Topical dura mater application of CFA induces enhanced expression of c-fos and glutamate in rat trigeminal nucleus caudalis: attenuated by KYNA derivate (SZR72)

Background

Migraine is a debilitating neurological disorder where trigeminovascular activation plays a key role. We have previously reported that local application of Complete Freund’s Adjuvant (CFA) onto the dura mater caused activation in rat trigeminal ganglion (TG) which was abolished by a systemic administration of kynurenic acid (KYNA) derivate (SZR72). Here, we hypothesize that this activation may extend to the trigeminal complex in the brainstem and is attenuated by treatment with SZR72.

Methods

Activation in the trigeminal nucleus caudalis (TNC) and the trigeminal tract (Sp5) was achieved by application of CFA onto the dural parietal surface. SZR72 was given intraperitoneally (i.p.), one dose prior CFA deposition and repeatedly daily for 7 days. Immunohistochemical studies were performed for mapping glutamate, c-fos, PACAP, substance P, IL-6, IL-1β and TNFα in the TNC/Sp5 and other regions of the brainstem and at the C₁-C₂ regions of the spinal cord.

Results

We found that CFA increased c-fos and glutamate immunoreactivity in TNC and C₁-C₂ neurons. This effect was mitigated by SZR72. PACAP positive fibers were detected in the fasciculus cuneatus and gracilis. Substance P, TNFα, IL-6 and IL-1β immunopositivity were detected in fibers of Sp5 and neither of these molecules showed any change in immunoreactivity following CFA administration.

Conclusion

This is the first study demonstrating that dural application of CFA increases the expression of c-fos and glutamate in TNC neurons. Treatment with the KYNA analogue prevented this expression.

KYNA analogue SZR72 modifies CFA-induced dural inflammation- regarding expression of pERK1/2 and IL-1β in the rat trigeminal ganglion

Background

Neurogenic inflammation has for decades been considered an important part of migraine pathophysiology. In the present study, we asked the question if administration of a novel kynurenic acid analogue (SZR72), precursor of an excitotoxin antagonist and anti-inflammatory substance, can modify the neurogenic inflammatory response in the trigeminal ganglion.

Methods

Inflammation in the trigeminal ganglion was induced by local dural application of Complete Freunds Adjuvant (CFA). Levels of phosphorylated MAP kinase pERK1/2 and IL-1β expression in V1 region of the trigeminal ganglion were investigated using immunohistochemistry and Western blot.

Findings

Pretreatment with one dose of SZR72 abolished the CFA-induced pERK1/2 and IL-1β activation in the trigeminal ganglion. No significant change was noted in case of repeated treatment with SZR72 as compared to a single dose.

Conclusions

This is the first study that demonstrates that one dose of KYNA analog before application of CFA can give anti-inflammatory response in a model of trigeminal activation, opening a new line for further investigations regarding possible effects of KYNA derivates.

Targeting of the kynurenic acid across the blood-brain barrier by core-shell nanoparticles

Core-shell nanoparticles (CSNPs) were developed to get over therapeutic amount of kynurenic acid (KYNA) across the blood-brain barrier (BBB). Bovine serum albumin (BSA) was used as core for encapsulation of KYNA and the BSA/KYNA composite was finally encapsulated by poly(allylamine) hydrochloride (PAH) polymer as shell. In the interest of the optimization of the synthesis the BSA and KYNA interaction was studied by two-dimensional surface plasmon resonance (SPR) technique as well. The average size of d~100 nm was proven by dynamic light scattering (DLS) and transmission electron microscopy (TEM), while the structure of the composites was characterized by fluorescence (FL) and circular dichroism (CD) spectroscopy. The in vitro release properties of KYNA were investigated by a vertical diffusion cell at 25.0 °C and 37.5 °C and the kinetic of the release were discussed. The penetration capacity of the NPs into the central nervous system (CNS) was tested by an in vitro BBB model. The results demonstrated that the encapsulated KYNA had significantly higher permeability compared to free KYNA molecules. In the neurobiological serial of in vivo experiments the effects of peripherally administered KYNA with CSNPs were studied in comparison with untreated KYNA. These results clearly proved that KYNA in the CSNPs, administrated peripherally is suitable to cross the BBB and to induce electrophysiological effects within the CNS. As the neuroprotective properties of KYNA nowadays are proven, the importance of the results is obvious.

Acetyl-L-carnitine and oxaloacetate in post-treatment against LTP impairment in a rat ischemia model. An in vitro electrophysiological study

A high proportion of research relating to cerebral ischemia focuses on neuroprotection. The application of compounds normally present in the organism is popular, because they do not greatly influence the synaptic activity by receptor modulation, and can be administered without serious side effects. Oxaloacetate (OxAc) and acetyl-L-carnitine (ALC) are such favorable endogenous molecules. ALC can exert a protective effect by improving the energy state of the neurons under ischemic conditions. A promising neuroprotective strategy is glutamate scavenging, which can be achieved by the intravenous administration of OxAc. This study involved the possible protective effects of ALC and OxAc in different post-treatment protocols against long-term potentiation (LTP) impairment. Ischemia was induced in rats by 2-vessel occlusion, which led to a decreased LTP relative to the control group. High-dose (200 mg/kg) ALC or OxAc post-treatment resulted in a higher potentiation relative to the 2VO group, but it did not reach the control level, whereas low-dose ALC (100 mg/kg) in combination with OxAc completely restored the LTP function. Many previous studies have concluded that ALC can be protective only as pretreatment. The strategy described here reveals that ALC can also be neuroprotective when utilized as post-treatment against ischemia.

Neuroprotective effect of oxaloacetate in a focal brain ischemic model in the rat

During an ischemic event, the well-regulated glutamate (Glu) homeostasis is disturbed, which gives rise to extremely high levels of this excitatory neurotransmitter in the brain tissues. It was earlier reported that the administration of oxaloacetate (OxAc) as a Glu scavenger reduces the Glu level in the brain by enhancing the brain-to-blood Glu efflux. Here, we studied the neuroprotective effect of OxAc administration in a new focal ischemic model in rats. Occlusion of the middle cerebral artery resulted in immediate reduction of the somatosensory-evoked responses (SERs), and the amplitudes remained at the reduced level throughout the whole ischemic period. On reperfusion, the SERs started to increase, but never reached the control level. OxAc proved to be protective, since the amplitudes started to recover even during the ischemia, and finally fully regained the control level. The findings of the histological measurements were in accordance with the electrophysiological data. After Fluoro Jade C staining, significantly fewer labeled cells were detected in the OxAc-treated group relative to the control. These results provide new evidence of the neuroprotective effect of OxAc against ischemic injury, which strengthens the likelihood of its future applicability as a novel neuroprotective agent for the treatment of ischemic stroke patients.

