Biomedical subjects

J Konopacki

Publications and source records attributed to J Konopacki.

At least 19 recordsLinked to original sources

PubMed2001

Window effect of temperature on carbachol-induced theta-like activity recorded in hippocampal formation in vitro.

The effect of different temperatures of ACSF (18-42 degrees C) on carbachol (CCH)-induced field potentials were examined in the present study. Two hundred and thirty one experiments were performed on hippocampal formation slices maintained in a gas-liquid interface chamber. All slices were perfused with 50 microM CCH. A recording electrode was positioned in the region of CA3c pyramidal cells. The experiments gave two main findings. First, in a presence of continuous cholinergic stimulation the temperature of the bathing medium per se determined the rate of synchronization of the field potentials and pattern of EEG activity recorded. Second, within the temperature range from 33 degrees to 37 degrees C a window effect of temperature on CCH-induced theta-like activity (TLA) was noted: in this temperature range all slices tested responded only with one pattern of EEG activity-TLA. The results are discussed in light of temperature effects on hippocampal neuronal networks.

Action Potentials↗

PubMed2001

Effect of posterior hypothalamic injection of procaine on the hippocampal theta rhythm in freely moving cats.

Earlier in vivo studies conducted on freely moving and anesthetized rats demonstrated that the posterior hypothalamus (PH) comprises pathways critical for producing the synchronous hippocampal formation (HPC) theta rhythm. In addition, these findings suggested that the frequency of the HPC theta was encoded in the PH and then was fed via the medial forebrain bundle to the medial septum and HPC. In the present study we attempted to verify this hypothesis with use of a different in vivo model--freely moving cats. The microinjection of the local anaesthetic, procaine, into the PH region reversibly suppressed the spontaneous as well as sensory and electrically induced HPC theta. However, in contrast to rats, in freely moving cats microinjection of procaine into the PH reduced the amplitude of the HPC theta but had no effect on theta frequency. We conclude that in freely moving cats the PH region comprises a critical part of the ascending brainstem pathway, for production of the HPC theta rhythm. In contrast to rats, in freely moving cats ascending inputs from the brainstem to the PH contribute mainly to the amplitude of the HPC theta rhythm.

Anesthetics, Local↗

PubMed2000

In vitro recorded theta-like activity in the limbic cortex: comparison with spontaneous theta and epileptiform discharges.

The generation of EEG theta rhythm in the mammalian limbic cortex is a prime example of rhythmic activity that involves central mechanisms of oscillations and synchrony. This EEG pattern has been extensively studied since 1938, when Jüng and Kornmüller (1938) demonstrated the first theta recordings in the hippocampal formation of rabbits. In 1986 in collaboration with Drs. B.H. Bland, S.H. Roth and B.M. MacIver we demonstrated for the first time that bath perfusion of hippocampal slices with the cholinergic agonist, carbachol, resulted in theta-like oscillations. Since this initial demonstration of in vitro theta-like activity, we have carried out a number of experiments in an attempt to answer the basic question: what are the similarities between cholinergic-induced in vitro theta-like activity and theta rhythm which naturally occurs in the in vivo preparation. Thus far, our studies have provided strong evidence that theta-like activity recorded in vitro shares many of the physiological and pharmacological properties of theta rhythm observed in vivo. The question whether in vitro theta-like oscillations reflect features of epileptiform activity is also addressed in this review.

Animals↗

PubMed2000

[Basic micro-electrophysiologic techniques used in neurobiology].

Problems of application of microelectrophysiological techniques in neurobiology are addressed. Authors focused on five basic recording techniques: micro-EEG, multi unit activity, single unit activity, intracellular recording and patch clamp techniques.

Action Potentials↗

PubMed2000

[Use of trans-slice technique for microencephalographic examinations in vitro].

The present paper reviews the experimental data concerning the use of trans-slice preparation technique in investigation of theta-like activity generation in the limbic cortex. Specific aspects of the technical arrangement of the hippocampal formation and entorhinal cortex microelectroencephalographic registration were emphasized.

Animals↗

PubMed1999

The effect of intraseptal procaine injection of hippocampal theta in freely moving cat.

Numerous studies have demonstrated that in the rodent, the septum is a critical site for the generation of hippocampla rhythmical field activity (theta, RSA). The aim of the present study was to clarify the role of the medial septal area in theta generation in the cat. Results indicate that (1) the microinfusion of the local anesthetic procaine into the medial septal region temporarily suppressed spontaneous as well as sensory and electrically induced hippocampal theta; (2) the suppression lasted 15 min and then amplitude and power of the hippocampal theta showed a progressive increase reaching preprocaine levels 60 min from the infusion onset. Theta frequency, in contrast, did not differ from control levels. The results provide evidence for the medial septal mediation of the hippocampal theta in the cat. This region is responsible for controlling theta amplitude but not its frequency. The present data supported the earlier results obtained in the rat and determined that the medial septal region plays a critical role in the generation of the hippocampal theta activity in cat.

