Morphometry and microanatomy of the barbels of the common sawshark Pristiophorus cirratus (Pristiophoridae): implications for pristiophorid behaviour.

The internal anatomy of the barbels of the common sawshark Pristiophorus cirratus was examined with light microscopy to clarify their sensory role. No sensory structures such as taste buds (chemoreception), ampullae of Lorenzini (electroreception) or free neuromasts (lateral line mechanoreception) could be located in the barbels. The presence of bundles of nerve fibres, however, indicates a tactile function for the barbels. Conveyance of information regarding potentially damaging stimuli (nociception) and temperature (thermoception) cannot be excluded at this stage. It is hypothesized that the barbels are used by P. cirratus to locate prey in both the water column and on the substratum via wake detection and sensing changes in surface texture. The barbels may also be involved in the detection of water currents for rheotaxis. Regression analyses on P. cirratus morphometric data showed that the width of the rostrum at two sections (the barbels and the rostrum tip) does not significantly correlate with total length. The regression analyses also suggested that the barbels of P. cirratus may be lateralised.

Magnetic properties of uncultivated magnetotactic bacteria and their contribution to a stratified estuary iron cycle.

Of the two nanocrystal (magnetosome) compositions biosynthesized by magnetotactic bacteria (MTB), the magnetic properties of magnetite magnetosomes have been extensively studied using widely available cultures, while those of greigite magnetosomes remain poorly known. Here we have collected uncultivated magnetite- and greigite-producing MTB to determine their magnetic coercivity distribution and ferromagnetic resonance (FMR) spectra and to assess the MTB-associated iron flux. We find that compared with magnetite-producing MTB cultures, FMR spectra of uncultivated MTB are characterized by a wider empirical parameter range, thus complicating the use of FMR for fossilized magnetosome (magnetofossil) detection. Furthermore, in stark contrast to putative Neogene greigite magnetofossil records, the coercivity distributions for greigite-producing MTB are fundamentally left-skewed with a lower median. Lastly, a comparison between the MTB-associated iron flux in the investigated estuary and the pyritic-Fe flux in the Black Sea suggests MTB play an important, but heretofore overlooked role in euxinic marine system iron cycle.

The frequency of CSF oligoclonal banding in multiple sclerosis increases with latitude.

BACKGROUND: With the advent of MRI scanning, the value of lumbar puncture to assess oligoclonal band (OCB) status-for the diagnosis of multiple sclerosis (MS) is increasingly uncertain. One major issue is that the reported frequency of cerebrospinal fluid (CSF)-restricted oligoclonal banding for the diagnosis of MS varies considerably in different studies. In addition, the relationship between OCB positivity and disease outcome remains uncertain, as reported studies are generally too small to assess comparative disability outcomes with sufficient power. METHODS: In order to further investigate variation of OCB positivity in patients with MS, we utilized MSBase, a longitudinal, Web-based collaborative MS outcomes registry following clinical cohorts in several continents and latitudes. We also assessed whether OCB positivity affects long-term disability outcome. RESULTS: A total of 13,242 patient records were obtained from 37 MS specialist centres in 19 different countries. OCB status was documented in 4481 (34%) patients and 80% of these were OCB positive. The presence of OCB was associated with degree of latitude (p = 0.02). Furthermore, the outcome of patients negative for CSF-specific OCB was significantly better in comparison to the OCB positive patients, as assessed by Expanded Disability Status Scale change (p < 0.001). CONCLUSIONS: The results of this study indicate that latitude could explain some of the inconsistencies in OCB status reported in different populations. The study confirms that OCB positivity in MS is associated with a worse long-term prognosis.

Reductions of Rubisco activase by antisense RNA in the C4 plant Flaveria bidentis reduces Rubisco carbamylation and leaf photosynthesis.

