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J Meek

Publications and source records attributed to J Meek.

At least 19 recordsLinked to original sources
PubMed2006

Activation of a sensorimotor pathway in response to a water temperature drop in a teleost fish.

When common carp, Cyprinus carpio L., experience a rapid temperature drop, the cerebral blood volume is strongly reduced to dampen the temperature drop in the brain. Simultaneously, the preoptic area and pituitary gland are activated to launch whole-body adaptive responses. However, the preferred reaction of fish to a temperature change is an escape reaction, which implies activation of a sensorimotor pathway. Here, we used blood oxygenation level-dependent (BOLD)- and cerebral blood volume (CBV)-weighted functional magnetic resonance imaging (fMRI) to identify a sensorimotor pathway, during a 10 degrees C temperature drop in common carp. Transient activation was observed in the region where the sensory root of the trigeminal nerve enters the brain, and in the valvula cerebelli. In both regions, metabolic activity increased (increased deoxyhemoglobin content demonstrated by a decreased BOLD signal) within 30 s after the onset of the temperature drop, peaked after 2-3 min, and then decreased, even though the temperature continued to drop for another 2 min. These brain structures appear to respond to temperature change, rather than to the absolute temperature. Thus, during a temperature drop, the sensorimotor pathway consisting of the trigeminal nerve, the primary sensory trigeminal nucleus, the valvula cerebelli and some motornuclei, is active, in line with perception of temperature change in the buccal cavity, leading to motor activity for escape. This pathway operates in parallel to an acclimation pathway, which involves the preoptic area to pituitary gland pathway.

Animals↗
PubMed2001

Myelinated dendrites in the mormyrid electrosensory lobe.

This is the third paper in a series on the morphology, immunohistochemistry, and synaptology of the mormyrid electrosensory lateral line lobe (ELL). The ELL is a highly laminated, cerebellum-like structure in the rhombencephalon that subserves an active electric sense: Objects in the nearby environment are detected on the basis of changes in the reafferent electrosensory signals that are generated by the animal's own electric organ discharge. This paper concentrates on the intermediate (cell and fiber) layer of the medial zone of the ELL and pays particular attention to the large multipolar neurons of this layer (LMI cells). LMI cells are gamma-aminobutyric acid (GABA)ergic and have one axon and three to seven proximal dendrites that all become myelinated after their last proximal branching point. The axon projects to the contralateral homotopic region and has ipsilateral collaterals. Both ipsilaterally and contralaterally, it terminates in the deep and superficial granular layers. The myelinated dendrites end in the deep granular layer, where they most likely do not make postsynaptic specializations, but do make presynaptic specializations, similar to those of the LMI axons. Because it is not possible to distinguish between axonal and dendritic LMI terminals in the granular layer, the authors refer to both as LMI terminals. These are densely filled with small, flattened vesicles and form large appositions with ELL granular cell somata and dendrites with symmetric synaptic membrane specializations. LMI cells do not receive direct electrosensory input on their somata, but electrophysiological recordings suggest that they nevertheless respond strongly to electrosensory signals (Bell [1990] J. Neurophysiol. 63:303-318). Consequently, the authors speculate that the myelinated dendrites of LMI cells are excited ephaptically (i.e., by electric field effects) by granular cells, which, in turn, are excited via mixed synapses by mormyromast primary afferents. The authors suggest that this ephaptic activation of the GABAergic presynaptic terminals of the myelinated dendrites may trigger immediate synaptic release of GABA and, thus, may provide a very fast local feedback inhibition of the excited granular cells in the center of the electrosensory receptive field. Subsequent propagation of the dendritic excitation down the myelinated dendrites to the somata and axon hillocks of LMI cells probably generates somatic action potentials, resulting in the spread of inhibition through axonal terminals to a wide region around the receptive field center and in the contralateral ELL. Similar presynaptic myelinated dendrites that subserve feedback inhibition, until now, have not been described elsewhere in the brain of vertebrates.

