BMP signaling through BMPRIA in astrocytes is essential for proper cerebral angiogenesis and formation of the blood-brain-barrier.

Bone morphogenetic protein (BMP) signaling is involved in differentiation of neural precursor cells into astrocytes, but its contribution to angiogenesis is not well characterized. This study examines the role of BMP signaling through BMP type IA receptor (BMPRIA) in early neural development using a conditional knockout mouse model, in which Bmpr1a is selectively disrupted in telencephalic neural stem cells. The conditional mutant mice show a significant increase in the number of cerebral blood vessels and the level of vascular endothelial growth factor (VEGF) is significantly upregulated in the mutant astrocytes. The mutant mice also show leakage of immunoglobulin around cerebral microvessels in neonatal mice, suggesting a defect in formation of the blood-brain-barrier. In addition, astrocytic endfeet fail to encircle cortical blood vessels in the mutant mice. These results suggest that BMPRIA signaling in astrocytes regulates the expression of VEGF for proper cerebrovascular angiogenesis and has a role on in the formation of the blood-brain-barrier.

Chronic nicotine treatment increases GABAergic input to striatal neurons.

Recent studies suggest the involvement of the dorsal striatum in the advanced stages of drug addiction as well as motor functions. We investigated the effect of chronic nicotine treatment on GABAergic synaptic transmission in the striatum of mice. Intrastriatal stimulation evoked GABAA receptor-mediated polysynaptic inhibitory postsynaptic currents more frequently in medium-sized spiny projection neurons of mice treated chronically with nicotine (1 mg/kg, twice-daily subcutaneous injections for 10-15 days) than in those of PBS-treated mice. The multiphasic inhibitory postsynaptic currents consisted of monosynaptic early and polysynaptic, nicotinic acetylcholine receptor-mediated late components. Dihydro-beta-erythroidine, an antagonist of the non-alpha7nicotinic acetylcholine receptor, suppressed only the late inhibitory postsynaptic current. These results suggest that chronic nicotine treatment increases GABAergic input to projection neurons in the dorsal striatum.

Comparison of alpha2 nicotinic acetylcholine receptor subunit mRNA expression in the central nervous system of rats and mice.

The nicotinic acetylcholine receptor (nAChR) alpha2 subunit was the first neuronal nAChR to be cloned. However, data for the distribution of alpha2 mRNA in the rodent exists in only a few studies. Therefore, we investigated the expression of alpha2 mRNA in the rat and mouse central nervous systems using nonradioactive in situ hybridization histochemistry. We detected strong hybridization signals in cell bodies located in the internal plexiform layer of the olfactory bulb, the interpeduncular nucleus of the midbrain, the ventral and dorsal tegmental nuclei, the median raphe nucleus of the pons, the ventral part of the medullary reticular nucleus, the ventral horn in the spinal cord of both rats and mice, and in a few Purkinje cells of rats, but not of mice. Cells that moderately express alpha2 mRNA were localized to the cerebral cortex layers V and VI, the subiculum, the oriens layer of CA1, the medial septum, the diagonal band complex, the substantia innominata, and the amygdala of both animals. They were also located in a few midbrain nuclei of rats, whereas in mice they were either few or absent in these areas. However, in the upper medulla oblongata alpha2 mRNA was expressed in several large neurons of the gigantocellular reticular nucleus and the raphe magnus nucleus of mice, but not of rats. The data obtained show that a similar pattern of alpha2 mRNA expression exists in both rats and mice, with the exception of a few regions, and provide the basis for cellular level analysis.

Endogenous zinc can be a modulator of glycinergic signaling pathway in the rat retina.

Zinc is a modulator of glutamatergic inputs in the hippocampus. In the retina, however, we previously reported that endogenous zinc is present in the non-glutamatergic neural processes and earlier electrophysiological studies suggest that zinc is a modulator of inhibitory signaling pathways, which are mediated by glycine and GABA. AII amacrine cells, a subpopulation of glycinergic amacrine cells, are identified by selective immunoreactivity for parvalbumin in the rat retina. In the present study, therefore, we focused on whether zinc is present in AII amacrine cells using silver amplification combined with immunohistochemistry in the rat retina. We also examined whether zinc modulate glycine response in the rat retina by the patch clamp technique. Association of silver precipitates with the parvalbumin-immunoreactive neural processes was observed at the ultrastructural level. We also found that zinc existed in the neural processes which were not parvalbumin-immunoreactive. Glycine-induced responses were augmented when the concentration of Zn(2+) was below 10 microM, but inhibited at Zn(2+) concentrations of 50 microM or more. Our results suggest the notion that zinc in neural processes of retinal neurons modulates the inhibitory signaling pathway, particularly that mediated by glycine receptors in AII amacrine cells.

