Faculty Bibliography

1. Eleven kittens were deprived of vision in one eye until the age of between 5 and 14 weeks. Their eyes were then reverse-sutured, they were allowed to survive for a further 3-63 days, and their brains were then examined histologically. 2. Measurement of the cross-sectional area of cells in the lateral geniculate nucleus (LGN) showed that when the reversal of lid suture was performed at the age of 8 or 14 weeks, the mean cell size was smaller in laminae connected to the initially closed right eye than it was in other laminae. 3. When the reversal of lid suture took place at 5 or 6 weeks of age there was a reversal of interlaminar size differences: the initially deprived eye was then connected to laminae containing larger cells. Even within 3 days after the reversal of lid suture, most of the morphological effects of the initial suture had been abolished, and they were fully reversed within 12 days. 4. These results are compared with physiological changes in the visual cortex of these and similarly reared animals

1. Eighteen kittens were monocularly deprived of vision until the age of 5, 6 or 7 weeks. Their eyes were then reverse-sutured, and they were allowed to survive for 3-63 days, before physiological recording from area 17. 2. At the time the reverse-suture was performed, and immediately before the recording session, each kitten was tested separately in the two eyes to elicit five simple behavioural responses: optokinetic nystagmus, visual startle reaction, visually-guided paw placing, visual following and negotiation of a 'visual cliff'. 3. Following the opening of their initially deprived eye, all kittens appeared behaviourally blind when forced to use that eye; their performance through the initially open eye was then perfect on all tests. After the period of reversed lid-suture, however, their performance when using the initially deprived eye had improved, while that through the initially open eye deteriorated. This complementary improvement and deterioration was most rapid in kittens reverse-sutured at the age of 5 weeks, and less rapid when reverse-suturing was delayed until the age of 6 or 7 weeks. 4. Most of the kittens showed gross abnormalities of interocular alignment, and exhibited marked exotropia or esotropia. 5. The results of these tests were well correlated with the changes seen in cortical ocular dominance in the same animals

1. Twenty-three kittens were monocularly deprived of vision until the age of 4, 5, 6 or 7 weeks. Their deprived eyes were then opened, and their experienced eyes shut for a further 3-63 days. After this time physiological recordings were made in the visual cortex, area 17. Three control kittens, monocularly deprived for various periods, showed that at the time of reverse-suturing, few neurones could be influenced at all from the deprived eye. 2. Following reverse-suturing, the initially deprived eye regained control of cortical neurones. This switch of cortical ocular dominance was most rapid following reverse-suturing at the age of 4 weeks. Delaying the age of reverse-suturing reduced the rate and then the extent of the cortical ocular dominance changes. 3. The cortex of reverse-sutured kittens is divided into regions of cells dominated by one eye or the other. The relative sizes of these ocular dominance columns changed during reversed deprivation. The columns devoted to the initially deprived eye were very small in animals reverse-sutured for brief periods, but in animals that underwent longer periods of reversed deprivation, the columns driven by that eye were larger, while those devoted to the initially open eye were smaller. 4. Clear progressions of orientation columns across the cortex were apparent in many of the kittens, but, in contrast to the situation in normal or strabismic kittens, these sequences were disrupted at the borders of eye dominance columns: the cortical representations of orientation and ocular dominance were not independent. 5. Binocular units in these kittens were rather rare, but those that could be found often had dissimilar receptive field properties in the two eyes. Commonly, a cell would have a normal orientation selective receptive field in one eye, and an immature, unselective receptive field in the other. Cells that had orientation selective receptive fields in both eyes often had greatly differing orientation preferences in the two eyes, occasionally by nearly 90 degrees. 6. During the reversal of deprivation effects, the proportion of receptive fields exhibiting mature properties declined in the initially experienced eye, while the proportion increased in the initially deprived eye. Similarly, the average band width of orientation tuning of receptive fields in the initially deprived eye decreased, while that of receptive fields in the initially experienced eye increased. 7. One kitten was reverse-sutured twice, to demonstrate that cortical ocular dominance may be reversed a second time, even after one reversal of ocular dominance. 8. It is suggested that the sensitive period for cortical binocular development consists of two phases. In the first phase, all cortical neurones may be modified by experience, but the rate at which they may be modified decreases with age. In the second phase, an increasing number of cortical neurones becomes fixed in their properties, while those that remain modifiable are as modifiable as they were at the end of the first phase. 9..

