Human pontine glioma cells can induce murine tumors.

Diffuse intrinsic pontine glioma (DIPG), with a median survival of only 9 months, is the leading cause of pediatric brain cancer mortality. Dearth of tumor tissue for research has limited progress in this disease until recently. New experimental models for DIPG research are now emerging. To develop preclinical models of DIPG, two different methods were adopted: cells obtained at autopsy (1) were directly xenografted orthotopically into the pons of immunodeficient mice without an intervening cell culture step or (2) were first cultured in vitro and, upon successful expansion, injected in vivo. Both strategies resulted in pontine tumors histopathologically similar to the original human DIPG tumors. However, following the direct transplantation method all tumors proved to be composed of murine and not of human cells. This is in contrast to the indirect method that included initial in vitro culture and resulted in xenografts comprising human cells. Of note, direct injection of cells obtained postmortem from the pons and frontal lobe of human brains not affected by cancer did not give rise to neoplasms. The murine pontine tumors exhibited an immunophenotype similar to human DIPG, but were also positive for microglia/macrophage markers, such as CD45, CD68 and CD11b. Serial orthotopic injection of these murine cells results in lethal tumors in recipient mice. Direct injection of human DIPG cells in vivo can give rise to malignant murine tumors. This represents an important caveat for xenotransplantation models of DIPG. In contrast, an initial in vitro culture step can allow establishment of human orthotopic xenografts. The mechanism underlying this phenomenon observed with direct xenotransplantation remains an open question.

Regeneration and recovery of the hearing function of the central auditory pathway by transplants of embryonic brain tissue in adult rats.

The present study is the first report of successful regeneration and recovery of hearing function of the central auditory pathway after transection in the adult rat. The ventral cochlear tract in the brain stem to pons was transected on one side in adult rats. Tissue from embryos (E14 to E16) was used to cover the lesion site. In 30% of the rats examined, the axons regrew beyond the transected site and regenerated into the denervated side and terminated at the normal targets. The hearing function of rats was elucidated by recording the auditory brain stem response (ABR). Rats with successful regeneration showed nearly normal ABR. In rats receiving simple transection without covering embryonic tissue, there was no regeneration and hearing function did not recover. Thus, the present findings contradict the widely held view that the adult mammalian central auditory system cannot be restored following damage.

Specific potentialities of embryonic rat serotonergic neurons to innervate different periventricular targets in the adult brain.

During the development of the central nervous system, neurons are directed by both genetic and environmental factors to differentiate and form connections with their targets. We took advantage of the abundant homogeneous serotonergic innervations of the ependyma forming the supra- and subependymal plexuses to investigate possible commitment of embryonic neurons to innervate specific targets during axogenesis in the rat. The origin of the supraependymal innervation was determined by retrograde transport of cholera toxin (CT) from the ventricles. The supraependymal plexuses of the fourth ventricle mainly originated from neurons in the dorsocaudal region of the raphe dorsalis (DRN), while the rostral DRN and raphe centralis (CRN) contained perikarya projecting into the third ventricle. This suggested the existence, along the rostrocaudal axis of the raphe, of different neuronal subsets able to form distinct supraependymal plexuses in the third or fourth ventricle. To determine whether serotonergic neurons were committed to innervate specific areas of the ependyma, different embryonic metencephalic segments (rostral, median, or caudal) from 14-day-old rat embryos were independently grafted into the third or fourth ventricle of an adult brain in which the serotonergic neurons had been previously destroyed. The distinctive patterns of re-innervation specific to each of grafted segments indicate that subsets of embryonic serotonergic neurons are indeed committed to innervate certain restricted ependymal areas of the adult brain, presumably in response to different neurotropic and/or neurotrophic cues.

Intracerebral grafting of fetal dorsal pons in genetically epilepsy-prone rats: effects on audiogenic-induced seizures.

The present experiments investigated if dorsal pontine tissue obtained from 16-day postconception rat fetuses and stereotaxically transplanted into the dorsal hippocampus or third ventricle of genetically epilepsy-prone rats (GEPRs) would alter the expression of audiogenic seizures. Of eight GEPR-9s receiving pontine-tissue grafts bilaterally into the dorsal hippocampus, none showed any reduction in AGS severity. In contrast, three of five GEPR-9s receiving grafts into the third ventricle eventually displayed a decreased seizure severity following transplantation. Of five GEPR-3s receiving transplants into the hippocampus, one animal showed a gradual and significant reduction in seizure severity after transplantation. Tyrosine-hydroxylase (TH) immunohistochemistry showed that transplanted tissue contained abundant TH-immunoreactive profiles including perikarya and fibers. The results of these preliminary studies suggest that the GEPR model of epilepsy may be useful in studying the corrective potential of neurotransplants.

Expression of the homeobox Chick-en gene in chick/quail chimeras with inverted mes-metencephalic grafts.

The homeobox gene Chick-en, sharing homologies to the engrailed gene of Drosophila, is expressed, during early steps of development, in a restricted area of the chick embryo including mes-metencephalic neuroepithelia. The expression of the Chick-en gene has been analyzed in chick/quail chimeric embryos in which a portion of the 2-day-old mes-metencephalic neuroepithelium has been transplanted in an inverted position. By means of a monoclonal antibody, "Mab 4D9," recognizing engrailed proteins, it is shown that the expression of the Chick-en gene is regulated in the inverted neuroepithelium according to its new position in the host neural tube. The regulation takes place within 20 hr after transplantation. These results, together with previous data demonstrating that the phenotypic expression of the inverted neuroepithelium depends, also, on its new position in the host neural tube, strongly suggest that the engrailed protein could play an important role in the positional specification of the mes-metencephalic neuroepithelium.

Transplantation of norepinephrine neurons into aged rats improves performance of a learned task.

A reproducible behavioral correlate of aging in rodents is deficient performance of inhibitory avoidance memory tasks. Impaired performance has been attributed, in part, to age-related changes in brain norepinephrine (NE) system function. To determine whether supplementation of brain NE can ameliorate avoidance deficits in aged animals, we transplanted noradrenergic locus coeruleus neurons from fetal rat donors into the third cerebral ventricle of 24-month-old male F344 rats. Aged rats that received NE-containing grafts exhibited significant improvement of inhibitory avoidance retention performance compared to both unoperated aged animals and aged animals that received grafts of cerebellar tissue. Improved behavioral performance was prevented by pretreatment of NE graft recipients with the beta-adrenergic receptor blocking agent, propranolol, and was mimicked by chronic intraventricular infusion of NE. Taken together, our findings support the view that age-related declines in brain NE content contribute to age-related deficits in inhibitory avoidance performance, and that NE replacement therapy can improve performance of this task in aged rats.