Animals↗
PubMed2000

Sodium phosphate enhances plasmid DNA expression in vivo.

Intramuscular injection of plasmid DNA results in myofiber cell expression of proteins encoded by the DNA. The preferred vehicle for plasmid DNA injections has been saline (154 mM sodium chloride) or PBS (154 mM NaCl plus 10 mM sodium phosphate). Here, it is shown that injection of luciferase or beta-galactosidase encoding plasmid DNA in a 150 mM sodium phosphate vehicle into murine muscle resulted in a two- to seven-fold increase in transgene expression compared with DNA injected in saline or PBS. When the DNA encoded secreted alkaline phosphatase, preproinsulin or interferon, sodium phosphate vehicle increased their serum levels by two- to four-fold. When the DNA encoded mouse erythropoietin, sodium phosphate vehicle increased hematocrits by two-fold compared with DNA injected in saline. When the DNA encoded influenza nucleoprotein, sodium phosphate increased anti-nucleoprotein antibody titers by two-fold. The expression of luciferase from plasmid DNA instilled into lung was increased five-fold compared with that in vehicle without sodium phosphate. Incubation of plasmid DNA with muscle extract or serum showed that sodium phosphate protected the DNA from degradation. Thus, a change from sodium chloride to sodium phosphate vehicle can enhance the expression of plasmid DNA in a tissue, possibly by inhibiting DNA degradation. Gene Therapy (2000) 7, 1171-1182.

Alkaline Phosphatase↗
PubMed1999

The paraventricular organ of mormyrid fish: uptake or release of intraventricular biogenic amines?

The paraventricular organ of Gnathonemus petersii was investigated with light and electronmicroscopical techniques. It contains high concentrations of dopamine, noradrenaline and serotonin, but the synthesizing enzymes are not or hardly present. Consequently, the cerebrospinal fluid-contacting neurons might pick up their biogenic amines from the ventricular fluid. Dense subependymal axonal plexuses in the everted telencephalon probably release these substances into the ventricle. However, electronmicroscopical observations suggest release rather than uptake by the paraventricular organ. The possible significance of intraventricular release, transport and uptake of biogenic amines is discussed.

Animals↗
PubMed1999

Structural organization of the mormyrid electrosensory lateral line lobe

The electrosensory lateral line lobe (ELL) of mormyrid teleosts is the first central stage in electrosensory input processing. It is a well-developed structure with six main layers, located in the roof of the rhombencephalon. Its main layers are, from superficial to deep, the molecular, ganglionic, plexiform, granular, intermediate and deep fiber layers. An important input arises from electroreceptors, but corollary electromotor command signals and proprioceptive, mechanosensory lateral line and descending electrosensory feedback inputs reach the ELL as well. The ELL input is processed by at least 14 cell types, which frequently show plastic responses to different inputs. The large ganglionic and large fusiform cells are the ELL projection cells. They are glutamatergic and project to the isthmic preeminential nucleus and the midbrain lateral toral nucleus. Interneurons are located in all ELL layers and are mostly GABAergic. The most remarkable interneurons are large multipolar cells in the intermediate layer, which have myelinated dendrites making presynaptic terminals contacting granular cells. With respect to the synaptic organization and microcircuitry of the ELL, a number of qualitative and quantitative aspects have been elucidated using electron microscopical and intracellular labeling techniques. However, the pathways by which primary afferent input influences the ELL projection cells are still undetermined: primary afferents do not seem to contact large fusiform or large ganglionic cells directly, but seem to terminate exclusively on granular cells, the axonal properties of which are not known. Consequently, more information of the structural organization of the ELL is still necessary for a detailed understanding of the neural basis of the plastic electrosensory input processing in mormyrids.

Journal Article↗
PubMed1999

Fast and accurate method for quantitating E. coli host-cell DNA contamination in plasmid DNA preparations.

