In an earlier paper an account was given of the preparation and some of the properties of a neurologically isolated slab of cerebral cortex, isolated in such a way that its blood supply was the only remaining connexion with the rest of the animal (Burns, 1949(Burns, , 1950. In these experiments isolation produced a disappearance of the 'spontaneous' activity found in the lightly anaesthetized brain, although the cells within the isolated area had not apparently been injured by the surgical operation, for they would still respond to electrical stimulation applied through electrodes on the brain's surface. All these earlier experiments, however, were made with preparations in cats under light chloralose anaesthesia, and it seemed possible to ascribe the inactivity of the isolated cortex to the anaesthetic used. It was therefore necessary to extend these experiments to the unanaesthetized animal. Fortunately, it proved possible to decerebrate cats in such a way that a part of one cerebral hemisphere remained in the cranial cavity, with all its nervous connexions cut but with undisturbed blood supply. The experiments reported have all been carried out with such preparations. METHODThe cats used weighed between 2-5 and 3 kg. A large cat has the advantage that it provides a greater surface area of accessible cerebral cortex, but has the disadvantage that haemorrhage during the operation is hard to control. The cats were anaesthetized with ethyl ether, and after the insertion of a tracheal tube the common carotid arteries were exposed. Because the isolated cortex was always prepared from the left cerebral hemisphere, the right common carotid was invariably tied off, while a thread was passed round the remaining carotid so that it could be easily found later on. The head of the animal was placed in a Czermak holder and clamped with the vertex upward and above the body of the cat. The right temporal muscle was reflected from the skull and the bone trephined and cut away so as to expose as much of the right hemisphere as possible; the opening in the skull was carried to within 3 mm. of the mid-line. The dura-mater was opened and cut away, and diathermy was then used to seal off, close to the cut margin of the skull, all the blood vessels supplying and draining the surface of the right hemisphere. At this stage of the operation the left common carotid was clamped, and the clamp was left on until the preparation was finished. A sharp knife was used to cut round the ring of cortex which had been hardened by diathermy; the greater part of the right hemisphere of the brain could then be removed by suction

Decamethonium was first investigated because, like D-tubocurarine, it caused neuromuscular block. It was shown, however, that the action of decamethonium was not only unlike that of curare but, in many important respects, was similar to that of acetylcholine (Paton & Zaimis, 1949; Buttle & Zaimis, 1949;Zaimis, 1951 Paton, unpublished). It was found, however, that the uptake of 24Na by frog sartorii from Ringer containing this isotope was not significantly greater in the presence of decamethonium iodide (0-01 %) than in its absence; further, the level of plasma 24Na in a cat which had received an injection of sodium chloride rich in this isotope, was altered by less than 1 % when a massive dose of decamethonium was injected which caused long-lasting neuromuscular block. Whether or not the argument on which these experiments were based was justified, the results made us suspect that the depolarizing effect of the drug was not uniform throughout the length of the muscle fibre, but was restricted to the region of the end-plate.Most of the experiments described in this paper have been on the cat's gracilis muscle, in which the end-plate region is conveniently localized. The results show that the depolarization due to decamethonium is confined to the membrane of the muscle fibre within 3-4 mm. ofthe end-plate. As a consequence of this local depolarization, electrical excitability around the end-plates falls,

No abstract

The responses to single electrical stimuli have been recorded from neurons in the brains of domestic chicks, by using an in vitro preparation consisting of a coronal slice taken from the forebrain. All slices were cut so that they contained the intermediate part of the medial hyperstriatum ventrale (IMHV). When such a slice is bathed in standard Krebs’ solution there is no evidence that the excitation produced by a single stimulus can be transmitted more than 1 mm either towards or away from the IMHV. The addition of bicuculline methiodide (more than 3 x 10 -6 M) to Krebs’ solution allows the excitation produced by a single stimulus to spread in all directions throughout the dorsal half of a coronal slice. At points remote (more than 1.5 mm) from the stimulated point, the magnitude of the spreading wave of excitation bears an all-or-nothing relation to the strength of stimulus used to excite it. This wave of excitation spreads from the excited point in all directions without attenuation at 0.9 + 0.017 (s. d.) m s -1 and consists of a prolonged burst of activity of the invaded neurons. The properties of coronal slices described above are also true of brain slices cut in a parasagittal plane. The spreading response to a single stimulus given in the presence of bicuculline, can be reduced in magnitude by the addition of AP-5 but it still spreads throughout the dorsal part of the slice at the same velocity. The response can be eliminated by the addition of kynurenic acid. The addition of curare to the bathing medium produces similar responses that spread in a similar fashion to those seen under bicuculline. These results suggest that the dorsal part of the forebrain of the domestic chick (in fact, the part derived from the embryological alar plate) contains a network of reciprocally connected local circuits. Transmission throughout the network is normally prevented by active inhibition.

This paper is concerned with the properties of the cat's cerebral cortex, treated as an isolated organ. The experiments have all been performed upon a layer composed of cortical grey matter with some of the underlying cortico-cortical fibres; this slab of tissue has been isolated from all connexion with either the central nervous system or the adjacent cortex, its blood supply being the only connexion with the rest of the animal.An attempt to determine the properties of isolated cortical tissue scarcely needs justification. Although the electrical activity seen in a preparation of this sort is, no doubt, far removed from the behaviou-r of the intact cortex, the properties of the isolated cortex, despite its diverse cell types and unknown intercellular connedions seem, in the present state of knowledge, to make an easier subject for research than does the behaviour of the intact brain. A short summary of the preliminary work with the preparation has already been reported (Burns, 1949).In reporting experiments carried out with a preparation of one type, it is easy to give the impression that the results obtained are applicable to all normal cortical tissue. I think it is important, therefore, to stress at the outset, the extremely limited nature of these experiments, all of which have been made on one small area of the cat's brain, using only one anaesthetic. METHODPreparation of the animal. All the cats used for these experiments received an intravenous injection of between 6 and 8 c.c./kg. of 1% chloralose while under initial ether anaesthesia. Adult animals weighing between 2 and 3-5 kg. were used. A tracheal cannula was inserted and loops of thread passed round both carotid arteries, in order that these might be easily found and clamped at any later stage of the operation. The cat was then turned with its ventral side on the operating table and the head was clamped in a Tschermak holder so that the vertex was some 20 cm. above the table.A skin incision was made in the mid-line, the temporal muscle was removed, and the skull was opened widely over the parietal and temporal surfaces of the dura-mater. Bleeding from the bone was reduced by clamping the appropriate common carotid, and, since finding that the clamping