Biomedical subjects

V V Stezhka

Publications and source records attributed to V V Stezhka.

10 recordsLinked to original sources

PubMed2000

Serotonergic transmission in the periaqueductal gray matter in relation to aversive behaviour: morphological evidence for direct modulatory effects on identified output neurons.

Intracellular recordings were made from 21 cells in the dorsolateral periaqueductal gray matter in coronal midbrain slices. In the majority (n = 20) bath application of 5-hydroxytryptamine (30 or 150 mM) evoked either hyperpolarizing (n = 11) or depolarizing (n = 9) responses. Reconstructions of 11 neurons in the dorsolateral periaqueductal gray matter after filling with biocytin revealed a population of output neurons whose axons followed a dorsolateral trajectory towards the perimeter of the ipsilateral periaqueductal gray matter. In seven cells, the axon could be followed into the adjacent mesencephalic reticular formation. At the light microscopic level, immunostaining for 5-hydroxytryptamine revealed immunoreactive processes throughout the dorsolateral periaqueductal gray matter but no labelled somata or dendrites. Close associations (i.e. no discernible gap) were observed between serotonergic profiles and the somata and dendrites of biocytin-filled cells. At the ultrastructural level, serial sections through 21 appositions on to biocytin-filled dendrites in three slices revealed 19 true appositions (i.e. having closely parallel plasma membranes with no intervening glial cell profiles) with the biocytin-filled dendrite. Only four of the appositions (21%) showed evidence of synaptic specializations which included aggregations of synaptic vesicles, and some thickening of the apposing membrane. The dense reaction product in the biocytin-filled cells precluded identification of the ultrastructure of postsynaptic elements. However, examination of contacts between 5-hydroxytryptamine-immunoreactive profiles and unlabelled elements in material taken from the contralateral side of the periaqueductal gray matter (i.e. no biocytin present) or in material taken from perfusion-fixed whole brain, in which ultrastructural preservation was superior compared with slices, revealed a similar incidence (21% and 23%, respectively) of synaptic specializations. The data indicate that serotonergic transmission on to output neurons in the dorsolateral periaqueductal gray matter is largely mediated by non-junctional contacts, suggesting that the actions of 5-hydroxytryptamine on these cells are mediated predominantly by volume rather than wiring transmission.

Animals↗

PubMed1999

Neurones in the dorsolateral periaqueductal grey matter in coronal slices of rat midbrain: electrophysiological and morphological characteristics.

Intracellular recordings using the whole-cell patch-clamp configuration were made from 87 neurones in the dorsolateral "aversive" region of the periaqueductal grey matter (PAG) in coronal slices of rat midbrain. Camera lucida reconstructions made of 28 of the cells, which had been filled with biocytin, revealed round, triangular or oval cell bodies 11-40 microm in diameter. Between two and seven primary dendrites were present, which branched further, often becoming varicose. The dendritic tree was always contained within the dorsal half of the PAG. Biocytin-filled axons could be followed for 177-2315 microm from the soma. The axons typically travelled to the perimeter of the dorsal half of the ipsilateral PAG, before either turning ventrolaterally to run parallel to the tecto-bulbopsinal fibres or continuing their trajectory into the deep collicular layers or the mesencephalic reticular formation. Electrophysiologically, two functional categories of cells could be distinguished: type-A cells (30%) showed inward rectification at membrane voltages in excess of -77 mV and had short action potentials (1.6+/-0.07 ms), which were followed by a biphasic afterpolarisation characterised by an initial fast and a later slow phase. Only 18.5% of the type-A cells were spontaneously active (<4 Hz). The second category of cell (type B, 70% of the recorded population) did not show rectification and had longer-duration action potentials (2.1+/-0.07 ms), which showed a smooth decay of the afterhyperpolarisation phase. Approximately one third (37%) of the type-B cells fired spontaneously (<4 Hz). The gross morphology of the two types of cells was similar. However, in type-A cells (n=6), the axons could be seen to originate from the cell soma, whereas, in the majority of the type-B population (10/13), the axon arose from a primary dendrite. The results show that coronal slices of midbrain contain a viable population of "output" or "projection" neurones, which are accessible to electrophysiological and pharmacological investigation. In conscious animals, efferent output from this part of the PAG is concerned with mediating the autonomic and somatomotor changes which are characteristic components of aversive emotional behaviour. The output neurones should therefore reflect the net level of excitability in the PAG in relation to its functional activity.