Acetyl-L-carnitine normalizes the impaired long-term potentiation and spine density in a rat model of global ischemia

As a consequence of an ischemic episode, energy production is disturbed, leading to neuronal cell death. Despite intensive research, the quest for promising neuroprotective drugs has largely failed, not only because of ineffectiveness, but also because of serious side-effects and dosing difficulties. Acetyl-l-carnitine (ALC) is an essential nutrient which plays a key role in energy metabolism by transporting fatty acids into mitochondria for β-oxidation. It is an endogenous compound and can be used at high dose without toxicity in research into ischemia. Its neuroprotective properties have been reported in many studies, but its potential action on long-term potentiation (LTP) and dendritic spine density has not been described to date. The aim of the present study was an evaluation of the possible protective effect of ALC after ischemic insults inflicted on hippocampal synaptic plasticity in a 2-vessel occlusion (2VO) model in rats. For electrophysiological measurements, LTP was tested on hippocampal slices. The Golgi-Cox staining technique was used to determine spine density. 2VO resulted in a decreased, unstable LTP and a significant loss of dendritic spines. ALC administered after 2VO was not protective, but as pretreatment prior to 2VO it restored LTP nearly to the control level. This finding paralleled the histological analysis: ALC pretreatment resulted in the reappearance of dendritic spines on the CA1 pyramidal cells. Our data demonstrate that ALC administration can restore hippocampal function and spine density. ALC probably acts by enhancing the aerobic metabolic pathway, which is inhibited during and following ischemic attacks.

Caries and ABO secretor status in a Hungarian population of children and adolescents: an exploratory study

ABO blood group antigen (ABGA) secretion into the saliva and other body fluids is a well-known phenomenon, and there is evidence to suggest a link between secretor status and the appearance of caries. It has been proposed that secretion of these antigens into the saliva might be caries-preventive, however, this proposition is still a matter of debate. Our aim was to examine the relationship between caries experience and secretor status in a group of Hungarian children and adolescents in a cross-sectional study. Altogether 130 children and adolescents participated in the study (aged 6-18 years). Participants were divided into two groups according to dentition (i.e. mixed and permanent). ABGA were determined from saliva. The DMF-T and dmf-t (decayed, missing, and filled) indices were calculated, as well as the oral health hygiene index-simplified plaque index. Association of these indices with secretor status was examined. In mixed dentition, the mean dmf-t values were significantly lower in the secretor group (2.1 ± 0.52 SEM), as compared to the nonsecretor group (3.8 ± 0.93 SEM; p < 0.05, Mann-Whitney U test). The finding that children of mixed dentition are apparently better protected against caries suggests that the assumed protective effect might be associated with deciduous teeth, but given the general paucity of knowledge about this topic, further research is indicated.

Post-ischemic treatment with L-kynurenine sulfate exacerbates neuronal damage after transient middle cerebral artery occlusion

Since brain ischemia is one of the leading causes of adult disability and death, neuroprotection of the ischemic brain is of particular importance. Acute neuroprotective strategies usually have the aim of suppressing glutamate excitotoxicity and an excessive N-methyl-d-aspartate (NMDA) receptor function. Clinically tolerated antagonists should antagonize an excessive NMDA receptor function without compromising the normal synaptic function. Kynurenic acid (KYNA) an endogenous metabolite of the tryptophan metabolism, may be an attractive neuroprotectant in this regard. The manipulation of brain KYNA levels was earlier found to effectively enhance the histopathological outcome of experimental ischemic/hypoxic states. The present investigation of the neuroprotective capacity of L-kynurenine sulfate (L-KYNs) administered systemically after reperfusion in a novel distal middle cerebral artery occlusion (dMCAO) model of focal ischemia/reperfusion revealed that in contrast with earlier results, treatment with L-KYNs worsened the histopathological outcome of dMCAO. This contradictory result indicates that post-ischemic treatment with L-KYNs may be harmful.

Fundamental interstrain differences in cortical activity between Wistar and Sprague-Dawley rats during global ischemia

Four-vessel occlusion (4VO), a frequently used model of global cerebral ischemia in rats, results in a dysfunction in wide brain areas, including the cerebral cortex and hippocampus. However, there are pronounced differences in response to global ischemia between the laboratory rat strains used in these studies. In the present work, the immediate acute effects of 4VO-induced global ischemia on the spontaneous electrocorticogram (ECoG) signals were analyzed in Wistar and Sprague-Dawley rats. The ECoG was isoelectric during the 10 min of global cerebral ischemia in Wistar rats and the first burst (FB) was seen 10-13 min after the start of reperfusion. In Sprague-Dawley rats, the FB was detected immediately after the start of 4VO or a few seconds later. The burst suppression ratio (BSR) in Wistar rats decreased to 45% in 5 min after FB, and after 25 min it was approximately 40%. In Sprague-Dawley rats, the BSR was 55% immediately after the FB and it decreased steeply to reach 0% by 10 min. There was also a significant difference between the two strains in the frequency composition of the ECoG pattern. The power spectral densities of the two strains differed virtually throughout the post-ischemic state. The histological results (Evans Blue, Cresyl Violet and Fluoro Jade C stainings) supplemented the electrophysiological data: the neuronal damage in the CA1 pyramids in Wistar rats was severe, whereas in the Sprague-Dawley animals it was only partial. These observations clearly demonstrate that the use of different rat strains (e.g. Wistar vs. Sprague-Dawley) can be a source of considerable variability in the results of acute experiments on global ischemia and it is important that the laboratory rats used in such experiments should be carefully chosen.

