Enrico Marani

The trigeminal system in man

1 Introduction.- 2 Material and Methods.- 3 Results.- 3.1 Normal Cyoarchitecture and Myeloarchitecture of the Trigeminal Nuclear Complex.- 3.1.1 The Motor Trigeminal Nucleus.- 3.1.2 The Principal Sensory Trigeminal Nucleus.- 3.1.3 The Intertrigeminal Nucleus.- 3.1.4 The Spinal Trigeminal Nucleus and Tract.- 3.1.4.1 Oral Spinal Trigeminal Nucleus.- 3.1.4.2 Interpolar Spinal Trigeminal Nucleus.- 3.1.4.3 Caudal Spinal Trigeminal Nucleus.- 3.1.4.4 The Spinal Trigeminal Tract, Its Interstitial Cells, and Cell Groups Lateral to It.- 3.1.5 The Mesencephalic Trigeminal Nucleus and Tract.- 3.1.6 Other Fiber Systems Associated with the Trigeminal Nuclear Complex.- 3.1.7 Nucleus Ovalis.- 3.2 Neuropathologic Cases.- 3.2.1 H 5151 Trigeminal System Lesion.- 3.2.2 H 5554 Trigeminal System Lesion and C1-C2 Rhizotomy.- 3.2.3 H 5017 Subtotal Motor Trigeminal Lesion.- 3.2.4 H 5517 Wallenbergs Syndrome.- 3.2.5 H 5797 Degeneration of the Trigeminal Nerve and Solitary Tract.- 3.2.6 H 5579 Wallenbergs Syndrome with Central Tegmental Tract and Pyramidal Tract Degeneration.- 3.2.7 H 6368 Partial lesion of the Trigeminal Nerve.- 3.2.8 H 6086 Corticofugal Fiber Degeneration.- 3.2.9 H 5671 Corticofugal, Striatal and Pallidal Degeneration.- 4 Discussion.- 4.1 Normal Structure of the Trigeminal Nuclei.- 4.1.1 Motor Trigeminal Nucleus.- 4.1.2 The Principal Sensory Nucleus.- 4.1.3 Supratrigeminal and Intertrigeminal Nuclei.- 4.1.4 Nucleus of the Spinal Tract.- 4.1.5 Cell Groups Close to the Spinal Trigeminal Nucleus.- 4.1.6 The Mesencephalic Trigeminal Nucleus.- 4.2 Discussion of the Trigeminal Pathways.- 4.2.1 Primary Afferents.- 4.2.1.1 Pain, Temperature and Tactile Receptors.- 4.2.1.2 Trigeminal Ganglion Neurons.- 4.2.1.3 Central Distribution of Trigeminal Primary Afferents.- 4.2.1.4 Extratrigeminal Primary Afferents.- 4.2.2 Other Afferent Connections.- 4.2.3 Efferent Connections of the Principal and Spinal Trigeminal Nuclei.- 4.2.3.1 Trigeminothalamocortical Connection.- 4.2.3.2 Other Efferent Connections.- 4.2.4 Connections of the Mesencephalic Trigeminal Nucleus.- 4.2.4.1 Primary Afferents.- 4.2.4.2 Other Afferent Connections.- 4.2.4.3 Central Connections of the Mesencephalic Trigeminal Nucleus.- 4.2.5 Connections of the Motor Trigeminal Nucleus.- 4.2.5.1 Afferent Connections.- 4.2.5.2 Efferent connections.- 5 Summary.- 5.1 Normal Structure of the Trigeminal Nuclei.- 5.2 Trigeminal Pathways.- Acknowledgements.- References.

The Effect of Learning on Bursting

We have studied the effect that learning a new stimulus-response (SR) relationship had within a neuronal network cultured on a multielectrode array. For training, we applied repetitive focal electrical stimulation delivered at a low rate (Lt1/s). Stimulation was withdrawn when a desired SR success ratio was achieved. It has been shown elsewhere, and we verified that this training algorithm, named conditional repetitive stimulation (CRS), can be used to strengthen an initially weak SR. So far, it remained unclear what the role of the rest of the network during learning was. We therefore studied the effect of CRS on spontaneously occurring network bursts. To this end, we made profiles of the firing rates within network bursts. We have earlier shown that these profiles change shape on a time base of several hours during spontaneous development. We show here that profiles of summed activity, called burst profiles, changed shape at an increased rate during CRS. This suggests that the whole network was involved in making the changes necessary to incorporate the desired SR relationship. However, a local (path-specific) component to learning was also found by analyzing profiles of single-electrode-activity phase profiles. Phase profiles that were not part of the SR relationship changed far less during CRS than the phase profiles of the electrodes that were part of the SR relationship. Finally, the manner in which phase profiles changed shape varied and could not be linked to the SR relationship.

