Nervous System Of Adult Rats Research Articles

Mapping of the distribution of polysialylated neural cell adhesion molecule throughout the central nervous system of the adult rat: An immunohistochemical study

In the nervous system, the neural cell adhesion molecule changes at the cell surface during development, from a form highly enriched in polysialic residues to several isoforms containing much less sialic acid, and is thought to participate in the structuring of neuronal groups and in the establishment of neuronal connections. Recent observations have indicated, however, that it may not be restricted to developing tissues since it is still present in certain adult neuronal centres which can undergo morphological reorganization. In this study, therefore, we examined systematically the distribution of polysialylated neural cell adhesion molecule immunoreactivity throughout the central nervous system of adult male and female rats, using light microscopic immunocytochemistry and immunoblot analysis with an antibody that specifically recognizes the polysialic residues of the molecule. Concomitantly, we compared this immunoreactivity to that due to all isoforms of the neural cell adhesion molecule, detected with a polyclonal serum raised against the NH 2-terminal of the protein. Immunoreactivity due to the polysialylated isoform was consistently visualized in several discrete areas of the adult brain and spinal cord. An intercellular punctate immunolabelling characterized the staining in certain hypothalamic and thalamic nuclei, superficial laminae of the dorsal horn of the spinal cord, ventral portion of the dentate gyrus of the hippocampus, lateral geniculate, parabrachial and habenular nuclei, bed nucleus of the stria terminalis, mesencephalic central gray and olfactory bulb. In other areas, such as the piriform cortex, dorsal aspect of the dentate gyrus and fimbria and lamina X of the spinal cord, isolated neuronal-like cells were either completely filled with immunolabel or showed a surface reaction on their cell bodies and processes. Highly immunoreactive isolated glial-like cells were also noted within the ependymal layer of the central canal and lateral ventricles and at times in the peripheral white matter of the spinal cord. In contrast to this discrete localization, staining due to all isoforms of the neural cell adhesion molecule was widespread and diffuse throughout the brain and spinal cord. The expression of the polysialylated isoform in the supraoptic nucleus and hippocampus was confirmed by immunoblot analysis; it occurred together with weakly sialylated isoforms. No obvious differences were detected in the amount or distribution of immunoreactivity due to the polysialylated isoform in relation to the sex or age of the animals (between three and 12 months of age). Our study thus demonstrates that well-defined areas of the central nervous system of the adult rat continue to express the polysialylated isoform of the neural cell adhesion molecule. Since many of these areas are known to undergo structural reorganization under particular physiological and experimental conditions, our observations support the hypothesis that polysialylation may be a crucial factor in allowing certain neurons and glial cells to manifest their capacity for structural plasticity in adulthood.

Effects of hypothyroidism upon the granular layer of the dentate gyrus in male and female adult rats: A morphometric study

The effects of hypothyroidism upon the structure of the central nervous system of adult rats are poorly understood in spite of evidence that the mature brain is vulnerable to this condition. Existing developmental studies show that the morphological changes induced by thyroid hormone deficiency are related to alterations in neurogenesis. We studied the granular layer of the dentate gyrus under different experimental conditions of hypothyroidism, because in rodents the neurogenesis of the granule cells continues during adulthood. The following groups of rats were analysed: 1) control; 2) hypothyroid from day 0 until day 180 (hypothyroid group); 3) hypothyroid until day 30 and henceforth maintained euthyroid (recovery group); and 4) hypothyroid since day 30 (adult hypothyroid group). Groups of 6 male rats and 6 female rats were analysed separately. The volume of the dentate gyrus granular layer and the numerical density of its neurons were evaluated, so we were able to estimate the total number of granule cells. Because in the experimental groups the volume of the granular layer and the numerical density of its neurons were reduced, the total number of granule cells was decreased. In the hypothyroid and recovery groups the alterations were identical and more striking than in the adult hypothyroid groups. The total number of granule cells displayed sexual differences in all groups studied except in the hypothyroid groups. The present results support the view that thyroid hormone deficiency interferes with the process of cell acquisition by reducing neuronal proliferation and that it also leads to increased cell death. These events underlie the irreversible morphological changes observed in the brain of hypothyroid rats, either during development or at maturity. The referred structural alterations are probably related to the functional deficits observed in this condition.