Plasmid DNA is being used successfully as a gene delivery vector in a variety of clinical applications. Similar to other pharmaceutical products for clinical use, the plasmid vectors must meet rigorous purity standards. One important contaminant is the DNA of the host cell used to produce the plasmids. We have developed a new method to accurately quantitate E. coli host-cell DNA in plasmid preparations. This method is based on kinetic PCR using the ABI PRISM 7700 with 23S rDNA as a target. This precise assay is significantly faster and has a lower limit of quantitation than the currently used Southern-based methods.

Blotting, Southern↗
PubMed1998

Epilepsy in very preterm infants: neonatal cranial ultrasound reveals a high-risk subcategory.

The aim of this study was to investigate the association between epilepsy and perinatal brain injury in a cohort of 610 infants born preterm at <33 weeks' gestation. The prevalence of epilepsy in this cohort was 4.3% as determined by a postal questionnaire survey. Most children with epilepsy (16 of 24) had high-risk cranial ultrasound lesions including haemorrhagic parenchymal infarction (HPI), posthaemorrhagic hydrocephalus, and cystic periventricular leukomalacia (PVL). Of all the children in our cohort with high-risk brain lesions, those with epilepsy were more likely to have HPI and significantly less likely to have cystic PVL, although it is possible that PVL was not noticed in some cases. Children with epilepsy and high-risk cranial ultrasound lesions also showed more cognitive impairment than children with high-risk lesions but no epilepsy, which suggested more cortical grey-matter damage. We suggest that brain injury has occurred outside the confines of the periventricular white matter in this group of preterm infants with epilepsy.

Brain↗
PubMed1998

Cerebral blood flow is independent of mean arterial blood pressure in preterm infants undergoing intensive care.

OBJECTIVE: Preterm infants are often presumed to have a pressure passive cerebral circulation implying that a low mean arterial blood pressure (MABP) results in reduced cerebral perfusion. The aim of this study was to determine whether cerebral blood flow (CBF) was compromised in preterm infants whose MABP fell below 30 mm Hg (4 kPa). METHODS: Thirty preterm infants undergoing intensive care were studied within the first 24 hours of life. CBF was measured using near infrared spectroscopy. The infants were analyzed in two groups on the basis of their MABP at the time of study: group 1 had a MABP below 30 mm Hg and group 2 more than 30 mm Hg. CBF in the two groups was compared. RESULTS: There was no significant difference in the mean CBF between the two groups. In group 1 the median MABP was 27.2 mm Hg (range, 23.7-29.9 mm Hg) and CBF was 13.9 (standard deviation, +/-6.9) mL . 100 g-1 . min-1. In group 2 the median MABP was 35.3 mm Hg (range, 30.1-39.3 mm Hg) and CBF was 12.3 (standard deviation, +/-6.4) mL . 100 g-1 . min-1. Mortality and incidence of cranial ultrasound scan abnormalities were also not significantly different. CONCLUSION: These results indicate that preterm infants undergoing intensive care are able to maintain adequate cerebral perfusion at a MABP in the range of 23.7 to 39.3 mm Hg.

Birth Weight↗
PubMed1997

Plasticity in the stress-regulating circuit: decreased input from the bed nucleus of the stria terminalis to the hypothalamic paraventricular nucleus in Wistar rats following adrenalectomy.

