PROMET: The effect of operator profession on non-laser transvenous lead extraction

Funding Acknowledgements

Type of funding sources: None.

OnBehalf

PROMET group

Background

As implantation of cardiac implantable devices (CIED) rises globally, there is a paralleled need for extraction of these devices. Indications for transvenous lead extraction (TLE) is expanding, fuelling demand. This lifesaving procedure is performed by cardiologists and cardiac surgeons (CS). Cardiologists are familiar with transvenous methods whilst cardiac surgeons possess the skillset to address the significant complications associated with this procedure.

We compared non-laser TLE outcomes performed by cardiologists and cardiac surgeons from six high-volume extraction centres across Europe.

Methods

Data was collected retrospectively from six major European TLE centres of 2205 patients and 3849 leads (PROMET). Propensity 1:1 score matching (PSM) was performed to account for confounding variables. PSM model with variables: lead dwell time, infection indication, biventricular system and defibrillator device, was best matched. This dataset was analysed to compare outcomes of TLE performed by the cardiologists and CS. Predictors of 30-day mortality and complications were identified using a multivariate regression analysis.

Results

Patients treated by CS and cardiologists were similar in age (64.7 vs 66.7 years, p = NS) and equally male (70.3% vs 72.3%, p = 0.39) with a parallel infectious indication (51.7% vs 47.6%, p = 0.1). Surgeons achieved a significantly higher proportion of clinical success than cardiologists (98.9% vs 96.4%, p = 0.001) and complete lead extraction (98% vs 95.9%, p < 0.01) with a higher rate of minor complications (4.1% vs 2.2%, p = 0.024); major complications were similar (0.9% vs 1.2%, respectively, p = 0.46) as was 30-day mortality (3.2% vs 2%, respectively, p = 0.28). Multivariate regression analysis revealed systemic infection (p < 0.001, OR 7.2 [CI 2.3-20.1]) and defibrillator system extraction (p = 0.025, OR 3.4 [CI 1.2-10.2]) increased the odds of 30-day mortality, whilst Evolution™ sheath use reduced the odds (p = 0.025, OR 0.34 [CI 0.13-0.88]); lead dwell time (p = 0.02, OR 1.005 [1-1.009] and Evolution™ sheath use (p = 0.023, OR 2.15[1.1-4.15]) increased the odds of complications.

Conclusion

Cardiac surgeons and cardiologists achieved a high rate of TLE procedural success and with a similar safety profile, replicating standards seen across Europe.

PROMET: the effect of age on patient outcomes in non-laser transvenous lead extraction

Funding Acknowledgements

Type of funding sources: None.

OnBehalf

PROMET group

Background

Cardiac implantable electronic devices (CIEDs) improve morbidity and mortality. This has fuelled an upsurge in implantation of these devices across all patient cohorts, simultaneously increasing the need for transvenous lead extractions (TLE). As the global population expands and life-expectancy extends, TLE will play a significant role in CIED management. Advancing patient age is a recognised risk factor for poor outcomes however the association between patient age and TLE outcomes remains unclear. 

We sought to evaluate the relationship between patient age and non-laser TLE outcomes.

Method

Data of 2205 patients (3849 leads) was collected retrospectively from six high-volume TLE institutes across Europe (PROMET) between January 2005-December 2018. Propensity 1:1 score matching was performed to limit the effects of confounding variables, pairing 353 patients in the >80 years of age category with 353 patients in <80 years of age group. Procedural outcomes were compared between the two age groups and multivariate regression analysis was used for predictors of 30-day mortality.

Results

In the <80 and >80 years-of-age cohorts, there was a similar proportion of male patients (65.3% vs 67.9%, p = 0.47) treated under general anaesthesia (96.5% vs 93.4%, p = 0.078) for a pre-dominant infectious indication (56.7% vs 60.3%, p = 0.52) but with a higher requirement of the EvolutionTM sheath in the octogenarians (39.4% vs 48.4%, p = 0.015). A similar clinical success per lead was achieved between the two age groups (96.6% vs 98%, <80 vs >80 years, p = 0.245) as was complete lead extraction (95.5% vs 96.6%, <80 vs >80 years, p = 0.44) with a comparable minor complication rate (2.3% vs 3.1%, <80 vs >80 years, p = 0.29) and major complications (1.1% vs 1.4%, <80 vs >80 years, p = 0.74). Thirty-day mortality was higher in the octogenarian cohort than the <80-year-olds without reaching statistical significance (5.4% vs 2.6%, p = 0.08); peri-procedural mortality was similar in both age groups (0.3% vs 0.6%, respectively, p = 0.56). Multivariate regression analysis revealed age (p = 0.013, OR 1.06 [1.01-1.12]), systemic infection (p = 0.026, OR 3.4 [1.16-10.35]) and lead dwell time (p = 0.007, OR 1.01 [1.003-1.017]) increased the odds of 30-day mortality.

Conclusion

Transvenous lead extraction is similar in efficacy and safety across all age groups. Thirty-day mortality is higher in the advanced age group, signifying the importance of post-procedural management in this cohort.

Transvenous lead revision for cardiac perforation: a single centre experience

Funding Acknowledgements

Type of funding sources: None.

Background

Cardiac perforation is an uncommon but life-threatening complication of cardiac implantable electronic device (CIED) implantation. Management strategy commonly relies on diagnostic Computed Tomography (CT) imaging and cardiac surgery. Emerging evidence has indicated a diversion from this approach. Transvenous culprit lead revision has been shown to be safe and efficacious in limited series.

