Mechanisms Underlying Circuit Dysfunction in Neurodevelopmental Disorders

Recent advances in genomics have revealed a wide spectrum of genetic variants associated with neurodevelopmental disorders at an unprecedented scale. An increasing number of studies have consistently identified mutations-both inherited and de novo-impacting the function of specific brain circuits. This suggests that, during brain development, alterations in distinct neural circuits, cell types, or broad regulatory pathways ultimately shaping synapses might be a dysfunctional process underlying these disorders. Here, we review findings from human studies and animal model research to provide a comprehensive description of synaptic and circuit mechanisms implicated in neurodevelopmental disorders. We discuss how specific synaptic connections might be commonly disrupted in different disorders and the alterations in cognition and behaviors emerging from imbalances in neuronal circuits. Moreover, we review new approaches that have been shown to restore or mitigate dysfunctional processes during specific critical windows of brain development. Considering the heterogeneity of neurodevelopmental disorders, we also highlight the recent progress in developing improved clinical biomarkers and strategies that will help to identify novel therapeutic compounds and opportunities for early intervention.

Cortical wiring by synapse type-specific control of local protein synthesis

Neurons use local protein synthesis to support their morphological complexity, which requires independent control across multiple subcellular compartments up to the level of individual synapses. We identify a signaling pathway that regulates the local synthesis of proteins required to form excitatory synapses on parvalbumin-expressing (PV+) interneurons in the mouse cerebral cortex. This process involves regulation of the TSC subunit 2 (Tsc2) by the Erb-B2 receptor tyrosine kinase 4 (ErbB4), which enables local control of messenger RNA {mRNA} translation in a cell type-specific and synapse type-specific manner. Ribosome-associated mRNA profiling reveals a molecular program of synaptic proteins downstream of ErbB4 signaling required to form excitatory inputs on PV+ interneurons. Thus, specific connections use local protein synthesis to control synapse formation in the nervous system.

Subcellular sorting of neuregulins controls the assembly of excitatory-inhibitory cortical circuits

The assembly of specific neuronal circuits relies on the expression of complementary molecular programs in presynaptic and postsynaptic neurons. In the cerebral cortex, the tyrosine kinase receptor ErbB4 is critical for the wiring of specific populations of GABAergic interneurons, in which it paradoxically regulates both the formation of inhibitory synapses as well as the development of excitatory synapses received by these cells. Here, we found that Nrg1 and Nrg3, two members of the neuregulin family of trophic factors, regulate the inhibitory outputs and excitatory inputs of interneurons in the mouse cerebral cortex, respectively. The differential role of Nrg1 and Nrg3 in this process is not due to their receptor-binding EGF-like domain, but rather to their distinctive subcellular localization within pyramidal cells. Our study reveals a novel strategy for the assembly of cortical circuits that involves the differential subcellular sorting of family-related synaptic proteins.

Distinct molecular programs regulate synapse specificity in cortical inhibitory circuits

How neuronal connections are established and organized into functional networks determines brain function. In the mammalian cerebral cortex, different classes of GABAergic interneurons exhibit specific connectivity patterns that underlie their ability to shape temporal dynamics and information processing. Much progress has been made toward parsing interneuron diversity, yet the molecular mechanisms by which interneuron-specific connectivity motifs emerge remain unclear. In this study, we investigated transcriptional dynamics in different classes of interneurons during the formation of cortical inhibitory circuits in mouse. We found that whether interneurons form synapses on the dendrites, soma, or axon initial segment of pyramidal cells is determined by synaptic molecules that are expressed in a subtype-specific manner. Thus, cell-specific molecular programs that unfold during early postnatal development underlie the connectivity patterns of cortical interneurons.

The Microtubule Regulator NEK7 Coordinates the Wiring of Cortical Parvalbumin Interneurons

Functional networks in the mammalian cerebral cortex rely on the interaction between glutamatergic pyramidal cells and GABAergic interneurons. Both neuronal populations exhibit an extraordinary divergence in morphology and targeting areas, which ultimately dictate their precise function in cortical circuits. How these prominent morphological differences arise during development is not well understood. Here, we conducted a high-throughput screen for genes differentially expressed by pyramidal cells and interneurons during cortical wiring. We found that NEK7, a kinase involved in microtubule polymerization, is mostly expressed in parvalbumin (PV+) interneurons at the time when they establish their connectivity. Functional experiments revealed that NEK7-deficient PV+ interneurons show altered microtubule dynamics, axon growth cone steering and reduced axon length, arbor complexity, and total number of synaptic contacts formed with pyramidal cells. Altogether, our results reveal a molecular mechanism by which the microtubule-associated kinase NEK7 regulates the wiring of PV+ interneurons.