To function, the catalytic sites of Rubisco (EC 4.1.1.39) need to be activated by the reversible carbamylation of a lysine residue within the sites followed by rapid binding of magnesium. The activation of Rubisco in vivo requires the presence of the regulatory protein Rubisco activase. This enzyme is thought to aid the release of sugar phosphate inhibitors from Rubisco's catalytic sites, thereby influencing carbamylation. In C3 species, Rubisco operates in a low CO2 environment, which is suboptimal for both catalysis and carbamylation. In C4 plants, Rubisco is located in the bundle sheath cells and operates in a high CO2 atmosphere close to saturation. To explore the role of Rubisco activase in C4 photosynthesis, activase levels were reduced in Flaveria bidentis, a C4 dicot, by transformation with an antisense gene directed against the mRNA for Rubisco activase. Four primary transformants with very low activase levels were recovered. These plants and several of their segregating T1 progeny required high CO2 (>1 kPa) for growth. They had very low CO2 assimilation rates at high light and ambient CO2, and only 10% to 15% of Rubisco sites were carbamylated at both ambient and very high CO2. The amount of Rubisco was similar to that of wild-type plants. Experiments with the T1 progeny of these four primary transformants showed that CO2 assimilation rate and Rubisco carbamylation were severely reduced in plants with less than 30% of wild-type levels of activase. We conclude that activase activity is essential for the operation of the C4 photosynthetic pathway.

Multiple sclerosis in Malta in 1999: an update.

OBJECTIVES: To ascertain the prevalence of multiple sclerosis (MS) in the islands of Malta and compare it with a previous study undertaken 21 years earlier, when a remarkably low prevalence was found. METHOD: Deaths with MS on the death certificate since the last study were reviewed. Sources of information about new patients were the Hospital Activity Analysis scheme, the MS Society of Malta, the records of the state hospitals, long stay private hospitals and nursing homes, lists provided by the state pharmacies, and magnetic resonance imaging, cerebrospinal fluid, and evoked response studies. Prevalence day was 1 January 1999. The Poser classification was used. RESULTS: Since 1978, 17 patients had died with a verified diagnosis of MS on the death certificate. They included all 10 deaths with MS from the original study and two immigrants. Fifty patients had clinically definite MS (CDMS) and 13 clinically probable MS (CPMS). The prevalence of CDMS was 13.2/100 000 (male 11.2, female 15.2). The prevalence of CDMS and CPMS combined was 16.7/100,000 (male 13.3, female 19.9). The annual incidence was 0.7/100,000. Twelve patients were found with CDMS among the 7213 immigrants resident in Malta (166/100,000). The expected rate was 1/100,000, determined at Maltese born rates. There were major changes in the population distribution during the 21 years between the two studies, with a big increase in the age groups with a high risk of MS. There is a longer expectation of life and the diagnosis in now made earlier. CONCLUSION: Malta still has a low MS prevalence. In comparison with Sicily and other Mediterranean countries of Europe it offers an opportunity to ascertain the genetic and environmental factors responsible for the disease.

Neuroimaging criteria for vascular dementia.

OBJECTIVE: To examine published imaging criteria that separate cranial computed tomographic (CT) scans into grades of increasing support for a diagnosis of vascular dementia (VaD). DESIGN: Patients were divided into 4 grades of increasing extent of vascular lesions on CT. The frequency of VaD was compared between these grades. SETTING: A university department of neurology. PATIENTS: Forty-two consecutive patients who underwent neuropsychological assessment for possible dementia and who had a CT scan performed within 6 months following any stroke causing dementia. Patients with delirium, severe aphasia, and motor and/or sensory deficits that impaired neuropsychological testing and patients with mass lesions or nonvascular white matter disease shown on CT were excluded. MAIN OUTCOME MEASURE: The National Institute of Neurological Disorders and Stroke and the Association Internationale pour la Recherche et l'Enseignement en Neurosciences criteria for probable VaD. RESULTS: The frequency of VaD was greater in patients with grade 1 (7 [50%] of 14, P = .01), grade 2 (2[50%] of 4, P = .2), and grade 3(7[78%] of 9, P = .002) scans than the frequency of VaD with grade O scans (1[7%] of 15). There was a linear association of the frequencies of VaD between imaging grades (P = .0008). In a subgroup of patients with neuropsychological deficits caused by cerebrovascular disease, there was a linear association of the severity of the deficits between imaging grades (P = .007). CONCLUSIONS: We conclude that our criteria can separate CTs into increasing levels of support for a diagnosis of VaD. The extent of vascular lesions on CT reflects the severity of associated neuropsychological deficts.

