Modified Hebbian rule for synaptic enhancement in the hippocampus and the visual cortex.
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Animals↗
Biomedical subjects
J Bolz
Publications and source records attributed to J Bolz.
Development of vasoactive intestinal polypeptide (VIP)-containing neurons in organotypic slice cultures from rat visual cortex.
Using immunohistochemistry we have been studying the postnatal maturation of vasoactive intestinal polypeptide (VIP)-positive neurons in organotypic slice cultures from rat visual cortex. The development in vitro is compared with the occurrence of VIP-containing cells in vivo, where they are first observed around postnatal day 5. A further increase in number and morphological maturation occurs within the following 3 weeks. In cultures prepared from 1- or 2-day-old rats, i.e. before VIP is expressed in vivo, VIP-containing neurons appear after about 5 days and gradually increase in number over the next 2 weeks. Thus the time course of postnatal expression of VIP in vitro and the morphology of VIP-immunoreactive neurons in culture closely matches the situation in vivo. These observations suggest that the maturation of VIP-containing neurons occurs independently of cortical afferents and that the intrinsic connectivity and activity is sufficient for their postnatal maturation. Therefore organotypic slice cultures should be a suitable system to study mechanisms of neurochemical maturation in the cortex.
Animals↗
Cellular organization and development of slice cultures from rat visual cortex.
Slice cultures from the visual cortex of young rats were prepared using the roller culture technique (Gähwiler 1984). After 10 days in vitro the cortical cultures flattened to 1-3 cell layers, surviving for up to 12 weeks. The cultures were organotypically organized, the typical layered structure of the cortex was preserved. The neuronal composition of slice cultures was studied using intracellular staining, Golgi impregnation and GABA immunohistochemistry. Both pyramidal cells and several types of nonpyramidal cells were identified in the slice cultures. Electrophysiological recordings showed that the electrical properties of cells in culture were similar to those measured in acute slice preparations; for some cells, however, the spontaneous activity was higher. The maintained activity was strongly increased by application of the GABA antagonist bicuculline and decreased by GABA, suggesting that GABAergic inhibition is present in these preparations. We could observe the postnatal maturation of some characteristic morphological features in culture. For example, pyramidal cells in 6 day-old rats in situ have very short basal dendrites with growth-cones, and the dendrites are free of spines. After 2-3 weeks in culture growth-cones were no longer observed. Instead, the cells had developed a large basal dendritic field and the dendrites were covered with spines. Slice cultures therefore may provide a useful tool for physiological, anatomical, pharmacological and developmental studies of cortical neurons in an organotypical environment.
Action Potentials↗
Pharmacological analysis of cortical circuitry.
The cortical circuitry of the visual cortex has been worked out in great detail. Anatomical investigations reveal stereotyped connections within cortical columns and specific long-range connections between distant columns. Pharmacological techniques for blocking the activity in individual cortical layers or columns allow the microdissection of the cortical circuit. These studies could relate specific functional roles to particular cortical connections.
Animals↗
Morphology of identified projection neurons in layer 5 of rat visual cortex.
We studied the morphology of neurons in layer 5 of rat visual cortex (area 17) projecting to the contralateral hemisphere and the superior colliculus. Double labelling with fluorescent tracers indicated that these projections arise from different populations of cells. To reveal the morphology of the cells we stained retrogradely labelled neurons intracellularly in living brain slices. Callosal projecting pyramidal cells have 3-6 basal dendrites and an apical dendrite which never reaches higher than layer 3. Corticotectal cells have 6-8 basal dendrites and a prominent apical dendrite which always forms a large tuft in layer 1. Thus, neurons in the same cortical layer that give rise to different projections also differ in their morphology. However, each population of neurons has a rather stereotyped dendritic branching pattern, despite a large variation in soma size.
Animals↗
Photopic action of thyrotropin-releasing hormone in the cat retina.
The effects of iontophoretically applied thyrotropin-releasing hormone (TRH) on cat retinal brisk-sustained(X) and brisk-transient(Y) ganglion cells were studied in the intact eye in vivo. Under photopic illumination we found a differential action of TRH on ON- and OFF-centre cells: the maintained activity and light response were suppressed in ON-centre cells and enhanced in OFF-centre cells. This was true for both brisk-sustained(X) and brisk-transient(Y) cells. In contrast, TRH did not influence the ganglion cell discharge under scotopic stimulus conditions. These results indicate that TRH acts on neurons presynaptic to ganglion cells and these neurons are only active under photopic conditions. We suggest that a possible functional role of this specific action of TRH is in light adaptation.
Adaptation, Ocular↗
Localization of aspartate aminotransferase and cytochrome oxidase in the cat retina.
Using immunohistochemical techniques, we demonstrate aspartate aminotransferase (AAT)-like immunoreactivity in cone pedicles and ganglion cells of the cat retina. An identical pattern was seen when we stained for cytochrome oxidase activity, a marker for neurons which have a high metabolic activity. Tetrodotoxin selectively blocked the cytochrome oxidase labeling of ganglion cells. AAT is a key enzyme in the metabolism of aspartate and glutamate and has been proposed as a marker for neurons which use aspartate/glutamate as a neurotransmitter. Due to the close correlation between AAT-like immunoreactivity and cytochrome oxidase activity, we suggest that, at least in the retina, AAT-like immunoreactivity in fact labels cells which have a high metabolic activity.
