Arterial hypertension and remodelling of the right ventricle.

BACKGROUND: In the case of long-term and physiological loads (e.g. during pregnancy or regular athletics training), reversible morphological changes occur in the heart - cardiomyocytes undergo hypertrophy; however, this is not accompanied by impairment of left ventricular function or myocyte metabolism. However, in the course of various pathological processes, as time goes by, gradually permanent morphological changes occur. These changes are referred to as remodelling of the heart muscle, which, regardless of the primary cause, can lead to the development of chronic heart failure. MATERIALS AND METHODS: The study was performed on post-mortem material of 35 human hearts obtained from forensic sections and anatomopathological sections of people who died of non-cardiac causes (mainly traffic accidents, suicide attempts, strokes, acute infections); material was fixed in a 4% formalin solution. The hearts were subjected to macro- and microscopic assessment. During microscopic assessment the features of remodelling were evaluated. RESULTS AND CONCLUSIONS: In vivo and echocardiographic tests, as well as macroscopic evaluation of post-mortem material, suggest the presence of some kind of right ventricular muscle remodelling; however, classic microscopic observations, presented in this study, do not provide such unambiguous evidence. Thus, the question arises: why and how the right ventricular function is disturbed, sometimes at early stages of arterial hypertension.

Development of the interatrial wall during the ontogenesis of foetuses and children up to one year of age.

BACKGROUND: The foramen ovale, present in foetal interatrial septum, plays an important role during foetal life. During delivery, foramen ovale closes and becomes fossa ovalis, starting the pulmonary circulation. The aim of our study was to describe the growth of the interatrial wall and changes in location of the foramen ovale, and fossa ovalis during the ontogenesis in the human hearts. MATERIALS AND METHODS: The study was performed on post-mortem material obtained from 92 human hearts from 22nd week of foetal life up to 1 year of age, fixed in a 4% formalin solution. RESULTS: The interatrial wall size in the studied development period was greater in the horizontal than in the vertical dimension. During ontogenesis up to 1 year old, the anterior and inferior parts of the interatrial wall increased their shares considerably by 8% and 6%, respectively. The percentage participation of foramen ovale in the interatrial wall construction in the foetal period formed more than 50% of its size and fairly decreased reaching in infants about 39%. CONCLUSIONS: Our study demonstrated that during ontogenesis, from the foetal period to infancy, the parts of the interatrial wall increase their dimensions unevenly. The foramen ovale growth is smaller, compared to the rest of the interatrial wall development. On the basis of our data we can assume that the foramen ovale centre tends to be found in the postero-inferior quadrant of the interatrial wall (foetuses) and in postero-superior quadrant of the interatrial wall - in infants.

Metric analysis of the lumbar region of human vertebral column.

Detailed measurement of lumbar spine, despite the many years of study, still provides new information, especially due to low back pain, which is increasing and unresolved worldwide health problem. This review includes historical background and evolution of measurement methods. The paper also focused on searching optimal animal model of lumbar spine and summarizes current knowledge and essential tips. In addition, practical application of lumbar metric analysis was presented. This summary is a starting point for further consideration.

Dietary supplementation with Lactobacillus plantarum and ß-glucan affects immune parameters in the tench (Tinca tinca) fry.

The aim of the experiment was to examine the effect of a diet enriched with Lactobacillus plantarum and/or ß-glucan on the immune parameters in the juvenile tench (Tinca tinca). Fish were fed for 14 days different diets (phase 1 of the experiment), a dry commercial starter feed in the control group or the same feed supplemented with: 1% ß-1,3/1,6-glucan in group G, 108 cfu L. plantarum g-1 in group L, 1% ß-1,3/1,6-glucan + 108 cfu L. plantarum g-1 in group G+L. During consecutive 14 days all fish were fed the commercial feed alone (phase 2). The stimulating effects of the tested preparations was evaluated twice, at the end of each experimental phase. Dietary supplementation of ß-1,3/1,6-glucan considerably improved the humoral innate immune response (activity of lysozyme and total Ig) and the pinocytotic activity of phagocytes. Supplement of L. plantarum improved the ability of the head kidney phagocytes (RBA) to carry out oxygen burst in L and G+L groups. A similar effect was observed for the killing activity of phagocytes (PKA) from the head kidney after the stimulation of A. hydrophila, and the effect persisted for two weeks after the commercial feed regime was resumed. A significant increase in the proliferative activity of B lymphocytes originating from the head kidney was observed in groups L and G+L. The study has revealed that the addition of the tested G+L synbiotic to dry diet stimulates the innate immune response mechanisms in the juvenile tench.

