Denervation-induced region-specific changes in fibre types in the soleus and plantaris muscles of rats

Muscle fibre composition was compared among the proximal (25%), middle (50%) and distal (75%) regions of muscle to investigate whether denervation induces region-specific changes of fibre types in the soleus and plantaris muscles of rats. Decreases in mass were observed in both muscles after denervation. In the soleus muscle, denervation increased the percentage of type I fibres with a concomitant increase in the proportion of type IIC and IIA fibres. The extent of such transformations was greater in the proximal region than the middle and distal regions. In normal plantaris muscle, the middle region showed a higher proportion of type IIA fibres with a lower percentage of type IIB fibres reciprocally than other regions. These regional differences in fibre types were not detected in the 4-week denervated plantaris muscle. These findings suggest that denervation-induced transformations from type I to type II fibres begin in the proximal region in the soleus muscle of rats. In addition, regional differences in fibre types along the muscle length could be regulated by neuromuscular activity through normal innervation in the plantaris muscle. Received: 17 November 1995 / Revised: 29 April 1996 / Accepted: 15 July 1996     

Effects of unilateral cochlea ablation on the distribution of calretinin mRNA and immunoreactivity in the guinea pig ventral cochlear nucleus

The predominantly neuronal, calcium-binding protein calretinin is highly expressed in the guinea pig auditory system. Within the ventral cochlear nucleus (VCN), calretinin-positive auditory nerve fibers terminate on many calretinin-containing bushy, octopus, and multipolar cells. The abundance of calretinin in the cochlear nucleus provides an ideal system for examining the effects of altered neuronal input on the expression of this calcium-binding protein. The present experiments examined the effects of unilateral cochlea ablation on calretinin immunoreactivity and mRNA levels in the VCN. Calretinin mRNA was labeled by in situ hybridization histochemistry using a radioactive oligonucleotide probe and was quantified by optical density measures on autoradiograms. Survival times of 1, 7, and 56 days postlesion were examined. The results revealed a consistent increase in calretinin mRNA in the rostral portion of the ipsilateral anterior VCN 1 day postlesion but no effect on calretinin mRNA in this region at 7 and 56 days postlesion. The intensity of immunohistochemical label was also increased at 1 and 7 days after surgery. In contrast, calretinin mRNA was not affected 1 day postlesion in the ipsilateral posterior VCN but was decreased at both 7 and 56 days postlesion. The decrease in calretinin mRNA in the posterior VCN at longer survival times was accompanied by decreased immunolabeling of fibers projecting from VCN cells to the superior olivary complex. These results suggest that calretinin gene expression is regulated in part by auditory nerve activity in some cochlear neurons but that additional factors related to the unique cellular milieu also control calretinin expression. © 1995 Wiley-Liss, Inc.     

The lack of effect of specific overexpression of IGF-1 in the central nervous system or skeletal muscle on pathophysiology in the G93A SOD-1 mouse model of ALS

The ability of insulin like growth factor 1 (IGF-1) to prevent the pathophysiology associated with amyotrophic lateral sclerosis (ALS) is currently being explored with animal models and in clinical trials with patients. Several studies have reported positive effects of IGF-1 in reducing motor neuron death, delaying the onset of motor performance decline, and increasing life span, in SOD-1 mouse models of ALS and in one clinical trial. However, a second clinical trial produced no positive results raising questions about the therapeutic efficacy of IGF-1. To investigate the effect of specific and sustained IGF-1 expression in skeletal muscle or central nervous system on motor performance, life span, and motor neuron survival, human-IGF-1 transgenic mice were crossed with the G93A SOD-1 mutant model of ALS. No significant differences were found in onset of motor performance decline, life span, or motor neuron survival in the spinal cord, between SOD+/IGF-1+ and SOD+/IGF-1- hybrid mice. IGF-1 concentration levels, measured by radioimmunoassay, were found to be highly increased throughout life in the central nervous system (CNS) and skeletal muscle of IGF-1 transgenic hybrid mice. Additionally, increased CNS weight in SOD+ mice crossbred with CNS IGF-1 transgenic mice demonstrates that IGF-1 overexpression is biologically active even after the disease is fully developed. Taken together, these results raise questions concerning the therapeutic value of IGF-1 and indicate that further studies are needed to examine the relationship between methods of IGF-1 administration and its potential therapeutic value.     