The bed nucleus of the stria terminalis is involved in the stress-regulating circuit by funnelling limbic information to the hypothalamic paraventricular nucleus. Since adrenalectomy influences both limbic structures (by inducing cell death in the hippocampus) and the hypothalamic paraventricular nucleus (by increased corticotrophin-releasing hormone synthesis), we investigated whether the bed nucleus of the stria terminalis is also influenced by adrenalectomy. For this purpose, we analysed and compared the projections from the bed nucleus of the stria terminalis to the hypothalamic paraventricular nucleus in normal and adrenalectomized rats by anterograde tracer injections in the bed nucleus of the stria terminalis. Quantitative analysis of the fibre pattern in the hypothalamic paraventricular nucleus of normal rats revealed a homogeneous distribution of fibres of the bed nucleus of the stria terminalis over the different subdivisions of the hypothalamic paraventricular nucleus. In adrenalectomized rats, the absolute fibre density was significantly lower in the whole hypothalamic paraventricular nucleus (1.17 +/- 0.27 10(-3) microm/microm3 in adrenalectomized rats versus 2.59 +/- 0.24 10(-3) microm/microm3 in normal rats; P < 0.01) and all its subdivisions. The largest decrease of fibre density was found in the corticotrophin-releasing hormone-rich part of the hypothalamic paraventricular nucleus (relative fibre density; adrenalectomized rats: 0.602 +/- 0.106, versus 1.095 +/- 0.019 in normal rats, P < 0.01). These results show a loss of input from the bed nucleus of the stria terminalis to the hypothalamic paraventricular nucleus, and particularly to the corticotrophin-releasing hormone neurons, following adrenalectomy. The data suggest that this pathway within the stress-regulating circuit is functionally affected by corticosteroids in adult rats and may imply that human disorders associated with corticosteroid imbalance are allied to a changed circuitry in the brain.

Adrenalectomy↗
PubMed1996

Projection neurons of the mormyrid electrosensory lateral line lobe: morphology, immunohistochemistry, and synaptology.

This paper describes the morphological, immunohistochemical, and synaptic properties of projection neurons in the highly laminated medial and dorsolateral zones of the mormyrid electrosensory lateral line lobe (ELL). These structures are involved in active electrolocation, i.e., the detection and localization of objects in the nearby environment of the fish on the basis of changes in the reafferent electrosensory signal generated by the animal's own electric organ discharge. Electrosensory, corollary electromotor command-associated signals (corollary discharges), and a variety of other inputs are integrated within the ELL microcircuit. The organization of ELL projection neurons is analyzed at the light and electron microscopic levels based on Golgi impregnations, intracellular labeling, neuroanatomical tracer techniques, and gamma-aminobutyric acid (GABA), gamma-aminobutyric acid decarboxylase (GAD), and glutamate immunohistochemistry. Two main types of ELL projection neurons have been distinguished in mormyrids: large ganglionic (LG) and large fusiform (LF) cells. LG cells have a multipolar cell body (average diameter 13 microns) in the ganglionic layer, whereas LF cells have a fusiform cell body (on average, about 10 x 20 microns) in the granular layer. Apart from the location and shape of their soma, the morphological properties of these cell types are largely similar. They are glutamaterigic and project to the midbrain torus semicircularis, where their axon terminals make axodendritic synaptic contacts in the lateral nucleus. They have 6-12 apical dendrites in the molecular layer, with about 10,000 spines contacted by GABA-negative terminals and about 3,000 GABA-positive contacts on the smooth dendritic surface between the spines. Their somata and short, smooth basal dendrites, which arborize in the plexiform layer (LG cells) or in the granular layer (LF cells), are densely covered with GABA-positive, inhibitory terminals. Correlation with physiological data suggests that LG cells are I units, which are inhibited by stimulation of the center of their receptive fields, and LF cells are E units, excited by electric stimulation of the receptive field center. Comparison with the projection neurons of the ELL of gymnotiform fish, which constitute another group of active electrolocating teleosts, shows some striking differences, emphasizing the independent development of the ELL in both groups of teleosts.

Animals↗
PubMed1996

Interneurons of the ganglionic layer in the mormyrid electrosensory lateral line lobe: morphology, immunohistochemistry, and synaptology.

