Novel-Type GABAB PAMs: Structure-Activity Relationship in Light of the Protein Structure

Selecting a known HTS hit with the pyrazolo[1,5-a]pyrimidine core, our project was started from CMPPE, and its optimization was driven by a ligand-based pharmacophore model developed on the basis of published GABAB positive allosteric modulators (PAMs). Our primary goal was to improve the potency by finding new enthalpic interactions. Therefore, we included the lipophilic ligand efficiency (LLE or LipE) as an objective function in the optimization that led to a carboxylic acid derivative (34). This lead candidate offers the possibility to improve potency without drastically inflating the physicochemical properties. Although the discovery of the novel carboxyl feature was surprising, it turned out to be an important element of the GABAB PAM pharmacophore that can be perfectly explained based on the new protein structures. Rationalizing the binding mode of 34, we analyzed the intersubunit PAM binding site of GABAB receptor using the publicly available experimental structures.

Discovery of Novel Steroid-Based Histamine H3 Receptor Antagonists/Inverse Agonists

Steroid-based histamine H3 receptor antagonists (d-homoazasteroids) were designed by combining distinct structural elements of HTS hit molecules. They were characterized, and several of them displayed remarkably high affinity for H3 receptors with antagonist/inverse agonist features. Especially, the 17a-aza-d-homolactam chemotype demonstrated excellent H3R activity together with significant in vivo H3 antagonism. Optimization of the chemotype was initiated with special emphasis on the elimination of the hERG and muscarinic affinity. Additionally, ligand-based SAR considerations and molecular docking studies were performed to predict binding modes of the molecules. The most promising compounds (XXI, XXVIII, and XX) showed practically no muscarinic and hERG affinity. They showed antagonist/inverse agonist property in the in vitro functional tests that was apparent in the rat in vivo dipsogenia test. They were considerably stable in human and rat liver microsomes and provided significant in vivo potency in the place recognition and novel object recognition cognitive paradigms.

Discovery and Characterization of RGH-122, a Potent, Selective, and Orally Bioavailable V1a Receptor Antagonist

The V1a receptor is a major contributor in mediating the social and emotional effects of arginine-vasopressin (AVP); therefore it represents a promising target in the treatment of several neuropsychiatric conditions. The aim of this research was to design and synthesize novel and selective V1a antagonists with improved in vitro and in vivo profiles. Through optimization and detailed SAR studies, we developed low nanomolar antagonists, and further characterizations led to the discovery of the clinical candidate compound 43 (RGH-122). The CNS activity of the compound was determined in a 3-chamber social preference test of autism in which RGH-122 successfully enhanced social preference with the lowest effective dose of 1.5 mg/kg.

6-Aryl-quinazolines as novel GABAB receptor positive allosteric modulators

The systemic use of GABA_B orthosteric agonist baclofen might be limited due to its detrimental properties: sedation and motor impairment. In contrast, GABA_B positive allosteric modulators produce less adverse effects. Using BHF-177 as a starting point, we found a new active scaffold: the 6-aryl-quinazoline scaffold. Further elaborating the scaffold, we identified several in vitro and in vivo active compounds.

Response-related sensorimotor rhythms under scopolamine and MK-801 exposures in the touchscreen visual discrimination test in rats

The human mu rhythm has been suggested to represent an important function in information processing. Rodent homologue rhythms have been assumed though no study has investigated them from the cognitive aspect yet. As voluntary goal-directed movements induce the desynchronization of mu rhythm, we aimed at exploring whether the response-related brain activity during the touchscreen visual discrimination (VD) task is suitable to detect sensorimotor rhythms and their change under cognitive impairment. Different doses of scopolamine or MK-801 were injected subcutaneously to rats, and epidural electroencephalogram (EEG) was recorded during task performance. Arciform ~ 10 Hz oscillations appeared during visual processing, then two characteristic alpha/beta desynchronization-resynchronization patterns emerged mainly above the sensorimotor areas, serving presumably different motor functions. Beyond causing cognitive impairment, both drugs supressed the touch-related upper alpha (10–15 Hz) reactivity for desynchronization. Reaction time predominantly correlated positively with movement-related alpha and beta power both in normal and impaired conditions. These results support the existence of a mu homologue rodent rhythm whose upper alpha component appeared to be modulated by cholinergic and glutamatergic mechanisms and its power change might indicate a potential EEG correlate of processing speed. The VD task can be utilized for the investigation of sensorimotor rhythms in rats.