Where does a migraine attack originate? In the brainstem

Migraine is a common, paroxysmal, highly disabling primary headache disorder. The origin of migraine attacks is enigmatic. Numerous clinical and experimental results suggest that the activation of distinct brainstem nuclei is crucial in its pathogenesis, but the primary cause of this activation is not fully understood. We conclude that the initialization of a migraine attack can be explained as an altered function of the neuronal elements of the brainstem nuclei. In light of our findings and the literature data, we can assume that migraine is a subcortical disorder of a specific brainstem area.

Synthesis and biological effects of some kynurenic acid analogs

The overactivation of excitatory amino acid receptors plays a key role in the pathomechanism of several neurodegenerative disorders and in ischemic and post-ischemic events. Kynurenic acid (KYNA) is an endogenous product of the tryptophan metabolism and, as a broad-spectrum antagonist of excitatory amino acid receptors, may serve as a protective agent in neurological disorders. The use of KYNA is excluded, however, because it hardly crosses the blood-brain barrier. Accordingly, new KYNA analogs which can readily cross this barrier and exert their complex anti-excitatory activity are generally needed. During the past 6 years, we have developed several KYNA derivatives, among others KYNA amides. These new analogs included one, N-(2-N,N-dimethylaminoethyl)-4-oxo-1H-quinoline-2-carboxamide hydrochloride (KYNA-1), that has proved to be neuroprotective in several models. This paper reports on the synthesis of 10 new KYNA amides (KYNA-1-KYNA-10) and on the effectiveness of these molecules as inhibitors of excitatory synaptic transmission in the CA1 region of the hippocampus. The molecular structure and functional effects of KYNA-1 are compared with those of other KYNA amides. Behavioral studies with these KYNA amides demonstrated that they do not exert significant nonspecific general side-effects. KYNA-1 may therefore be considered a promising candidate for clinical studies.

Syntheses, transformations and pharmaceutical applications of kynurenic acid derivatives

The syntheses and transformations of 4-hydroxyquinoline-2-carboxylic acid, kynurenic acid, are reviewed, and special attention is paid to the pharmacological activities and pharmaceutical applications of its derivatives.

Beta-amyloid pathology in the entorhinal cortex of rats induces memory deficits: implications for Alzheimer's disease

Alzheimer's disease is characterized by the presence of senile plaques in the brain, composed mainly of aggregated amyloid-beta peptide (Abeta), which plays a central role in the pathogenesis of Alzheimer's disease and is a potential target for therapeutic intervention. Amyloid plaques occur in an increasing number of brain structures during the progression of the disease, with a heavy load in regions of the temporal cortex in the early phases. Here, we investigated the cognitive deficits specifically associated with amyloid pathology in the entorhinal cortex. The amyloid peptide Abeta(1-42) was injected bilaterally into the entorhinal cortex of rats and behavioral performance was assessed between 10 and 17 days after injection. We found that parameters of motor behavior in an open-field as well as spatial working memory tested in an alternation task were normal. In contrast, compared with naive rats or control rats injected with saline, rats injected with Abeta(1-42) showed impaired recognition memory in an object recognition task and delayed acquisition in a spatial reference memory task in a water-maze, despite improved performance with training in this task and normal spatial memory in a probe test given 24 h after training. This profile of behavioral deficits after injection of Abeta(1-42) into the entorhinal cortex was similar to that observed in another group of rats injected with the excitotoxic drug, N-methyl-d-aspartate. Immunohistochemical analysis after behavioral testing revealed that Abeta(1-42) injection induced a reactive astroglial response and plaque-like deposits in the entorhinal cortex. These results show that experimentally-induced amyloid pathology in the entorhinal cortex induces selective cognitive deficits, resembling those observed in early phases of Alzheimer's disease. Therefore, injection of protofibrillar-fibrillar Abeta(1-42) into the entorhinal cortex constitutes a promising animal model for investigating selective aspects of Alzheimer's disease and for screening drug candidates designed against Abeta pathology.

Kynurenine in combination with probenecid mitigates the stimulation-induced increase of c-fos immunoreactivity of the rat caudal trigeminal nucleus in an experimental migraine model

Nitroglycerin, often used as a migraine model, results in increased number of c-fos immunoreactive secondary sensory neurons in the caudal trigeminal nucleus. Since synapses between first- and second-order trigeminal neurons are mediated by excitatory amino acids, NMDA receptors are presumably inhibited by kynurenic acid, the only known endogeneous NMDA receptor antagonist. Although kynurenic acid does not cross the BBB, its precursor, kynurenine, if combined with probenecid, crosses it readily. Systemic kynurenine + probenecid treatment significantly diminishes nitroglycerin-induced increase of c-fos immunoreactivity in the brainstem.

Kynurenines, Parkinson's disease and other neurodegenerative disorders: preclinical and clinical studies

The kynurenine pathway is the main pathway of tryptophan metabolism. L-kynurenine is a central compound of this pathway since it can change to the neuroprotective agent kynurenic acid or to the neurotoxic agent quinolinic acid. The break-up of these endogenous compounds' balance can be observable in many disorders. It can be occur in neurodegenerative disorders, such as Parkinson's disease, Huntington's and Alzheimer's disease, in stroke, in epilepsy, in multiple sclerosis, in amyotrophic lateral sclerosis, and in mental failures, such as schizophrenia and depression. The increase of QUIN concentration or decrease of KYNA concentration could enhance the symptoms of several diseases. According to numerous studies, lowered KYNA level was found in patients with Parkinson's disease. It can be also noticeable that KYNA-treatment prevents against the QUIN-induced lesion of rat striatum in animal experiments. Administrating of KYNA can be appear a promising therapeutic approach, but its use is limited because of its poorly transport across the blood-brain barrier. The solution may be the development of KYNA analogues (e.g. glucoseamine-kynurenic acid) which can pass across this barrier and disengaging in the brain, then KYNA can exert its neuroprotective effects binding at the excitatory glutamate receptors, in particular the NMDA receptors. Furthermore, it seems hopeful to use kynurenine derivatives (e.g. 4-chloro-kynurenine) or enzyme inhibitors (e.g. Ro-61-8048) to ensure an increased kynurenic acid concentration in the central nervous system.

