Nervous System Of Adult Rats Research Articles

Rodent Experimental Model of Konzo: Characterization of Motor Impairment and Neurodegeneration after Cassava Neurotoxicity in the Rat

Konzo is a motor neuron neurodegenerative disease caused by bitter cassava toxicity that presents as a non-progressive spastic paraparesis. The ability of bitter cassava to produce behavioural and structural changes in adult rat nervous system was examined. Twenty five rats were used for this study, and pruned to 20 after consistent baseline performance was achieved (n=20; control=5, cassava chow=15). The rats were switched to a cassava diet for another 5 weeks (n=15). After the cassava consumption period, 5 rats underwent rehabilitation training three times a week and their performance tested once in a week for 5 weeks. Quantitative and qualitative assessments using a reaching movement scale and reach-to-grasp success rate were respectively carried out. Animals subjected to cassava toxicity performed significantly worse than the controls when determining the success rate in a reach-to-grasp experiment (baseline=69.8%, cassava diet=21.4%, post-cassava diet =48.9%). The various movement of the rat was analysed using ANOVA and there was significant difference (p < 0.05) in the performance. The rats couldn’t pronate, grasp, withdraw or open the digits properly when fed with cassava diet. Histology showed neuropathological damages on the motor cortex, less neurons in the motor neuron pool of the spinal cord and disruption of pyramidal layer of the hippocampus when rats were given bitter cassava. Immunofluorescence stain shows motor neurons and numerous choline acetyltransferase (ChAT+) processes and some C-boutons. There are behavioural evidence and neuropathological changes in the motor cortex and ventral horn of the spinal cord that may underlie movement impairments in rats fed with bitter cassava.

Fluoride exposure during pregnancy and lactation triggers oxidative stress and molecular changes in hippocampus of offspring rats

Long-term exposure to high concentrations of fluoride (F) can damage mineralized and soft tissues such as bones, liver, kidney, intestine, and nervous system of adult rats. The high permeability of the blood–brain barrier and placenta to F during pregnancy and lactation may be critical to neurological development. Therefore, this study aimed to investigate the effects of F exposure during pregnancy and lactation on molecular processes and oxidative biochemistry of offspring rats’ hippocampus. Pregnant Wistar rats were randomly assigned into 3 groups in accordance with the drinking water received: G1 – deionized water (control); G2 – 10 mg/L of F and G3 – 50 mg/L of F. The exposure to fluoridated water began on the first day of pregnancy and lasted until the 21st day of breastfeeding (when the offspring rats were weaned). Blood plasma samples of the offspring rats were collected to determine F levels. Hippocampi samples were collected for oxidative biochemistry analyses through antioxidant capacity against peroxyl (ACAP), lipid peroxidation (LPO), and nitrite (NO2−) levels. Also, brain-derived neurotrophic factor (BDNF) gene expression (RT-qPCR) and proteomic profile analyses were performed. The results showed that exposure to both F concentrations during pregnancy and lactation increased the F bioavailability, triggered redox imbalance featured by a decrease of ACAP, increase of LPO and NO2− levels, BDNF overexpression and changes in the hippocampus proteome. These findings raise novel questions regarding potential repercussions on the hippocampus structure and functioning in the different cognitive domains.

Neurochemical dysfunction in motor cortex and hippocampus impairs the behavioral performance of rats chronically exposed to inorganic mercury

Chronic exposure to mercury chloride (HgCl2) has been shown to promote oxidative stress and cell death in the central nervous system of adult rats displaying motor and cognitive impairments. However, there are no investigations about neurochemical function after this type of exposure in rodents that may be associated with those behavioral changes already reported. Thus, the aim of this study was to analyze glutamatergic and GABAergic dysfunctions in the motor cortex and hippocampus of adult rats, in a model of chronic exposure to HgCl2 in. Twenty rats were exposed to a daily dose of 0.375 mg/kg for 45 days. After this period, they were submitted to motor and cognitive functions tests and euthanized to collect the motor cortex and hippocampus for measurement of mercury (Hg) levels in the parenchyma and neurochemical assays for analysis of glutamatergic and GABAergic functions. It was observed that chronic exposure to HgCl2 promoted increase in total Hg levels in these two brain areas, with changes in glutamatergic transport, but without changes in GABAergic transport. Functionally this model of exposure caused the decrease of the spontaneous motor locomotion and in the process of learning and memory. In this way, our results provide evidences that glutamatergic neurochemical dysfunction can be pointed out as a strong causal factor of motor and cognitive deficits observed in rats exposed to this HgCl2.

