Smoking cessation on the African continent: Challenges and opportunities.

Tobacco smoking is one of the world's single biggest preventable causes of death. Over 8 million people die each year of a tobacco-related illness - both directly and as a result of second-hand smoke. Combating this epidemic requires commitment from policy makers, healthcare workers and civil society. The WHO has invested extensively in supporting policy frameworks to assist countries to combat tobacco advertising, sales and promotion. Despite these interventions, over 1 billion people actively smoke, of whom >80% live in low- or middle-income countries. Strong policies, high taxation and cigarette pricing dissuade smokers effectively, but the clinician is frequently the individual who is faced with the smoker wishing to quit. Although many African countries have policies regarding tobacco control, very few have programmes to support smokers who wish to quit, and even fewer have active training programmes to equip healthcare practitioners to assist active smokers in breaking their addiction to nicotine. We present a perspective from several countries across the African continent, highlighting the challenges and opportunities to work together to build capacity for smoking cessation services throughout Africa.

A multi-perspective view of genetic variation in Cameroon.

In this study, we report the genetic variation of autosomal and Y-chromosomal microsatellites in a large Cameroon population dataset (a total of 11 populations) and jointly analyze novel and previous genetic data (mitochondrial DNA and protein coding loci) taking geographic and cultural factors into consideration. The complex pattern of genetic variation of Cameroon can in part be described by contrasting two geographic areas (corresponding to the northern and southern part of the country), which differ substantially in environmental, biological, and cultural aspects. Northern Cameroon populations show a greater within- and among-group diversity, a finding that reflects the complex migratory patterns and the linguistic heterogeneity of this area. A striking reduction of Y-chromosomal genetic diversity was observed in some populations of the northern part of the country (Podokwo and Uldeme), a result that seems to be related to their demographic history rather than to sampling issues. By exploring patterns of genetic, geographic, and linguistic variation, we detect a preferential correlation between genetics and geography for mtDNA. This finding could reflect a female matrimonial mobility that is less constrained by linguistic factors than in males. Finally, we apply the island model to mitochondrial and Y-chromosomal data and obtain a female-to-male migration Nnu ratio that was more than double in the northern part of the country. The combined effect of the propensity to inter-populational admixture of females, favored by cultural contacts, and of genetic drift acting on Y-chromosomal diversity could account for the peculiar genetic pattern observed in northern Cameroon.

The electro-dynamics of the dendritic space in Purkinje cells of the cerebellum.

The functional geometry of the reconstructed dendritic arborization of Purkinje neurons is the object of this work. The combined effects of the local geometry of the dendritic branches and of the membrane mechanisms are computed in passive configuration to obtain the electrotonic structure of the arborization. Steady-currents applied to the soma and expressed as a function of the path distance from the soma form different clusters of profiles in which dendritic branches are similar in voltages and current transfer effectiveness. The locations of the different clusters are mapped on the dendrograms and 3D representations of the arborization. It reveals the presence of different spatial dendritic sectors clearly separated in 3D space that shape the arborization in ordered electrical domains, each with similar passive charge transfer efficiencies. Further simulations are performed in active configuration with a realistic cocktail of conductances to find out whether similar spatial domains found in the passive model also characterize the active dendritic arborization. During tonic activation of excitatory synaptic inputs homogeneously distributed over the whole arborization, the Purkinje cell generates regular oscillatory potentials. The temporal patterns of the electrical oscillations induce similar spatial sectors in the arborization as those observed in the passive electrotonic structure. By taking a video of the dendritic maps of the membrane potentials during a single oscillation, we demonstrate that the functional dendritic field of a Purkinje neuron displays dynamic changes which occur in the spatial distribution of membrane potentials in the course of the oscillation. We conclude that the branching pattern of the arborization explains such continuous reconfiguration and discuss its functional implications.

An avian model of genetic reflex epilepsy.