Neural circuit dysfunction in mouse models of neurodevelopmental disorders

Neuropsychiatric disorders arise from the alteration of normal brain developmental trajectories disrupting the function of specific neuronal circuits. Recent advances in human genetics have greatly accelerated the identification of genes whose variation increases the susceptibility for neurodevelopmental disorders, most notably for autism spectrum disorder (ASD) and schizophrenia. In parallel, experimental studies in animal models-most typically in mice-are beginning to shed light on the role of these genes in the development and function of specific brain circuits. In spite of their limitations, understanding the impact of pathological gene variation in animal models at the level of specific neuronal populations and circuits will likely contribute to orienting human clinical studies in the search for precise disease mechanisms and novel treatments.

Shaping Early Networks to Rule Mature Circuits: Little MiRs Go a Long Way

Normative cortical processing depends on precise interactions between excitatory and inhibitory neurons. In this issue of Neuron, Lippi et al. (2016) identify miR-101 as a master regulator coordinating molecular programs during development that ultimately impact the activity of mature networks.

Activity-Dependent Gating of Parvalbumin Interneuron Function by the Perineuronal Net Protein Brevican

Activity-dependent neuronal plasticity is a fundamental mechanism through which the nervous system adapts to sensory experience. Several lines of evidence suggest that parvalbumin (PV+) interneurons are essential in this process, but the molecular mechanisms underlying the influence of experience on interneuron plasticity remain poorly understood. Perineuronal nets (PNNs) enwrapping PV+ cells are long-standing candidates for playing such a role, yet their precise contribution has remained elusive. We show that the PNN protein Brevican is a critical regulator of interneuron plasticity. We find that Brevican simultaneously controls cellular and synaptic forms of plasticity in PV+ cells by regulating the localization of potassium channels and AMPA receptors, respectively. By modulating Brevican levels, experience introduces precise molecular and cellular modifications in PV+ cells that are required for learning and memory. These findings uncover a molecular program through which a PNN protein facilitates appropriate behavioral responses to experience by dynamically gating PV+ interneuron function.

Abnormal wiring of CCK+ basket cells disrupts spatial information coding

The function of cortical GABAergic interneurons is largely determined by their integration into specific neural circuits, but the mechanisms controlling the wiring of these cells remain largely unknown. This is particularly true for a major population of basket cells that express the neuropeptide cholecystokinin (CCK). Here we found that the tyrosine kinase receptor ErbB4 was required for the normal integration into cortical circuits of basket cells expressing CCK and vesicular glutamate transporter 3 (VGlut3). The number of inhibitory synapses made by CCK+VGlut3+ basket cells and the inhibitory drive they exerted on pyramidal cells were reduced in conditional mice lacking ErbB4. Developmental disruption of the connectivity of these cells diminished the power of theta oscillations during exploratory behavior, disrupted spatial coding by place cells, and caused selective alterations in spatial learning and memory in adult mice. These results suggest that normal integration of CCK+ basket cells in cortical networks is key to support spatial coding in the hippocampus.

Erbb4 deletion from fast-spiking interneurons causes schizophrenia-like phenotypes

Genetic variation in neuregulin and its ErbB4 receptor has been linked to schizophrenia, although little is known about how they contribute to the disease process. Here, we have examined conditional Erbb4 mouse mutants to study how disruption of specific inhibitory circuits in the cerebral cortex may cause large-scale functional deficits. We found that deletion of ErbB4 from the two main classes of fast-spiking interneurons, chandelier and basket cells, causes relatively subtle but consistent synaptic defects. Surprisingly, these relatively small wiring abnormalities boost cortical excitability, increase oscillatory activity, and disrupt synchrony across cortical regions. These functional deficits are associated with increased locomotor activity, abnormal emotional responses, and impaired social behavior and cognitive function. Our results reinforce the view that dysfunction of cortical fast-spiking interneurons might be central to the pathophysiology of schizophrenia.

