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J Konopacki

Publications and source records attributed to J Konopacki.

At least 37 records · Page 2Linked to original sources
PubMed1992

In vivo intracellular correlates of hippocampal formation theta-on and theta-off cells.

Using urethane-anesthetized rat, intracellular recordings were made in hippocampal formation cells classified according to previously established criteria as either theta-on or theta-off, in order to further define the electrophysiological characteristics of these cells. Four cells classified as phasic theta-off cells had short duration spikes (less than 1 ms), high input resistances (54-61 M omega) and large fast afterhyperpolarizations (6-10 mV), thus sharing some of the properties of identified hippocampal interneurons. Phasic theta-off cells also exhibited rhythmic membrane potential oscillations (MPOs) ranging from 4 to 10 mV in amplitude during the simultaneous occurrence of extracellular theta field activity, but not during the occurrence of large amplitude irregular field activity (LIA). The MPOs of phasic theta-off cells were the same frequency as and were highly coherent with the extracellular theta field activity. In all four phasic theta-off cells the positive peak of the MPO was in phase with the positive peak of the local theta field activity. At the onset of extracellular theta field activity above 4-5 Hz, the membrane potentials of phasic theta-off cells showed a 5-10-mV hyperpolarizing shift, accompanied by MPOs without spike discharges. As theta frequency slowed down there was a return to baseline membrane potential levels and spike discharges occurred near the positive peak of the MPOs. The seven cells classified as phasic theta-on had longer duration spikes (greater than 1 ms), lower input resistances (22-36 M omega) and small (approx. 1.0 mV) fast afterhyperpolarizations, thus sharing some of the properties of hippocampal projection cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗
PubMed1992

Theta rhythms in the rat medial entorhinal cortex in vitro: evidence for involvement of muscarinic receptors.

Slice preparation obtained from the rat were used to study cholinergically induced field potentials in the medial entorhinal cortex. Perfusion of slices containing medial entorhinal cortex with acetylcholine, muscarine and eserine induced theta-like activity in a frequency range of 3-10 Hz and an amplitude of 200-300 microV. Nicotine, in contrast, did not produce any rhythmical slow waveforms. The cholinergically induced theta-like oscillations were abolished by perfusion of the muscarinic antagonists atropine sulphate and scopolamine but were unaffected by the nicotine blockers hexamethonium and mecamylamine.

Acetylcholine↗
PubMed1992

Carbachol-induced rhythmic slow activity (theta) in cat hippocampal formation slices.

Application of the cholinergic agonist, carbachol, produced theta-like rhythmical waveforms, recorded in the stratum moleculare of the dentate gyrus in the cat hippocampal formation slices. This effect of carbachol was antagonized by atropine but not D-tubocurarine. These results provide first direct evidence that the hippocampal formation neuronal network in the cat is capable of producing synchronized slow wave activity when isolated from pulsed rhythmic inputs of the medial septum.

Animals↗
PubMed1992

Carbachol-induced theta-like activity in entorhinal cortex slices.

The present study was conducted for two purposes: the first was to evaluate whether activation of cholinergic receptors of the entorhinal cortex in vitro (complete deafferentation) with carbachol (100 microM) was capable of producing theta (theta)-like slow activity. The second purpose was to determine whether carbachol-induced slow waveforms were mediated by muscarinic or nicotinic receptors. We demonstrated that carbachol was capable of producing theta-like slow activity. This activity was not altered by nicotinic antagonists, (+)-tubocurarine and hexametonium. Atropine and scopolamine, in contrast, completely blocked in vitro induced slow waves, indicating entorhinal muscarinic receptors to be actively involved in the mechanism generating cholinergic theta rhythm.

Animals↗
PubMed1992

Cholinergically-induced theta-like oscillations in the hippocampal formation of freely moving cats.

The present investigation was undertaken to assess the role of the cholinergics in the production of theta (theta) rhythm in the cat hippocampal formation. Intrahippocampal injections of carbachol, muscarine or eserine produced a well synchronized high frequency cholinergic theta activity (HFC) in a range of 5-12 Hz. Subsequent intrahippocampal injection of muscarinic antagonist, atropine sulphate, completely blocked this cholinergic-induced EEG pattern. The nicotinic antagonist, hexamethonium, was without any effect on the cholinergic-induced rhythmical waves. We suggest that HFC may result from the activation of the oscillatory mechanism intrinsic to the cat hippocampal formation.

