Differential distribution of calcium-binding proteins in the dorsal column nuclei of rats: a combined immunohistochemical and retrograde tract tracing study

Regional chemoarchitecture of the brain of lungfishes based on calbindin D-28K and calretinin immunohistochemistry

Lungfishes are the closest living relatives of land vertebrates, and their neuroanatomical organization is particularly relevant for deducing the neural traits that have been conserved, modified, or lost with the transition from fishes to land vertebrates. The immunohistochemical localization of calbindin (CB) and calretinin (CR) provides a powerful method for discerning segregated neuronal populations, fiber tracts, and neuropils and is here applied to the brains of Neoceratodus and Protopterus, representing the two extant orders of lungfishes. The results showed abundant cells containing these proteins in pallial and subpallial telencephalic regions, with particular distinct distribution in the basal ganglia, amygdaloid complex, and septum. Similarly, the distribution of CB and CR containing cells supports the division of the hypothalamus of lungfishes into neuromeric regions, as in tetrapods. The dense concentrations of CB and CR positive cells and fibers highlight the extent of the thalamus. As in other vertebrates, the optic tectum is characterized by numerous CB positive cells and fibers and smaller numbers of CR cells. The so-called cerebellar nucleus contains abundant CB and CR cells with long ascending axons, which raises the possibility that it could be homologized to the secondary gustatory nucleus of other vertebrates. The corpus of the cerebellum is devoid of CB and CR and cells positive for both proteins are found in the cerebellar auricles and the octavolateralis nuclei. Comparison with other vertebrates reveals that lungfishes share most of their features of calcium binding protein distribution with amphibians, particularly with salamanders.

Propidium iodide staining: a new application in fluorescence microscopy for analysis of cytoarchitecture in adult and developing rodent brain

Immunohistochemical visualization of antigens in specimen has evolved to an indispensable technique in biomedical research for investigations of cell morphology and pathology both in bright field and fluorescence microscopy. While there are couple of staining methods that reveal entire cytoarchitecture in bright field microscopy such as Nissl or hemalaun-eosin, there are still limitations in visualizations of cytoarchitecture in fluorescence microscopy. The present study reports a simple staining method that provides the required illustration of cell allocations and cellular composition in fluorescence microscopy in adult and in developing rodent central nervous system using the fluorophore propidium iodide (PI, 5μg/mL). PI is a well-accepted marker for degenerating cells when applied prior to fixation (pre-fixation PI staining). Here, PI was added to the sections after the fixation (post-fixation PI staining). This revised labeling procedure led to similar cytoarchitectural staining patterns in fluorescence microscopy as observed with hemalaun in bright field microscopy. This finding was proven in organotypic hippocampal slice cultures (OHSC) and brain sections obtained from different postnatal developmental stages. Excitotoxically lesioned OHSC subjected to pre-fixation PI staining merely showed brightly labeled condensed nuclei of degenerating neurons. In contrast, post-fixation PI staining additionally revealed extensive labeling of neuronal cell bodies and glial cells within the OHSC, thus allowing visualization of stratification of neuronal layers and cell morphology. Furthermore, post-fixation PI staining was combined with NeuN, calbindin, calretinin, glial fibrillary acidic protein or Griffonia simplicifolia isolectin B4 (IB(4)) in post natal (p1 and p9) and adult rats. In early post-natal brain sections almost all mentioned cellular markers led to an incomplete staining of the native cell organization and resulted in an inaccurate estimation of cell morphology when compared to adult brains. In contrast, post-fixation PI staining allowed investigation of the whole cytoarchitecture independent of the developmental stage. Taken together, post-fixation PI staining provides a detailed insight in the morphology of both developing and adult brain tissues in fluorescence microscopy.

Calbindin-D32k is localized to a subpopulation of neurons in the nervous system of the sea cucumber Holothuria glaberrima (Echinodermata)

