Closed-loop optogenetic control of the dynamics of neural activity in non-human primates.

Electrical neurostimulation is effective in the treatment of neurological disorders, but associated recording artefacts generally limit its applications to open-loop stimuli. Real-time and continuous closed-loop control of brain activity can, however, be achieved by pairing concurrent electrical recordings and optogenetics. Here we show that closed-loop optogenetic stimulation with excitatory opsins enables the precise manipulation of neural dynamics in brain slices from transgenic mice and in anaesthetized non-human primates. The approach generates oscillations in quiescent tissue, enhances or suppresses endogenous patterns in active tissue and modulates seizure-like bursts elicited by the convulsant 4-aminopyridine. A nonlinear model of the phase-dependent effects of optical stimulation reproduced the modulation of cycles of local-field potentials associated with seizure oscillations, as evidenced by the systematic changes in the variability and entropy of the phase-space trajectories of seizures, which correlated with changes in their duration and intensity. We also show that closed-loop optogenetic neurostimulation could be delivered using intracortical optrodes incorporating light-emitting diodes. Closed-loop optogenetic approaches may be translatable to therapeutic applications in humans.

Spatial characterization of interictal high frequency oscillations in epileptic neocortex.

Interictal high frequency oscillations (HFOs), in particular those with frequency components in excess of 200 Hz, have been proposed as important biomarkers of epileptic cortex as well as the genesis of seizures. We investigated the spatial extent, classification and distribution of HFOs using a dense 4 x 4 mm(2) two dimensional microelectrode array implanted in the neocortex of four patients undergoing epilepsy surgery. The majority (97%) of oscillations detected included fast ripples and were concentrated in relatively few recording sites. While most HFOs were limited to single channels, approximately 10% occurred on a larger spatial scale with simultaneous but morphologically distinct detections in multiple channels. Eighty per cent of these large-scale events were associated with interictal epileptiform discharges. We propose that large-scale HFOs, rather than the more frequent highly focal events, are the substrates of the HFOs detected by clinical depth electrodes. This feature was prominent in three patients but rarely seen in only one patient recorded outside epileptogenic cortex. Additionally, we found that HFOs were commonly associated with widespread interictal epileptiform discharges but not with locally generated 'microdischarges'. Our observations raise the possibility that, rather than being initiators of epileptiform activity, fast ripples may be markers of a secondary local response.

Transmitochondrial embryonic stem cells containing pathogenic mtDNA mutations are compromised in neuronal differentiation.

OBJECTIVES: Defects of the mitochondrial genome (mtDNA) cause a series of rare, mainly neurological disorders. In addition, they have been implicated in more common forms of movement disorders, dementia and the ageing process. In order to try to model neuronal dysfunction associated with mitochondrial disease, we have attempted to establish a series of transmitochondrial mouse embryonic stem cells harbouring pathogenic mtDNA mutations. MATERIALS AND METHODS: Transmitochondrial embryonic stem cell cybrids were generated by fusion of cytoplasts carrying a variety of mtDNA mutations, into embryonic stem cells that had been pretreated with rhodamine 6G, to prevent transmission of endogenous mtDNA. Cybrids were differentiated into neurons and assessed for efficiency of differentiation and electrophysiological function. RESULTS: Neuronal differentiation could occur, as indicated by expression of neuronal markers. Differentiation was impaired in embryonic stem cells carrying mtDNA mutations that caused severe biochemical deficiency. Electrophysiological tests showed evidence of synaptic activity in differentiated neurons carrying non-pathogenic mtDNA mutations or in those that caused a mild defect of respiratory activity. Again, however, neurons carrying mtDNA mutations that resulted in severe biochemical deficiency had marked reduction in post-synaptic events. CONCLUSIONS: Differentiated neurons carrying severely pathogenic mtDNA defects can provide a useful model for understanding how such mutations can cause neuronal dysfunction.

Neonatal monocular enucleation and the geniculo-cortical system in the golden hamster: shrinkage in dorsal lateral geniculate nucleus and area 17 and the effects on relay cell size and number.

We have examined the effects of neonatal monocular enucleation on the volume of the dorsal lateral geniculate nucleus (dLGN), the area of area 17, and the size and numbers of geniculate relay neurons identified by retrograde transport of HRP from cortex. Compared to values for normal animals, the only significant change contralateral to the remaining eye was an increase in relay cell radius. The effects ipsilateral to the remaining eye were more widespread: we found significant reductions in the volume of the dLGN (27% reduction), the area of striate cortex (22%), and the number (16%) and average soma radius (6%) of geniculate relay neurons. The relay neurons were also more densely packed, suggesting that other geniculate cell types were affected similarly, although this was not explicitly examined. These changes were not uniform throughout the nucleus, and as such, reflected the changes in retinal input. The greatest reduction in cell size occurred in the region of the ipsilateral dLGN receiving the most sparse retinal input subsequent to enucleation. Nor was the shrinkage of the dLGN uniform, being most apparent in the coronal plane especially along the axis orthogonal to the pia; there appeared to be little change in the anteroposterior extent. Shrinkage in area 17 ipsilateral to the remaining eye was the same (about 22%) whether it was defined by myelin staining or transneuronal transport of WGA-HRP. These results show that the transneuronal changes seen in the organization of visual cortex after early monocular enucleation in rodents are associated with only a moderate loss of geniculate relay cells.

Altered Topography in the Geniculo-cortical Projection of the Golden Hamster Following Neonatal Monocular Enucleation.

The consequence of neonatal eye removal on the adult organization of the geniculo-cortical pathway was studied anatomically in hamsters. Separate discrete injections of rhodamine- and green-fluorescent latex microspheres were made into the primary visual cortex of adult hamsters. The distribution of labelling in the dorsal lateral geniculate nucleus (dLGN) of normal animals was compared with that seen in animals monocularly enucleated at birth. In the normal animals, as expected, the projection has a precise topographic order. This is also true of the projection contralateral to the remaining eye in the enucleated animals. However, on the side ipsilateral to the remaining eye, the visual cortex appears to receive two convergent projections from the deafferented dLGN, one mirroring the other. A single injection made in very lateral cortex labels cells in two discrete regions of the dLGN. As the injection is made progressively more medial, the two patches of labelled cells converge. Eventually, the two patches are no longer discrete so that injections into central area 17 produce just one, extended patch of labelling. These results suggest that the altered retinal input to the dLGN may affect the subsequent development of ordered geniculo-cortical projections.