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D L McNeill

Publications and source records attributed to D L McNeill.

At least 37 records · Page 2Linked to original sources
PubMed1989

Changes in dorsal horn synaptic disc numbers following unilateral dorsal rhizotomy.

The present study estimates the numbers of synaptic discs and numbers of degenerating synaptic terminals in laminae I-IV of the rat S2 dorsal horn ipsi- and contralateral to unilateral dorsal rhizotomy. These data allow us to estimate the loss of synapses of primary afferents and to correlate this loss with the rate of axon disappearance in the proximal stump of a transected S2 dorsal root. Our first findings are that 47% of the ipsilateral synapses and 27% of the contralateral synapses disappear within a day following unilateral rhizotomy. Conclusions are that the predominant synaptic population in this part of the rat spinal cord is of primary afferent origin and that there is an extensive bilateral projection of the dorsal root fibers. The contralateral projection is confirmed by the appearance of numerous degenerating terminals on the contralateral side. We also find that synaptic loss and appearance of degenerating terminals occur relatively synchronously in laminae I-IV. Finally we find that the time course of the synaptic loss correlates primarily with the disappearance of unmyelinated fibers in the proximal stump of the transected dorsal root.

Animals↗
PubMed1989

Glutamate immunoreactivity in rat dorsal root axons.

Approximately 8.5% of the unmyelinated and 2.5% of the myelinated primary afferent axons in lumbar dorsal roots of normal rats are immunostained for glutamate. Thus unmyelinated fibers are the predominantly immunostained population under the conditions of our experiments. The mean size of the unmyelinated fibers is greater at L6 than at L4 and L2. The meaning of this is not clear, but it may imply that pelvic visceral afferents are slightly larger than afferents from other areas. We emphasize that the immunostained axons can be demonstrated in otherwise normal animals, so changes in the percentages of labeled axons in response to various stimuli will be of interest.

Animals↗
PubMed1989

Peptide immunoreactivity of unmyelinated primary afferent axons in rat lumbar dorsal roots.

The present study demonstrates calcitonin gene-related peptide (CGRP), somatostatin (SOM), bombesin (BOM), and substance P (SP) at the electron microscopic level in lumbar dorsal root axons of normal rats. The highest percentages of labeled axons were for CGRP (14%) and then, in descending order, for SP (8.6%), SOM (6.8%), and BOM (3.1%). The labeled axons were exclusively unmyelinated for SP, SOM, and BOM, and predominantly unmyelinated for CGRP. These data are consistent with the data for labeled sensory cell bodies for these same compounds. We emphasize that these peptides were immunocytochemically visualized in the dorsal roots without experimental manipulation, such as colchicine or dorsal root ligation. Quantitative sampling of this type can be used to assay changes in response to physiological stimuli in numbers of sensory axons that contain identifiable concentrations of these peptides.

Animals↗
PubMed1988

Numbers of synapses in laminae I-IV of the rat dorsal horn.

The present study determines numerical densities (NVsyn) and total numbers of synaptic discs in laminae I-IV of the rat S2 dorsal horn. Previous methods for NVsyn have the advantage of being relatively simple, but these assume that the discs are round, flat, and of uniform size. In our material, serial reconstructions indicate that these assumptions are not met. Accordingly we use a stereological method that is not as dependent on these assumptions. This method is to divide the surface density of the discs by the mean surface area of a disc (NVsyn = SVsyn/Ssyn). We refer to this as a reconstruction method because synaptic discs are reconstructed from serial sections. We also calculate numerical densities by several previously used standard methods, and the findings are similar but not identical. We find that numerical density and total synaptic numbers are smallest in lamina I, and densities and total numbers are not significantly different when lamina II is compared to laminae III and IV. Thus the intense labeling of terminals with certain compounds that characterize lamina I and II does not imply an increase in total synaptic numbers or in synaptic density. In addition there is a general increase in synaptic densities and numbers as one proceeds from lamina I to lamina IV. Another point is that the numerical density of synapses in the dorsal horn is approximately that of the cerebral cortex. These data will serve as a basis from which to judge the effects of denervations and other manipulations that purportedly change synaptic numbers.

