Biomedical subjects

K Funke

Publications and source records attributed to K Funke.

At least 37 records · Page 2Linked to original sources

PubMed1993

Modulatory effects of acetylcholine, serotonin and noradrenaline on the activity of cat perigeniculate neurons.

We studied the modulatory actions of microiontophoretically applied acetylcholine (ACH), serotonin (5-HT, 5-hydroxytryptamine) and noradrenaline (NA), and those of the adrenoceptor agonists phenylephrine (PHE, alpha 1), clonidine (CLO, alpha 2) and isoprenaline (ISO, beta) on spontaneous and visually induced activities in cat perigeniculate (PGN) and thalamic reticular (NRT) neurons (only spontaneous) during extracellular recordings performed in vivo. ACH and 5-HT were found to affect the ongoing (spontaneous) and visually evoked activity of PGN cells and also the spontaneous activity of NRT cells in an opposite fashion. ACH inhibited tonic firing and often induced burst activity. By contrast, 5-HT exerted an excitatory influence, which caused a long-lasting, very regular, high-frequency activity between about 35 and 120 Hz. Spontaneous as well as 5-HT-induced firing was found to prefer three distinct frequency ranges: 35-42 Hz, 60-67 Hz and 80-120 Hz. Opposite actions of ACH and 5-HT were also evident when applied simultaneously. ACH dampened the high-frequency activity elicited with 5-HT, and 5-HT could replace the burst activity induced with ACH application by a regular tonic activity. The absolute strength of visual responses (in spikes per second) was only slightly enhanced or reduced by ACH and 5-HT, respectively, but due to the strong effects on background activity, ACH clearly elevated the signal-to-noise ratio and 5-HT reduced it. Despite its excitatory action, 5-HT did not facilitate visual responses. Spontaneous changes in ongoing activity were found to affect the visual response amplitude in the same way. Noradrenaline, the alpha 1-agonist PHE and the beta-agonist ISO exerted a weak depressant action on high-frequency maintained activity, but during low-frequency single spike activity and/or burst activity a facilitatory effect was evident, which prevented the generation of burst discharges and slightly increased single spike firing. Visually evoked activity was little affected, but signal-to-noise ratio changed with changes in ongoing activity. The alpha 2-agonist CLO clearly attenuated both spontaneous activity and visual responses. We suggest that, in addition to direct effects of ACH and 5-HT on geniculate relay cells, the balance between the opposite actions of ACH and 5-HT on PGN cells determines the mode of operation in the recurrent inhibitory circuit: either a global, tonic inhibition of relay cells during a dominating 5-HT influence or a less tonic but phasic inhibition during increased activity in the cholinergic system.

Acetylcholine↗

PubMed1993

Noradrenergic modulation of retinogeniculate transmission in the cat.

1. Relay neurones were extracellularly recorded from the A-layers of the dorsal lateral geniculate nucleus (dLGN) of the anaesthetized cat. The noradrenergic influence on retinogeniculate transmission was investigated through microiontopheretic techniques in a total of 140 dLGN relay cells using three experimental approaches: (i) the effects of agonists for alpha 1-, alpha 2- and beta-adrenoceptors were separately analysed; (ii) the noradrenergic influence was related to the global state of activity of the relay neurones, which was associated with discrete patterns of the electroencephalogram (EEG); (iii) distinct phases of visual responses evoked from the area of the retinal receptive field, and of binocular and lateral inhibitory responses, were evaluated before, during and after the action of noradrenergic agonists. 2. The spontaneous generation of high-frequency bursts of spikes in dLGN relay neurones, associated with periods of highly synchronized, delta-like patterns of the EEG, was selectively suppressed by the beta-adrenoceptor agonist isoprenaline or the alpha 1- adrenoceptor agonist phenylephrine. Single action potentials, occurring at a low frequency between bursts, were significantly less affected. Depending upon the ejection level of the adrenoceptor agonists, burst activity was suppressed by 23-73%, compared with a reduction in single spike firing in the range 7-24%. The suppression of burst firing occurred in all functional types of dLGN relay neurones (X, Y; on, off), enhanced burst activity was observed in less than 1% of the cells. 3. On-going tonic sequences of action potentials (around 15 Hz), occurring during periods of EEG activity characterized by lower amplitudes and higher frequencies, were separately affected by adrenoceptor agonists. Isoprenaline had no significant effect, phenylephrine induced a global reduction of spike firing with no obvious relation to the ejection level, and the alpha 2-adrenoceptor agonist clonidine inhibited action potential generation in a near dose-dependent manner. 4. Visual response properties were investigated during periods of less synchronized states of EEG activity. Responses to visual stimulation of the retinal receptive field centre were not significantly influenced by isoprenaline, while phenylephrine or clonidine attenuated the phasic and the tonic response component in all functional types of relay neurones and independent of the stimulus contrast being used. At low ejection levels, slight facilitatory effects were observed with isoprenaline (65% of neurones that were tested) or phenylephrine (15%). The inhibitory influence of the antagonistic surround area of the receptive field appeared unaltered during action of isoprenaline or phenylephrine.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗

PubMed1992

EEG-dependent modulation of response dynamics of cat dLGN relay cells and the contribution of corticogeniculate feedback.