Focal adhesion kinase regulates actin nucleation and neuronal filopodia formation during axonal growth

The establishment of neural circuits depends on the ability of axonal growth cones to sense their surrounding environment en route to their target. To achieve this, a coordinated rearrangement of cytoskeleton in response to extracellular cues is essential. Although previous studies have identified different chemotropic and adhesion molecules that influence axonal development, the molecular mechanism by which these signals control the cytoskeleton remains poorly understood. Here, we show that in vivo conditional ablation of the focal adhesion kinase gene (Fak) from mouse hippocampal pyramidal cells impairs axon outgrowth and growth cone morphology during development, which leads to functional defects in neuronal connectivity. Time-lapse recordings and in vitro FRAP analysis indicate that filopodia motility is altered in growth cones lacking FAK, probably owing to deficient actin turnover. We reveal the intracellular pathway that underlies this process and describe how phosphorylation of the actin nucleation-promoting factor N-WASP is required for FAK-dependent filopodia formation. Our study reveals a novel mechanism through which FAK controls filopodia formation and actin nucleation during axonal development.

Vav3 is involved in GABAergic axon guidance events important for the proper function of brainstem neurons controlling cardiovascular, respiratory, and renal parameters

Vav3 is a phosphorylation-dependent activator of Rho/Rac GTPases that has been implicated in hematopoietic, bone, cerebellar, and cardiovascular roles. Consistent with the latter function, Vav3-deficient mice develop hypertension, tachycardia, and renocardiovascular dysfunctions. The cause of those defects remains unknown as yet. Here, we show that Vav3 is expressed in GABAegic neurons of the ventrolateral medulla (VLM), a brainstem area that modulates respiratory rates and, via sympathetic efferents, a large number of physiological circuits controlling blood pressure. On Vav3 loss, GABAergic cells of the caudal VLM cannot innervate properly their postsynaptic targets in the rostral VLM, leading to reduced GABAergic transmission between these two areas. This results in an abnormal regulation of catecholamine blood levels and in improper control of blood pressure and respiration rates to GABAergic signals. By contrast, the reaction of the rostral VLM to excitatory signals is not impaired. Consistent with those observations, we also demonstrate that Vav3 plays important roles in axon branching and growth cone morphology in primary GABAergic cells. Our study discloses an essential and nonredundant role for this Vav family member in axon guidance events in brainstem neurons that control blood pressure and respiratory rates.

Control of cortical GABA circuitry development by Nrg1 and ErbB4 signalling

Schizophrenia is a complex disorder that interferes with the function of several brain systems required for cognition and normal social behaviour. Although the most notable clinical aspects of the disease only become apparent during late adolescence or early adulthood, many lines of evidence suggest that schizophrenia is a neurodevelopmental disorder with a strong genetic component. Several independent studies have identified neuregulin 1 (NRG1) and its receptor ERBB4 as important risk genes for schizophrenia, although their precise role in the disease process remains unknown. Here we show that Nrg1 and ErbB4 signalling controls the development of inhibitory circuitries in the mammalian cerebral cortex by cell-autonomously regulating the connectivity of specific GABA (gamma-aminobutyric acid)-containing interneurons. In contrast to the prevalent view, which supports a role for these genes in the formation and function of excitatory synapses between pyramidal cells, we found that ErbB4 expression in the mouse neocortex and hippocampus is largely confined to certain classes of interneurons. In particular, ErbB4 is expressed by many parvalbumin-expressing chandelier and basket cells, where it localizes to axon terminals and postsynaptic densities receiving glutamatergic input. Gain- and loss-of-function experiments, both in vitro and in vivo, demonstrate that ErbB4 cell-autonomously promotes the formation of axo-axonic inhibitory synapses over pyramidal cells, and that this function is probably mediated by Nrg1. In addition, ErbB4 expression in GABA-containing interneurons regulates the formation of excitatory synapses onto the dendrites of these cells. By contrast, ErbB4 is dispensable for excitatory transmission between pyramidal neurons. Altogether, our results indicate that Nrg1 and ErbB4 signalling is required for the wiring of GABA-mediated circuits in the postnatal cortex, providing a new perspective to the involvement of these genes in the aetiology of schizophrenia.