Excision of HIV-1 DNA by gene editing: a proof-of-concept in vivo study.

A CRISPR/Cas9 gene editing strategy has been remarkable in excising segments of integrated HIV-1 DNA sequences from the genome of latently infected human cell lines and by introducing InDel mutations, suppressing HIV-1 replication in patient-derived CD4+ T-cells, ex vivo. Here, we employed a short version of the Cas9 endonuclease, saCas9, together with a multiplex of guide RNAs (gRNAs) for targeting the viral DNA sequences within the 5'-LTR and the Gag gene for removing critically important segments of the viral DNA in transgenic mice and rats encompassing the HIV-1 genome. Tail-vein injection of transgenic mice with a recombinant Adeno-associated virus 9 (rAAV9) vector expressing saCas9 and the gRNAs, rAAV:saCas9/gRNA, resulted in the cleavage of integrated HIV-1 DNA and excision of a 978 bp DNA fragment spanning between the LTR and Gag gene in the spleen, liver, heart, lung and kidney as well as in the circulating lymphocytes. Retro-orbital inoculation of rAAV9:saCas9/gRNA in transgenic rats eliminated a targeted segment of viral DNA and substantially decreased the level of viral gene expression in circulating blood lymphocytes. The results from the proof-of-concept studies, for the first time, demonstrate the in vivo eradication of HIV-1 DNA by CRISPR/Cas9 on delivery by an rAAV9 vector in a range of cells and tissues that harbor integrated copies of viral DNA.

Characterization of lake minnow Eupallasella percnurus semen in relation to sperm morphology, regulation of sperm motility and interpopulation diversity.

Sperm morphology and regulation of sperm motility of lake minnow Eupallasella percnurus, an endangered cyprinid, were investigated. Milt characteristics from two isolated populations of E. percnurus were compared to characterize the interpopulation diversity. Electron microscopic studies revealed that E. percnurus spermatozoa comprise simple, uniflagellate, anacrosomal aquasperm with species-specific features as an eccentrically located implantation of nuclear fossa and eccentric insertion of flagellum. Sperm motility was significantly inhibited by relatively low ion concentrations (150, 150 and 8 mM for NaCl, KCl and CaCl2 , respectively). Sperm maintained a high motility rate over a wide pH range (5.5-10.5), which may reflect adaptation to a highly variable environment. The two E. percnurus populations were markedly different in milt volume, sperm concentration, seminal plasma pH, sperm motility and beat cross frequency, which may result from genetic differences and environmental conditions.

Low potency and limited efficacy of antiepileptic drugs in the mouse 6 Hz corneal kindling model.

Corneal kindling is a useful alternative to electrically induced amygdala or hippocampal kindling, which requires advanced surgical and EEG techniques that may not be easily available in many laboratories. Therefore the first aim of this study was to evaluate whether repeated 6 Hz corneal stimulation in mice would lead to an increased and persistent seizure response as described for higher frequency (50/60 Hz) corneal kindling. Male NMRI mice stimulated twice daily (except weekends) for 3 s with 6 Hz electrical current at 44 mA displayed robust kindling development, i.e., a progressive increase in seizure severity. The majority of the animals (about 90%) developed a fully kindled state, defined as at least 10 consecutive stage 3-5 seizures within 5 weeks of corneal stimulation. Afterwards, the fully kindled state was maintained for at least 8 weeks with only two days of stimulations per week. Next, the protective efficacy of four mechanistically different antiepileptic drugs (AEDs; clonazepam, valproate, carbamazepine and levetiracetam) was assessed and compared between 6 Hz and 50 Hz fully kindled mice. All tested AEDs showed a relatively lower potency in the 6 Hz kindling model and a limited efficacy against partial seizures was observed with carbamazepine and levetiracetam. We can conclude that 6 Hz kindling may be more advantageous than the previously described 50/60 Hz corneal kindling models due to its robustness and persistence of the fully kindled state. Furthermore, the observed low potency and limited efficacy of AEDs in 6 Hz fully kindled mice suggest that this model could be a useful tool in the discovery of novel AEDs targeting treatment resistant epilepsy.