Action Potentials↗

PubMed1997

Projections from dorsal raphe nucleus to the periaqueductal grey matter: studies in slices of rat midbrain maintained in vitro.

In coronal slices of rat midbrain localised injections of FluoroGold or DiO into the dorsolateral periaqueductal grey matter (PAG) labelled cells retrogradely in the dorsal half of the dorsal raphe nucleus (DRN) and the ipsilateral ventrolateral PAG. Low intensity electrical stimulation in the dorsolateral PAG (22.9 +/- 1.9 microA) evoked antidromic responses in neurones recorded intracellularly in the dorsal subnucleus of the DRN. Antidromic responses could also be evoked in neurones in the ventral DRN and its wings but only at much higher currents (40.9 +/- 2.5 microA) which likely spread to activate axons in the ventrolateral PAG that originated from perikarya in the ventral DRN. The findings are discussed in relation to modulation of the excitability of the aversive system in the dorsolateral PAG by the DRN.

Animals↗

PubMed1995

Dye coupling between dorsal raphe neurones.

Neurones in the dorsal raphe nucleus (DRN) were impaled and filled with biocytin in coronal slices of midbrain taken from young adult rats. The electrophysiological properties and gross morphology of the cells were similar to those reported previously for serotonergic neurones in the DRN. Of 27 cases in which filled neurones were recovered in histological material, almost half (48%) showed labelling of two or three cells, although only one cell had been recorded from. Coupled cells were identified as close or distantly coupled, depending on the distance from the soma of the presumed impaled cell (23.5 +/- 15 microns, n = 7 and 150 +/- 26.5 microns, n = 10 respectively). Whereas close-coupled cells may have been artefactually "coupled" by the penetrating electrode, coupling between distant cells is most likely to be a result of transfer of biocytin through gap junctions. Camera lucida reconstructions of pairs of labelled cells revealed extensive overlap of dendritic fields and numerous crossings between dendrites. When examined at high magnification under a light microscope, many of the crossing dendrites were found to travel in different focal planes. Nevertheless, for each pair of cells, at least one point of close apposition was observed between dendrites or between the axon and a dendrite of the presumed impaled and coupled cell. The incidence of dye coupling between neurones in the DRN may reflect a relatively high level of electronic coupling between the neurones. This form of coupling may be important in determining the synchronous nature of firing of neurones in the DRN.

Action Potentials↗

PubMed1994

Inhibitory and excitatory projections from the dorsal raphe nucleus to neurons in the dorsolateral periaqueductal gray matter in slices of midbrain maintained in vitro.

