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H Meissl

Publications and source records attributed to H Meissl.

At least 37 records · Page 2Linked to original sources
PubMed1990

Characterization of the light response in the pineal gland of intact and sympathectomized rats.

Electrophysiological recordings were performed in the pineal gland of pigmented rats BD9 to investigate the possible contribution of a direct neural connection of the gland with the central nervous system in the transmission of photic information. Extracellular potentials were recorded during brief photic stimulation of the eyes before and after bilateral sympathectomy. Two types of responses could be distinguished in intact as well as in sympathectomized rats: spontaneously active units which were unresponsive to light flashes and units responding to photic stimulation with ON and ON/OFF discharges. Spectral sensitivity curves recorded from the pineal organ of dark adapted rats showed a maximum at 500 nm. Interruption of the sympathetic innervation by bilateral denervation or removal of the superior cervical ganglia did not alter the spectral properties of pineal units. Additionally, response-intensity curves and response threshold (about 0.0017 microW/cm2) were not changed after sympathectomy. These results suggest that the pineal gland of the rat receives projections from the visual system via a central pinealopetal innervation.

Action Potentials↗
PubMed1990

Neural elements in the pineal complex of the frog, Rana esculenta, I: Centrally projecting neurons.

The pineal complex of anuran amphibians is a directly photosensory organ, encompassing both an extracranial portion, the frontal organ, and an intracranial portion, the pineal organ proper. The projection neurons of the frontal organ respond differentially according to the wavelengths of the light stimuli. The pineal organ, on the other hand, functions mainly as a luminosity meter. Most of its centrally projecting neurons respond to all increases in ambient illumination with decreases in spontaneous firing of action potentials, although some neural units in the pineal organ may respond according to wavelength. This difference in responses to light stimulation may be reflected in the neural organization of the two parts of the pineal complex. In the present study, we have analyzed the morphology of the projection neurons of the frontal and pineal organs of the frog, Rana esculenta, by backfilling of the neurons with horseradish peroxidase through their cut axons. In the pineal organ, several types of centrally projecting neurons were observed: peripherally situated unipolar and multipolar neurons, the dendrites of which extend into a superficial axon plexus that surrounds the pineal epithelium; smaller unipolar, bipolar, or multipolar neurons situated close to the central pineal tract; and radially oriented bipolar neurons, with short dendritic processes oriented towards the lumen of the pineal organ.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Neural elements in the pineal complex of the frog, Rana esculenta, II: GABA-immunoreactive neurons and FMRFamide-immunoreactive efferent axons.

The photosensory pineal complex of anurans comprises an extracranial part, the frontal organ, and an intracranial part, the pineal organ proper. Although the pineal organ functions mainly as a luminosity detector, the frontal organ may monitor the relative proportions of short and intermediate/long wavelengths in the ambient illumination. The major pathway of information processing in the pineal and frontal organs is the photoreceptor to ganglion cell synapse. It is not known whether interneurons form part of the neural circuitry. In the present study, we demonstrate GABA-immunoreactive (GABA-IR) neurons in the pineal and frontal organs of the frog, Rana esculenta. No GABA-IR axons were observed in the pineal nerve between the frontal and pineal organs, or in the pineal tract that connects the pineal complex with the brain. The GABA-IR neurons differed in morphology from centrally projecting neurons visualized by retrograde labeling with horseradish peroxidase. Thus, we suggest that the GABA-IR neurons in the pineal and frontal organs represent local interneurons. Axons of central origin, immunoreactive with a sensitive antiserum against the tetrapeptide Phe-Met-Phe-Arg-NH2 (FMRFamide), were observed in the intracranial portion of the photosensory pineal organ. The immunoreactive axons enter the caudal pole of the pineal organ via the posterior commissure. The largest density of axons was observed in the caudal part, while fewer axons were detected in the rostral portion. The uneven distribution of the FMRFamide-immunoreactive axons may be related to the distribution of different types of intrapineal neurons. FMRFamide-immunoreactive varicose axons were observed in the extracranial frontal organ. A central innervation of the pineal organ, previously known exclusively from amniotes, is probably not per se linked with the evolutionary transition of the pineal organ from a directly photosensory organ to a neuroendocrine organ. It could rather represent a centrifugal input to a sensory system which has been retained when the directly sensory functions have changed, during phylogeny, to neuroendocrine functions.

