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An attempt to demonstrate subliminal ‘silent synapses’ in the visual cortex of deprived cats
77 This paper describes research on the effect of punishment on fornicotomized rats in two simple learning situations -- lever pressing and food reinforced approach in a straight runway. (1) Lever pressing: control rats displayed a relationship between food deprivation level and behaviour following punishment. The greater the deprivation, the more time spent near the bar and the shorter the latency of the next lever press. Rats with fornical lesions showed no consistent relationship between deprivation level and location in the Skinner box or latency of the next lever press following punishment. Their response latencies were similar to those of higher deprivation controls. These results suggest that fornicotomized rats can inhibit lever pressing as well as controls, and that the differences in behaviour which were observed arise from the failure of fornicotomized rats to show an approach-avoidance gradient relative to the place in the box in which they had been shocked. (2) Runway behaviour: rats were punished in different locations in a runway. Control rats hesitated in the start box of the runway no matter where they were shocked, even though they could n o t observe the runway cues in the presence of which they had been shocked. Rats with fornical lesions inhibited responding only when very near to cues in the presence of which they had been shocked. These results suggest that control rats responded in terms of their knowledge of spatial relations among objects and locations in the environment while rats with fornical lesions did not.
An attempt to demonstrate subliminal 'silent synapses' in the visual cortex of deprived cats
COLIN BLAKEMORE* and PETER HILLMAN (Physiological Laboratory, University of Cam bridge }
In normal cats the majority of neurones in the visual cortex can clearly be excited by visual stimulation of either eye: but a variety of developmental misadventures early in a kitten's life can lead to the loss of functional input from one eye or the other. Monocular deprivation, even for just a few days, causes virtually total silencing of the input from the deprived eye [3] ; the induction of an artificial strabismus leads to the establishment of two predominant populations of monocularly driven cells [1]. We have tried to determine whether these changes represent the complete loss of synaptic input from one eye or the other, or whether the synapses might still be present but merely reduced in strength. We employed a m e t h o d logically similar to that used by Merrill and Wall [2] in their work on subliminal input to cells in the dorsal horn of the spinal cord. We inserted concentric bipolar stimulating electrodes intraocularly, in
78
both eyes, and placed them on the optic discs, so that the t w o optic nerves could be independently stimulated electrically. Such electrodes do not interfere with natural visual stimulation of the retinae. Action potentials were recorded from cells in the visual cortex and their excitability for both natural and electrical stimulation was tested in each eye separately. Several cats monocularly deprived for long or short periods and one strabismic cat were studied. Fewer than half of all cells (29 o u t of 63) could be excited by electrical stimulation b u t of those that were, the relative excitability in the two eyes was very similar for visual and electrical stimulation. In particular, only two cells that were totally inexcitable b y visual stimulation of one of the eyes could be excited by electrical stimulation of the optic disc in that eye. We conclude that developmental changes in binocularity in cortical cells may reflect changes in the actual distribution of afferent terminals within the cortex. 1 Hubel, D.H. and Wiesel, T.N., Binocular interaction in striate cortex of kittens reared with artificial squint, J. Neurophysiol., 28 (1965) 1041--1059. 2 Merrill, E.G. and Wall, P.D., Factors forming the edge of a receptive field: the presence of relatively ineffective afferent terminals, J. Physiol. (Lond.), 226 (1972) 825--846. 3 Wiesel, T.N. and Hubel, D.H., Single-cell responses in striate cortex of kittens deprived of vision in one eye, J. Neurophysiol., 26 (1963) 1003--1017.
Are androgens converted into oestrogens before they exert their behaviourai influences via the brain?
