Spaceflight induces changes in the synaptic circuitry of the postnatal developing neocortex.

The establishment of the adult pattern of neocortical circuitry depends on various intrinsic and extrinsic factors, whose modification during development can lead to alterations in cortical organization and function. We report the effect of 16 days of spaceflight [Neurolab mission; from postnatal day 14 (P14) to P30] on the neocortical representation of the hindlimb synaptic circuitry in rats. As a result, we show, for the first time, that development in microgravity leads to changes in the number and morphology of cortical synapses in a laminar-specific manner. In the layers II/III and Va, the synaptic cross-sectional lengths were significantly larger in flight animals than in ground control animals. Flight animals also showed significantly lower synaptic densities in layers II/III, IV and Va. The greatest difference was found in layer II/III, where there was a difference of 344 million synapses per mm(3) (15.6% decrease). Furthermore, after a 4 month period of re-adaptation to terrestrial gravity, some changes disappeared (i.e. the alterations were transient), while conversely, some new differences also appeared. For example, significant differences in synaptic density in layers II/III and Va after re-adaptation were no longer observed, whereas in layer IV the density of synapses increased notably in flight animals (a difference of 185 million synapses per mm(3) or 13.4%). In addition, all the changes observed only affected asymmetrical synapses, which are known to be excitatory. These results indicates that terrestrial gravity is a necessary environmental parameter for normal cortical synaptogenesis. These findings are fundamental in planning future long-term spaceflights.

Functional regeneration in a rat Parkinson's model after intrastriatal grafts of glial cell line-derived neurotrophic factor and transforming growth factor beta1-expressing extra-adrenal chromaffin cells of the Zuckerkandl's organ.

Intrabrain transplantation of chromaffin cell aggregates of the Zuckerkandl's organ, an extra-adrenal paraganglion that has never been tested for antiparkinsonian treatment, induced gradual improvement of functional deficits in parkinsonian rats. These beneficial effects were related to long survival of grafted cells, striatal reinnervation, and enhancement of dopamine levels in grafted striatum. Grafted cells were not dopaminergics, but they expressed glial cell line-derived neurotrophic factor (GDNF) and transforming growth factor-beta(1). These factors were detected in the host striatal tissue, indicating that chromaffin cells secreted them after grafting. Because glial cell line-derived neurotrophic factor possesses neurorestorative properties over dopaminergic neurons, and transforming growth factor-beta(1) is a cofactor that potentiates the neurotrophic actions of GDNF, functional regeneration was likely caused by the chronic trophic action of neurotrophic factors delivered by long-surviving grafted cells. This work should stimulate research on the clinical applicability of transplants of the Zuckerkandl's organ in Parkinson's disease.

The human temporal cortex: characterization of neurons expressing nitric oxide synthase, neuropeptides and calcium-binding proteins, and their glutamate receptor subunit profiles.

Immunocytochemical techniques were used to examine the distribution of neurons immunoreactive (-ir) for nitric oxide synthase (nNOS), somatostatin (SOM), neuropeptide Y (NPY), parvalbumin (PV), calbindin (CB) and calretinin (CR), in the inferotemporal gyrus (Brodmann's area 21) of the human neocortex. Neurons that colocalized either nNOS or SOM with PV, CB or CR were also identified by double-labeling techniques. Furthermore, glutamate receptor subunit profiles (GluR1, GluR2/3, GluR2/4, GluR5/6/7 and NMDAR1) were also determined for these cells. The number and distribution of cells containing nNOS, SOM, NPY, PV, CB or CR differed for each antigen. In addition, distinct subpopulations of neurons displayed different degrees of colocalization of these antigens depending on which antigens were compared. Moreover, cells that contained nNOS, SOM, NPY, PV, CB or CR expressed different receptor subunit profiles. These results show that specific subpopulations of neurochemically identified nonpyramidal cells may be activated via different receptor subtypes. As these different subpopulations of cells project to specific regions of pyramidal cells, facilitation of subsets of these cells via different receptor subunits may activate different inhibitory circuits. Thus, various distinct, but overlapping, inhibitory circuits may act in concert in the modulation of normal cortical function, plasticity and disease.

Changes in the colocalization of glutamate ionotropic receptor subunits in the human epileptic temporal lobe cortex.

Double-labeling immunocytochemical techniques and confocal microscopy were used to quantify possible differences in the degree of colocalization of glutamate ionotropic receptor subunits between non-spiking and spiking neocortex removed from temporal lobe epileptic patients. Spiking neocortex was characterized by laminar-specific changes in the number of cells immunoreactive for NMDAR1, GluR2/3 and GluR5/6/7 subunits, as well as the percentage of cells which colocalized various combinations of these receptors. These changes may lead to profound modifications in the functioning of excitatory synaptic circuits in spiking cortex.