Distribution of the dopamine innervation in the macaque and human thalamus

We recently defined the thalamic dopaminergic system in primates; it arises from numerous dopaminergic cell groups and selectively targets numerous thalamic nuclei. Given the central position of the thalamus in subcortical and cortical interplay, and the functional relevance of dopamine neuromodulation in the brain, detailing dopamine distribution in the thalamus should supply important information. To this end we performed immunohistochemistry for dopamine and the dopamine transporter in the thalamus of macaque monkeys and humans to generate maps, in the stereotaxic coronal plane, of the distribution of dopaminergic axons. The dopamine innervation of the thalamus follows the same pattern in both species and is most dense in midline limbic nuclei, the mediodorsal and lateral posterior association nuclei, and in the ventral lateral and ventral anterior motor nuclei. This distribution suggests that thalamic dopamine has a prominent role in emotion, attention, cognition and complex somatosensory and visual processing, as well as in motor control. Most thalamic dopaminergic axons are thin and varicose and target both the neuropil and small blood vessels, suggesting that, besides neuronal modulation, thalamic dopamine may have a direct influence on microcirculation. The maps provided here should be a useful reference in future experimental and neuroimaging studies aiming at clarifying the role of the thalamic dopaminergic system in health and in conditions involving brain dopamine, including Parkinson's disease, drug addiction and schizophrenia.

BDNF mobilizes synaptic vesicles and enhances synapse formation by disrupting cadherin-beta-catenin interactions

Neurons of the vertebrate central nervous system have the capacity to modify synapse number, morphology, and efficacy in response to activity. Some of these functions can be attributed to activity-induced synthesis and secretion of the neurotrophin brain-derived neurotrophic factor (BDNF); however, the molecular mechanisms by which BDNF mediates these events are still not well understood. Using time-lapse confocal analysis, we show that BDNF mobilizes synaptic vesicles at existing synapses, resulting in small clusters of synaptic vesicles “splitting” away from synaptic sites. We demonstrate that BDNF's ability to mobilize synaptic vesicle clusters depends on the dissociation of cadherin–β-catenin adhesion complexes that occurs after tyrosine phosphorylation of β-catenin. Artificially maintaining cadherin–β-catenin complexes in the presence of BDNF abolishes the BDNF-mediated enhancement of synaptic vesicle mobility, as well as the longer-term BDNF-mediated increase in synapse number. Together, this data demonstrates that the disruption of cadherin–β-catenin complexes is an important molecular event through which BDNF increases synapse density in cultured hippocampal neurons.

Critical role of integrin-linked kinase in granule cell precursor proliferation and cerebellar development

Integrin-linked kinase (ILK) is a serine/threonine protein kinase that plays an important role in integrin signaling and cell proliferation. We used Cre recombinase (Cre)-loxP technology to study CNS restricted knock-out of the ilk gene by either Nestin-driven or gfap-driven Cre-mediated recombination. Developmental changes in ilk-excised brain regions are similar to those observed in mice lacking the integrin beta1 subunit in the CNS, including defective laminin deposition, abnormal glial morphology, and alterations in granule cell migration. Decreases in 6-bromodeoxyuridine (BrdU) pulse labeling and proliferating cell nuclear antigen expression in the external granule cell layer of the cerebellum demonstrated that proliferation is disrupted in granule cells lacking ILK. Previous studies have shown that laminin-sonic hedgehog (Shh)-induced granule cell precursor (GCP) proliferation is dependent on beta1 integrins, several of which bind laminin and interact with ILK through the beta1 cytoplasmic domain. Both ex vivo deletion of ilk and a small molecule inhibitor of ILK kinase activity decreased laminin-Shh-induced BrdU labeling in cultured GCPs. Together, these results implicate ILK as a critical effector in a signaling pathway necessary for granule cell proliferation and cerebellar development.

The primate thalamus is a key target for brain dopamine

The thalamus relays information to the cerebral cortex from subcortical centers or other cortices; in addition, it projects to the striatum and amygdala. The thalamic relay function is subject to modulation, so the flow of information to the target regions may change depending on behavioral demands. Modulation of thalamic relay by dopamine is not currently acknowledged, perhaps because dopamine innervation is reportedly scant in the rodent thalamus. We show that dopaminergic axons profusely target the human and macaque monkey thalamus using immunolabeling with three markers of the dopaminergic phenotype (tyrosine hydroxylase, dopamine, and the dopamine transporter). The dopamine innervation is especially prominent in specific association, limbic, and motor thalamic nuclei, where the densities of dopaminergic axons are as high as or higher than in the cortical area with the densest dopamine innervation. We also identified the dopaminergic neurons projecting to the macaque thalamus using retrograde tract-tracing combined with immunohistochemistry. The origin of thalamic dopamine is multiple, and thus more complex, than in any other dopaminergic system defined to date: dopaminergic neurons of the hypothalamus, periaqueductal gray matter, ventral mesencephalon, and the lateral parabrachial nucleus project bilaterally to the monkey thalamus. We propose a novel dopaminergic system that targets the primate thalamus and is independent from the previously defined nigrostriatal, mesocortical, and mesolimbic dopaminergic systems. Investigating this "thalamic dopaminergic system" should further our understanding of higher brain functions and conditions such as Parkinson's disease, schizophrenia, and drug addiction.

