Beneficial effects of sigma agonists on the age-related learning impairment in the senescence-accelerated mouse (SAM)

A beneficial effect of sigma (sigma) agonists was previously described on several pharmacological models of learning impairments. We examined this effect in senescence-accelerated mice (SAM), which has been developed as a murine model of aging and cognitive dysfunction. SAMP8/Ta (P8, senescence-prone substrain), 10-12 months of age, showed significant impairments in mnemonic capacities, as compared to age-matched SAMR1/Ta controls (R1, senescence-resistant substrain). Tests included open-field behavior, spontaneous alternation performances in the Y-maze, step-down passive avoidance and place learning after repetitive training in a water-maze. Pretreatment with the sigma agonists JO-1784 (igmesine) or PRE-084, at 0.1-3 mg/kg, s.c., significantly improved spontaneous alternation and passive avoidance performances in P8. JO-1784 or PRE-084, at 1 mg/kg, also improved place learning in the water-maze, and retention, in term of escape latency. The implication of sigma sites was indicated by the lack of significant effect of JO-1783, the inactive enantiomer of JO-1784, and by the ability of BMY-14802 (5 mg/kg, i.p.) to antagonize the effects on passive avoidance of JO-1784 (0.5 mg/kg) or PRE-084 (1 mg/kg). Subchronic treatments with JO-1784 (0.5 mg/kg/day) or PRE-084 (1 mg/kg/day) during 10 days, allowed a significant improvement of learning during training in the water-maze, but retention was not significantly ameliorated. These results confirmed the interest of the SAM substrains as an experimental model for senile memory impairment and showed that sigma agonists could improve the quality of learning, although they seem less effective on long-term memory retrieval upon chronic administration.

Reversion of beta 25-35-amyloid peptide-induced amnesia by NMDA receptor-associated glycine site agonists

The effects of D-cycloserine (DCS), a N-methyl-D-aspartate receptor-associated glycine site agonist, and milacemide (MIL), a glycine prodrug, were examined on learning impairments induced by administration of beta 25-35-amyloid peptide (3 nmol i.c.v.). Mice were examined for spontaneous alternation and step-down passive avoidance, 7 and 14 days after beta 25-35, respectively. The beta 25-35-induced deficits were reversed by DCS, 1-30 mg/kg i.p., or MIL, 3-100 mg/kg i.p., each drug being ineffective on control mice behaviours. These observations strengthen the therapeutic potential of glycine site agonists against the memory impairments induced by beta-amyloid peptides.

An adenovirus vector encoding tyrosine hydroxylase activity may enter human CNS cells in primary dissociated cultures

An adenovirus encoding tyrosine hydroxylase (TH) activity was inserted in neuronal and glial cultured cells obtained from human fetal central nervous system (CNS) tissue. Using a double fluorescence immunostaining, we characterized inoculated CNS cells, with a TH antiserum and one of the following antibodies: microtubule-associated protein (MAP2) and GABA for neuronal cells, vimentin (Vim) for glial cells and glial fibrillary acidic protein (GFAP) for astrocytes. The characterization of inoculated neuronal cells was established by the detection of TH-MAP2-stained neurons in cultures obtained from the thoracic and lumbar parts of the spinal cord where no intrinsic TH cells are described. Inoculated glial cells were characterized by the detection of TH-Vim and TH-GFAP-stained CNS cultured cells. We also observed GABA neurons expressing TH immunoreactivity which could be considered as inoculated neurons expressing the GABA phenotype. Whatever the time of inoculation, transfection was observed in both neuronal and glial cells, after up to 4 months of culture. Although no precise quantitation was performed, the percentage of inoculation was found on microscopic inspection to be greater in glia than in neurons, as previously reported. We concluded that a gene coding for a key neuronal enzyme can be incorporated in embryonic human glial and neuronal cells through the use of a recombinant adenovirus.

