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Biomedical subjects

J G Johnston

Publications and source records attributed to J G Johnston.

At least 19 recordsLinked to original sources
PubMed1995

The mouse mutation reeler causes increased adhesion within a subpopulation of early postmitotic cortical neurons.

Early postmitotic cortical neurons are mostly corticofugal projection neurons that take up positions in deep cortical laminae. Later postmitotic neurons are preferentially localized to superficial cortical laminae. In reeler mutant mice it appears that cortical laminar positions with respect to birthdate are reversed (Caviness, 1982). In a reanalysis of reeler lamination we found that early postmitotic cortical neurons labeled by embryonic day (E) 11-13 injections of a birthdate marker, or by early postnatal day (PND) 2 retrograde labeling through their output projections, appear to take up positions both in the superficial and deep cortex. Neurons born on E11 and E12 are more likely to be situated superficially in the reeler cortex and neurons born on E13 are more likely to be situated in the deep reeler cortex. Many corticofugal projection neurons in the deep (but not superficial) reeler cortex either die or retract their axons before PND 21. We hypothesize that the earliest postmitotic (E11-E12) of the early postmitotic reeler cortical neurons are overly adhesive and act as a barrier to later postmitotic migrating neurons. In vitro cortical aggregation cultures confirmed that early postmitotic (E12) reeler neurons are more adhesive than early postmitotic (E12) wild-type neurons or late postmitotic (E16) reeler or wild-type cortical neurons. We suggest that the moderate wild-type preferential adhesion of early postmitotic cortical neurons to each other helps deep and superficially fated lineages to form cortical laminae.

Animals↗
PubMed1993

Spatially localized neuronal cell lineages in the developing mammalian forebrain.

The role of cell lineage in the organization of the cerebral cortex and striatum of the developing rat forebrain was analysed using retroviral-mediated gene transfer to mark the progeny of individual progenitors. Injections around the onset of neurogenesis (embryonic day 14) produced neuronal- and glial-specific clones in the striatum and cortex. The majority of the neuronal clones were restricted to either the deep or superficial layers of the cortex and to either the striatal patch or matrix compartments of the striatum. Moreover, modeling the distributions of the neuronal clones in various ways revealed that grouping the clones into deep vs superficial cortical compartments and patch vs matrix striatal compartments best accounted for the clone distributions. These results suggest that at the onset of neurogenesis there is a heterogeneity of neuronal progenitors within the proliferative ventricular zone.

Animals↗
PubMed1992

Ten-year review of treatment of the undescended testis in the west of Ireland.

Advances continue to be made in the treatment of the undescended testis, and treatment recommendations are continually changing. We reviewed 543 patients admitted for treatment of undescended testes in the 10-year period 1977 to 1986. The side and position of the testis were recorded, the patient's age at operation and the procedure carried out. The presence of an associated inguinal hernia was noted. The necessity for reoperation was recorded and predisposing factors sought. We found the mean age at operation to be 9.5 years and this decreased significantly over the study period. Dartos pouch orchiopexy was the commonest operation (69%). No significant link was found between the procedure performed or the presence of a hernia and the need for further procedures; 2.7% of patients required such further procedures. A coherent classification of position is lacking for abnormally descended testes. We report a classification which we used to tackle this situation.

Adolescent↗
PubMed1991

Contrasting enrollment trends for BSN students in the United States and in New York State: an assessment and analysis.

The paper provides a description, assessment, and analysis of enrollment trends for generic and registered nurse students in baccalaureate programs in both the United States and New York state over the past 30 years. The analysis focuses on the reasons for the recent declining enrollment of both types of BSN students in New York state. Primary data sources were the National League for Nursing's annual student census statistics, policy statements and reports of the NLN and the American Nurses Association (ANA), and statements on the recruitment and retention of nurses.

American Nurses' Association↗
PubMed1990

Mechanisms of striatal pattern formation: conservation of mammalian compartmentalization.

