[The concept map of SENTIERI Project: a communication interactive digital tool of the national epidemiological surveillance system of Italian contaminated sites]

This paper describes the development and the envisioned use of concept maps in the framework of the SENTIERI communication strategies as an information and scientific communication tool applied to epidemiological surveillance in contaminated sites. The concept map of SENTIERI 2019-2022 was designed and implemented to foster access to complex scientific information ensuring usability of the contents and communication with the various stakeholders. The concept map aims to promote environmental health literacy in contaminated sites. The methodology adopted to create the map includes the following phases: 1. choice of a dynamic focus question; 2. selection of the representative terms of the addressed topics; 3. elaboration of the glossary of the selected terms; 4. representation of the links among the selected terms; 5. identification of the significant propositions that make explicit the meaning of each link. Online access to the map is guaranteed by the Mindomo software. The use of the concept map promotes active learning of the topics that characterize SENTIERI 2019-2022 through knowledge paths chosen because of the specific interests and learning purposes. The concept map derives from the integration of specific approaches of the epidemiological discipline with those of the social sciences and offers the possibility of developing site-specific maps through the interactions with local actors and the integration of elements related to emerging problems as well as institutional and local interests.

Long-term outcome after off-pump coronary artery bypass grafting: implication for public health

Background

The debate on the benefits and limitations of off-pump (OPCAB) coronary artery bypass grafting (CABG) on long-term outcomes is not yet settled. This study aimed to compare the impact of OPCAB vs on-pump CABG on long-term outcomes and to evaluate possible public health implications linked to their use.

Methods

The PRIORITY project was planned to evaluate the long-term outcomes of two prospective multicenter studies on CABG conducted between 2002-2004 and 2007-2008. Data on isolated CABG were linked to administrative data in order to retrieve patients' late outcome. Time-to-event distributions were analyzed accordingly to primary event-type (death, major adverse cardiac events (MACEs)) using the Kaplan-Meier and the Cox proportional hazards methods.

Results

The study population consisted of 11 021 patients who underwent isolated CABG (27.2% OPCAB). The median follow-up time was 8.0 years (interquartile range 7.6-10.0 years). OPCAB had comparable late all-cause mortality to on-pump CABG (HR 0.94, 95%CI 0.85-1.03, p = 0.19), but it was associated to an increased risk of MACE (adjusted HR 1.14, 95%CI 1.06-1.23, p = 0.001). In particular, OPCAB had an increased risk of repeated revascularization with percutaneous cardiac intervention (PCI) (adjusted HR 1.33, 95%CI 1.16-1.53, p < 0.001) compared to on-pump CABG.

Conclusions

OPCAB does not affect long-term mortality, but it significantly increases the risk of MACEs. In particular, OPCAB had an increased risk of repeated revascularization with PCI. These findings may have important implications towards health resources allocation.

Key messages

Off-pump coronary artery bypass grafting strategy is associated with an increased long-term risk of MACE and repeated PCI. Off-pump strategy is mainly based on operator preferences and can have important implications in terms of healthcare costs.

Trends in mortality and heart failure after acute myocardial infarction in Italy from 2007 to 2017

Background

Uncertainties on long-term outcomes after acute myocardial infarction (AMI) still exist, despite the ongoing progresses in the management of patients with AMI. This study aims to appraise early and 1-year outcome of patients hospitalized due to AMI and to describe the role of heart failure (HF) as complication affecting prognoses.