We sought to evaluate the outcomes of transvenous lead revision in patients with cardiac perforation.

Method

Data was collected retrospectively of patients admitted to a single tertiary centre with CIED-related cardiac perforation between December 2013 – October 2019. Transvenous lead revision was performed as standard with cardiac surgery on standby. Patient demographics, use of CT imaging, method of removal and 30-day outcomes were recorded.

Results

Of the 46 recorded CIED-related cardiac perforations, the majority occurred in female patients (63%) and hypertensives (61%), whilst a proportion had cancer (20%) and ischaemic heart disease (30%). The culprit in most cases was a standard pacing lead (92%) of an active fixation (98%) in the right ventricle (80%) positioned at the ventricular apex (65%). The median time to presentation from implant was 14 days [IQR 4-50 days] with chest pain (44%); abnormal pacing indices was highly prevalent (95%) whilst a pericardial effusion was noted in the majority of cases (57%). CT scanning was performed in 19 cases (41%) for various indications but deemed essential in only 4, all of which had non-diagnostic pacing indices and imaging. Chest X-ray (CXR) found clear perforation, lead displacement or pleural effusion in 74% of cases, whilst an echocardiogram found these in 64% of cases. The culprit lead was replaced in the majority of cases (87%) under local anaesthesia (76%) with surgical backup. The median hospital stay was 7 days [IQR 3-10 days] with zero procedural and 30-day mortality.

Conclusion

Transvenous lead revision for CIED-related cardiac perforation is safe and efficacious. CT modality for diagnostic purposes is useful in providing incremental value in a minority of cases; patients with non-diagnostic pacing parameters and non-CT imaging benefit most from this.

Rapid and selective detection of viruses using virus-imprinted polymer films

We prepared a nanopatterned polymer film of polydimethylsiloxane (PDMS) via virus imprinting. The imprinted surface exhibited nanoscale cavities with the mean size of 120 ± 4 nm. These cavities demonstrated the ability to preferentially capture a target virus from an aqueous suspension of ultralow volume (5 μL) after only 1 minute of contact. Two inactivated viruses with similar shape, Influenza A (HK68) and Newcastle Disease Virus (NDV), were employed as model pathogens. The polymer film, which was first imprinted with HK68 and exposed sequentially to suspensions containing fluorescently labeled NDV and HK68, was able to preferentially bind HK68 at a capture ratio of 1 : 8.0. When we reversed the procedure and imprinted with NDV, the capture ratio was 1 : 7.6. These results were obtained within 20 minutes of static exposure. The suspensions contained viruses at concentrations close to those occurring physiologically in influenza infections. The limit of detection was approximately 8 fM. Production of virus-imprinted films can be readily scaled to large quantities and yields a disposable, simple-to-use device that allows for rapid detection of viruses.

Medial septum mediates the increase in post-ictal behaviors and hippocampal gamma waves after an electrically induced seizure

Hippocampal EEG and behavior of freely moving rats were studied before and after a hippocampal afterdischarge (AD), with or without reversible inactivation of the medial septum (MS) by muscimol. Muscimol suppressed the normal hippocampal EEG, including theta (5-10 Hz) and gamma (30-70 Hz) waves. After a hippocampal AD, hippocampal gamma waves were decreased for about 2 min and then increased at 3-10 min, while power of EEG of <30 Hz was decreased at </=3 min and showed no increase after an AD. Muscimol injection in the MS before the AD blocked the post-ictal increase of the gamma waves. In rats injected with vehicle in the MS, post-ictal increase in gamma waves was accompanied by an increase in horizontal locomotion, rearings, face washes, and wet dog shakes. In rats injected with muscimol in the MS before the AD, both the post-ictal increase in gamma waves and behaviors were completely suppressed. Muscimol injection in the MS after the AD significantly suppressed both gamma waves and post-ictal behaviors, as compared to vehicle-injected rats, but to a lesser degree than rats injected with muscimol in the MS before the AD. Hippocampal AD duration was not significantly affected by muscimol injection in the MS. We conclude that the MS is responsible for the maintenance of the normal and the post-ictal gamma waves. We suggest that the post-ictal gamma waves in the hippocampus may drive post-ictal behaviors, and in previous studies, we showed that this may occur through the nucleus accumbens.

Effects of a water-soluble antitumor ether phosphonoinositide, D-myo-inositol 4-(hexadecyloxy)-3(S)-methoxybutanephosphonate (C4-PI), on inositol lipid metabolism in breast epithelial cancer cell lines

We have demonstrated previously that D-myo-inositol 4-(hexadecyloxy)-3(S)-methoxybutanephosphonate (C4-PI), an isosteric phosphonate analog of phosphatidylinositol developed to inhibit inositol lipid metabolism, was unable to inhibit phosphatidylinositol (PI) 3-kinase activity. We now report the effects of the compound on other aspects of inositol metabolism. We demonstrated that C4-PI inhibits the activity of purified recombinant PI-phospholipase C-beta (PLC-beta) at all concentrations tested; it enhanced the activity of PI-PLC-gamma and PI-PLC-delta at low concentrations (10 microM), while severely inhibiting their activities at higher concentrations. In the breast cancer cell lines MCF-7 (estrogen receptor positive) and MDA-MB-468 (estrogen receptor negative), C4-PI had no effect on the uptake of D-myo-inositol but severely inhibited its incorporation into PI. In spite of the drastic decrease in PI synthesis, C4-PI did not affect the levels of inositol incorporated into phosphatidylinositol 4,5-bisphosphate (PIP2) in the cells. In vitro assays showed that C4-PI inhibited PI synthase activity (inhibition of 35% at 50 microM) but had little effect on PI 4-kinase activity (inhibition of 13% at 150 microM). C4-PI inhibited the proliferation of MCF-7 and MDA-MB-468 cell lines with IC(50) values of 12 and 18 microM. Taken together, the results suggest that the accumulation of [3H]inositol in PIP2 in cells incubated with C4-PI may be due to the inhibition of PIP2 hydrolysis in the cells with no effect on its synthesis. The role of these C4-PI-induced effects in the mechanism of growth inhibition by C4-PI remains to be established.

