Glutamatergic and morphological alterations associated with early life seizure-induced preconditioning in young rats.

Postnatal day (P)20 rats are sensitive to CA1 injury following a single injection of kainic acid (KA) but are resistant to this injury when animals have a history of two neonatal seizures. We hypothesized that the two earlier seizures led to neuroprotection by a preconditioning mechanism. Therefore, morphology, [Ca(2+)](i) and NMDA subunit proteins of the hippocampus were examined after KA was administered once (1 × KA, on P6, P9, P13 or P20), twice (2 × KA, on P6 and P9) or three times (3 × KA, on P6, P9, P13 or P20). After 1 × KA on P20, the Golgi method revealed marked decreases in spine densities and aborization of CA1 and CA3 apical dendrites. After 3 × KA, morphological alterations were attenuated in CA1 neurons and were similar to pruning observed after 1 × KA on P6 or 2 × KA. After 1 × KA at P13, baseline [Ca(2+)](i) was elevated within pyramidal and dentate granule cells. N-methyl-D-aspartate (NMDA) responses were simultaneously enhanced. After 3 × KA, Ca(2+) elevations were attenuated. Immunohistochemistry revealed selective depletion of the NR2A/B subunit modulator in the same areas. NR1 subunit expression was downregulated in the subiculum and increased in the CA3, causing a significant shift in the NR1:NR2A/B ratio throughout the hippocampus. After 1 × KA or 3 × KA at P20, reduced expression was only observed in areas of cell injury. Results indicate that different changes in morphology and excitatory responses occur depending upon when seizures begin. Partial pruning and persistent shift in the NR1:NR2A/B ratio among excitatory synapses of the hippocampus early in life may produce epileptic tolerance and protect against subsequent insults.

Renewed growth of identified brainstem axons into fetal cortical transplants in adult rat.

Transplantation of fetal neocortex into the site of trigeminal brainstem injury induces regeneration of trigeminal primary afferent axons in adult rats. Renewed growth of injured primary afferent fibers into donor cortex can be extensive, though the innervation pattern does not resemble that normally seen in either brainstem or somatosensory cortex. Examination of the structural and functional characteristics of individual regenerate axon collaterals suggests that their morphology is determined by both intrinsic and postsynaptic target factors. Marked topographic alterations, however, question the utility of fetal cortical transplantation procedures in effecting functional recovery from brainstem injury.

N-ethyl-N-nitrosourea-induced teratogenesis of brain in the rat. A cellular and cytoarchitectural analysis of the neocortex.

N-Ethyl-N-nitrosourea (ENU) was administered intravenously to pregnant Wistar-albino rats on days 14--21 of gestation in order to study the teratological effects of the carcinogen on the developing brain. Offspring were killed 60 days postnatally, and the brains examined histologically by cresyl violet staining and Golgi-Cox preparations. Macroscopic examination of the brains revealed a graded pattern of microcephaly. Injection of ENU on day 14 of gestation gave the most severe effects and injection on day 21 the least effects. Microscopic examination of the neocortex revealed a graded reduction in the lateral and sagittal lengths, thickness, and the number of cells in a sample slab of the cortex. In the Golgi-Cox preparations the pyramidal neurons of cortical layers III and V, as well as neurons of other layers, were seen to have fewer secondary and tertiary dendrites, and the length of their dendrites appeared stunted. These characteristics also were graded in relation to the day of injection of ENU. Altered cytology and cytoarchitecture of the neocortex and possible underlying mechanisms are discussed.

Current trends in the pharmacologic and surgical treatment of Parkinson's disease.

Recently, there has been a surge in the research regarding the pharmacologic and surgical treatment of Parkinson's disease. This article reviews the latest modes of medical and surgical therapy for Parkinson's disease. The latest drug therapy has consisted of levodopa, a combination of levodopa and carbidopa (Sinemet/Sinemet CR), and monoamine oxidase type B (MAO-B) inhibitors (selegiline hydrochloride). The surgical treatment modalities have been stereotaxic implantations of dopamine-producing tissues (such as adrenal medulla and fetal mesencephalon) into the caudate nucleus and ventral pallidotomy of patients with Parkinson's disease. The most recent work has been in the field of gene therapy. The implantation of cells genetically modified to express trophic factors and tyrosine hydroxylase for the synthesis of L-dopa from tyrosine has been proposed as a possible route for the treatment of Parkinson's disease. Although the etiology of the disease is still unknown, two recent theories are discussed.