Effects of neonatal maternal separation on the colonic motility and enteric nervous system of adult rats

Effects of neonatal maternal separation on the colonic motility and enteric nervous system of adult rats

Cloning and characterization of rat Luman/CREB3, a transcription factor highly expressed in nervous system tissue.

Human Luman/CREB3 is a basic leucine zipper transcription factor involved in regulation of the unfolded protein response, dendritic cell maturation, and cell migration. But despite reported expression in primary sensory neurons, little is known about its role in the nervous system. To begin investigations into its role in the adult rat nervous system, the rat Luman/CREB3 coding sequence was isolated so its expression within the nervous system could be determined. The rat Luman/CREB3 clone contains a full-length open reading frame encoding 387 amino acids. The recombinant protein generated from this clone activated transcription in a manner equivalent to human Luman/CREB3 from a CAT reporter plasmid construct containing the unfolded protein response element. Quantitative RT-PCR revealed that rat Luman/CREB3 transcripts in a variety of rat tissues with the highest levels in nervous system tissue. In situ hybridization performed on tissue sections confirmed the findings and demonstrated that the Luman/CREB3 mRNA hybridization signal localizes to neurons and satellite glial cells in dorsal root ganglia, the cytoplasm of hepatocytes in liver, and the hippocampal pyramidal cell layers of CA1 and CA3 and the granular cell layer of the dentate gyrus. Collectively, these findings support a role for Luman/CREB3 in the regulation of nervous system function.

Myosin Va associates with mRNA in ribonucleoprotein particles present in myelinated peripheral axons and in the central nervous system

Sorting of specific mRNAs to particular cellular locations and regulation of their translation is an essential mechanism underlying cell polarization. The transport of RNAs by kinesins and dyneins has been clearly established in several cell models, including neurons in culture. A similar role appears to exist in higher eukaryotes for the myosins. Myosin Va (Myo5a) has been described as a component of ribonucleoprotein particles (RNPs) in the adult rat nervous system and associated to ZBP1 and ribosomes in ribosomal periaxoplasmic plaques (PARPs), making it a likely candidate for mediating some aspects of RNA transport in neurons. To test this hypothesis, we have characterized RNPs containing Myo5a in adult brains of rats and mice. Microarray analysis of RNAs co-immunoprecipitated with Myo5a indicates that this motor may associate with a specific subpopulation of neuronal mRNAs. We found mRNAs encoding α-synuclein and several proteins with functions in translation in these RNPs. Immunofluorescence analyses of RNPs showed apparent co-localization of Myo5a with ribosomes, mRNA and RNA-binding proteins in discrete structures present both in axons of neurons in culture and in myelinated fibers of medullary roots. Our data suggest that PARPs include RNPs bearing the mRNA coding for Myo5a and are equipped with kinesin and Myo5a molecular motors. In conclusion, we suggest that Myo5a is involved in mRNA trafficking both in the central and peripheral nervous systems.

Immunohistochemical detection and gene expression of tyrosine hydroxylase and vesicular monoamine transporter type 2 in intrinsic cardiac ganglia of socially isolated rats

Social isolation induced a significant increase in resting heart rate and reduction in heart rate variability. Dysfunction of the intrinsic cardiac nervous system is implicated in the genesis of cardiovascular diseases. Previous evidence suggests that cardiac ganglia contain noradrenergic neurons. Thus, immunohistochemical expression of catecholaminesynthesizing enzyme tyrosine hydroxylase (TH) and vesicular monoamine transporter 2 (VMAT2) were analyzed, as well as the effects of social isolation stress on mRNA and protein levels of this enzyme and transporter in the intrinsic cardiac nervous system of adult rats. Our results indicate that cardiac ganglion neurons express TH and VMAT2 immunoreactivity. Chronic isolated stress of rats caused a decrease in TH mRNA and VMAT2 mRNA in the neurons of intrinsic cardiac ganglia. No significant alterations in the protein levels of TH and VMAT2 were observed in these neurons. These data indicate that the neurons of intrinsic cardiac ganglia express TH as well as VMAT2 but that social isolation stress does not change their protein levels.