Animals↗
PubMed1989

Signal processing in a simple vertebrate photoreceptor system: the teleost pineal organ.

The integrating circuitry and efferent pathways for neural signals evoked in the photosensory pineal organ by changes in ambient illumination have been investigated by a multidisciplinary approach. Intrapineal efferent neurons were identified by means of retrograde filling with horseradish peroxidase (HRP). In addition to several types of neurons, photoreceptor cells that emitted axons to the brain via the pineal tract were observed. The presence of several populations of local interneurons (putatively cholinergic, GABAergic and substance P-containing) and possible afferent (putatively noradrenergic and peptidergic) central innervations were established by means of immunocytochemistry. The anatomical substrate for processing of neural signals thus delineated, the responses of pineal sensory and neural elements to photic stimulation were investigated by means of intracellular recording. Successful recordings were followed by intracellular injection with HRP or Lucifer Yellow CH, for subsequent light or electron microscopical investigation. The recordings indicate the presence of at least two types of photoreceptor cells, that display morphological and physiological features of both retinal rods and cones. In addition, one type of (sign-conserving) interneuron was identified. The photosensory pineal organ thus possess an integrative neural circuitry that may be involved in the elaboration of neural signals to the brain, and/or in the local control of intrapineal functions, e.g. indoleamine synthesis.

Animals↗
PubMed1988

Intracellular staining of physiologically identified photoreceptor cells and hyperpolarizing interneurons in the teleost pineal organ.

The directly photosensory pineal organ of the rainbow trout functions primarily as a luminance detector. Its neutral output reflects the level of ambient illumination in an almost linear fashion over several orders of magnitude. It may thus transmit information about the daily light-dark cycle to central projection targets in the brain, and exert an important control over putative central oscillators. We have studied single neural elements in the explanted pineal organ of the rainbow trout by combining intracellular recording with intracellular injections of either the fluorescent dye Lucifer Yellow CH or the electron dense marker horseradish peroxidase. After physiological characterization, dye was injected, and the pineal organs were processed for fluorescence or electron microscopy. Horseradish peroxidase-injected cells were selected with light microscopy, and were serially sectioned for electron microscopy. By examining the entire series of ultrathin sections of several labeled cells the following results were obtained. (1) Intensity-graded hyperpolarization that was elicited by light stimuli of all wavelengths could be either purely monophasic at all light intensities, or monophasic at low and intermediate light intensities but with an initial peak transient at response saturation. These two types of responses could be demonstrated to emanate from photoreceptor cells. (2) In addition, an interneuron that responded to light stimulation with intensity-graded hyperpolarizations that decreased in amplitude at high light intensities was identified by analysis of serial ultrathin sections. This interneuron was situated in close opposition to a photoreceptor-like element and another interneuron, both of which contained transcellularly transferred horseradish peroxidase. Transcellular transfer of horseradish peroxidase was repeatedly observed, although in the majority of cases only single cells were labeled. Intracellular injection of Lucifer Yellow CH consistently revealed dye-coupling between photoreceptors and between (inter)neurons. The numbers of labeled elements varied between two and eight cells, after intracellular injection of one cell. The present results indicate that the net neural output of the pineal organ is the result of a relatively complicated neural circuitry, encompassing different types of photoreceptors, interneurons and projection neurons. Electrical coupling between photoreceptors, between neurons, and between photoreceptors and neurons may provide spatial signal averaging. The very slow photoreceptor responses to photic stimulation may provide temporal signal averaging.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1988

Photoreceptor responses to light in the isolated pineal organ of the trout, Salmo gairdneri.