The Fayoumi strain of chickens (Fepi) carries a recessive autosomal gene mutation in which homozygotes are afflicted with a photogenic and audiogenic reflex epilepsy. Seizures consist of stimulus-locked motor symptoms followed by generalized self sustained convulsions. EEG recordings show spikes and spike and waves patterns at rest which are suppressed during seizures and replaced by a desynchronized pattern of activity. Neurones of the prosencephalon discharge in bursts at rest, while neurones of the mesencephalon are bursting during seizures. Living neural chimeras were obtained by replacing specific embryonic brain vesicles in a normal chicken embryo with equivalent vesicles from a Fepi donor. These chimeras show that the epileptic phenotype can be totally or partially transferred from the Fepi to the normal chickens. Total transfer of photogenic and audiogenic seizures was obtained by substitution of both the prosencephalon and mesencephalon, while substitution of the prosencephalon alone resulted in transfer of interictal paroxysmal activity and substitution of the mesencephalon alone resulted principally in transfer of ictal motor symptoms. Increased expression of the c-fos protooncogene, as revealed by the western blot technique, confirmed the distinct encephalic localizations of the symptoms of the photogenic and audiogenic reflex epilepsy of the Fepi shown with the methods of electrophysiology and brain chimeras. We conclude that the Fepi is a good model of brain stem reflex epilepsy and suggest that the brain stem is a generator of some other animal and human genetic reflex "epileptic syndromes".

Increased calbindin-D28K immunoreactivity in rat cerebellar Purkinje cell with excitatory amino acids agonists is not dependent on protein synthesis.

The calcium binding protein Calbindin-D28K (CaBP) is abundantly expressed in cerebellar Purkinje cells and show increased immunoreactivity (CaBP-IR) when challenged with glutamate or an analog agonist for the ionotropic glutamate receptor (iGluR). Here we report that t-ACPD, a metabotropic glutamate receptor (mGluR) agonist, produced small increases in CaBP-IR which was potentiated by a mGluR antagonist The increase in CaBPIR was not due to de novo protein synthesis because the translational inhibitors (cycloheximide and emetine) or transciptional inhibitors (actinomycine-D and a-amanitine), did not prevent the EAA enhanced CaBP-IR. The CaBP-IR in the PC appears to be coupled to the ionotropic rather than the metabotropic glutamate receptors, but the latter become effective in the presence of their blocker, L-AP3. The results suggest that CaBP may increase its IR through a conformational change of the protein itself.

Synaptic long-term depression (LTD) in vivo recorded on the rat cerebellar cortex.

Long-Term Depression (LTD) of the parallel fiber synapses of the cerebellar cortex has been intensively studied over the last 20 years and is now considered to be a physiological mechanism underlying learning and memory of the cerebellar cortex. With microelectrode recording in vivo, the induced LTD is recorded reliably up to 2 hours. Using surface electrodes we have recorded parallel fiber responses due to the currents generated by the AMPA type receptors of the dendritic spines in the intact vermal cortex of decerebrated rats. We have found that by conjunctively stimulating the climbing and parallel fiber pathways, an LTD was induced which persisted for as long as the recording conditions permitted. The longest lasting LTD of our present results was for 5 hours.

Purkinje cell inhibitory responses to 3-APPA (3-aminopropylphosphinic acid) in RAT cerebellar slices.

3-APPA is considered to be a GABA(B) agonist more potent than baclofen. We report here the results obtained by applying this agonist to Purkinje cells (PCs) recorded in current clamp mode on cerebellar slices. The responses were compared to those obtained with other GABA agonists and antagonists. The drugs were delivered either in the perfusion solution or by pressure to the molecular layer near the recorded cell. When applied to the PCs either in the bathing medium or by pressure, 3-APPA evoked a potent inhibitory response which was however different from that obtained with baclofen. The response was complex and similar to that evoked by application of GABA, the endogenous neurotransmitter. In fact it showed: (1) very sensitive dose-response not affected by TTX in the bath; (2) an equilibrium potential compatible with Cl-channel conductance; (3) a massive reduction with the competitive GABA(A) antagonist bicuculline; (4) a small reduction, if any, with the potent competitive GABA(B) antagonist CGP55845A; (5) persistence of the responses under 4-AP (4-aminopyridine), the potassium channel blocker, and inhibition of the 4-AP-induced calcium bursts of spikes. The conclusion was reached that the inhibitory response of PCs to 3-APPA is induced, like GABA inhibition, by binding to both GABA(A) and GABA(B) postsynaptic receptors.

GABA(B) receptor activation of Purkinje cells in cerebellar slices.

The metabotropic GABA(B) receptors are densely represented in the molecular layer of the cerebellar cortex which contains the dendritic tree of the Purkinje cells (PCs). We report here the results obtained by applying Baclofen, the specific GABA(B) agonist, to PCs recorded intrasomatically in cerebellar slices. Diluted in the perfusion solution or applied by pressure to the molecular layer near to the recorded cell, Baclofen dose-dependently inhibited the PCs as seen by the suppression of Na and Ca dependent action potentials accompanied by a variable membrane hyperpolarization. The weak hyperpolarization was interpreted as due to the dendritic localization of the receptors. These results concerned postsynaptic receptor sites since they persisted after bath applied TTX blocking presynaptic activity. They also persisted in the presence of bicuculline, the GABA(A) antagonist, but they were reduced by bath application of 2-OH saclofen and CGP55845A, both being GABA(B) receptor antagonists. Current clamp experiments revealed a conductance increase with an equilibrium potential consistent with a K+ channel opening. The conclusions were reached that GABA inhibition of the PCs is mediated by GABA(B) receptors in the dendrites and GABA(A) receptors in the soma and dendrites. Therefore, the GABA released by stellate cells modulate PC activity through two inhibitory mechanisms.