Resveratrol protects neurons from cannulae implantation injury: implications for deep brain stimulation.

Brain-implantable electrodes such as those used in deep brain stimulation (DBS) have a promising future in end-stage Parkinson's disease therapy. However, there is considerable injury when electrodes penetrate brain tissue. For instance, broken blood vessels and glial scar formation may impede continual DBS or electrical recording from specific neurons. To begin addressing this key safety issue, we tested the therapeutic potential of resveratrol in reducing brain trauma caused by DBS-like surgery. Microinfusion of resveratrol (10 µM) directly applied to the sub-thalamic nucleus (STN) of the rat brain significantly minimized the formation of astrocytic gliosis in response to a 27-G precision-glide cannula implant. The therapeutic effects of resveratrol extended to the "kill zone", a boundary zone of about 100 µm comprising the cannula implant and surrounding neurons. We also found that resveratrol not only provided almost complete protection from mechanical injury to the brain, but that it also prevented undesirable motor deficits often seen in animals with lesions to the STN. Lastly, continuous infusion of resveratrol over a 4-week period led to the inhibition of pro-apoptotic, neurodegenerative and cell division cycle genes that may be associated with a reduction in astrocytic gliosis and glial scar formation within the STN. Taken together, these data suggest that application of resveratrol to the brain is an effective adjunct surgical procedure for minimizing acute neuronal injury when electrodes are implanted directly into the STN.

Silent information regulator 1 mediates hippocampal plasticity through presenilin1.

Silent information regulator 1 (SIRT1) is a nicotinamide adenine dinucleotide (NAD+)-dependent deacetylase directly implicated in protecting a wide range of organisms against internal and external metabolic insults. However, the identification of SIRT1-specific DNA targets that confer such protection have remained elusive. Using human cells, we show that SIRT1 binds to, and transcriptionally regulates, a gene locus encoding presenilin1 (PSEN1), a protein intrinsically involved in the function of the γ-secretase protein complex. We also demonstrate that rats fed with resveratrol exhibit a significant increase in sirt1 and psen1 expression. Finally, dietary consumption of resveratrol also leads to an enhanced proliferative state of neuronal stem cells in the rat hippocampus. Our findings reveal a strong link between resveratrol-dependent SIRT1 signaling and hippocampal plasticity in the mammalian brain.

Endothelial heat shock response in cerebral ischemia.

Blood vessels and nerve fibers often course alongside one another in an orderly fashion throughout the brain. This clustering gives rise to a reciprocal signaling network between endothelial and nerve cells that follows highly stereotyped anatomical patterns. One such molecular signal that is produced by endothelial cells and acts on surrounding neurons is heat shock protein 70. Here we briefly review recent studies that have revealed a critical role of this signaling pathway during harmful insults to the brain, particularly during episodes of cerebral ischemia.

An aberrant nucleus in the telencephalon following administration of ENU during neuroembryogenesis.

Administration of ENU to rats during embryonic development caused the emergence of aberrant nuclei in the dorsal telencephalon. They were located in the corpus callosum, and were composed of pyramidal and stellate neurons. This suggested that the aberrant nuclei arose out of the neurons of cerebral cortex that had failed to migrate during embryogenesis. The aberrant nuclei were found predominantly in the animals receiving ENU on day 18 or earlier of gestation.

Transplantation of brain tissue in the brain of adult rats.

Brain tissues obtained from rat embryos were transplanted in the forebrain and/or cerebellum of the adult rats. The transplants survived, grew and achieved normal cellular and cytoarchitectural differentiation. They had become anatomically integrated with the host brain. The animals did not show any obviously detectable abnormal behavior or pathology of the brain. The transplants survived as long as the animals did suggesting that they had become a part and parcel of the host brain.

Structure-function relationships in rat brain stem subnucleus interpolaris. IX. Inputs from subnucleus caudalis.