Intranasal Oxytocin Improves Social Behavior in Laboratory Beagle Dogs (Canis familiaris) Using a Custom-Made Social Test Battery

For a long time, oxytocin has been thought to have a generally positive effect on social cognition and prosocial behavior; however, recent results suggested that oxytocin has beneficial effects only under certain conditions. The aim of the present study was to explore potential associations between social competence and the effect of intranasal oxytocin on the social behavior of laboratory beagle dogs. We expected oxytocin treatment to have a more pronounced positive effect on dogs with lower baseline performance in a social test battery. Thirty-six adult dogs of both sexes received 32 IU intranasal oxytocin and physiological saline (placebo) treatment in a double-blind, cross-over design, with 17–20 days between the two sessions. Forty minutes after the treatment, dogs participated in a social test battery consisting of eight situations. The situations were carried out within one session and took 20–30 min to complete. Principal component analysis on the coded behaviors identified four components (Willingness to interact, Preference for social contact, Non-aversive response to nonsocial threat, and Non-aversive response to social threat). The subjects' behavior during the placebo condition was used to assess their baseline performance. We found that oxytocin treatment had a differential effect on the behavior depending on the baseline performance of the individuals in all components, but only two treatment × baseline performance interactions remained significant in a less sensitive analysis. In accordance with our hypothesis, oxytocin administration increased dogs' contact seeking and affiliative behaviors toward humans but only for those with low baseline performance. Dogs with low baseline performance also showed significantly more positive (friendly) reactions to social threat after oxytocin administration than after placebo, while for dogs with high baseline performance, oxytocin administration led to a more negative (fearful) reaction. These results indicate that similar to those on humans, the effects of oxytocin on dogs' social behavior are not universally positive but are constrained by individual characteristics and the context. Nevertheless, oxytocin administration has the potential to improve the social behavior of laboratory beagle dogs that are socially less proficient when interacting with humans, which could have both applied and animal welfare implications.

Convergent cross-species pro-cognitive effects of RGH-235, a new potent and selective histamine H3 receptor antagonist/inverse agonist

The histamine H₃ receptor is a favourable target for the treatment of cognitive deficits. Here we report the in vitro and in vivo profile of RGH-235, a new potent, selective, and orally active H₃ receptor antagonist/inverse agonist developed by Gedeon Richter Plc. Radioligand binding and functional assays were used for in vitro profiling. Procognitive efficacy was investigated in rodent cognitive tests, in models of attention deficit hyperactive disorder (ADHD) and in cognitive tests of high translational value (rat touch screen visual discrimination test, primate fixed-foreperiod visual reaction time task). Results were supported by pharmacokinetic studies, neurotransmitter release, sleep EEG and dipsogenia. RGH-235 displayed high affinity to H₃ receptors (K_i = 3.0-9.2 nM, depending on species), without affinity to H₁, H₂ or H₄ receptors and >100 other targets. RGH-235 was an inverse agonist ([³⁵S] GTPγS binding) and antagonist (pERK1/2 ELISA), showing favourable kinetics, inhibition of the imetit-induced dipsogenia and moderate effects on sleep-wake EEG. RGH-235 stimulated neurotransmitter release both in vitro and in vivo. RGH-235 was active in spontaneously hypertensive rats (SHR), generally considered as a model of ADHD, and revealed a robust pro-cognitive profile both in rodent and primate tests (in 0.3-1 mg/kg) and in models of high translational value (e.g. in a rodent touch screen test and in non-human primates). The multiple and convergent procognitive effects of RGH-235 support the view that beneficial cognitive effects can be linked to antagonism/inverse agonism of H₃ receptors.