N-[1-(2-Benzo(b)thiophenyl)cyclohexyl]piperidine (BTCP) and cocaine induce similar effects on striatal dopamine: a microdialysis study in freely moving rats

N-[1-(2-Benzo(b)thiophenyl)cyclohexyl]piperidine (BTCP) and cocaine inhibit dopamine (DA) uptake but bind to different sites on the transporter. Their dose-dependent effects (i.p. administration) on extracellular DA levels in the rat striatum were measured by in vivo microdialysis. Both drugs dose-dependently increased DA levels with a maximum effect 60 min post injection. BTCP (20 mg/kg) had a greater peak effect than cocaine (40 mg/kg). For doses inducing similar behavioral effects (cocaine, 20mg/kg; BTCP, 10 mg/kg) similar DA increases were observed in the striatum and the nucleus accumbens. Although both drugs bind on the DA transporter on different sites and induce different behavioral effects when administered chronically, their acute administration increased striatal DA level in a similar way.

Evaluation of the function of microdialysis probes permanently implanted into the rat CNS and coupled to an on-line HPLC system of analysis

The aim of the microdialysis technique is to reflect as closely as possible the status and fluctuations of substances contained in the extracellular space. Most often, microdialysis is performed with repetitively implanted probes. We have recently devised an experimental set-up which allows microdialysis to be performed in the spinal cord of unrestrained rats through chronically permanently implanted probes. In the present study, we have compared the in vitro recovery of a non-biogenic amine (DHBA) and of 5-HT, and the in vivo recovery of the former. Thus, we could extrapolate the in vivo recovery of endogenous 5-HT released. Moreover, we have found that the recovery does not vary irrespective of whether the animal is at rest or performing sustained physical exercise, and that it also remains stable with time, from 8 to 36 days after permanent implantation of the probe. We conclude that this simple method can be applied to standard experiments of microdialysis, and thus allow one to measure the actual rate of recovery for a given probe. Moreover, it permits control of the stability of dialysis parameters with time for long-term permanently implanted probes.

Disrupted glial fibrillary acidic protein network in astrocytes from vimentin knockout mice

Glial fibrillary acidic protein (GFAP) is an intermediate filament protein expressed predominantly in astrocytes. The study of its expression in the astrocyte lineage during development and in reactive astrocytes has revealed an intricate relationship with the expression of vimentin, another intermediate filament protein widely expressed in embryonic development. these findings suggested that vimentin could be implicated in the organization of the GFAP network. To address this question, we have examined GFAP expression and network formation in the recently generated vimentin knockout (Vim-) mice. We show that the GFAP network is disrupted in astrocytes that normally coexpress vimentin and GFAP, e.g., those of the corpus callosum or the Bergmann glia of cerebellum. Furthermore, Western blot analysis of GFAP protein content in the cerebellum suggests that posttranslational mechanisms are implicated in the disturbance of GFAP network formation. The role of vimentin in this process was further suggested by transfection of Vim-cultured astrocytes with a vimentin cDNA, which resulted in the normal assembly of the GFAP network. Finally, we examined GFAP expression after stab wound-induced astrogliosis. We demonstrate that in Vim- mice, reactive astrocytes that normally express both GFAP and vimentin do not exhibit GFAP immunoreactivity, whereas those that normally express GFAP only retain GFAP immunoreactivity. Taken together, these results show that in astrocytes, where vimentin is normally expressed with GFAP fails to assemble into a filamentous network in the absence of vimentin. In these cells, therefore, vimentin appears necessary to stabilize GFAP filaments and consequently the network formation.

Immunohistochemical localization and immunoblotting of androgen receptor in spinal neurons of male and female rats

Androgen activity in the central nervous system, as in other tissues, is mediated by the androgen receptor. We performed the precise localization of the androgen receptor in spinal cord of male and female adult rats by immunohistochemistry using polyclonal antibodies. Light microscopy indicated immunoreactivity in the anterior horn with a strong staining in motoneurons, but staining was also observed in the posterior horn. Electron microscopy showed a predominant nuclear immunostaining. A weaker but significant immunoreactive androgen receptor was also noted in the perinuclear/ intracysternal position. Moreover, no differences were found between male and female rats. Immunoblotting demonstrated that the androgen receptor is expressed in both ventral and dorsal spinal cord, with an apparent molecular mass identical to that noted in other androgen-dependent tissues. The expression of androgen receptor in motoneurons corroborates the role of androgens in motoneuron growth, development and regeneration and underlies the possibility that androgen receptor abnormality leads to the motoneuron degeneration observed in X-linked spinal and bulbar muscular atrophy.