A voltage clamp study of the presynaptic terminal in squid stellate ganglion has given quantitative results relating inward Ca2+ current to presynaptic membrane potential and postsynaptic response to inward Ca2+ current. The results indicate an S-shaped curve for the relationship between presynaptic potential and Ca2+ current and a linear relationship between Ca2+ current and postsynaptic potential. A similar S-shaped curve was found for the time-dependent properties of the Ca2+ conductance. Based on these results a mathematical model was developed which accounts for the experimental results in this and previously published papers by other authors. The model suggests that five subunits are involved in the Ca2+ gate and that the subunits change noncooperatively from an inactive to an active form upon membrane depolarization.

1. Cyclic AMP was introduced into ventricular muscle by a cut-end method. Trabecular bundles were pulled through a partition which divided the preparation into a loading region and a test region. The loading region was exposed to Ca-free solution, cut transversely near the partition, and then briefly exposed to cyclic AMP. The test region was continually superfused with Tyrode soltuion. 2. In preliminary experiments, cell-to-cell movements were studied in long bundles by including [3H]cyclic AMP in the loading procedure and allowing redistribution to occur. After suitable test periods, the bundles were removed, frozen, and sliced into segments. Segment radioactivity was plotted against distance and fitted by a theoretical diffusion curve. 3. The results showed longitudinal redistribution of label over many cell lengths with an average effective diffusivity of 8 X 10(-7) cm2/sec. This value did not appear sensitive to the length of the test period or to the presence of a phosphodiesterase inhibitor. 4. The metabolic fate of cyclic AMP introduced by the cut-end method was determined by chromatographic separation of [3H]cyclic AMP and its break-down products. Most of the cyclic AMP was metabolized, but the results suggest that cell-to-cell movements of cyclic AMP contribute to the overall redistribution of label. 5. The cut-end method was used to study the influence of cyclic AMP on the contractile activity in the test region. Introduction of cyclic AMP evoked a delayed increase in twitch tension, about 25% above control. The inotropic effect peaked about 50 min after the end of the loading procedure, a delay which seemed compatible with slow longitudinal diffusion into the test region. 6. In control experiments, the cut-end procedure was repeated with 5'AMP (the immediate break-down product of cyclic AMP) instead of cyclic AMP. No delayed increase in twitch tension was observed. 7. Introduction of dibutyryl cyclic AMP increased twitch amplitude by 130%, with a delayed time course similar to that found for cyclic AMP. 8. The results using the cut-end procedure provide new evidence that cyclic AMP helps mediate adrenergic effects on the strength of contraction

Electrophysiological evidence for the existence of dendritic spikes in the Purkinje cells of pigeon cerebellar cortex is presented. Intradendritic records indicate that the electroresponsive properties of the dendrites linger after voltage-dependent sodium and potassium conductances are reduced by superfusion of the cortex with Ringer's solution containing 20 mug/ml tetrodotoxin and 5 mM 3-aminopyridine. Dendritic spikes could be evoked, in the complete absence of activity from all cerebellar afferents and from the soma and axon of the Purkinje cells, by direct electrical activation of the surface of the cerebellar cortex or by intracellular injection of current via the recording electrode. The denritic electroresponsiveness was blocked by superfusion with 20 mM Mn2+ or Co2+. It is thus concluded that dendrites of Purkinje cells in birds are capable of generating calcium-dependent spikes. The possible role of such a calcium current in neuronal function is discussed.