Intraganglionic AAV6 Results in Efficient and Long-Term Gene Transfer to Peripheral Sensory Nervous System in Adult Rats

We previously demonstrated safe and reliable gene transfer to the dorsal root ganglion (DRG) using a direct microinjection procedure to deliver recombinant adeno-associated virus (AAV) vector. In this study, we proceed to compare the in vivo transduction patterns of self-complementary (sc) AAV6 and AAV8 in the peripheral sensory pathway. A single, direct microinjection of either AAV6 or AAV8 expressing EGFP, at the adjusted titer of 2×109 viral particle per DRG, into the lumbar (L) 4 and L5 DRGs of adult rats resulted in efficient EGFP expression (48±20% for AAV6 and 25±4% for AAV8, mean ± SD) selectively in sensory neurons and their axonal projections 3 weeks after injection, which remained stable for up to 3 months. AAV6 efficiently transfers EGFP to all neuronal size groups without differential neurotropism, while AAV8 predominantly targets large-sized neurons. Neurons transduced with AAV6 penetrate into the spinal dorsal horn (DH) and terminate predominantly in superficial DH laminae, as well as in the dorsal columns and deeper laminae III-V. Only few AAV8-transduced afferents were evident in the superficial laminae, and spinal EGFP was mostly present in the deeper dorsal horn (lamina III-V) and dorsal columns, with substantial projections to the ventral horn. AAV6-mediated EGFP-positive nerve fibers were widely observed in the medial plantar skin of ipsilateral hindpaws. No apparent inflammation, tissue damage, or major pain behaviors were observed for either AAV serotype. Taken together, both AAV6 and AAV8 are efficient and safe vectors for transgene delivery to primary sensory neurons, but they exhibit distinct functional features. Intraganglionic delivery of AAV6 is more uniform and efficient compared to AAV8 in gene transfer to peripheral sensory neurons and their axonal processes.

Expression and immunolocalization of Gpnmb, a glioma‐associated glycoprotein, in normal and inflamed central nervous systems of adult rats

Glycoprotein nonmetastatic melanoma B (Gpnmb) is a type I transmembrane protein implicated in cell differentiation, inflammation, tissue regeneration, and tumor progression. Gpnmb, which is highly expressed in glioblastoma cells, is a potential therapeutic target. However, little is known about its expression, cellular localization, and roles in non-tumorous neural tissues. In this study, we examined Gpnmb expression in the central nervous system of adult rats under both normal and inflammatory conditions. Reverse transcription-polymerase chain reaction analysis revealed that Gpnmb mRNA was expressed in the cerebrum, cerebellum, brain stem, and spinal cord of normal adult rats. Immunoperoxidase staining revealed that Gpnmb-immunoreactive cells were widely distributed in the parenchyma of all brain regions examined, with the cells being most prevalent in the hippocampal dentate gyrus, cerebellar cortex, spinal dorsal horn, choroid plexus, ependyma, periventricular regions, and in layers II and III of the cerebral cortex. Double immunofluorescence staining showed that these cells were co-stained most frequently with the microglia/macrophage marker OX42, and occasionally with the radial glia marker RC2 or the neuronal marker NeuN. Furthermore, an intraperitoneal injection of bacterial endotoxin lipopolysaccharide increased the number of Gpnmb and OX42 double-positive cells in the area postrema, which is one of the circumventricular organs, indicating infiltration of hematogenous macrophages. These results suggest that Gpnmb, which is expressed in microglia and macrophages in non-tumorous neural tissues, plays an important role in the regulation of immune/inflammatory responses.

NADPH-diaphorase expression in the rat jejunum after intestinal ischemia/reperfusion

The purpose of this study was to analyze the nicotinamide adenine dinucleotide phosphate - diaphorase (NADPH-d) activity in the rat jejunum after a mesenteric ischemia/reperfusion injury. Nitric oxide, synthetised from L-arginine by the enzyme nitric oxide synthase, is a nonadrenergic noncholinergic relaxant neurotransmitter of the intestinal smooth muscle. It plays an important role in the process of plasticity after the ischemia/reperfusion injury. Experimental animals were divided in two groups: the control group and the ischemic/reperfusion group, with different period of the reperfusion. The NADPH-d histochemical method has been used as a marker for the nitric oxide synthase. NADPH-d activity has been rapidly decreased in the neurons of both enteric nervous systems in plexuses of the jejunum after 1 h mesenteric ischemia and 1 h reperfusion. Differences were predominantly detected in the myenteric plexus; they were seen in change of the neuronal shape, in the arrangement of neurons and in intensity of their staining. The NADPH-d positivity was absent in the intestinal crypts. After 1 h ischemia and 24 h reperfusion, the NADPH-d activity was gradually increased, but it was lower in comparison with the control group. On the 30th day following the ischemia/reperfusion there were no changes in NADPH-d positivity compared with the control animals. These results indicated that the jejunal ischemia/reperfusion has affected the neurons of the enteric nervous system of adult rats and resulted in the early decrease of NADPH-d positivity 1 h of the reperfusion insult. The gradual increasing of NADPH-d activity in 24 h following the reperfusion could be considered as a result of the plasticity process. On the 30th day after the ischemia/reperfusion all histochemical changes were returned to the control levels.