Electrophysiological and microiontophoretic analysis of the habenulo-hippocampal circuit.

In the cat, the effects of lateral habenula stimulation, at different ranges of frequency, on hippocampal units were studied. Habenular stimulation at low frequency excited, while at high frequency inhibited the greater part of hippocampal units. Moreover, in order to clarify the possible pathway involved in the habenulo-hippocampal circuit, the effects of iontophoretic acetylcholine and serotonin on hippocampal units were compared with those of habenular stimulation. Iontophoretic acetylcholine induced both excitatory and inhibitory responses while serotonin induced only inhibitory responses. Iontophoretic atropine blocked the effects of acetylcholine ejection but did not antagonize stimulation effects; ion-tophoretic methysergide induced an increase of basal firing of hippocampal units and antagonized both serotonin and habenular stimulation inhibition. The results suggest an influence of lateral habenula to the hippocampus which does not appear to be cholinergically-mediated. A possible involvement of the raphe as a relay station in the habenulo-hippocampal pathway is discussed.

Dopaminergic control of feline hippocampal epilepsy: a nigro hippocampal pathway.

Substantia nigra is a mesencephalic structure inserted along several circuits which appear to play a key role in epilepsy. In previous researches we postulated that substantia nigra pars compacta (SNpc) may be the site of a precise control of hippocampal epilepsy while substantia nigra pars reticulata (SNpr) may exert a modulation of both neocortical epilepsy and spreading of hyperactivity toward a motor target. In order to better understand mechanisms subserving nigral action in feline hippocampal epilepsy we electrically stimulated SNpc (dopaminergic), before and after sulpiride (dopamine receptor-antagonist) intravenous injection. Furthermore we compared hippocampal epileptiform activity prior to and after apomorphine (dopamine receptor-agonist) intrahippocampal injection as well as prior to and after SNpc electrolytic destruction. Results showed that SNpc is able to regulate hippocampal epilepsy. This effect is selectively antagonized by sulpiride while apomorphine exerts, synergically with SNpc stimulation, inhibitory effects. On the contrary SNpc lesions induces a significant enhancement of hippocampal epileptiform spikes. Experimental findings suggest that SNpc represents a strategic region for the control of hippocampal excitability and that this regulation appears to be dopaminergic in nature.

A feature of caudate control of focal hippocampal epilepsy: evidence for an anterograde pathway.

Previous experimental evidences showed that the caudate nucleus has a modulatory effect on hippocampal epilepsy. The caudate's regulating action might reach the hippocampus either via the septal region or, retrogradely, via the accumbens nucleus. In order to obtain new data about the pathway involved in caudate hippocampal influence the spreading of abnormal activity towards the nucleus accumbens was studied. Furthermore the effects of caudate stimulation in animals with electrolytic lesions of the nucleus accumbens were analyzed. It was observed that abnormal penicillin-induced activity spreaded from the hippocampus to the nucleus accumbens in about 30 minutes. In animals with and without lesions of nucleus accumbens, caudate stimulation brought about a significant decrease in the frequency and amplitude of hippocampal activity. The results suggest that the nucleus accumbens is reached by the spreading of hippocampal epilepsy but does not participate in the control exerted by the caudate nucleus on the hippocampus. Thus the caudate-induced inhibition takes place through an anterograde caudate-hippocampal circuit, while at the same time excluding retrograde activation by way of a caudate-accumbens-hippocampal pathway.

Nigral influence on focal epilepsy.