A role of subicular and hippocampal afterdischarges in initiation of locomotor activity in rats

The possible role of a hippocampal afterdischarge (AD) episode in eliciting locomotor movements was evaluated in freely moving rats. Electrical stimulation of either the ventral subiculum (VSB) or the hippocampal CA1 region evoked an AD of 6-50 s in duration, which was followed by an increase in locomotor activity. Similar results were also observed after unilateral injection of N-methyl-d-aspartic acid (NMDA, 0.25 microg or 1 microg), a glutamate receptor agonist, into the VSB. Locomotor activity was not observed when either electrical or chemical stimulation of the VSB, or electrical stimulation of the CA1 region did not elicit an AD. In addition, the duration of the AD was positively correlated with the number of locomotor movements induced by stimulation of VSB or CA1 region. It is suggested that the hippocampal/subicular AD may be a necessary condition to induce locomotor activity by either chemical or electrical stimulation of the hippocampus in rats.

A convenient synthesis of D-myo-inositol 1,4,5-trisphosphate (Ins(1,4,5)P3) and L-myo-inositol 1,4,5-trisphosphate (Ins(3,5,6)P3)

An efficient synthesis of an optically active inositol derivative that is a precursor to D-myo-inositol 1,4,5-trisphosphate (Ins(1,4,5)P3, (-)) is described. Crystallization of the diastereomers of (+/-)-1-O-[(+)-menthoxycarbonyl]-6-O-benzyl-2,3:4,5-di-O-isopropyl idene-myo- inositol diastereomers from methanol gives only one diastereomer. Alkaline hydrolysis gives the useful inositol derivative (-)-6-O-benzyl-2,3:4,5-di-O-isopropylidene-myo-inositol. Likewise, crystallization of the diastereomers of (+/-)-3-O-[(-)-menthoxycarbonyl]-4-O-benzyl-1,2:5,6-di-O-isopropyl idene-myo- inositol from methanol gave a pure compound which could be hydrolyzed to give (+)-4-O-benzyl-1,2:5,6-di-O-isopropylidene-myo-inositol, a precursor to D-myo-inositol 3,5,6-trisphosphate (Ins(3,5,6)P3,(+)). The ease with which these enantiomerically pure inositol derivatives were isolated may facilitate the synthesis of more complex inositol phosphate derivatives such as D-myo-inositol 1,3,4,5-tetrakisphosphate.

Involvement of the nucleus accumbens-ventral pallidal pathway in postictal behavior induced by a hippocampal afterdischarge in rats

The hypothesis that postictal motor behaviors induced by a hippocampal afterdischarge (AD) are mediated by a pathway through the nucleus accumbens (NAC) and ventral pallidum (VP) was evaluated in freely moving rats. Tetanic stimulation of the hippocampal CA1 evoked an AD of 15-30 s and an increase in number of wet-dog shakes, face washes, rearings and locomotor activity. Bilateral injection of haloperidol (5 micrograms/side) or the selective dopamine D2 receptor antagonist, (+/-)-sulpiride (200 ng/side) before the hippocampal AD, into the NAC selectively reduced rearings and locomotor activity, but not the number of wet-dog shakes and face washes. Injection of R(+)-SCH-23390 (1 microgram/side), a D1 receptor antagonist, or rimcazole (0.4 mg/side), a sigma opioid receptor antagonist, into the NAC did not significantly alter postictal behaviors. Bilateral injection of muscimol (1 ng/side), a gamma-aminobutyric acid (GABAA) receptor agonist, into the VP before the AD significantly blocked all postictal behaviors. It is concluded that postictal locomotor activity induced by a hippocampal AD is mediated by activation of dopamine D2 receptors in the NAC and a pathway through the VP.

Evaluation of the hypothesis that hippocampal interictal spikes are caused by long-term potentiation

Hippocampal spontaneous interictal spikes (SISs) occur in the EEG after repeated afterdischarges (ADs) induced by high-frequency (200 Hz) stimulation trains. Because SISs resemble population excitatory postsynaptic potentials (EPSPs), and SISs persist for several days like some types of hippocampal long-term potentiation (LTP), LTP has been suggested as a mechanism for SISs. We specifically examined the hypothesis that SISs are caused by basal-dendritic LTP in CA1. Rats were chronically implanted with bilateral electrodes in the hippocampal CA1 region. In the first experiment, 10-18 patterned primed burst (PB) stimulations were delivered hourly for 2-3 days to activate the commissural basal-dendritic EPSP in CA1. Robust LTP of the basal-dendritic CA1 synapse was detected, typically saturating at 100% enhancement after five stimulations. However, few SISs were detected if ADs were not elicited. In the second experiment, repeated commissurally evoked ADs induced a high rate of SISs, together with LTP of the basal-dendritic and apical-dendritic EPSP in CA1, but the SIS rate was not necessarily related to the level of LTP. In the third experiment, an intraventricular dose (20 micrograms) of an N-methyl-D-aspartate (NMDA) receptor antagonist 2-amino-5-phosphonovalerate (APV) was used to block the basal-dendritic LTP in CA1. The increase in SISs induced by a single AD was not blocked, however, suggesting that NMDA receptors were not critical in generation of SISs. In the fourth experiment, PBs (that induced LTP but no ADs) were able to increase the rate of SISs marginally when SISs were already present. In all, the experiments suggest that LTP at the basal dendrites of CA1 is not critical in generation of hippocampal SISs, although an increase in LTP may increase the rate of SISs marginally when SISs are already present.