Anesthetics, Local↗

PubMed1998

Theta-like activity in the limbic cortex in vitro.

The generation of EEG theta rhythm in the mammalian limbic cortex is a prime example of rhythmic activity that involves central mechanisms of oscillations and synchrony. This EEG pattern has been extensively studied since 1938, when Jung and Kornmuller (28) (Eine methodik der ableitung lokalisierter potential schwankingen aus subcorticalen hirnyebieten, Arch. Psychiat. Neruenkr. 109 (1938) 1-30) demonstrated the first theta recordings in the hippocampal formation of rabbits. In 1986 we demonstrated for the first time that bath perfusion of hippocampal slices with the cholinergic agonist, carbachol, resulted in theta-like oscillations. Since this initial demonstration of in vitro theta-like activity, we have carried out a number of experiments in an attempt to answer the following question: what are the similarities between cholinergic-induced in vitro theta-like activity and theta rhythm which naturally occurs in the in vivo preparation. Thus far, our studies have provided strong evidence that theta-like activity recorded in vitro shares many of the physiological and pharmacological properties of theta rhythm observed in vivo.

Animals↗

PubMed1997

Theta-like activity in hippocampal formation slices: the effect of strong disinhibition of GABAA and GABAB receptors.

The involvement of GABAA and GABAB receptors in neural mechanisms responsible for the production of theta rhythms in hippocampal formation (HPC) slices is addressed in the present study. In a number of papers published in the last decade, we have demonstrated that theta-like activity can be successfully recorded in the limbic cortex maintained in vitro when the cholinergic agonists, acetylcholine, carbachol or muscarine, were added to the bath. Recently, we have also shown a strong GABAA modulation of the cholinergic-induced in vitro theta-like activity. This study presents a report of the first demonstration of in vitro theta-like field responses induced a consequence of simultaneously inhibiting hippocampal GABAA and GABAB receptors. HPC slices (350 microns) were maintained in a gas-liquid interface chamber (35 degrees C). Theta-like activity was induced in the presence of bath perfusion of bicuculline (GABAA antagonist) and 2-hydroxysaclophen (GABAB antagonist). This in vitro induced field response was antagonized both by muscimol (GABAA agonist) and baclophen (GABAB agonist). In addition, the experiments presented here revealed that bicuculline/2-hydroxysaclophen-induced in vitro theta-like activity also had a strong cholinergic M1 involvement: it was abolished by hemicholinium-3 (choline transport blocker) and pirenzepine (specific antagonist of M1 receptor), but not by gallamine (specific antagonist of M2 receptor). The results of the present study provided further evidence for a strong GABAergic/cholinergic interaction in the neural mechanism responsible for production of theta-like activity in the hippocampal formation slices.

Animals↗

PubMed1996

Evidence for differential control of posterior hypothalamic, supramammillary, and medial mammillary theta-related cellular discharge by ascending and descending pathways.

Single-unit discharge was recorded from cells in the posterior hypothalamic nucleus (PH), supramammillary nucleus (SuM), and medial mammillary nucleus (MM) during hippocampal theta (theta) elicited by stimulation of the reticular nucleus pontis oralis (RPO). In agreement with previously published work, theta-related cells in the PH (12 cells) were all classified as tonic theta-ON (increased tonic discharge rate during hippocampal theta), whereas those in the SuM (9 cells) and MM (15 cells) were all classified as phasic theta-ON (rhythmic discharge, in phase with ongoing theta). The effect of RPO stimulation on cell discharge was tested after hippocampal theta was abolished by infusion of procaine into the medial septum/vertical limb of the diagonal band. The RPO-elicited discharge patterns of all PH tonic theta-ON cells and all SuM phasic theta-ON cells survived septal procaine infusion. Further, the discharge rate of PH cells and the frequency of burst discharge of SuM cells during RPO stimulation both increased after the infusion. In contrast, septal procaine infusion abolished the RPO-elicited rhythmic discharge pattern in MM phasic theta-ON cells and attenuated their discharge rates. These results indicate that the PH and SuM form parts of an ascending system mediating hippocampal theta, whereas the MM receives (and perhaps relays to other parts of the limbic system) rhythmic input descending from the septo-hippocampal system. In addition, PH and SuM receive descending inputs that limit the discharge rates of their theta-related cells during hippocampal theta.

Afferent Pathways↗

PubMed1996

Kainic acid versus carbachol induced emotional-defensive response in the cat.