Contribution of analog signaling to neurotransmitter interactions and behavior: Role of transporter-mediated nonquantal dopamine release

Neuronal networks cause changes in behaviorally important information processing through the vesicular release of neurotransmitters governed by the rate and timing of action potentials (APs). Herein, we provide evidence that dopamine (DA), nonquantally released from the cytoplasm, may exert similar effects in vivo. In mouse slice preparations, (+/-)-3,4-methylenedioxy-methamphetamine (MDMA, or ecstasy) and β-phenylethylamine (β-PEA)-induced DA release in the striatum and nucleus accumbens (NAc), two regions of the brain involved in reward-driven and social behavior and inhibited the axonal stimulation-induced release of tritiated acetylcholine ([3 H]ACh) in the striatum. The DA transporter (DAT) inhibitor (GBR-12909) prevented MDMA and β-PEA from causing DA release. GBR-12909 could also restore some of the stimulated acetylcholine release reduced by MDMA or β-PEA in the striatum confirming the fundamental role of DAT. In addition, hypothermia could prevent the β-PEA-induced release in the striatum and in the NAc. Sulpiride, a D2 receptor antagonist, also prevented the inhibitory effects of MDMA or β-PEA on stimulated ACh release, suggesting they act indirectly via binding of DA. Reflecting the neurochemical interactions in brain slices at higher system level, MDMA altered the social behavior of rats by preferentially enhancing passive social behavior. Similar to the in vitro effects, GBR-12909 treatment reversed specific elements of the MDMA-induced changes in behavior, such as passive social behavior, while left others including social play unchanged. The changes in behavior by the high level of extracellular DA-- a significant amount originating from cytoplasmic release--suggest that in addition to digital computation through synapses, the brain also uses analog communication, such as DA signaling, to mediate some elements of complex behaviors, but in a much longer time scale.

Cariprazine alleviates core behavioral deficits in the prenatal valproic acid exposure model of autism spectrum disorder

RATIONALE

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by deficits in social communication and interaction and restricted, repetitive behaviors. The unmet medical need in ASD is considerable since there is no approved pharmacotherapy for the treatment of these deficits in social communication, interaction, and behavior. Cariprazine, a dopamine D₃-preferring D₃/D₂ receptor partial agonist, is already approved for the treatment of schizophrenia and bipolar I disorder in adults; investigation in patients with ASD is warranted.

OBJECTIVES

The aim of this study was to investigate the effects of cariprazine, compared with risperidone and aripiprazole, in the rat prenatal valporic acid (VPA) exposure model on behavioral endpoints representing the core and associated symptoms of ASD.

METHODS

To induce the ASD model, time-mated Wistar rat dams were treated with VPA during pregnancy. Male offspring were assigned to groups and studied in a behavioral test battery at different ages, employing social play, open field, social approach-avoidance, and social recognition memory tests. Animals were dosed orally, once a day for 8 days, with test compounds (cariprazine, risperidone, aripiprazole) or vehicle before behavioral assessment.

RESULTS

Cariprazine showed dose-dependent efficacy on all behavioral endpoints. In the social play paradigm, only cariprazine was effective. On the remaining behavioral endpoints, including the reversal of hyperactivity, risperidone and aripiprazole displayed similar efficacy to cariprazine.

CONCLUSIONS

In the present study, cariprazine effectively reversed core behavioral deficits and hyperactivity present in juvenile and young adult autistic-like rats. These findings indicate that cariprazine may be useful in the treatment of ASD symptoms.

Cariprazine alleviates core behavioral deficits in the prenatal valproic acid exposure model of autism spectrum disorder

RATIONALE

Autism spectrum disorder (ASD) is a neurodevelopmental condition characterized by deficits in social communication and interaction and restricted, repetitive behaviors. The unmet medical need in ASD is considerable since there is no approved pharmacotherapy for the treatment of these deficits in social communication, interaction, and behavior. Cariprazine, a dopamine D₃-preferring D₃/D₂ receptor partial agonist, is already approved for the treatment of schizophrenia and bipolar I disorder in adults; investigation in patients with ASD is warranted.