Coronal slices of midbrain from adult rats, maintained in an interface chamber at 33-35 degrees C, were used to investigate projections from the dorsal raphe nucleus to the dorsolateral periaqueductal gray matter. Extracellular recordings were made from neurons in the dorsolateral periaqueductal gray matter. The majority of cells were silent but activity could readily be induced by iontophoretic application of D, L-homocysteic acid from the recording pipette. Neuronal perikarya in the dorsal raphe nucleus were activated either by topical application of 15-100 nl droplets of 1 or 10 mM D,L-homocysteic acid or by iontophoresis into the dorsal raphe nucleus of 0.1 M D,L-homocysteic acid from a five-barrelled glass micropipette. Both forms of stimulation evoked increases or decreases in firing in neurons in the dorsolateral periaqueductal gray matter. The excitatory responses were evoked only from stimulation sites in the dorsal subnucleus of the dorsal raphe nucleus, whilst inhibitory responses could be evoked by stimulating throughout the nucleus. 5-Hydroxytryptamine was applied by iontophoresis to 55 neurons in the dorsolateral periaqueductal gray matter. Of these, 89% were inhibited whilst the remaining 11% were excited. No unresponsive cells were found. In a second series of experiments anterograde transport of biocytin was used to study projections from the dorsal raphe nucleus to the periaqueductal gray matter in vitro. Following injections of pellets of biocytin into the dorsal subnucleus of the dorsal raphe nucleus, two types of labelled axons could be distinguished which had either smooth or beaded profiles. Both types of axon could be followed into the region of the dorsolateral periaqueductal gray matter, from which recordings were made in the electrophysiological experiments. In contrast, following deposits of biocytin into the ventral half of the periaqueductal gray matter, very few labelled axons were found in the dorsolateral periaqueductal gray matter, although the ventrolateral periaqueductal gray matter was heavily labelled. We conclude that both excitatory and inhibitory projections from the dorsal raphe nucleus to the dorsolateral periaqueductal gray matter are present in the coronal midbrain slice preparation. Excitatory projections originate from the dorsal subnucleus of the dorsal raphe nucleus and may be mediated by a direct pathway. The inhibitory effects evoked from the ventral half of the dorsal raphe nucleus are probably mediated indirectly, perhaps by activation of inhibitory interneurons in the ventrolateral periaqueductal gray matter.

Animals↗

PubMed1994

Physiological properties of anatomically identified axo-axonic cells in the rat hippocampus.

1. The properties of a well-defined type of GABAergic local circuit neuron, the axo-axonic cell (n = 17), were investigated in rat hippocampal slice preparations. During intracellular recording we injected axo-axonic cells with biocytin and subsequently identified them with correlated light and electron microscopy. Employing an immunogold-silver intensification technique we showed that one of the physiologically characterized cells was immunoreactive for gamma-aminobutyric acid (GABA). 2. Axo-axonic cells were encountered in the dentate gyrus (n = 5) as well as subfields CA3 (n = 2) and CA1 (n = 10). They generally had smooth, beaded dendrites that extended throughout all hippocampal layers. Their axons ramified densely in the cell body layers and in the subjacent stratum oriens or hilus, respectively. Tested with electron microscopy, labeled terminals (n = 53) established synapses exclusively with the axon initial segment of principal cells in strata oriens and pyramidale and rarely in lower radiatum. Within a 400-microns slice a single CA1 axo-axonic cell was estimated to be in synaptic contact with 686 pyramidal cells. 3. Axo-axonic cells (n = 14) had a mean resting membrane potential of -65.1 mV, an average input resistance of 73.9 M omega, and a mean time constant of 7.7 ms. Action potentials were of short duration (389-microseconds width at half-amplitude) and had a mean amplitude of 64.1 mV. 4. Nine of 10 tested cells showed a varying degree of spike frequency adaptation in response to depolarizing current injection. Current-evoked action potentials were usually curtailed by a deep (10.2 mV) short-latency afterhyperpolarization (AHP) with a mean duration of 28.1 ms. 5. Cells with strong spike frequency accommodation (n = 5) had a characteristic firing pattern with numerous spike doublets. These appeared to be triggered by an underlying depolarizing afterpotential. In the same cells, prolonged bursts of action potentials were followed by a prominent long-duration AHP with a mean time constant of 1.15 s. 6. Axo-axonic cells responded to the stimulation of afferent pathways with short-latency excitatory postsynaptic potentials (EPSPs) or at higher stimulation intensity with up to three action potentials. Axo-axonic cells in the dentate gyrus could be activated by stimulating the CA3 area as well as the perforant path, whereas in the CA1 area responses were elicited after shocks to the perforant path, Schaffer collaterals, and the stratum oriens-alveus border. 7. In the CA1 area the EPSP amplitude increased in response to membrane hyperpolarization.(ABSTRACT TRUNCATED AT 400 WORDS)

Afferent Pathways↗

PubMed1992

Analysis of extrathalamic synaptic influences on reactions of sensorimotor cortical neurons during conditioning.

