Search PubMed⌕ Search

Biomedical subjects

L F Kromer

Publications and source records attributed to L F Kromer.

28 records · Page 2Linked to original sources
PubMed1981

Innervation of embryonic hippocampal implants by regene-rating axons of cholinergic septal neurons in the adult rat.

The regeneration of the septal cholinergic system in adult rats has been studied in animals bearing transplants of hippocampus taken from 20-40 mm rat fetuses (approximately 17-21 days of gestation). The septal axons located within the fimbria and the dorsal fornix were lesioned and a cavity was prepared at the rostral end of the hippocampus. The embryonic tissue was placed adjacent to the severed end of the fornix-fimbria. The time-course of ingrowth of cholinergic fibers into the transplant was monitored by acetylcholine esterase (AChE) histochemistry and the determination of the levels of choline acetyltransferase (ChAT). Both methods indicate that there is a progressive ingrowth into the transplant of cholinergic fibers up to 3 months after transplantation. The newly-formed AChE-positive fibers in the transplant remain beyond one year after transplantation and are thus presumably permanent. Both horseradish peroxidase (HRP) injections into the implant and radiofrequency lesions of the septal-diagonal band area indicate that the principal source of these fibers is the AChE-positive neurons of the medial septum and the nucleus of the diagonal band which normally form the septohippocampal cholinergic projection. The results suggest: (1) that implants of a normal embryonic target tissue can promote axonal regeneration in mature neurons of the mammalian central nervous system; (2) that some neurons in the adult mammalian CNS retain at least part of their embryonic capacity to generate axons and recognize specific postsynaptic targets in developing CNS tissue; and (3) that this host-implant interaction can result in the formation of quite specific innervation patterns in the implanted target tissue.

Acetylcholine↗
PubMed1981

Regeneration of the septohippocampal pathways in adult rats is promoted by utilizing embryonic hippocampal implants as bridges.

The ability of embryonic hippocampal tissue to promote regeneration of cholinergic axons in the septohippocampal system has been studied in adult rats. Strips of embryonic hippocampus, taken from 7-40 mm rat fetuses, were implanted into a 2-3 mm wide cavity which completely transected the septal cholinergic axons innervating the intrinsic hippocampus. The ingrowth of cholinergic fibres into the denervated host hippocampal formation was monitored by measuring the activity of the enzyme, choline acetyltransferase (ChAT), and by acetylcholine esterase (AChE) histochemistry. The results demonstrated a gradual, partial return of both ChAT enzyme activity and AChE-positive fibres in the initially denervated hippocampal formation of the adult recipient. Time-course studies indicated that this ingrowth progressed from the implant into the rostral tip of the host hippocampus, and continued caudally to cover the entire dorsal hippocampus by 3-6 months postoperative. Although the regenerating AChE-positive fibres reached the hippocampal target in the recipient along abnormal routes, they reinnervated selectively the appropriate terminal areas within the host hippocampus and dentate gyrus, suggesting the presence of quite specific mechanisms to guide the regenerating axons back to their original targets. Lesions of the medial septum-diagonal band area of the host and horseradish peroxidase (HRP) injections into the host hippocampus, caudal to the implant, indicated that the origin of the regenerating axons was predominately from the ipsilateral ventral medial septum and diagonal band area of the host. The results provide evidence that axonal regeneration and reinnervation of a denervated target zone can be promoted by utilizing implants of embryonic CNS tissue to bridge a tissue defect between the target and the lesioned axonal stumps.

Acetylcholinesterase↗
PubMed1980

Differentiation of embryonic hypothalamic transplants cultured on the choroidal pia in brains of adult rats.

