György Székely

Hyaluronan accumulates around differentiating neurons in spinal cord of chicken embryos.

One major component of the extracellular matrix is hyaluronan (HA) which is thought to play a crucial role in the development of different organs including the central nervous system (CNS). HA is bound by specific receptors, CD44 and RHAMM, depending on cell types of CNS. However, data are lacking on the relation of HA to different cell populations in developing CNS. To provide new data about the co-localization of HA with the various cellular structures of the developing spinal cord, we studied the distribution pattern of hyaluronan in chicken embryos at Hamburger-Hamilton (HH) stages 8-39. A biotinylated HA-binding complex was used in combination with immunohistochemistry for proliferating and differentiating neurons. The intensity of the HA signal was determined by digital densitometry from histological sections. We found three mediolaterally oriented layers in the HA distribution pattern in stage HH23: (1) a moderate HA signal was detected in the ventricular zone; (2) strong HA accumulation was measured around Lim1,2-expressing cells (differentiating neurons) and early MNR2-expressing neurons (early motoneurons), corresponding to the intermediate zone; (3) a strong pericellular HA reaction was found around the neurons of the marginal zone. Interestingly, the peripheral nerves did not show HA signals. These findings suggest a crucial role of HA during neuronal development. We propose that HA may be involved in cell migration and axonal growth in the developing spinal cord.

Extracellular matrix molecules and their possible roles in the regeneration of frog nervous system.

Recent biochemical and histochemical analyses explored different components of the extracellular matrix (ECM) in the nervous system, and either permissive or non-permissive roles in neuronal development and regeneration were suggested. The aim of this study was to detect the distribution pattern of a few of these molecules in the nervous system of intact frogs and during nerve regeneration. The hyaluronan (HA) and tenascin C reactions were negative in the peripheral nerves, but appeared in their entry zones. In the CNS, different populations of neurons were surrounded with HA and tenascin C-positive material, forming a perineuronal net (PN). The phosphacan reaction was weakly positive in the PNS, and a moderate intensity was detected in the entry zone and in the PN. Laminin and fibronectin immunoreactivity was strong in the PNS, but laminin could not be detected in the CNS. In animals with cut and regenerating vestibulocochlear nerve, the distribution of the ECM molecules in the CNS and PNS characteristically changed from that of the normal pattern. Our results showed a non-homogenous distribution of ECM components in the frog nervous system that could be associated with their different roles in physiological and pathological processes.

Dendrodendritic and dendrosomatic contacts between oculomotor and trochlear motoneurons of the frog, Rana esculenta

Gaze fixation requires very fast movements of the eye during body displacement. The morphological and physiological background of the very fine and continuous tuning of gaze fixation is not yet fully understood. In a previous study we have shown that the dendrites of oculomotor neurons form bundles which invade the trochlear nucleus, and vice versa, trochlear dendritic bundles invade the oculomotor nucleus. Earlier physiological observations demonstrating electrotonic coupling between dendrites of spinal motoneurons in the frog suggest a similar mechanism between the oculomotor and trochlear motoneurons. We studied a possible morphological basis of gaze fixation. The experiments were carried out on common water frogs, Rana esculenta. The trochlear and oculomotor nerves were cut, and their proximal stumps were labeled simultaneously with different retrograde fluorescent tracers. Using confocal laser scanning microscope we detected a large number of close contacts in both nuclei, the majority of them were dendrodendritic apposition. The distance between the adjacent profiles suggested close membrane appositions without intercalating glial or neuronal elements. At the ultrastructural level, the dendrodendritic and dendrosomatic contacts did not show any morphological specialization; the long membrane appositions may provide ephaptic interactions between the neighboring profiles. This electrotonic coupling between the oculomotor and trochlear nerve motoneurons may promote the co-activation of the muscles responsible for vertical eye movements.

Organization of last-order premotor interneurons related to the protraction of tongue in the frog, Rana esculenta.