OBJECTIVES

The aim of this study was to investigate the effects of cariprazine, compared with risperidone and aripiprazole, in the rat prenatal valporic acid (VPA) exposure model on behavioral endpoints representing the core and associated symptoms of ASD.

METHODS

To induce the ASD model, time-mated Wistar rat dams were treated with VPA during pregnancy. Male offspring were assigned to groups and studied in a behavioral test battery at different ages, employing social play, open field, social approach-avoidance, and social recognition memory tests. Animals were dosed orally, once a day for 8 days, with test compounds (cariprazine, risperidone, aripiprazole) or vehicle before behavioral assessment.

RESULTS

Cariprazine showed dose-dependent efficacy on all behavioral endpoints. In the social play paradigm, only cariprazine was effective. On the remaining behavioral endpoints, including the reversal of hyperactivity, risperidone and aripiprazole displayed similar efficacy to cariprazine.

CONCLUSIONS

In the present study, cariprazine effectively reversed core behavioral deficits and hyperactivity present in juvenile and young adult autistic-like rats. These findings indicate that cariprazine may be useful in the treatment of ASD symptoms.

Measuring sociability of mice using a novel three-chamber apparatus and algorithm of the LABORAS™ system

BACKGROUND

The social approach and social novelty tests utilizing the three-chamber apparatus are widely accepted to measure social behavior of rodents. The LABORAS™ system offers a possibility to assess sociability of mice in a reliable and objective manner.

NEW METHOD

We assessed the capability of the LABORAS™ sociability cage and algorithm (2.6.6) to detect social behaviors in mice. Furthermore, we investigated whether the system is able to detect various levels of sociability due to genetic background or after pharmacological treatments.

RESULTS

By comparing manual scoring with various detection zone settings of the automated registration, the most fitting algorithm with a detection zone radius of 90 mm was identified. When different strains were investigated, C57Bl/6 J and NMRI mice proved to be social, while CD1 mice were found asocial. The system was able to detect the sociability increasing effect of R-baclofen (0.5 mg/kg i.p.) and oxytocin (12 ng i.c.v.) in asocial CD1 mice. The negative control PCP impaired social behavior of C57Bl/6 J mice (1 mg/kg i.p.) and increased social avoidance in CD1 mice (0.3 mg/kg i.p.).

COMPARISON WITH EXISTING METHOD(S)

This setup, in contrast to video frame analysis softwares, determines signal changes caused by movements of rodents allowing accurate detection and analysis of trajectories. Parallel automated measurements also allow replacing time and labor intensive, highly subjective human observational work.

CONCLUSIONS

The set-up provides a fast and reliable method to examine social behavior of mice in the three-chamber apparatus. The system is capable of detecting pro or antisocial activity of pharmacological agents.

Disrupted Social Hierarchy in Prenatally Valproate-Exposed Autistic-Like Rats

Autism spectrum disorder (ASD) is characterized by impaired socio-communicational function, repetitive and restricted behaviors. Valproic acid (VPA) was reported to increase the prevalence of ASD in humans as a consequence of its use during pregnancy. VPA treatment also induces autistic-like behaviors in the offspring of rats after prenatal exposure; hence it is a preclinical disease model with high translational value. In the present study, our aim was to characterize ASD relevant behaviors of socially housed, individually identified male rats in automated home cages. The natural behavior of rats was assessed by monitoring their visits to drinking bottles in an environment without human influence aiming at reducing interventional stress. Although rodents normally tend to explore their new environment, prenatally VPA-treated rats showed a drastic impairment in initial and long-term exploratory behavior throughout their stay in the automated cage. Furthermore, VPA rats displayed psychogenic polydipsia (PPD) as well as altered circadian activity. In the competitive situation of strict water deprivation controls switched to an uneven resource sharing and only a few dominant animals had access to water. In VPA animals similar hierarchy-related changes were completely absent. While the control rats secured their chance to drink with frequent reentering visits, thereby “guarding” the water resource, VPA animals did not switch to uneven sharing and displayed no evidence of guarding behavior.