Localization of lipoprotein lipase to discrete areas of the guinea pig brain

Lipoprotein lipase is a key enzyme in lipoprotein metabolism present primarily in extrahepatic tissues with high turnover of fatty acids. Using immunocytochemistry we have explored where lipoprotein lipase is localized in guinea pig brain. The enzyme was found to be associated with neuronal cells and vascular endothelial surfaces. The distribution was strikingly uneven with intense reaction in some areas, and virtually no reaction in adjacent areas. The highest reactivity was in neocortex, in hippocampus, in Purkinje cells of the cerebellum and in some motor nuclei of the brainstem. The results suggest marked differences between individual brain areas in utilization of plasma lipoproteins.     

Organized projection of the goldfish saccular nerve onto the Mauthner cell lateral dendrite

Application of horseradish peroxidase (HRP) to the proximal end of the transected saccular nerve in the goldfish results in uptake by fibers projecting to the distal half of the Mauthner (M) cell's lateral dendrite. More discrete HRP injections reveal an organized projection from the saccular nerve onto the lateral dendrite, as small groups of stained fibers terminate there in restricted regions. The possibility that this represents a tonotopic projection onto the M-cell is considered.     

Evidence for coexistence of serotonin and noredrenaline in sympathetic nerves supplying brain vessels of guinea pig

Nerve fibers containing 5-hydroxytryptamine (5-HT) were demonstrated immunohistochemically in the wall of pial vessels associated with the circle of Willis in the guinea pig. The fibers formed a network structure which was more dense in the rostral part of the arterial circle and its branches than in the caudal part. The 5-HT immunoreactive fibers disappeared in all arteries studied after bilateral superior cervical ganglionectomy, and unilateral ganglionectomy eliminated the 5-HT immunoreactivity in the ipsilateral part of the middle cerebral, posterior cerebral and superior cerebellar arteries. Decentralization of the superior cervical ganglion had no effect on the perivascular nerve plexus. Subsequent staining with dopamine-β-hydroxylase (DBH) antiserum following elution of the first antibody revealed that 5-HT was present in the noradrenergic nerve fibers. Small intensive fluorescent cells with positive immunoreaction for 5-HT and DBH, respectively, were located in clusters within the ganglion, which showed no immunohistochemical evidence for the presence of serotonergic neurons. It is concluded that 5-HT is probably not synthesized in truly serotonergic fibers but rather taken up and stored together with noradrenaline in cerebrovascular sympathetic nerves originating in the superior cervical ganglia.     

Axonal transport of substance P in the vagus and sciatic nerves of the guinea pig

The axonal transport and apparent subcellular distribution of substance P-like immunoreactive material (SPLI) were examined in nerves of guinea pigs by means of a sensitive radioimmunoassay and by immunohistofluorescence. Crushes or ligations were made at various levels above and below the nodose ganglion of the vagus, on the sciatic nerve, and on the central process of the S1 spinal ganglion. From the relative rates of accumulation of SPLI in the adjacent segments, it was concluded that the bulk of the substance P produced in the sensory ganglion cells was being exported toward the terminal regions of their peripheral branches. The average velocity of transport of SPLI in the peripheral direction was calculated to be 1 mm/h in the sciatic nerve and 1.25 mm/h in the vagus. The removal of SPLI from regions of nerve distal to a ligature indicated that only 26% of the peptide in vagus nerve and 17% of the peptide in sciatic nerve was available for rapid transport. It was therefore estimated that the mean velocity of the moving fraction was 5-6 mm/h. Stop-flow experiments with local cooling and rewarming in vivo suggested that some SPLI may have been transported as rapidly as 10 mm/h. The behavior of SPLI during ultracentrifugation of nerve and ganglion extracts indicated that this peptide was normally present both in a soluble form and in association with particles but was transported primarily in the latter form.     

A sexually dimorphic vasopressin innervation of auditory pathways in the guinea pig brain

Vasopressin-like immunoreactivity was detected in the auditory brainstem of female guinea pigs. Stained cell bodies and fibres were found in the inferior colliculus and in the ventral trapezoid body, and immunoreactive fibres in the dorsal cochlear nucleus. No vasopressin immunoreactivity was detected in the auditory brainstem of male guinea pigs. Using oxytocin antisera we found neither immunoreactive perikarya nor fibres in the auditory pathways of guinea pigs of both sexes.     

