Neurotransmitter phenotypic plasticity in the mammalian embryo

Long-lasting effect of catecholamine deficiency on differentiating vasopressin and oxytocin neurons in the rat supraoptic nucleus

According to our earlier study, the catecholamine depletion in neonatal rats resulted in stimulation of the vasopressin and oxytocin gene expression in the neurons of the supraoptic nucleus. The present study extends this line, evaluating whether the catecholamine deficiency provides a long-lasting effect on the differentiating vasopressin and oxytocin neurons of the supraoptic nucleus. Catecholamines were depleted by daily injections of an inhibitor of the catecholamine synthesis, alpha-methyl-p-tyrosine, first, to pregnant rats from the 9th to the 21st day of gestation and, then, to their pups from the 2nd to the 10th postnatal day. The animals, injected with saline instead of drugs, served as controls. The pharmacologically-treated and control rats were kept for four months under normal laboratory conditions until processing the materials for semi-quantitative in situ hybridization and immunocytochemistry of vasopressin and oxytocin messenger RNAs and peptides, respectively. There were no differences in the vasopressin and oxytocin messenger RNA concentrations in the supraoptic nucleus in rats following preliminary catecholamine depletion compared to controls. Conversely, the catecholamine deficiency resulted in an increased content of the vasopressin-immunoreactive material in cell bodies and processes. This was also the case for the oxytocin-immunoreactive cell bodies but only in females, suggesting an interference of catecholamines with sexual steroids in their action. The number and size of vasopressin and oxytocin neurons did not change in pharmacologically-treated rats compared to the controls. Thus, the catecholamine deficiency in the course of the neuron differentiation resulted in a long-lasting augmentation of the intracellular content of vasopressin and oxytocin but did not influence the vasopressin and oxytocin gene expression. This might be explained rather by the reduced level of peptide release than by an increased level of the peptide production.

Global and serial neurons form A hierarchically arranged interface proposed to underlie memory and cognition

It is hypothesized that the cholinergic and monoaminergic neurons of the brain from a global network. What is meant by a global network is that these neurons operate as a unified whole, generating widespread patterns of activity in concert with particular electroencephalographic states, moods and cognitive gestalts. Apart from cholinergic and monoaminergic global systems, most other mammalian neurons relay sensory information about the external and internal milieu to serially ordered loci. These "serial" neurons are neurochemically distinct from global neurons and commonly use small molecule amino acid neurotransmitters such as glutamate or aspartate. Viewing the circuitry of the mammalian brain within the global-serial dichotomy leads to a number of novel interpretations and predictions. Global systems seem to be capable of transforming incoming sensory data into cognitive-related activity patterns. A comparative examination of global and serial systems anatomy, development and physiology reveals how global systems might turn sensation into mentation. An important step in this process is the permanent encoding of memory. Global neurons are particularly plastic, as are the neurons receiving global inputs. Global afferents appear to be capable of reorganizing synapses on recipient serial cells, thus leading to enhanced responding to a signal, in a particular context and state of arousal.

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.

Development of the suprachiasmatic nucleus in rats during ontogenesis: tyrosine hydroxylase immunopositive cell bodies and fibers

This study has evaluated differentiation of tyrosine hydroxylase-immunopositive neurons in the suprachiasmatic nucleus as well as the innervation of this nucleus by tyrosine hydroxylase-immunopositive axons in rats during ontogenesis. Tyrosine hydroxylase-containing structures were detected with electron-microscopic pre-embedding immunocytochemistry at the 22nd fetal day as well as at the second, ninth and 21st postnatal days. Rare uni- and bipolar small tyrosine-hydroxylase-immunopositive neurons were observed in the suprachiasmatic nucleus both in fetuses and postnatal rats. These neurons underwent differentiation over the perinatal period that was mainly manifested in the increase of their size as well as in the development of the Golgi complex, granular endoplasmic reticulum and the onset of the dense core vesicle production. Concomitantly, tyrosine hydroxylase-immunopositive neurons, cell bodies and dendrites, became innervated by immunonegative axons first making presynapses, and, then, symmetric (Gray-type II) and asymmetric (Gray-type I) synapses. In addition to cell bodies and dendrites, tyrosine hydroxylase-immunopositive axons were regularly observed in ventral, ventrolateral and ventromedial regions of the suprachiasmatic nucleus in fetuses and postnatal rats. Tyrosine hydroxylase-immunopositive axons were observed either in simple appositions with the immunonegative neurons or making presynapses in fetuses and symmetric and asymmetric synapses in postnatal animals. The nature of the tyrosine hydroxylase-immunopositive axons and the functional significance in the suprachiasmatic nucleus in ontogenesis are discussed.

Adrenergic regulation of visuocortical plasticity: a role of the locus coeruleus system

Noradrenaline-beta-adrenoceptor-mediated neural plasticity in cat visual cortex exemplifies clearly established roles of the locus coeruleus system in brain function. The prime role of the noradrenaline-beta-adrenoceptor system in the regulation of ocular dominance plasticity is discussed in this chapter and includes a newly invented paradigm of ocular dominance changes under anesthesia and paralysis without benefit of visual attention. Based on our recent findings, we have sought to integrate positive contributions of muscarinic cholinergic receptors to the beta-adrenoceptor-mediated regulatory processes. The issue of "activity dependency" is important and we recognize the necessity of designing new studies in which relationships between activity dependency within the visual pathway and global neurochemical/cellular factors can be tested directly. Further, we critically reviewed the involvement of gamma-aminobutyric acidA type receptors and N-methyl-D-aspartate receptors in the regulation of ocular dominance plasticity.