Single unit recordings were made extracellularly from the dorsal lateral geniculate nucleus (dLGN) in the anaesthetized and paralysed cat. The impulse rates of phasic (peak) and tonic components of visual responses to stimulation of the receptive field center by a flashing spot were determined during different states of the EEG, during local cortical cooling and during micro-iontophoretic application of the excitatory amino acid receptor agonists, quisqualate (QUIS) and N-methyl-D-aspartate (NMDA). Typically, visual responses were phasic during low frequency/high amplitude EEG patterns, resembling slow wave sleep (SWS). During high frequency EEG patterns (non-SWS) visual responses of X- and Y-cells exhibited a prominent tonic response component. This tonic component could be clearly reduced during ipsilateral cortical cooling in the non-SWS state. QUIS or NMDA, applied in order to mimic corticofugal activity, augmented the tonic response component, most efficiently during SWS EEG. The effects did not differ significantly for X- and Y-cells. During non-SWS EEG Y-cells exhibited a tonic response component similar to X-cells, but because of their higher peak rates the responses of Y-cells were on average more phasic than those of X-cells. Our results indicate that state-dependent changes in CNS activity modulate dL'GN responsiveness in part via the corticogeniculate feedback, and that predominantly the tonic response component is modulated.

Animals↗

PubMed1991

Retinogeniculate transmission by NMDA and non-NMDA receptors in the cat.

The contributions of N-methyl-D-aspartate (NMDA) and non-NMDA excitatory amino acid (EAA) receptors to retinogeniculate transmission were investigated in the cat. The EAA antagonists 2-amino-5-phosphonovaleric acid (APV) and kynurenic acid (KYN) were used to block the NMDA receptors and all EAA receptors, respectively. Antagonistic effects on the visual response were assessed with single On/Off stimuli of 2 s duration or repetitive flicker stimulation (5 Hz) with a light spot projected onto the receptive field center. With APV, the NMDA response could be almost completely abolished but the visual response to repetitive stimulation was reduced on average by only 34%. Initial (transient) components of the single flash response were attenuated on average by 23%, the residual (sustained) component by 48%. With KYN the responses to NMDA, quisqualate (QUIS) and glutamate (GLU) were abolished or strongly reduced as was the visual response to flicker (mean 58%) and single flash stimulation (mean transient 73%, sustained 90%). Prolonged iontophoretic applications of the agonists GLU, QUIS and NMDA revealed receptor desensitization or competitive interactions with the naturally released transmitter in a dose-dependent manner. When the responses to any of the 3 agonists declined during continuous application, superimposed visual responses were clearly reduced in amplitude. Visual response amplitudes were also reduced when superimposed on steady state QUIS responses but unchanged in amplitude when superimposed on steady state NMDA responses. In conclusion, non-NMDA as well as NMDA receptors seem to participate in cat retinogeniculate transmission. Non-NMDA receptors appear to be most important for the initial component but can also maintain the visual response, while the NMDA receptors seem to be more effective during the later component of the response.

2-Amino-5-phosphonovalerate↗

PubMed1991

Anatomical correlations between soma size, axon diameter, and intraretinal length for the alpha ganglion cells of the cat retina.

