1. In chronically prepared, freely moving rats, electrical stimulation was applied to the angular bundle, and responses were recorded extracellularly at a variety of sites in the ipsilateral hippocampal formation. At each recording site the stimulus-response relationship was tested during four different behavioral states. These were slow-wave sleep (SWS), REM sleep ( REM), and also two waking behaviors consisting of the still, alert condition (labeled SAL), and voluntary movement (AW theta). 2. Two varieties of evoked responses were recorded: those due to the synchronous firing of neuronal action potentials (EAPs) and those produced by excitatory synaptic activity (ESPs). The overall pattern of monosynaptic, di-, and trisynaptic responses found was similar in the rat to that found by Andersen et al. (3-5) in cat and rabbit. 3. When the trisynaptic EAP was recorded in CA1, the threshold was similar during all four behavioral states. However, suprathreshold stimuli evoked a greater response during SWS than during the other three states. The trisynaptic ESP was also greater during SWS. 4. Disynaptically, EAPs were recorded in CA3. These were greater in magnitude during SWS than during SAL, but were intermediate in mean amplitude during AWtheta and REM. Response variability was much greater during AWtheta and REM. 5. The monosynaptic EAP recorded in the upper blade of the dentate gyrus (DG) exhibited the same behaviorally correlated properties found disynaptically in CA3. 6. The monosynaptic ESP recorded in the DG, in contrast to the EAP, was greater in magnitude during SAL than during SWS. 7. The primary afferent volley was also recorded at high gain in the DG. The amplitude of this was found to be dependent solely on stimulus intensity and not on behavioral state. 8. The results are interpreted as suggesting that the granule cell membranes in the DG are relatively hyperpolarized during SAL compared with SWS as the result of either tonic excitatory bombardment occurring during SWS or tonic inhibitory bombardment during SAL.

Electrical stimuli were applied to the angular bundle of the freely moving rat, and the neuronal responses were recorded ipsilaterally in the dentate gyrus and the CA1 field of the hippocampus. The number of neurons responding monosynaptically in the dentate gyrus was relatively small when the animal was alert and not moving but was much greater both during slow-wave sleep and during rapid eye movement sleep. In Ca1, however, the trisynaptic population response was considerably smaller during rapid eye movement sleep and when the animal was alert than during slow-wave sleep. These findings are interpreted in terms of a set of behaviorally dependent "neural gates". Measurement of the synaptic current at the dentate gyrus induced monosynaptically by stimulation of the angular bundle further suggests that the mechanism by which gating occurs at this level is either a tonic inhibitory synaptic influence exerted upon the granule cells during the alert state, a tonic excitatory influence during slow-wave sleep, or both.

No abstract

SUMMARY1. We have investigated the possibility that individual lateral vestibulospinal tract (LVST) axons branch so as to innervate more than one spinal cord level.2. LVST cells in Deiters' nucleus were activated antidromically by means of electrical stimulation applied through fine metal electrodes inserted into the spinal cord. Both by directly measuring the spread of effect of stimulus current, and from theoretical considerations (Appendix), we determined that in most cases an estimate of spread of effect of stimulus current was 10 #tm/,tA. From the magnitude of the threshold stimulus and from the location of the stimulus point we could often exclude the possibility that the stimulus was spreading to the LVST instead of activating local branches.3. Movable stimulating electrodes, or multi-electrode arrays placed in fixed position, were used to activate 115 LVST neurones antidromically by stimulation of local branches in the lower cervical or upper thoracic cord. Of these cells, 50 % were also fired antidromically by stimulation of the LVST at levels ranging from Li to L4 (Lc cells). The remaining cells were not activated by the lumbar stimulus (C cells). An additional group of cells was only fired by the lumbar tract stimulus (L cells). The distribution of locations of L, cells within Deiters' nucleus moreclosely resembles that of L cells than that of C cells. In addition the median conduction velocity of Lc cells is similar to that of L cells, but higher than that of C cells.5. Much of the information reaching the lower cervical level from neurones of the LVST is information that is also simultaneously being passed downward to the lumbar region. Such integration makes it possible for a single neurone to be used to co-ordinate widespread motor activity.C. ABZUG AND OTHERS 6. A theory is presented in a separate section (Appendix) to account for the spread of effect of stimulus current upon a myelinated axon submerged in an isotropic medium. The threshold for stimulation of a node by a nearby monopolar electrode is predicted to be proportional to the electrode-node spacing. The constant of proportionality is given in a closed form that depends on the electrical properties of both the neurone and the surrounding medium. The predictions of the theory are shown to be in good accord with the experimental results.

In one series of experiments, vestibular neurons that could be activated antidromically by stimulation of the contralateral medial reticular formation were studied with extracellular recording in cats under pentobarbital anesthesia. These neurons were found in all of the four main vestibular nuclei, but were less prevalent in dorsal Deiters' nucleus and in the central region of the superior vestibular nucleus than elsewhere. Regions of the pontine and medullary reticular formation from which neurons in different vestibular nuclei were activated corresponded to the pattern of vestibuloreticular projections described by neuroanatomists. 2. Latencies of antidromic responses to stimulation of the contralateral reticular formation ranged from 0.6 to over 3 ms, indicating a relatively slow transfer of activity from vestibular nuclei to reticular formation.

No abstract

No abstract

No abstract