The striatum is composed of two neuroanatomically and neurochemically defined compartments, termed the patches and matrix. We compared this compartmentalization of the striatum in sections from the rat, rhesus monkey and human, in terms of (1) total striatal area, (2) the ratio of patch to matrix areas, (3) the number of patches and (4) the cross-sectional area of individual patches. Dense mu-opiate receptor binding and immunohistochemical staining for enkephalin were used as histochemical markers for the patch compartment and heavy immunostaining for calcium binding protein was used as a matrix marker. Analysis of coronal sections revealed that a relatively constant ratio of 15% patch to 85% matrix area is maintained in each species. The numbers of patches also remain relatively constant across species, despite a 19-fold increase in total striatal area from rat to human. The constant ratio of patch to matrix areas is maintained by an increase in the size of the individual patches. We hypothesize that the maintenance of a 15% patch to 85% matrix ratio in the striata of different mammalian species occurs through proportionate changes in the length of striatal neurogenesis and the numbers of striatal precursors in the ventricular zone, whereas the maintenance of average patch number is proposed to be a function of reciprocal connections with the substantia nigra and adhesive factors that are specific to patch cells.

Animals↗
PubMed1989

Protooncogene expression identifies a transient columnar organization of the forebrain within the late embryonic ventricular zone.

Immunocytochemical studies using monoclonal antibodies directed against oncogenic peptides revealed a heterogeneous distribution of the peptides within the ventricular zone of the embryonic day 18 rat forebrain. The sis-, src-, ras-, and myc-encoded peptides were concentrated in the same isolated clusters of 5-25 radial glial cells (also identified by vimentin staining), providing a transient columnar compartmentalization to the ventricular zone. An increased number of [3H]thymidine-labeled ventricular zone cells were observed within the protooncogene stained radial glial cell columns as compared to noncolumn areas. The columnar heterogeneity of radial glial cells reveals the mosaicism of the embryonic ventricular zone and the differential proliferation of its cells.

Animals↗
PubMed1989

Changing demographics in New York State: implications for nursing education and practice.

In the past, most women and men entering nursing in New York State were the children of European immigrants. In recent years, with changes in federal immigration laws, the ethnic composition of high-school and college age students has become more diverse. Demographic changes, combined with the fact that more career opportunities are available to women, have resulted in an increasingly heterogeneous population in nursing schools statewide. One effect of this diversity has been that many schools of nursing now have varying percentages of students who are non-primary speakers of English. The findings of a study conducted in one such baccalaureate school of nursing with an extremely ethnically and linguistically diverse student population indicated that language was the major variable predictive of success on the NCLEX-RN, exerting a greater effect than the academic parameters of grades and scores on standardized tests. The effects of the demographic changes on the recruitment and retention of nursing students able both to complete a program and to achieve success on the NCLEX-RN has implications for nursing education and practice in New York State.

Demography↗
PubMed1987

Compartmentalization of the embryonic striatum after intraocular transplantation.

In order to assess the intrinsic potential of the isolated embryonic striatum to develop its adult patch and matrix compartments, embryonic day 16 striata were transplanted into the anterior eye chamber of adult host rats. After 2-12 weeks of survival the transplants showed heterogeneous and in the majority of cases complementary distributions of opiate receptor binding and acetylcholinesterase staining, which mark the patch and matrix compartments of the adult striatum, respectively. The complementarity of patch and matrix markers in the transplants shows that the transplants do compartmentalize. However, the density of the markers in the transplants did not reach the levels seen in the adult striatum. The results suggest that the commitment of cells to a striatal compartment is a very early event in the embryonic development of the forebrain.

Acetylcholinesterase↗
PubMed1987

Small bowel obstruction: a review of 456 cases in a west of Ireland region.