Neuregulin‐1 at synapses on phrenic motoneurons

The neuregulin (NRG) family of trophic factors is present in the central and peripheral nervous systems and participates in the survival, proliferation, and differentiation of many different cell types, including motoneurons. NRG1 was first characterized by its role in the formation of the neuromuscular junction, and recently it was shown to play a crucial role in modulating glutamatergic and cholinergic transmission in the central nervous system of adult rats. However, little is known about NRG1's role in adult motor systems. Motoneurons receive dense glutamatergic and cholinergic input. We hypothesized that NRG1 is present at synapses on phrenic motoneurons. Confocal microscopy and 3D reconstruction techniques were used to determine the distribution of NRG1 and its colocalization with these different neurotransmitter systems. We found that NRG1 puncta are present around retrogradely labeled motoneurons and are distributed predominantly at motoneuron somata and primary dendrites. NRG1 is present exclusively at synaptic sites (identified using the presynaptic marker synaptophysin), making up ∼30% of all synapses at phrenic motoneurons. Overall, NRG1 immunoreactivity is found predominantly at cholinergic synapses (75% ± 14% colocalize with the vesicular acetylcholine transporter; VAChT). Nearly all (99% ± 1%) VAChT-immunoreactive synapses expressed NRG1. NRG1 also is present at a subset of glutamatergic synapses expressing the vesicular glutamate transporter (VGLUT) type 2 (∼6%) but not those expressing VGLUT type 1. Overall, 26% ± 6% of NRG1 synapses are VGLUT2 immunoreactive. These findings provide the first evidence suggesting that NRG1 may modulate synaptic activity in adult motor systems.

Neonatal endotoxin exposure suppresses experimental autoimmune encephalomyelitis through regulating the immune cells responsivity in the central nervous system of adult rats

Early-life exposure to bacterial endotoxin (lipopolysaccharide, LPS) affects the susceptibility to a variety of systemic organic inflammation in adulthood. To determine the long-term effects of neonatal LPS exposure on inflammatory responses in the central nervous system (CNS) in adulthood, we examined the effects on the development of experimental autoimmune encephalomyelitis (EAE) in adult rats as well as the potential regulatory immune mechanisms involved. The results showed that neonatal LPS exposure significantly reduced the morbidity (p<0.01) and severity (p<0.05) of EAE in adult rats, and decreased inflammatory cell infiltration and demyelination in the CNS compared with neonatal saline controls (p<0.05). Neonatal LPS-treated animals showed reduced activation of microglia and astrocytes, as detected by immunocytochemistry, accompanied by down-regulation of the pro-inflammatory cytokines interleukin-17 and interferon-γ but up-regulation of anti-inflammatory cytokine interleukin-10 in the CNS (p<0.05). At the same time, cerebrum mRNA levels of the transcription factors T-bet and RORγt were lower in neonatal LPS-compared with saline- treated animals (p<0.05) accompanied with increased STAT-6 and Foxp3 levels in the neonatal LPS-treated group (p<0.05). These findings suggest that early-life exposure to LPS could provide an important neuroprotective effect on the development of EAE in adult rats due to modulation of inflammatory responses in the CNS.

Immunohistochemical Study on the Distribution of Insulin-like Growth Factor Binding Protein 7 (IGFBP7) in the Central Nervous System of Adult Rats

In the present study, we performed immunohistochemical studies to investigate the detailed distribution of insulin-like growth factor binding protein 7(IGFBP7) in the central nervous system of adult rats. Twelve adult (4~6 month old) Sprague-Dawley rats were examined in this study. Immunohistochemistry using specific antibodies against IGFBP7 was performed in accordance with the free-floating method. In the present study, IGFBP7 immunoreactivity was observed in the cerebral cortex, hippocampus, brainstem, cerebellum and spinal cord. In the cerebral cortex, heavily stained neurons were seen in layers Ⅱ-Ⅵ. In the hippocampus, pyramidal cells in CAI-3 region were strongly immunoreactive for IGFBP7. Strong immunoreactive neurons were also found in the supraoptic nucleus, paraventricular nucleus, periaqueductal gray and oculomotor nucleus. In the cerebellum, IGFBP7 immunoreactivity was prominent in the Purkinje cells and cerebellar output neurons. IGFBP7-immunoreactive neurons were prominent in the superior vestibular nucleus, cochlear nucleus. trigeminal motor nucleus, nucleus of the trapezoid, and facial nucleus. IGFBP7-immunoreactive neurons were also observed mainly in the anterior horn of the spinal cord. The first demonstration of IGFBP7 localization in the whole brain may provide useful data for the future investigations on the structural and functional properties of IGFBP7.