Upregulation of Calbindin-D-28k immunoreactivity by excitatory amino acids.

Excessive or prolonged exposure to excitatory amino acids (EAA) are thought to be neurotoxic by altering calcium homeostasis. A protective role of Calbindin-D-28 k (Calbindin) has been postulated due to its capacity to buffer calcium. Calbindin is highly expressed in the Purkinje cells (PCs), of the cerebellar cortex. Changes of the Calbindin immunoreactivity (IR) by the EAA has been here investigated in cerebellar slices maintained in vitro. It was found that at low temperature, PCs are very slightly immunoreactive and therefore the experiments were done at 22 degrees C. The results show that Calbindin-IR increases in PCs exposed to the neurotoxic agonists, Kainic acid (KA) and AMPA as well as to glutamate (Glu), the endogenous EAA. The increase is very rapid and slowly reversible; is induced by excitatory and excitotoxic concentrations of the agonists; is independent of the calcium influx. While KA- and AMPA-induced Calbindin-IR is blocked by CNQX, the KA/AMPA receptor antagonist, Glu-induced Calbindin-IR is only slightly decreased by CNQX and AP5, the NMDA receptor antagonist. It is concluded that Calbindin-containing neurons can increase their calcium buffering capacity in response to EAA binding to specific receptors, the response being independent of, but concomitant to calcium influx.

Changes in the expression of the extracellular matrix molecules tenascin-C and tenascin-R after 3-acetylpyridine-induced lesion of the olivocerebellar system of the adult rat.

In the central nervous system of rodents, the extracellular matrix glycoproteins tenascin-C and tenascin-R are expressed predominantly by astrocytes and oligodendrocytes respectively. Both molecules support neurite outgrowth from several neuronal cell types when presented as uniform substrates. When offered as a sharp boundary with a permissive substrate, however, both molecules prevent neurite elongation. On the basis of these observations it has been suggested that tenascin-C and tenascin-R may be relevant in determining the cellular response after injury in the adult rodent central nervous system. To investigate whether tenascin-C and tenascin-R may play important functional roles in the lesioned central nervous system, we have analysed their expression in the olivocerebellar system of the adult rat after 3-acetylpyridine-induced degeneration of nerve cells in the inferior olivary nucleus. Tenascin-C mRNA was not detectable at any time in the unlesioned or lesioned inferior olivary nucleus by in situ hybridization. In the cerebellar cortex, tenascin-C mRNA in Golgi epithelial cells was down-regulated 3 days after the lesion and returned to control values 80 days after the lesion. Tenascin-R mRNA was expressed by distinct neural cell types in the unlesioned olivocerebellar system. After a lesion, the density of cells containing tenascin-R transcripts increased significantly in the inferior olivary nucleus and in the white matter of the cerebellar cortex. Immunohistochemical and immunochemical investigations confirmed these observations at the protein level. Our data thus suggest differential functions of tenascin-C and tenascin-R in the injured central nervous system.

Embryonic neural chimeras in the study of vertebrate brain and head development.

Construction of neural chimeras between quail and chick embryos has been employed since 1969 when the unique nucleolar structure of the quail nucleus and its use to devise a cell marking technique by associating quail and chick cells in ovo were described in the "Bulletin Biologique de la France et de la Belgique." This method was first applied to the ontogeny of the neural crest, a structure whose development involves extensive cell migration, and, since 1984, to that of the central nervous system (CNS). This chapter highlights some of the most significant findings provided by this approach concerning the CNS, such as (i) demonstration of the common origin of the floor plate and notochord from a group of cells localized in the "organizer", i.e., Hensen's node, and the way in which these two structures become positioned respectively within and under the neural tube during gastrulation and neurulation in Amniotes; (ii) the neural crest origin of the skull vault and the facial and hypobranchial skeleton. This means that the mesodermal contribution to the skull is limited to the occipital and otic regions and extends only to the rostral limit of the notochord. A correlation can be drawn between the development of the telencephalon and the mesectodermally derived skull in the vertebrate phylum; (iii) demonstration that the midbrain-hindbrain junction, at the stage of the encephalic vesicles, acts as an organizing center for tectal and cerebellar structures. This function was correlated with the activity of several developmental genes, thus providing insight into their function during neurogenesis; (iv) the pattern of morphogenetic movements and cell migration taking place in defined brain-to-be areas, as well as the origin of various cell types of nervous tissues; and (v) a new avenue for studying brain localization of either behavioral traits or genetically encoded brain disorders.