Animals↗
PubMed1988

Evidence that activation of in vitro hippocampal theta rhythm only involves muscarinic receptors.

The present study was conducted for two purposes: the first was to evaluate whether activation of nicotinic receptors in the hippocampal formation in vitro (slice) preparation was capable of producing type 2 (atropine-sensitive) theta rhythm. The cholinergic nature and involvement of muscarinic receptors in this type of theta has been previously well documented. The second purpose was to determine whether perfusion of a number of (other) putative neurotransmitters shown to be present in the hippocampal formation could elicit type 1 (atropine-resistant) theta in the slice preparation. Further experiments were conducted to determine if these agents interacted in any manner with cholinergically-induced type 2 theta. Electroencephalic (EEG) theta activity was not induced by nicotine, providing evidence for an exclusive muscarinic receptor involvement in this cholinergically-induced type 2 theta. In addition, theta activity was not elicited by the application of gamma-aminobutyric acid (GABA), glutamate, norepinephrine, dopamine or serotonin. The application of any of these agents did not significantly alter the production of cholinergically-induced theta. These results suggest that type 1 theta originates in regions extrinsic to the hippocampus, or is the result of the interaction of several neurotransmitters on different receptors.

Animals↗
PubMed1988

Carbachol-induced EEG 'theta' in hippocampal formation slices: evidence for a third generator of theta in CA3c area.

The topography of carbachol-induced EEG theta activity was studied using the hippocampal formation slice preparation. Systematic tracking with electrodes exhibited two amplitude maxima of cholinergic-induced theta, one located in the stratum oriens of the CA1 pyramidal cells and the other in a region of CA3c pyramidal neurons. In addition, mapping experiments demonstrated EEG theta in the CA3a and CA3b cell body layers, but not in the subicular and parasubicular regions, or the ventral blade of the dentate gyrus. Furthermore, transected slice (trans-slice) preparations used in the present study revealed that the CA3c region could generate carbachol-induced theta independently of CA1 and dentate gyrus generator zones and conversely, CA1 and dentate gyrus areas were capable of generating cholinergic-induced theta rhythm independently of the CA3c region. These results provide strong evidence for 3 independent, anatomically separated generators of theta: one located in the stratum oriens of CA1 neurons, a second in the stratum moleculare of the dentate gyrus and a third one in the region of Ca3c cells. In addition, the results support previous in vivo suggestions that theta rhythm can be either elicited or blocked by cholinergic agents acting on sites within the hippocampal formation.

Animals↗
PubMed1988

Intracellular records of carbachol-induced theta rhythm in hippocampal slices.

Intracellular recordings were made in the CA1, CA3 and dentate cell layers prior to, during and after the bath perfusion of 50 microM carbachol on hippocampal slices. Fifty-six percent of the cells in this sample were termed theta (theta)-related, i.e., they exhibited membrane potential oscillations of 5-28 mV and rhythmic spike discharges related to the carbachol-induced extracellular theta-rhythm. The remaining 44% of the cells did not show the above relationships to the extracellular theta-rhythm. Carbachol produced an overall depolarization in all cells, in the range of 10-20 mV. These results demonstrated the cellular basis of carbachol-induced theta in hippocampal slices. This preparation will be a valuable model for studying cellular mechanisms and network properties underlying electroencephalographic activity.

Animals↗
PubMed1988

The development of carbachol-induced EEG 'theta' examined in hippocampal formation slices.

The development of carbachol-induced EEG theta (theta) activity was studied in the CA1 and dentate regions of hippocampal formation slices obtained from neonatal rats (4, 6, 8, 10, 12 and 14 days of age). When perfused with carbachol (50 microM), 4- and 6-day-old hippocampal slices exhibited only short-lasting irregular activity. The initial appearance of carbachol-induced rhythmic waves were observed in slices obtained from 8-day-old rats. From the time that theta appeared at 8 days of age, a steady increase in amplitude and frequency was noted. This observed in vitro developmental pattern of hippocampal theta-rhythm closely resembles the development of theta activity in in vivo preparations.