Prominent expression of acidic fibroblast growth factor in motor and sensory neurons

Several growth factors originally characterized and named for their action on a variety of cells have more recently been suggested to be importantly involved in the development and maintenance of the nervous system. Acidic fibroblast growth factor (aFGF) is a member of a family of seven structurally related polypeptide growth factors. The cells responsible for expression of aFGF in the nervous system of adult rats have been identified using an affinity-purified antibody to aFGF in immunohistochemical studies and synthetic oligonucleotide probes for in situ hybridization studies. High levels of aFGF expression were observed in motoneurons, primary sensory neurons, and retinal ganglion neurons. Glial cells did not express detectable amounts of aFGF. Confocal and electron microscopic analysis suggested that a large portion of aFGF immunoreactivity was associated with the cytoplasmic face of neuronal membranes, consistent with the hypothesis that aFGF is a sequestered growth factor.

The KROX-24 protein, a new transcription regulating factor: Expression in the rat central nervous system following afferent somatosensory stimulation

The expression of the protein product encoded by the Krox-24 gene was investigated immunocytochemically in the central nervous system of adult rats. Immunoreactivity (IR) of the KROX-24 protein which is a nuclear transacting transcription factor, showed a pattern of nuclear staining. Basal KROX-24-IR was visible in the superficial layers of spinal dorsal horn and trigeminal nucleus, and in many areas of the brain including the cerebellum, nucleus raphe magnus, colliculi, periaqueductal gray, hypothalamus, geniculate nuclei, caudate putamen, amygdala, hippocampus, lateral septal nucleus, olfactory tubercle and cerebral cortex. Electrical stimulation of sciatic nerve A- and C-fibers, but not of Aα- and Aβ-fibers alone, induced transient expression of KROX-24 in numerous spinal neurons in the termination area of the stimulated nerve. One hour following the onset of this stimulation of the sciatic nerve the distribution of KROX-24-IR was investigated in the brain and compared to untreated rats. In stimulated animals, the KROX-24-IR was induced in many areas including the lateral reticular nucleus, parabrachial nucleus, periaqueductal gray, hypothalamus, amygdala and lateral habenular nucleus.

A monoclonal antibody that recognizes somatic motor neurons in the mature rat nervous system

In order to obtain markers selective for motor neurons, an in vitro immunization was carried out using a crude homogenate of embryonic rat ventral spinal cord. We have generated a monoclonal antibody, MO-1, that binds selectively to the cell bodies of somatic motor neurons in the brain stem and spinal cord of the adult rat nervous system. In a survey of both peripheral and central nervous systems, intense labeling by MO-1 appears exclusive to this class of cholinergic neuron. Immunoreactivity is predominantly intracellular and is detectable within the somata as well as the proximal regions of processes but is absent along fiber tracts and at neuromuscular junctions. This staining pattern indicates that MO-1 does not recognize other molecules known to be present in motor neurons, such as choline acetyltransferase, acetylcholinesterase, agrin, or the calcitonin-gene-related-peptide. In the spinal cord, antibody binding begins to be detectable in motor neurons late in development, during the second postnatal week. Thus, MO-1 appears to recognize a novel cellular component that accumulates in somatic motor neurons during terminal stages of differentiation.