PAUL F. BRAIN and NIGEL J. BOWDEN* (Department of Zoology, University College
of Swansea )
It has been suggested that some behavioural influences of androgens in male rodents are a consequence of peripheral sensory actions and that other behavioural influences are a consequence of central motivational actions. The former actions may involve androgenic conversion to 5a-dihydrotestosterone (DHT) and the latter neural aromatization to oestrogens [2]. Studies were undertaken in this laboratory to determine whether aromatization is involved in the influence of intramuscularly injected androgens on intermale fighting in castrated, 'aggressive' [1] mice. Findings,included: (a) steroids maintain, rather than induce, this motivation; (b) low (0.1--1/~g/day) doses of oestradioI benzoate are effective, whereas 50 gg/day of testosterone (T) has a comparable action; (c) 2 rag/day o f anti-androgen (cyproterone acetate, CA) did n o t block fighting in castrates implanted subcutaneously with 25 mg T, b u t 2 mg/day of anti-oestrogen (MER 25) did. However, with lower doses of injected T, CA m a y be the more effective; (d) 50 pg/day of D H T did, in one study, significantly maintain fighting; (e) 19-hydroxytestosterone
An attempt to demonstrate subliminal 'silent synapses' in the visual cortex of deprived cats
COLIN BLAKEMORE* and PETER HILLMAN (Physiological Laboratory, University of Cam bridge }
In normal cats the majority of neurones in the visual cortex can clearly be excited by visual stimulation of either eye: but a variety of developmental misadventures early in a kitten's life can lead to the loss of functional input from one eye or the other. Monocular deprivation, even for just a few days, causes virtually total silencing of the input from the deprived eye [3] ; the induction of an artificial strabismus leads to the establishment of two predominant populations of monocularly driven cells [1]. We have tried to determine whether these changes represent the complete loss of synaptic input from one eye or the other, or whether the synapses might still be present but merely reduced in strength. We employed a m e t h o d logically similar to that used by Merrill and Wall [2] in their work on subliminal input to cells in the dorsal horn of the spinal cord. We inserted concentric bipolar stimulating electrodes intraocularly, in
78
both eyes, and placed them on the optic discs, so that the t w o optic nerves could be independently stimulated electrically. Such electrodes do not interfere with natural visual stimulation of the retinae. Action potentials were recorded from cells in the visual cortex and their excitability for both natural and electrical stimulation was tested in each eye separately. Several cats monocularly deprived for long or short periods and one strabismic cat were studied. Fewer than half of all cells (29 o u t of 63) could be excited by electrical stimulation b u t of those that were, the relative excitability in the two eyes was very similar for visual and electrical stimulation. In particular, only two cells that were totally inexcitable b y visual stimulation of one of the eyes could be excited by electrical stimulation of the optic disc in that eye. We conclude that developmental changes in binocularity in cortical cells may reflect changes in the actual distribution of afferent terminals within the cortex. 1 Hubel, D.H. and Wiesel, T.N., Binocular interaction in striate cortex of kittens reared with artificial squint, J. Neurophysiol., 28 (1965) 1041--1059. 2 Merrill, E.G. and Wall, P.D., Factors forming the edge of a receptive field: the presence of relatively ineffective afferent terminals, J. Physiol. (Lond.), 226 (1972) 825--846. 3 Wiesel, T.N. and Hubel, D.H., Single-cell responses in striate cortex of kittens deprived of vision in one eye, J. Neurophysiol., 26 (1963) 1003--1017.
Are androgens converted into oestrogens before they exert their behaviourai influences via the brain?
PAUL F. BRAIN and NIGEL J. BOWDEN* (Department of Zoology, University College
of Swansea )
It has been suggested that some behavioural influences of androgens in male rodents are a consequence of peripheral sensory actions and that other behavioural influences are a consequence of central motivational actions. The former actions may involve androgenic conversion to 5a-dihydrotestosterone (DHT) and the latter neural aromatization to oestrogens [2]. Studies were undertaken in this laboratory to determine whether aromatization is involved in the influence of intramuscularly injected androgens on intermale fighting in castrated, 'aggressive' [1] mice. Findings,included: (a) steroids maintain, rather than induce, this motivation; (b) low (0.1--1/~g/day) doses of oestradioI benzoate are effective, whereas 50 gg/day of testosterone (T) has a comparable action; (c) 2 rag/day o f anti-androgen (cyproterone acetate, CA) did n o t block fighting in castrates implanted subcutaneously with 25 mg T, b u t 2 mg/day of anti-oestrogen (MER 25) did. However, with lower doses of injected T, CA m a y be the more effective; (d) 50 pg/day of D H T did, in one study, significantly maintain fighting; (e) 19-hydroxytestosterone