Methods

Retrospective nationwide cohort study based on administrative data on patients with AMI admitted in all Italian hospitals from 2007 to 2017. Index admission mortality rate (I-MR), 30-day and 1-year post-discharge mortality rate (PD-MR), and 30-day and 1-year total mortality rate (T-MR) were analysed; mortality average annual changes (AC) and their 95% CI were calculated; the Cox model, adjusting for age, sex, comorbidities and length of stay, was used to analyse 1-year PD-MR

Results

1,148,820 patients were considered. From 2007 to 2017, both I-MR and T-MR up to 1 year decreased significantly (from 10.9 to 8.4%; AC: -0.28%; CI: -0.31 to -0.25 and from 20.2% to 17.1%: AC: -0.33%; CI: -0.39 to -0.28, respectively). From 2010, also the rate of PD-MR decreased significantly from 11.7% to 10.4%, with such favourable trend confirmed at multivariable analyses. The HF diagnosis at the index admission is always associated with a significant increase in the risk of death (1-year T-MR average: 43% and 12% in patients with or without HF, respectively; both patients with and without HF show a constant improvement in I-MR, T-MR and PD-MR over time.

Conclusions

In the last decade, the remarkable improvements in the in-hospital treatment of patients with AMI and in the overall prognosis up to 1 year are confirmed by a constant decrease in both early and long-term mortality. Since complication from HF remains a dangerous condition that significantly worsens the prognosis of the AMI patient, appropriate management strategies must be identified and implemented to guarantee best results from both clinic and public health perspective.

Key messages

Remarkable improvements achieved in overall prognosis after AMI over the past 10 years. HF confirms to be a condition able to worsen AMI patients’ prognosis.

Hospitalization costs related to long-term management of patients undergoing CABG (PRIORITY project)

Background

Identifying potential tools that could help improving the standard of care and lead to a better allocation of economic resources represents a main objective of research in public health. Using data from the PRIORITY cohort, this study aims to describe inpatients costs after a discharge for isolated coronary artery bypass surgery (CABG).

Methods

The PRIORITY project was designed to evaluate the long-term outcomes of 2 large multicenter cohort studies on CABG conducted between 2002-04 and 2007-08. For each patient discharged alive after a CABG intervention, costs of hospitalizations were estimated as the sum of costs of all the admissions occurred during 3 years of follow-up. NHS reimbursement rates were used as standard costs (in Euros). Inpatients costs were analysed according to their baseline risk factors.

Results

Among the 7363 patients included in this analysis, the median 3-year hospitalization costs were 4341€ (IQR: 1865-11699). Median costs were around 4.000€ for subjects alive at the end of follow up but higher for patients dying within 1 (about 8.600€) and 2-3 years of follow up (about 20.000€). The presence of comorbidities (such as diabetes and cancer) lead to higher median hospitalization costs while the on-pump approach was associated to lower median cost. Sixteen per cent of patients were at zero cost having no re-hospitalizations during the 3 years of follow-up (97% alive). Subjects at zero cost received more frequently on-pump approach, had a lower frequency of cancer, arteriopathy and ictus, but a higher frequency of angina and infarction.

Conclusions

Inpatient costs after isolated CABG are affected by preoperative comorbidities and by operative variables that could be removed or managed. Identifying independent risk factors for re-hospitalization will lead to the definition of a preoperative clinical and decision-making path that will bring both a clinical advantage for the patient and an optimization of costs for the NHS.

Key messages

Inpatient costs after isolated CABG are affected by preoperative comorbidities and operative characteristics like the on-pump approach. Appropriate management of operative approaches mainly based on operator preferences can have important implications in terms of healthcare costs.

Bilateral internal thoracic artery grafting in coronary surgery: 10-year outcomes

Background

The advantages to use the bilateral internal thoracic artery grafting (BITA) technique for coronary artery bypass grafting (CABG) have been recently questioned, but data on long-term follow-up is limited. Using data from the PRIORITY project, this study aims to assess the outcome with the use of BITA grafting and its implications for public health.

Methods

The PRIORITY project was planned to evaluate the long-term outcomes of two prospective multicenter studies on CABG conducted between 2002-2004 and 2007-2008. Data on isolated CABG were linked to administrative data in order to retrieve patients' late outcome. Time-to-event distributions were analyzed accordingly to primary event-type (death, major adverse cardiac events (MACEs)) using the Kaplan-Meier and the Cox proportional hazards methods.