Calbindin D-28k and parvalbumin in the rat nervous system

This paper describes the distribution of structures stained with mono- and polyclonal antibodies to the calcium-binding proteins calbindin D-28k and parvalbumin in the nervous system of adult rats. As a general characterization it can be stated that calbindin antibodies mainly label cells with thin, unmyelinated axons projecting in a diffuse manner. On the other hand, parvalbumin mostly occurs in cells with thick, myelinated axons and restricted, focused projection fields. The distinctive staining with antibodies against these two proteins can be observed throughout the nervous system. Calbindin D-28k is primarily associated with long-axon neurons (Golgi type I cells) exemplified by thalamic projection neurons, strionigral neurons, nucleus basalis Meynert neurons, cerebellar Purkinje cells, large spinal-, retinal-, cochlear- and vestibular ganglion cells. Calbindin D-28k occurs in all major pathways of the limbic system with the exception of the fornix. Calbindin D-28k is, however, also found in some short-axon cells (Golgi type II), represented by spinal cord interneurons in layer II and interneurons of the cerebral cortex. It is also detectable in some ependymal cells and abundantly occurs in vegatative centres of the hypothalamus. The “paracrine core” of the nervous system and its adjunct (1985, Nieuwenhuys, Ghemoarchitecture of the Brain. Springer, Berlin) is very rich in calbindin D-28k. The distribution of calbindin D-28k-positive neurons is very similar to that of the dihydroperydine subtype of calcium channels. Most of the cells containing calbindin D-28k are vulnerable to neurodegenerative processes. Parvalbumin-immunoreactive neurons have a different, and mostly complementary distribution compared with those which react with calbindin D-28k antisera, but in a few cases (Purkinje cells of the cerebellum, spinal ganglion neurons), both calcium-binding proteins co-exist in the same neuron. Many parvalbumin-immunoreactive cells in the central nervous system are interneurons (Golgi type II) and, to a lesser extent, long-axon cells (Golgi type I), whereas conditions are vice versa in the peripheral nervous system. Intrinsic parvalbuminic neurons are prominent in the cerebral cortex, hippocampus, cerebellar cortex and spinal cord. Long-axon parvalbumin-immunoreactive neurons are, for example, the Purkinje cells, neurons of the thalamic reticular nucleus, globus pallidus, substantia nigra (pars reticulata) and a subpopulation among large spinal-, retinal-, cochlear- and vestibular ganglion cells. Parvalbumin is rich in cranial nerve nuclei related to eye movements. In addition to nervous elements, parvalbumin immunoreactivity occurs in a few ependymal cells and in some pillar cells of the organ of Corti. In contrast to calbindin D-28k, parvalbumin is virtually absent from vegetative centres and pathways. Parvalbumin co-exists with GABA in cortical neurons and is, in general, preferentially associated with “fast-firing” neurons. Whole functional systems are revealed by either parvalbumin or calbindin D-28k immunohistochemistry. Parvalbumin, for example, occurs in the whole chain of neurons of the epicritic sensibility in the somatosensory system. Calbindin D-28k, on the other hand, occurs in the whole taste pathway. With antibodies against calbindin D-28k and parvalbumin it is possible to reveal at least two as yet undescribed brain nuclei: one in the hypothalamus (parvalbumin 1), the second in the medulla (calbindin D-28k 1). Calbindin D-28k and parvalbumin are evenly distributed within the various domains of the same neuron, but in some instances their levels vary between soma and cell processes. The immunostaining with calbindin D-28k and parvalbumin antisera show gradations in intensity among neurons belonging to different populations, a phenomenon compatible with the presence of varying concentrations of these proteins. Calbindin D-28k and parvalbumin are excellent new neuroanatomical markers which can be utilized to selectively visualize certain neurons and pathways in the central nervous system and peripheral nervous system.

Astrocytes and Schwann Cells Are Virus-Host Cells in the Nervous System of Rats with Borna Disease

Borna disease virus (BDV) replicates only in cells in the central (CNS) and peripheral (PNS) nervous system in adult rats. Infection of the nervous system is associated with a transient, intense mononuclear meningoencephalitis and immunemediated loss of BDV-infected neurons. The identification of BDV antigen in neurons and the accompanying immunologically-specific lysis of these cells led to the prediction that the CNS would be virus-free after the animal had recovered from encephalitis. However, BDV infectivity and antigen persist for the lifetime of the animal. It appeared, therefore, that other neural cells might be hosts for viral replication and provide a reservoir for the virus. Morphological criteria were used to identify astrocytes and Schwann cells which expressed BDV antigens in vivo. Borna disease virus (BDV) infected astrocytes were identified by double labeling tissue sections with combined cell-specific and BDV-specific antibodies in an avidin-biotin immunocytochemical assay. Examination of serial I micrometer-thick cryosections of hippocampus and sciatic nerve preparations revealed several cells that expressed both glial and BDV antigens. Infectious virus was recovered from cultures of Schwann cells from infected rats. Borna disease virus-infected glial elements persisted beyond the period of inflammation and massive neuronal destruction, and represented a major class of infected cells during chronic disease.

