Effect of median-nerve electrical stimulation on BOLD activity in acute ischemic stroke patients

OBJECTIVE

To investigate blood oxygenation level-dependent (BOLD) activation during somatosensory electrical stimulation of the median nerve in acute stroke patients and to determine its correlation with ischemic damage and clinical recovery over time.

METHODS

Fourteen acute stroke patients underwent functional magnetic resonance imaging (fMRI) during contralesional median-nerve electrical stimulation 12-48 h after stroke. Findings were then validated by diffusion tensor imaging (DTI) and motor evoked potential by transcranial magnetic stimulation (TMS).

RESULTS

Poor clinical recovery at three months was noted in four patients with no activation in the early days after stroke, whereas good clinical recovery was observed in eight patients with a normal activation pattern in the primary sensory motor area in the acute phase. In two patients BOLD activation correlated weakly with clinical recovery. Findings from TMS and DTI partially correlated with clinical recovery and functional scores.

CONCLUSIONS

Clinically relevant insights into the "functional reserve" of stroke patients gained with peripheral nerve stimulation during fMRI may carry prognostic value already in the acute period of a cerebrovascular accident.

SIGNIFICANCE

BOLD activation maps could provide insights into the functional organization of the residual systems and could contribute to medical decision making in neurological and rehabilitative treatment.

GABAergic neurons expressing p75 in rat substantia innominata and nucleus basalis

In vitro findings suggested a role for the p75 neurotrophin receptor in the maturation of GABAergic neurons residing in the basal forebrain (BF), a brain area known to have p75 expression only on cholinergic neurons. We document here the presence of GABAergic neurons which express p75 in the BF in vivo. Colocalization of p75 with the cholinergic marker choline-acetyltransferase (ChAT) and/or the GABAergic marker glutamic acid decarboxylase-67 (GAD67) was investigated in the BF at birth, at two weeks, and in adulthood. A subset of GAD67(+) neurons was p75(+) (p75(+)/GAD67(+)) but ChAT(-) in the substantia innominata and nucleus basalis magnocellularis at birth, whereas all p75(+)/GAD67(+) neurons were also ChAT(+) from two weeks onward. These phenotypic features suggest that a subpopulation of GABAergic neurons could be sensitive to neurotrophins during brain maturation. To unravel this issue, we then pursued a functional analysis by assessing p75 expression profile, and its modulation by nerve growth factor (NGF) or brain-derived neurotrophic factor (BDNF) in primary BF cell cultures. NGF increased p75 expression exclusively in cholinergic neurons, whereas BDNF induced p75 expression only in a subset of GABAergic neurons (p75(+)/GAD67(+)/ChAT(-)) through a p75- and tyrosine-kinase-dependent mechanism. The latter findings point to a selective role of BDNF in the induction of p75 expression in BF GABAergic neurons. Altogether these results confirm the role of neurotrophins in the developing and mature circuitry of GABAergic neurons in the BF regions.

Effect of a Static Magnetic Field (1.5T) on Brain Oscillatory Activities in Resting State Condition

The aim of the present study was to compare the EEG signal recorded outside and inside a 1.5T magnetic resonance (MR) scanner. The EEG was recorded in eyes open and eyes closed conditions using a digital recording MR-compatible system. To characterize how a static magnetic field induces changes in EEG signal, EEG data were analyzed using FFT frequency analysis. No significant difference between the alpha powers recorded outside and inside the magnetic field was observed in eyes closed conditions. However, in eyes open condition there was a significant increase in alpha power inside the magnet in comparison to the outside position. The changes in alpha power according to the eyes open/closed conditions could be inversely correlated to a subject's state of wakefulness and due to some physiological changes, rather than an effect of the magnetic field. This experiment suggests that subjects' state of wakefulness is of prime concern when performing functional MRI.

Continuous EEG-fMRI in Pre-Surgical Evaluation of a Patient with Symptomatic Seizures: Bold Activation Linked to Interictal Epileptic Discharges Caused by Cavernoma

We used continuous electroencephalography-functional magnetic resonance imaging (EEG-fMRI) to identify the linkage between the “epileptogenic” and the “irritative” area in a patient with symptomatic epilepsy (cavernoma, previously diagnosed and surgically treated), i.e. a patient with a well known “epileptogenic area”, and to increase the possibility of a non invasive pre-surgical evaluation of drug-resistant epilepsies. A compatible MRI system was used (EEG with 29 scalp electrodes and two electrodes for ECG and EMG) and signals were recorded with a 1.5 Tesla MRI scanner. After the recording session and MRI artifact removal, EEG data were analyzed offline and used as paradigms in fMRI study. Activation (EEG sequences with interictal slow-spiked-wave activity) and rest (sequences of normal EEG) conditions were compared to identify the potential resulting focal increase in BOLD signal and to consider if this is spatially linked to the interictal focus used as a paradigm and to the lesion. We noted an increase in the BOLD signal in the left neocortical temporal region, laterally and posteriorly to the poro-encephalic cavity (residual of cavernoma previously removed), that is around the “epileptogenic area”. In our study “epileptogenic” and “irritative” areas were connected with each other. Combined EEG-fMRI may become routine in clinical practice for a better identification of an irritative and lesional focus in patients with symptomatic drug-resistant epilepsy.

f-MRI in Epilepsy with Spike and Wave Activity Evoked by Eye Closure: Different Bold Activation in a Patient with Idiopathic Partial Epilepsy with Occipital Spikes and a Control Group

We performed functional magnetic resonance imaging (fMRI) in a 30-year-old man with idiopathic partial epilepsy with occipital spikes whose scalp EEG activity was characterized by persistent epileptiform discharges on eye closure, ceasing upon eye opening. We compared BOLD activation in the patient and in a control group of three normal volunteers. f-MRI showed that occipital cortex and frontal areas were activated in relation to eye movement in normal subjects during eye opening but not during eye closing. While persistent interictal spike and wave activity was present over the posterior and anterior scalp in the patient upon eye closing, f-MRI showed bilateral activation of the parietal and temporal regions. This fMRI study documents the activation of posterior and temporal areas related to continuous intercritical spikes evoked by eye closure, which are diffuse over the scalp. This activation was absent in the control group during eye closure.

Functional architecture of the major light-harvesting complex from higher plants

Light-harvesting complexes (Lhc) catalyse sunlight harvesting for photosynthesis as well as other essential functions, including photoprotection by quenching of harmful chlorophyll triplet states and prevention of photoinhibition by dissipation of excitation energy in excess. In addition, folding of Lhc proteins depends on the availability of both xanthophylls and carotenoids, thus preventing the potential formation of harmful chlorophyll-protein complexes lacking photoprotectors. We have used the mutation analysis in order to study the association of the different functions to three protein domains, each composed of a xanthophyll molecule and of neighbour chlorophylls a and b, within the major antenna complex of photosystem II, i.e. LHCII. We have found that the xanthophyll to chlorophyll energy transfer is a shared property of the whole pigment-protein complex, and occurs with similar efficiency in each of the three structural domains. Photoprotection by quenching of chlorophyll triplets is catalysed mainly by lutein bound to site L1, and occurs via energy transfer from chlorophylls A1 and B1. This domain is essential for pigment-induced protein folding. The domains L2 and N1 weakly influence either the protein stability or the photoprotection; however, replacement of xanthophyll species bound to these structural domains modulates the fluorescence quantum yield of LHCII, and suggests that non-radiative dissipation of excess energy can be regulated through allosteric modification of the protein structure by exchanging xanthophylls in these sites.