Regional study of spinal alpha 2-adrenoceptor densities after intraspinal noradrenergic-rich implants on adult rats bearing complete spinal cord transection or selective chemical noradrenergic denervation

One of the challenges of restorative neuronal transplantation in the CNS of mammals is the appropriate integration of grafted cells in the host circuitry. One key parameter is the specific influence of grafted cells upon corresponding receptors. In order to test this issue on the lesioned spinal cord of adult rats, two models of spinal cord denervation were used: the first one consisted of a complete transection 1 week prior to an intraspinal transplantation of embryonic locus coeruleus (LC) primordia cell suspension; the second one was a chemical destruction of the spinal noradrenergic (NA) system 1 month prior to a similar transplantation. Five weeks after transplantation, spinal sections were processed for autoradiographic quantification of alpha 2-adrenoceptor binding sites densities. In most regions, alpha 2-adrenoceptor densities remained comparable or higher than before graft; interestingly, in lumbar dorsal horn, lumbar intermediate zone and sacral distal dorsal horn of transected-grafted rats, they returned to control level. Results are discussed in relation to the parallel study performed concerning alpha 1-adrenoceptors.

Transplantation of embryonic noradrenergic neurons in two models of adult rat spinal cord injury: ultrastructural immunocytochemical study

The synaptic connections established by grafted noradrenergic (NA) neurons into the lesioned adult rat spinal cord were analysed using immunocytochemistry at the electron microscopic level. An embryonic cell suspension of the locus coeruleus region from E-13 rat embryos was transplanted into the spinal cord following either: (1) spinal cord transection or (2), partial selective denervation by 6-hydroxy dopamine (6-OH DA). One month after grafting, the NA-neurons established, in the two models, an innervation pattern similar to that found in the intact spinal cord. In both models, the transplanted NA-immunoreactive neurons formed extensive synaptic contacts with dendrites, spines and perikarya. The proportion of axodendritic and axospinous contacts was inverse in the two models. The first model thus reproduced more closely the normal synaptic pattern prefering dendritic targets, which could correspond to a better integration of the graft. In the second model, a partially NA-denervated spinal cord, there existed a competition between residual intrinsic and grafted neuron-derived fibres, which presumably affects synaptogenesis. In conclusion, the present study illustrate the complexity of cell interations conducting to the formation of a specific circuitry. Recognition phenomenon are likely modulated by space constraints, which ultimately shape-up the geometry of synaptic contacts.

Amnesia induced in mice by centrally administered beta-amyloid peptides involves cholinergic dysfunction