An immunocytochemical and biochemical study of the microtubule-associated protein MAP-2 during post-lesion dendritic remodeling in the central nervous system of adult rats

A monoclonal antibody against the microtubule-associated protein MAP-2 was used to examine the fate of this molecule during post-lesion dendritic remodeling in the hippocampus and septum of adult rats. Qualitative and quantitative immunocytochemical analyses were carried out in the dentate gyrus after unilateral destruction of the entorhinal cortex (EC). An increase in MAP-2 immunoreactivity was detected in dendritic processes located in the outer 2 3 of the ipsilateral molecular layer (ML) 2 days after the lesion, whereas dendritic staining decreased considerably in the inner 1 3 of the same ML. The increase of staining was also detected 4, 6 and 8 days after the lesion; it was accompanied by an increase in the immunoreactivity in the inner 1 3 of the ML. After that period, a progressive decrease in anti-MAP-2 staining toward control levels was detected along the whole extent of the ipsilateral ML. This was concurrent with alterations in dendritic orientation, and a decrease in stained dendrites in the inner 1 3 of the ML. By 30 days post-lesion anti-MAP-2 staining was almost identical to that of the contralateral ML, although the alterations in dendritic morphology were still present in the ipsilateral ML. Changes in MAP-2 levels were also evaluated by densitometry of Western blots or dot immunobinding of hippocampal extracts obtained at different post-lesion intervals. The results obtained revealed a pattern of change in MAP-2 levels identical to that observed with the immunohistochemical stain. A similar, immunocytochemical and biochemical, analysis conducted in the lateral septal nucleus after unilateral transection of the fimbria showed no changes in the distribution and/or content of MAP-2 at any post-lesion interval analyzed (2, 10 and 20 days post-lesion). The present observations show that post-lesion dendritic remodeling is concurrent with modifications in the levels and distribution of MAP-2. These modifications suggest that the dendritic cytoskeleton is dynamically changing in response to perturbation of the synaptic environment. In addition, our results indicate that these changes may only occur in those neurons which have the capability to remodel their post-synaptic surface in response to deafferentation.

Capsaicin‐induced neuronal degeneration: Silver impregnation of cell bodies, axons, and terminals in the central nervous system of the adult rat

Capsaicin is a neurotoxic substance valued in neurobiological research because of its ability to selectively damage small unmyelinated primary sensory neurons. Previous work has indicated that systemic capsaicin administration causes permanent neuronal degeneration in neonatal rats, but evidence that capsaicin has a similar effect in adults is equivocal and incomplete. Therefore, we used silver impregnation, a method that labels degenerating neurons, to examine the central nervous system of adult rats after systemic capsaicin treatment. Adult rats were injected with a single intraperitoneal dose of capsaicin (50 or 90 mg/kg) or vehicle solution and killed 6, 12, 18, 24, 48, 96, or 240 hours later. Sections of brain and spinal cord were stained with the Carlsen-de Olmos cupric silver method. As reported previously, stained sections revealed degeneration in areas known to be innervated by small-diameter primary sensory fibers: the substantia gelatinosa of the spinal cord dorsal horn and spinal trigeminal nucleus, the solitary nucleus and tract, and the lateral borders of the area postrema. In addition, axon and terminal degeneration was observed in several discrete forebrain and hindbrain areas not previously associated with capsaicin-induced degeneration in either adult or neonatal rats: the inferior olive, the olivary pretectal nucleus, the interpeduncular nucleus, the suprachiasmatic nucleus, and the lateral septum/medial accumbens region. Furthermore, degenerating cell bodies were observed in the intrafascicular nucleus of the ventromedial midbrain tegmentum, in the supramammillary nucleus, and in the posterior hypothalamic area. Unilateral nodose ganglionectomy produced terminal staining on the denervated side very similar to that induced bilaterally by capsaicin. In addition, unilateral nodose ganglionectomy 1 month prior to capsaicin injection greatly attenuated staining in the ipsilateral nucleus of the solitary tract, confirming the hypothesis that capsaicin damages vagal sensory neurons innervating this nucleus. Capsaicin-induced damage in adult rats was long-lasting, since the second of two capsaicin treatments spaced 4.5 months apart produced no additional degeneration.