Power spectral density analysis of physiological, rest and action tremor in Parkinson’s disease patients treated with deep brain stimulation

BackgroundObservation of the signals recorded from the extremities of Parkinson’s disease patients showing rest and/or action tremor reveal a distinct high power resonance peak in the frequency band corresponding to tremor. The aim of the study was to investigate, using quantitative measures, how clinically effective and less effective deep brain stimulation protocols redistribute movement power over the frequency bands associated with movement, pathological and physiological tremor, and whether normal physiological tremor may reappear during those periods that tremor is absent.MethodsThe power spectral density patterns of rest and action tremor were studied in 7 Parkinson’s disease patients treated with (bilateral) deep brain stimulation of the subthalamic nucleus. Two tests were carried out: 1) the patient was sitting at rest; 2) the patient performed a hand or foot tapping movement. Each test was repeated four times for each extremity with different stimulation settings applied during each repetition. Tremor intermittency was taken into account by classifying each 3-second window of the recorded angular velocity signals as a tremor or non-tremor window.ResultsThe distribution of power over the low frequency band (<3.5 Hz – voluntary movement), tremor band (3.5-7.5 Hz) and high frequency band (>7.5 Hz – normal physiological tremor) revealed that rest and action tremor show a similar power-frequency shift related to tremor absence and presence: when tremor is present most power is contained in the tremor frequency band; when tremor is absent lower frequencies dominate. Even under resting conditions a relatively large low frequency component became prominent, which seemed to compensate for tremor. Tremor absence did not result in the reappearance of normal physiological tremor.ConclusionParkinson’s disease patients continuously balance between tremor and tremor suppression or compensation expressed by power shifts between the low frequency band and the tremor frequency band during rest and voluntary motor actions. This balance shows that the pathological tremor is either on or off, with the latter state not resembling that of a healthy subject. Deep brain stimulation can reverse the balance thereby either switching tremor on or off.

Phase-dependent effects of stimuli locked to oscillatory activity in cultured cortical networks.

The archetypal activity pattern in cultures of dissociated neurons is spontaneous network-wide bursting. Bursts may interfere with controlled activation of synaptic plasticity, but can be suppressed by the application of stimuli at a sufficient rate. We sinusoidally modulated (4 Hz) the pulse rate of random background stimulation (RBS) and found that cultures were more active, burst less frequently, and expressed oscillatory activity. Next, we studied the effect of phase-locked tetani (four pulses, 200 s(-1)) on network activity. Tetani were applied to one electrode at the peak or trough of mRBS stimulation. We found that when tetani were applied at the peak of modulated RBS (mRBS), a significant potentiation of poststimulus histograms (PSTHs) occurred. Conversely, tetani applied at the trough resulted in a small but insignificant depression of PSTHs. In addition to PSTHs, electrode-specific firing rate profiles within spontaneous bursts before and after mRBS were analyzed. Here, significant changes in firing rate profiles were found only for stimulation at the peak of mRBS. Our study shows that rhythmic activity in culture is possible, and that the network responds differentially to strong stimuli depending on the phase at which they are delivered. This suggests that plasticity mechanisms may be differentially accessible in an oscillatory state.

Ionic Conductances in Cultured Pre-Infundibular Cells from the Hypothalamic Arcuate Region

The hypothalamic arcuate nucleus plays an important role in the gating system controlling the secretion of hypothalamic neurons. In order to analyze this gating mechanism, arcuate neurons from rats aged 21-22 days were cultured in a chemically defined medium. Addition of nerve growth factor to this medium increased the survival of the arcuate neurons. Neuron characterization was done with the Lucifer Yellow liposome technique and neurofilament immunocytochemistry. Electrophysiological information was obtained with the patch-clamp technique by whole-cell recordings and single-channel measurements. This qualitative inventory demonstrated the presence of at least five types of conductances: a sodium conductance, two potassium conductances, a calcium-activated conductance, presumably determined by potassium, and a leakage conductance.

Synchrony in Parkinson's disease: importance of intrinsic properties of the external globus pallidus

The mechanisms for the emergence and transmission of synchronized oscillations in Parkinsons disease, which are potentially causal to motor deficits, remain debated. Aside from the motor cortex and the subthalamic nucleus, the external globus pallidus (GPe) has been shown to be essential for the maintenance of these oscillations and plays a major role in sculpting neural network activity in the basal ganglia (BG). While neural activity of the healthy GPe shows almost no correlations between pairs of neurons, prominent synchronization in the β frequency band arises after dopamine depletion. Several studies have proposed that this shift is due to network interactions between the different BG nuclei, including the GPe. However, recent studies demonstrate an important role for the properties of neurons within the GPe. In this review, we will discuss these intrinsic GPe properties and review proposed mechanisms for activity decorrelation within the dopamine-intact GPe. Failure of the GPe to desynchronize correlated inputs can be a possible explanation for synchronization in the whole BG. Potential triggers of synchronization involve the enhancement of GPe-GPe inhibition and changes in ion channel function in GPe neurons.