Photoreceptor potentials were recorded intracellularly from the isolated pineal organ of the teleost, Salmo gairdneri, maintained in tissue culture medium for 2-20 h. After electrophysiological characterization the photoreceptor cells were iontophoretically injected with Lucifer Yellow or with horseradish peroxidase for subsequent morphological identification. A brief flash of light elicited a hyperpolarization which was graded with light intensity in the dark-adapted photoreceptor. For dim flashes, the responses were purely monophasic. At higher intensities responses either remained purely monophasic or displayed an initial transient wave which became prominent for supersaturating intensities. The latency of the responses and their rise time decreased with increasing light intensity. Threshold responses showed latencies of about 600 ms, reached a maximum in about 1100 ms and returned to the dark potential in about 5 s. Saturating flashes considerably diminished the latency to 55 ms, the rise time to about 250 ms, but increased the time of recovery from peak to dark potential up to 60 s. Intracellular responses to background illumination exhibited two different response types. One type repolarized immediately, when the background light was extinguished, whereas the other type was characterized by a slow recovery of the dark potential. The spectral sensitivity of all intracellular recorded photoreceptors peaked at lambda max = 520-530 nm.

Animals↗
PubMed1988

Dark and light adaptation of pineal photoreceptors.

Dark and light adaptation of pineal photoreceptors was studied in the isolated pineal organ of the rainbow trout, Salmo gairdneri. After intracellular recording, the photoreceptors were iontophoretically injected with Lucifer yellow CH or with horseradish peroxidase for morphological characterization. Pineal photoreceptor cells responded to light with a hyperpolarization whose amplitude was graded with intensity. Following a 30-60 s bleach, receptor responsiveness was greatly reduced with a gradual recovery in the dark. Recovery of membrane potential was complete within 2-4 min in the dark. In response to flashes the hyperpolarizing response increased in darkness in amplitude and duration over a period of more than 30 min and the voltage-intensity curves continuously shifted to lower intensities. After exposure to strong light the time-course of dark adaptation, determined with a threshold criterion, was monophasic and receptor sensitivity increased by at least 5-6 log units. The results show that pineal photoreceptors exhibited the full characteristics of dark adaptation processes previously ascribed to cells proximal to the receptors, i.e. to ganglion cells. Exposure to steady illumination of different intensities induced graded and sustained hyperpolarizations of the receptor membrane potential. The incremental voltage range of responses to test flashes superimposed on the backgrounds was reduced. Voltage-intensity curves were shifted to higher intensities with increasing background illumination indicating that adaptation occurred over a range of about 2.5 log units before the receptors saturated.

Adaptation, Ocular↗
PubMed1987

Action spectra of the lateral eyes recorded from mammalian pineal glands.

Single neuronal units from the pineal stalk and the pineal body of hamsters, guinea pigs and rats were recorded during photic stimulation of the lateral eyes in order to identify the retinal photoreceptor that mediates the environmental control of the mammalian pineal. Two cell types could be distinguished: one type was characterized by spontaneous spike discharges that were irresponsive to light stimulation of the eyes and the pineal body; the other, also spontaneously active, responded to flash stimulation of the lateral eye with On- and Off-discharges. With increasing light intensity, the spike frequency of the second response type followed a sigmoidal function up to a saturation level. Spectral sensitivity curves of all dark-adapted animals peaked at 500 nm. During light adaptation (18 microW/cm2) action spectra exhibited an additional maximum in the red (560 nm, rats and hamsters) and in the blue (450 nm, guinea pigs) light, respectively. Chromatic adaptation to orange light diminished the sensitivity at longer wavelengths, whereas adaptation to blue-green light enhanced the sensitivities at longer wavelengths. Thus, the spectral sensitivity recorded from pineal units of hamsters, guinea pigs and rats corresponds to those described for retinal ganglion cells, which indicates that both rods and cones contribute to the light-sensitivity of the mammalian pineal gland. Direct illumination of the pineal gland did not influence the activity of pineal units.

