Aromatic L-amino acid decarboxylase-immunoreactive structures in human midbrain, pons, and medulla.

The objective of the present study was to determine with precision the localization of neurons and fibers immunoreactive (ir) for aromatic L-amino acid decarboxylase (AADC), the second-step enzyme responsible for conversion of L-dihydroxyphenylalanine (L-DOPA) to dopamine (DA) and 5-hydroxytryptophan (5-HTP) to serotonin (5-hydroxytryptamine: 5-HT) in the midbrain, pons, and medulla oblongata of the adult human brain. Intense AADC immunoreactivity was observed in a large number of presumptive 5-HT neuronal cell bodies distributed in all of the raphe nuclei, as well as in regions outside the raphe nuclei such as the ventral portions of the pons and medulla. Moderate to strong immunoreaction was observable in presumptive DA cells in the mesencephalic reticular formation, substantia nigra, and ventral tegmental area of Tsai, as well as in presumptive noradrenergic (NA) cells, which were aggregated in the locus coeruleus and dispersed in the subcoeruleus nuclei. In the medulla oblongata, immunoreaction of moderate intensity was distributed in the mid and ventrolateral portions of the intermediate reticular nucleus, which constitutes the oblique plate of A1/C1 presumptive adrenergic and/or NA neurons. The dorsal vagal AADC-ir neurons were fewer in number and stained more weakly than cells immunoreactive for tyrosine hydroxylase (TH). AADC immunoreactivity was not identified in an aggregate of TH-ir neurons lying in the gelatinous subnucleus of the solitary nucleus, a restricted region just rostroventral to the area postrema. Nonaminergic AADC-positive neurons (D neurons), which are abundant in the rat and cat midbrain, pons, and medulla, were hardly detectable in homologous regions in the human brain, although they were clearly distinguishable in the forebrain.

VEGF overexpression in the astroglial cells of rat brainstem following ozone exposure.

Ozone, a major photochemical pollutant, produces rapid damages in the pulmonary airway tract and in the central nervous system. This study focused on the neural mechanisms underlying the adaptive responses to an acute ozone exposure. Vascular endothelial growth factor (VEGF) is a factor associated with cellular recovery following brain injury. The aim of this study was to assess and localize the cellular expression of VEGF, since the central respiratory areas show a neuroplasticity in response to ozone. Adult rats were subjected to 0.5ppm ozone for 3h and then recovered for further 3h. The expression of VEGF was evaluated by immunocytochemistry in the central respiratory areas, i.e., the nucleus tractus solitarius (NTS) and the ventrolateral medulla (VLM). The data show a VEGF overexpression at the end of ozone exposure, which persisted during the 3-h recovery. Interestingly, using confocal analysis the bulk of VEGF labeling was observed in astroglial cell bodies and branches, while neuronal labeling was hardly noticed. Moreover, VEGF colocalized with IL-6 and TNFalpha in astrocytes closely apposed to blood vessel walls. The vasculature area was markedly increased (+58%) during post-ozone recovery. The data show that an acute ozone exposure affects primarily glial cells in the central nervous system. The VEGF up-regulation which persists after ozone exposure may contribute to brain repair and consecutive functional adaptations.

Localization of L-DOPA uptake and decarboxylating neuronal structures in the cat brain using dopamine immunohistochemistry.

The present study examined dopamine-immunoreactive neuronal structures using immunohistochemistry in conjunction with an anti-dopamine antiserum, following injection of l-3,4-dihydroxyphenylalanine (L-DOPA) with or without an inhibitor of monoamine oxidase (Pargyline) in the cat brain. L-DOPA injection made it possible to detect dopamine immunoreactivity in presumptive serotonergic and noradrenergic cell bodies and axons. Weak to moderate dopamine immunoreactivity was observed in non-aminergic cells (possibly so-called "D" cells containing aromatic L-amino acid decarboxylase (AADC)) in several hypothalamic, midbrain, pontine and medullary nuclei. Intense dopamine immunoreactivity became visible in a large number of cells and axons (possibly containing AADC) with wide distribution in the brain following administration of L-DOPA with Pargyline. AADC is most likely active in cells and axons that take up L-DOPA, where it decarboxylates the L-DOPA to dopamine. However, newly synthesized dopamine in such cells is rapidly oxidized by monoamine oxidase.

[Brain and sleep mechanism].

It is now accepted that sleep is induced by biological clock located in the suprachiasmatic nucleus and/or sleep promoting substances, which influence ventrolateral preoptic (VLPO) neurons. The VLPO neurons affects more caudally situated posterior hypothalamic ones containing orexine and/or histamine, reciprocally. When these neurons inhibit lower brainstem aminergic ones, sleep is induced. REM (Rapid Eye Movement) sleep can be induced mainly by brainstem cholinergic neurons, when aminergic ones are completely inhibited. During this stage, tonic activities and phasic Ponto-Geniculate-Occipital (PGO) ones originated within brainstem cholinergic neurons activate irregularly many parts of the brain such as the cerebral cortex and limbic system to produce dream-like activity. Muscle atonia is also observed during REM sleep. This atonia is caused by neurons in the pontine reticular inhibitory area (PIA), which is normally inhibited by aminergic inputs. The PIA affects medullary neurons of the paramedian and/or magnocelullar nuclei to regulate motoneurons in the ventral horn. Therefore. muscle atonia is produced when these PPT cells are active during REM sleep. In addition, based upon many recent data, sleep is not a passive state but rather an active state, during which recuperation of neuronal system is promoted and information processing is executed.

