Development of specificity in corticospinal connections by axon collaterals branching selectively into appropriate spinal targets

Corticospinal projections in adult rodents arise exlusively from layer V neurons in the sensorimotor cortex. These neurons are topographically organized in their connections to spinal cord targets. Previous studies in rodents have shown that the mature distribution pattern of corticospinal neurons develops during the first 2 weeks postnatal from an initial widespread pattern that includes the visual cortex to a distribution restricted to the sensorimotor cortex. To determine whether specificity in corticospinal connections also emerges from an intially diffuse set of projections, we have studied the outgrowth of corticospinal axons and the formation of terminal arbors in developing hamsters. The sensitive fluorescent tracer 1, 1′, dioctadecyl-3, 3, 3′, 3′-tetramethylindocarbocyanine perchlorat (DiI) was used to label corticospinal axons from the visual cortex or from small regions of the forelimb or hindlimb sensorimotor cortex in living animals at 4–17 days postnatal. Initially axon outgrowth was imprecise. Some visual cortical axons extended transiently beyond their permanent targets in the pontine nuclei, by growing through the pyramidal decussation and in some cases extending as far caudally as the lumbar enlargement. Forelimb sensorimotor axons also extended past their targets in the cervical enlargement, in many cases growing in the corticospinal tract to lumbar levels of the cord. By about 17 days postnatal these misdirected axons or axon segments were withdrawn from the tract. Despite these errors in axon trajectories within the corticospinal tract, terminal arbors branching into targets in the spinal gray matter were topographically appropriate from the earliest stages of innervation. Thus visula cortical axons never formed connections in the spinal cord, forelimb sensorimotor axons arborized only in the cervical enlargement, and hindlimb cortical axons terminated only in the lumbar cord at all stages of development examined. Corticospinal arbors formed from collaterals that extended at right angles from the shafts of primary axons, most likely by the process of interstitial branching after the primary growth cone had extended past the target. Once collaterals extended into the spinal gray matter, highly branched terminal arbors formed within 2–4 days, beginning at about 4 and 8 days postnatal for the cervical and lumbar enlargements, respectively. These results show that specificity in connectivity is achieved by selectivty growth of axon collaterals in to appropriate spinal targets from the beginning and not by the later remodeling of intially diffuse connections. In contrast, errors occur in the initial outgrowth of axons in the corticospinal tract, which are subsequently corrected. Copyright © 1994 Wiley-Liss, Inc.     

Alternative brain organization after prenatal cerebral injury: convergent fMRI and cognitive data.

The current study presents both longitudinal behavioral data and functional activation data documenting the effects of early focal brain injury on the development of spatial analytic processing in two children, one with prenatal left hemisphere (LH) injury and one with right hemisphere (RH) injury. A substantial body of evidence has shown that adults and children with early, lateralized brain injury show evidence of spatial analytic deficits. LH injury compromises the ability to encode the parts of a spatial pattern, while RH injury impairs pattern integration. The two children described in this report show patterns of deficit consistent with the site of their injury. In the current study, their longitudinal behavioral data spanning the age range from preschool to adolescence are presented in conjunction with data from a functional magnetic resonance imaging (fMRI) study of spatial processing. The activation results provide evidence that alternative profiles of neural organization can arise following early focal brain injury, and document where in the brain spatial functions are carried out when regions that normally mediate them are damaged. In addition, the coupling of the activation with the behavioral data allows us to go beyond the simple mapping of functional sites, to ask questions about how those sites may have come to mediate the spatial functions.     

Risk-Taking among Adolescents Who Say They Can Get a Handgun

In a survey of 5657 community-residing adolescents, those who said they could get a handgun in two days reported similar and those who said they could not get a handgun reported fewer risk behaviors and less violence perpetration and victimization than adolescents who have their own handgun. Adolescents who said they could get a handgun reported more exposure to and experience with firearms than those who said they could not get a handgun. Risk reduction efforts regarding adolescents should be expanded to include adolescents who say they can get a handgun.     

Assessing Performance and Expecting More: PART Assessments of Federally-Funded Addictions Treatment Programs

Effective programs set ambitious goals, achieve results, are managed well, and improve efficiency. Assessing performance, managing results, and assuring effective use of tax dollars is challenging and complex. This column describes how the federal government uses the Performance Assessment Rating Tool (PART) to ensure that its programs perform well and use public resources responsibly, and includes summaries of the performance assessments of three federally funded addiction treatment programs. An understanding of this process may help local addiction treatment programs implement similar strategies to improve their own performance, and thus contribute in a more meaningful way to improved outcomes for populations being treated for addictive disorders.     

An Atypical Recurrence of Endometrial Carcinoma Following Estrogen Replacement Therapy

Following an abdominal hysterectomy and bilateral salpingoophorectomy wherein a superficial (1.6 mm) well-differentiated endometrial cancer and bilateral ovarian serous cystadenomas were discovered, estrogen replacement was given. One year later the patient presented with a 9 × 7-cm left groin recurrence. Patients with endometrial carcinoma may request estrogen replacement. The benefits of such replacement are well recognized; however, these patients also need to be counselled that hormonal replacement may be complicated by recurrence. Physicians need to be cognizant of symptoms or signs which would suggest disease recurrence at unusual sites in these patients who are perceived as being at low risk for recurrent disease.     

Newspaper coverage of residential fires: an opportunity for prevention communication.

BACKGROUND: Worldwide, fire-related burns are a major cause of unintentional injury, morbidity and mortality, with the majority of deaths occurring in developing countries. In the US, as in other countries, most fatal fires occur in the home. Effective prevention strategies for residential fires are, however, currently underutilized. The news media is one available communication channel to promote such strategies, and analyzing current news coverage is a first step towards incorporating media advocacy into injury prevention efforts related to residential fires. METHODS: Four daily newspapers circulating widely in Maryland were monitored for 1 year. Articles describing residential fires were coded for measures of prominence, content and frame. Analysis focused on measures of issue newsworthiness, reporting of causation and consequences of fires, and inclusion of public health context and conveyance of prevention messages. RESULTS: The data indicate that fires are newsworthy, with 374 relevant news articles in a 1-year period, 32% of which appear on the first page of a section. Coverage generally concerned recent local fire events. Most articles discussed the consequences of fires (88%), and identified a causal factor (58%). Only 36%, however, included prevention information, and less than one-quarter set residential fires in a public health context. CONCLUSION: The newsworthiness of residential fires provides a clear opportunity for widespread communication around injury prevention. Improving media advocacy will entail framing discussion of recent fire events in such a way as to support inclusion of prevention strategies and a public health context in news coverage.     

Construct Validity of a Clinical-performance-evaluation Tool in Community Health Nursing

An evaluative research study was conducted to examine the construct validity and applicability of a selected clinical-performance-evaluation tool. The tool was designed for baccalaureate students in a community health nursing course. Eighteen senior students functioning in two urban clinical agencies participated in the study. Data were collected at two evaluation points over one semester. Results indicated strong support for construct validity of the tool. This finding suggests a high level of correlation between theoretical concepts and clinical practice. Recommendations for use of the clinical performance evaluation tool are discussed.