Transneuronal tracing of diverse CNS circuits by Cre-mediated induction of wheat germ agglutinin in transgenic mice

Systems neuroscience addresses the complex circuits made by populations of neurons in the CNS and the cooperative function of these neurons. Improved approaches to the neuroanatomical analysis of CNS circuits are thus of great interest. In fact, significant advances in tract-tracing methods have recently been made by using transgenic mice that express transneuronal lectin tracers under the control of neuron-specific promoters. The utility of those animals, however, is limited to the CNS circuit influenced by the particular promoter. Here, we describe a new transgenic mouse that can be used for transneuronal tracing analysis of circuits in any region of the brain or spinal cord. The transgene in these mice results in expression of LacZ in neurons throughout the CNS. Excision of the LacZ gene by Cre-mediated recombination initiates expression of the lectin, wheat germ agglutinin (WGA). To illustrate the diverse uses of these ZW (LacZ-WGA) mice, we triggered WGA expression either by crossing the mice with two Cre-expressing transgenic mouse lines or by microinjecting a Cre-expressing adeno-associated virus into the cerebellum or cerebral cortex. Both approaches resulted in extensive WGA expression in the cell bodies and dendrites of neurons in which the recombination event occurred, as well as anterograde and transneuronal transport of the lectin to second and third order neurons. Because the lectin can be induced in developing and adult animals, and in all regions of the brain and spinal cord, these ZW may prove extremely valuable for numerous studies of CNS circuit analysis.

TrkB receptor signaling is required for establishment of GABAergic synapses in the cerebellum

Neurotrophins are essential to the normal development and maintenance of the nervous system. Neurotrophin signaling is mediated by Trk family tyrosine kinases such as TrkA, TrkB and TrkC, as well as by the pan-neurotrophin receptor p75NTR. Here we have deleted the trkB gene in cerebellar precursors by Wnt1-driven Cre--mediated recombination to study the function of the TrkB in the cerebellum. Despite the absence of TrkB, the mature cerebellum of mutant mice appears similar to that of wild type, with all types of cell present in normal numbers and positions. Granule and Purkinje cell dendrites appear normal and the former have typical numbers of excitatory synapses. By contrast, inhibitory interneurons are strongly affected: although present in normal numbers, they express reduced amounts of GABAergic markers and develop reduced numbers of GABAergic boutons and synaptic specializations. Thus, TrkB is essential to the development of GABAergic neurons and regulates synapse formation in addition to its role in the development of axon terminals.

Distribution of acetylcholinesterase and choline acetyltransferase in the main and accessory olfactory bulbs of the hedgehog (Erinaceus europaeus)

The distribution of cholinergic markers was studied in the main olfactory bulb (MOB) and accessory olfactory bulb (AOB) of the western European hedgehog (Erinaceus europaeus) by using choline acetyltransferase (ChAT) immunocytochemistry and acetylcholinesterase (AChE) histochemistry. A dense network of AChE-containing and ChAT-immunoreactive fibers was observed innervating all layers of the MOB except the olfactory nerve layer, where neither AChE- nor ChAT-labeled elements were found. The highest density of AChE- and ChAT-positive axons was found in the glomerular layer (GL)/external plexiform layer (EPL) boundary, and in the internal plexiform layer. This general distribution pattern of ChAT- and AChE-stained axons resembled the distribution pattern found in rodents. Nevertheless, some interspecies differences, such as the lack of atypical glomeruli in the hedgehog, were also found. In addition to fibers, a population of noncholinergic and presumably cholinoceptive AChE-active neurons was observed in the hedgehog. All mitral and tufted cells of the hedgehog MOB showed a dark AChE staining unlike previous observations in the mitral and tufted cells of rodents. As in other species previously reported, subpopulations of external tufted cells and short-axon cells were also AChE-active. Finally, a population of small AChE-containing cells was observed in the EPL of the hedgehog MOB. The size, shape, and location of these cells coincided with those of satellite and perinidal cells, two neuronal types described previously in the EPL of the hedgehog and not present in the rodent MOB. The AOB of the hedgehog showed a distribution of AChE- and ChAT-positive fibers similar to the rodent AOB. Nevertheless, a heterogeneous innervation of vomeronasal glomeruli by bundles of AChE- and ChAT-labeled axons found in the hedgehog has not been previously found in any other species. As in the MOB, all mitral cells in the AOB showed a strong AChE activity. These results demonstrate some similarities but also important differences between the distribution of ChAT and AChE in the MOB and AOB of rodents and this primitive mammalian. These variations may indicate a different organization of the cholinergic modulation of the olfactory information in the insectivores.