Peritubular capillary damage in acute humoral rejection: an ultrastructural study on human renal allografts

The ultrastructural features of peritubular capillary (PC) damage was studied in 12 kidney allografts with acute humoral rejection (AHR). AHR manifested in diffuse linear PC staining for C4d, and histology consistent with Banff grade III in 7 recipients and Banff grade II in 5. Allografts with acute tubular necrosis served as controls. First biopsies (post-transplantation day 16.2 +/- 2.2): The intra-capillary exudate comprised monocytes (59%), polymorphonuclears (14%), lymphocytes (12%) and not otherwise specified mononuclears (15%). Three patterns of focal PC endothelial injury were observed: lysis, an increased rate of apoptosis and fragmentation. No correlation was found between the respective damage types and the inflammatory cell types or the Banff grades. Controls revealed endothelial swelling, detachment from basement membrane and fragmentation. Follow-up biopsies: Monocytes transformed into macrophages intra-luminally. The reparative changes comprised endothelial cytoplasmic protrusions, binucleated endothelial cells and capillary sprouts. Early transplant capillaropathy and transplant glomerulopathy were noted in 2 recipients. Literature data indicate that lysis is mediated by anti-HLA alloantibodies; apoptosis, demonstrated first in the present study, may be induced by non-HLA-type anti-endothelial antibodies. Fragmentation is caused by ischemia. Ongoing endothelial injury leads to transplant capillaropathy and transplant glomerulopathy, the characteristic lesions of chronic rejection.

Pentapeptides derived from Aβ1–42 protect neurons from the modulatory effect of Aβ fibrils—an in vitro and in vivo electrophysiological study

Short fragments and fragment analogues of beta-amyloid 1-42 peptide (Abeta1-42) display a protective effect against Abeta-mediated neurotoxicity. After consideration of our earlier results with in vitro bioassay of synthetic Abeta-recognition peptides and toxic fibrillar amyloids, five pentapeptides were selected as putative neuroprotective agents: Phe-Arg-His-Asp-Ser amide (Abeta4-8) and Gly-Arg-His-Asp-Ser amide (an analogue of Abeta4-8), Leu-Pro-Tyr-Phe-Asp amide (an analogue of Abeta17-21), Arg-Ile-Ile-Gly-Leu amide (an analogue of Abeta30-34), and Arg-Val-Val-Ile-Ala amide (an analogue of Abeta38-42). In vitro electrophysiological experiments on rat brain slices demonstrated that four of these peptides counteracted with the field excitatory postsynaptic potential-attenuating effect of Abeta1-42; only Arg-Val-Val-Ile-Ala amide proved inactive. In in vivo experiments using extracellular single-unit recordings combined with iontophoresis, all these pentapeptides except Arg-Val-Val-Ile-Ala amide protected neurons from the NMDA response-enhancing effect of Abeta1-42 in the hippocampal CA1 region. These results suggest that Abeta recognition sequences may serve as leads for the design of novel neuroprotective compounds.

Kynurenine administered together with probenecid markedly inhibits pentylenetetrazol-induced seizures. An electrophysiological and behavioural study

The kynurenine pathway converts tryptophan into various compounds, including l-kynurenine, which in turn can be converted to the excitatory amino acid receptor antagonist kynurenic acid, which may therefore serve as a protective agent in such neurological disorders as epileptic seizures. Kynurenic acid, however, has a very limited ability to cross the blood-brain barrier, whereas kynurenine passes the barrier easily. In this study, we tested the hypothesis that kynurenine administered systemically together with probenecid, which inhibits kynurenic acid excretion from the cerebrospinal fluid, results in an increased level of kynurenic acid in the brain that is sufficiently high to provide protection against the development of pentylentetrazol-induced epileptic seizures. CA3 stimulation-evoked population spike activity was recorded from the pyramidal layer of area CA1 of the rat hippocampus, and in another series of behavioural experiments, water maze and open-field studies were carried out to test the presumed protective effect of kynurenine + probenecid pre-treatment against pentylenetetrazol-induced seizures. This study has furnished the first electrophysiological proof that systemic kynurenine (300 mg/kg, i.p.) and probenecid (200 mg/kg, i.p.) administration protects against pentylenetetrazol-induced (60 mg/kg, i.p.) epileptic seizures.

HLA immunization of haemodialysed patients in the transfusion and the erythropoietin eras

The frequency of transfusions and the development of HLA alloimmunization in the years 1986 and 1995, representing the 'transfusion era' and the 'erythropoietin era', have been compared. The introduction of erythropoietin was found to reduce the need for transfusion in haemodialysed patients on the waiting list from 65.2% to 5.7%. The elimination of transfusions resulted in a decrease in HLA immunization from 56.5% to 35%. In those patients who were still immunized, antibody production was probably caused either by immunomodulation or by transfusions given to treat complications. Erythropoietin could be used instead of transfusions in almost all cases, except for complications involving severe bleeding.

A combined electrophysiological and behavioural study for the assessment of activity-dependent changes in mice

Activity-dependent adaptive changes in the nervous system involve structural and functional changes in the cortical circuitry. In this work the cortical function was studied by repeated recording of the somatosensory and motor potentials evoked by whisker deflections after altered sensory-motor experience in adult mice. The latencies of motor and somatosensory evoked potentials were found to shorten, while their amplitudes decreased, after a behavioural challenge involving the vibrissal apparatus. Sensory deprivation achieved by whisker trimming resulted in a partial reversal of the changes observed after increased activity. The derived parameters imply that cortical information processing speeds up as a result of experience, while decreased activity has the opposite effect. The methods used throughout the experiment were minimally invasive, and thus proved to be sufficient for the long-term follow-up of cortical functions.

The modulatory effect of estrogen on the neuronal activity in the barrel cortex of the rat. An electrophysiological study

In acute experiments, the effects of iontophoretically applied 17 beta-estradiol hemisuccinate on the activity of the primary somatosensory cortical neurons were studied in ovariectomized rats by extracellular single-unit recording. 17 beta-Estradiol increased both the spontaneous and the vibrissa deflection-evoked responses, with an average latency of 24 min. It is suggested that this relatively long latency of the 17 beta-estradiol effect is based not so much on membrane mechanisms as on genomic mechanisms.