Application of weak electric field to the hindpaw enhances sciatic motor nerve regeneration in the adult rat

Direct current (DC) electrical stimulation of the hindpaw is shown to enhance sciatic motor nerve regeneration in the adult rat. Cathodal stimulation, using weak currents (10 microA/cm2; field strength approximately 100 mV/cm) increased the reinnervation of the hindpaw muscles as measured by evoked electromyograms. This enhanced regeneration only occurred after cut-and-suture lesions, but not after crushing injury of the sciatic nerve. This enhancement of motor nerve regeneration by weak DC fields had been previously described in amphibians but we are the first to describe this phenomenon in mammals.     

An approach to the complexity of the brain

The establishment of ordered neuronal connections is supposed to take place under the control of specific cell adhesion molecules (CAM) which guide neuroblasts and axons to their appropriate destination. The extreme complexity of the nervous system does not provide a favorable medium for the development of deterministic connections. Simon's [112] theorems offer a mean to approach the high level of complexity of the nervous system. The basic tenet is that complex systems are hierarchically organized and decomposable. Such systems can arise by selective trial and error mechanisms. Subsystems in complex systems only interact in an aggregate manner, and no significant information is lost if the detail of aggregate interactions is ignored. A number of nervous activities, which qualify for these requirements, are shown. The following sources of selection are considered: internal and external feedbacks, previous experience, plasticity in simple structures, and the characteristic geometry of dendrites. The role played by CAMs and other membrane-associated molecules is discussed in the sense that they are either inductor molecules that turn on different homeobox genes, or downstream products of genes, or both. These molecules control cellular and tissular differentiation in the developing brain creating sources of selection required for the trial and error process in the organization of the nervous tissue.     

The response of human and rat fetal ventral mesencephalon in culture to the brain-derived neurotrophic factor treatment

Brain-derived neurotrophic factor (BDNF) has been shown to increase the survival of dopaminergic neurons in rodent mesencephalic cultures. The mRNAs of BDNF and trk B receptor have been found to be expressed in the substantia nigra of rat. In this study, the action of BDNF was studied on the survival and transmitter-specific differentiation of dopaminergic neurons of fetal human CNS aged 9–10-week in vitro. Dopaminergic neuron viability and phenotypic expression were monitored by tyrosine hydroxylase (TH) immunohistochemistry and measurement of dopamine (DA) content with HPLC, respectively. After seven days of treatment with BDNF there were 2.2-fold greater number of TH⁺ neurons surviving than in untreated cultures. Although very low levels of DA were detectable in human tissue, considerable amounts of DA was found in the culture medium from around 13 days in vitro (DIV), indicating that DA in human fetal tissue tended to be synthesised and released into the incubation medium more readily than from cultured rat fetal tissue during the same period. The content of DA in the BDNF-treated cultures was approximately double that of untreated cultures after 7 days. In rat fetal tissue, the capacity of each TH⁺ neuron to produce DA was not changed in the BDNF-treated cultures (7 DIV) compared with control cultures, suggesting that BDNF does not up-regulate the production of DA but rather acts to reduce cell death rates. Ciliary neurotrophic factor (CNTF) treatment of rat mesencephalic culture failed to improve the period of survival of fetal dopaminergic neurons and had no effect on the production of DA in cultures. Taken together, our results suggest that BDNF has potent trophic effect on both rat and human fetal mesencephalic dopaminergic neurons in culture and has a potential application in the treatment of Parkinson's disease.     

改良Dandy手术入路切除脑干腹外侧肿瘤

目的探讨改良Dandy手术入路切除脑干腹外侧肿瘤的手术方法及其优缺点。方法对25例脑干腹外侧肿瘤采用改良Dandy手术入路进行显微外科手术切除。结果显微镜下肿瘤全切除20例,次全切除5例,面神经解剖保留者24例,保留有效听力者14例,术后并发皮下积液1例,出现短暂Ⅸ-Ⅺ颅神经刺激症状2例,无菌性脑膜炎1例,死亡1例。结论改良Dandy手术入路切除脑干腹外侧肿瘤疗效满意。     

