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Eccentricity dependent position differences between upper and lower layer receptive fields in cat striate cortex
70 INFLUENCE OF MICROIONTOPHORETICAPPLICATION OF PENTAGASTRINAND OXYTOCIN ON THE SINGLE UNIT ACTIVITY OF THE HIPPOCAMPDURING ALIMENTARY BEHAVIOUROF THE RABBITS BAJIC,M., LAZETIC, B., FILIPOVIC, D., STERIO, Dj., SUDAKOV, S.K. I n s t i t u t e of Physiology, Medical Faculty, Novi Sad, Yugoslavia and I n s t i t u t e of Physiology AMN SSR, Moscow, Russia The integrative processes at the neuronal level represent an especially acute problem. Therefore, we chose to undertake electrophysiological and neurochemical investigations of the neurons of the dorsal hippocamp in the rabbit. The experiments were performed on 18 adult, freely moving Chinc h i l l a rabbits, with the body weight ranging 2.5 - 3.0 kg. We used multibarrel glass microelectrodes for the registration of the extracellular impulsive a c t i v i t y of the neurons, and for the microiontophoretic application of pentagastrin and oxytocin. An experimental model of alimentary behaviour with a simultaneous application of a painful electroskin stimulation was used. The irregular impulsive a c t i v i t y of hippocampal neurons turned into bursting a c t i v i t y under the conditions of a l i mentary motivation. Painful electroskin stimulations and alimentary motivation made irregular impulsive a c t i v i t y of hippocampal neurons persist. The microiontophoretic application of oxytocin suppressed the impulsive neuronal a c t i v i t y under the conditions of alimentary motivation and feeding accompanied by painful elctroskin stimulation. The simultaneous microiontophoretic application of oxytocin and pentagastrin quickly restored the impulsive neuronal a c t i v i t y with a l l their previous characteristics.
ECCENTRICITY DEPENDENT POSITION DIFFERENCES BETWEEN UPPERAND LOWER LAYER RECEPTIVE FIELDS IN CAT STRIATE CORTEX
BAUER, R. Abteilung fur Vergleichende Neurobiologie der Universit~t Ulm, 7900 Ulm/Donau, F.R.G. Receptive f i e l d s (RFs) of cells have been measured in penetrations approximately perpendicular to the cortical layers, using the conventional method of plotting minimum response f i e l d s . Theywere situated in the lower visual f i e l d along the vertical meridian between 0 and 12 deg. of minus elevation and between -3 and +3 deg. of azimuth in agreement with the cortical coordinates of the penetrations. A superposition of a l l RFs in a given penetration as an aggregate f i e l d shows that in many cases the lower layer RFs are shifted in position against the upper layer RFs with different degrees of overlap. This effect is eccentricity dependent, being hardly measurable or non existent near the horizontal meridian. I t increases along the vertical meridian to about1.5 deg. of visual angle as center to center difference
at 10 deg. of eccentricity. The mean depth of these position
changes is 1.14 mm (s.d. = 0.22) which coincides f a i r l y well with a zone of transition from middle to lower layers. The data are discussed in relaticn to the magnification factor, mean RF size, aggregate RF overlap between neighbouring hypercolumns and in the context of available anatomical data in the
7! l i t e r a t u r e . A a whole they f u r t h e r favour the view that upper and lower layers in visual cortex function as r e l a t i v e autonomous subsystems. The e f f e c t of t h e i r v e r t i c a l interconnection remains speculative, but i t may r e s u l t as an i n t r i c a t e combination of a c t i v a t i o n and i n h i b i t i o n , providing functional contrast and s e p a r a b i l i t y for each subsystem.
PLASTICITY OF THE RECEPTIVE FIELD OF NEURONES OF AREA 18 OF THE CAT BISTI, S., CHALUPA, L . * , GALLI, L. and MAFFEI, L. I s t i t u t o di Neurofisiologia del CNR di Pisa, I t a l y *Department of Psychology, University of C a l i f o r n i a , CA 95616, U.S.A. Recently i t has been reported that the spatial frequency s e l e c t i v i t y of neurones of area 18 of the cat s h i f t s towards lower spatial frequencies with increasing the v e l o c i t y of the d r i f t i n g s t i mulus. Since the size of the c e l l receptive f i e l d is inversely related with the optimal spatial f r e quency to which the c e l l responds we have investigated whether t h i s s h i f t of optimal spatial frequency at increasing the stimulus v e l o c i t y corresponds to an increase in the receptive f i e l d size. We selected two gratings one of high spatial frequency d r i f t i n g at low v e l o c i t y and another one of low spatial frequency d r i f t i n g at high v e l o c i t y to which the c e l l gave comparable responses. The results show that the minimal masking of the c e l l receptive f i e l d which abolishes the response to the high frequency grating does not prevent the c e l l from responding to the low frequency grating. An i n t e r p r e t a t i o n of these r e s u l t s is that the size of the receptive f i e l d of neurones in area 18 depends upon the c h a r a c t e r i s t i c s of the stimulus.