Moving visual stimuli elicit a sequence of coordinated activity of muscles including tongue protraction. Morphological and physiological studies fail to reveal any direct tectal projections to hypoglossal motoneurons suggesting that the last-order premotor interneurons (LOPI) are the direct recipients of neural activities generated in the optic tectum. The aim of this study is to analyze the topographical organization of the last-order premotor interneurons related to protractor muscles of the tongue. In Rana esculenta, biotinylated dextran amine (BDA) was injected by iontophoresis into the subnucleus of the hypoglossal nerve containing the motoneurons of protractor muscles of the tongue. For visualizing BDA, sections were treated with avidin-biotin complex and a nickel-enhanced DAB chromogen reaction. The position of labeled neurons was reconstructed with a Neurolucida equipment. Morphologically heterogeneous populations of neurons were detected bilaterally, the majority of them were distributed ipsilateral to the site of injection and extended 1200 microm in rostral and 500 microm in caudal directions. Labeled neurons were found in the rhombencephalic reticular formation, the vestibular nuclei, the nucleus prepositus hypoglossi, the nucleus of solitary tract, the spinal nucleus of trigeminal nerve and the dorsal column nuclei. Our results indicate that the majority of last-order premotor interneurons related to protractor muscles of the tongue are located in the reticular formation of the brainstem. Since this area also receives a significant input from the vestibular system and from proprioceptive fibers, the last-order premotor interneurons presented here may be the target of convergence of sensory modalities involved in prey-catching behavior.

The effect of vestibular nerve section on the expression of the hyaluronan in the frog, Rana esculenta

Following postganglionic lesion of the eighth cranial nerve, the changes in the expression of hyaluronan (HA), one of the extracellular matrix macromolecules, were examined in the medial (MVN) and lateral (LVN) vestibular nuclei and in the entry or transitional zone (TZ) of the nerve in the frog. HA was detected in different survival times by using a specific biotinylated hyaluronan-binding probe. HA expression was defined by the area-integrated optical density (AIOD), calculated from pixel intensities of digitally captured images. During the first postoperative days the perineuronal net (PN), a HA-rich area around the neurons, was not distinguishable from the surrounding neuropil in the MVN and LVN, characterized by a bilateral drop of AIOD specifically on the operated side. From postoperative day 14 onwards AIOD increased whilst the PN reorganized. In contrast, the AIOD wobbled up and down bilaterally without any trend in the TZ. Statistical analysis indicated that AIOD changes in the structures studied ran parallel bilaterally presumably because of the operation. Our results demonstrated for the first time that (1) the lesion of the eighth cranial nerve is accompanied by the modification of AIOD reflected HA expression in the MVN, LVN and TZ, (2) different tendencies exist in the time course of AIOD in the structures studied and (3) these tendencies are similar on the intact and operated sides. Our findings may suggest an area dependent molecular mechanism of HA in the restoration of vestibular function.

Somatosensory and Motor Evoked Potentials in Patients with Tumours in the Spinal Canal

Summary Motor and sensory evoked potentials were recorded in 27 patients with expanding spinal tumour. The patients were divided into 2 groups: I. tumours at the level of the spinal cord [18] and II. at the level of the cauda equina [9]. On the basis of the localization of the tumour, midline and lateral subgroups were distinguished. The latencies of motor evoked potentials were prolonged in most of the patients, even those without paresis, in both groups. The motor evoked potentials detected subclinical motor lesions in 7 patients. All patients but one manifested sensory deficits, which could not be shown with the somatosensory evoked potentials. Significantly more prolonged cortical motor latencies were found in most of the patients with a laterally located tumour on the tumour side than contralaterally, whereas in somatosensory evoked potentials this difference was not apparent. On the basis of these observations, we concluded that motor evoked potentials, 1. could more reliably detect the neural deficit than somatosensory evoked potentials; 2. could show the side where the tumour was located; 3. proved useful in the detection of subclinical motor lesions. The general conclusion may be drawn that this electrophysiological method can provide useful information for the surgeon.

Transtracheal electrical stimulation of the spinal cord for intraoperative monitoring of the motor pathway

Because of the suppressant effects of anesthetic drugs and muscle relaxants on motor responses elicited by either magnetic or electrical transcranial stimulation, intraoperative monitoring of the motor system, and especially monitoring of lower limb function, presents many difficulties.The upper part of the spinal cord was stimulated in 14 anesthetized and relaxed dogs with a cathode attached to the intratracheal tube and an anode fixed above the upper cervical spinous processes. Action potentials evoked by single and serial stimuli were recorded from the exposed right femoral nerve and quadriceps muscle Averaging was necessary for serial stimulations.Reproducible early and late responses to both single and serial stimulations were recorded during regular anesthesia. The origin of the different responses is discussed.Transtracheal stimulation of the spinal cord is easy to perform and the responses recorded from the peripheral nerve or limb muscle are well reproducible in regular anesthesia. The method seems to be appropriate for intraoperative monitoring of the thoracolumbar spine.