The emotional-defensive response (EDR) and accompanied neurotoxic and electroencephalographic (EEG) effects induced by injection of kainic acid (KA, 0.1; 0.2 microgram) into the midbrain periaqueductal grey region (PAG) and antero-medial hypothalamus (AMH) in the cat were examined and compared with EDR and accompanied neurotoxic and EEG effects induced by injection of cholinergic agent, carbachol (CCH), into the same sites. The injections of KA (0.2 microgram) into the PAG induced EDR which closely resembled the defense behavior typically observed after administration of CCH. However, in contrast to CCH-induced EDR, the defensive response induced by KA was found to be accompanied by EEG symptoms of epileptiform activity in the limbic cortex and a massive cell loss in the site of injection. It is proposed that KA-induced EDR and seizure activity may have resulted from the activation of different cell populations localized either in the vicinity of the injection (i.e., PAG region) and in the area remote from the injection loci, the limbic cortex. KA induced activation of PAG neuronal network would trigger the 'local response' (emotional-defensive response) and produce a remote effect-epileptiform activity.

Agonistic Behavior↗

PubMed1996

Cholinergic/GABAergic interaction in the production of EEG theta oscillations in rat hippocampal formation in vitro.

The generation of EEG theta rhythm (RSA) in the hippocampal formation is a prime example of rhythmic activity involving central mechanisms of oscillation and synchrony. Cholinergic nature of the in vitro and in vivo induced RSA has been undoubtedly established. Recently, we have demonstrated in vitro that the hippocampal formation theta rhythm resulted from interaction between the cholinergic and GABAergic systems. In the present study we have provided additional in vitro evidence that the hippocampal GABA-A receptors are actively involved in the mechanism of theta production. Specifically, we demonstrated that bicuculline-GABA-A antagonist significantly augmented carbachol induced theta response increasing amplitude and power of rhythmical slow waves. In separate experiments the carbachol+bicuculline induced RSA were studied in the presence of muscarinic M1 and M2 antagonists--pirenzepine and gallamine (respectively) and GABA-A agonist--muscimol. Both pirenzepine and muscimol antagonized induced theta oscillations and gallamine was found to be completely ineffective in blocking this EEG response. The results provided evidence for M1 cholinergic/GABA-Aergic interaction in mechanisms responsible for theta production.

Animals↗

PubMed1996

The spontaneous theta rhythm recorded from the hypothalamus posterior in the cat in vivo.

Rhythmical slow activity (theta) was mapped in the hypothalamic region in freely moving cats. We recorded well synchronized and high amplitude theta rhythm in the medial part of the hypothalamus posterior area. The EEG recordings made from lateral part of this hypothalamic region contained only irregular activity. These findings support earlier observations concerning the topography of hippocampal formation desynchrony and synchrony system. The observations of the present study also suggest that the hypothalamus posterior area is actively involved in the mechanisms responsible for generating theta oscillations in the cat.

Animals↗

PubMed1996

The rhythmic slow activity recorded from entorhinal cortex in freely moving cats.

The relationships between the entorhinal cortex (EC) and the hippocampal formation (Hipp) field potentials were examined in the present study. The detailed analyses of the signal let us group the patterns of theta appearance into three categories: (1) Theta rhythm dominating in both recordings from the EC and from the Hipp (2) Theta rhythm dominating in the Hipp with irregular activity in the EC (3) Theta rhythm dominating in the EC with irregular activity in the Hipp. These findings provide the evidence for the intrinsic generator of theta rhythm to be localized in entorhinal cortex in cats.

Animals↗

PubMed1996

Development of oscillatory activity in the limbic cortex in vitro.

The generation of EEG theta rhythms in the mammalian limbic cortex is a prime example of rhythmic activity that involves central mechanisms of oscillations and synchrony. In 1985 for the first time we demonstrated that bath perfusion of the hippocampal formation slices with cholinergic agonists resulted in theta-like oscillations. Since this initial demonstration of the in vitro theta activity, we have carried out a number of experiments in an attempt to answer the general question: what are the similarities between the cholinergic-induced in vitro theta and theta rhythm which naturally occurs in the vivo preparation. Thus far, our in vitro studies provided strong evidence that the in vitro recorded theta oscillations replicate many physiological and pharmacological properties of the in vivo observed theta rhythm. In addition, our studies validate the in vitro maintained limbic cortex as a model for studying central mechanisms of oscillations and synchrony.

Animals↗

PubMed1995

Discharge patterns of hippocampal theta-related cells in the caudal diencephalon of the urethan-anesthetized rat.