Substantial evidences suggest that the increased cerebral deposition, and neurotoxic action of the beta-amyloid peptide, the major constituent of senile plaques, may represent the underlying cause of the cognitive deficits observed in Alzheimer's disease. Herein, we attempted to verify this hypothesis by inducing a potential Alzheimer's-type amnesia after direct intracerebroventricular administration of aggregated beta 25-35-amyloid peptide in mice. In this aim, mnesic capacities were evaluated after 6-13 days, using spontaneous alternation in the Y-maze, step-down type passive avoidance and place learning in a water-maze. Pretraining administration of aggregated beta 25-35 peptide induced dose-dependent decreases in both alternation behaviour and passive avoidance, at doses of 3 and 9 nmol/mouse. A reduced but still significant impairment was observed when the peptide was not aggregated, or 'aged', by preincubation for 4 days at 37 degrees C. The beta 1-28 peptide, at 3 nmol/mouse, also induced a marked decrease in step-down latency. Posttraining, but not preretention, administration of beta 25-35 peptide also significantly impaired learning. The beneficial effects of cholinergic agents on beta 25-35-induced amnesia was examined using the cholinesterase inhibitor tacrine (THA, 1.3 and 4.3 mumol/kg i.p.) and the nicotinic receptor agonist (-)-nicotine (NIC, 0.06 and 0.2 mumol/kg i.p.). Both drugs induced a dose-dependent abrogation of the beta 25-35-induced decreases in alternation behaviour and passive avoidance. Furthermore, THA, at 1.3 mumol/kg, and NIC, at 0.2 mumol/kg, also reversed the beta 25-35-induced impairment of place learning and retention in the water-maze. Histological examination of Cresyl violet-stained brain sections indicated a moderate but significant cell loss within the frontoparietal cortex and the hippocampal formation of mice treated with aged beta 25-35 peptide (9 nmol). Examination of Congo red-stained sections in the same animals demonstrated the presence of numerous amyloid deposits throughout these brain areas. These results confirm that the deposition of beta-amyloid peptide in the brain is in some way related to impairment of learning and cholinergic degeneration and suggest that the [25-35] fragment of the beta-amyloid protein, sufficient to induce neuronal death in cultures, also induces an Alzheimer's-type amnesia in mice.

Differential effect of ischemia/reperfusion on pigmented and albino rabbit retina

The purpose of the study was to compare the retinal sensitivity of pigmented and albino rabbits to ischemia/reperfusion-induced electroretinogram (ERG) alterations and optic nerve morphological changes. High intraocular pressure (HIOP) was induced by applying a suction-cup on the eye and a depression with an ophthalmodynamometer. HIOP was maintained for lengths of time (30-75 min). Flash ERGs were recorded in dark-adapted animals for ischemia and 2 h reperfusion periods. Two weeks later, histological examination of the retinas and optic nerves was done. Albino rabbits submitted to 45 min HIOP failed to recover b-wave ERG amplitude after 2 h reperfusion, whereas pigmented animals presented a total ERG recovery even if ischemia was maintained as long as 75 min. Intravenous treatment of albino animals with Lazaroid U74389G led to significant ERG recovery at reperfusion. Histological studies show that pigmented rabbit optic nerves suffered less damage than the albino ones. These results emphasize the role of the pigmentary status of the animals in the retinal sensitivity to ischemia. Neuroprotection afforded by the antioxidant U74389G suggests that ocular pigments could also protect the retinal functional integrity through a free radical scavenging activity.

Immunocytochemical characterization of a new marker of fibrous and reactive astrocytes

A specific monoclonal antiserum (Mab 6.17) inducing a strong immunostaining of the neuromuscular junction has been used to detect the possible occurrence of the corresponding antigen throughout the intact or lesioned central nervous system of adult rats. In intact animals, 6.17-immunolabeling was essentially detected in astrocyte-like structures located in white matter fasciculi of the brain, such as the optic tract, corpus callosum, fornix, and in the white matter of the spinal cord. The astroglial nature of such 6.17-immunolabeled profiles was verified by performing double or triple immunofluorescent labeling with Mab 6.17 and with specific antisera against astrocytic markers, such as S100 protein, glial fibrillary acidic protein and vimentin. In the white matter, all the structures reactive to Mab 6.17 were also reactive to antibodies against S100 protein, glial fibrillary acidic protein and vimentin. On the other hand, astrocytes of the grey matter that were immunoreactive to S100 and glial fibrillary acidic protein but negative to vimentin, were devoid of 6.17-immunoreactivity. After lesions including stab wound through the diencephalon or transection of the spinal cord, a marked increase of 6.17-immunostaining was noted in the regions surrounding the lesions. In these regions, 6.17-immunolabeling was associated with S100-, GFAP- and vimentin-positive astrocytes constituting the glial scar. The ultrastructural localization of 6.17-immunoreactivity indicated that, similar to glial fibrillary acidic protein and vimentin, the recognized antigen was mainly associated with gliofilaments. These observations indicate that, in the central nervous system of adult rats, Mab 6.17 recognizes a molecule associated with gliofilaments, which is essentially associated to reactive astrocytes expressing high levels of vimentin.