The dog (Canis familiaris) as a translational model of autism: It is high time we move from promise to reality

Selecting appropriate animal models for a particular human phenomenon is a difficult but important challenge. The difficulty lies in finding animal behaviors that are not only sufficiently relevant and analog to the complex human symptoms (face validity) but also have similar underlying biological and etiological mechanisms (translational or construct validity), and have "human-like" responses to treatment (predictive validity). Over the past several years, the domestic dog (Canis familiaris) has become increasingly proposed as a model for comparative and translational neuroscience. In parallel to the recent advances in canine behavior research, dogs have also been proposed as a model of many human neuropsychiatric conditions, including autism spectrum disorder (ASD). In this opinion paper we will shortly discuss the challenging nature of autism research then summarize the different neurocognitive frameworks for ASD making the case for a canine model of autism. The translational value of a dog model stems from the recognition that (a) there is a large inter-individual variability in the manifestation of dogs' social cognitive abilities including both high and low phenotypic extremes; (b) the phenotypic similarity between the dog and human symptoms are much higher than between the rodent and human symptoms; (c) the symptoms are functionally analogous to the human condition; and (d) more likely to have similar etiology. This article is categorized under: Psychology > Comparative Psychology Cognitive Biology > Evolutionary Roots of Cognition.

Altered neurite morphology and cholinergic function of induced pluripotent stem cell-derived neurons from a patient with Kleefstra syndrome and autism

The aim of the present study was to establish an in vitro Kleefstra syndrome (KS) disease model using the human induced pluripotent stem cell (hiPSC) technology. Previously, an autism spectrum disorder (ASD) patient with Kleefstra syndrome (KS-ASD) carrying a deleterious premature termination codon mutation in the EHMT1 gene was identified. Patient specific hiPSCs generated from peripheral blood mononuclear cells of the KS-ASD patient were differentiated into post-mitotic cortical neurons. Lower levels of EHMT1 mRNA as well as protein expression were confirmed in these cells. Morphological analysis on neuronal cells differentiated from the KS-ASD patient-derived hiPSC clones showed significantly shorter neurites and reduced arborization compared to cells generated from healthy controls. Moreover, density of dendritic protrusions of neuronal cells derived from KS-ASD hiPSCs was lower than that of control cells. Synaptic connections and spontaneous neuronal activity measured by live cell calcium imaging could be detected after 5 weeks of differentiation, when KS-ASD cells exhibited higher sensitivity of calcium responses to acetylcholine stimulation indicating a lower nicotinic cholinergic tone at baseline condition in KS-ASD cells. In addition, gene expression profiling of differentiated neuronal cells from the KS-ASD patient revealed higher expression of proliferation-related genes and lower mRNA levels of genes involved in neuronal maturation and migration. Our data demonstrate anomalous neuronal morphology, functional activity and gene expression in KS-ASD patient-specific hiPSC-derived neuronal cultures, which offers an in vitro system that contributes to a better understanding of KS and potentially other neurodevelopmental disorders including ASD.

Establishment of EHMT1 mutant induced pluripotent stem cell (iPSC) line from a 11-year-old Kleefstra syndrome (KS) patient with autism and normal intellectual performance

Peripheral blood was collected from a clinically characterized female Kleefstra syndrome patient with a heterozygous, de novo, premature termination codon (PTC) mutation (NM_024757.4(EHMT1):c.3413G>A; p.Trp1138Ter). Peripheral blood mononuclear cells (PBMCs) were reprogrammed with the human OSKM transcription factors using the Sendai-virus (SeV) delivery system. The pluripotency of transgene-free iPSC line was verified by the expression of pluripotency-associated markers and by in vitro spontaneous differentiation towards the 3 germ layers. Furthermore, the iPSC line showed normal karyotype. Our model might offer a good platform to study the pathomechanism of Kleefstra syndrome, also for drug testing, early biomarker discovery and gene therapy studies.