1. Single-unit discharge patterns of cells in specific nuclei of the caudal diencephalon were characterized in relation to simultaneously recorded field activity from the stratum moleculare of the dentate gyrus according to the criteria that have been used previously to classify cells in the hippocampal formation (including entorhinal cortex), medial septum, and cingulate cortex. Theta (theta)-related cells were classified as 1) tonic theta-ON, if they discharged nonrhythmically and increased their discharge rates during hippocampal theta relative to large, irregular hippocampal field activity (LIA); 2) tonic theta-OFF, if they discharged nonrhythmically and decreased their discharge rates during theta relative to LIA; or 3) phasic theta-ON, if they discharged rhythmically and in phase with ongoing theta, but nonrhythmically during LIA. Cells not meeting any of the above criteria were classified as nonrelated. 2. Recordings were obtained in a total of 127 cells from the caudal diencephalon. Recordings were made in 54 cells from the posterior hypothalamic nucleus (PH), 16 from the supramammillary nucleus (SuM), 20 from the PH/SuM border, and 23 from the medial mammillary nucleus (MM). Recordings were also made from nine cells from the central medial nucleus of the thalamus (CM) and five from the dorsomedial hypothalamic nucleus (DMH). 3. Of the 54 PH cells, 43 (80%) were classified as tonic theta-ON and 11 (20%) as nonrelated. Tonic theta-ON cells in the PH discharged at significantly higher rates during theta, either occurring spontaneously (9.6 +/- 1.7 Hz, mean +/- SE) or elicited with a tail pinch (TP theta; 10.6 +/- 1.9 Hz), than during LIA (3.6 +/- 1.4 Hz). Of the nine CM cells, seven (78%) were tonic theta-ON and two (22%) were nonrelated. Tonic theta-ON cells discharged at significantly higher rates during theta (17.5 +/- 7.8 Hz) or TP theta (18.0 +/- 7.1 Hz) than during LIA (7.3 +/- 4.8 Hz). All DMH cells were nonrelated. 4. Of the 20 PH/SuM border cells, 15 (75%) were classified as tonic theta-OFF and discharged at significantly higher rates during LIA (5.3 +/- 1.5 Hz) than during theta (0.8 +/- 0.4 Hz) or TP theta (0.4 +/- 0.3 Hz). Five (25%) cells in the PH/SuM border were nonrelated. 5. All of the 16 cells (100%) recorded from the body of the SuM were phasic theta-ON. The discharge rates of these cells did not change significantly across hippocampal field states (LIA = 8.3 +/- 1.6; theta = 7.3 +/- 1.6; TP theta = 8.6 +/- 1.7 Hz).(ABSTRACT TRUNCATED AT 400 WORDS)

Anesthesia↗

PubMed1994

Muscarinic (M1) mediation of carbachol-induced theta in the cat entorhinal cortex in vitro.

Entorhinal cortex slice preparations obtained from the cat exhibited theta rhythm during perfusion with 50 microM carbachol. The effect of carbachol was antagonized by the muscarinic blocker atropine sulphate, but not by hexamethonium and mecamylamine, which are antagonists of the nicotinic receptor. Further analysis of the pharmacological profile of these carbachol-induced theta oscillations showed that M1 receptor subtype to be involved in mediation of this EEG activity: the theta rhythm was antagonized by the M1 receptor blocker pirenzepine, but was unaffected by gallamine, an antagonist of the M2 receptor subtype.

Animals↗

PubMed1993

Muscarinic (M1) mediation of hippocampal spontaneous theta rhythm in freely moving cats.

The effects of intrahippocampally applied different doses of muscarinic (atropine sulphate, pirenzepine, gallamine) and nicotinic (hexamethonium, mecamylamine) antagonists on the spontaneous theta rhythm in the cat hippocampal formation were investigated. The injections of atropine and pirenzepine abolished spontaneous theta but administration of gallamine did not affect the EEG pattern. The intrahippocampally administered nicotinic blockers, hexamethonium and mecamylamine, were completely ineffective in antagonizing theta waves. The data suggest that the spontaneous theta rhythm in the cat is mediated by the M1 receptor subtype.

Animals↗

PubMed1993

Theta-like activity in hippocampal formation slices: cholinergic-GABAergic interaction.

Brain slice preparations obtained from the rat were used to study cholinergic GABAergic interaction in mechanisms responsible for production of theta-like activity in hippocampal slices maintained in vitro. Bicuculline, a GABA-A antagonist, applied at 25 microM facilitated the effect of low concentration carbachol (25 microM) in inducing theta-like oscillations. At 100 microM, bicuculline increased the amplitude of carbachol-induced theta-like slow waves. This carbachol-bicuculline induced field potential was antagonized by a muscarinic blocker, atropine sulphate, and a GABA-A agonist, muscimol. These results provide in vitro evidence for cholinergic-GABAergic interaction in the production of hippocampal theta-like slow waves.

Animals↗