Colocalization of glutamate ionotropic receptor subunits in the human temporal neocortex.

alpha-Amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA), kainate and N-methyl-D-aspartate (NMDA) receptors represent major classes of glutamate receptors (GluR) which play fundamental roles in normal excitatory synaptic activity and, probably, in the etiology of several brain diseases. These receptors are composed of multiple receptor subunit proteins, and the differential expression of these subunits in cortical neurons is considered to be one of the substrates for the functional diversity of cortical excitatory circuitry. In the monkey neocortex, different subpopulations of neurons have been identified on the basis of immunocytochemical colocalization studies using subunit-specific antibodies, but no comparable investigations have been made in the human neocortex. The aim of the present study was to determine quantitatively GluR subunit combinations in the human temporal neocortex by double-labeling immunocyto- chemical experiments. We quantified the neuronal populations expressing different receptor subtypes with fluorescent tags visualizing them with confocal laser microscopy. We studied AMPA, kainate- and NMDA-receptor subunits, using antibodies against GluR1, GluR2, GluR2/3, GluR2/4, GluR5/6/7 and NMDAR1 subunits. A high degree of colocalization (93-100%) using combinations of antibodies against GluR2 with GluR2/3, GluR2/3 with GluR2/4, and GluR2 or GluR2/4 with NMDAR1 was found, whereas for other combinations the degree of colocalization varied between 38% and 88%. Some of the percentages reported here are similar to those found in the monkey cortex, whereas others differ considerably. These results emphasize the diversity of excitatory circuits in the human neocortex, and suggest species differences with regard to some of these GluR-mediated circuits.

Distribution and patterns of connectivity of interneurons containing calbindin, calretinin, and parvalbumin in visual areas of the occipital and temporal lobes of the macaque monkey.

Immunocytochemical techniques were used to examine the distribution of double-bouquet cells and chandelier cells that were immunoreactive (-ir) for the calcium-binding proteins calbindin (CB), calretinin (CR), and parvalbumin (PV) in the primary visual area (V1), the second visual area (V2), and cytoarchitectonic area TE in the macaque monkey. Furthermore, the connections between CB-, CR-, and PV-ir neurons in these visual areas were investigated at the light microscope level by using a dual-immunocytochemical staining procedure. The most significant findings were three-fold. First, the number and distribution of CB-ir and CR-ir double-bouquet cells and PV-ir chandelier cells differed considerably between different visual areas. In particular, the different distribution of double-bouquet cells was illustrated dramatically at the V1/V2 border, where CB-ir double-bouquet axons were very few or lacking in V1 but were very numerous in V2. Furthermore, PV-ir chandelier cell terminals were relatively sparse in V1, more frequent in V2, and most frequent in area TE. Second, the percentage of CB-, CR-, and PV-ir neurons receiving multiple contacts on their somata and proximal dendrites from other calcium-binding protein neurons varied between 22% and 85%. The highest percentage of contacts found between immunolabelled cells and multiterminals were for the combinations CR/CB (76-85%; percent of cells immunoreactive for CB that were innervated by multiterminals immunoreactive for CR), followed by the combination PV/CR (42-48%), and then by the other combinations that had similar percentages (22-32% for CR/PV; 26-37% for CB/CR; 29-42% for CR/PV). Third, differences in the relative proportions of CB, CR, and PV terminals in contact with CB-, CR-, and PV-ir neurons were consistent between the different cortical areas studied. Thus, certain characteristics of intraareal circuits differ, whereas others remain similar, in different areas of the occipitotemporal visual pathway. The differences may represent regional specializations related to the different processing of visual stimuli, whereas the similarities may be attributed to general functional requisites for interneuronal circuitry.

Chandelier cell axons are immunoreactive for GAT-1 in the human neocortex.

We have examined the pattern of immunostaining for the high-affinity GABA transporter GAT-1 in the human temporal neocortex. Immunocytochemistry for GAT-1 labels terminal-like puncta in the neuropil and around unstained cell bodies. The characteristic terminal portions of chandelier cell axons (Ch-terminals, which form multiple inhibitory GABAergic synaptic contacts with the axon initial segments of pyramidal cells) were among the strongest immunocytochemically stained elements for GAT-1. Since Ch-terminals are immunoreactive for the calcium-binding protein parvalbumin, experiments were carried out to study the co-localization of GAT-1 and parvalbumin in Ch-terminals. These experiments showed that the vast majority of Ch-terminals immunoreactive for GAT-1 were also immunoreactive for PV. We concluded that GAT-1 transporter may have an important functional role in controlling pyramidal cell activity.