2011 Special Issue: The pedunculopontine nucleus as an additional target for deep brain stimulation

The pedunculopontine nucleus has been suggested as a target for DBS. In this paper we propose a single compartment computational model for a PPN Type I cell and compare its dynamic behavior with experimental data. The model shows bursts after a period of hyperpolarization and spontaneous firing at 8 Hz. Bifurcation analysis of the single PPN cell shows bistability of fast and slow spiking solutions for a range of applied currents. A network model for STN, GPe and GPi produces basal ganglia output that is used as input for the PPN cell. The conductances for projections from the STN and the GPi to the PPN are determined from experimental data. The resulting behavior of the PPN cell is studied under normal and Parkinsonian conditions of the basal ganglia network. The effect of high frequency stimulation of the STN is considered as well as the effect of combined high frequency stimulation of the STN and the PPN at various frequencies. The relay properties of the PPN cell demonstrate that the combined high frequency stimulation of STN and low frequency (10 Hz, 25 Hz, 40 Hz) stimulation of PPN hardly improves the effect of exclusive STN stimulation. Moreover, PPN-DBS at low stimulation amplitude has a better effect than at higher stimulation amplitude. The effect of PPN output on the basal ganglia is investigated, in particular the effect of STN-DBS and/or PPN-DBS on the pathological firing pattern of STN and GPe cells. PPN-DBS eliminates the pathological firing pattern of STN and GPe cells, whereas STN-DBS and combined STN-DBS and PPN-DBS eliminate the pathological firing pattern only from STN cells.

Impedance Sensing for Monitoring Neuronal Coverage and Comparison With Microscopy

We investigated the applicability of electric impedance sensing (IS) to monitor the coverage of adhered dissociated neuronal cells on glass substrates with embedded electrodes. IS is a sensitive method for the quantification of changes in cell morphology and cell mobility, making it suitable to study aggregation kinetics. Various sizes of electrodes were compared for the real-time recording of the impedance of adhering cells, at eight frequencies (range: 5 Hz-20 kHz). The real part of the impedance showed to be most sensitive at frequencies of 10 and 20 kHz for the two largest electrodes (7850 and 125 600 μm2). Compared to simultaneous microscopic evaluation of cell coverage and cell spreading, IS shows more detail.

Neural networks on chemically patterned electrode arrays: towards a cultured probe

One type of future, improved neural interfaces is the cultured probe. It is a hybrid type of neural information transducer or prosthesis, for stimulation and/or recording of neural activity. It would consist of a micro-electrode array (MEA) on a planar substrate, each electrode being covered and surrounded by a local circularly confined network (island) of cultured neurons. The main purpose of the local networks is that they act as bio-friendly intermediates for collateral sprouts from the in vivo system, thus allowing for an effective and selective neuron electrode interface. As a secondary purpose, one may envisage future information processing applications of these intermediary networks. In this chapter, first, progress is shown on how substrates can be chemically modified to confine developing networks, cultured from dissociated rat cortex cells, to islands surrounding an electrode site. Additional coating of neurophobic, polyimide coated substrate by tri-block-copolymer coating enhances neurophilic-neurophobic adhesion contrast. Secondly, results are given on neuronal activity in patterned, unconnected and connected, circular island networks. For connected islands, the larger the island diameter (50, 100 or 150 microm), the more spontaneous activity is seen. Also, activity may show a very high degree of synchronization between two islands. For unconnected islands, activity may start at 22 days in vitro (DIV), which is two weeks later than in unpatterned networks.

Low Frequency Changes in Skin Surface Potentials by Skin Compression: Experimental Results and Theories

Human living skin generates an increase in the skin potential when compressed. This was measured on eight subjects with a matrix of nine Ag/AgCl electrodes. The potential increased with the pressure until it reached a maximum. When the pressure was increased stepwise, the response showed an overshoot at each step. Human cadaver skin did not show these potential increments. Neither did pads of collagen, paper tissue soaked in a KCl solution, nor layers of cultured keratinocytes. Three theories are described that may explain the origin of the measured skin potentials. The first is based on the piezoelectric characteristics of proteins in the skin. The second theory assumes that the skin is a charged membrane which generates a streaming potential when deformed. A third theory is proposed in which deformation of absorbed charged protein layers on structures in the skin change the alignment of Donnan potentials in the surrounding tissue.