Comparison of adrenal medullary, carotid body and PC12 cell grafts in 6-OHDA lesioned rats

The survival and functional properties of dispersed cell implants of catecholaminergic cells obtained from the peripheral nervous system of adult rats (adrenal medulla and carotid body glomus cells) and PC12 cells from a rat pheochromocytoma cell line were examined following transplantation into the striatum of the adult rat. The host animals, all with unilateral 6-hydroxydopamine (6-OHDA) nigrostriatal lesions, were divided into 5 groups: (1) PC12 cells transplanted into Cyclosporin-A treated hosts; (2) PC12 cell grafts into hosts without Cyclosporin-A treatment; (3) grafts of adrenal medullary cells; (4) grafts of glomus cells; and (5) vehicle controls. All animals were sacrificed one month after transplantation. Immunocytochemical staining for tyrosine hydroxylase, the rate-limiting enzyme for catecholamine synthesis, was used to identify and characterize the grafted cells. PC12 cells were detected in four of six Cyclosporin-A treated rats, and two of these grafts developed into tumors. However, only one of the six non-Cyclosporin-A treated hosts was found to have surviving PC12 cells, and none of these rats developed tumors. No significant differences in rotational behavior were seen in either of the PC12 cell recipient groups. Grafted cells could be identified in all of the adrenal medullary and glomus cell recipients. However, the number of surviving cells was quite limited, with not more than 100 tyrosine hydroxylase-positive grafted cells found in any one recipient. Tyrosine hydroxylase-positive fibers were present adjacent to the transplants in these latter graft recipients, but the fibers appeared to be of host origin rather than from the grafts. The behavioral data showed that the implantation of both adrenal medullary and glomus cells significantly ( p<0.05) reduced the amphetamine-induced rotational behavior in 6-OHDA lesioned rats compared to the control group. Due to the small number of surviving grafted chromaffin and glomus cells and the apparent sprouting of host tyrosine hydroxylase-containing fibers, the present study raises questions about whether the behavioral recovery is due to catecholamine released by the grafted cells or from graft induced-recovery of host systems.

A developmentally regulated antigen associated with neural cell and process migration

The distribution of an epitope recognized by the monoclonal antibody JONES has been studied immunohistochemically in the developing nervous system of the rat. In the present report, we survey selected regions of the fetal, postnatal, and adult rat nervous system to test the hypothesis that JONES binding is invariably associated with neural cell migration and axon growth in the developing rat. A series of selected developmental stages extending from embryonic day (E) 9 to adult were used in this investigation. The distribution of JONES binding was examined using indirect immunofluorescence, as well as the immunogold procedure. Particular attention was paid to regions where the positions and timing of cell and axon migrations have been well described for the rat. JONES immunoreactivity first appears at E11-12, when it is localized to the lamina terminalis, the telencephalic-diencephalic junction, the midbrain, and the rhombic lip regions of the cytologically undifferentiated neural tube. In all the regions studied, during embryonic and early postnatal life, the labeling is very intense in the ventricular zone and shows a radial array in the adjacent intermediate and marginal zones. The expression of JONES epitope correlates particularly with times of cell migration in the retina, superior colliculus, cerebellum, and telencephalon and in regions undergoing neurite extension, such as the developing optic tract, the white matter of the cerebellum, the dorsal roots, the trigeminal system, and olfactory nerve. JONES binding becomes progressively restricted in the postnatal period. In the adult brain, immunoreactivity is present only in the retina and cerebellum. In the retina, JONES labeling is present in the outer plexiform layer and optic fiber layer. The labeling in the optic fiber layer extends to the optic nerve head and stops abruptly outside the orbit. In the cerebellum, JONES shows a radially oriented pattern throughout the molecular layer and delineates the cell bodies in the Purkinje cell layer. The only non-neural regions that show JONES immunoreactivity are the adrenal medulla and the kidney glomeruli. We conclude that the antigens recognized by the JONES monoclonal antibody are associated with the migration of subsets of cells and axons within the developing rat nervous system and, consequently, may play a role in conveying selectivity to these processes.