A movement-associated fast rolandic rhythm

A stereotyped 32 Hz rolandic rhythm maximal over the mesial cortex and occurring only with voluntary movement is described in a patient with tonic postural seizures. This abnormal but nonictal rhythm, which is probably generated subcortically, is expressed synchronously at the level of the cortex and peripherally in the EMG.

Intrinsic membrane potential oscillations in hippocampal neurons in vitro

Membrane potential oscillations (MPOs) of 2-10 Hz and up to 6 mV were found in almost all stable hippocampal CA1 and CA3 neurons in the in vitro slice preparation. MPOs were prominent for pyramidal cells but less pronounced in putative interneurons. MPOs were activated at threshold depolarizations that evoked a spike and the frequency of the MPOs increased with the level of depolarization. MPOs were distinct from and seemed to regulate spiking, with a spike often riding near the top of a depolarizing MPO wave. Analysis of the periodicity of the oscillations indicate that the period of MPOs did not depend on the afterhyperpolarization (AHP) following a single spike. MPOs persisted in low (0-0.1 mM) Ca2+ medium, with or without Cd2+ (0.2 mM), when synaptic transmission was blocked. Choline-substituted low-Na+ (0-26 mM) medium, 3 microM tetrodotoxin (TTX) or intracellular injection of QX-314 reduced or abolished the fast Na(+)-spike and reduced inward anomalous rectification. About 40% of CA1 neurons had no MPOs after Na+ currents were blocked, suggesting that these MPOs were Na(+)-dependent. In about 60% of the cells, a large depolarization activated Ca(2+)-dependent MPOs and slow spikes. MPOs were not critically affected by extracellular Ba2+ or Cs2+, or by 0.2 mM 4-aminopyridine, with or without 2 mM tetraethylammonium (TEA). However, in 5-10 mM TEA medium, MPOs were mostly replaced by 0.2-3 Hz spontaneous bursts of wide-duration spikes followed by large AHPs. Low Ca2+, Cd2+ medium greatly reduced the spike width but not the spike-bursts. In conclusion, each cycle of an MPO in normal medium probably consists of a depolarization phase mediated by Na+ currents, possibly mixed with Ca2+ currents activated at a higher depolarization. The repolarization/hyperpolarization phase may be mediated by Na+/Ca2+ current inactivation and partly by TEA-sensitive, possibly the delayed rectifier, K+ currents. The presence of prominent intrinsic, low-threshold MPOs in all hippocampal pyramidal neurons suggests that MPOs may play an important role in information processing in the hippocampus.

Spontaneous hippocampal interictal spikes following local kindling: time-course of change and relation to behavioral seizures

Spontaneous interictal spikes (SISs) were recorded in the hippocampus in freely behaving rats following hippocampal stimulations that resulted in afterdischarges (ADs). Hippocampal SISs were detected after an average of 5 (range 2-10) daily ADs. The rate of SISs typically increased minutes after a tetanus, and then decayed with time constants of approximately 70 min and 1.5 days. Seizure onset in the kindling paradigm was not related to a consistent change in SIS rate. Following the interruption of daily kindling, SIS rate invariably decreased to near zero by 4-8 days while seizure susceptibility, as tested by the ability to evoke generalized convulsions, remained unchanged. Despite having a low or zero SIS rate the hippocampus seemed to retain an excitability after kindling interruption, as demonstrated by the observation that an average of 1.7 rekindling stimulations resulted in a high SIS rate. In conclusion, changes in hippocampal SISs were closely time-locked to an AD, and not to evoked behavioral seizures. Hippocampal SISs probably reflect an excitability change that is more local than that necessary for evoking behavioral convulsions. The persistence of SISs in terms of hours and days suggests the involvement of long-term potentiation.

The role of serotonin in the control of cerebral activity: studies with intracerebral 5,7-dihydroxytryptamine

Intact rats treated with centrally acting antimuscarinic (atropinic) drugs display large amplitude irregular slow waves in both the neocortex and hippocampus during behavioral immobility and some stereotyped automatic behaviors (Type 2 behavior). However, rhythmical slow activity in the hippocampus and low voltage fast activity in the neocortex occur in close correlation with spontaneous changes in posture, head movement, walking, rearing, swimming or struggling when held (Type 1 behavior). It has previously been proposed that these waveforms, jointly referred to as atropine-resistant cerebral activation (ARCA) are dependent on ascending serotonergic projections. As a further test of this hypothesis, we have studied rats in which forebrain levels of serotonin and 5-hydroxyindoleacetic acid were reduced to 3-10% of control levels as a result of multiple intrabrainstem injections of 5,7-dihydroxytryptamine. This treatment strongly reduced or abolished ARCA in most cases but did not reduce atropine-sensitive cerebral activation which appears to be dependent on ascending cholinergic projections from the basal forebrain to the cerebral cortex. Therefore, ARCA appears to be dependent on ascending serotonergic inputs to the forebrain.