Oral administration of live Shigella vaccine candidates in rhesus monkeys show no evidence of competition for colonization and immunogenicity between different serotypes.

Live oral monovalent Shigella flexneri 2a vaccine candidates as well as bivalent formulations with Shigella sonnei were evaluated in a rhesus monkey model for colonization and immunogenicity. Freshly harvested suspensions of S. flexneri 2a vaccine candidates WRSf2G12 and WRSf2G15 as well as S. sonnei vaccine candidate WRSs3 were nasogastrically administered to groups of rhesus monkeys, Macaca mulatta, either in a monovalent form or when combined with each other. The animals were monitored daily for physical well-being, stools were subjected to quantitative colony immunoblot assays for bacterial excretion and blood and stools were evaluated for humoral and mucosal immune responses. No clinical symptoms were noted in any group of animals and the vaccine candidates were excreted robustly for 48-72h without significant changes in either the magnitude or duration of excretion when given as a monovalent or as bivalent mixtures. Similarly, immunological interferences were not apparent in the magnitude of humoral and mucosal immune responses observed toward Shigella-specific antigens when monkeys were fed monovalent or bivalent formulations. These results predict that a multivalent live oral vaccine of more than one serotype can have a favorable outcome for protection against shigellosis.

Development and preclinical evaluation of a trivalent, formalin-inactivated Shigella whole-cell vaccine.

Studies were undertaken to manufacture a multivalent Shigella inactivated whole-cell vaccine that is safe, effective, and inexpensive. By using several formalin concentrations, temperatures, and incubation periods, an optimized set of inactivation conditions was established for Shigella flexneri 2a, S. sonnei, and S. flexneri 3a to produce inactivated whole cells expressing a full repertoire of Ipa proteins and lipopolysaccharide (LPS). The inactivation conditions selected were treatment with 0.2% formalin (S. flexneri 2a and 3a) or 0.6% formalin (S. sonnei) for 48 h at 25°C. Vaccine formulations prepared under different inactivation conditions, in different doses (10E5, 10E7, and 10E9 cells), and with or without the inclusion of double-mutant heat-labile toxin (dmLT) were evaluated in mice. Two intranasal immunizations with ≥10E7 inactivated whole cells resulted in high levels of anti-Invaplex and moderate levels of LPS-specific IgG and IgA in serum and in lung and intestinal wash samples. Addition of dmLT to the vaccine formulations did not significantly enhance humoral immunogenicity. Minimal humoral responses for IpaB, IpaC, or IpaD were detected after immunization with inactivated whole Shigella cells regardless of the vaccine inactivation conditions. In guinea pigs, monovalent formulations of S. flexneri 2a of 3a or S. sonnei consisting of 10E8, 10E9, or 10E10 cells were protective in a keratoconjunctivitis assay. A trivalent formulation provided protection against all three serotypes (S. flexneri 2a, P = 0.018; S. flexneri 3a, P = 0.04; S. sonnei, P < 0.0001). The inactivated Shigella whole-cell vaccine approach incorporates an uncomplicated manufacturing process that is compatible with multivalency and the future development of a broadly protective Shigella vaccine.

Expression pattern of synaptic vesicle protein 2 (SV2) isoforms in patients with temporal lobe epilepsy and hippocampal sclerosis.