Properties of receptors for nerve growth factor in the mature rat nervous system

The binding properties of receptors for nerve growth factor (NGF) in the adult rat nervous system have been analyzed in membrane fractions from discrete regions and in radioautographs of tissue sections. Steady-state experiments with both preparations revealed specific binding of radioiodinated NGF that was heterogeneous in distribution and affinity. Of the regions in the central nervous system that were sampled, the dorsal spinal cord and basal forebrain were richest in NGF receptor. By 4 independent methods of analysis a high-affinity binding site was detected in the basal forebrain with half-maximal saturation estimated at 20–60 pM NGF. Binding at lower affinity was also seen but difficult to analyze quantitatively. Cross-linking studies followed by electrophoresis showed the NGF receptor in the rat basal forebrain to have an apparent molecular weight of 90 kDa. The binding and molecular properties of NGF receptors on adult mammalian neurons resemble those described on other NGF-responsive cells.

Monoclonal antibodies distinguish several differentially phosphorylated states of the two largest rat neurofilament subunits (NF-H and NF-M) and demonstrate their existence in the normal nervous system of adult rats

A new panel of greater than 300 monoclonal antibodies (mAbs) was prepared to the high, middle, and low Mr rat neurofilament (NF) subunits (NF-H, NF-M and NF-L, respectively). NF proteins were purified both from native, i.e., phosphorylated rat NFs and from enzymatically dephosphorylated rat NFs. The resulting mAbs were used to biochemically and immunochemically distinguish and characterize distinct and differentially phosphorylated isoforms of NF subunits. By immunoblot, all mAbs specific for NF-L and some mAbs specific for NF-M detected their specific NF subunit regardless of whether or not the NFs had been treated with alkaline phosphatase, and such antibodies were termed "phosphate-independent" or P[ind] mAbs. The other mAbs were specific for NF-M, NF-H, or for both NF-M and NF-H, and they recognized epitopes in the COOH termini of these subunits. Significantly, the latter mAbs could discriminate different isoforms of NF-M and NF-H, depending on the phosphorylation state of each variant. Such mAbs were assigned to one of 4 distinct categories on the basis of their performance in immunoblots of progressively dephosphorylated rat NF samples and by immunohistochemistry of various adult rat nervous tissues: (1) P[-] mAbs preferentially stained neuronal perikarya and dendrites, and they recognized only extensively dephosphorylated (and nonphosphorylated) NF-H; (2) P[+] mAbs stained axons more strongly than perikarya, and primarily blotted phosphorylated, but not nonphosphorylated, forms of NF-H and NF-M; (3) P[++] mAbs stained axons almost to the exclusion of perikarya, and in blots recognized only the extensively phosphorylated forms of NF-H and NF-M (i.e., subunits subjected to limited enzymatic dephosphorylation); (4) P[ ] mAbs also predominantly stained axons, but the briefest alkaline phosphatase treatment abolished the NF-M and NF-H immunobands produced by these mAbs. Two-dimensional gel analysis and immunoblotting of total proteins from adult rat dorsal root ganglion verified mAb specificity in situ, and showed that differentially phosphorylated isoforms of NF-M and NF-H occur in vivo. This provided additional evidence that mAbs can detect all 4 phosphorylation-dependent endogenous isoelectric variants of NF-H and NF-M.(ABSTRACT TRUNCATED AT 400 WORDS)

The use of peripheral nerve grafts to enhance neuronal survival, promote growth and permit terminal reconnections in the central nervous system of adult rats.