Results

The study population consisted of 11021 patients who underwent isolated CABG. BITA grafting was employed in 24.6% of patients. The median follow-up time was 8.0 years (interquartile range 7.6-10.0 years). After adjustment for potential confounding factors, BITA grafting was significantly associated with better survival (HR 0.85, 95%CI 0.76-0.95, p = 0.003). Moreover, using BITA grafting reduced the incidence of MACE (HR 0.87, 95%CI 0.80-0.94, p = 0.001), showing to be a protective factor for recurrent acute myocardial infarction (HR 0.84, 95%CI 0.71-0.99, p = 0.05) and for rehospitalization for percutaneous cardiac intervention (HR 0.82, 95%CI 0.70-0.96, p = 0.013).

Conclusions

BITA grafting during isolated CABG is associated with survival advantage at 10-year with a significantly reduced incidence of MACE. Being the choice to perform isolated CABG with or without BITA based mainly on operator personal preferences, these findings may have important implications from a public health perspective.

Key messages

The choice to perform CABG with or without BITA grafting is associated to different outcomes. The choice to perform CABG with or without BITA grafting is mainly based on operator preferences and may have important implications in terms of healthcare expenditures.

Hospital management of patients with acute coronary syndrome: influence of age and gender

Background

Although the improvement of therapeutic strategies is leading to a dramatic decline of in-hospital acute coronary syndrome (ACS) death rates, differences in care and prognosis of ACS patients exist when age, gender and admission department are considered.

Methods

The national administrative hospital discharge record (HDR) system was used. Only data recorded from January 1, 2017 to Dicember 31, 2018 were analyzed. This approach allowed to identify 205775 patients reporting ACS as primary or secondary diagnosis: 122812 with non-ST-elevation ACS (NSTE-ACS) and 82963 with ST-elevation ACS (STEMI). The ACS cohort was stratified by age (<75 and ≥75 years) and gender. The proportion of STEMI patients treated in general medicine or cardiology departments requiring a coronary procedure or extensive investigations were analyzed.

Results

Among the 205775 patients hospitalized for ACS, 6% of STEMI and 8.3% of NSTE-ACS patients have been treated only in a general medicine ward and have never passed through a specific cardiology ward. For STEMI patients, the proportion becomes 4% when males are considered, increases up to 10% for females and up to 13% for elderly patients (≥75 years). During the index hospitalization, about 25% of female and more than 30% of elderly patients with STEMI do not undergo a coronary procedure or other extensive investigations; the same happens only in about 10% of male and 6% of younger patients. The proportion of improperly managed patients reaches 35% for women aged ≥75 years.

Conclusions

In-hospital management of women and elderly patients with ST-elevation ACS does not completely comply with the recommended guidelines and exposes them to unfavourable prognosis.

Key messages

Women and elderly STEMI patients are markedly less intensively investigated and treated in cardiologic departments. This medical policy could lead to unfavourable prognosis.

Optical Coherence Tomography (OCT) in Retinal Angiomatous Proliferation (RAP)

Purpose

To verify the utility of optical coherence tomography (OCT) for diagnosing retinal angiomatous proliferations (RAP) in patients with exudative age-related macular degeneration (AMD).

Methods

Multiple cross-sections were taken with OCT from 41 eyes of 39 consecutive patients with AMD and RAP. The presence and the location of the angiomatous complexes had already been documented by fluorescein angiography (FA) and high-speed confocal indocyanine green videoangiography (ICGA).

Results

RAP was detectable by OCT scans in all 41 eyes, appearing as a focal hyper-reflecting area in the neuroretinal layers; it was frequently located close to the inner surface of the retinal pigment epithelium (29 eyes [70.7%]). All eyes had either no or only a low-reflecting OCT signal surrounding the RAP, caused by serous intraretinal edema. Only 13 eyes (31.7%), however, had large serous retinal detachment (SRD). OCT detected pigment epithelium detachment in 31 eyes (75.6%), but none had underlying choroidal neovascularization.

