Faculty Bibliography

The dynamic organization of the olivocerebellar afferent input to Purkinje cells was examined in rat cerebellar cortex. The distribution of synchronous Purkinje cell complex spike activity was characterized, bilaterally, utilizing multiple electrode recordings in crus IIa folium under ketamine anaesthesia. The results confirmed the existence of rostrocaudal complex spike isochronicity bands with a mediolateral width of 500 microm. For a given band, no finer spatial submicrostructures could be discerned at a first-order approximation (two-dimensional projection). Closer analysis determined that isochronicity between bands is not continuous in space but demonstrates discrete discontinuities at the mediolateral boundaries. Principal component multivariate analysis revealed that the first principal component of the spatio-temporal variance is synchronicity along the rostrocaudal band with a decreased level of coupling in the mediolateral direction at the band boundary. Furthermore, this discrete banding isochronicity is organized by the distribution of feedback inhibition from the cerebellar nuclei on to the inferior olive nucleus. The usual multiple band structure can be dynamically altered to a single wide-band dynamic architecture, or to other patterns of activity, as may be required by movement coordination

Historically different states of awareness have been correlated with coherent oscillatory neural activity at different frequencies. These brain rhythms are usually measured noninvasively with either EEG or MEG technology. However, few studies have attempted to localize the sources of the electromagnetic fields underlying these cognitive states. In this study, an anatomically constrained iterative source imaging method was used to characterize the current density distribution of the ganerators of the different brain rhythms. Magnetic activity was recorded with a 148-channel neuromagnetometer array (4D Neuroimaging) while subjects rested with eyes closed during wakefulness (WA), slow wave sleep (SWS), or REM sleep (RS). EKG and EOGs were recorded and used for artifact removal based on QRS modeling and ICA. Spectral analysis was performed using multitaper methods. The cross spectral density matrices, their SVD, and the coherence across frequencies were computed. Sources were analyzed for different frequencies. Spectral analysis indicates that during both WA and RS there is enhanced power in the alpha, beta, and gamma bands. During SWS there is enhanced delta, theta, and 14Hz sleep spindles, while beta and gamma are reduced. Source analysis indicates that alpha currents are distributed in occipital and parietal cortex during WA and RS, but shifts to the frontal lobe during SWS. Beta and gamma sources showed more complex distributions throughout different cortical regions. Sources of delta and theta activity were more widely distributed throughout the temporal, frontal, and occipital cortex. Slow delta was more frontal. Sleep spindles were localized to parietal cortex

Purkinje cell LTD was evoked in mouse cerebellar slices by pairing either a) direct b) glutamate iontophoresis, or c) climbing fiber activation with parallel fiber stimulation. Patch clamping was implemented at the soma which supported parallel fiber evoked synaptic current measurements as well as direct activation of the Purkinje cell. The stimulus paradigm consisted of low frequency pairing (1Hz) for a period of 5 minutes of the either of the three (a, b or c) activation modes with parallel fiber stimuli. Parallel fiber Purkinje cell LTD was evoked by all three paring paradigms and the depression was followed for periods of over one hour. Slice pre-incubation with the neuroprotection agent T-588 (Toyama Chemical Co., Ltd.), at concentration less than 1 microM, produced a total suppression of LTD under similar conditions as describe above. Two-photon microscopy determination of calcium concentration profiles in Purkinje cells demonstrated a good correlation between I Ca2+ increase and LTD. This calcium increase was prevented in the presence of T-588. The results suggest that LTD is triggered to prevent cellular damage due to excessive intracellular calcium concentration. Thus, the presence of T-588 obviates the necessity of triggering LTD neuroprotection. These results are particularly significant, as T-588 while preventing LTD in vitro, does not impair motor learning in pretreated animals