Dendritic spinules in rat nigral neurons revealed by acetylcholinesterase immunocytochemistry and serial sections of the dendritic spine heads.

Dendritic spinules of rat nigral neurons were visualized at electron microscopic level by acetylcholinesterase immunocytochemistry and serial sections of the nigral dendrites. The spinules (at least 150 nm in length and 10-20 nm in width) which protruded from the spine heads are found in extracellular space in the neuropil and particularly between nerve terminals of the presynaptic neurons and fine glial processes. The nigral spinules are, however, not observed as invaginated processes in the nerve terminals. The dendritic spinule may be endowed with synaptic plasticity and metabolic exchange between nerve terminals and glial processes.

OFF-cholinergic-pathway-selective localization of P2X2 purinoceptors in the mouse retina.

It is known that, in the retina, extracellular adenosine triphosphate (ATP) inhibits acetylcholine (ACh) release from cholinergic neurons, but the types of purinoceptors on cholinergic neurons have not been examined. In the present work, we immunohistochemically examined the distribution of the purinoceptors P2X1, P2X2, P2X4, and P2X7 in relation to the cholinergic system of the retina in wild-type mice and transgenic mice expressing green fluorescent protein (GFP). Immunoreactivity for P2X2 was very strong in sublamina a of the inner plexiform layer but very weak in sublamina b of the inner plexiform layer of the retina. Immunoreactivity for P2X2 was colocalized with that for choline acetyltransferase (ChAT). When transgenic mice were treated with the immunotoxin-mediated cell-targeting technology to ablate cholinergic amacrine cells selectively, immunoreactivity for P2X2 and the signals for GFP disappeared in parallel and selectively in the OFF pathway. The distribution of immunoreactivity for P2X1, P2X4, and P2X7 differed from that of ChAT immunoreactivity. The selective distribution of P2X2 purinergic receptors in OFF-type cholinergic amacrine cells indicates that the P2X2 purinergic signaling systems in the ON and OFF pathways of the inner plexiform layer of the mouse retina are functionally different. The distribution of P2X2 purinoceptors may be responsible for the selective regulation of ACh release in the OFF pathway.

Neuron-specific distribution of P2X7 purinergic receptors in the monkey retina.

Extracellular ATP is a signaling molecule, working through P2X purinoceptors in the nervous system. P2X7 is a major subtype of the purinoceptors in the brain, where it is expressed mostly in glia cells and considered to work as a trigger of cytolysis. In the rodent retina, however, P2X7 is expressed in several classes of neurons including ganglion cells. In the present study we identified cells immunopositive for P2X7 by double immunolabeling. Immunoreactivity for P2X7 was observed in the inner nuclear layer (INL), the inner plexiform layer (IPL), and the ganglion cell layer (GCL). In the INL, strongly immunopositive cells corresponded to the subpopulation of horizontal cells. In the IPL, fine processes were immunopositive. In the GCL, most of the ganglion cells showed P2X7 immunoreactivity. At the ultrastructural level, immunoreactivity was confirmed in the cytoplasm of ganglion cells. No P2X7 immunoreactivity was found in non-neural cells, i.e., Müller cells or microglia. The immunohistochemical distribution of other purinoceptor subtypes (P2X1, P2X2, and P2X4) was also examined in the monkey retina. Immunoreactivity for P2X1 was strongly detected in a band, in sublamina a of the IPL. The band existed at almost the same level as tyrosine hydroxylase immunoreactivity, but did not seem to actually overlap. P2X2 was not expressed in the retina, and P2X4 was only faintly expressed at the scleral margin of the INL. Because P2X7 in the primate retina is expressed exclusively in neurons, it may in this location be involved in neural transmission rather than in cytolysis, as found for glia cells.