AIMS: Synaptic vesicle proteins 2 (SV2) are neuronal vesicles membrane glycoproteins that appear as important targets in the treatment of partial and generalized epilepsies. Therefore, we analysed the expression of SV2 isoforms in the hippocampus of patients with temporal lobe epilepsy (TLE). METHODS: SV2A, SV2B and SV2C immunostaining and QuantiGene branched DNA assay were performed on biopsies from 31 consecutive TLE patients with mesial temporal sclerosis (MTS) and compared with 10 autopsy controls. SV2 expression was further compared with Timm's staining, and synaptophysin, Zinc transporter 3 (ZnT3), dynorphin, vesicular glutamate transporter 1 (VGLUT1) and vesicular GABA transporter (VGAT) expression. RESULTS: In TLE patients, SV2A and SV2B expression was decreased in areas of synaptic loss. SV2C, which is weakly expressed or absent in the hippocampus of controls, was overexpressed in 10/11 cases with classical MTS1A and mossy fibre sprouting but not in cases with other types of MTS. SV2C staining was located in the inner molecular layer of the dentate gyrus and colocalized with dynorphin, ZnT3 and VGLUT1, suggesting selective expression in presynaptic glutamatergic Zn(2+) -rich terminals of abnormal sprouting fibres. SV2 expression patterns correlated with histological subtypes of MTS, but not with clinical features or therapeutic regimens in this patient cohort. CONCLUSION: In classical MTS1A, the expression of SV2 isoforms is altered with a marked decrease of SV2A and SV2B paralleling synaptic loss and a selective increase of SV2C in sprouting mossy fibres. These findings suggest a different physiology of sprouting synapses and the possibility to target them with SV2C-specific strategies.

Modulation of the conformational state of the SV2A protein by an allosteric mechanism as evidenced by ligand binding assays.

BACKGROUND AND PURPOSE: Synaptic vesicle protein 2A (SV2A) is the specific binding site of the anti-epileptic drug levetiracetam (LEV) and its higher affinity analogue UCB30889. Moreover, the protein has been well validated as a target for anticonvulsant therapy. Here, we report the identification of UCB1244283 acting as a SV2A positive allosteric modulator of UCB30889. EXPERIMENTAL APPROACH: UCB1244283 was characterized in vitro using radioligand binding assays with [(3)H]UCB30889 on recombinant SV2A expressed in HEK cells and on rat cortex. In vivo, the compound was tested in sound-sensitive mice. KEY RESULTS: Saturation binding experiments in the presence of UCB1244283 demonstrated a fivefold increase in the affinity of [(3)H]UCB30889 for human recombinant SV2A, combined with a twofold increase of the total number of binding sites. Similar results were obtained on rat cortex. In competition binding experiments, UCB1244283 potentiated the affinity of UCB30889 while the affinity of LEV remained unchanged. UCB1244283 significantly slowed down both the association and dissociation kinetics of [(3)H]UCB30889. Following i.c.v. administration in sound-sensitive mice, UCB1244283 showed a clear protective effect against both tonic and clonic convulsions. CONCLUSIONS AND IMPLICATIONS: These results indicate that UCB1244283 can modulate the conformation of SV2A, thereby inducing a higher affinity state for UCB30889. Our results also suggest that the conformation of SV2A per se might be an important determinant of its functioning, especially during epileptic seizures. Therefore, agents that act on the conformation of SV2A might hold great potential in the search for new SV2A-based anticonvulsant therapies.

Functional role of vasoactive intestinal polypeptide in inhibitory motor innervation in the mouse internal anal sphincter.