Retinal ganglion cells within the same region of the retina may have different lengths of axon before reaching the optic disc depending on the route they take with respect to the temporal raphe. We have investigated whether there is a correlation between soma and intraretinal axon diameter and how these parameters relate to intraretinal axon length on both sides of the cat temporal raphe. Retinas were wholemounted and alpha-cell somata and fibers stained with a modified neurofibrillar method. Moving peripherally from the area centralis along the raphe there was a progressively increasing difference between the intraretinal axon lengths for nearly adjacent cells across the raphe, which reached a maximum of 4-5 mm at the retinal periphery. Cells on the nasal aspect of the raphe had shorter axons than did adjacent cells on the temporal aspect of the raphe. Comparison of soma diameter samples across the raphe showed there was no clear trend between soma diameter and intraretinal length. Replotting the raphe and sample areas on a cell density map indicated that differences in soma diameter could be attributed to ganglion-cell density differences between the sampled areas. Examination of the stained cells revealed that within the initial length of the axon there was a region showing a reduction of axon diameter (diameter less than 1 micron), which varied in length from cell to cell. The axon was, therefore, divided into three segments: the portion of axon prior to thinning (A), the thin segment itself (B), and the part of the axon after the thin segment (C). The diameter of each segment (A,B,C) and the lengths of the first and second segments (A,B) were significantly correlated with soma diameter (P less than 0.001). From measurements of the axon diameter of segment C, it was concluded that alpha-cell axons continue to increase in diameter along their path towards the optic disc. The present report indicates that alpha-cell soma size, when going from the area centralis to the periphery along the raphe, reaches a plateau and then declines within more peripheral retinal locations in spite of increasing intraretinal axon length. Thus, there is no positive correlation between soma or axon diameter and intraretinal axon length. The anatomical findings are discussed in relation to previous reports of retinal development and complementary conduction times within intraretinal and extraretinal visual pathways.

Animals↗

PubMed1989

Somatosensory areas in the telencephalon of the pigeon. I. Response characteristics.

Two somatosensory regions in the pigeon's telencephalon were investigated electrophysiologically with recordings of field potentials as well as single- and multi-unit responses which were evoked by electrical stimulation of all four extremities or by feather movements produced with airpuffs or by hand. The outline of both areas, was studied in detail with the use of grid-like recordings of single or multi-units. One somatosensory area is located rostrally in the hyperstriatum accessorium (HA), rostral to the visual "Wulst". A caudal area comprises the medial aspects of two different cell layers: the neostriatum intermedium (NI) and adjacent neostriatum caudale (NC) as well as the overlying hyperstriatum ventrale (HV). The two areas differ considerably in their response characteristics. Field potentials of the NI/NC-HV area were more complex than those of the HA area and their shapes and latencies varied mainly in dependence of the recording site (NI, NC, HV). Multi-unit responses showed strong excitation and short latencies in NI/NC and weak excitation and longer latencies in HV. Both responses and latencies were uniform in the HA area and latencies generally longer than in NI/NC but shorter than in HV. The HA area processes somatosensory information more specifically. Its neurons have relatively small receptive fields which seem to be arranged in a somatotopic order in such a way that rostral parts of the body are represented superficially and caudal parts in deeper layers. In contrast, the NI/NC-HV area was found to be largely multimodal, receiving also auditory and visual information. Neurons in this region have large somatic receptive fields, often including one and sometimes even both sides of the body surface. A somatotopic arrangement could not be recognized. The whole body surface was representated in both areas, but there was a dominance of wing and back receptive fields in the NI/NC-HV area and leg and neck receptive fields in the HA area.

Anesthetics↗

PubMed1989

Somatosensory areas in the telencephalon of the pigeon. II. Spinal pathways and afferent connections.

There are two somatosensory areas in the telencephalon of the pigeon which receive an input from the spinal somatosensory system: one in the rostral Wulst which consists of the three hyperstriatal layers (h. accessorium (HA), h. intercalatus superior (HIS) and h. dorsale (HD] and one in the caudal telencephalon (neostriatum caudale (NC), neostriatum intermedium (NI) and hyperstriatum ventrale (HV]. Recordings of evoked single unit or multi unit activity and of field potentials before and after lesions of spinal pathways at a high cervical level (C4) were made to determine the contribution of these pathways to the transmission of somatosensory signals to these telencephalic areas. The rostral Wulst area receives somatic signals only through dorsal tracts contralateral to the recording site. Inputs from the wing arise mainly through the dorsal columns (DC) and those from the leg largely through the dorsolateral funiculus (DLF). The spinal projection pathway to the caudal neostriatal area includes the dorsal tracts and parts of the lateral funiculi on both sides. There was no difference in response form between the wing and leg responses. Signals transmitted through the lateral pathways were found to elicit the earliest responses (6-13 ms, electrical stimulation) in the caudal forebrain, while signals travelling through the DC arrive later in the caudal area (about 14 ms for wing stimulation) than in the rostral Wulst area (about 9 ms). The afferent thalamic and intratelencephalic connections of the two somatosensory areas in the telencephalon of the pigeon were investigated with retrograde transport of the neuronal tracers horseradish-peroxidase (HRP) or wheatgerm agglutinated HRP (WGA-HRP), Fast Blue (FB) and Rhodamine-isothiocyanat (RITC). Small tracer-injections were made under electrophysiological control at somatosensory responsive locations. These investigations confirm the projection of the caudal part of the nucleus dorsolateralis posterior (DLPc) to the caudal area and of the nucleus dorsalis intermedius ventralis anterior (DIVA) to the rostral area. In addition, it could be shown that the NI/NC projects to the HV thus confirming the electrophysiological results reported in a companion paper (Funke 1989) that the HV is a secondary area. The integrative function of HV is supported by connections to other sensory and motor telencephalic areas. Combined injections of FB and RITC revealed a topographic projection from the DIVA to the anterior Wulst.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1988

Spinal projections to the dorsal column nuclei in pigeons.

