Alpha2-adrenergic receptor activation reinstates motor deficits in rats recovering from cortical injury.

Norepinephrine plays an important role in motor functional recovery after a brain injury caused by ferrous chloride. Inhibition of norepinephrine release by clonidine is correlated with motor deficits after motor cortex injury. The aim of this study was to analyze the role of α2-adrenergic receptors in the restoration of motor deficits in recovering rats after brain damage. The rats were randomly assigned to the sham and injury groups and then treated with the following pharmacological agents at 3 hours before and 8 hours, 3 days, and 20 days after ferrous chloride-induced cortical injury: saline, clonidine, efaroxan (a selective antagonist of α2-adrenergic receptors) and clonidine + efaroxan. The sensorimotor score, the immunohistochemical staining for α2A-adrenergic receptors, and norepinephrine levels were evaluated. Eight hours post-injury, the sensorimotor score and norepinephrine levels in the locus coeruleus of the injured rats decreased, and these effects were maintained 3 days post-injury. However, 20 days later, clonidine administration diminished norepinephrine levels in the pons compared with the sham group. This effect was accompanied by sensorimotor deficits. These effects were blocked by efaroxan. In conclusion, an increase in α2-adrenergic receptor levels was observed after injury. Clonidine restores motor deficits in rats recovering from cortical injury, an effect that was prevented by efaroxan. The underlying mechanisms involve the stimulation of hypersensitive α2-adrenergic receptors and inhibition of norepinephrine activity in the locus coeruleus. The results of this study suggest that α2 receptor agonists might restore deficits or impede rehabilitation in patients with brain injury, and therefore pharmacological therapies need to be prescribed cautiously to these patients.

Glutamate, Glutamine, GABA and Oxidative Products in the Pons Following Cortical Injury and Their Role in Motor Functional Recovery.

Brain injury leads to an excitatory phase followed by an inhibitory phase in the brain. The clinical sequelae caused by cerebral injury seem to be a response to remote functional inhibition of cerebral nuclei located far from the motor cortex but anatomically related to the injury site. It appears that such functional inhibition is mediated by an increase in lipid peroxidation (LP). To test this hypothesis, we report data from 80 rats that were allocated to the following groups: the sham group (n = 40), in which rats received an intracortical infusion of artificial cerebrospinal fluid (CSF); the injury group (n = 20), in which rats received CSF containing ferrous chloride (FeCl2, 50 mM); and the recovery group (n = 20), in which rats were injured and allowed to recover. Beam-walking, sensorimotor and spontaneous motor activity tests were performed to evaluate motor performance after injury. Lipid fluorescent products (LFPs) were measured in the pons. The total pontine contents of glutamate (GLU), glutamine (GLN) and gamma-aminobutyric acid (GABA) were also measured. In injured rats, the motor deficits, LFPs and total GABA and GLN contents in the pons were increased, while the GLU level was decreased. In contrast, in recovering rats, none of the studied variables were significantly different from those in sham rats. Thus, motor impairment after cortical injury seems to be mediated by an inhibitory pontine response, and functional recovery may result from a pontine restoration of the GLN-GLU-GABA cycle, while LP may be a primary mechanism leading to remote pontine inhibition after cortical injury.

Early Expression of Neuronal Dopaminergic Markers in a Parkinson's Disease Model in Rats Implanted with Enteric Stem Cells (ENSCs).

BACKGROUND: Parkinson's Disease (PD) is a common neurodegenerative disorder affecting the dopaminergic (DAergic) system. Replacement therapy is a promising alternative aimed at reconstructing the cytoarchitecture of affected brain regions in PD. Experimental approaches, such as the replacement of DAergic neurons with cells obtained from the Enteric Nervous System (ENS) has yet to be explored. OBJECTIVE: To establish and characterize a cell replacement strategy with ENS Cells (ENSCs) in a PD model in rats. METHODS: Since ENSCs can develop mature DAergic phenotypes, here we cultured undifferentiated cells from the myenteric plexus of newborn rats, establishing that they exhibit multipotential characteristics. These cells were characterized and further implanted in the Substantia nigra pars compacta (SNpc) of adult rats previously lesioned by a retrograde degenerative model produced by intrastriatal injection of 6-Hydroxydopamine (6-OHDA). DAergic markers were assessed in implants to validate their viability and possible differentiation once implanted. RESULTS: Cell cultures were viable, exhibited stem cell features and remained partially undifferentiated until the time of implant. The retrograde lesion induced by 6-OHDA produced DAergic denervation, reducing the number of fibers and cells in the SNpc. Implantation of ENSCs in the SNpc of 6-OHDAlesioned rats was tracked after 5 and 10 days post-implant. During that time, the implant increased selective neuronal and DAergic markers, Including Microtubule-Associated Protein 2 (MAP-2), Dopamine Transporter (DAT), and Tyrosine Hydroxylase (TH). CONCLUSION: Our novel results suggest that ENSCs possess a differentiating, proliferative and restorative potential that may offer therapeutic modalities to attenuate neurodegenerative events with the inherent demise of DAergic neurons.