There is evidence that vasoactive intestinal polypeptide (VIP) participates in inhibitory neuromuscular transmission (NMT) in the internal anal sphincter (IAS). However, specific details concerning VIP-ergic NMT are limited, largely because of difficulties in selectively blocking other inhibitory neural pathways. The present study used the selective P2Y1 receptor antagonist MRS2500 (1 µm) and the nitric oxide synthase inhibitor N(G)-nitro-l-arginine (l-NNA; 100 µm) to block purinergic and nitrergic NMT to characterize non-purinergic, non-nitrergic (NNNP) inhibitory NMT and the role of VIP in this response. Nerves were stimulated with electrical field stimulation (0.1-20 Hz, 4-60 s) and the associated changes in contractile and electrical activity measured in non-adrenergic, non-cholinergic conditions in the IAS of wild-type and VIP(-/-) mice. Electrical field stimulation gave rise to frequency-dependent relaxation and hyperpolarization that was blocked by tetrodotoxin. Responses during brief trains of stimuli (4 s) were mediated by purinergic and nitrergic NMT. During longer stimulus trains, an NNNP relaxation and hyperpolarization developed slowly and persisted for several minutes beyond the end of the stimulus train. The NNNP NMT was abolished by VIP6-28 (30 µm), absent in the VIP(-/-) mouse and mimicked by exogenous VIP (1-100 nm). Immunoreactivity for VIP was co-localized with neuronal nitric oxide synthase in varicose intramuscular fibres but was not detected in the VIP(-/-) mouse IAS. In conclusion, this study identified an ultraslow component of inhibitory NMT in the IAS mediated by VIP. In vivo, this pathway may be activated with larger rectal distensions, leading to a more prolonged period of anal relaxation.

Precise determination of the f0(600) and f0(980) pole parameters from a dispersive data analysis.

We use our latest dispersive analysis of ππ scattering data and the very recent K(ℓ4) experimental results to obtain the mass, width, and couplings of the two lightest scalar-isoscalar resonances. These parameters are defined from their associated poles in the complex plane. The analytic continuation to the complex plane is made in a model-independent way by means of once- and twice-subtracted dispersion relations for the partial waves, without any other theoretical assumption. We find the f(0)(600) pole at (457(-13))+14))-i(279(-7)(+11)) MeV and that of the f(0)(980) at (996 ± 7)-i(25(-6)(+10)) MeV, whereas their respective couplings to two pions are 3.59(-0.13)(+0.11) and 2.3 ± 0.2 GeV.

Shigella sonnei vaccine candidates WRSs2 and WRSs3 are as immunogenic as WRSS1, a clinically tested vaccine candidate, in a primate model of infection.

Shigella causes diarrhea and dysentery through contaminated food and water. Shigella sonnei live vaccine candidates WRSs2 and WRSs3 are attenuated principally by the loss of VirG(IcsA) that prevents bacterial spread within the colonic epithelium. In this respect they are similar to the clinically tested vaccine candidate WRSS1. However, WRSs2 and WRSs3 are further attenuated by loss of senA, senB and WRSs3 also lacks msbB2. As previously shown in cell culture assays and in small animal models, these additional gene deletions reduced the levels of enterotoxicity and endotoxicity of WRSs2 and WRSs3, potentially making them safer than WRSS1. However the behavior of these second-generation VirG(IcsA)-based vaccine candidates in eliciting an immune response in a gastrointestinal model of infection has not been evaluated. In this study, WRSs2 and WRSs3 were nasogastrically administered to rhesus monkeys that were evaluated for colonization, as well as for systemic and mucosal immune responses. Both vaccine candidates were safe in rhesus monkeys and behaved comparably to WRSS1 in bacterial excretion rates that demonstrated robust intestinal colonization. Furthermore, humoral and mucosal immune responses elicited against bacterial antigens appeared similar in all categories across all three strains indicating that the additional gene deletions did not compromise the immunogenicity of these vaccine candidates. Based on data from previous clinical trials with WRSS1, it is likely that, WRSs2 and WRSs3 will not only be safer in human volunteers but will generate comparable levels of systemic and mucosal immune responses that were achieved with WRSS1.

Brivaracetam does not alter spatial learning and memory in both normal and amygdala-kindled rats.

