Eduardo Eidelberg

Commissural projection to the dentate gyrus of the rat: evidence for feed-forward inhibition

We studied the response properties of interneurons of the dentate gyrus to stimulation of the commissural and perforant path inputs in urethane-anesthetized rats. Commissural stimulation inhibited the population spike evoked by concurrent stimulation of the perforant path. Stimulation thresholds of the interneurons were significantly lower than thresholds of the projection cells. The latency of 3 interneurons was shorter than the onset of the commissurally evoked field response. The results suggest that commissural fibers directly excite interneurons of the dentate gyrus, and the activity of the projection cells may be inhibited in a feed-forward manner.

Cerebral revascularization: common carotid to distal middle cerebral artery bypass

A right common carotid to distal middle cerebral artery bypass utilizing a saphenous vein graft was performed in a patient with episodic cerebral ischemia and reversible ischemic neurological deficit. The patient was relieved of his symptoms, and there was improved motor function in the left hand. Postoperative angiography revealed flow through the graft with excellent filling of the middle cerebral circulation, both retrograde and antegrade. This bypass procedure provided an immediate source of high volume blood flow and thereby provided immediate protection to the hemisphere.

Convergence of associational and commissural pathways on CA1 pyramidal cells of the rat hippocampus

The interaction of the commissural and associational systems to the CA1 region of the hippocampus was studied by recording extracellular field potentials and single unit activity in anesthetized rats. Associational fibers were activated by stimulating the stratum oriens of the CA1 region contralateral to recording: this stimulation activated the Schaffer collaterals by antidromically firing the pyramidal cells of the CA3 region on the side of recording. Commissural fibers were stimulated where they emerge from CA3 region. Both pathways excited both the basal and apical dendrites of the CA1 pyramidal cells. Commissural activation in stratum oriens was more efficient than associational path stimulation, while the opposite was seen in stratum radiatum. Responses elicited by associational path activation had their peak negativity 100--150 micrometers deeper in stratum radiatum than commissurally evoked responses. Both pathways were able to discharge pyramidal neurons. Both homonymous and heteronymous double pulse stimulation showed response facilitation. Simultaneous activation of both pathways induced a greater amplitude population spike than predicted by algebraic summation of the independent responses. Over 80% of the responsive CA1 cells could be fired by either pathway. These results show a considerable convergence of the commissural and associational pathways on CA1 pyramidal cells, although their predominant locus of excitation might be different.

Recovery of locomotor function after hemisection of the spinal cord in cats.

Cats were subjected to high lumbar hemisection of the spinal cord, on the right side. The initial paralysis of the right hindlimb became rapidly attenuated, and they walked again in one week or less after surgery. Minor residual deficits in gait remained, that may be permanent. Electrical stimulation of the bulbar reticulospinal formation showed residual crossed connections reaching the right lumbosacral cord via the left hemicord. Recovery from Brown-Séquards syndrome may be primarily due to the survival of low crossing descending projections to the spinal cord.

Cerebral revascularization: proximal external carotid to distal middle cerebral artery bypass with a synthetic tube graft.

A right proximal external carotid to distal middle cerebral artery bypass with a prosthetic tube graft was performed in a patient with intermittent cerebral ischemia due to middle cerebral artery stenosis. The patient was relieved of his symptoms, and he was neurologically normal 3 months after operation. Angiography 3 months postoperatively revealed flow through the graft and excellent filing of the middle cerebral circulation, both retrograde and antegrade. Early results suggest that an expanded polytetrafluoroethylene graft may be useful as a vascular conduit if suitable autogenous vessels are unavailable or have failed.

Behavioral and biochemical studies in monkeys made hemiparkinsonian by MPTP

Monkeys were required to press a lever rapidly for food, using either the right or the left hand. After stable baseline performance was established, MPTP (N-methyl-4-phenyl-2,3,5,6-tetrahydropyridine) was injected into the internal carotid of one side via a transfemoral catheter. The onset and time course of clinically severe, Parkinson-like symptoms were paralleled by a significant decrease of bar-pressing activity in the side contralateral to injection, while the forelimb in the unaffected side continued normal pressing. The unilaterality of effects was confirmed biochemically after sacrifice by a 95% drop in striatal dopamine (DA) levels of the injected compared to the uninjected hemisphere. The results show that hemiparkinsonism achieved by carotid injection is very stable; that normal motor behavior is maintained on the unaffected side and that goal-achieving strategies remain active, but that the affected side is unable to execute the task unless extrinsic levodopa is provided.

Effects of vestibulospinal lesions upon locomotor function in cats.

We used cats to study the consequences of bilateral ablation of the vestibular complex. The animals were very severely ataxic and incapable of head support for nearly two weeks. They gradually regained the ability to stand and to walk on a treadmill, at first with a marked reduction of the extensor components of stepping. After stabilization of recovery we could not obtain decompensation by dorsal hemisection. We conclude that the key consequence of these lesions is a temporary reduction in facilitatory drive to joint extensor muscle groups. Neither the corticospinal nor the rubrospinal tracts mediate the functional recovery observed.

Asymmetrical regional changes in energy metabolism of the central nervous system during walking.

Cats were injected with 2-deoxy- [14C]glucose (2-DG) while walking on a moving treadmill (experimental group), or sitting down on a stationary one (controls). After a 45-min equilibration period they were anesthetized, and their central nervous system (CNS) was removed rapidly and frozen. The tissue blocks were sectioned serially, and X-ray film exposed to the sections was used for quantitative densitometric analysis by Sokoloffs method. The utilization of glucose in a CNS region (LCMRg) was regarded as a measure of that regions energy metabolic activity and--indirectly--of its functional status. The walking cats exhibited significantly higher LCMRg in many but not all places of the neuraxis, compared to the control group. Also, LCMRg was symmetrical (side to side) in the control group but significantly asymmetrical in certain regions of the CNS in the experimental group. In all but one of these cats the LCMRg was greater in the right side of the gray matter of the cervical spinal cord and in the left visual and motor cortices and caudate nucleus. The finding that the motor cortex and other supraspinal regions become more active during walking suggests they may contribute to the control of locomotion and/or processing of related sensory data. The side to side asymmetry in the spinal cord and hemispheres during walking may be related to the phenomenon of lateral dominance.