Synaptic connections of Purkinje cell axons with nucleocortical neurones in the cerebellar medial nucleus of the rat.

The cerebellar nucleocortical neurones may be part of a cortico-nucleocortical loop. It has not yet been demonstrated, however, whether they are directly afferented by Purkinje cell axons. This question has been addressed by using electron microscopic methods. WGA-HRP injections into the cerebellar vermis anterogradely labelled Purkinje cell terminals and retrogradely labelled nucleocortical neurones of the nucleus medialis. Postembedding GABA immunolabelling was used to double-labelled PC terminals and identified the GABA-immunoreactive nuclear neurones. Of the identified nucleocortical neurones, the majority were immunonegative, but a few were GABA-immunoreactive. Both types were in synaptic contact with identified Purkinje cell terminals.

Brain chimeras in birds: application to the study of a genetic form of reflex epilepsy.

A strain of chicken, called here FEpi (for Fayoumi epileptic), bearing an autosomal recessive mutation, exhibits a form of reflex epilepsy with EEG interictal paroxysmal manifestations and generalized seizures in response to either light or sound stimulations. By using the brain chimera technology, we demonstrate here that the epileptic phenotype can be partially or totally transferred from an FEpi to a normal chick by grafting specific regions of the embryonic brain. The mesencephalon contains the generator of all epileptic manifestations whether they involve visual or auditory neuronal circuits, with the exception of the abnormal EEG which is transmitted exclusively by telencephalic grafts. This analysis supports the hypothesis that certain forms of human and mammalian epilepsies have a brainstem origin.

Effects of lesion of the inferior olivary complex in learning of the equilibrium behavior in the young rat during ontogenesis. I. Total lesion of the inferior olive by 3-acetylpyridine.

Young DA/HAN strain rats were submitted to an equilibrium test consisting in maintaining equilibrium upon a rotorod rotating at 10 or 20 rpm. They were either intact or lesioned, the lesion consisting in destruction of the inferior olivary complex (IOC) by 50-95 mg/kg i.p. administration of 3-acetylpyridine (3-AP) at day 15, followed, 2 to 4 h later, by i.p. injection of niacinamide (300 mg/kg). All the 3-AP-treated animals included in this study were completely lesioned, the extent of the lesion being estimated by both the response of the rats to harmaline and histological controls at the end of the experiments. The IOC lesioned rats were either naive (tested at one given day) or trained every day (10 trials per day); among the latters, some were trained before and after the lesion, the others being trained either before or only after. Control rats were submitted to the same training schedule. Both quantitative (time during which the animals maintained the equilibrium upon the rotating rod) and behavioral data (strategy used by the animals to maintain equilibrium) were obtained. The results demonstrate that, compared to those of controls rats, the quantitative and behavioral scores of the IOC lesioned animals were altered. Comparison of naive and trained animals shows that the impairment of the equilibrium behavior is not only due to the ataxia provoked by the IOC lesion but is also due to cognitive deficits. However, prelesion training facilitates the acquisition of a more efficient postlesion equilibrium behavior. From these results, it can be concluded that the olivo-cerebellar pathway is involved in the adaptation of motor behavior to the environmental conditions.

Brain chimeras for the study of an avian model of genetic epilepsy: structures involved in sound and light-induced seizures.