Conclusions

OCT findings confirm the intraretinal localization of the RAP which are always associated with impressive exudative phenomena. OCT is therefore a useful diagnostic tool, adding information to FA and high-speed ICGA.

Anastomosis of nasal mucosal and lacrimal sac flaps in endoscopic dacryocystorhinostomy

Endoscopic dacryocystorhinostomy (DCR) is a well-established alternative to external approaches in the treatment of nasolacrimal canal obstruction. From July 2004 to December 2008, 92 endoscopic DCRs were performed on 88 patients at the Department of Otorhinolaryngology, San Raffaele Hospital, Milan. All patients were affected by chronic dacryocystitis with epiphora. Preoperative work-up included Jones tests, lacrimal pathways irrigation, nasal endoscopy, and imaging evaluation by computed tomography. The technique involved anastomosis of nasal mucosal, lacrimal sac flaps and a large bony ostium. A silicone tube was inserted in all patients that remained for a period of 3 months. The first endoscopic intervention was successful in 91.30% of patients. After a second revision endoscopic DCR, the overall success rate raised to 95.65%. Anastomosis of nasal mucosal between lacrimal sac flaps plays a key role in endoscopic DCR with a high success rate both in primary nasolacrimal obstructions and in revision cases.

Optical coherence tomography (OCT) angiomatous prolifieration (RAP) in retinal

PURPOSE

To verify the utility of optical coherence tomography (OCT) for diagnosing retinal angiomatous proliferations (RAP) in patients with exudative age-related macular degeneration (AMD).

METHODS

Multiple cross-sections were taken with OCT from 41 eyes of 39 consecutive patients with AMD and RAP. The presence and the location of the angiomatous complexes had already been documented by fluorescein angiography (FA) and high-speed confocal indocyanine green videoangiography (ICGA).

RESULTS

RAP was detectable by OCT scans in all 41 eyes, appearing as a focal hyper-reflecting area in the neuroretinal layers; it was frequently located close to the inner surface of the retinal pigment epithelium (29 eyes [70. 7%]). All eyes had either no or only a low-reflecting OCTsignal surrounding the RAP, caused by serous intraretinal edema. Only 13 eyes (31.7%), however, had large serous retinal detachment (SRD). OCT detected pigment epithelium detachment in 31 eyes (75.6%), but none had underlying choroidal neovascularization.

CONCLUSIONS

OCT findings confirm the intraretinal localization of the RAP which are always associated with impressive exudative phenomena. OCT is therefore a useful diagnostic tool, adding information to FA and high-speed ICGA.

Cellular mechanisms underlying spontaneous interictal spikes in an acute model of focal cortical epileptogenesis

The cellular mechanisms involved in the generation of spontaneous epileptiform potentials were investigated in the pirifom cortex of the in vitro isolated guinea-pig brain. A single, unilateral injection of bicuculline (150-200 nmol) in the anterior piriform cortex induced locally spontaneous interictal spikes that recurred with a period of 8.81+/-4.47 s and propagated caudally to the ipsi- and contralateral hemispheres. Simultaneous extra- and intracellular recordings from layer II and III principal cells showed that the spontaneous interictal spike correlates to a burst of action potentials followed by a large afterdepolarization. Intracellular application of the sodium conductance blocker, QX-314 (80 mM), abolished bursting activity and unmasked a high-threshold slow spike enhanced by the calcium chelator EGTA (50 mM). The slow spike was abolished by membrane hyperpolarization and by local perfusion with 2 mM cadmium. The depolarizing potential that followed the primary burst was reduced by arterial perfusion with the N-methyl-D-aspartate receptor antagonist, DL-2-amino-5-phosphonopentanoic acid (100-200 microM). The non-N-methyl-D-aspartate glutamate receptor antagonist, 6-cyano-7-nitroquinoxaline-2,3-dione (20 microM), completely and reversibly blocked the spontaneous spikes. The interictal spikes were terminated by a large afterpotential blocked either by intracellular QX-314 (80 mM) or by extracellular application of phaclofen and 2-hydroxysaclofen (10 and 4 mM, respectively). The present study demonstrates that, in an acute model of epileptogenesis, spontaneous interictal spikes are fostered by a primary burst of fast action potentials that ride on a regenerative high-threshold, possibly calcium-mediated spike, which activates a recurrent, glutamate-mediated potential responsible for the entrainment of adjacent and remote cortical regions. The bursting activity is controlled by a GABA(B) receptor-mediated inhibitory synaptic potential.