This is the second paper in a series that describes the morphology, immunohistochemistry, and synaptology of the mormyrid electrosensory lateral line lobe (ELL). The ELL is a highly laminated cerebellum-like structure in the rhombencephalon that subserves an active electric sense: Objects in the nearby environment of the fish are detected on the basis of changes in the reafferent electrosensory signals that are generated by the animal's own electric organ discharge. The present paper describes interneurons in the superficial (molecular, ganglionic, and plexiform) layers of the ELL cortex that were analyzed in the light and electron microscopes after Golgi impregnation, intracellular labeling, neuroanatomical tracing, and gamma-aminobutyric acid (GABA) immunohistochemistry. The most numerous interneurons in the ganglionic layer are GABAergic medium-sized ganglionic (MG) cells and small ganglionic (SG) cells. MG cells have 10-20 spiny apical dendrites in the molecular layer, a cell body of 10-12 microns diameter in the ganglionic layer, a single basal dendrite that gives rise to fine, beaded, axon-like branches in either the plexiform layer (MG1 subtype) or the deeper granular layer (MG2 subtype), and an axon that terminates in the plexiform layer. Their apical dendritic tree has 12,000-22,000 spines that are contacted by GABA-negative terminals, and it receives, 1,250-2,500 GABA-positive contacts on the smooth dendritic surface between the spines. The average ratio of GABA-negative to GABA-positive contacts on the interneuron apical dendrites (14:1) is significantly higher than that for the efferent projection cells that have been described previously (Grant et al. [1996] J. Comp. Neurol., this issue). The somata and basal dendrites of MG cells receive a low to moderate density of GABAergic synaptic input, and their axons make GABAergic synaptic contacts with the somata and cell bodies of MG as well as with large ganglionic (LG) cells. SG cells probably represent immature, growing MG cells. Other interneurons in the superficial ELL layers include GABAergic stellate cells in the molecular layer, two types of non-GABAergic cells with smooth dendrites in the deep molecular layer that are named thick-smooth dendrite cells and deep molecular layer cells, and horizontal cells that are encountered particularly in the plexiform layer. Comparison with the ELL of waveform gymnotiform fish, which is another group of active electrolocating teleosts that has been investigated thoroughly, shows striking differences. In these fish, no GABAergic interneurons are found in the ganglionic (pyramidal) layer of the ELL, and GABA-negative interneurons with smooth dendrites in the molecular layer also seem to be lacking. At present, the phylogenetic origin of the described superficial interneurons in the mormyrid ELL is uncertain.

Animals↗
PubMed1996

An improved plasmid DNA expression vector for direct injection into skeletal muscle.

In previous work, the direct injection of 50 micrograms of a plasmid DNA vector encoding firefly luciferase (VR1205) into murine quadriceps muscle produced an average of 6.5 ng of luciferase per muscle at 7 days postinjection. In this report, various elements of the VR1205 vector were modified to increase gene expression levels or to eliminate undesired viral sequences. Expression of the modified vectors was then compared to VR1205 using the intramuscular injection assay. In general, modifications to promoter, enhancer, and intronic sequences either decreased luciferase expression levels or had no effect. However, modifications to the polyadenylation and transcriptional termination sequences, plasmid backbone elements, and the luciferase gene itself each increased luciferase expression levels. The best-expressing vector, designated VR1255, contained a combination of these incrementally beneficial changes. A single intramuscular injection of 50 micrograms of VR1255 produced 300 ng of luciferase at 7 days postinjection, an expression level 46-fold higher than the VR1205 vector (or 22-fold higher, excluding modifications to the luciferase gene) and 154-fold higher than a commercially available luciferase expression vector. Thus, VR1255 represents an improved plasmid DNA vector that may be useful for gene therapy applications.

Animals↗
PubMed1996

Assessing and overcoming situational obstacles to dietary adherence in adolescents with IDDM.