Hippocampal interictal spikes induced by kindling: relations to behavior and EEG

Hippocampal spontaneous interictal spikes (SISs) were recorded during the course of daily tetanization (kindling) of afferent fibers to the hippocampal CA1 region. SISs were detected after 3-10 tetanizations. A clear variation of SIS rate with behavior was observed. SIS rate was high during slow-wave sleep (SWS), waking immobility, face-washing and chewing and low during rapid-eye-movement sleep (REMS), walking and rearing. Scopolamine hydrochloride (2.5-5 mg/kg i.p.) increased the SIS rate during walking. Despite the negative correlation of SIS occurrence with the theta rhythm in normal rats, abolishing the theta rhythm by medial septal lesions did not affect the suppression of SISs during REMS as compared to SWS. When interictal or postictal spikes were seen together with the theta rhythm, the spikes tended to occur at a phase of about 240 degrees after the positive peak of the alvear surface rhythm.

APV, an N-methyl-D-aspartate receptor antagonist, blocks the hippocampal theta rhythm in behaving rats

2-Aminophosphonovaleric acid (APV), an N-methyl-D-aspartate (NMDA) receptor antagonist, was infused into the lateral ventricles of behaving rats. A 10 or 20 microgram dose of APV attenuated the hippocampal theta rhythm and the theta phase-shift at the apical dendrites of hippocampal CA1 region. A selective suppression of the atropine-sensitive theta rhythm was suggested.

Hippocampal electrical activity following local tetanization. I. Afterdischarges

Following a short (1-10 s) train of repetitive stimulation delivered to the hippocampal CA1 region, the following sequelae of afterdischarges (ADs) was seen: (1) a silent period of 2-4 s, (2) a large primary (1 degree) AD usually alvear-surface negative and deep positive, (3) a period of suppressed hippocampal EEG, (4) a secondary (2 degrees) hippocampal AD, and after 3-6 min, (5) 15-25 min of enhanced (up to 10 times normal) fast (30-70 Hz) waves. The 2 degrees hippocampal AD was preceded by or simultaneous with large AD at the amygdaloid electrodes. Electrolytic lesions (n = 7) or large heat lesions of the amygdala (n = 5) or electrolytic lesions of the medial septum (n = 10) were not successful in suppressing the 2 degrees hippocampal AD. However, 4 rats with radiofrequency lesion and 3 rats with bilateral aspiration lesion of the entorhinal cortex had diminished or no 2 degrees hippocampal AD. The fast waves after tetanization were reversed 180 degrees across surface and deep CA1 electrodes. The fast wave increase was blocked by atropine sulfate (25-50 mg/kg i.p.), scopolamine hydrochloride (5 mg/kg i.p.) and medial septal lesions. It was concluded that the 2 degrees hippocampal AD may depend on a reverberation of neural circuitry involving the entorhinal cortex. The 2 degrees AD recorded from amygdala electrodes may partly reflect spreading of activities from the entorhinal cortex. On the other hand, the increase in fast waves after tetanization requires an intact septohippocampal, muscarinic cholinergic input, and may depend on an enhanced cholinergic input or an increased response.

Hippocampal electrical activity in the diabetes insipidus (Brattleboro) rat

Theta rhythm was recorded from the hippocampus in normal male and female rats, and from female rats with homozygous alleles (HODI) and heterozygous alleles of diabetes insipidus (HEDI). Second-by-second spectral analysis of the complete period of rapid eye-movement sleep indicated that HODI and HEDI rats had the same theta frequency range as normals, but the mean theta frequency (6.4 cycles c/s) was lower than normal (6.8 c/s), mainly in having a smaller proportion of frequencies greater than or equal to 7.8 c/s. Pharmacological studies in the waking rat demonstrated a theta rhythm in the HODI and normal rats after atropine or after urethane and eserine, indicating the presence of both atropine-sensitive and atropine-resistant pathways. However, after eserine, a huge increase in hippocampal fast waves (30 to 55 c/s) accompanying struggling (as compared with immobility) was found in the HODI rat, which was double that in the normal rat. An enhanced cholinergic input or response at the septal or hippocampal level may account for the large fast wave as well as the lower mean theta frequency in the HODI rat.

Transcallosal evoked potentials in relation to behavior in the rat: effects of atropine, p-chlorophenylalanine, reserpine, scopolamine and trifluoperazine

Single pulse electrical stimulation of the sensorimotor cortex in waking rats produced an evoked response in the contralateral sensorimotor cortex. The slow wave response consisted of: (1) an early component that was negative at the pial surface and in layer V, and was associated with multiunit discharge; and (2) a late component that was mainly negative at the surface, positive in layer V, and was associated with multiunit suppression. Previous research suggests that the early component represents summed excitatory postsynaptic potentials; the late component summed inhibitory postsynaptic potentials. Both components could be elicited by direct stimulation of the corpus callosum and both were abolished by midline callosal section. The amplitude and duration of the late component varied with concurrent motor activity in a striking manner. It was large during waking immobility and also during face-washing, licking the paws, chewing food and drinking water, but was much reduced or absent during head movements, walking and changes in posture. Only minor changes were associated with the transition from waking immobility to slow wave sleep. A series of pharmacological experiments indicated that the behavior-related variation in the late component of the transcallosal evoked response was dependent on both cholinergic and serotonergic transmission.