A population of cholinergic neurons is present in the macaque monkey thalamus

Three new cholinergic markers were employed to study the cholinergic innervation in the thalamus of adult macaque monkeys. They were: two antibodies against choline acetyltransferase (ChAT), one polyclonal and one monoclonal; and a polyclonal antibody against the vesicular transporter of acetylcholine (VAChT), a powerful new marker that colocalizes with ChAT. This approach led to an unexpected finding: the three antibodies positively immunostained a population of neurons in the paracentral nucleus. The immunostained cells are confined to the dorsal region of this nucleus along its rostrocaudal extent. Measurement of the somatic areas of the immunostained neurons indicated that they correspond to a population of large neurons thought to be projection neurons. Because dorsal paracentral neurons are known to project to the dorsal striatum and specific cortical areas involved in visual and visuomotor mechanisms, these structures might be modulated by cholinergic thalamic neurons.

Adrenergic innervation of the monkey thalamus: an immunohistochemical study

The distribution and function of the neurotransmitter adrenaline in the primate brain are poorly understood. Biochemical studies have shown the presence of adrenaline or its biosynthetic enzyme, phenylethanolamine-N-methyltransferase, in the rat and human thalamus. However, the distribution of the adrenergic fibres in the thalamus has only been demonstrated in rats. We study the adrenergic innervation of the macaque monkey thalamus using immunohistochemistry against phenyletanolamine-N-methyltransferase. The distribution of phenyletanolamine-N-methyltransferase-immunoreactive fibres is markedly heterogeneous and principally restricted to those nuclei, or their portions, that are located in or close to the midline, with the highest density being found in the paraventricular, parafascicular and mediodorsal nuclei. The paraventricular nucleus is densely innervated by adrenergic axons throughout, while the densest innervation of the parafascicular nucleus is located in its medial part and the strongest mediodorsal nuclear immunolabelling is found in its most posterior and medial region. Moderate or low concentrations of phenyletanolamine-N-methyltransferase-immunopositive fibres are present in the paratenial nucleus, and all parts of the central nucleus, nucleus reuniens, central medial nucleus, centromedian nucleus, medial geniculate body and medial pulvinar nucleus, while only scattered immunoreactive axons are found in other thalamic nuclei. The morphology of the phenyletanolamine-N-methyltransferase-immunoreactive axons is quite diverse, as they have different diameters and most are endowed with diversely-shaped varicosities. These findings are the first morphological evidence for the presence of adrenergic innervation in the primate thalamus and reveal that this innervation is highly selective, heterogeneous and more widely distributed in primates than in rats. The thalamic nuclei innervated by adrenaline are connected to widespread limbic and associative cortical areas as well as to subcortical structures, in particular the neostriatum and amygdala. We hypothesize that thalamic adrenaline may be implicated in emotional, social and attentional mechanisms through its facilitation of co-ordinated action by these brain regions.

Ultrastructural study of the Pacinian corpuscles in the newborn and adult dog forefoot

Pacinian corpuscles (PC) of the newborn and adult dog forefoot were studied by electron microscopy. The PC of newborn dog forefoot show a rare development: they exhibit a lamellar arrangement, although the lamellar compartments do not surround completely the fiber. The outer core cells show a well-developed perinuclear endoplasmic reticulum. They are surrounded by a discontinuous basal lamina. Mast cells between the lamellae of the outer core are observed. Desmosome-like and zonula adherens junctions, as well as pinocytotic vesicles, are shown in the inner core cells. Intermediate filaments are also observed in the glial cells of the inner core. In PC of adult dog forefoot a general organization of a concentrically arranged capsule, outer core, intermediate layer and inner core around a nerve ending is always present. In the intermediate layer, lamellar cells (specialized fibroblast) do not surround completely the inner core. The inner core lamellae possess numerous pinocytotic vesicles, an extensive network of filaments, special cell junctions (gap, desmosome) and a discontinuous basal lamina. The present results show a conservative structural organization in PC, although differences among species are discussed.