During both development and regeneration, the survival of neurones and the growth of axons are controlled by inherent neuronal properties, conditions in the axonal environment, and the establishment of appropriately timed and specific functional contacts. To study the effects of extrinsic influences on the survival, growth and connectivity of axotomized neurones in the mature mammalian CNS, we replaced the optic nerve in adult rats with segments of autologous peripheral nerve (PN) and used morphometric techniques, neuroanatomical tracer substances and immunological cell markers to examine retinal ganglion cells (RGCs), their axons in the PN grafts and their terminals in the superior colliculi (SC) of these animals. We observed that: (1) the survival of axotomized RGCs was enhanced by the PN grafts; (2) in the PN-grafted eyes, approximately 20% of the surviving RGCs regrew their axons into the grafts and (3) some of the RGC axons that regenerated along the PN grafts bridging the eye and the tectum re-entered the SC, arborized and made synaptic contacts with tectal neurones. It is not known if the terminal connections established between RGCs and cells in the SC are appropriate, functional or capable of influencing the long-term survival of their cells of origin.

Cloning of Complementary DNA for GAP-43, a Neuronal Growth-Related Protein

GAP-43 is one of a small subset of cellular proteins selectively transported by a neuron to its terminals. Its enrichment in growth cones and its increased levels in developing or regenerating neurons suggest that it has an important role in neurite growth. A complementary DNA (cDNA) that encodes rat GAP-43 has been isolated to study its structural characteristics and regulation. The predicted molecular size is 24 kilodaltons, although its migration in SDS-polyacrylamide gels is anomalously retarded. Expression of GAP-43 is limited to the nervous system, where its levels are highest during periods of neurite outgrowth. Nerve growth factor or adenosine 3',5'-monophosphate induction of neurites from PC12 cells is accompanied by increased GAP-43 expression. GAP-43 RNA is easily detectable, although at diminished levels, in the adult rat nervous system. This regulation of GAP-43 is concordant with a role in growth-related processes of the neuron, processes that may continue in the mature animal.

Chapter 30 Regeneration of axons from the central nervous system of adult rats

Publisher Summary This chapter discusses the studies of the origin and course of the central nervous system (CNS) axons that regenerate along peripheral nerve grafts and summarizes preliminary observations on the terminations of such axons when they are directed to reenter the CNS. In contrast to the well-documented failure of interrupted axons to regenerate within the CNS of adult mammals, many neuronal populations in the brain and spinal cord of adult rats can regrow axons after injury, if the growing axonal tips are exposed to the milieu provided by the nonneuronal environment of peripheral nerve grafts. This regenerative capacity, suspected by earlier investigators by using light microscopy, has now been established by the use of retrograde labeling methods that permit the identification of the CNS neurons whose axons have grown into the peripheral nerve grafts. Neurons in most regions of the CNS are able to elongate their axons into peripheral nerve grafts. However, there are examples of unequal responses among different populations of neurons in the same region.

Histochemical demonstration of copper in normal rat brain and spinal cord

The high sensitivity of the magnesium-dithizonate silver-dithizonate (MDSD) staining procedure makes this method very suitable for the histochemical localization of copper in different regions of the central nervous system of adult rats. In the telencephalon (bulbus olfactorius, nucleus caudatus-putamen, septum pellucidum and area dentata), diencephalon (nucleus habenulae medialis, nuclei of the hypothalamus in the vicinity of the third ventricle, and corpus mamillare), mesencephalon (substantia nigra), cerebellum (mainly in the nodulus), pons (locus coeruleus, nucleus vestibularis), medulla oblongata (nucleus tractus solitarii) and spinal cord, the glial cells exhibit specific copper staining. The glial cells of some circumventricular organs (e.g. the subfornical organ) are also stained using the MDSD method. The significant staining observed in white-matter glial cells (e.g. in the corpus callosum, cerebellum and spinal cord) further indicates the very high sensitivity of this method. In glial cells of the same regions, the presence of copper can likewise be demonstrated using the modified sulphide silver method. On the basis of the present histochemical results, it is suggested that copper may play an important role in the normal physiological functioning of glial cells and also, via glial-neuron interactions, in neuronal processes.