Animals↗
Action and localization of gamma-aminobutyric acid in the cat retina.
The effects of iontophoretically applied GABA (gamma-aminobutyric acid) and bicuculline on retinal ganglion cells were studied in the optically intact eye of the anaesthetized cat. GABA suppressed both the spontaneous activity and light-evoked discharge of all retinal ganglion cells, regardless of their type and regardless of the visual stimulus used. Bicuculline antagonized the action of iontophoretically applied GABA. Bicuculline enhanced the spontaneous activity of on-centre cells, but suppressed the spontaneous activity of most off-centre cells. The light-evoked response of on-centre cells was increased by bicuculline. A more complicated picture emerged for off-centre cells. Weak light responses were suppressed by bicuculline, but during strong light responses the initial transient phase of the response was dramatically enhanced. Amacrine cells of the inner nuclear layer and displaced amacrine cells of the ganglion cell layer were labelled, using glutamic acid decarboxylase (GAD) immunohistochemistry and [3H]muscimol uptake. GAD-positive dendrites were found throughout the inner plexiform layer and no sign of dendritic stratification was detected.
Action Potentials↗
Action and localization of glycine and taurine in the cat retina.
The effects on retinal ganglion cells of iontophoretically applied glycine, taurine and strychnine were studied in the optically intact eye of the cat. Glycine and taurine suppressed the light-evoked discharge of all on-centre and off-centre brisk ganglion cells, regardless of the visual stimulus used. Strychnine blocked the action of externally applied glycine and taurine. The light-evoked response of all ganglion cells was raised by strychnine. The tonic discharge of the light response was suppressed or raised by the drugs more than the phasic response. A population of amacrine cells, which was heavily labelled by [3H]glycine, did not take up [3H]taurine. [3H]taurine was only weakly accumulated by inner nuclear layer neurones and was predominantly located in the outer retina.
Action Potentials↗
Morphological features of the interaction between mucus and surfactant on the bronchial mucosa.
The secretion layer over the bronchial epithelium was investigated on human biopsy material. In the sol phase of the secretion, phospholipid membranes stretched out or arranged in vesicular structures could regularly be demonstrated. They displayed the same structure as the surfactant material in the alveolar space. It can be inferred therefrom that the surfactant is excreted via the bronchial system. It probably contributes to the stabilization of the sol phase of the mucus and thus influences the sliding capacity of the gel phase. So the surfactant has an important function in maintaining mucociliary clearance at the bronchial mucosa.
Adolescent↗
Cholecystokinin in the cat retina. Action of exogenous CCK8 and localization of cholecystokinin-like immunoreactivity.
The effects of applying cholecystokinin (CCK8) iontophoretically onto cat retinal ganglion cells were studied in the optically intact eye of the cat. CCK8 suppressed both the maintained and the light evoked discharge of brisk ganglion cells, irrespective of their being on- or off-center, brisk-transient, or brisk-sustained and independent of the state of light adaptation. The inhibitory action of CCK8 in the cat retina is opposite from its excitatory action in other parts of the brain. Using an antiserum to cholecystokinin, immunoreactivity was localized in horizontal cells and amacrine cells of the cat retina. Inconsistently immunoreactivity also was found in ganglion cells and fibers.
Animals↗
Kainic acid induces sprouting of retinal neurons.
The neurotoxin kainic acid caused dose-dependent morphological changes in horizontal cells of the retinas of adult cats and rabbits. High concentrations of kainic acid killed the cells, but when exposed to sublethal doses they contracted their dendritic fields and sent sprouting processes into the inner retina. It appears that kainic acid can induce neuronal growth as well as degeneration and that the potential for morphological plasticity is still present in neurons of the adult mammalian retina.
Animals↗
Pharmacological modulation of on and off ganglion cells in the cat retina.