Involvement of the Auditory Pathway in Spinocerebellar Ataxia Type 7.

BACKGROUND: Spinocerebellar ataxia type 7 (SCA7) is an autosomal dominant disorder caused by a mutation in the ATXN7 gene. The involvement of the brainstem auditory pathway in pathogenesis of this disease has not been systematically assessed. AIM: To determine involvement of the brainstem auditory pathway in SCA7 patients and its relationship to clinical features of the disease. METHODS: In this case-control study, brainstem auditory-evoked potentials (BAEPs) were assessed in 12 SCA7 patients with clinical and molecular diagnosis, compared to 2 control groups of 16 SCA2 patients and 16 healthy controls. RESULTS: SCA7 patients exhibited significant prolongation of I-wave and III-wave latencies, whereas SCA2 patients showed increased latencies for III and V waves and I-III interpeak interval. SCA7 patients with larger I-wave latencies exhibited larger CAG repeats, earlier onset age, and higher SARA scores, but in SCA2 cases, these were not observed. CONCLUSIONS: BAEP tests revealed functional involvement of the auditory pathway in SCA7 (mainly at) peripheral portions, which gave new insights into the disease physiopathology different from SCA2 and may unravel distinct pathoanatomical effects of polyQ expansions in the central nervous system. SIGNIFICANCE: These findings offer important insights into the distinctive disease mechanisms in SCA7 and SCA2, which could be useful for differential diagnosis and designing specific precision medicine approaches for both conditions.

CaMKII Requirement for in Vivo Insular Cortex LTP Maintenance and CTA Memory Persistence.

Calcium-calmodulin/dependent protein kinase II (CaMKII) plays an essential role in LTP induction, but since it has the capacity to remain persistently activated even after the decay of external stimuli it has been proposed that it can also be necessary for LTP maintenance and therefore for memory persistence. It has been shown that basolateral amygdaloid nucleus (Bla) stimulation induces long-term potentiation (LTP) in the insular cortex (IC), a neocortical region implicated in the acquisition and retention of conditioned taste aversion (CTA). Our previous studies have demonstrated that induction of LTP in the Bla-IC pathway before CTA training increased the retention of this task. Although it is known that IC-LTP induction and CTA consolidation share similar molecular mechanisms, little is known about the molecular actors that underlie their maintenance. The purpose of the present study was to evaluate the role of CaMKII in the maintenance of in vivo Bla-IC LTP as well as in the persistence of CTA long-term memory (LTM). Our results show that acute microinfusion of myr-CaMKIINtide, a selective inhibitor of CaMKII, in the IC of adult rats during the late-phase of in vivo Bla-IC LTP blocked its maintenance. Moreover, the intracortical inhibition of CaMKII 24 h after CTA acquisition impairs CTA-LTM persistence. Together these results indicate that CaMKII is a central key component for the maintenance of neocortical synaptic plasticity as well as for persistence of CTA-LTM.

CaMKII requirement for the persistence of in vivo hippocampal mossy fiber synaptic plasticity and structural reorganization.

CaMKII has been proposed as a molecular substrate for long-term memory storage due to its capacity to maintain an active autophosporylated state even after the decay of the external stimuli. The hippocampal mossy fiber-CA3 pathway (MF-CA3) is considered as a relevant area for acquisition and storage of different learning tasks. MF-CA3 pathway exhibits a form of LTP characterized by a slow initial increase in the EPSP slope that is independent of NMDA receptors activation. Our previous studies show that application of high frequency stimulation sufficient to elicit MF-CA3 LTP produces structural reorganization, in a manner independent of LTP induction, at the stratum oriens of hippocampal CA3 area 7days after stimulation. However, the molecular mechanisms that underlie the maintenance of MF-CA3 LTP as well as the concomitant structural reorganization in this area remain to be elucidated. Here we show that acute microinfusion of myr-CaMKIINtide, a noncompetitive inhibitor of CaMKII, in the hippocampal CA3 area of adult rats during the late-phase of in vivo MF-CA3 LTP blocked its maintenance and prevented the accompanying morphological reorganization in CA3 area. These findings support the idea that CaMKII is a key molecular substrate for the long-term hippocampal synaptic plasticity maintenance.