Electrical activity of the cingulate cortex. I. Generating mechanisms and relations to behavior

Spontaneous slow waves (EEG) and multiple unit activity (MUA) were recorded in the posterior cingulate cortex (area 29) and the dorsal hippocampus of the freely moving rat by means of chronically implanted electrodes. Three different wave patterns were discerned in the cingulate EEG. Irregular slow waves occurred during grooming, drinking, eating (Type II behavior) and slow-wave sleep (SWS). The irregular waves also contained sharp transients of about 20 ms duration called EEG-spikes. EEG-spikes reversed their polarity within the cingulate cortex and correlated with an increase in cingulate MUA. They were probably generated by deep (layer IV to VI) neurons in the cingulate cortex. Theta rhythm of 6-10 Hz accompanied walking, rearing, postural shifts, head movements (Type I behavior) and rapid-eye-movement sleep (REMS). MUA of low-amplitude units was phase-locked to the local theta waves, suggesting local generation of the slow waves. However, volume-conduction from the hippocampus would likely contribute to the cingulate theta since no reversal of the theta waves was found in the cingulate cortex. Fast waves of greater than 30 Hz were generally larger during Type I than during Type II behavior. Cellular generators for fast waves are not known. High-amplitude (greater than 100 microV) MUA only appeared during Type II behavior, and in particular during SWS. During REMS, these units were silent. Stimulation of the contralateral homotopic cingulate cortex gave antidromic and synaptic components in the average evoked potential (AEP). The long latency waves of the AEP varied with behaviors and appeared oscillatory (25-40 Hz) during Type I but not during Type II behavior. In summary, the cingulate cortex has a rich gamut of spontaneous and evoked electrical activities which bears some resemblance to that of the hippocampus.

Electrical activity of the cingulate cortex. II. Cholinergic modulation

The role of the cholinergic innervation in the modulation of cingulate electrical activity was studied by means of pharmacological manipulations and brain lesions. In the normal rat, an irregular slow activity (ISA) accompanied with EEG-spikes was recorded in the cingulate cortex during immobility as compared to walking. Atropine sulfate, but not atropine methyl nitrate, increased ISA and the frequency of cingulate EEG-spikes. Pilocarpine suppressed ISA and EEG-spikes during immobility, and induced a slow (4-7 Hz) theta rhythm. Unilateral or bilateral lesions of the substantia innominata and ventral globus pallidus area using kainic acid did not significantly change the cingulate EEG or its relation to behavior. Large electrolytic lesions of the medial septal nuclei and vertical limbs of the diagonal band generally decreased or abolished all theta activity in the cingulate cortex and the hippocampus. However, in 5 rats the cingulate theta rhythm increased while the hippocampal theta disappeared after a medial septal lesion. The large, postlesion cingulate theta, accompanied by sharp EEG-spikes during its negative phase, is an unequivocal demonstration of the existence of a theta rhythm in the cingulate cortex, independent of the hippocampal rhythm. Cholinergic afferents from the medial septum and diagonal band nuclei are inferred to be responsible for the behavioral suppression of cingulate EEG-spikes and ISA, and partially for the generation of a local cingulate theta rhythm. However, an atropine-resistant pathway and a theta-suppressing pathway, possibly coming from the medial septum or the hippocampus, may also be important in cingulate theta generation.

Topographical projection of cholinergic neurons in the basal forebrain to the cingulate cortex in the rat

The cholinergic innervation of the rat's posterior cingulate cortex (Brodmann's area 29) was studied using acetylcholinesterase (AChE) histochemistry. Electrolytic lesion of the ipsilateral medial septum and diagonal band region (MS-DB) reduced the diffuse AChE staining in layers I, II, III and V of the cingulate cortex. Kainic acid lesion of the ipsilateral globus pallidus and substantia innominata area (GP-SI) abolished the dense band of AChE stain in layer IV, with small reductions of AChE stain in other layers. The results indicate that the medial cholinergic pathway from MS-DB terminates diffusely in layers I, II, III and V while the lateral cholinergic pathway from the GP-SI predominantly ends in layer IV of the posterior cingulate cortex.

Pathways through cingulate, neo- and entorhinal cortices mediate atropine-resistant hippocampal rhythmical slow activity

Rats prepared with a lesion separating the entorhinal cortex from the neocortex and cingulate cortex displayed apparently normal hippocampal rhythmical slow activity (RSA) with a frequency of 6-12 Hz in both CA1 and dentate gyrus during Type 1 behavior (locomotion, head movements, changes in posture). Variations in the commissural average evoked potential (AEP) and increased power in the 30-100 Hz range (fast waves) also correlated with Type 1 behavior. Urethane did not abolish the RSA. However, systemic administration of atropinic drugs eliminated all RSA and eliminated or attenuated the Type 1 behavior-related variations in the AEP and fast waves. Thus, the normally present atropine-resistant RSA was eliminated by the cortical lesion while atropine-sensitive RSA remained intact. Removal of cingulate cortex alone was partially effective in suppressing atropine-resistant RSA but a lesion of the neocortex only, sparing cingulate cortex, had a minimal effect on it. Lesions of the amygdala, the anterior or medial thalamus or the cerebellum had little or no effect on atropine-resistant RSA. Previous work has shown that lesions of the entorhinal cortex or lateral hypothalamus eliminate atropine-resistant RSA. We suggest that atropine-resistant RSA is mediated by a somewhat diffuse pathway which traverses the hypothalamus, cingulate cortex, and neocortex before reaching the hippocampus via the entorhinal cortex.