Several antiepileptic drugs (AEDs) may induce memory deficits when tested in preclinical models at doses that exert significant protection against seizures. Brivaracetam (BRV) is a novel high-affinity SV2A ligand also displaying inhibitory activity at neuronal voltage-gated sodium channels. In the present study we have investigated the effects of BRV, at doses that exerted marked anticonvulsant effects in kindled rats, upon cognitive functioning and memory in both normal and amygdala-kindled rats using place learning version of Morris water maze. In addition the effect of BRV on long-term potentiation (LTP) in rat hippocampal slices has been investigated. BRV (2.1, 6.8 or 21.0mg/kg i.p.) was injected daily, 60min before each session. Results indicated that in both normal and amygdala-kindled rats BRV did not alter the latency to find the hidden platform or swimming speed during the four consecutive days of learning. Similarly, the time spent in the target quadrant, used as a further independent index of spatial memory, was not modified by BRV treatment. Likewise, BRV did not affect the LTP induction in CA1 hippocampal region when tested at 3-30microM concentration range, which had been demonstrated to significantly reduce epileptiform activity in slice models. Based on the results of the present study it can be expected that BRV will not have detrimental effects on hippocampal-dependent cognitive functions in patients with epilepsy.

Safety and immunogenicity of a Shigella flexneri 2a Invaplex 50 intranasal vaccine in adult volunteers.

Shigellosis is a leading cause of diarrhea worldwide prompting vaccine development. The Shigella flexneri Invaplex 50 is a macromolecular complex containing IpaB, IpaC, and LPS, formulated from an aqueous extract of virulent Shigella delivered via nasal administration. Preclinical vaccine testing demonstrated safety, immunogenicity and efficacy. An open-label dose-escalating phase 1 study evaluated a 3-dose (2-week intervals) regimen via nasal pipette delivery. Thirty-two subjects were enrolled into one of four vaccine dose groups (10, 50, 240, or 480 microg). The vaccine was well tolerated with minor short-lived nasal symptoms without evidence of dose effect. Antibody-secreting cell (ASC) responses were elicited at doses > or =50 microg with the highest IgG ASC, Invaplex 50 (100%) and S. flexneri 2a LPS (71%), as well as, serologic responses (43%) occurring with the 240 microg dose. Fecal IgA responses, Invaplex 50 (38.5%) and LPS (30.8%), were observed at doses > or =240 microg. The Invaplex 50 nasal vaccine was safe with encouraging mucosal immune responses. Follow-on studies will optimize dose, delivery mechanism and assess efficacy in a S. flexneri 2a challenge study.

Modulation of AMP deaminase in rat hearts subjected to ischemia and reperfusion by purine riboside.

Changes in AMP deaminase (AMPD) activity influence heart function and progression of heart disease, but the underlying mechanism is unknown. We evaluated the effect of purine riboside (Purr) on the activity of AMPD in perfused rat hearts and in isolated rat cardiomyocytes. Brief perfusion of the pre-ischemic heart with 200 micro M Purr resulted in activation of AMPD, more pronounced degradation of the adenine nucleotides, and reduced recovery of the adenine nucleotide pool during reperfusion. Brief incubation of rat cardiomyocytes with 200 micro M Purr also activated AMPD, while prolonged exposure resulted in enzyme inhibition. We conclude that Purr activates AMPD, whereas metabolites of this compound may inhibit the enzyme.

The dopamine D3/D2 agonist (+)-PD-128,907 [(R-(+)-trans-3,4a,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano[4,3-b]-1,4-oxazin-9-ol)] protects against acute and cocaine-kindled seizures in mice: further evidence for the involvement of D3 receptors.