Pudendal afferent innervation of the guinea pig external anal sphincter

Background Sensory nerves to the external anal sphincter (EAS) contribute to mechanisms promoting continence and defecation, yet we know little about their function. We investigated the function of pudendal mechanoreceptors to the guinea pig EAS. Methods Extracellular recordings from pudendal nerve branches to 14 EAS preparations, in vitro, were used to characterize extrinsic primary afferent nerve endings activated by circumferential distension. Key Results All 42 pudendal nerve afferents were silent under non‐distended conditions. Thirty‐three of 42 afferents had slowly adapting, low‐threshold responses to circumferential stretch that correlated with stretch length (R² = 0.40, P < 0.001). Twenty of 20 slowly adapting afferents reduced firing when stretch was maintained for 60 s (P < 0.0001). They had low thresholds to von Frey hairs (0.1–0.5 mN). Firing frequency correlated with degree of compression (R² = 0.40, P < 0.0001). Nine of 42 afferents had rapidly adapting responses at the onset/offset of isometric stretch. During ramp stretch, small vibrations from the stepper motor evoked rapid bursts of firing at frequencies up to 200 Hz. Instantaneous frequency was unrelated to either the rate or degree of stretch. Rapidly adapting units had low thresholds (0.1–0.2 mN) to von Frey hairs and small punctate mechanotransduction sites. Responses to von Frey hair compression were also rapidly adapting, and instantaneous frequency was unrelated to the degree of compression. Conclusions & Inferences The EAS has two functional classes of mechanoreceptors: slowly adapting low‐threshold and rapidly adapting low‐threshold mechanoreceptors. These two classes of afferents are likely to be involved in the maintenance of continence, and the process of defecation.     

The levels of adenosine and its metabolites in the guinea pig and rat brain during complete ischemia-in vivo study

Changes in levels of adenosine, inosine, hypoxanthine and ATP during complete ischemia after decapitation were determined in various areas of the guinea pig and rat brain using an HPLC method. These results were compared with levels in brains fixed by microwave irradiation. The levels of adenosine during 60 min of complete ischemia were extremely high and unevenly distributed while levels in the microwaved brains were very low and evenly distributed. The ratios of inosine plus hypoxanthine levels to adenosine which indicate the rate of metabolic degradation from adenosine into inosine and hypoxanthine, were also unevenly distributed during complete ischemia in the cerebellum, superior colliculus, cerebral cortex and hippocampus of the guinea pig and rat, and the highest ratio was observed in the cerebellum of the guinea pig and the superior colliculus of the rat. The activities of adenosine deaminase (ADA), one of the enzymes involved in adenosine metabolism, were measured in the four regions of the guinea pig. The ADA activities were unevenly distributed and the highest ADA activity was found in the cerebellum. These regional differences in ADA activities are in good agreement with the regional differences in the ratio of inosine plus hypoxanthine levels to adenosine during complete ischemia. Furthermore, the administration of EHNA [erythro-9-(2-hydroxy-3-nonyl)adenine hydrochloride] (10 mg/kg, i.p.), an ADA inhibitor, caused a significant increase of adenosine and decrease of inosine formation in all four regions and a drastic effect on the cerebellum with high ADA activity compared with the other regions in the guinea pig brain. These results indicate that the changes in concentrations of adenosine and its metabolites (inosine and hypoxanthine) during complete ischemia depend on ADA activity in each brain region.     

Effects of slow muscle stretch on the responses of primary and secondary endings to small amplitude periodic stretches in de-efferented soleus muscle spindles

The responses of primary and secondary endings of de-efferented soleus spindles to small amplitude periodic stretches superimposed on slow ramp stretches have been studied. For primary endings, the responses become progressively larger especially during the last period of the ramp whereas for secondary endings, after an initial period of moderate growth, the amplitude of the responses display a relative reduction precisely when the responses of the primary endings are the largest. These differences can be interpreted in terms of progressive increase in stiffness of the striated polar portions of the intrafusal muscle fibers.     

Fibre composition of the feline trochlear and abducens nerves

Cat trochlear and abducens nerves were studied by electron microscopy at two different levels. Five mm peripheral to the exit from the brainstem, the average number of myelinated axons is 965 in the trochlear nerve and 1901 in the abducens nerve. The size spectrum is unimodal and small myelinated axons predominate. Both nerves contain 16% unmyelinated axons at this level. At the PNS/CNS transition, the nerve fascicles contain few unmyelinated axons, but bundles of such axons are present in the adjacent pia mater. We suggest that the trochlear and abducens nerves may channel unmyelinated sensory and/or autonomic axons to the leptomeningeal blood vessels and the pia mater of the brainstem.     