Facial nerve injury-induced disinhibition in the primary motor cortices of both hemispheres

Unilateral facial nerve transection induces plastic reorganization of the somatotopic order in the primary motor cortex area (MI). This process is biphasic and starts with a transient disinhibition of connections between cortical areas in both hemispheres. Little is known about the underlying mechanisms. Here, cortical excitability has been studied by paired pulse electrical stimulation, applied either within the MI or peripherally to the trigeminal nerve, while the responses were recorded bilaterally in the MI. The ratios between the amplitudes of the second and first evoked potentials (EPs or fEPSPs) were taken as measures of the inhibitory capacity in the MI ipsilateral or contralateral to the nerve injury. A skin wound or unilateral facial nerve exposure immediately caused a transient facilitation, which was followed by a reset to some level of inhibition in the MI on both sides. After facial nerve transection, the first relatively mild reduction of inhibition started shortly (within 10 min) after denervation. This was followed by a second step, involving a stronger decrease in inhibition, 40-45 min later. Previous publications have proved that sensory nerve injury (deafferentation) induces disinhibition in corresponding areas of the sensory cortex. It is now demonstrated that sham operation and, to an even greater extent, unilateral transection of the purely motoric facial nerve (deefferentation), each induce extended disinhibition in the MIs on both sides.

Cross-modal plasticity of the corticothalamic circuits in rats enucleated on the first postnatal day

Reorganization of the reciprocal corticothalamic connections was studied as a possible anatomical substrate of the cross-modal compensation of the missing visual input of the visual cortex by somatosensory-evoked activities in neonatally enucleated rats. The use of quantitative retrograde tract-tracing techniques revealed that the contribution of the lateral posterior thalamic nucleus (LP) is significantly increased following enucleation, while that of the dorsolateral geniculate and the lateral dorsal nuclei is decreased in the thalamocortical afferentation of a region in visual cortical area 17. In contrast with the control rats, a dense terminal arborization of afferents was labelled in the LP after the injection of anterograde tracer into the barrel cortex of the enucleated rats. The injection of anterograde tracer into the visual cortex also demonstrated a massive afferentation into the LP of the enucleated rats. Visual and somatosensory corticothalamic afferents exhibited similar ultrastructural features in the LP after enucleation, but their synaptic organizations differed as regards the diameter of the postsynaptic dendrites. Taken together with the previous observations, these results suggest a central role for the LP in the transmission of the somatosensory-evoked activities to the visual cortex after early blindness.

Estrogen effects on arcuate neurons in rat. An in situ electrophysiological study

In acute experiments, the effects of i.p. 17beta-estradiol on the activity of arcuate neurons were studied in ovariectomized rats. 17Beta-estradiol (100 microg/100g, i.p.) increased the spontaneous activity of the observed arcuate neurons with a latency of 20-25 min. In some neurons spontaneous activity could be influenced by stimulation of the olfactory and somatosensory systems. Activation of the trigeminal system significantly increased the spontaneous activity of the studied units, while stimulation of the accessory olfactory bulb decreased it, both with and without 17beta-estradiol treatment. It is suggested that the 20-25 min latency of the 17beta-estradiol effect is based not so much on membrane as on genomic mechanisms. This suggestion is supported by immunocytochemical studies: 17beta-estradiol treatment significantly decreased the number of GABA-positive axo-somatic synapses in the arcuate nucleus.

Facial nerve injury produces a latent somatosensory input through recruitment of the motor cortex in the rat

Short-latency effects of unilateral facial nerve transection were studied on neuronal activation evoked in the primary motor cortex (MI) on both sides by vibrissa stimulation in adult rats. In the controls, unilateral trigeminal stimulation evoked activity in the whisker representation of both the contralateral somatosensory cortex (SI) and MI, but never in the ipsilateral MI. Unilateral transection of the facial motoric nerve facilitated evoked responses in the contralateral MI, and induced further neuronal activation (gross potentials and unit activity) in the MI ipsilateral to the stimulation. Since these changes appeared rapidly and could be mimicked by picrotoxin application onto the SI contralateral to the stimulation, they are considered to be based on the disinhibition of preexisting associative and commissural connections, which are unmasked by facial nerve transection.

Comparative study of the neuronal plasticity along the neuraxis of the vibrissal sensory system of adult rat following unilateral infraorbital nerve damage and subsequent regeneration

The aim of the present study was to examine the physiological consequences of a unilateral infraorbital nerve lesion and its regeneration at different levels of the somatosensory neuraxis. In animals whose right infraorbital nerve had been crushed, a large unresponsive area was found in the main brainstem trigeminal nucleus (Pr5). Responses evoked by ipsilateral vibrissal deflection in the middle of Pr5 reappeared only on days 22-35 after the nerve had been transected, whereas recovery from the nerve crush took only 7-9 days. However, no sign of short-term neuronal plasticity was observed in Pr5 after peripheral nerve injury. An enlargement of the receptive fields in two-thirds of the units and a lengthening in the delay of the evoked responses were observed as long-term plastic changes in Pr5 neurons after peripheral-nerve regeneration. In the ventral posteromedial nucleus of the thalamus (VPM) of partly denervated animals, however, only minutes or hours after the nerve crush, certain units were found to respond in some cases not only to the vibrissae, but also to mechanical stimulation of the face over the eye (two units), the nose (one unit), and the midline (one unit). Apart from the experiments involving incomplete denervation, the vibrissal representation areas of the VPM were unresponsive to stimulation of both the vibrissae and other parts of the face until nerve regeneration had occurred. In the somatosensory cortex, an infraorbital nerve crush immediately resulted in a large cortical area being unresponsive to vibrissal deflection. It was noteworthy, however, that shortly after the nerve crush, this large unresponsive whisker representation cortical area was invaded from the rostromedial direction by responses evoked by stimulation of the forepaw digits. In spite of the reappearance of vibrissa-evoked responses 7-10 days after the nerve crush, an expanded digital representation could still be observed 3 weeks after the nerve crush, resulting in an overlapping area of digital and vibrissal representations. The withdrawal of the expanded representation of forepaw digits was completed by 60 days after the nerve crush. The results obtained in Pr5, the VPM, and the cortex strongly suggest that the higher the station in the neuraxis, the greater the degree of plasticity after infraorbital nerve injury.