The effects of iontophoretic application of acetylcholine, noradrenaline, serotonin and their blockers on neuronal activity were studied in the cat before and during fulfillment of conditioned instrumental placing reflex. It was found that acetylcholine increased the background neuronal activity through muscarinic cholinergic receptors and noradrenaline decreased it through beta-adrenoceptors in a considerable proportion of the cortical neurons. Serotonin had no reliable effect on the background activity. At the same time, it facilitated an initial component of the impulse reaction to conditioned stimulus and part of the impulse reaction preceding the start of the conditioned movement. Acetylcholine applied iontophoretically also facilitated the evoked responses in some cortical neurons via nicotinic cholinergic receptors. On the contrary, iontophoretic application of noradrenaline or ephedrine decreased the evoked activity of some neurons. Application of beta-adrenergic receptor blocker, propranolol, led to an increase of neuronal responses to conditioned stimuli. Evidently, noradrenergic projections exert a steady inhibitory influence on the cortical neurons during natural functioning of the cortex. It is concluded that cortical reactions evoked by activation of thalamic projections and intracortical connections are modulated and regulated by extrathalamic projections to the cortex.

Acetylcholine↗

PubMed1990

[The effect of noradrenaline on the neuronal reactions of the motor cortex evoked by conditional stimulation].

In chronic experiments on cats the influence of iontophoretic application of adrenomimetic ephedrin and beta-adrenoblocker obsidan (propranolol) on motor cortex neuron reactions following conditional stimuli was investigated under instrumental placing reaction. It was shown for a majority of neurons that the background impulse activity and reactions following conditional stimulation were suppressed by the influence of ephedrin and on the contrary were increased by obsidan application. It is concluded that there exists a consistent tonic suppressing influence of the noradrenergic system on background and evoked cortical neurons impulse activity in the natural state. It is supposed that noradrenergic influence temporal increase may serve as an important link in mechanisms of external inhibition during stress situations, aversive effects, and distractive external excitations.

Acetylcholine↗

PubMed1990

[The effect of serotonin on the neuronal reactions of the sensorimotor cortex evoked by tactile and conditional acoustic stimulation].

Responses of the sensorimotor cortex neurons to tactile and conditional sound stimuli have been investigated before and after serotonin and lysergoamide iontophoretic application. Three functional neuronal groups were distinguished according to their responses to unconditional and conditional stimuli. It was shown that serotonin application facilitated early and late impulse responses to tactile stimuli, facilitated and modulated impulse responses of many cortical neurons to conditional stimuli. Changes in responses to conditioning occurred during initial phase of the placing reaction and just after initiation of the conditional movement. Serotonin application promoted involving new neurons in response to sound. All these changes in the reactions developed with unsignificant background activity fluctuation. It is supposed that facilitation of neuronal responses caused by serotonin was linked with activation of excitatory receptors (S2). An increase of the background and evoked impulse activity following application of lysergoamide may depend on inhibitory serotonin receptors (S1B).

Acoustic Stimulation↗

PubMed1989

[The effect of acetylcholine and cholinergic transmission blockers on the neuronal impulse activity of the cat motor cortex in a conditioned reflex].

Influence of acetylcholine, atropine, d-turbocurarine and hexonium on the background and evoked impulse activity of the motor cortex neurons was investigated in cat under instrumental placing reaction. Only those neurons were analyzed whose responses preceded conditional movement. It was shown that acetylcholine increased the background impulse activity in one group of cortical neurons and decreased it in the other neuronal group. During iontophoretic application of acetylcholine the background activity of some neurons declined in spite of the increase of their evoked conditional response. Atropine inhibited background impulse activity, the conditional impulse response being preserved. The background impulse activity increased and evoked conditional response was inhibited during iontophoretic application. Hexonium inhibited the background activity and conditional evoked impulse activity. It is suggested that cholinergic fibers in the natural state participate in supporting the background activity of cortical neurons by means of m-cholinoreceptors and at the sam time they evoke the impulse activity linked with conditional responses through n-cholinoreceptors.

Acetylcholine↗