Spectral analysis of hippocampal EEG in the freely moving rat: effects of centrally active drugs and relations to evoked potentials

Hippocampal EEG signals derived from chronically implanted electrodes in the freely moving rat were recorded before and after administration of centrally acting drugs, and analyzed by power and coherence spectra. Eserine, ether or urethane induced a low frequency (3-6 c/sec) theta power and coherence peak in the immobile rat, which was sensitive to atropine or scopolamine. After phencyclidine, theta that occurred during walking (7-8 c/sec) was virtually abolished by atropine while in the normal rat, absolute theta power was not affected by atropine. The residue spectrum, defined as the EEG spectrum with the theta harmonics removed, was sensitive to centrally acting drugs. Ether, urethane and pentobarbital suppressed fast waves of 50-100 c/sec, and under some conditions, enhanced 15-50 c/sec waves. Eserine enhanced (30-60 c/sec) fast waves during walking while atropine suppressed fast waves and increased irregular slow activity (less than 30 c/sec). The main effects of drugs and behavior on the residue spectra and on the average evoked potentials following stimulation of the Schaffer collaterals could be explained by a previously proposed model (Leung 1982) which suggests a continuum of hippocampal 'activation' (tonic input) under the various conditions.

Timing pulse and sampling programs implemented on a laboratory microcomputer

This paper presents two programs implemented on a microcomputer for analog-to-digital (A-to-D) conversion of neurophysiological signals. The first program, TIMET, sets flexible pulse trains for the timing of the A-to-D conversions, executed by the second program, ADC8. TIMET contains options for a continuous or a triggered pulse train with variable onset delay. ADC8 allows sampling up to 30 kHz for one channel and 9 kHz for the maximum of 7 channels, with about 8 microseconds lag between channels. The digitized data are displayed with interactive gain control from keyboard input, and selected sweeps can be stored on disk files.

Model of gradual phase shift of theta rhythm in the rat

CA1 pyramidal cell is modeled by a linked series of passive compartments representing the soma and different parts of the dendritic tree. Intracellular postsynaptic potentials are simulated by conductance changes at one or more compartments. By assuming an infinite homogeneous extracellular medium and a particular geometrical arrangement of pyramidal cells, field potential profiles are generated from the current source-sinks of the compartments. The pyramidal cells are driven at the theta (theta)-frequency at different sites of the dendritic tree in order to simulate external driving of hippocampus by the septal cells. Inhibitory or excitatory driving at different sites gives extracellular dipole fields of different null zones and maxima. Phase reversal (180 degrees) of a dipole field generated by synchronous synaptic currents is completed within a depth of 150 micron. By driving two spatially distinct but overlapping dipole fields slightly phase-shifted (30-90 degrees) from each other, the resultant field shows a gradual phase shift of 180 degrees in over 400 micron depth and no (stationary) null zones. The latter field correspond to the theta-profiles seen in the freely moving rat. Somatic inhibition is proposed to be the synaptic process generating the theta-field potentials (named dipole I) in the urethananesthetized or curarized rat. Dipole I has amplitude maxima at the basal dendritic and the distal apical dendritic layers, with a distinct null zone and phase reversal at the apical side of the CA1 pyramidal cell layer. Rhythmic distal dendritic excitation, time-delayed to somatic inhibition, is proposed to be the additional dipole (dipole II) found in freely moving rats. The combination of dipoles I and II, phase-shifted from each other, causes the gradual theta-field phase shift. Experimental studies indicate that dipole I is atropine-sensitive and probably driven by a cholinergic septohippocampal input, whereas dipole II is atropine-resistant and may come from a pathway through both the septum and the entorhinal cortex. Variations of the phase profiles of the theta-field in freely moving rats by administration of anesthetic and cholinergic drugs and by normal changes in theta-frequency could be accounted for by the proposed model. Changes of the intracellular membrane potential, cellular firing rate, and evoked excitability at different phases of the theta-rhythm in anesthetized and freely moving rats can be predicted from the model, and they are in general agreement with the extant literature. In conclusion, theta-field is generated by a rhythmic somatic inhibition phase-shifted with a distal apical-dendritic excitation.(ABSTRACT TRUNCATED AT 400 WORDS)

Spectral analysis of hippocampal unit train in relation to hippocampal EEG

Sampling and analysis programs are implemented on a microcomputer for the computation of autopower, coherence and phase spectra of unit train and EEG. Application to the hippocampus reveals that both theta and fast activity in the EEG are correlated with different phase relationships with unit activity. The estimate of coherence and phase spectra of unit-EEG relationship has not been reported before and is unique for the present method.