The dorsal column (DC) system was investigated in the pigeon by electrophysiological and anatomical methods. Field potentials recorded from the dorsal column nuclei (DCN) and evoked by electrical stimulation of cutaneous nerves showed two peaks in the case of wing nerve stimulation and one peak with leg nerve stimulation. Lesions of the DC or the ipsilateral dorsolateral funiculus (DLF) at a high cervical level (C4) indicate that a main input exists from the wing through the DC and from the leg through the DLF. With small injections of the fluorescent dye Fast blue into parts of the DCN it could be shown that aside from a primary afferent projection a well-developed postsynaptic dorsal column system exists only for the wing and that it takes its origin in the neurons of the lamina IV of the spinal dorsal horn.

Action Potentials↗

PubMed1986

Cells of origin of ascending pathways in the spinal cord of the pigeon.

Horseradish peroxidase was applied to ascending spinal pathways at high cervical levels to determine the cells of origin of these pathways in the pigeon. In addition to primary afferent fibers many ipsilaterally located lamina IV neurons of cervical segments project to the dorsal columns, indicating a substantial postsynaptic dorsal column pathway in birds. Cells projecting in the dorsolateral part of the white matter were predominantly located in lamina I and V throughout the spinal cord (bilaterally) and in the avian Clarke's column (ipsilateral at cervical and contralateral at lumbar levels). Neurons in the ventral horn (laminae VI-VIII) project to lateral and ventral parts of the lateral funiculus.

Afferent Pathways↗

PubMed1985

Prostaglandins and myocardial noradrenaline overflow after sympathetic nerve stimulation during ischemia and reperfusion.

The effects of a stable prostacyclin mimetic, iloprost (30 nmol/l), and of indomethacin (3 mumol/l) on ischemia-plus-reperfusion-induced changes in myocardial hemodynamics and sympathetic nerve function were examined in Langendorff-perfused rabbit heart isolated except for the postganglionic sympathetic cardiac nerves. Noradrenaline overflow was measured during an initial 1-min period of nerve stimulation (S1), compared with an identical stimulation (S2) made after 2 h of low-flow ischemia followed by a 30-min reperfusion period. Myocardial catecholamine content of left ventricular tissue was also measured. Pretreatment with iloprost, indomethacin, or vehicle began 10 min before ischemia. Global ischemia plus reperfusion reduced myocardial catecholamine content by 19% (vehicle), and the reduction was greater in indomethacin-pretreated hearts (37%, p less than 0.05), whereas iloprost increased tissue noradrenaline 18% above vehicle control (p less than 0.05). Initially, nerve stimulation-induced noradrenaline overflow ranged from 213 to 247 pmoles, and was significantly reduced after ischemia and reperfusion, the difference (S1-S2) being 198 pmoles (vehicle) and 117 pmoles (indomethacin), but only 44 pmoles after iloprost pretreatment (all groups p less than 0.01). In addition, iloprost improved the recovery of active systolic pressure development, coronary perfusion and left ventricular compliance on reperfusion, whereas a tendency toward further deterioration was observed in indomethacin-pretreated hearts. The results suggest that iloprost may protect both myocardial muscle and nerve cells from ischemia-plus-reperfusion injury. Preservation of myocardial catecholamine levels and sympathetic nerve responsiveness may contribute to improved recovery of reperfused ischemic myocardium.

Animals↗

PubMed1985

[Primary intraocular malignant melanomas in dogs and cats].

22 primary intraocular malignant melanomas in the dog and 5 in the cat were classified histologically. Pigmented epithelioid cells and mixed cell type melanomas with high reticulin fiber content and areas of necrosis were associated with the highest mortality rate. Metastases were found in one case each in the dog and the cat. The average age at diagnosis was 8 years in the dog and 9 years in the cat. There was no indication that intraocular melanomas are more prevalent in certain breeds. In the dog the cases were equally distributed between the sexes, whereas in the cat males were overrepresented. The most frequent location for the tumor was the uvea anterior (ciliary body). Bilateral tumor expression was observed once in a dog. In all cases the clinical diagnosis, tumor induced secondary effects, differential diagnosis and catamnesis are given.

Animals↗

PubMed1984