MECHANISMS OF LONG-TERM POTENTIATION IN THE HIPPOCAMPUS BLISS, T.V.P. National I n s t i t u t e f o r Medical Research, M i l l H i l l ,
London NW7 IAA, United Kingdom
Hippocampal synapses display the property of synaptic p l a s t i c i t y to a s t r i k i n g degree; b r i e f t r a i n s of high-frequency s t i m u l i can cause a potentiation of synaptic e f f i c a c y which occurs within seconds and lasts for hours or days. The mechanism of long-term potentiation (LTP), as t h i s e f f e c t is c a l l e d , is not well understood, and even i t s locus of action is uncertain. In p r i n c i p l e , an enhancement of synaptic transmission could be achieved by presynaptic mechanisms leading to an increase in the amount of t r a n s m i t t e r released, by postsynaptic mechanisms such as changes in the number of receptors, or by a l t e r a t i o n s in synaptic morphology. Evidence has been adduced in support of each of these p o s s i b i l i t i e s .
I shall discuss experiments suggesting that potentiation is at least p a r t l y due
to a sustained increase in the release of t r a n s m i t t e r , and attempt to reconcile t h i s view with other evidence which points to a postsynaptic involvement in the induction of the e f f e c t .
ECCENTRICITY DEPENDENT POSITION DIFFERENCES BETWEEN UPPERAND LOWER LAYER RECEPTIVE FIELDS IN CAT STRIATE CORTEX
BAUER, R. Abteilung fur Vergleichende Neurobiologie der Universit~t Ulm, 7900 Ulm/Donau, F.R.G. Receptive f i e l d s (RFs) of cells have been measured in penetrations approximately perpendicular to the cortical layers, using the conventional method of plotting minimum response f i e l d s . Theywere situated in the lower visual f i e l d along the vertical meridian between 0 and 12 deg. of minus elevation and between -3 and +3 deg. of azimuth in agreement with the cortical coordinates of the penetrations. A superposition of a l l RFs in a given penetration as an aggregate f i e l d shows that in many cases the lower layer RFs are shifted in position against the upper layer RFs with different degrees of overlap. This effect is eccentricity dependent, being hardly measurable or non existent near the horizontal meridian. I t increases along the vertical meridian to about1.5 deg. of visual angle as center to center difference
at 10 deg. of eccentricity. The mean depth of these position
changes is 1.14 mm (s.d. = 0.22) which coincides f a i r l y well with a zone of transition from middle to lower layers. The data are discussed in relaticn to the magnification factor, mean RF size, aggregate RF overlap between neighbouring hypercolumns and in the context of available anatomical data in the
7! l i t e r a t u r e . A a whole they f u r t h e r favour the view that upper and lower layers in visual cortex function as r e l a t i v e autonomous subsystems. The e f f e c t of t h e i r v e r t i c a l interconnection remains speculative, but i t may r e s u l t as an i n t r i c a t e combination of a c t i v a t i o n and i n h i b i t i o n , providing functional contrast and s e p a r a b i l i t y for each subsystem.
PLASTICITY OF THE RECEPTIVE FIELD OF NEURONES OF AREA 18 OF THE CAT BISTI, S., CHALUPA, L . * , GALLI, L. and MAFFEI, L. I s t i t u t o di Neurofisiologia del CNR di Pisa, I t a l y *Department of Psychology, University of C a l i f o r n i a , CA 95616, U.S.A. Recently i t has been reported that the spatial frequency s e l e c t i v i t y of neurones of area 18 of the cat s h i f t s towards lower spatial frequencies with increasing the v e l o c i t y of the d r i f t i n g s t i mulus. Since the size of the c e l l receptive f i e l d is inversely related with the optimal spatial f r e quency to which the c e l l responds we have investigated whether t h i s s h i f t of optimal spatial frequency at increasing the stimulus v e l o c i t y corresponds to an increase in the receptive f i e l d size. We selected two gratings one of high spatial frequency d r i f t i n g at low v e l o c i t y and another one of low spatial frequency d r i f t i n g at high v e l o c i t y to which the c e l l gave comparable responses. The results show that the minimal masking of the c e l l receptive f i e l d which abolishes the response to the high frequency grating does not prevent the c e l l from responding to the low frequency grating. An i n t e r p r e t a t i o n of these r e s u l t s is that the size of the receptive f i e l d of neurones in area 18 depends upon the c h a r a c t e r i s t i c s of the stimulus.
MECHANISMS OF LONG-TERM POTENTIATION IN THE HIPPOCAMPUS BLISS, T.V.P. National I n s t i t u t e f o r Medical Research, M i l l H i l l ,
London NW7 IAA, United Kingdom
Hippocampal synapses display the property of synaptic p l a s t i c i t y to a s t r i k i n g degree; b r i e f t r a i n s of high-frequency s t i m u l i can cause a potentiation of synaptic e f f i c a c y which occurs within seconds and lasts for hours or days. The mechanism of long-term potentiation (LTP), as t h i s e f f e c t is c a l l e d , is not well understood, and even i t s locus of action is uncertain. In p r i n c i p l e , an enhancement of synaptic transmission could be achieved by presynaptic mechanisms leading to an increase in the amount of t r a n s m i t t e r released, by postsynaptic mechanisms such as changes in the number of receptors, or by a l t e r a t i o n s in synaptic morphology. Evidence has been adduced in support of each of these p o s s i b i l i t i e s .
I shall discuss experiments suggesting that potentiation is at least p a r t l y due
to a sustained increase in the release of t r a n s m i t t e r , and attempt to reconcile t h i s view with other evidence which points to a postsynaptic involvement in the induction of the e f f e c t .