1. In an accompanying paper, Jacquin et al. (1990) described the effects of cortical ablation on the receptive-field (RF) properties of neurons in spinal trigeminal (SpV) subnucleus interpolaris (SpVi). A similar ablation paradigm was used here to clarify the role of an additional source of SpVi RF modulation, the extensive projection from caudally adjacent subnucleus caudalis (SpVc). 2. Intra- and extracellular recording, electrical stimulation, and RF mapping techniques were used to study the responses and projections of 356 SpVi cells in 11 rats 58-141 days after surgical isolation of SpVc from SpVi. This was achieved by a transverse knife cut through the lateral one-half of the left medulla just caudal to the obex. Because this lesion severs trigeminal (V) primary afferents caudal to SpVi, as well as postsynaptic intersubnuclear axons traversing to and from SpVi, kainic acid was used in other animals to selectively lesion SpVc inputs to SpVi. Seven rats received kainic acid injections into SpVc 5-28 days before providing similar electrophysiological data on 300 SpVi cells. Results were compared with that of 330 cells from 9 normal adult rats. 3. Knife-cut or kainic-acid lesions did not alter the topography of SpVi cells or the RF properties of 71 ipsilateral V primary afferents. However, both types of lesions produced the same profound changes in the response character of SpVi cells. Statistically reliable increases were found in the relative percentages of cells that 1) expressed convergence from multiple receptor organs, 2) were unresponsive to mechanical stimulation of orofacial regions, 3) responded tonically to a maintained peripheral stimulus, 4) were spontaneously active, 5) were directionally sensitive, 6) responded to stimulation of body surfaces innervated by cervical primary afferents, and 7) had split RFs. 4. RFs were also reliably larger for whisker-activated local circuit and projection neurons after both types of lesions. Over one-third of this local circuit group responded to more than one whisker in both experimental groups, whereas in normals all responded to one whisker. 5. All other SpVi response indices were unchanged by SpVc lesions. The most notable negative result was a normally low percentage of cells that were responsive to nociceptive stimuli. 6. To assess whether these RF changes reflected altered collateral morphology of V primary afferents in SpVi, whisker (n = 11) and guard-hair- (n = 7) activated axons were stained with horseradish peroxidase rostral to knife-cut or kainic-acid lesions.(ABSTRACT TRUNCATED AT 400 WORDS)

Transplantation of neural tissues in the brains of laboratory mammals: technical details and comments.

Various technical details on the transplantation of the embryonic neural tissues in the brains of the neonatal and adult rats are presented. Conditions determining successful or leading to unsuccessful survival, growth and differentiation of these transplants are critically examined.

Transplantation of brain tissue in the brain of rat. I. Growth characteristics of neocortical transplants from embryos of different ages.

Differential growth of neural transplants as related to the age of the donor embryos was investigated in this study. Neocortical tissue of constant volume, obtained from embryos of 15, 16, 17, 18, 19, 20, and 21 days' gestational age, was transplanted into the cerebellum of 10-day-old rats. The fully grown transplants were analyzed quantitatively and qualitatively 90 days after transplantation. The ultimate volume of the transplants and the estimated total number of neurons in them followed a gradient in relation to the age of the donor embryos. At one extreme, the neural transplants from 15-day-old embryos grew very large, showing a 21-fold increase in size, and at the other extreme, those from 21-day-old embryos grew less than two-fold in volume. These differences were determined by the developmental history of the transplants. Neural tissue obtained from 15-day-old embryos contained predominantly neuroepithelial cells which continued to proliferate even after transplantation. This resulted in the large size of these transplants. At the other extreme, neural tissue from 21-day-old embryos contained predominantly preformed neuroblasts, and they simply differentiated afte transplantation. Due to this, the transplants were small in size. Neural tissues obtained from other embryos of different gestational ages between these two extremes contained neuroepithelial cells and preformed neuroblasts in differential ratios. The number of neuroepithelial cells in the transplants and their differential proliferative activity after transplantation, and the number of neuroblasts present, determined the differential sizes of these transplants. In histological preparations, all transplants were seen to contain normal-looking and well-differentiated neurons, and normal-looking neuropil. The transplants were integrated with the host brain, in that there was neither any gap nor any scar tissue between the transplants and the host neural tissue surrounding them. Neither the transplants nor the host brains showed any pathological reaction or neoplastic growth.

Transplantation of brain tissue in the brain of rat. II. Growth characteristics of neocortical transplants in hosts of different ages.