Specific and efficient gene transfer strategy offers new potentialities for the treatment of motor neurone diseases

Several growth factors are candidates for the therapy of motor neurone diseases. However, there is no efficient, safe, and practicable administration route which hampers the clinical use of these potentially therapeutic agents. We show that specific and high yield gene transfer into motor neurones can be obtained by peripheral intramuscular injections of recombinant adenoviruses. These vectors are retrogradely transported from muscular motor units to motor neurone cell bodies. Gene transfer can thus be specifically targeted to particular regions of the spinal cord by appropriate choice of the injected muscle. The efficiency of gene transfer is high, with 58-100% of the motor neurones afferent to the injected muscle expressing the transgene. This new therapeutic protocol allows specific targeting of motor neurones without lesioning the spinal cord, and should avoid undesirable side effects associated with systemic administration of therapeutic factors.

Direct evidence for the link between monoaminergic descending pathways and motor activity. I. A study with microdialysis probes implanted in the ventral funiculus of the spinal cord

Monoaminergic projections to the spinal cord are involved in the modulation of motor, autonomic, and sensory functions. More specifically, the increase of electrical activity of serotonergic neurons in raphe obscurus has been correlated with locomotion in treadmill-trained cats [Jacobs, B.L. and Fornal, C., Trends Neurosci., 9 (1993) 346-352]. In order to test the direct correlation between locomotion and the release of monoamines, microdialysis probes were permanently implanted for 45 days into the ventral funiculus of the spinal cord (white matter) of adult rats. Eight days after implantation, these rats were subjected to an endurant exercise on a treadmill, and dialysis sessions were organized in such a way that microdialysate samples of 15 min duration were collected during pre-, per- and post-exercise periods. Measurements of serotonin, 5-hydroxyindoleacetic acid, dopamine and 3-methoxy-4-hydroxyphenylethylglycol concentration in the extracellular space showed significant increases during locomotion when compared with both pre- and post-exercise values. Histological analysis shows that serotonergic axons were present close to the dialysis probe. These results demonstrate that the implantation of a microdialysis probe in the ventral funiculus, close to a potential target of monoaminergic projections, is a suitable technique for the collection of neuromediators released during spontaneous running.

Comparative distribution of GAD65 and GAD67 mRNAs and proteins in the rat spinal cord supports a differential regulation of these two glutamate decarboxylases in vivo

Gamma-aminobutyric acid (GABA) synthesis can result from the action of at least two glutamic acid decarboxylase (GAD) isoforms, GAD65 and GAD67, possibly involved in distinct mechanisms. We have made the hypothesis that GAD65 may respond to short-term changes and is present in neurons with a phasic activity, while GAD67 may rather provide GABA for the metabolic pool and for supporting tonic levels of synaptic transmission (Erlander et al.: Neuron 7:91-100, 1991; Feldblum et al.: J Neurosci Res 34:689-706, 1993). In the present work we have tested this hypothesis in the rat spinal cord where both types of activities have been identified. The correlation of GABA immunodetection with the distribution of GAD65 and GAD67 mRNAs and proteins has evinced in the dorsal horn a differential regulation of the two isoforms. In situ hybridization has revealed, in the dorsal horn, relatively higher levels of GAD67 mRNA than of GAD65, while immunodetection of the proteins demonstrated numerous punctate profiles with both GAD antisera. Reverse transcription-polymerase chain reaction (RT-PCR) data confirmed the abundance of the GAD67 transcripts compared to GAD65 in the rat spinal cord. In contrast, within the ventral horn, there was a greter number of GAD67-immunoreactive (IR) profiles mostly located around motoneurons. The paucity of GAD65 immunoreactivity in the ventral horn cannot be related to a different accessibility of the antigens to the epitopes since on the same section a dense GAD65 staining was detected in the dorsal horn. Hence, a number of biochemical and electrophysiological data support the concept of the involvement of glycine as the major inhibitory system within the ventral horn which may explain the low levels of GAD transcription in this region. The paucity of GAD65 in the ventral horn may also reflect a functional difference, suggesting a predominance of GAD67 in neurons under tonic activity. In the dorsal horn, where neurons with phasic and tonic firing patterns have been disclosed, GAD65 may, in addition, provide GABA for responses to short-term changes.