Members of the calbindin subfamily serve as markers of subpopulations of neurons within the vertebrate nervous system. Although markers of these proteins are widely available and used, their application to invertebrate nervous systems has been very limited. In this study we investigated the presence and distribution of members of the calbindin subfamily in the sea cucumber Holothuria glaberrima (Selenka, 1867). Immunohistological experiments with antibodies made against rat calbindin 1, parvalbumin, and calbindin 2, showed that these antibodies labeled cells and fibers within the nervous system of H. glaberrima. Most of the cells and fibers were co-labeled with the neural-specific marker RN1, showing their neural specificity. These were distributed throughout all of the nervous structures, including the connective tissue plexi of the body wall and podia. Bioinformatics analyses of the possible antigen recognized by these markers showed that a calbindin 2-like protein present in the sea urchin Strongylocentrotus purpuratus, corresponded to the calbindin-D32k previously identified in other invertebrates. Western blots with anti-calbindin 1 and anti-parvalbumin showed that these markers recognized an antigen of approximately 32 kDa in homogenates of radial nerve cords of H. glaberrima and Lytechinus variegatus. Furthermore, immunoreactivity with anti-calbindin 1 and anti-parvalbumin was obtained to a fragment of calbindin-D32k of H. glaberrima. Our findings suggest that calbindin-D32k is present in invertebrates and its sequence is more similar to the vertebrate calbindin 2 than to calbindin 1. Thus, characterization of calbindin-D32k in echinoderms provides an important view of the evolution of this protein family and represents a valuable marker to study the nervous system of invertebrates.

Muscarinic ACh receptor-mediated control of thalamic activity via G(q)/G (11)-family G-proteins

A genetic knock out was used to determine the specific contribution of G(q)/G(11)-family G-proteins to the function of thalamocortical relay (TC) neurons. Disruption of Galpha(q) function in a conditional forebrain-specific Galpha(q)/Galpha(11)-double-deficient mouse line (Galpha(q)/Galpha(11)(-/-) had no effects on the resting membrane potential (V (rest)) and the amplitude of the standing outward current (I (SO)). Stimulation of muscarinic acetylcholine (ACh) receptors (mAChR; muscarine, 50 microM) induced a decrease in I (SO) amplitude in wild-type mice (36 +/- 4%, n = 5), a constitutive Galpha(11)-deficient mouse line (Galpha(11)(-/-; 36 +/- 3%, n = 8), and Galpha(q)/Galpha(11)(-/-) (11 +/- 2%, n = 16). Current-clamp recordings revealed a muscarine-induced positive shift in V (rest) of 23 +/- 2 mV (n = 6), 18 +/- 5 mV (n = 5), and 2 +/- 1 mV (n = 9) in wild type, Galpha(11)(-/-), and Galpha(q)/Galpha(11)(-/-), respectively. This depolarization was associated with a change in TC neuron activity from burst to tonic firing in wild type and Galpha(11)(-/-), but not in Galpha(q)/Galpha(11)(-/-). The use of specific antibodies and of pharmacological agents with preferred affinity points to the contribution of m(1)AChR and m(3)AChR. In conclusion, we present two novel aspects of the physiology of the thalamocortical system by demonstrating that the depolarization of TC neurons, which is induced by the action of transmitters of ascending brainstem fibers, is governed roughly equally by both m(1)AChR and m(3)AChR and is transduced by Galpha(q) but not by Galpha(11).

Neurochemical characterization of neuronal populations expressing protein kinase C gamma isoform in the spinal cord and gracile nucleus of the rat

Protein kinase C gamma (PKCgamma) is widely distributed throughout the CNS and is thought to play a role in long term hyper-excitability in nociceptive neurones. Here, we provide the first report of PKCgamma cells in the dorsal column nuclei of the adult rat. Retrograde labeling of PKCgamma cells from the thalamus with choleragenoid revealed that 25% of the PKCgamma positive gracile cells projected to the thalamus. Further, we have characterized the distribution of PKCgamma within gracile nucleus in terms of colocalization with various neurotransmitter receptors or enzymes and calcium binding proteins, and compared this with PKCgamma colocalization in cells of laminae I-III of the spinal cord. We show that approximately 90% of the PKCgamma cells in the gracile nucleus and 60% in the dorsal horn were immuno-positive for the AMPA receptor subunit glutamate 2/3 (GluR2/3). Little coexpression was seen with neurokinin 1 receptor, nitric oxide synthase (NOS) and the AMPA receptor subunit GluR1, markers of distinct neuronal subpopulations. In the spinal cord, a quarter of PKCgamma cells expressed calbindin, but very few cells did so in the gracile nucleus. Electrical stimulation at c-fiber strength of the normal or injured sciatic nerve was used to induce c-fos as a marker of postsynaptic activation in the spinal cord and gracile nucleus. Quantitative analysis of the number of PKCgamma positive gracile cells that expressed also c-fos increased from none to 24% after injury, indicating an alteration in the sensory activation pattern in these neurones after injury. C-fos was not induced in inner lamina II following c-fiber electrical stimulation of the intact or axotomized sciatic nerve, indicating no such plasticity at the spinal cord level. As dorsal column nuclei cells may contribute to allodynia after peripheral nerve injury, pharmacological modulation of PKCgamma activity may therefore be a possible way to ameliorate neuropathic pain after peripheral nerve injury.