Previous findings have demonstrated a protective role for dopamine D(3)/D(2) receptor agonists in the convulsant and lethal effects of acutely administered cocaine. Data are provided here to establish that the protection occurs through a D(3)-linked mechanism and that protection is extended to seizure kindling. The D(3) antagonist SB-277011-A [4-quinolinecarboxamide,N-[trans-4-[2-(6-cyano-3,4-dihydro-2(1H)-isoquinolinyl)ethyl]-cyclohexyl]-(9CI)] prevented the anticonvulsant effect of the D(3)/D(2) receptor agonist (+)-PD-128,907 [(R-(+)-trans-3,4a,10b-tetrahydro-4-propyl-2H,5H-[1]benzopyrano[4,3-b]-1,4-oxazin-9-ol)] on cocaine-induced seizures. The protection afforded by the D(3)/D(2) agonist, (+)-PD-128,907, was eliminated in D(3) receptor-deficient mice. In D(2) receptor knockout mice, the anticonvulsant effects of (+)-PD-128,907 were preserved. (+)-PD-128,907 also prevented the acquisition and expression of cocaine-kindled seizures engendered by repeated daily dosing with 60 mg/kg cocaine. (+)-PD-128,907 also blocked the seizures induced in mice fully seizure kindled to cocaine. Although repeated dosing with cocaine increased the potency of cocaine to produce seizures and lethality (decreased ED(50) values), daily coadministration of (+)-PD-128,907 significantly prevented this potency shift. In mice treated daily with cocaine and (+)-PD-128,907, the density, but not the affinity, of D(3) receptors was increased. The specificity with which (+)-PD-128,907 acts upon this cocaine-driven process was demonstrated by the lack of a significant effect of (+)-PD-128,907 on seizure kindling to a GABA(A) receptor antagonist, pentylenetetrazol. Taken together and with literature findings, the data indicate that dopamine D(3) receptors function in the initiation of a dampening mechanism against the toxic effects of cocaine, a finding that might have relevance to psychiatric disorders of drug dependence, schizophrenia, and bipolar depression.

The initial zones of the atrioventricular node: really neglected anatomical features of potential clinical significance?

The constant evolution of medical knowledge and accompanying development of diagnostic and treatment possibilities for arrhythmias and conduction disturbances has reawakened interest in the structure and function of the conduction system of the human heart, especially in the region of the atrioventricular (AV) junction and within the junction itself. Of the large number of studies dealing with the AV junction few focus on the initial zones of the AV node. These were described for the first time by Tawara in 1906. Similarly, Anderson et al. distinguished two origins of the AV node, the left one running towards the basis of the mitral valve and the right one leading towards the tricuspid valve. The differences in length and scale could be the result of the adoption of different reference points. The study was carried out on the material of 50 human hearts, of both sexes and ranging in age from 22 to 93, which were fixed in 10% formalin and 98% ethanol solution. The tissue obtained was fixed in the 10% formalin solution and, after being sunk in the paraffin, was cut into layers of about 10 mum thick. According to the age of the hearts, every 10(th) or 6(th) section was stained by the Masson-Goldner method. The preparations were examined under a LEICA 2000 and BIOLAR 2 microscope at magnifications of 2x to 400x. Each of the 50 examined hearts contained the atrioventricular node and its initial parts. We observed that the initial zone of the AV node is created by an assembly of cells typical for a conduction system that can create three groups that are initially independent of each other and are always arranged around the AV nodal artery. In all the hearts examined we found at least two initial parts of the node: the superior and inferior. These two groups were present in 45 hearts (90%). In the last 5 cases (10%) there was also a middle group. No cases were found either with a single initial group or without any initial groups. In the sections examined the superior group appeared to be first in 27 hearts (54%), while in 23 cases (46%) the inferior group was first. The length of each group was measured from its first appearance to its first direct contact with the second part. The length of the superior part varied from 0.15 to 2.91 mm (mean 0.90 +/- 0.6 mm), the inferior from 0.11 to 2.41 mm (mean 0.88 +/- 0.6 mm) and the middle from 0.67 to 2.21 mm (mean 1.04 +/- 0.7 mm). As mentioned above, in all 50 hearts there was a direct connection between the atrial muscle and the upper origin of AV node. Furthermore, in all sections (100%) the same part of the interatrial septal muscle was connected to the compact part of the node. Additionally, in 3 cases (6%) we were able to observe direct connections between the muscle fibres running from the fasciculus limbicus inferior to the initial zone of the AV node: in 2 cases (4%) with the superior group and in 1 case (2%) with the inferior group. In 8% of the material the atrial muscle of the supra-orificial zone made direct contact with the superior initial group and the compact zone of the node and in 10% there was contact between the suborificial muscle and the inferior group and the compact part of the node. This configuration was not observed in relation to the middle and inferior groups.