Ciglitazone increases basal cytokine expression in the central nervous system of adult rats

Ciglitazone, rosiglitazone, and pioglitazone belong to a relatively new class of antidiabetic agents referred to as thiazolidinediones (TZDs). Later, TZDs were found to be peroxisome proliferator-activated receptor (PPAR)-γ agonists and to elicit anti-inflammatory effects in both in vitro and in vivo models in response to stimuli such as lipopolysaccharide (LPS) and phorbol 12-myristate 13-acetate (PMA). In the present study, we sought to investigate the effects of oral administration of ciglitazone on basal inflammatory cytokine expression in healthy adult rats. The analysis of cytokine expression in the spleen revealed a reduction in IL-4 production after ciglitazone treatment. In contrast, in the brain, ciglitazone administration increased IL-1β synthesis at the protein and mRNA level, while TNF-α protein expression was also increased. To ensure that the latter findings were not an indirect effect originating from the periphery, we delivered ciglitazone intracerebrally for a 7-day period using an osmotic pump, which confirmed the increase in IL-1β and TNF-α expression. Our results show that despite anti-inflammatory effects described for ciglitazone in “primed” models, ciglitazone can positively modulate basal inflammatory mediators within the central nervous system (CNS) of healthy adult rodents.

Distribution of the galectin-1 mRNA in the rat nervous system: its transient upregulation in rat facial motor neurons after facial nerve axotomy

Galectin-1 is a member of the animal lectin family that displays conserved consensus sequences and similar carbohydrate binding specificities. Recent analyses revealed that galectin-1 plays an important role in the process of nerve regeneration. We analyzed the topological expression of galectin-1 mRNA in adult rat nervous system. Galectin-1 mRNA was predominantly observed in the cell bodies of neurons such as oculomotor nucleus (III), trochlear nucleus (IV), trigeminal motor nucleus (V), abducens nucleus (VI), facial nucleus (VII), hypoglossal nucleus (XII), red nucleus, and locus ceruleus. Neurons in pineal gland and dorsal root ganglia expressed galectin-1 mRNA. We next tested whether the axotomy of facial nerve altered the expression of galectin-1 mRNA in motor neurons. In the adult rats, the axotomy of facial nerve induced transient upregulation of galectin-1 mRNA around 6 h after axotomy. These results indicate that galectin-1 may play roles in the early event of the nerve injury and regeneration through the transient change of its expression level.

Nogo-A expression in the intact and injured nervous system

The expression of Nogo-A mRNA and protein in the nervous system of adult rats and cultured neurons was studied by in situ hybridisation and immunohistochemistry. Nogo-A mRNA was expressed by many cells in unoperated animals, including spinal motor, DRG, and sympathetic neurons, retinal ganglion cells, and neocortical, hippocampal, and Purkinje neurons. Nogo-A protein was strongly expressed by presumptive oligodendrocytes, but not by NG2+glia and was abundant in motor, DRG, and sympathetic neurons, retinal ganglion cells, and many Purkinje cells, but was difficult to detect in dentate gyrus neurons and some neocortical neurons. Cultured fetal mouse neocortical neurons and adult rat DRG neurons strongly expressed Nogo-A in their perikarya, growth cones, and axonal varicosities. All axons in the intact sciatic nerve contained Nogo-A and many but not all regenerating axons were strongly Nogo-A immunopositive after sciatic nerve transection. Ectopic muscle fibres that developed among the regenerating axons were also Nogo-A immunopositive. Following injury to the spinal cord, Nogo-A mRNA was upregulated around the lesion and Nogo-A protein was strongly expressed in injured dorsal column fibres and their sprouts which entered the lesion site. Following optic nerve crush, Nogo-A accumulated in the proximal and distal stumps bordering the lesions.