Specific and efficient gene transfer strategy offers new potentialities for the treatment of motor neurone diseases

Several growth factors are candidates for the therapy of motor neurone diseases. However, there is no efficient, safe, and practicable administration route which hampers the clinical use of these potentially therapeutic agents. We show that specific and high yield gene transfer into motor neurones can be obtained by peripheral intramuscular injections of recombinant adenoviruses. These vectors are retrogradely transported from muscular motor units to motor neurone cell bodies. Gene transfer can thus be specifically targeted to particular regions of the spinal cord by appropriate choice of the injected muscle. The efficiency of gene transfer is high, with 58-100% of the motor neurones afferent to the injected muscle expressing the transgene. This new therapeutic protocol allows specific targeting of motor neurones without lesioning the spinal cord, and should avoid undesirable side effects associated with systemic administration of therapeutic factors.

Corrigendum to 'the pentadecapeptide [Ser1]histogranin impairs passive avoidance learning in mice' [Eur. J. Pharmacol. 283 (1995) 251-254]

The peptides, histogranin and [Ser1]histogranin, were recently shown to modulate NMDA receptor function. In the present study, the effects of intracerebroventricular (i.c.v.) administration of [Ser1]histogranin and of the histogranin receptor antagonist, histogranin-(1-10), were examined on step-down type passive avoidance learning in mice. [Ser1]Histogranin (30-60 nmol) impaired retention, after post-training administration, but not when it was administered just prior to the retention assay. Histogranin-(1-10) (60 nmol) facilitated learning during training, without affecting retention. Co-administration of histogranin-(1-10) with [Ser1]histogranin (60 nmol each) led to a significant prevention of [Ser1]histogranin-induced learning impairment. These results indicate that [Ser1]histogranin impairs passive avoidance learning according to the pattern of NMDA receptor antagonists and involving specific histogranin sites.

Distribution of glucocorticoid receptor mRNA in the rat spinal cord

Using in situ hybridization (ISH), we studied the distribution of rat glucocorticoid receptors (GR) mRNA in rat spinal cord. mRNA encoding for GR was abundant throughout the white matter and a clear pattern of distribution was detected within the grey matter. In the grey matter mRNA was primarily localized in the ventral horn, where motoneurones were strongly labelled. In the dorsal horn, the distribution appears more diffuse but the superficial layers (I and II) clearly exhibited a shigher signal. We conclude that, in rat spinal cord, GR are present in both glial and neuronal cells. In particular, both somatosensory and motor pathways contain GR.

Immunocytochemical study of phenotypic plasticity of cultured dorsal root ganglion neurons during development

Rat dorsal root ganglia (DRG) were cultured from different stages of development ranging from embryonic day-14 to adult. The expression of eight neurotransmitter phenotypes was examined with immunocytochemical detection and the percentages of each phenotype were calculated with reference to the whole neuronal population defined by the expression of neuron-specific enolase (NSE). The expression of peptides, calcitonin gene-related peptide (CGRP), substance P (SP), cholecystokinin (CCK) and neuropeptide Y (NPY) was always present whatever the age at onset of the cultures. Although the percentage of CGRP remained stable, that of the other peptides declined progressively. Their in-vitro expression did not differ markedly from that found in vivo. Another group of neurotransmitters, including 5-hydroxytryptamine (5-HT), thyrotropin-releasing hormone (TRH) and gamma-aminobutyric acid (GABA) was never expressed in situ in DRG neurons. In culture, they were expressed in a high percentage of neurons, especially for 5-HT and TRH, and they showed a similar evolution, with a decrease at early postnatal ages followed by a further increase. This profile suggests that the expression of these transmitters is strongly environment-dependent and may be repressed in situ. Finally, somatostatin (SOM) was found only in cultures prepared from adult tissues, whereas it was present in situ from the embryo onwards. The expression of this peptide would thus require a stabilization by a long exposure to environmental factors. We can conclude that the great diversity of phenotypic expression found in DRG neurons in situ is the result of a wide variety of influences occurring at different stages of development in a large potential repertory present in these neurons.