Activation of the primary motor cortex by somatosensory stimulation in adult rats is mediated mainly by associational connections from the somatosensory cortex

In anaesthetized adult rats, facial nerve injury causes a disinhibition of the interhemispheric connections between homotopic representation fields in the primary motor cortex with a latency of 4 min (Toldi et al., 1996, Neurosci Lett. 203, 179-182). One possible explanation for the induction of such rapid changes is an alteration of the somatosensory input to the motor cortex. To test this hypothesis, unit activity in primary motor cortex was recorded during electrical stimulation of trigeminal afferents in the contralateral whisker-pad. About one-third of all recorded primary motor cortex neurons responded with latencies shorter than in the ventrolateral and posterior nuclei of the thalamus. Responses failed at stimulation frequencies > or = 10 Hz and after elimination or inactivation of the somatosensory cortex. Within primary motor cortex, the activatable neurons displayed a bilaminar distribution and were identified as pyramidal neurons by neurobiotin labelling. The results suggest that trigeminal afferents participate in modulation of the activity of primary motor cortex output neurons via primary somatosensory cortex-to-primary motor cortex associational connections, even under anaesthesia.

Does the cortical representation of body parts follow both injury to the related sensory peripheral nerve and its regeneration?

A study was made of the borderline between the physiological representations of the digits (D2, D3 and D4) and sinus whiskers in the rat primary somatosensory cortex after a contralateral infraorbital nerve crush. Following the injury, the physiological representation of the digits of the contralateral forepaw extended posterolaterally, occupying the anterolateral part of the whisker region (posteromedial barrel subfield). The extended physiological representation of the digits, though somewhat shrunken, remained after the reappearance of whisker-evoked responses, forming an overlapping area between the obligate digit and whisker representations. The findings emphasize the importance of afferent inputs in modulating cortical organization, but show that a reversible change in a sensory input (nerve damage) does not result in a perfectly reversible change in cortical representation.

Stimulus-dependent muscarinic effects on evoked unit activity in the rat barrel cortex

The cerebral cortex receives a prominent cholinergic innervation, which is thought to play an important role in the regulation of its normal function. Electrophysiological studies have shown that activation of muscarinic cholinergic receptors results in a marked enhancement of excitatory stimuli onto cortical neurons. In the present study, we examined the effects of acetylcholine (ACh) and its muscarinic agonists (applied by pressure injection) on the response components of individual cortical neurons in layers IV and V of the rat somatosensory cortex in identified barrels (C2 and C3). It was found that the muscarinic agonists could modify the evoked unit activity (in most cases, they caused units to respond to previously minimally effective whisker stimuli), but the modulatory effect was highly dependent on the stimulus parameters, and in most cases, the effect was limited to only one component of 'on' or 'off' responses consisting of 2-4 spikes.

Neuronal plasticity induced by neonatal monocular (and binocular) enucleation

Monocular (ME) and binocular enucleation has become a useful experimental tool for analyzing the mechanisms of neural plasticity. ME when performed during an early postnatal period (up to 15 days after birth) initiates a series of adaptive reactions in the visual (and other sensory) system(s) which tend to compensate for the lost sensory capacity. Extirpation of one eye (usually the right) destroys afferents to both lateral geniculate bodies dorsal nucleus (CGLd) and superior colliculi (CS), being severely impaired by the degeneration of retino-geniculate and collicular synapses. The sprouting of retinogeniculate fibers coming from the remaining eye replaces these synapses in both CGLds. Ipsilateral representation of the remaining eye (usually of minor significance) becomes extended in the left CGLd and consequently in the left visual area, just as in the superior colliculi. A similar but somewhat smaller extension takes place in the contralateral CGLd and visual cortex. The strengthening of commissural connections results in a remarkable extension of callosally connected stripes and patches in both hemispheres. After ME in the critical period, the control over behavior is taken over by the remaining eye. Its power of resolution is improved because of the higher survival of (mainly ipsilaterally projecting) ganglion cells. Therefore, both hemispheres are still available for storing visual information. In ME rats the learning of visual tasks requires both hemispheres, but relearning is still possible after extirpation of the contralateral one. The possible two main mechanisms of adaptive plastic changes are: (i) replacement of degenerated synapses by sprouting collaterals of ingrowing foreign fibers, and (ii) neurons having morphologically intact but inactive synapses establishing connections with afferent fibers other than the usual. The same mechanism is seen operating in cross-modal adaptive reactions as well.

Biphasic reorganization of somatotopy in the primary motor cortex follows facial nerve lesions in adult rats

Effects of facial nerve transection were studied on muscle responses evoked by electrical stimulation in the primary motor cortex (MI) of adult rats. In intact animals, activated muscles varied according to the somatotopic representation map, and responses were restricted to the contralateral side. Unilateral transection of the facial nerve extinguished contralateral vibrissal responses, while ipsilateral vibrissae began to respond within 4 min. This abnormal response (primary change) was transient and gradually disappeared within hours to days. Instead, contralateral movements of forepaw and eye/eyelid muscles could be evoked from increasing portions of the former vibrissal field (secondary change), in which many points became unresponsive. After 4 days, the former vibrissal field had shrunk to a small central part, where ipsilateral vibrissae responsiveness remained. The secondary modification was stable for at least 2 weeks. Since the primary change is rapid, transient and may be mimicked by picrotoxin, it may be based on disinhibition of commissural connections, while the secondary change is longlasting and therefore may include some form of reorganization of associational synapses.

Muscarinic cholinergic effects on stimulus-evoked responses in rat primary somatosensory cortex. An electrophysiological study

Neuron terminals originating from the nucleus basalis megnocellularis (NBM) are the major source of the cortical cholinergic innervation, which is thought to play an essential role in higher brain functions. Electrophysiological studies have shown that activation of muscarinic cholinergic receptors caused a marked enhancement of sensory stimuli onto cortical neurons. Diminished cholinergic innervation of somatosensory cortical areas are manifested in decreased stimulus-evoked activity and impaired performance in a sensory discrimination task. We examined the effects of ACh and its muscarinic agonists on the response properties of layer IV-V barrel cortex neurons evoked by precisely controlled vibriasa deflections. The cholinergic pharmacons displayed their mostly facilitatory effects in latency-dependent manner: In most cases only one latency component of On and/or Off responses were changed.