In this study the growth of neural transplants was analyzed in relation to the age of the host animals and the site of transplantation. The influence of these two host parameters on the growth of neural transplants with high growth potential (tissue from 15-day-old embryos) and low growth potential (tissue from 18-day-old embryos) was investigated. Neocortical neural tissues of constant volume, obtained from 15- and 18-day-old embryos, were transplanted into the forebrain or cerebellum of 5-, 10-, 20-, 25-, 30-, 35- and 180-day-old host animals and analyzed, quantitatively well as qualitatively, 90 days after transplantation. The transplants grew larger in volume in the cerebellum than in the forebrain region of the hosts of all ages. In both sites, tissue from 15-day-old embryos yielded larger transplants than tissue from 18-day-old embryos. Transplants from 15-day-old embryos grew most extensively in 5-day-old host animals (33-fold in the cerebellum, and 23-fold in the forebrain region.) In older host animals it grew less extensively, and without much variation in size that could be attributed to the age of host animals. Tissue from 18-day-old embryos grew little, regardless of site of transplantation or age of host. Apparently the age of the host animals and the site of transplantation had greater influence on the growth of the neural transplants with high growth potential than on those with low growth potential. Histologically, the neural transplants in all cases contained normal-looking and fully differentiated neurons and were anatomically integrated with the host brain.

Study of sympathetic innervation of cranial bones by axonal transport of horseradish peroxidase in the rat: preliminary findings.

This study performed by intraneuronal tracing directly demonstrates the presence of sympathetic postganglionic fibers in the cranial vault of the rat. Superior cervical sympathetic ganglia were injected with horseradish peroxidase (HRP), and after a 48-hour period, to permit anterograde axonal transport, the animals were sacrificed after in situ perfusion. An area of the calvaria that included portions of the frontal and parietal bones was fixed, decalcified and sectioned. HRP-containing axons were localized in the developing frontal and parietal bones of the calvaria. Adrenergic innervation was not demonstrated in sutural tissue (superior sagittal, coronal or metopic) by this technique. To our knowledge, this study is the first to trace sympathetic nerve fibers in the rat calvaria by intra-axonal transport of HRP.

Developing retina and PNS segments for transplantation into the adult host eye: reconstruction of the mammalian visual system. 1. Methodology.

Various techniques have been explored to determine the uses and limitations of techniques that enable the adult CNS to regenerate, but relatively little attention has been given to the consideration of a "reconstructed" visual system. Using this approach, one can design experiments to study the uses of exogenous tissues in reestablishing neuronal circuits that have been damaged. Toward this end, experiments were designed to determine whether embryonic retinal ganglion cells can project axons into a grafted PNS "bridge", and enter adult host targets that were partially deafferented. Embryonic eyes of E11, E14, E18 and E21 rats were sutured to peripheral nerve segments which served as bridges between the host eye and frontal cortex. Projections between the developing retina and the host brain could then be evaluated using HRP tracing techniques. From a methodological standpoint, the preparations are 65% effective; i.e., a viable bridge results between the embryonic eye and the host forebrain. The results presented in the accompanying paper demonstrate that the technique can yield results indicative of embryonic retinal development and axonal projection through the graft and into the host brain. This partial reconstruction of the visual system may prove a useful tool in understanding the uses and limitations of grafting in the CNS.

Developing retina and PNS segments for transplantation into the adult host eye: reconstruction of the mammalian visual system. 2. Results.

The previous companion paper detailed a technique which allowed embryonic retinal ganglion cell axons to grow from the anterior eye chamber across a PNS bridge, and enter the adult host forebrain. Embryonic eyes of E11, E14, E18 and E21 animals were sutured to a PNS bridge, the embryonic eye implanted into an adult host eye, and the distal end of the bridge implanted into the host forebrain. Results indicate that when eyes of all ages are used for implantation, axons could be observed to grow from the embryonic retina, through the bridge and into the adult host forebrain. The axons extend for long distances in the host brain, reach various layers of the cortex and in a few animals enter the caudate/putamen complex. Control studies show that the bridge is used exclusively as the conduit to the brain, as opposed to the degenerated host optic nerve. Thus, the results presented in this paper indicate that successful grafting and transplantation is possible using the aforementioned technique. The results suggest that the described visual system reconstruction technique can be used for the study of development and transplantation in this system.