Nitric oxide regulates the firing rate of neuronal subtypes in the guinea pig ventral cochlear nucleus

The gaseous free radical, nitric oxide (NO) acts as a ubiquitous neuromodulator, contributing to synaptic plasticity in a complex way that can involve either long term potentiation or depression. It is produced by neuronal nitric oxide synthase (nNOS) which is presynaptically expressed and also located postsynaptically in the membrane and cytoplasm of a subpopulation of each major neuronal type in the ventral cochlear nucleus (VCN). We have used iontophoresis in vivo to study the effect of the NOS inhibitor L‐NAME (L‐NG‐Nitroarginine methyl ester) and the NO donors SIN‐1 (3‐Morpholinosydnonimine hydrochloride) and SNOG (S‐Nitrosoglutathione) on VCN units under urethane anaesthesia. Collectively, both donors produced increases and decreases in driven and spontaneous firing rates of some neurones. Inhibition of endogenous NO production with L‐NAME evoked a consistent increase in driven firing rates in 18% of units without much effect on spontaneous rate. This reduction of gain produced by endogenous NO was mirrored when studying the effect of L‐NAME on NMDA(N‐Methyl‐D‐aspartic acid)‐evoked excitation, with 30% of units showing enhanced NMDA‐evoked excitation during L‐NAME application (reduced NO levels). Approximately 25% of neurones contain nNOS and the NO produced can modulate the firing rate of the main principal cells: medium stellates (choppers), large stellates (onset responses) and bushy cells (primary‐like responses). The main endogenous role of NO seems to be to partly suppress driven firing rates associated with NMDA channel activity but there is scope for it to increase neural gain if there were a pathological increase in its production following hearing loss.     

An ultrastructural analysis of the sympathetic neuromuscular junctions on arterioles of the submucosa of the guinea pig ileum

The relationship of the varicosities of sympathetic postganglionic nerve terminals to the smooth muscle cells of arterioles in the submucosa of the guinea pig ileum has been investigated quantitatively by electron microscopy. Longitudinal sections were cut through arterioles about 50 micron in diameter after fixation in vitro or in situ under pressure. About 13% of the varicosities in individual ultrathin sections made contact with the outer surface of the smooth muscle cells. The neuromuscular junctions resembled those in skeletal muscle: the basal laminae of the axon bundle and of the smooth muscle were fused, and synaptic vesicles were accumulated close to the region of fusion. When individual varicosities were examined in serial sections, 92% and 83% in two preparations were found to form junctions of this kind. Most of the noncontacting varicosities were bare of Schwann cell toward the arteriolar surface and separated from it by less than 200 nm. Almost all axon profiles contained synaptic vesicles with electron dense cores after exposure to 5-hydroxydopamine. In electrophysiological experiments, ionophoretic application of noradrenaline to the arteriolar surface along the nerve bundles (demonstrated subsequently by fluorescence histochemistry) produced responses resembling those evoked by nerve stimulation. These anatomical and physiological data, taken together with the evidence for quantal release in this preparation (see Hirst et al., '85), suggest that neuromuscular transmission involves the rare release of a quantum of noradrenaline at discrete points on the smooth muscle membrane.     

The GDNF family members neurturin, artemin and persephin promote the morphological differentiation of cultured ventral mesencephalic dopaminergic neurons

Neurturin (NRTN), artemin (ARTN), persephin (PSPN) and glial cell line-derived neurotrophic factor (GDNF) form a group of neurotrophic factors, also known as the GDNF family ligands (GFLs). They signal through a receptor complex composed of a high-affinity ligand binding subunit, postulated ligand specific, and a common membrane-bound tyrosine kinase RET. Recently, also NCAM has been identified as an alternative signaling receptor. GFLs have been reported to promote survival of cultured dopaminergic neurons. In addition, GDNF treatments have been shown to increase morphological differentiation of tyrosine hydroxylase immunoreactive (TH-ir) neurons. The present comparative study investigated the dose-dependent effects of GFLs on survival and morphological differentiation of TH-ir neurons in primary cultures of E14 rat ventral mesencephalon. Both NRTN and ARTN chronically administered for 5 days significantly increased survival and morphological differentiation of TH-ir cells at all doses investigated [0.1–100 ng/ml], whereas PSPN was found to be slightly less potent with effects on TH-ir cell numbers and morphology at 1.6–100 ng/ml and 6.3–100 ng/ml, respectively. In conclusion, our findings identify NRTN, ARTN and PSPN as potent neurotrophic factors that may play an important role in the structural development and plasticity of ventral mesencephalic dopaminergic neurons.