Spatial pattern analysis of nitrergic neurons in the developing myenteric plexus of the human fetal intestine

BACKGROUND

Enteric nervous system precursors derived from the neural crest migrate along defined pathways to colonize the bowel. The individual cells in different environments experience different growth, differentiation, and survival conditions. Hence, the spatial distribution of the neurons is determinant with regard to functional maturation. The question arises as to whether the distribution is random or nonrandom.

METHODS

Nitrergic cells were visualized by means of nicotinamide adenine dinucleotide phosphate diaphorase histochemistry. Stained specimens were photographed, and the borders of the myenteric plexus and the nuclei of the nitrergic neurons were digitalized. Plexus Pattern Analysis software was used to count the nuclei of nitrergic neurons, calculate the proportions of the areas covered by the plexus and the gut wall, and perform randomization analyses.

RESULTS

The distribution pattern of the nitrergic neurons changed markedly between weeks 14 and 22 of gestation. The nitrergic neurons were randomly distributed at week 14 but were aggregated in the plexus and within the individual ganglia at week 19. The dynamics of these changes exhibited regional differences.

CONCLUSIONS

The results suggest that, in addition to the gut wall and the plexus, other intraganglionic constituents may contribute to the aggregation of nitrergic cells and such examinations should be extended to other cell types in the future.

Computer-aided morphometric analysis of the developing concentric structure of the human fetal intestinal tube

The Image-Pro Plus 3.0 morphometric program was used to study the region-specific organization of the human fetal intestine across the radial axis of the gut at weeks 12 and 18 of gestation. The thicknesses of the epithelium, the submucosa, the muscular layers and the myenteric ganglia were measured in resin-embedded semithin sections. Statistical analysis of the collected data was performed by using the two-way ANOVA, the SNK test and the Pearson correlation. The structural changes relating to the gut morphogenesis within this developmental period were followed both light and electron microscopically. The various tissues forming the radial axis of the intestinal tube exhibited different trends concerning their individual development. The thickness of the epithelium did not change in the fetal period investigated, although the epithelial surface displayed characteristic ultrastructural changes. The thickness of the submucosal layer increased significantly, but with different dynamics along the longitudinal axis, whereas the increases in size of the muscular layers and the myenteric ganglia did not differ significantly along the longitudinal axis of the embryonic intestine. The Pearson correlation revealed a significant correlation between the development of the circular muscle layer and that of the myenteric plexus along the whole length of the intestinal tube. The epithelium, the submucosa and the longitudinal muscle layers developed independently between weeks 12 and 18 of gestation.

Evaluation of the total number of myenteric neurons in the developing chicken gut using cuprolinic blue histochemical staining and neurofilament immunocytochemistry

The aim of this study was to find an improved method with which to stain the entire population of myenteric neurons in the different segments of the developing chicken intestine. Histochemical staining with cuprolinic blue (quinolinic phthalocyanine) and immunostaining against neurofilament (NF) were performed on whole mounts prepared from intestinal segments of embryonic (day 19 of incubation) and hatched (1, 2, 4 and 7 days after hatching) chickens. Double labelling was performed to evaluate to what extent the two markers visualise the same nerve cell population. Cuprolinic blue stained neuronal somata highly selectively, whereas processes and glia cells were poorly labelled. The cuprolinic blue-positive neurons were uniform in shape. NF immunostaining revealed a morphologically highly variable neuron population. Double labelling with cuprolinic blue and NF resulted in an intensification of both stainings, allowing an accurate morphological classification of NF-stained myenteric neurons. Data obtained from the counting of cuprolinic blue-positive neurons were subjected to two-way ANOVA and the Tukey probe. The densities of ganglia and neurons were found to decrease, and the mean number of neurons per myenteric ganglion to increase, with different dynamics along the longitudinal axis of the gut during the examined time span. The variances in the number of NF-positive neurons were not homogeneous, and the data were therefore not suitable for ANOVA. Accordingly, only semiquantitative conclusions could be drawn.