Aging↗
PubMed1987

Cholinergic theta rhythm in transected hippocampal slices: independent CA1 and dentate generators.

The controversy concerning intrahippocampal theta (theta) generators, arising as a result of in vivo investigations, prompted us to record theta-activity from isolated populations of CA1 pyramidal or dentate granule neurons in vitro. In the present study, transected slices (trans-slices) of the hippocampal formation were used to isolate the CA1 area from the dentate gyrus, providing a method for testing the 'two generator' hypothesis. We demonstrated that neurons in both the CA1 area and dentate gyrus could independently generate carbachol-induced (type 2) electroencephalogram (EEG) theta-activity. This activity could be completely blocked by the muscarinic receptor antagonist atropine sulfate but was unaffected by the nicotinic blocker, (+)-tubocurarine. These in vitro results provide the first direct evidence for the two-generator hypothesis and confirm the cholinergic-muscarinic nature of type 2 slow wave theta.

Animals↗
PubMed1987

Phase shifting of CA1 and dentate EEG theta rhythms in hippocampal formation slices.

Carbachol-induced hippocampal EEG theta-rhythms were recorded simultaneously from the CA1 and dentate areas in rat hippocampal brain slices. Phase shifts ranging from 0 to 180 degrees between the CA1 and dentate theta generators were observed. The differences in slow wave theta phase relations between in vitro and in vivo preparations were interpreted as resulting from deafferentation of the hippocampal slices.

Animals↗
PubMed1987

Carbachol-induced EEG 'theta' activity in hippocampal brain slices.

Application of the cholinergic agonist carbachol (50 microM) produced theta-like rhythmical waveforms, recorded in the stratum moleculare of the dentate gyrus. Atropine sulfate (50 microM) antagonized the carbachol-induced theta-like activity, consistent with this action of atropine in vivo. These results provide the first direct evidence that hippocampal neurons are capable of producing synchronized slow-wave activity when isolated from pulsed rhythmic inputs of the medial septum and other brain regions.

Animals↗
PubMed1987

Theta in hippocampal slices: relation to synaptic responses of dentate neurons.

The effects of cholinergic agents on isolated dentate neurons were studied to characterize cellular mechanisms underlying carbachol-induced 'theta' EEG activity. Carbachol, eserine, and acetylcholine produced a synchronization of slow wave activity (theta) accompanied by depression of perforant path to dentate field potentials. These effects were antagonized by atropine but not d-tubocurarine. The results suggest that muscarinic receptors mediate theta activity resulting from a depolarization of dentate neurons.

Acetylcholine↗
PubMed1986

Effect of intracerebroventricular injection of prostaglandin E2 on anterior pituitary cell proliferation.

The influence of an intracerebroventricular (i.c.v.) injection of prostaglandin E2 (PGE2) on the mitotic activity of the rat anterior pituitary was investigated. It was found that i.c.v. PGE2 (3 micrograms/20 microliters) resulted in a significant decrease of the mitotic activity in the anterior pituitary. This drop involved mainly chromophobic cells. No mitoses were found in acidophilic cells either in controls or in PGE2-treated rats. It is suggested that PGE2 may release an unidentified hypothalamic factor which inhibits the cell proliferation of the anterior pituitary.

Animals↗
PubMed1986

The effect of amphetamine on hippocampal EEG and EOG activity in cats.

The effect of anorectic dose of amphetamine on some correlates of arousal (hippocampal EEG and EOG activity) was examined in cats. After injection of amphetamine the frequency of hippocampal rhythmic slow activity and EOG activity increased when preinjection value of rhytmic slow activity was low, but decreased when it was high. Thus, amphetamine anorexia may be accompained with an increase as well as with a decrease of arousal level.

Amphetamine↗
PubMed1986

The effect of darkness on amphetamine induced stereotyped behavior in cats.

Transient elimination of visual stimuli (20 min darkness in the experimental chamber) did not affect the amphetamine induced stereotyped behavior and accompanied arousal in cats. It is concluded that anqhetamine stereotyped behavior in cats represents centrally initiated event of animal response to drug which is, under some conditions, independent of environmental visual input.

Amphetamine↗