on the evoked contractions was more pronounced in adult cats compared to that in young cats. In adult animals Met-enk, 1 microM, almost completely inhibited the evoked contractions (94.6 +/- 2.6% of inhibition) while in the young cats its inhibitory effect was less pronounced (52.1 +/- 6.8%). Met-enk decreased the EFS-evoked release of [3H]-ACh by 44.6 +/- 4.6% in adult cats and by 21.6 +/- 1.6% in young cats. The data suggest opioid modulation of cholinergic transmission in cat terminal ileum at neuronal level occurring as early as the postnatal period and increasing with the ontogenesis.

Development of innervation in cat gastrointestinal sphincters during the postnatal period. (Functional studies)

The development of function in the intramural nerves was investigated by evaluating the mechanical responses of the smooth muscle of cat gastrointestinal sphincters to transmural electrical stimulation (2-20 Hz, 0.5 msec, supramaximal intensity for 20 sec) between 1 and 60 days postnatal. The intramural nervous system of the gastrointestinal sphincters was found to develop functionally in a cranio-caudal sequence. The cholinergic innervation in the lower esophageal sphincter (LES) was well developed in the first postnatal days. The development of the non-cholinergic, non-adrenergic innervation, however, proceeded further. An age-determined increase in the amplitude of the adrenoblocker-resistant primary relaxation of LES evoked by switching on the electrical stimulation, was established. The cholinergic innervation in the pyloric sphincter (PS) and ileocecal sphincter (ICS) was developed in the first postnatal days. The non-cholinergic, non-adrenergic innervation appeared in PS between 10- and 15-days postnatal and in ICS between 15- and 60-days postnatal. Noradrenaline (1 mumol) elicited responses typical of adult cats as early as the first postnatal days: contraction in LES and relaxation in PS. In ICS it did not evoke the typical response, contraction, until 15 days after birth.

Changes in the responsiveness of the cat ileocecal sphincter to adrenergic agents during the postnatal period

The changes in the responsiveness of the cat ileocecal sphincter (ICS) to adrenergic agents during the postnatal period were studied by the effect of noradrenaline (applied cumulatively: 0.01-100 mumol) on the mechanical activity:smooth muscle tone and phasic contractions. Noradrenaline contracted the ICS smooth muscle through alpha 1-adrenergic receptors. These receptors were differentiated in the first postnatal days but continue to develop functionally even after 60 days postnatal. An age-determined decrease in the EC50 values of noradrenaline, inducing tonic contractions, was established. Noradrenaline inhibited the phasic contractions of ICS. This effect increased after beta-adrenergic receptor blockers, and disappeared after blocking of alpha 1-adrenergic receptors, which suggests the existence of a postjunctional inhibitory adrenergic receptor of alpha 1 type. The beta-adrenergic receptors in the ICS smooth muscle are not differentiated until 15 days postnatal. They developed functionally towards 30 days postnatal.

The enteric nervous system in tissue culture. III. Studies on neuronal survival and the retention of biochemical and morphological differentiation

The maintenance of differentiated properties and survival rates of enteric neurons, grown in explant cultures for periods of up to 3 weeks, was studied. Using catecholamine fluorescence, immunohistochemistry and autoradiography, it was found that adrenergic neurons, VIP-containing neurons and putative GABAergic neurons, which constitute small subpopulations of guinea pig myenteric neurons in vivo, were all represented in plexus explants after maintenance in culture for 2-3 weeks. The pattern of expression of the transmitter-related enzymes, acetylcholinesterase and monoamine oxidase, paralleled that found in in situ studies. Investigation of neuronal structure by intracellular injection of horseradish peroxidase revealed that the cultured neurons continue to express the wide diversity in gross morphology which characterizes these cells in vivo. Employing autoradiography following uptake of [3H]GABA to label putative GABAergic neurons, their survival rate from days 1 to 15 of culturing was determined. No neuronal death was detected between days 1 and 5, while the number of neurons decreased between days 5 and 15. These observations suggest that enteric neurons maintained in explant cultures survive well and maintain to a high degree their histochemical and morphological properties.