Increased chondroitin sulfate proteoglycan expression in denervated brainstem targets following spinal cord injury creates a barrier to axonal regeneration overcome by chondroitinase ABC and neurotrophin-3

Increased chondroitin sulfate proteoglycan (CSPG) expression in the vicinity of a spinal cord injury (SCI) is a primary participant in axonal regeneration failure. However, the presence of similar increases of CSPG expression in denervated synaptic targets well away from the primary lesion and the subsequent impact on regenerating axons attempting to approach deafferented neurons have not been studied. Constitutively expressed CSPGs within the extracellular matrix and perineuronal nets of the adult rat dorsal column nuclei (DCN) were characterized using real-time PCR, Western blot analysis and immunohistochemistry. We show for the first time that by 2 days and through 3 weeks following SCI, the levels of NG2, neurocan and brevican associated with reactive glia throughout the DCN were dramatically increased throughout the DCN despite being well beyond areas of trauma-induced blood brain barrier breakdown. Importantly, regenerating axons from adult sensory neurons microtransplanted 2 weeks following SCI between the injury site and the DCN were able to regenerate rapidly within white matter (as shown previously by Davies et al. [Davies, S.J., Goucher, D.R., Doller, C., Silver, J., 1999. Robust regeneration of adult sensory axons in degenerating white matter of the adult rat spinal cord. J. Neurosci. 19, 5810-5822]) but were unable to enter the denervated DCN. Application of chondroitinase ABC or neurotrophin-3-expressing lentivirus in the DCN partially overcame this inhibition. When the treatments were combined, entrance by regenerating axons into the DCN was significantly augmented. These results demonstrate both an additional challenge and potential treatment strategy for successful functional pathway reconstruction after SCI.

Characterisation of transverse slice culture preparations of postnatal rat spinal cord: preservation of defined neuronal populations

Spinal cord injury induces degenerative and regenerative processes and complex interactions of neurons with non-neuronal cells. In order to develop an in vitro tool for the investigation of such processes, we prepared and characterised spinal cord slice cultures (SCSC) from Wistar rats (p0-12). SCSC were sustained in vitro up to 12 days and characterised by immunohistochemistry. Calbindin+ neurons, distributed across the entire gray matter, were visible also after longer culture periods. NeuN+ neurons were best preserved in the dorsal horn whereas large NeuN+ and choline acetyltransferase+ motoneurons in the ventral horn vanished after 3 days in vitro. Nestin immunoreactivity was found in animals of all age groups, either in cells interspersed in the ependymal lining around the central canal or in cells resembling protoplasmic astrocytes. Glial fibrillary acidic protein+ astrocytes, initially restricted to the white matter, invaded the gray matter of SCSC early during the culture period. Microglial cells, stained by Griffonia simplicifolia isolectin B4, were rapidly activated in the dorsal tract and in the gray matter but declined in number with time. SCSC derived from p0 or p3 animals showed a better preservation of the cytoarchitecture than cultures derived from older animals. In summary, SCSC undergo degenerative changes, but they contain defined neuronal populations, the cytoarchitecture is partially preserved and the glial reaction is limited.

Quantitative stereological evaluation of the gracile and cuneate nuclei and their projection neurons in the rat

Stereological methods were employed to estimate the volume and neuron numbers of the rat dorsal column nuclei (DCN). These methods were applied to Nissl-stained sections from control animals and cases that received injections of horseradish peroxidase in the thalamus, the cerebellum, or the spinal cord. Additional cases received combinations of fluorescent tracers in the same structures, to examine whether some of the retrogradely labeled neurons sent collaterals to different targets. The mean volume of the DCN is 0.81 mm(3) (range 0.65-1.10 mm(3)), of which 3%, 39%, and 59% correspond, respectively, to the nucleus of Bischoff (Bi), the gracile (Gr), and the cuneate (Cu) nuclei. Within Cu, the middle division (CuM) is the largest (42%), followed by the rostral (CuR; 36%) and caudal (CuC; 22%) divisions. The mean total number of neurons in the DCN is 16,000 (range 12,400-19,500), of which 2.4%, 34.0% and 63.6% correspond, respectively, to Bi, Gr, and Cu. Within Cu, CuM contains 48% of all neurons, and 27% correspond to CuR and 25% to CuC. Interanimal variability is moderate for the whole DCN and Cu but increases when individual nuclei are considered. About 80% of DCN neurons project to the thalamus, 3% to the spinal cord, and 7% to the cerebellum. Thalamic-projecting cells are more numerous in CuM and Gr (83%), and relatively less common in Bi and CuC (72-74%). Most of the DCN neurons projecting to the spinal cord appear in CuC and CuM. Two-thirds of the neurons projecting to the cerebellum are located in CuR, 20% in CuM, and 15% in Gr. A small fraction of neurons projects simultaneously to spinal cord and thalamus.

