p75-deficient sensory axons are immunoreactive for the glycoprotein L1 in mice overexpressing nerve growth factor.

Nerve growth factor (NGF) regulates the expression of the glycoprotein L1 among neural cell populations. The purpose of this investigation was to determine whether NGF equally affects the immunolocalization of L1 on both sympathetic and sensory axons, and whether the functional expression of the p75 neurotrophin receptor (p75NTR) is required for the immunodetection of this glycoprotein on peripheral axons. Two lines of transgenic mice overexpressing NGF among glial cells were used in this study: (1) one line of mice possessing two normal alleles for p75NTR, and (2) another line of mice possessing two mutated alleles for p75NTR. In both types of animals, sensory axons stained immunohistochemically for calcitonin gene-related peptide and sympathetic axons stained immunohistochemically for tyrosine hydroxylase invaded the deep white matter portions of the cerebellum (a central structure containing high levels of transgene expression and synthesis); the cerebella of wild type (C57Bl/6) and p75NTR-deficient mice lacked these sensory and sympathetic fibers. Both lines of transgenic animals also possessed a dense plexus of L1-immunoreactive axons in their cerebella; the spatial distribution of these L1-immunostained axons paralleled that seen for the sensory and sympathetic axons. A unilateral removal of the superior cervical ganglion in both lines of transgenic animals caused a complete reduction of tyrosine hydroxylase-immunopositive axons in the cerebellum but did not affect the density of L1-immunopositive axons. From these in vivo data, we conclude that collateral branches of sensory axons which invade a NGF-rich target area display L1 immunoreactivity, and that such immunodetection does not require the functional expression of p75NTR.

The misrepresented uterus. The progression of uterine depictions in anatomical atlases between the sixteenth and eighteenth centuries.

Between the sixteenth and eighteenth centuries, the depiction of the female uterus progressed toward greater anatomical accuracy. However, as Karen Newman (1996) indicates, common elements persist throughout such illustrations: the fetus is represented as an active inhabitant of the uterus while the female body is rendered as either passive or absent.

Sensory nociceptive axons invade the cerebellum of transgenic mice overexpressing nerve growth factor.

Transgenic mice possessing elevated levels of mRNA expression and synthesis for the neurotrophin nerve growth factor among astrocytes display a robust ingrowth of new sympathetic fibers to the cerebellum. In this investigation, we report that the cerebellum of these mice also possesses a dense plexus of aberrant axons of sensory origin. Axons stained immunohistochemically for calcitonin gene-related peptide were seen in the transgenic cerebellum as early as one week after birth. The density of these axons dramatically increased with age. Immunopositive axons were confined predominantly to the deep white matter of the cerebellum in the adult transgenic mice, with a smaller number of axons seen coursing along blood vessels in the gray matter. Axons stained immunohistochemically for the neurotrophin receptor, p75NTR, displayed a similar pattern of distribution and density as those immunostained for calcitonin gene-related peptide. Wild-type post-natal and adult animals lacked such calcitonin gene-related peptide- and p75NTR-immunoreactive axons in the cerebellum. Retrograde labelling revealed that these axons within the transgenic cerebellum originated from neurons in the sensory trigeminal and dorsal root ganglia (upper cervical levels). This investigation demonstrates that overexpression of nerve growth factor is capable of inducing the directional growth of collateral axons of sensory neurons into the undamaged mammalian central nervous system.