Animals↗
PubMed1987

An attempt to record neuronal activity in the paraventricular organ of Rana esculenta by means of a direct access to the infundibular recess.

In submammalian vertebrates, the paraventricular organ (PVO) of the third ventricle is a complex circumventricular structure composed of cerebrospinal fluid-contacting neurons and corresponding deeper formations of nerve cells. A new in-vivo technique enables us to approach the paraventricular organ of the frog, Rana esculenta, via the lobus infundibularis. In this preparation, blood flow in the capillary loops beneath the PVO and the flow of the cerebrospinal fluid in the infundibular recess can be directly observed. Electrical recordings of neural activity in and near the PVO show continuous and phasic, spontaneous activity. Light stimulation of the retina and direct illumination of the brain were not followed by alterations of nerve cell activity. A major problem in the electrophysiological investigation is the diminution in spontaneous activity of the recorded neurons after exchange of CSF.

Animals↗
PubMed1986

Neural response mechanisms in the photoreceptive pineal organ of goldfish.

In order to classify the different cell types involved in signal transmission of the photoreceptive pineal organ of the goldfish, Carassius auratus, intra- and extracellular electrical responses were recorded from photoreceptors and second-order neurons. Photoreceptor responses to light consisted of hyperpolarizing potentials up to 30 mV. The responses were graded with intensity and their voltage-intensity relation followed the hyperbolic function V/Vmax = In/In + sigma n. Latencies varied between 500 msec for responses near threshold and 60 msec for supersaturating flashes. The response duration increased up to 60 sec for flashes 2 log units above the saturation level. Action spectra of individual photoreceptors peaked at lambda max = 530 nm and corresponded to measurements of extracellular slow mass potentials or spike potentials. Slow mass potentials exhibited similar characteristics as intracellular recorded photoreceptor potentials with respect to latency, voltage-intensity curves and spectral sensitivity. Ganglion cells showed maintained discharges under conditions of steady illumination. The discharge rate changed inversely with the logarithm of steady illumination over a range of 8 log units. The response to light flashes was purely achromatic and consisted of inhibition of the maintained discharge. The physiological properties demonstrate that the pineal organ of the goldfish is an effective functional photoreceptor organ operating both in dim and in bright light. The light-induced hyperpolarization of photoreceptors lead to an inhibition of the nervous discharge of ganglion cells. The direct flow of information from photoreceptors to ganglion cells is the basic channel of data processing in the goldfish pineal.

Acclimatization↗
PubMed1985

Effect of GABA and its antagonists, bicuculline and picrotoxin, on nerve cell discharges of the photosensory pineal organ of the frog, Rana esculenta.

The effect of gamma-aminobutyric acid (GABA) and its antagonists, bicuculline and picrotoxin, was studied on pineal neurons of the frog, Rana esculenta. The drugs were applied by microiontophoresis while monitoring the spontaneous activity and light-evoked responses of electrophysiologically identified achromatic (luminance) neurons of the pineal organ. Almost all neurons investigated were sensitive to GABA. The inhibitory action was characterized by its rapid onset and its reversibility. The GABA antagonists, bicuculline and picrotoxin, were able to antagonize the inhibitory action of the amino acid. The light-evoked inhibition of the maintained ganglion cell activity interfered with the GABA-induced inhibition, i.e. light reduced the strength of inhibition and shortened the effect of GABA. The investigation suggests a major role of GABAergic mechanisms in the ganglion cell output of pineal neurons.

Animals↗
PubMed1984

Electrophysiological studies on neuronal transmission in the frog's photosensory pineal organ. The effect of amino acids and biogenic amines.