Neonatal monocular enucleation-induced cross-modal effects observed in the cortex of adult rat

The cortices of neonatally enucleated rats were explored for somatosensory responses with special reference to an extension into the occipital cortex. Monocular enucleation was performed on rats at birth. The animals were raised and from the age of three months the activity evoked by either electric stimulation of the vibrissa pad or bending of the vibrissae was tested in the contralateral cortex by electric recording and autoradiography. It was found that early enucleation caused an expansion of the somatosensory responses, among others into the visual area. Neurons responsive to visual and somatosensory stimuli were demonstrated in the anterior part of the primary and secondary visual areas, contralateral to the enucleation. Electrophysiological and autoradiographic studies unambiguously proved that early enucleation exerted a significant cross-modal effect on the somatosensory responsive area.

Neonatal enucleation induces cross-modal changes in the barrel cortex of rat. A behavioural and electrophysiological study

The present study was undertaken to determine whether neonatal enucleation leads to functional changes in the somato-sensory system and whether it has any behavioural effects. Binocular enucleation was performed on newborn rats. The effects of enucleation were tested versus controls in a rectangular maze on 10 successive days starting on postnatal day 80. Immediately after the 10-day behavioural study session, electro-physiological experiments were performed on 5 enucleated and 5 control rats. All the whiskers of the remaining animals were clipped off on both sides, and these animals continued the maze running for four additional sessions. The behavioural study demonstrated that the maze performance achieved by the neonatally enucleated animals was better than that of the controls. This suggested that cross-modal compensatory changes took place in other sensory systems, presumably somatosensory too. This was supported by the result of the experiment preceded by bilateral vibrissa clipping. The electrophysiological experiments clearly revealed that functional changes took place in the somatosensory system of enucleated rats. In these animals, the cells in some barrels (C1 and E3) displayed enlarged receptive fields, while in an other barrel (A3) an increased angular sensitivity for deflection of its related whisker was observed. This combined study clearly demonstrates that neonatal enucleation is able to induce cross-modal compensatory changes in the somatosensory system of the rat.

Compensation of a sensory deficit inflicted upon newborn and adult animals. A behavioural study

Somatosensory deprivation (bilateral vibrissa clipping) was performed on newborn (P1) and adult (P80) rats and, on 10 successive days starting on day 81, the effect of sensory deprivation was tested in a rectangular maze versus controls. The maze performance (the time to reach the goal-box with food reward) of the P80 animals was significantly poorer than that of P1 animals. The tests repeatedly demonstrated, however, that the maze performance achieved by the P1 animals was better than that of the controls. This behavioural study clearly revealed that early sensory deprivation induced (probably cross-modal) compensatory changes in other sensory systems.

The effect of levo-acetyl-carnitine on visual cognitive evoked potentials in the behaving monkey

We studied acute and chronic effects of levo-acetyl-carnitine (LAC) on event-related potentials (ERPs) in 3 monkeys trained in a "go"/"no-go" visual "oddball" discrimination task. The stimuli were 2.5 cpd sinusoidal gratings differing in their respective orientation only (0 degrees or 45 degrees). Each monkey was trained to release a lever during a prespecified time window. Target stimulus presentation probabilities were between 0.25 and 0.5. ERPs had comparable mean latencies and amplitudes in all monkeys. Primary evoked potentials recorded to either the target or non-target stimulus did not change significantly as a result of LAC treatment. On the other hand, P300 latency decreased following LAC administration, with a maximum occurring in 15-20 min. The major effects of LAC were consistent within each animal and for all three of them.

Deep sensibility of the mystacial pad in the rat and its cortical representation

The cortical representation of the rat's mystacial pad was examined with the aid of evoked field potentials and recording of single cell activity. Mechanical bending of the vibrissae activated the well-known area within the somato-sensory cortex. Electrical stimulation of the mystacial pad with inserted needle electrodes, bi- and monopolarly, caused a widespread activation extending practically to the whole exposed cortex, including visual, acoustic and motor areas (MSS potentials). The evoked field potentials were accompanied by well-recordable unit activity, mainly in the upper 1000 microns of the cortical depth. Capsaicin, injected into the mystacial pad on the 8th-10th postnatal day heavily impaired the MSS potentials as recorded at 2 months of age, and only moderately acted on the mechanically evoked potentials. So did also the acutely injected capsaicin. Peak latency of the MSS potentials seemed to be in correlation with the distance from the punctum maximum. The latencies of unit potentials, however, did not show such dependence, they were between 8 and 10 ms. MSS potentials are thought to represent cortical projection mainly of thermo- and nociceptive fibers, which play an important role in the early postnatal life.

Capsaicin differentially influences somatosensory cortical responses evoked by peripheral electrical or mechanical stimulation

The effects of capsaicin injected intraperitoneally (200 micrograms/kg) or applied locally to the cortical surface (10(-5) M) were studied on cortical potentials evoked by peripheral electrical or mechanical stimulation. Capsaicin treatment (i.p.) differentially influenced the cortical evoked potentials depending on the type of stimulation. Just after both types of capsaicin application, the responses to both kinds of stimuli decreased in amplitude. Additionally, during this time a short fall in blood pressure was observed. Half an hour later, however, only in the case of interperitoneal application the potentials evoked by electrical stimulation were facilitated, while the potentials evoked by vibrissa deflection had recovered and stayed around the control levels thereafter. In addition, the responsive cortex area activated by electrical stimulation became enlarged after the i.p. injection of capsaicin, while that of the cortex region activated by mechanical stimulation did not change significantly. Capsaicin applied locally to the cortex resulted neither in the facilitation of evoked potentials nor in the enlargement of the responsive cortical area. The present findings are the first to demonstrate that the i.p. (but not local) administration of capsaicin, in low dosage, differentially influences the cortical responses evoked by electrical and mechanical stimulation of somatosensory afferents.

