Neuronal control of neurotransmitters biosynthesis during development

The Gut's Little Brain in Control of Intestinal Immunity

The gut immune system shares many mediators and receptors with the autonomic nervous system. Good examples thereof are the parasympathetic (vagal) and sympathetic neurotransmitters, for which many immune cell types in a gut context express receptors or enzymes required for their synthesis. For some of these the relevance for immune regulation has been recently defined. Earlier and more recent studies in neuroscience and immunology have indicated the anatomical and cellular basis for bidirectional interactions between the nervous and immune systems. Sympathetic immune modulation is well described earlier, and in the last decade the parasympathetic vagal nerve has been put forward as an integral part of an immune regulation network via its release of Ach, a system coined "the cholinergic anti-inflammatory reflex." A prototypical example is the inflammatory reflex, comprised of an afferent arm that senses inflammation and an efferent arm: the cholinergic anti-inflammatory pathway, that inhibits innate immune responses. In this paper, the current understanding of how innate mucosal immunity can be influenced by the neuronal system is summarized, and cell types and receptors involved in this interaction will be highlighted. Focus will be given on the direct neuronal regulatory mechanisms, as well as current advances regarding the role of microbes in modulating communication in the gut-brain axis.

Current approaches to development of the autonomic nervous system: clues to clinical problems

A number of different approaches to autonomic development utilizing a variety of experimental models and analytical techniques have been outlined. A scheme, which attempts to delineate a series of events involving separate but sometimes overlapping mechanisms, is proposed for the complex process of formation and maintenance of functional autonomic neuroeffector junctions. The relevance of these basic mechanisms of a variety of clinical abnormalities of autonomic function is discussed.

Pregnancy induces degenerative and regenerative changes in the autonomic innervation of the female reproductive tract

The uterus is supplied with an extensive system of adrenergic nerves. The neurobiological properties of this innervation have been investigated in a series of studies primarily using the guinea-pig as model. The guinea-pig uterus is supplied from three different sources: the paracervical plexus, containing short adrenergic neurons; the inferior mesenteric ganglion; and a cranial source, probably the aorticorenal plexus, via nerves in the uterine suspensory ligaments. The nerve density is higher in the tubal end of the uterine horn and in the cervix than in the main part of the uterine horn. The turnover rate of transmitter is lower in the uterus than in a control organ, such as the heart. Noradrenaline levels in the uterus, but not the heart, are influenced by alterations in the endocrine milieu, e.g. during the oestrous cycle and after treatment with sex steroids. In the uterine tissue surrounding the conceptus during pregnancy, there is an early and drastic decay in various functional parameters related to the adrenergic nerve plexus and primarily reflecting a local, pregnancy-induced axonal degeneration. In the main part of the empty horn, in unilateral pregnancy, there is an extensive decay in various adrenergic functional parameters; these, however, reflect changes in a nerve plexus that has an essentially intact structure. No sign of functional impairment is seen in the adrenergic nerves of the uterine cervix. The increased turnover rate and reduced transmitter content in this region during late pregnancy may reflect increased frequency of firing of the adrenergic nerves. The tubal end of the uterine horn shows no signs of altered sympathetic function. This is the only part of the uterine horn that appears unaffected by pregnancy. The deficient recovery post partum of the changes in the uterine horn that previously contained the fetuses suggests permanent damage to the adrenergic nerve plexus after a pregnancy. The post partum recovery of changes seen in the previously empty horn, however, is more pronounced but still incomplete by comparison with the innervation before pregnancy. Studies on the adult human uterus indicate that similar events to those described for the guinea-pig model occur in human pregnancy.

Development of choline acetyltransferase and cholinesterase activities in enteric ganglia derives from presumptive adrenergic and cholinergic levels of the neural crest

The cholinergic differentiation of enteric ganglia in embryos of chick and quail was studied with particular reference to cholinesterase and choline acetyltransferase activities. Differentiation during normal development was compared with that obtained after culture of the neural primordium or neural crest in direct association with aneural hindgut. Biochemically differentiated cholinergic ganglia developed in explants containing cells from either the 'vagal' (presumptive cholinergic) or 'truncal' (presumptive adrenergic) levels of the neural crest. Neither extra-intestinal migration of neural crest cell nor the presence of central preganglionic fibres is a prerequisite for enteric ganglion differentiation.

The effect of a single dose of reserpine administered prior to incubation on the development of tyrosine hydroxylase activity in chick sympathetic ganglia

A single dose of reserpine administered into the yolk sac of chicken eggs prior to incubation produces two distinct periods of significant increase in tyrosine hydroxylase (TH) activity over controls. The first period is 21 days of incubation (55%) and the second is between day 14 and 30 after hatching (a.h.) (69%). Cholineacetyltransferase (ChAc) and dopadecarboxylase (DDC) are not modified in the two periods of increased TH activity. Reserpine had no effect on cholinergic parasympathetic synapses and neurons in the ciliary ganglion, as judged by ChAc activity. When reserpine was acutely administered in three different posthatching periods only the injection at the latest period (days 26 and 27) caused a significant (38%) increase in TH activity at day 30. Postsynaptic nicotinic receptors were blocked selectively by injecting chlorisondamine in the chick starting at hatching for one week. The administration of chlorisondamine almost completely abolished the reserpine induced increase of TH activity at day 15 a.h. The present results support the view that the development of enzyme activities specifically related to neurotransmitter biosynthesis in chick autonomic ganglia is regulated not only by transsynaptic influences but also by regulatory inputs originating in the periphery.