Synaptic connectivity of distinct hilar interneuron subpopulations

Dual intracellular recordings of hilar interneurons and CA3 pyramidal cells were performed in transverse slices of guinea pig hippocampus in the presence of the convulsant compound 4-aminopyridine (4-AP) and ionotropic glutamate receptor antagonists. Under these conditions, interneurons burst fire synchronously, producing synchronized inhibitory postsynaptic potentials (sIPSPs) in pyramidal cells. Three different hilar interneuron subpopulations that contributed to the sIPSP were identified based on their projection properties and morphology. These three types were pyramidal-like stellate interneurons, spheroid interneurons, and oviform interneurons. Physiologically, pyramidal-like stellate interneurons could be differentiated from the other interneuron subpopulations because they generated short synchronized bursts of action potentials coincident with the hyperpolarizing and depolarizing gamma-aminobutyric acid-A (GABAA)-mediated inhibitory postsynaptic potentials (IPSPs) recorded in pyramidal cells. The bursts in pyramidal-like stellate cells were abolished by theGABAA-receptor blocker, bicuculline. In contrast, spheroid interneurons of the dentate-hilus (D-H) border and oviform hilar interneurons exhibited prolonged bicuculline-resistant bursts that occurred coincident with the GABAB pyramidal cell sIPSPs. Pyramidal-like stellate interneurons likely did not contribute to the generation of synchronized GABAB responses in hippocampal pyramidal cells. Spheroid interneurons were unique among these subpopulations of interneurons in that the bicuculline-resistant bursts in spheroid interneurons were sustained by a synaptic depolarization that persisted in the presence of antagonists of ionotropic glutamate, GABAA and GABAB receptors [6-cyano-7-nitroquinoxaline-2,3-dione, 20 microM; 3-3(2-carboxipiperazine-4-yl)propyl-1-phosphonate, 20 microM; bicuculline, 10-15 microM; CGP 55845A, 20 microM]. This novel depolarizing potential reversed between -30 and 0 mV. No noticeable synaptic depolarization sustaining burst firing could be isolated in oviform interneurons, suggesting that firing in this interneuron subpopulation was synchronized by nonsynaptic mechanisms. The results of the present study indicate that the hilar inhibitory circuit is composed of at least three different subpopulations of interneurons, distinguishable by their morphological characteristics and synaptic inputs and outputs. These findings give further support to the hypothesis that there are distinct populations of interneurons producing GABAA and GABAB responses with defined functional roles within the hippocampal inhibitory circuit. Notably, we found that spheroid interneurons were unique among the hilar interneurons studied, in that the synchronized bursts observed in these cells are sustained by a novel ionotropic glutamate and GABA receptor-independent synaptic depolarization.