The epileptic homozygotes of the Fayoumi strain of chickens (Fepi) are affected by photogenic reflex epilepsy with complete penetrance. Here we demonstrate that they are equally affected by audiogenic reflex epilepsy induced by intense sound stimulation. All the Fepi display sound-induced seizures from hatching to adulthood consisting of initial 'ictal arousal' and running fits usually followed by generalized clonico-tonic convulsions. A running fit is the preconvulsive motor symptom specifically induced by auditory stimulation while neck myoclonus is the preconvulsive motor symptom specifically induced by photic stimulation. The EEG interictal spikes and spike and waves are suppressed and replaced by a desynchronized trace during the seizures of both kinds. Viable neural chimeras were obtained by graft of embryonic brain vesicles from Fepi donors into normal chick embryos. Transfer of the complete audiogenic and photogenic phenotypes was obtained in chimeras resulting from embryonic substitution of both the prosencephalon and mesencephalon. The substitution of the prosencephalon alone resulted in transfer of interictal paroxysmal EEG activity accompanied by the sound and light-induced desynchronization and 'ictal arousal' with no motor seizures. Chimeras with embryonic substitution of the mesencephalon alone displayed running fits and convulsions induced by sound stimulation but only neck myoclonus following light stimulation. The conclusions are reached that: (i) the Fepi is a model of audiogenic and photogenic reflex epilepsy; (ii) in both types, the seizure initiator and the convulsion generator are localized in the brainstem, although reinforcement from telencephalic visual structures is needed to trigger photogenic generalized convulsions.

Reflex epilepsy of the fowl and its transfer to normal chickens by brain embryonic grafts.

The genetic photosensitive epilepsy of the Fayoumi chicken was transferred to normal chickens by in situ grafts at 2 days of incubation, of both the prosencephalic and mesencephalic brain vesicles taken from epileptic embryos. However, mesencephalic graft is sufficient to allow convulsions under sound stimulation. Typical EEG patterns are recorded in chimeras having the prosencephalon plus or not the mesencephalon. We conclude that, in this mutant, the whole neural tissue is affected, but the seizure generator is localized inside the mesencephalon, and specific sensory pathways are necessary for seizures to occur.

Development of epileptic activity in embryos and newly hatched chicks of the Fayoumi mutant chicken.

The homozygous Fayoumi strain of epileptic chickens (Fepi) is affected by generalized convulsions consistently induced by intermittent light stimulation (ILS) and by intense sound. Although interictal EEG recordings show continuous spikes and spike and wave activity, desynchronization and flattening (DF) of the EEG are observed during seizures. We have studied development of the epileptic phenotype in embryonic (E) and posthatching (P) Fepi. As compared with those of chicken embryos of a normal strain, no differences were observed in the EEG before embryonic day (E) 16. Clearly differentiated spikes and spike and waves appeared at E17 in Fepi. Metrazol-induced EEG seizures were observed at E16 in normal embryos and at E17 in Fepi. The Fepi showed some characteristics: Spontaneous EEG seizure-like discharges also appeared at E17 but decreased toward hatching; visual or acoustic hyperexcitability developed at E20 together with evoked responses in normal chickens; desynchronization of the EEG, typical of the epileptic seizure of the adult, could be induced by ILS at B20, but ILS- or sound-induced generalized motor seizures appeared at P1, a few hours after hatching. Results show that Fepi phenotype reaches full expression at P1, but the electric paroxysms are expressed earlier, paralleling synaptic maturation.

Transfer of a genetic form of epilepsy in the chicken by embryonic brain grafts.

The genetic photosensitive epilepsy of the Fayoumi chickens was transferred to normal chickens by grafting, in situ, on the 2nd day of incubation, the prosencephalic and mesencephalic vesicles from epileptic embryos. Such chimeras displayed typical interictal EEG and developed intermittent light stimulation-induced seizures phenotypically and electrically similar to the epileptic strain seizures.

Glutamate, GABA, calbindin-D28k and parvalbumin immunoreactivity in the pulvinar-lateralis posterior complex of the cat: relation to the projection to the Clare-Bishop area.

Neurons of the pulvinar-lateralis posterior complex (Pul-LP) containing glutamate (Glu) and GABA, as presumed neurotransmitters, and calbindin- D28k (calbindin) and parvalbumin (PV), as Ca-binding proteins, were identified in the cat by using immunohistochemical methods. In vibratome sections, neurons immunoreactive (IR) to each of the four antibodies were observed throughout the Pul-LP. In semithin sections, GABA-IR neurons were also PV-IR but not calbindin-IR and some of them also co-localized Glu. The Glu-IR neurons which were negative for GABA co-localized calbindin but not PV. The neurons of the Pul-LP projecting to the Clare-Bishop area (CB) in the suprasylvian gyrus were identified with a retrogradely transported tracer and the sections were then immunostained for Glu, GABA, calbindin and PV. Only Glu- and calbindin-IR neurons were retrogradely labeled. These results show that, if calbindin and PV have a Ca-binding role, the presumably excitatory Glu-IR neurons projecting to the CB are use calbindin whereas the presumably inhibitory GABA-IR neurons are intrinsic and use PV. This relationship implies that these proteins probably have other roles specifically related to the kind of agonist to be released at the neuron.