T-588 is a promising drug for the treatment of Alzheimer's disease, undergoing phase II clinical trials in Japan as well as UK. We investigated the neuroprotective effect of T-588 on potential cell damage produced by high-potassium concentration or glutamate addition to the culture medium in cerebellum organotypic slice cultures. Cerebellum slices were prepared from 9-12 days old rats and cultured on microporous membranes in horse serum medium for an initial period of a week. Slices were then exposed to a 30 mM potassium medium for 7 days in the presence or absence of T-588 at several concentrations. After this treatment, organotypic cultures were immunostained for Calbindin D-28K, a marker for Purkinje neurons, to evaluate morphological changes. High potassium treatment, without T-588, demonstrated poor survival of Purkinje cells and clearly altered dendritic trees, compared to non-treated explants. Indeed T-588 prevented the decrease of Purkinje cell number in a concentration dependent manner at less than 1 microM, which is the equivalent level to the clinical studies. T-588 showed similar protective effect against glutamate receptor agonists (1-3 mM glutamate for 48 hr exposure) induced Purkinje cell damage. These findings indicate that T-588 could be a significant therapeutic agent in the treatment of neurodegenerative disorders

The interaction between cortical input frequency and intrinsic thalamic neuron (TN) properties were investigated using intracellular recordings from mice TNs in thalamocortical (TC) slices. Excitatory postsynaptic potentials (EPSPs) of corticothalamic (CT) origin were recorded at TN membrane potentials (V-m) held, by current clamp means, between -59 and -55 mV to avoid low-threshold calcium currents (I-T) activation. EPSPs elicited in ventrobasal neurons (n = 25) by stimulation in the internal capsule showed constant latency, relatively fast rise time (2.9 +/- 0.56 ms) and short duration (26.6 +/- 9.11 ms). EPSPs evoked by threshold stimulation (n = 10) showed similar characteristics (mean rise time, 2.74 +/- 0.42 ms; mean duration, 30 +/- 8.00 ms). The time course of CT synaptic facilitation was determined using pairs of stimuli. Paired-pulse facilitation (PPF) of CT EPSPs peaked at 25-30 ms stimulus intervals and decayed exponentially with an average time constant of 130 ms (n = 50). Application of the NMDA receptor blocker APV (25 mu M, n = 4) did not modify PPF for any interstimulus interval studied but suppressed frequency facilitation evoked by trains of CT stimuli. We compared the number of spikes per stimulus (F-s) evoked in TNs by repetitive CT stimulation over a range of frequencies at different V-m. At hyperpolarized V-m (below -65 mV) and frequencies of stimulation >= 10 Hz, F-s decreased along the train while at depolarized V-m (above -59 mV) F-s increased along the train. Decremental patterns resulted from the activation of I-T while facilitatory patterns emerged from superposition of synaptic and intrinsic mechanisms. At hyperpolarized V-m steady-state F-s was maximal for frequencies <= 2 Hz, intermediate for frequencies between 2 and 10 Hz and zero at >= 10 Hz. At depolarized V-m, steady-state F-s increased with increasing frequencies (from 1 to 40 Hz).We conclude that the CT-TN junctions are tuned to establish stable thalamocortical resonant dynamics

Thalamocortical dysrhythmias (TCD) may underlie a variety of neurological and neuropsychiatric symptoms. In TCD, pathological theta-range (4-8 Hz) activity from thalamic deafferentation or disfacilitation has been hypothesized to trigger thalamocortical (TC) domains to function at low frequency, surrounded by areas of gamma-band activity. This intersection has been viewed as creating an 'edge effect' which underlies some positive symptoms. TC properties could also maintain and distribute TCD. Spontaneous neuromagnetic activity was recorded from patients suffering from refractory obsessive-compulsive disorder (OCD) and/or major depression (MD) and from healthy controls. Recordings were performed with a whole-head magnetoencephalogram (MEG) (4-D Neuroimaging) in a shielded room. Activity was recorded for 5-10 min while subjects rested with eyes closed. Spectral analysis using a multitaper technique and cross-correlations between spectral amplitudes were calculated using Matlab (Mathworks, Inc.) and in-house software on a Linux cluster computer system. Power spectra from control recordings demonstrated typical alpha-rhythms, while spectra from OCD and MD subjects showed robust activity in the theta range and increased total power compared to controls. Coherence patterns from controls displayed activation of discrete frequency ranges, while patterns from OCD and MD subjects showed high coherence over a wide range of frequencies. This may reflect theta-range recursive corticothalamic activation