The substantia nigra (SN) has been proposed as a structure involved in epileptiform phenomena. Previous investigations demonstrated that SN is able to elicit hippocampal rhythmic slow activity (RSA) as well as to inhibit hippocampal interictal spikes induced by parenteral administration of penicillin. The present series of experiments was carried out in order to characterize the action of SN on a focal model of hippocampal epilepsy. Experiments were performed on encéphale isolé cats in which steady epileptiform activity was induced by locally applied penicillin. Electrical stimulation of SN pars reticulata (pr) caused a statistically significant decrease of hippocampal spike frequency and amplitude in 30% of the total number of stimulation sessions. Stimulation of SN pars compacta (pc) was even more effective. It induced inhibitory effects on hippocampal spikes in 91% of the cases. In 30% of the cats, RSA was noted on hippocampal recordings in correspondence to nigral activation. Experimental data support the hypothesis that the SNpc influences hippocampal excitability: a differential role may be played by SNpc and SNpr in the control of seizure processes.

Striatonigral suppression of focal hippocampal epilepsy.

Both caudate nucleus (CN) and substantia nigra (SN) appear to be involved in the control of epileptogenic events. Previous investigations had demonstrated that both CN and SN stimulations are able to induce hippocampal theta (theta) rhythm and an inhibition of epileptiform spikes. Since the two structures are reciprocally linked by fibre pathways, experiments were carried out to test the possibility that CN influences the hippocampus via SN or vice versa. To this end, changes in penicillin-induced hippocampal spikes by CN or SN stimulation were studied before and after destruction of SN and CN respectively. Steady interictal activity was induced in the hippocampus of encéphale isolé cats by local injection of penicillin. Stimulations of both CN and SN induced statistically significant reduction of hippocampal spike frequency, and in some cases a clear and regular theta-rhythm. These effects were unchanged by the destruction of either CN or SN. The results add further information to the role played by the basal ganglia and SN in the control of epilepsy, and underline the possibility that caudate and nigral influences on the hippocampus are mediated by different pathways.

[Neurophysiologic study of the influence of the habenula on the hippocampus: electroencephalographic aspects]. / Studio neurofisiologico dell'influenza abenulare sull'ippocampo: aspetti elettroencefalografici.

The habenula, an epithalamic structure considered as a part of the limbic system, is able to control interictal activity of the hippocampus. Its influence seems to be facilitatory and to have the raphé as a relay station. Habenular action might putatively be ascribed to activation of the serotonergic system.

An electrophysiological study of habenular influence on hippocampus.

The action of lateral habenula (LH) stimulation on focal epileptiform activity in the hippocampus was studied. Local microinjection of sodium penicillin induced a steady interictal activity in the dorsal hippocampus. Low frequency electrical stimulation of the habenula caused a marked enhancement of spike activity in both frequency and amplitude. The effect was blocked by intraperitoneally injected methysergide. The facilitatory influence of the habenula on hippocampal activity might be due to a disinhibitory mechanism. The results are regarded as suggesting that the habenula may be a relay station between the basal ganglia and the hippocampal formation. LH as well as basal ganglia might modulate hippocampal excitability, exerting a control on the genesis and diffusion of abnormal activities.

Effects of substantia nigra and pallidum stimulation on hippocampal interictal activity in the cat.

In the present work the role played by substantia nigra pars compacta and globus pallidus pars interna on hippocampal bioelectrical activity is studied. Injections of sodium penicillin (i.v.) produce steady interictal spikes in the hippocampus. Substantia nigra stimulation induces regular theta rhythm and inhibits the spikes. Pallidal stimulation, on the contrary, appears to strongly enhance epileptiform activity, proceeding to generalized seizure activity. The results are discussed in the light of the interrelationships between basal ganglia and hippocampus, hypothesizing a putative feedback loop from striatal to limbic centers.

Striatal and septal influence on hippocampal theta and spikes in the cat.

The experiments studied the modulation exerted by the septum and the caudate nucleus on hippocampal activity in the cat. Injections (i.v.) of sodium penicillin were performed in order to obtain a steady interictal epileptic activity. Hippocampal slow rhythmic activity showed a marked decrease either in duration or in frequency following penicillin activation. Both septal and caudate electrical stimulation inhibited spike frequency through a theta eliciting mechanism. Caudate stimulation failed to determine any sort of effect after medial septum lesions. The importance of the septum as modulation station between basal ganglia and hippocampus is emphasized.