Cellular bases of hippocampal EEG in the behaving rat

Rats implanted with recording and stimulating electrodes were trained to run in an activity wheel for a water reward. Unitary discharges and slow activity were recorded by a movable tungsten microelectrode and by fixed electrodes. Single cells were classified according to their spontaneous and evoked response properties as pyramidal cells, granule cells and interneurons. Unit activity, EEG and their interrelations were studied by spectral and spike-triggered averaging methods. Gradual phase-shifts of RSA were observed both in CA1 and the dentate gyrus. Movement-related RSA was correlated with a decrease in firing rate of pyramidal cells and an increase in the firing of both interneurons and granule cells. In the CA1 region pyramidal cells and interneurons fired preferentially on the negative and positive phases of the locally derived RSA, respectively. In the dentate gyrus both granule cells and interneurons discharged mainly on the positive portion of the local RSA waves, about 90 degrees before the CA1 pyramidal cells. Fourier analysis of the spike trains of interneurons and granule cells showed high power at RSA frequency, coherent with the concurrent EEG. Phase relations between discharges of interneurons and RSA remained unchanged following urethane anesthesia. In waking rats, atropine administration resulted in a decreased discharge of interneurons at RSA frequency, and reduced coherence with RSA. Lesions of the septum or the fimbria-fornix abolished RSA and the rhythmic discharges of the interneurons. Isolation of the entorhinal cortex (EC) from its cortical inputs did not change either EEG or neuronal firing. However, in such a preparation atropine completely abolished RSA and related rhythmicity of interneurons. During drinking and immobility but not during walking, sharp waves (SPW) of about 40-100 ms duration appeared in the EEG. SPWs were invariably accompanied by synchronous discharges of several pyramidal cells and interneurons. CA3 pyramidal cells also discharged in synchronous bursts but without local SPWs. Laminar profiles of SPWs and the field potentials evoked by stimulation of Schaffer collaterals were essentially identical. The behavior-dependent occurrence of SPWs was retained following atropine administration, septal lesion or EC isolation but was lost after fimbria-fornix-neocortex lesion or following atropine administration in EC isolated rats. In addition to relations to RSA and SPWs, interneurons were phase-locked to the fast EEG pattern (25-70 Hz). This relationship was preserved following lesions of the septum or the fimbria-fornix complex.(ABSTRACT TRUNCATED AT 400 WORDS)

Two types of interictal transients of reversed polarity in rat hippocampus during kindling

Two different types of spontaneous interictal transients (SITs) have been found in the course of the development of an epileptogenic focus by Schaffer collateral kindling in the CA1 region of rat hippocampus. The first type has peak amplitudes of 250 microV up to 1 mV, a duration of about 80 msec and the same polarity as field potentials recorded from the same sites evoked by Schaffer collateral stimulation. These SITs occur early during kindling, but are also observed at later stages. The second type, which is dominant in later stages of kindling, has peak amplitudes of 2-3 mV, a duration of about 20 msec and the opposite polarity; in a later stage it may also contain a clear population spike. Both types can be considered as being caused by equivalent dipoles situated across the pyramidal cell layer of CA1 but with inverted polarities.

Potentials evoked by alvear tract in hippocampal CA1 region of rats. I. Topographical projection, component analysis, and correlation with unit activities

1. The field potentials and unit activities evoked by the alvear tract (AT) in CA1 region of the dorsal hippocampus of rats were studied under sodium pentobarbital anesthesia. 2. The localized activity evoked anterior to an AT stimulus began as a compound action potential, followed by a slower negative wave, and ended in a long-lasting, slow positive wave. Observed with a 64-electrode recording array, topographical projections of the AT in CA1 were seen as parallel strips inclined at an angle of 5-30 degrees medially from the sagittal plane. 3. Three overlapping components in the averaged evoked potentials (AEPs) were distinguished. The first event (component I) was a brief compound antidromic action potential of pyramidal cells. The second field event (component II) reversed from surface negative to deep positive at 200 micrometer from the ventricular surface, increased rapidly with stimulus intensity, potentiated with double shocks, and followed stimulus frequency up to 50/s. The third component was long lasting (up to 200 ms), surface positive and ventral negative (turnover at 150 micron below the pyramidal layer), followed stimulus frequency up to about 10/s, and saturated at a low stimulus intensity (about 3 x threshold). 4. In some preparations, another fast negative peak of about 2 ms duration was found to follow the axon compound action potential on the hippocampal surface and appeared to propagate from the pyramidal layer to the ventricular surface. It was probably of nonsynaptic origin, perhaps due to the centrifugal basal dendritic spikes of the pyramidal cells. 5. Single units were recorded in CA1. Antidromic units were identified by their firing at a fixed latency (1.5 ms) and ability to follow high stimulus frequencies. Units firing at about 2.7 ms latency possessed characteristics of monosynaptic excitation. Under light anesthesia, many of the latter units also showed a late, prolonged suppression of background firing. Tentative interneuronal types fired with peak latencies of 4-5 ms or showed prolonged increase in firing rate. 6. From the correlation with unit post-stimulus time histograms, AEP component II was inferred to be the extracellular, monosynaptic, excitatory postsynaptic potentials, and component III the di- or polysynaptic inhibitory postsynaptic potentials. These postsynaptic potentials were generated by the pyramidal cells and interneurons.

Orthodromic activation of hippocampal CA1 region of the rat

(1) The posterior alveus (PA), the anterior alveus (AA) and the Schaffer collaterals (SCH) evoked field potential components which were organized as parasagittal strips of various widths. Spatially continuous and interactive lamellae are suggested. (2) By correlation with unit activities, the early postsynaptic components evoked by PA, AA and SCH were inferred to be extracellular excitatory postsynaptic potentials (EPSPs) and the late, long-duration components, the inhibitory postsynaptic potentials (IPSPs). The hypothesis that interneurons as well as pyramidal cells generate the field is proposed and discussed. (3) One- and two-dimensional profiles of deep evoked potentials and current source-sink analysis revealed excitatory synapses in stratum oriens for the PA and AA inputs and in stratum radiatum for the SCH input. The late dipole field evoked by PA and AA possessed current sources in strata radiatum and pyramidale, the sites of the inhibitory synapses. The late dipole field evoked by SCH had another component possibly generated by recurrent activity, afterpotentials or relayed activity through CA3.