[AIDS and human rights]

AIDS and human rights are closely related issues. This paper describes the relationship between AIDS and human rights, the impact and consequences of discrimination and the importance of the defense of human rights as a cornerstone strategy in AIDS prevention. Some general ethical aspects are addressed and two dilemmas which have been raised by the epidemic are discussed: the apparent conflict between individual and community rights and the reactions of intolerance and repression from those who claim that only through coercive strategies will the epidemic be brought under control. Specific problems in Mexico are described based on data collected at CONASIDA's Human Rights Department between 1992 and 1994. Finally some conclusions are stated emphasizing that, in the AIDS epidemic, the defense of human rights is the cornerstone of any public health strategy.

[Campaigns against AIDS in Mexico: the sounds of silence or a bridge over troubled waters?]

This paper analyzes the mass media campaigns developed by the Mexican Council for AIDS Control and Prevention (CONASIDA) from 1987 to 1994. This paper presents the lessons learned, a discussion of obstacles and mistakes, and the different evaluation methods which have been used in CONASIDA'S mass media communication strategies and their results. Knowing the opinion of some clue informants was considered relevant--taking into account that evaluations were made by and at CONASIDA--and seven in-depth interviews were conducted among intellectuals, non-governmental organizations (NGO) leaders and public opinion leaders. The importance of society's involvement in AIDS prevention is stated, and two examples of mass media campaigns developed by civil groups are commented. A section about the importance of research as a requisite to produce preventive messages is included, along with some examples. Finally, some conclusions are presented, useful to us, as well as others, in developing new educational campaigns.

Synthesis and structural, conformational, and pharmacological study of some of esters derived from 3-phenethyl-3-azabicyclo[3.2.1]octan-8-beta-ol and the corresponding N-endo-methyl quaternary derivatives

A series of 8-beta-acyloxy-3-phenethyl-3-azabicyclo[3.2.1]octane and its N-endo methiodides were synthesized and studied by 1H and 13C NMR spectroscopy, and the crystal structure of 8-beta-p-chlorobenzoyloxy-3-phenethyl-3-azabicyclo[3.2.1]octane methiodide (2c) was determined by X-ray diffraction. In CDCl3 solution, 1b-1e display the same preferred conformation. The cyclopentane and piperidine rings adopt an envelope conformation flattened at C-8 and a distorted chair conformation puckered at C-8 and flattened at N-3, respectively, with the N-substituent in the equatorial position with respect to the piperidine ring. In all cases, methylation takes place from the endo position. The ability of the title compounds to antagonize the acetylcholine-induced contraction of guinea pig ileum is also reported. An initial structure-activity relationship is proposed.

Evaluation of phagolysosome fusion in acridine orange stained macrophages infected with Histoplasma capsulatum

A phagosome-lysosome (PL) fusion was performed in vitro using peritoneal cells from normal BALB/c mice and the J774.2 macrophage cell line infected with the yeast phase of the fungus Histoplasma capsulatum at ratios of 5 x 10(5), 5 x 10(6) or 1 x 10(7) yeasts per 1 x 10(6) macrophages, and phagocytosis was allowed to proceed for 5, 30 and 60 min. Macrophage lysosomes were pre-labelled with acridine orange and the cells were challenged with the parasite. Fusion was evaluated by fluorescence microscopy and the number of macrophages with stained yeast cells was scored. The phagolysosome fusion frequency (PLFF) was calculated by subtracting the specific fusions of infected macrophages from the non-specific fusions of uninfected macrophages and normalizing the total number of bound yeasts. The PLFF was determined using different doses and strains of H. capsulatum. Results showed that PLFF in infected macrophages depends on the infection dose. Inhibition of PL fusion was detected mainly at a high infection ratio (1 x 10(7) yeasts/1 x 10(6) macrophages), and PL fusion varied with phagocytosis time. No significant differences were observed in the fusions when different Histoplasma strains were used. Results with J774.2 cells were similar to peritoneal cells, indicating that both methodology and fusion calculations employed were useful, in spite of the heterogeneity of macrophage populations used.