Neonatal enucleation induces correlated modification in sensory responsive areas and pial angioarchitecture of the parietal and occipital cortex of albino rats

This study was carried out to investigate whether correlations existing in normal adult rats (Ambach et al., '86) between functional characteristics of neocortical areas and their pial angioarchitecture can be correspondingly modified under pathological conditions. The right eyes of albino rats were enucleated on the 1st, 8th, 15th and 30th day after birth, respectively. At the age of 3 to 4 months, the responsiveness of the parieto-occipital cortex to sensory stimuli was studied in enucleated animals and age matched controls. After the mapping of visually and somatosensorily evoked potentials, the vascular system was filled with dye. Monocular enucleation at birth induced bilateral modifications in sensory responsiveness and corresponding changes in pial angioarchitecture, especially in the venous drainage fields. In comparison with the controls, a considerable expansion was observed in the overlapping zone between visually and somatosensorily responsive areas. In contrast, borders of the visual cortex toward the auditory and retrosplenial areas were essentially stable. Corresponding changes were found in the pial distribution patterns of cerebral veins but not of arteries. The major effect of neonatal enucleation on angioarchitecture was a change in the subdivision of the parieto-occipital veins drainage fields. This was due to a significant enlargement of the anterior accessory occipital (O3) vein, which compressed the drainage fields of the parietal and occipital veins and completely separated them from one another. The results suggest that during ontogenesis: (1) alterations in the formation of sensory input may interfere with neocortical angiogenesis, especially the structuring of veins, (2) after monocular enucleation this influence is prominent in parietal and occipital cerebral veins, and (3) these angiogenetic processes are vulnerable only during the perinatal and early postnatal period.

Modification induced in visual cortical activity of rat by neonatal monocular enucleation

Monocular enucleation was performed on rats at birth. The animals were raised and from the age of 3 months the evoked activity was tested in the contralateral visual cortex both by mapping of evoked potentials and by autoradiography. It was found that monocular enucleation changed the distribution of the evoked activity characteristically. The focus of activity shifted laterally and was restricted to the binocular part of the primary visual cortex, while hardly any evoked activity or labelled neurons were found in its medial part.

Late consequences of cryogenic brain lesion in rat; an electrophysiological study

The left somatosensory cortex of PVG/C rats was subjected to a transcranial cold lesion, spontaneous and evoked cortical activity was studied 2-3 weeks after the lesion. The spontaneous activity underwent a depression at the focus of the lesion. Close to the epicentre of the lesion, the amplitude of the potentials evoked by electrical stimulation of the contralateral whisker pad was considerably smaller than in the controls and an almost complete reduction of the initial positive phase was found. Perifocally, 3-4 mm from the epicentre, evoked potentials with enhanced amplitudes were recorded in all experiments. It seems that considerable damage took place at the epicentre of the lesion, while perifocally an excitatory (and/or inhibitory?) mechanism was activated.

Sodium bromide treatment influences the plasticity of somatosensory responses in the rat cortex as induced by enucleation

Effects of sodium bromide were studied on central neuroplasticity induced by early binocular enucleation. It has previously been found that enucleation on the day of birth, but not later than the first postnatal week, resulted in changes in the occipital cortex, such as the invasion of somatosensory evoked activity into the visual cortex areas. The present results showed that sodium bromide treatment extended at least up to 15 days after birth, the critical period during which somatosensory projections could be modified by visual deafferentation. Together with observations of Frost [J. comp. Neurol. (1981) 203, 227-256; Devl Brain Res. (1982) 3, 627-636], the present results suggest a mutual dependency of visual and somatosensory projection development. The present study is the first demonstration that the critical period of development, during which a specific type of neural plasticity can be induced, may be prolonged by pharmacological means, i.e. by chronic treatment with sodium bromide.

Functional consequences of modification of callosal connections by perinatal enucleation in rat visual cortex

The effects of neonatal monocular enucleation (right eye) on the callosal connections in the rat visual cortex were studied by physiological and morphological methods. Evoked activity was recorded in the left hemisphere, i.e. contralaterally to the enucleated eye. After enucleation, trans-callosally evoked responses were recorded in a widened stripe of the lateral visual cortex. Compared with the controls, the responsive area was expanded laterally and medially, i.e. into the lateral part of the primary visual area and within the secondary visual cortex (lateral part). Within about 0.5 mm of the expansion, the responses did not differ from those recorded in areas with "normal" callosal connections. Morphological evidence is presented suggesting that this expansion of evoked responses with high amplitudes and short latencies corresponds to an extension of callosal connections with a high density of axon terminals in layers two and three. Further medially within the primary visual cortex, callosally evoked responses with low amplitudes and longer latencies were recorded. The main types of unit responses and characteristic interactions between visually and callosally evoked responses are shown and discussed. These results suggest that following neonatal enucleation (1) the callosal connections expand and form functional synapses in the lateral part of the visual cortex, (2) these connections can activate cortical neurons either directly or by mediation of associational connections between the lateral secondary and primary visual cortex areas and (3) callosal connections can interact with visually evoked potentials and unit responses.

Modified distribution patterns of responses in rat visual cortex induced by monocular enucleation

Monocular enucleation was performed on rats at birth or on the 8th or 15th day, respectively. The animals were raised and from the age of 3 months the evoked activity was tested in the visual cortex. It was found that monocular enucleation changed the distribution of visually evoked responses. In the right hemisphere (contralateral to the preserved eye) two focuses of evoked potentials appeared with large amplitudes shifted to both sides, towards the lateral and medial borders of the primary visual area. In the left hemisphere the focus of the evoked potentials was shifted slightly laterally and posteriorly. Early enucleation caused an expansion of the somatosensory responses into the visual area. Bimodal neurons (responsive to visual and somatosensory stimuli) were observed in the anterior part of the primary and secondary visual areas contralateral to the enucleation. These changes became moderate with increasing age at which enucleation was performed and were not found in animals enucleated on the 15th day after birth.

Transient increase of calcium in pre- and postsynaptic organelles of rat superior cervical ganglion after tetanizing stimulation

The stimulation-dependent translocation and redistribution of intracellular calcium was studied in synapses of the rat superior cervical ganglion. For the cytochemical demonstration of calcium at the ultrastructural level the oxalate-pyroantimonate technique was used. Calcium-containing deposits were observed as electron-dense particles in synaptic vesicles and occasionally in presynaptic mitochondria. On the postsynaptic side, vesicles and vacuoles in dendrites contained increased amounts of reaction product. Following a short train of impulses (20 s, 20 c.p.s.), the ganglionic response to a single stimulus was increased. This potentiation effect which lasted about 1-5 min was accompanied by a change in the distribution of calcium at fine structural level. In ganglia fixed 1 and 5 min after the train, but not later, the number of calcium-containing synaptic vesicles and postsynaptic vacuoles increased significantly.