Novel glutamate- and GABA-independent synaptic depolarization in granule cells of guinea-pig hippocampus

1. Dual intracellular recordings of granule cells, hilar interneurons and CA3 pyramidal cells were performed in transverse slices of guinea-pig hippocampus. At resting membrane potential, in the presence of 4-aminopyridine, ionotropic glutamate receptor antagonists and the GABAA receptor antagonist bicuculline, granule cells showed spontaneous, large amplitude depolarizations correlated with synchronous bursting activity of interneurons. 2. Under these conditions, pyramidal cells exhibited large amplitude monophasic GABAB inhibitory postsynaptic potentials (IPSPs) synchronous with the GABAergic interneuron burst discharges. The granule cells also received a GABAB input, which was evident only when the neurons were depolarized by DC injection. The GABAB receptor antagonist CGP 55,845A (CGP) blocked the GABAB IPSPs in both pyramidal cells and granule cells; however, the depolarizing potential in granule cells was unaffected by the drug. 3. The granule cells depolarization in the presence of CGP was monophasic and exhibited linear voltage dependence with a reversal potential around -40 mV, suggesting that it was generated by a synaptic input activating a mixed cationic current. 4. The granule cell depolarization was abolished following the addition of tetrodotoxin to the bath. In addition, perfusing the slice with a low Ca(2+)-containing solution (0.5 mM Ca(2+)-10 mM Mg2+) also abolished the granule cell depolarization, confirming the synaptic origin of the event. 5. (S)-Methyl-4-carboxyphenylglycine, L-(+)-2-amino-3-phosphonopropionic acid, propranolol and atropine did not affect the granule cell depolarization, indicating that metabotropic glutamate receptors, beta-adrenergic receptors and muscarinic cholinergic receptors were not involved in generating the granule cell depolarizing synaptic response. 6. These findings indicate that, in the absence of both glutamatergic and GABAergic inputs, synchronous interneuronal activity can produce a depolarizing synaptic response in granule cells. The neurochemical responsible for the depolarization is currently under investigation.

Persistent excitability changes in the piriform cortex of the isolated guinea-pig brain after transient exposure to bicuculline

The development of long-lasting excitability changes after a single intracerebral injection of bicuculline (1 mM) in a restricted region of the anterior piriform cortex was studied by means of simultaneous intra- and extracellular recordings in the isolated guinea-pig brain preparation maintained in vitro by arterial perfusion. The transitory disinhibition induced by bicuculline revealed transient afterdischarges that were followed by the activation of a synaptic potential mediated by the recurrent propagation of the focal epileptiform activity along cortico-cortical associative fibres. The epileptiform associative potential persisted for the duration of the experiment. Both the induction and the long-term expression of the epileptiform associative potential were dependent on the activation of glutamatergic receptors of the NMDA type, as demonstrated by perfusion with the NMDA receptor antagonist 2-aminopentanoic acid (AP5) (100 microM). After bicuculline washout, piriform cortex neurons responded to afferent stimulation with a burst discharge superimposed on a paroxysmal depolarizing potential. The early component of the burst was mediated by a Ca(2+)-dependent, non-synaptic potential located at the proximal apical dendrites and soma of layer II-III cells, since (i) it was abolished by membrane hyperpolarization, (ii) it was not affected by AP5, (iii) it was correlated with a current sink in layer II, as demonstrated by current source density analysis of field potential laminar profiles, and (iv) it was abolished by cadmium (2-5 mM) applied locally in layer II. The late component of the burst response (i) coincided in time with the extracellular epileptiform associative potential, (ii) increased linearly in amplitude during membrane hyperpolarization, (iii) was blocked by AP5, and (iv) was correlated with an extracellular sink in layer Ib, where the associative fibres contact the distal apical dendrites of piriform cortex neurons. The results presented here indicate that a transient focal disinhibition promotes persistent intrinsic and synaptic excitability changes in piriform cortex neurons. These changes may be responsible for the propagation of epileptiform activity and for the induction of secondary epileptogenesis.