Sensorimotor Intervention Recovers Noradrenaline Content in the Dentate Gyrus of Cortical Injured Rats.

Nowadays, a consensus has been reached that designates the functional and structural reorganization of synapses as the primary mechanisms underlying the process of recovery from brain injury. We have reported that pontine noradrenaline (NA) is increased in animals after cortical ablation (CA). The aim of the present study was to explore the noradrenergic and morphological response after sensorimotor intervention (SMI) in rats injured in the motor cortex. We used male Wistar adult rats allocated in four conditions: sham-operated, injured by cortical ablation, sham-operated with SMI and injured by cortical ablation with SMI. Motor and somatosensory performance was evaluated prior to and 20 days after surgery. During the intervening period, a 15-session, SMI program was implemented. Subsequently, total NA analysis in the pons and dentate gyrus (DG) was performed. All groups underwent histological analysis. Our results showed that NA content in the DG was reduced in the injured group versus control, and this reduction was reverted in the injured group that underwent SMI. Moreover, injured rats showed reduction in the number of granule cells in the DG and decreased dentate granule cell layer thickness. Notably, after SMI, the loss of granule cells was reverted. Locus coeruleus showed turgid cells in the injured rats. These results suggest that SMI elicits biochemical and structural modifications in the hippocampus that could reorganize the system and lead the recovery process, modulating structural and functional plasticity.

Sensorimotor recovery from cortical injury is accompanied by changes on norepinephrine and serotonin levels in the dentate gyrus and pons.

Monoamines such as norepinephrine (NE) and serotonin (5-HT) have shown to play an important role in motor recovery after brain injury. The effects elicited by these neurotransmitters have been reported as distal from the area directly affected. Remote changes may take place over minutes to weeks and play an important role in post-stroke recovery. However, the mechanisms involved in spontaneous recovery have not been thoroughly delineated. Therefore, we determined the NE and 5-HT content, in the pons and hippocampal dentate gyrus (DG) as well as motor deficit and spontaneous activity in rats after 3, 10 and 20 days cortical iron injection. Three days post-lesion the pontine NE content diminished, this effect was accompanied by deficient spontaneous activity and impaired sensorimotor evaluation. Ten and twenty days after lesion the NE levels were similar to those of control group, and animals also showed behavioral recovery. Monoamines content on DG 3 days post-lesion showed no differences as compared to controls. Interestingly, ten and twenty days after cortical injury, animals showed increased NE and 5-HT. These results suggest that behavioral recovery after brain damage involve changes on monoamines levels on DG, an important structure to plastic processes. In addition, the results herein support evidence to propose these neurotransmitters as key molecules to functional recovery in the central nervous system.

PKMζ inhibition prevents the metaplastic change induced by conditioned taste aversion on insular cortex long-term potentiation in vivo.

The activity history of a given neuron or pathway has been suggested to influence its future responses to synaptic inputs. In particular, training in several learning tasks produces a metaplastic change, that is, a change in the ability to induce subsequent synaptic plasticity. Experimental evidence shows that the maintenance of long term memory and long-term potentiation (LTP) requires the persistent action of the atypical protein kinase Cisoform, protein kinase M ζ (PKM ζ ). Recent work has demonstrated that the inactivation of PKM ζ in the insular cortex (IC) abolishes conditioned taste aversion (CTA) long term memory. Our previous studies in the IC have demonstrated that the induction of LTP in the basolateral amygdaloid nucleus (Bla)-IC projection previous to CTA training enhances the retention of this task. Moreover, recently, we have observed that CTA training blocks the subsequent induction of LTP in the Bla-IC projection. The aim of the present study was to investigate the participation of PKM ζon the CTA-dependent modification of the ability to induce subsequent LTP in the Bla-IC projection in vivo . Thus, we have delivered high-frequency stimulation in the Bla-IC projection in order to induce in vivo IC-LTP in the rats that underwent or did not have an impairment of CTA retention due to the intracortical administration of the selective PKM ζ pseudosubstrate inhibitory peptide, ZIP. Our results show that the microinfusion of ZIP into the IC of the behaving rats impairs long-term memory of CTA and prevents its effects on IC-LTP. These results indicate that PKM ζ is a key component of the cellular mechanisms necessary for the persistence of lasting memory traces as well as for those underlying metaplastic changes in neocortex, contributing to the persistence of aversive memories.