Neonatal hyperthyroidism: effects on sympathetic responses to stress in adult rats.

Treatment of developing rats with thyroid hormone results in accelerated maturation of sympathetic and adrenal medullary responses to reflex activation of central sympathetic outflow. In this study, we examined the effects of neonatal hyperthyroidism on the responsiveness of the sympathetic nervous system of adult rats to acute stress. Hyperthyroidism was produced in Long-Evans hooded rats by injections of thyroxine (neo-T4, 1 mg/kg body wt) on postnatal days 1-4. Littermate controls received injections of vehicle only. In adulthood, male rats of the two groups were prepared with chronic tail artery catheters to allow repeated sampling of blood and direct measurements of mean arterial pressure (MAP, mmHg) and heart rate (HR, beats/min). Two days after surgery, rats were stressed by exposure to 1 min of inescapable foot shock (2.0 mA, 0.6-s duration, every 6 s). The activity of the sympathetic nervous system was assessed by measuring plasma levels of norepinephrine (NE) and epinephrine (E). Basal plasma levels of NE and E and resting MAP did not differ between neo-T4 and control rats. However, basal HR was elevated in neo-T4 rats. Footshock-induced increments in plasma levels of both catecholamines were greater in neo-T4 compared with control rats even though behavioral responses to footshock were similar across groups. However, neo-T4 rats were more active when tested in an open field on each of 3 consecutive days. These findings indicate that neonatal treatment with T4 results in hyperresponsiveness of the sympathoadrenal medullary system to acute stress that persists into adulthood.

A cell surface protein of astrocytes, Ran-2, distinguishes non-myelin-forming Schwann cells from myelin-forming Schwann cells.

Defining the molecular phenotype of adult glial cells in the peripheral nervous system in situ forms a good basis for subsequent studies on the development of these cells, and for determining the role of neurons in the attainment and maintenance of the mature glial phenotype. We report here the characterization of the glial surface antigen, Ran-2, and describe its distribution in the peripheral and central nervous system of adult rats. Immunoprecipitation of the antigen from cultured astrocytes with monoclonal Ran-2, antibodies, showed that Ran-2 is a protein with an apparent molecular weight of 140,000 daltons. In immunofluorescence studies of teased nerve preparations, Ran-2 was found on the surface of non-myelin-forming Schwann cells in all nerves surveyed, i.e. the sciatic, dorsal and ventral roots, cervical sympathetic trunk and the brachial plexus. In contrast, it was not detected immunohistochemically on myelin-forming Schwann cells. The antigen was also absent, or present at very low levels, on the satellite cells of dorsal root sensory ganglia, although, as we reported previously, it was present on the glial cells of the enteric nervous system. The Ran-2 antigen was also associated with perineurial cells. In short-term cell cultures of the sciatic nerve and cervical sympathetic trunk from 19-day-old rats, Ran-2 could be localized on the surface of individual viable Schwann cells. In the central nervous system, the antigen was present on astrocytes in sections of the optic nerve.

3-methylbutanal metabolism in the adult rat.

1. 3-Methylbutanal is a normal constituent of human plasma and is elevated in patients with hepatic encephalopathy. Therefore these studies examined the possible source and site of synthesis of 3-methylbutanal and its effect on the central nervous system of adult rats. 2. 3-Methylbutanal was found to be a normal constituent of rat plasma and increased two to five times when leucine comprised 5% of the diet. Neomycin in the diet prevented the leucine-induced rise in plasma 3-methylbutanal. When this was injected at a dose of 120 mg/kg abnormal EEG patterns and sleep-like behaviour occurred, whereas smaller amounts (30 mg/kg) increased brain serotonin concentrations. 3. 3-Methylbutanal is a normal component of rat plasma: it may be derived in part from colonic bacterial breakdown of leucine and may influence central nervous system function. A possible relationship of 3-methylbutanal to the pathogenesis of hepatic encephalopathy is suggested.