Epileptiform activity in the piriform cortex of the in vitro isolated guinea pig brain preparation

Brief intracerebral injections of bicuculline in the anterior portion of the piriform cortex of the isolated guinea pig brain preparation induce a transient, localized disinhibition confined to the site of drug application. The epileptiform activity generated at the bicuculline focus propagates and induces secondary excitability changes in remote cortical regions within the olfactory lobe. Long lasting changes in synaptic potentials were observed in the posterior piriform cortex, where long-projective cortico-cortical fibers originating from the site of bicuculline injection terminate. The activation of rhythmic, transient afterdischarges at the bicuculline focus was critical for the development of persistent 'epileptiform' associative synaptic potentials in remote cortical regions. When transient afterdischarges were prevented, epileptiform associative potentials in the posterior piriform cortex appeared only transiently and vanished within 20 min. The persistent secondary changes in synaptic excitability that occur in cortical regions distant from the acutely-induced primary epileptic focus may represent one of the transition mechanisms toward chronic epileptogenesis.

Propagation of epileptiform potentials in the guinea-pig piriform cortex is sustained by associative fibres

The role of the associative connections in the propagation of epileptiform discharges originating from an acute, localized epileptic focus in the anterior piriform cortex has been characterized recently in the in vitro isolated guinea-pig brain preparation. The present study demonstrates that the dorsal propagation of epileptiform synaptic potentials generated in APC is carried by long-projective associative fibres. Current source density analysis of the field potential profiles evoked by stimulation of the lateral olfactory tract has been utilized to describe the functional circuit activated in rostral and caudal regions of the piriform cortex, before and after the induction of a bicuculline epileptic focus in the anterior piriform cortex. Separate stimulation of the lateral olfactory tract at two sites, caudal and rostral to a tract incision, activates epileptiform potentials that are generated at the site of primary focus in the anterior piriform cortex and travel along associative fibres. Selective cutting of the long-projective associative fibres abolishes the epileptic associative potential in the cortical regions caudal to the section. The present study demonstrates directly that epileptiform potentials propagate along associative fibres to cortical regions that are synaptically related to the focus of origin. Such a pattern of propagation may sustain the generation of secondary foci in cortical regions remote from the primary epileptic focus.

Multifocal spontaneous epileptic activity induced by restricted bicuculline ejection in the piriform cortex of the isolated guinea pig brain

1. We investigated the development of epileptic activity in the limbic lobe of the in vitro isolated brain preparation after induction of a restricted epileptic focus in the rostral portion of the anterior piriform cortex (APC) by means of local bicuculline ejection. 2. The modifications of the local responses evoked by stimulation of the lateral olfactory tract were consistent with an increase in excitability of layer II pyramidal neurons. The abnormal discharge output of the epileptic focus propagated throughout the piriform cortex (PC) and generated late synaptic stimulus-evoked epileptiform potentials in layer Ib, where corticocortical associative fibers contact the distal dendrites of pyramidal cells. 3. Spontaneous epileptiform potentials (SEPs) originated in the primary focus at the bicuculline ejection site 10-15 min after drug application and propagated via associative fibers to the posterior PC (PPC). 4. Autonomous secondary foci generating SEPs independently from the primary anterior focus developed in the PPC within 2 h after the bicuculline application. 5. Ictal events seldom occurred spontaneously in PC but could be induced by tetanic afferent stimulation. Evoked ictal events in PC had the characteristics of afterdischarges, being short in duration and localized in space and showing a progressively decreasing firing rate. 6. Self-sustained spontaneous ictal discharges were observed in the entorhinal cortex and hippocampus but not in PC after activation of the APC focus. 7. We conclude that in an acute pharmacological model of focal epilepsy, associative corticocortical connections hold a primary role 1) in the propagation of interictal epileptiform activity throughout the limbic lobe and 2) in the generation of secondary epileptic foci. We also demonstrate that self-sustained ictal events are not spontaneously generated in PC, although paroxysmal seizure-like discharges occur in hippocampus. We discuss the relevance of the rostral-to-caudal-directed associative fiber system in generation of limbic seizures.