Hypothalmic tissue from 16 to 18-day fetal rats was transplanted onto the choridal pia overlying the superior colliculus in adult female rats. After survival periods of 2 weeks to 19 months, brains containing transplants were processed for monoamine fluorescence histochemistry, immunohistochemistry for three neuropeptides (LHRH, somatostatin, neurophysin), or for autoradiography in ovariectomized hosts that received [3 H] estradiol. Most of the transplants survived and retained or increased in size; 14 of 25 transplants examined by fluorescence histochemistry were found to contain median eminence-like structures. In almost all of the transplants that were stained for neuropeptides, beaded processes and occasional cell bodies were observed. Although immunoreactive fibers were found near blood vessels, no palisade arrangement typical of the normal median eminence was evident. Each of the hypothalamic transplants on which steroid autoradiography was performed contained clusters of estrophilic neurons, the intensity of labeling of which was comparable to that seen in the host hypothalamus. These results indicate that many characteristic morphological and chemical features of the hypothalamus, which are not evident in the 16 to 18-day fetus, are elaborated in transplants during the survival period in the host. Transplantation of fetal hypothalamus to adult choridal pia thus appears to be a valuable approach for studying the factors, humoral or neural, that regulate the differentiation of this brain region.

Animals↗
PubMed1980

Norepinephrine innervation of the cochlear nuclei by locus coeruleus neurons in the rat.

The cochlear nuclei (CN) contain a moderate concentration of norepinephrine (445 +/- 20 ng/g tissue) with dopamine levels (46 +/- 14 ng/g) that are low and within the precursor range expected for a norepinephrine (NE) terminal system. Lesion and horseradish peroxidase (HRP) experiments indicate that this innervation is bilateral and arises from fusiform and multipolar neurons in the locus coeruleus. Autoradiographic and fluorescence histochemical experiments demonstate that locus coeruleus fibers reach the ipsilateral ventral cochlear nuclei via a rostral pathway that projects from the rostral locus coeruleus laterally through the brain stem to the rostral tip of the ventral nuclei. This pathway is located dorsal to the motor and spinal trigeminal nuclei and ventral to the middle cerebellar peduncle. Descending coeruleo-cochlear fibers travel between the fourth ventricle and the vestibular nuclei to enter the acoustic striae. These fibers innervate both the dorsal and ventral nuclei. Contralateral locus fibers reach the CN by crossing in the pontine central gray at the rostral border of the fourth ventricle and by decussating with the fibers of the mesencephalic trigeminal nucleus ventral to the medial longitudinal fasciculus. The bilateral locus coeruleus innervation of the cochlear nuclei comprises a highly collateralized network of varicose axons which are not topographically organized. Unlike the cochlear nerve fibers in the CN which form specific projections, the locus coeruleus afferents to these sensory nuclei are diffuse and non-specific.

Animals↗
PubMed1979

Intracephalic implants: a technique for studying neuronal interactions.

Implants of embryonic neural tissue from all regions of the neuraxis survive grafting to the brains of adult rats. After implantation, neurogenesis and differentiation continue, and connections are formed with the mature host brain. Thus, the intracephalic implants provide excellent model systems for studying cellular interactions that regulate synaptogenesis and determine the cytoarchitectonic organization of developing neural tissues.

Animals↗
PubMedDate not supplied

Cholinergic axons from delayed septal implants and sympathetic fibers co-exist in the denervated dentate gyrus.

Adult female rats received a unilateral fornix/fimbria lesion 6 weeks prior to obtaining an implant of embryonic septal tissue. The ingrowth of cholinergic axons from the delayed implants into the denervated dentate gyrus was visualized by acetylcholinesterase (AChE) histochemistry. Since sprouting of anomalous sympathetic fibers also occurs following fornix/fimbria transection, the organization of these fibers was identified with the monoamine histofluorescence technique. Lesion control specimens with fornix/fimbria lesions demonstrate that sympathetic fibers are present along the septo-temporal axis of the dentate gyrus by 6 weeks postlesion. In specimens with delayed septal implants there is ingrowth of AChE fibers along the septo-temporal axis of the dentate gyrus with the densest distribution of fibers located at the septal pole of the dentate. The sympathetic fibers which are present in the dentate prior to the implantation of the septal tissue still persist in regions which contain a moderate density of AChE fibers but appear absent or diminished in regions with a dense cholinergic ingrowth. The data suggest that the postsynaptic signals necessary for the selective reinnervation of the dentate gyrus by the septal cholinergic axons are not abolished by synaptic reorganization in the neuropil which occurs prior to the implantation of the septal tissue. Moreover, there may be some competition between the cholinergic and sympathetic fibers for this postsynaptic signal and for space within the dentate neuropil.

Acetylcholinesterase↗