Nogo-A expression in the intact and injured nervous system

The expression of Nogo-A mRNA and protein in the nervous system of adult rats and cultured neurons was studied by in situ hybridisation and immunohistochemistry . Nogo-A mRNA was expressed by many cells in unoperated animals, including spinal motor, DRG, and sympathetic neurons, retinal ganglion cells, and neocortical, hippocampal, and Purkinje neurons. Nogo-A protein was strongly expressed by presumptive oligodendrocytes , but not by NG2+glia and was abundant in motor, DRG, and sympathetic neurons, retinal ganglion cells, and many Purkinje cells , but was difficult to detect in dentate gyrus neurons and some neocortical neurons. Cultured fetal mouse neocortical neurons and adult rat DRG neurons strongly expressed Nogo-A in their perikarya , growth cones , and axonal varicosities. All axons in the intact sciatic nerve contained Nogo-A and many but not all regenerating axons were strongly Nogo-A immunopositive after sciatic nerve transection. Ectopic muscle fibres that developed among the regenerating axons were also Nogo-A immunopositive. Following injury to the spinal cord, Nogo-A mRNA was upregulated around the lesion and Nogo-A protein was strongly expressed in injured dorsal column fibres and their sprouts which entered the lesion site. Following optic nerve crush, Nogo-A accumulated in the proximal and distal stumps bordering the lesions.

Functional role of a specific ganglioside in neuronal migration and neurite outgrowth

Cell migration occurs extensively during mammalian brain development and persists in a few regions in the adult brain. Defective migratory behavior of neurons is thought to be the underlying cause of several congenital disorders. Knowledge of the dynamics and molecular mechanisms of neuronal movement could expand our understanding of the normal development of the nervous system as well as help decipher the pathogenesis of neurological developmental disorders. In our studies we have identified and characterized a specific ganglioside (9-O-acetyl GD3) localized to the membrane of neurons and glial cells that is expressed in regions of cell migration and neurite outgrowth in the developing and adult rat nervous system. In the present article we review our findings that demonstrate the functional role of this molecule in neuronal motility.

Distribution of Fluorescence following Injection of Recombinant Adeno-Associated Virus Encoding Green Fluorescent Protein into the Paraventricular Nucleus

We have used recombinant type 2 adeno-associated virus to deliver the gene encoding green fluorescent protein into the central nervous system of adult rats. Gene expression, determined by fluorescent microscopy, was observed not only at the site of injection but also in axons following known neuroanatomical pathways. We have demonstrated a spread of enhanced green fluorescent protein from the paraventricular nucleus of the hypothalamus into the median eminence and neurohypophysis. Cell bodies containing enhanced green fluorescent protein were also visualized in the paraventricular nucleus contralateral to the side of injection. These findings suggest that gene transfer by recombinant adeno-associated virus could be used as a tool to investigate hypothalamic-pituitary interactions and, elsewhere in the central nervous system, to trace axonal pathways.

Neuregulin-1 isoforms are differentially expressed in the intact and regenerating adult rat nervous system.

Our knowledge on Neuregulin-1 (Nrg-1) during development of the nervous system is increasing rapidly, but little is known about Nrg-1-ErbB signaling in the adult brain. Nrg-1 is involved in determination, proliferation, differentiation, and migration of neurons and glial cells in the developing brain. In the peripheral nervous system, Nrg-1 signaling is required for Schwann cell differentiation and myelination, and establishment of neuromuscular junctions (NMJs). Multiple alternative splicing of Nrg-1 was shown, but correlation of its structural and functional diversity was rarely addressed. Therefore, we investigated the expression of Nrg-1 isoforms in the rat brain and brain-derived cell types, and their involvement in regeneration of the adult brain, using immunohistochemistry, in situ hybridization, and semiquantitative RT-PCR. We found expression of at least 12 distinct Nrg-1 isoforms in the brain and altered expression of several isoforms in the facial motor nucleus after peripheral transection of the seventh cranial nerve. An upregulation of Nrg-1 type-I mRNA, probably type- I-alpha, was observed in reactive astrocytes of the facial nucleus 1 d postaxotomy. Nrg-1 type-III and the splice variants beta1 and beta5 are dramatically downregulated in axotomized motoneurons, which lack contact to their target tissue. Baseline expression levels were reestablished when the first axons reached the facial muscles and reformed NMJs. Nrg-1-beta1 and -beta5 might act in maintenance of NMJs. The splice variants beta2 and beta4 display an initial downregulation of mRNA levels, followed by an increase during the period of axon remyelination. Thus, Nrg- 1-beta2 and -beta4 might be involved in myelination.