A variety of putative neurotransmitter substances and their analogues were used to characterize the synaptic connections from photoreceptors to ganglion cells in the pineal organ of the frog. The effects of all agents were tested on electrophysiologically identified luminance cells of the pineal organ. L-Aspartate and L-glutamate caused a significant increase of neuronal cell firing, the effects were dose-related, reversible and reproducible. The aspartate and glutamate agonists N-methyl-D-aspartate and kainate possess a similar ability to induce neuronal excitations in the pineal organ, N-methyl-D-aspartate being more potent than kainic acid. The excitatory action of all agents persisted if the ganglion cells were isolated from other synaptic inputs by Co2+ treatment. The excitatory action of the amino acids was antagonized by D-alpha-aminoadipate (D-alpha-AA); the order of sensitivity to antagonism by D-alpha-AA was: N-methyl-D-aspartate greater than L-aspartate greater than L-glutamate approximately equal to kainate. Taurine, by far the most abundant amino acid in pineal tissues, markedly decreased the spontaneous activity in half of the neurons tested, the remaining cells being unresponsive. The indoleamine serotonin effectively depressed the maintained activity also in half of the cells tested. Acetylcholine had only small effects on pineal luminance cells. It is concluded that L-aspartate (and/or glutamate) might interact with postsynaptic receptors in the ganglion cell membrane and mimics the action of the natural photoreceptor transmitter.

2-Aminoadipic Acid↗
PubMed1984

Photosensory properties of the pineal organ. Microiontophoretic application of excitatory amino acids onto pineal neurons.

Extracellular recordings were performed on electrophysiologically identified achromatic neurons of the photosensitive pineal organ of the frog. The effects of iontophoretically applied aspartate and glutamate as well as one aspartate antagonist (D-alpha-aminoadipate) were observed on spontaneous activity and light-evoked responses of pineal neurons. Aspartate and glutamate showed a powerful excitatory effect on achromatic neurons. The effect was dose-related and reversible. D-alpha-Aminoadipate substantially diminished the excitatory aspartate effect. The changes observed in the ganglion cell responses after application of the drugs are discussed in light of the possible neuronal circuitry of the pineal organ.

2-Aminoadipic Acid↗
PubMed1981

Pineal complex of the clawed toad, Xenopus laevis Daud.: structure and function.

The morphological and physiological properties of the pineal complex of Xenopus laevis were investigated in larval, juvenile and adult animals. In a representative majority of adult X. laevis, the frontal organ does not display signs of degeneration. Fully differentiated frontal organs contain photoreceptors typical of the pineal complex of lower vertebrates. By means of the acetylcholinesterase (AChE)-reaction approximately 30 neurons of two different types were demonstrated in the frontal organ. The frontal-organ nerve is composed of approximately 10 myelinated and 40 unmyelinated nerve fibers. The neuropil areas of the frontal organ are generally similar to the corresponding structures of the intracranial epiphysis. The neuronal apparatus of the epiphysis cerebri of X. laevis consists of (i) photoreceptor cells, (ii) approximately 100 AChE-positive neurons, (iii) complex neuropil areas, and (iv) a pineal tract formed by approximately 10 myelinated and approximately 100 unmyelinated nerve fibers. Some of them exhibit granular inclusions indicating that pinealopetal elements may enter the pineal complex of X. laevis via this pathway. The topography of the pineal tract of X. laevis differs considerably from that in ranid species. The most conspicuous element of the plexiform zones is the ribbon synapse. The basal processes of the photoreceptor cells may be presynaptic elements of simple, tangential, dyad or triad synaptic contacts. Conventional synapses were observed only occasionally. Electrophysiological recordings revealed that the pineal complex of Xenopus laevis is directly sensitive to light. In response to light stimuli, two types of responses, achromatic and chromatic, were recorded from the nerve of the frontal organ. In contrast, the epiphysis exhibited only achromatic units. The opposed color mechanism of the chromatic response showed a maximum sensitivity at approximately 360 nm for the inhibitory and at 520 nm for the excitatory event. The action spectrum of the achromatic response of the epiphysis and the frontal organ peaked between 500 and 520 nm and showed no Purkinje-shift during dark adaptation. The functional significance of these phenomena is discussed.

Acetylcholinesterase↗