Influence of prosthesis size and left ventricular mass on left ventricular diastolic reserve in patients with aortic valve prostheses

BACKGROUND AND AIM OF THE STUDY

The study aim was to determine the influence of valve size and left ventricular (LV) mass on long-term LV diastolic reserve in patients subjected to aortic valve replacement for stenosis.

METHODS

Seventy-four patients (33 women, 41 men; mean age 64 years) after aortic valve replacement with 40 pericardial bioprostheses and 34 bileaflet mechanical prostheses were studied. All valves were of nominal size 19, 21 or 23 mm. The patients were studied by Doppler echocardiography, at rest and during peak effort, between 12 and 47 months after valve replacement.

RESULTS

All patients achieved significantly increased heart rate, blood pressure and cardiac output in response to effort. Effort also significantly modified transvalvular pressure drops and valve areas. The mean diastolic reserve was 29.3 ml, and mean stroke volume reserve 23.2 ml; in neither case were there any significant differences between valve types, or among valve sizes.

CONCLUSION

At about one year after surgery, the diastolic reserve of patients subjected to aortic valve replacement on account of stenosis was considerable, and independent of valve size. Despite the persistence of LV hypertrophy after valve replacement, LV diastolic function during effort was similar to that of the normal heart.

Quantitative distribution of NADPH-diaphorase-positive myenteric neurons in different segments of the developing chicken small intestine and colon

NADPH-diaphorase (NADPH-d) was used as a marker for neuronal nitric oxide synthase in order to investigate the nitrergic neurons of the developing myenteric ganglia on whole-mount preparations in the proximal and distal segments of the small intestine and in the colon of the chicken embryo, between incubation days 12 and 19. Neurons that were positive for NADPH-d were counted in randomly selected myenteric ganglia. The data obtained from each area and each age group were subjected to two-way analysis of variance (ANOVA) and the Student-Newman-Keuls test. Between incubation days 12 and 19, the originally narrow-meshed myenteric plexus with its high ganglionic density progressively became wide-meshed and the ganglionic density decreased significantly. Quantitative analysis further revealed a significant decrease in the NADPH-d-positive nerve cell density with age. At the same time, the constant or even increasing number of nitrergic cells per ganglion may indicate that the decreasing cell density may be a result of the growth of the bowel with decreasing ganglion density rather than a decrease in the total number of myenteric nitrergic cells. Regional differences in the dynamics of the quantitative changes were revealed. A significant decrease in the nitrergic cell number appeared earlier in the proximal than in the distal segments of the small intestine or in the colon. In contrast, the significant decline of the ganglionic density was first noticed in the colon at the same time.

Quantitative distribution of NADPH-diaphorase-positive myenteric neurons in different segments of the developing chicken small intestine and colon

NADPH-diaphorase (NADPH-d) was used as a marker for neuronal nitric oxide synthase in order to investigate the nitrergic neurons of the developing myenteric ganglia on whole-mount preparations in the proximal and distal segments of the small intestine and in the colon of the chicken embryo, between incubation days 12 and 19. Neurons that were positive for NADPH-d were counted in randomly selected myenteric ganglia. The data obtained from each area and each age group were subjected to two-way analysis of variance (ANOVA) and the Student-Newman-Keuls test. Between incubation days 12 and 19, the originally narrow-meshed myenteric plexus with its high ganglionic density progressively became wide-meshed and the ganglionic density decreased significantly. Quantitative analysis further revealed a significant decrease in the NADPH-d-positive nerve cell density with age. At the same time, the constant or even increasing number of nitrergic cells per ganglion may indicate that the decreasing cell density may be a result of the growth of the bowel with decreasing ganglion density rather than a decrease in the total number of myenteric nitrergic cells. Regional differences in the dynamics of the quantitative changes were revealed. A significant decrease in the nitrergic cell number appeared earlier in the proximal than in the distal segments of the small intestine or in the colon. In contrast, the significant decline of the ganglionic density was first noticed in the colon at the same time.