Gene therapy in the central nervous system: direct versus indirect gene delivery

Over the last decade, the combination of molecular biology and cell transplantation techniques has given rise to a powerful method for gene therapy. The implantation of genetically modified cultured cells has been extensively used in the central nervous system (CNS) in various experimental models of neurologic disorders. More recently, viral and chemical methods have been developed to further efforts to shuttle transgenes into the relatively inaccessible brain. Adenoviral and liposomal synthetic vectors carry transgenes into neural tissue in situ and are beginning to show promise as new methods for CNS therapy.

[Treatment of the future for spinal cord injuries]

Future therapy of spinal cord trauma is based on the careful analysis of pathophysiological phenomena secondary to the initial lesion. The toxicity of excitatory amino-acids, which is an early phenomenon, can be treated by specific antagonists. Axonal regrowth, which spontaneously occurs within days after the trauma must be supported by trophic factors on the one hand, and by blocking of the glial scar formation on the other hand. Finally, neuronal loss can be replaced by grafts either from embryonic neurons, or from genetically engineered cells, or direct gene therapy using viral vectors. Clinical applications are on their way for the early toxic phenomena, more remote for axonal regrowth and grafts. In any case, future treatment will have to use concurrently these three approaches, in specialized spinal units.

The pentadecapeptide [Ser1]histogranin impairs passive avoidance learning in mice

The peptides, histogranin and [Ser1]histogranin, were recently shown to modulate NMDA receptor function. In the present study, the effects of intracerebroventricular (i.c.v.) administration of [Ser1]histogranin and of the histogranin receptor antagonist, histogranin-(1-10), were examined on step-down type passive avoidance learning in mice. [Ser1]Histogranin (30-60 nmol) impaired retention, after post-training administration, but not when it was administered just prior to the retention assay. Histogranin-(1-10) (60 nmol) facilitated learning during training, without affecting retention. Co-administration of histogranin-(1-10) with [Ser1]histogranin (60 nmol each) led to a significant prevention of [Ser1]histogranin-induced learning impairment. These results indicate that [Ser1]histogranin impairs passive avoidance learning according to the pattern of NMDA receptor antagonists and involving specific histogranin sites.

Fictive motor activities in adult chronic spinal rats transplanted with embryonic brainstem neurons

The present study was designed to examine the effects of an intraspinal transplantation of embryonic brainstem neurons on fictive motor patterns which can develop in hindlimb nerves of adult chronic spinal rats. Seventeen adult rats were spinalized at T8-9 level and, 8 days later, a suspension of embryonic cells obtained either from the raphe region (RR, n = 8) or from the locus coeruleus (LC, n = 9) was injected caudally (T12-13) to the cord transection. Eight control animals (control rats) were spinalized and injected with vehicle under the same conditions. One to three months later, the animals were decorticated and fictive motor patterns were recorded in representative hindlimb nerves. The data revealed that both control and grafted spinal rats could exhibit two distinctly different fictive motor patterns, one which could be associated with stepping and the other with hindlimb paw shaking. They further showed that following transplantation of embryonic RR or LC neurons the excitability of the spinal stepping generator was increased, whereas that of the spinal neural circuits which generate hindlimb paw shaking was not significantly affected. A histological analysis performed on the spinal cord segments below the transection revealed complete absence of serotonin and noradrenaline immunoreactivity in control spinal animals and, in both types of grafted rats, an extensive monoaminergic reinnervation with synaptic contacts between monoaminergic transplanted neurons and host interneurons and/or motoneurons. The possible mechanisms by which grafted monoaminergic neurons can influence the spinal motor networks are discussed.