Single eight-hour shift of light-dark cycle increases brain-derived neurotrophic factor protein levels in the rat hippocampus.

We previously reported that an eight hour phase advance in the light-dark (LD) cycle increases sleep in rats. Brain-derived neurotrophic factor (BDNF) is suggested to be one of the sleep and circadian regulating factors. We have therefore observed the responses of BDNF protein in the hippocampus, cerebellum and brainstem under conditions of LD change. BDNF protein was quantitatively measured using an ELISA kit. Under an 8-h LD phase advance, the levels of hippocampal BDNF were significantly increased on the day of the phase change, while the levels in the cerebellum and brainstem remained constant. Plasma corticosterone levels were not largely affected. Thus, a single LD shift acutely affects hippocampal BDNF metabolism with no large stress response.

L-3,4-Dihydroxyphenylalanine as a neurotransmitter candidate in the central nervous system.

Historically, 3,4-dihydroxyphenylalanine (DOPA) has been believed to be an inert amino acid that alleviates the symptoms of Parkinson's disease by its conversion to dopamine via the enzyme aromatic L-amino acid decarboxylase. In contrast to this generally accepted idea, we propose that DOPA itself is a neurotransmitter and/or neuromodulator, in addition to being a precursor of dopamine. Several criteria, such as synthesis, metabolism, active transport, existence, physiological release, competitive antagonism, and physiological or pharmacological responses, must be satisfied before a compound is accepted as a neurotransmitter. Recent evidence suggests that DOPA fulfills these criteria in its involvement mainly in baroreflex neurotransmission in the lower brainstem and in delayed neuronal death by transient ischemia in the striatum and the hippocampal CA1 region of rats.

Circadian rhythm of aromatic L-amino acid decarboxylase in the rat suprachiasmatic nucleus: gene expression and decarboxylating activity in clock oscillating cells.

BACKGROUND: Aromatic L-amino acid decarboxylase (AADC) is the enzyme responsible for the decarboxylation step in both the catecholamine and indoleamine synthetic pathways. In the brain, however, a group of AADC containing neurones is found outside the classical monoaminergic cell groups. Since such non-monoaminergic AADC is expressed abundantly in the suprachiasmatic nucleus (SCN), the mammalian circadian centre, we characterized the role of AADC in circadian oscillation. RESULTS: AADC gene expression was observed in neurones of the dorsomedial subdivision of the SCN and its dorsal continuant in the anterior hypothalamic area. These AADC neurones could uptake exogenously applied L-DOPA and formed dopamine. AADC was co-expressed with vasopressin and the clock gene Per1 in the neurones of the SCN. Circadian gene expression of AADC was observed with a peak at subjective day and a trough at subjective night. The circadian rhythm of AADC enzyme activity in the SCN reflects the expression of the gene. CONCLUSIONS: Non-monoaminergic AADC in the SCN is expressed in clock oscillating cells, and the decarboxylating activity of master clock cells are under the control of the circadian rhythm.

Colocalization of NO and VIP in neurons of the submucous plexus in the rat intestine.

Since very few previous studies have carried out the quantitative analysis for the colocalization of nitric oxide (NO) and vasoactive intestinal peptide (VIP) in the submucous neurons in the rat digestive tract, we applied in vivo treatment of colchicine to enhance the immunoreactivity and examined the colocalization of NO synthase (nNOS) and VIP in neurons of the submucous plexus throughout the rat digestive tract. The density of nNOS-containing neurons in the submucous plexus in the stomach corpus (103+/-25 cells/cm(2), n=3) and that in the antrum (157+/-9 cells/cm(2), n=3) were significantly lower than those in small and large intestine. However no difference was detected in the cell density among duodenum (1967+/-188 cells/cm(2), n=3), jejunum (2640+/-140 cells/cm(2), n=3), ileum (2070+/-42 cells/cm(2), n=3), proximal colon (2243+/-138 cells/cm(2), n=3) and distal colon (2633+/-376 cells/cm(2), n=3). The proportion of nNOS-immunoreactive (IR), nNOS/VIP-IR and VIP-IR neurons to the total number of submucous neurons was examined. nNOS/VIP-IR neurons comprised 45-55% of total number of submucous neurons from the duodenum to the proximal colon, however those comprised 66.4+/-5.1% in the distal colon. The results showed that the dense distribution of nNOS-containing neurons was found in the submucous plexus throughout the small and large intestine, and large population of submucous neurons co-stored nNOS and VIP.