Kazushige Watabe

Functional relationship between cat brainstem neurons during sleep and wakefulness.

Abstract The mode of interaction between so-called sleep-wakefulness centers in the cat lower brainstem was studied on 100 neurons. The magnitude of the spike response of a neuron in one center to electrical stimulation of another center was measured to calculate the index of responsiveness. During REM sleep the index was, in a great majority of cases, significantly smaller as compared with that during wakefulness and slow wave sleep. This reduction in the effectiveness of information transmission between different centers might be the basis of characteristic events occurring during REM sleep. From the behavior of the indexes during sleep-wakefulness cycle, it is suggested that different phases of sleep and wakefulness are realized by a complicated interplay of many sleep-wakefulness centers which would be communicating with one another not only through channels which are activated in a phase-specific manner, but also through a larger number of channels of which activity is modulated differentially during different phases.

The characteristics of the antidromic discharge of cat dorsal raphe neurons during repetitive activation

Slowly discharging neurons in the cat dorsal raphe could be classified into 3 types according to the behavior of antidromic spike discharges during repetitive stimulation of the medial forebrain bundle at 10 Hz. In the types 1 and 2, the latency of antidromic discharge was gradually prolonged to reach an asymptote, whereas no marked change occurred in the type 3. The type 2 neurons, which had a slower conduction velocity, showed a greater prolongation than the type 1 neurons. The maximum length of this prolongation was not significantly correlated with the initial latency. During 10 Hz stimulation some neurons showed repeatedly a conduction block after a sequence of initial decrease and later increase in latency. The spontaneous discharge was strongly suppressed during 10 Hz stimulation. During 1 Hz stimulation just after the cessation of 10 Hz stimulation, the prolonged antidromic latency was gradually restored in parallel with the recovery of the spontaneous discharge. Circumstantial evidences seem to be in favor of the idea that hyperpolarization of the axonal and somatic membranes is mainly responsible for the observed behavior of antidromic spikes of type 1 and 2 neurons.

Attenuation during paradoxical sleep of signals from tooth pulp to thalamus.

Quantitative evaluation of the response of thalamic neurons to tooth pulp stimulation was made in chronically prepared cats. The latency, duration and intensity of the responses were measured from the post-stimulus time histograms to estimate, from various aspects, the alteration in the responsiveness during different phases of sleep and wakefulness. During slow wave sleep, tooth pulp-evoked impulses tended to be transmitted to the thalamus in a similar or slightly higher intensity compared to wakefulness. In contrast, during paradoxical sleep the signals were often attenuated in many aspects. The results seem to be in favor of the idea that the impairment of signal to noise ratio in a variety of neuronal networks is one of the characteristics of paradoxical sleep.

Two types of rostroventral medulla neurons projecting to the trigeminal spinal nucleus as differentiated by the response to antidromic activation and the histological location

A population of neurons in the rostroventral medulla, which send their axons to the subnucleus oralis of the trigeminal spinal nucleus of rats, could be differentiated into two types on the basis of their location and the variability of antidromic latency during repetitive stimulation at 10 Hz. Type A neurons were mostly located in the raphe magnus and were activated antidromically with a relatively long latency, which gradually increased during repetitive stimulation. By contrast, type B neurons were located in the medial portion of the gigantocellular reticular nucleus, and responded with a relatively short, stable antidromic latency.

Antidromic discharge property of meso-accumbens dopaminergic VTA neurons in rats

Three groups of meso-accumbens (Acc) neurons in the ventral tegmental area were differentiated by their antidromic discharge property; dopaminergic type 1 (n = 10), non-dopaminergic type 2 (n = 2) and unclassified (n = 2) neurons. During repetitive activation at 10 Hz, the latency of the initial segment (IS) spike, which was often not followed by the somadendritic (SD) spike, was gradually prolonged in type 1, but not in type 2 and unclassified neurons. The latency prolongation of type 1 neurons was reduced to about a half of the normal in rats treated with kainic acid plus haloperidol, but only slightly when treated with kainic acid or picrotoxin. The rate of SD invasion tended to increase after all kinds of chemical treatment. Stimulation of the medial forebrain bundle in type 1 neurons gave responses comparable to Acc stimulation. It is suggested that the latency prolongation of IS spike is produced mainly by axonal mechanism. But additional somatic mechanisms such as dopaminergic self-inhibition and GABAergic and non-GABAergic inputs from the Acc would make some contribution, and at the same time produce frequent suppression of the antidromic SD spike.

Some dorsal raphe axons of the cat bifurcate to project into bilateral medial forebrain bundles

Seventy-one dorsal raphe (DR) neurons of the cat were antidromically activated by electrical stimulation of the medial forebrain bundle (MFB). It was found that not a small number of DR neurons send their axons contralaterally. Seven out of 67 DR neurons (10.4%) responded to stimulation of both sides of MFB. Positive collision test for the bilaterally evoked responses indicates that single axons of these DR neurons bifurcate to innervate bilateral forebrain structures.