Recent techniques for tracing pathways in the central nervous system of developing and adult mammals

Over the last 20 years, the choice of neural tracers has increased manyfold, and includes newly introduced anterograde tracers that allow quantitation of single-axon morphologies, and retrograde tracers that can be combined with intracellular fills for the study of dendritic arbors of neurons which have a specific projection pattern. The combination of several different tracers now permits the comparison of multiple connections in the same animal, both quantitatively and qualitatively. Moreover, the finding of new virus strains, which infect neural cells without killing them, provides a tool for studying multisynaptic connections that participate in a circuit. In this paper, the labeling characteristics, mechanism of transport and advantages/disadvantages of use are discussed for the following recently introduced neural tracers: carbocyanine dyes, fluorescent latex microspheres, fluorescent dextrans, biocytin, dextran amines, Phaseolus vulgaris leucoagglutinin, cholera toxin and viruses. We also suggest the choice of specific tracers, depending on the experimental animal, age and type of connection to be studied, and discuss quantitative methodologies.

Postnatal expression pattern of calcium-binding proteins in organotypic thalamic cultures and in the dorsal thalamus in vivo

The present study describes the postnatal expression of calbindin, calretinin and parvalbumin and glutamic acid decarboxylase (GAD) and microtubule-associated protein 2 (MAP2) in organotypic monocultures of rat dorsal thalamus compared to the thalamus in vivo. Cultures were maintained for up to 7 weeks. Cortex-conditioned medium improved the survival of thalamic cultures. MAP2-immunoreactive material was present in somata and dendrites of small and large-sized neurons throughout the cultures. Parvalbumin immunoreactivity was present in larger multipolar or bitufted neurons along the edge of a culture. These neurons also displayed strong parvalbumin mRNA and GAD mRNA expression, and GABA immunoreactivity. They likely corresponded to cells of the nucleus reticularis thalami. Parvalbumin mRNA, but neither parvalbumin protein nor GAD mRNA, was expressed in neurons with large somata within the explant. They likely represented relay cells. GAD mRNA, but not parvalbumin mRNA, was expressed in small neurons within the explants. Small neurons also displayed calbindin- and calretinin-immunoreactivity. The small neurons likely represented local circuit neurons. The time course of expression of the calcium-binding proteins revealed that all were present at birth with the predicted molecular weights. A low, but constant parvalbumin expression was observed in vitro without the developmental increase seen in vivo, which most likely represented parvalbumin from afferent sources. In contrast, the explantation transiently downregulated the calretinin and calbindin expression, but the neurons recovered the expression after 14 and 21 days, respectively. In conclusion, thalamic monocultures older than three weeks represent a stable neuronal network containing well differentiated neurons of the nucleus reticularis thalami, relay cells and local circuit neurons.

Thalamic-projecting preprocholecystokinin messenger RNA-expressing neurons in the dorsal column nuclei of the rat

This study aimed at investigating the expression of preprocholecystokinin messenger RNA among thalamic-projecting neurons in the dorsal column nuclei of the rat. Thalamic-projecting neurons were identified by injection of cholera toxin subunit b into the ventroposterolateral nucleus. Following immunohistochemical detection of retrogradely transported tracer substance, the expression of preprocholecystokinin messenger RNA in the projection neurons of the dorsal column nuclei was detected by in situ hybridization, using autoradiographic visualization of a 35S-labeled RNA probe complementary to preprocholecystokinin messenger RNA. Many preprocholecystokinin-expressing neurons were seen in the dorsal column nuclei. A large proportion of these neurons were also labeled with cholera toxin. The double-labeled neurons, as well as neurons single-labeled with preprocholecystokinin messenger RNA or cholera toxin, were preferentially found within the middle region of the dorsal column nuclei, located just caudal to the obex. These findings demonstrate that neurons in the dorsal column nuclei express preprocholecystokinin messenger RNA, and show that these neurons provide a peptidergic projection from the dorsal column nuclei to the ventroposterolateral nucleus of the thalamus. These observations suggest that cholecystokinin may be involved in the transmission of somatosensory (tactile) information from the dorsal column nuclei to the thalamus.