A retrospective study was carried out of 456 patients with small bowel obstruction (SBO). The operative findings of all patients who presented with SBO between 1977 and 1982 were compared and contrasted with those who presented during equivalent periods in the previous three decades. Obstructed hernias still account for the highest percentage of cases. Surprisingly, adhesions as a causative factor are not significantly more common than they were three decades ago, despite the enormous increase in the frequency with which abdominal surgery is now being carried out. The postoperative mortality rate for the period 1977-82 was 14%.

Adolescent↗
PubMed1975

Epidemic Venezuelan equine encephalitis in North America in 1971: vector studies.

A major epidemic of Venezuelan equine encephalitis occurred in south Texas in the summer of 1971. More than 1500 equines died of VEE in Texas, and 110 human cases with no deaths were reported. Vector studies in south Texas and northern Tamaulipas revealed that the overall mosquito infection rates during the peak of the epidemic were about 1:100, one of the highest rates observed for a major epidemic. Mosquito infection rates of this magnitude could easily explain the intensity of VEE outbreaks in both equines and man. A total of 943 VEE virus isolations were made from mosquitoes. Eight of the 12 mosquito species found infected were implicated in the epidemic cycle of VEE for the first time. Sufficient laboratory and field evidence is available to prove that Psorophora confinnis was one of the primary vectors of VEE. The lack of laboratory evidence necessitates the use of the term "probable" primary vectors for other species apparently equally as involved on the basis of field infections; these include Aedes sollicitans, Aedes thelcter and Psorophora discolor. Eight other species from which less than 10 VEE virus isolations were made were considered auxiliary vectors. Mosquitoes of some species were tested individually; such tests showed 2-4% of the probable primary vectors to be infected. The first isolation of VEE virus of the epidemic was made from P. confinnis on June 28, 1971. Highest mosquito infection rates occurred during the week of July 5. Mosquito infection rates declined precipitously in the last 3 weeks of July 1971, signaling the end of the epidemic in the study area. One explanation for the decline was that equines, the principal epidemic hosts, were eliminated as a source of virus by death or by acquisition of natural or induced immunity. Mosquito control appeared to be effective in reducing the infected mosquito population while the immunization of equines with TC 83 VEE vaccine was accomplished. Quarantines appeared to be effective in restricting the VEE virus activity to south Texas. Undoubtedly all of the control measures contributed to stopping the epidemic. Continued VEE surveillance by various government and other agencies failed to reveal any further epidemic VEE activity in the US in 1972. Other arboviruses isolated during the VEE studies in south Texas included St. Louis encephalitis virus, and San Angelo subtype of the California Group. A virus of the Bunyamwera Group was also isolated from Palo Blanco, Tamaulipas.

Animals↗
PubMed1975

Epidemic Venezuelan equine encephalitis in North America in 1971: vertebrate field studies.

Epidemic Venezuelan equine encephalitis in North America in 1971: vertebrate field studies. Am J Epidemiol 101:36-50, 1975.-In June 1971, epidemic Venezuelan equine encephalitis (VEE) invaded the lower Rio Grande Valley in south Texas. The Boca Chica area of Cameron County was selected as a study site to investigate vertebrate involvement in the natural cycle of epidemic VEE on the basis of considerable evidence of VEE virus activity there in equines, humans, and mosquito vectors. Only one VEE virus isolation was made from 4739 wild and domestic non-equine vertebrates, although numerous equine and human VEE virus isolations were made in concurrent studies. Serologic studies indicated that VEE virus activity was far greater in large domestic animals than in wild birds, wild mammals, or reptiles. Apparently epidemic VEE virus failed to establish itself in a wild vertebrate cycle in south Texas, since VEE antibody was found only in rabbits in 1972. Eventual cessation of VEE transmission in south Texas has been attributed 1) to the elimination of equines as a source of VEE virus by death, naturally acquired antibodies, or vaccination, 2) to quarantines, 3) to mosquito control, and 4) to the failure of epidemic VEE virus to become established in the wild vertebrate population. Equines emerge as the most important vertebrate host in the amplification and spread of virus during an epidemic of VEE.

Animals↗