We studied the effects of 2-amino-4-phosphonobutyric acid and 2-amino-4-phosphonovaleric acid, which are antagonists to excitatory amino acids, on brisk-sustained(X) and brisk-transient(Y) ganglion cells in the cat retina. The ganglion cells were recorded extracellularly with a multibarreled electrode in the intact eye in vivo and drugs were applied iontophoretically. We found contrasting effects of 2-amino-4-phosphonobutyric acid and 2-amino-4-phosphonovaleric acid on ON- and OFF-centre cells irrespective of the brisk-sustained(X)/brisk-transient(Y) dichotomy. The maintained discharge and the light response of ON-centre cells decreased during 2-amino-4-phosphonobutyric acid and 2-amino-4-phosphonovaleric acid application, whereas the maintained discharge of OFF-centre cells increased. The light response of OFF-centre cells was not significantly affected. 2-Amino-4-phosphonovaleric acid was generally less potent than 2-amino-4-phosphonobutyric acid. It was shown in the mudpuppy retina [Slaughter and Miller (1981) Science, N.Y. 211, 182-185; Slaughter and Miller (1981) Invest. ophthal. Vis. Sci. 20, 44] that 2-amino-4-phosphonobutyric and 2-amino-4-phosphonovaleric acid selectively block the response of ON-bipolar cells. Assuming that these drugs act on the same synaptic sites in the cat retina, one expects a block of ON-centre ganglion cells. Moreover, the drug response of OFF-centre ganglion cells is then consistent with Sterling's hypothesis [Sterling (1983) A. Rev. Neurosci. 6, 149-185] that OFF-ganglion cells receive a direct inhibitory input from ON-bipolars. For some period 19 out of 108 cells responded to 2-amino-4-phosphonobutyric acid and 2-amino-4-phosphonovaleric acid in an opposite way to that described above: ON-centre cells increased and OFF-centre cells decreased their maintained discharge. It is proposed that this "reverse response" may be mediated by autoreceptors to excitatory amino acids or due to different receptor sites triggering antagonistic response mechanisms.
2-Amino-5-phosphonovalerate↗
Brain stem auditory evoked responses in psychiatric patients and healthy controls.
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Adult↗
Response latency of brisk-sustained (X) and brisk-transient (Y) cells in the cat retina.
1. Several methods for evaluating light-evoked response latency and its variability in brisk-sustained (X) and brisk-transient (Y) retinal ganglion cells were tested. The most accurate procedure proved to be that described by Levick (1973), in which the time of the occurrence of the fourth impulse after stimulus onset is taken as an estimate of the latency.2. The shortest response latencies are obtained when the stimuli are the same size as the receptive field centre. At medium and high response amplitudes (> 150 impulses/sec) the response of brisk-transient (Y) cells to these optimal stimuli is 10-15 msec faster than that of adjacent brisk-sustained (X) cells.3. The response latency of brisk-sustained (X) cells for stimuli larger than the receptive field centre increases, whereas that of brisk-transient (Y) cells remains constant. Brisk-sustained (X) cells respond faster than do brisk-transient (Y) cells to stimuli smaller than the receptive field centre.4. No systematic difference exists between brisk-sustained (X) and brisk-transient (Y) cells in regard to the temporal variability of the response. The standard deviation of the latency for stimuli of optimal size decreases from 2.0-8.0 msec at medium stimulus contrast to 0.6-2.0 msec at high stimulus contrast.5. The response of OFF-centre cells to the disappearance of a light spot is always slower than that of an ON-centre cell of the same class to the onset of this stimulus. However, when OFF-centre cells are stimulated with dark spots, their response latency does not differ from that of ON-centre cells of the same class.6. No simple relationship exists between the response latency and the response amplitude. At medium and high discharge rates, most brisk-transient (Y) cells respond faster than an adjacent brisk-sustained (X) cell with equal response. At the same response amplitude, the latencies become shorter as the background illumination is raised. The same discharge rate can be obtained with stimuli of sub-optimal and supra-optimal size, but the latency for the larger stimulus is shorter than that for the smaller one. Latency, therefore, is an additional parameter characterizing the light-evoked response.
Action Potentials↗
The relationship between P3-latency and reaction time in depression.
A random series of frequencies and infrequent clicks was presented to 13 primary depressives and 13 healthy controls matched for age and gender. Subjects were instructed to press a button as fast as possible in response to the infrequent clicks. P3 amplitudes and latencies as well as correlations between P3 latency and reaction time were calculated on a single trial basis using Woody's adaptive filter. While reaction times were significantly longer in patients, neither P3 latencies nor P3 amplitudes differed between the groups. Thus, delayed reaction time of depressives seems to be a consequence of impaired selection, activation, or execution of the motor response rather than of delayed stimulus evaluation. The correlation between P3 latency and reaction time was significantly smaller in patients then in controls.
Adult↗
Controllability of an aversive stimulus in depressed patients and health controls: a study using slow brain potentials.
Slow brain potentials (CNV and PINV) were recorded from 18 patients with primary depression and 18 health controls under three experimental conditions. A short tone (S1) indicated the occurrence of an aversive tone stimulus (S2) which could not be terminated by a motor reaction in Condition 1 (C1) but was terminated in C2. In C3 the reaction time (RT) had to be faster than the shortest mean RT from C1 and C2 in order to stop the aversive stimulus. For both groups the RT decreased from C1 to C2 to C3 and the CNV increased from C2 to C3. CNV and RT did not differ between the groups in either condition. In C1 and C3 (uncontrollability and restricted control over the aversive stimulus) patients developed a marked PINV which was not observed in the control group. In view of other investigations which found a PINV in normal subjects in situations of sudden, unexpected uncontrollability, the present results demonstrate that depressed patients are more sensitive to levels and variation of uncontrollability than healthy subjects. A possible relationship to Seligman's concept of helplessness is discussed.
Arousal↗
Pre- and postimperative negative variation (CNV and PINV) under different conditions of controllability in depressed patients and healthy controls.
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Cerebral Cortex↗