PURPOSE: To develop and evaluate a tool for assessing selected aspects of dietary adherence in adolescents with diabetes mellitus (IDDM). METHODS: The Situational Obstacles to Dietary Adherence Questionnaire (SODA) is a 30-item inventory that yields a total self-efficacy score and scales that measure cognitive and behavioral coping strategies. Alternative forms of the SODA were administered at the beginning and end of a summer camp for youngsters with IDDM in order to obtain evidence for its reliability and validity, and to evaluate the impact of an educational intervention. The program consisted of two 50-minute small group sessions intended to help adolescents with IDDM improve their ability to cope with challenging dietary situations. Using the method of anchored instruction, the campers first viewed a video about a teenager with diabetes who faces common situations that make diabetes self-management difficult. Group problem-solving sessions led by a registered dietitian were used to help campers learn more effective ways to solve dietary problems. RESULTS AND CONCLUSIONS: Results suggested that the SODA has reasonable reliability and validity. In addition, anchored instruction improved dietary self-efficacy and changed young adolescents' estimates of how often they would use selected cognitive and behavioral strategies to solve dietary problems.

Adolescent↗
PubMed1995

The hypothalamic paraventricular nucleus in two types of Wistar rats with different stress responses. I. Morphometric comparison.

The present study evaluates the role of the hypothalamic paraventricular nucleus (PVH) in stress regulation by a morphometric comparison of the vascular, neuronal and synaptic properties of this nucleus in two lines of Wistar rats. It has been previously reported that these two lines of rats, indicated as APO-SUS (apomorphine-susceptible) and APO-UNSUS (apomorphine-unsusceptible) rats on the basis of their reactivity to a subcutaneous injection of apomorphine, display a variety of pharmacological and behavioral differences, including differences in their stress-coping mechanisms (Cools et al., Neuropsychobiology, 28 (1993) 100-105). The results show a similar vascular and neuronal organization of the PVH in both lines, but distinct synaptic differences. The PVH (0.12 mm3 volume with about 15,000 neurons on one side) has an overall vascular density of 5.6%, with significant differences between subdivisions (parvocellular central part: 8.3%, parvocellular dorsal/ventral/posterior part: 4.6-5.3%), which means that vascularity is a useful tool to delineate subdivisions in the parvocellular PVH. The neuronal density of 132 x 10(3)/mm3 as found in the present study is two times higher than reported in a previous study Possible reasons for this discrepancy are extensively discussed. The most significant finding of the present study is the observation that APO-SUS rats have a significantly higher synaptic density (158 x 10(6)/mm3) in the PVH than APO-UNSUS rats (108 x 10(6)/mm3). It is discussed in which way this synaptic difference may be correlated with the different activity of the hypothalamo-pituitary-adrenal axis in both lines of Wistar rats.

Animals↗
PubMed1995

The hypothalamic paraventricular nucleus in two types of Wistar rats with different stress responses. II. Differential Fos-expression.

The present study investigates the role of corticotropin-releasing hormone (CRH) neurons in stress regulation by a comparison of stress induced Fos-immunoreactivity and CRH-immunoreactivity in the hypothalamic paraventricular nucleus (PVH) of APO-SUS (apomorphine-susceptible), APO-UNSUS (apomorphine-unsusceptible), normal Wistar and adrenalectomized Wistar (ADX) rats. The first two types represent a good model to study the role of the PVH in stress regulation, since they show different stress responses and a differential synaptic organization of the PVH. After placement on an open field for 15 min all rats showed an increase in the number of Fos-immunoreactive nuclei compared to control handling. Interestingly, open field stress, but not control handling, induces significantly fewer Fos-immunoreactive nuclei in the PVH of APO-SUS rats (1255 +/- 49) compared to APO-UNSUS rats (1832 +/- 201). Experiments with ADX rats revealed that 93% of the CRH-immunoreactive neurons contained a Fos-immunoreactive nucleus, which suggests that the differential Fos-expression in APO-SUS and APO-UNSUS rats represents a differential activation of the CRH neurons. This hypothesis is discussed in relation to reported differences in stress responses, stress-induced ACTH levels and synaptic organization of the PVH.

Adrenal Glands↗