Animals↗
PubMed1988

Organization of calcitonin gene-related peptide-immunoreactive terminals in the primate dorsal horn.

The present paper is concerned with the arrangement of axons and synaptic terminals immunostained for calcitonin gene-related peptide (CGRP), a primary afferent marker, in the primate (Macaca fascicularis) dorsal horn. The CGRP axons and terminals are uniformly distributed in laminae I and II outer (o) but they are concentrated laterally and distributed intermittently in the reticulated region of lamina V. A prominent bundle of labeled axons is seen in the sacral cord dorsal to the central canal. Emphasis is given to the relation of CGRP-immunoreactive terminals to other terminals, both labeled and unlabeled, in laminae I and IIo. In this regard, adjacent CGRP-immunoreactive terminals are often united by puncta adhaerentia. Of particular interest is the observation that CGRP-immunoreactive terminals can be found presynaptic to other terminals which sometimes resemble central primary afferent endings. In addition CGRP-immunoreactive terminals end on other CGRP terminals. Both findings suggest that primary afferent terminals interact synaptically with other primary afferent terminals.

Animals↗
PubMed1988

Calcitonin gene-related peptide immunostained axons provide evidence for fine primary afferent fibers in the dorsal and dorsolateral funiculi of the rat spinal cord.

The hypothesis being tested in the present paper is that there are large numbers of fine primary afferent axons in the dorsal and dorsolateral funiculi of the lumbar spinal cord of the rat. The data show numerous calcitonin gene-related peptide labeled fine myelinated and unmyelinated axons in these funiculi. Approximately 95% of the labeled axons disappear after dorsal rhizotomy. Accordingly, the hypothesis is confirmed. Thus it is becoming apparent that fine primary afferent fibers are more widely distributed in spinal white matter than had been previously recognized. Implications are that it is not possible to find areas in the spinal white matter that contain only large myelinated sensory axons and that significant numbers of fine primary afferent fibers will be lost even if lesions are restricted to the dorsal funiculus. The sizable population of fine myelinated primary afferent axons in the dorsal funiculus is emphasized. An obvious question, suggested by significant differences in average diameters of the axons in the different pathways, is whether there are differences in the types of information carried by the fine afferent fibers in their different locations in the white matter of the lumbar cord.

Afferent Pathways↗
PubMed1988

A light and electron microscopic study of calcitonin gene-related peptide in the spinal cord of the rat.

The present study localized calcitonin gene-related peptide at the light and electron microscopic levels in the lumbar spinal cord of the rat. One finding was that axons and terminals were labeled in both lamina I and IIo medially but only in lamina I laterally. The functional implications of this innervation pattern are not clear but presumably this anatomic arrangement bears on both dorsoventral and mediolateral patterns of organization of primary afferent input into the dorsal horn. We also found that although the means of labeled myelinated and unmyelinated axon diameters in the tract of Lissauer were different, there was great overlap in these populations. Furthermore, subcellular localizations indicated that immunostaining of calcitonin gene-related peptide was associated primarily with microtubules in axons and cores of large dense-core vesicles in presynaptic terminals. Finally, labeled presynaptic terminals contained relatively few large dense-core vesicles and formed the presynaptic elements of simple axodendritic contacts almost exclusively. These last findings contrast with localizations of calcitonin gene-related peptide in the monkey, which has many more large dense-core vesicles in labeled terminals and in which a much higher proportion of labeled endings form the central parts of glomeruli.

Animals↗
PubMed1987

A light and electron microscopic level analysis of calcitonin gene-related peptide (CGRP) in the spinal cord of the primate: an immunohistochemical study.

In the present study, the distribution of calcitonin gene-related peptide (CGRP)-stained fibers and varicosities are demonstrated in the lumbar spinal cord of the monkey at the light microscopic level. Immunostained fibers and varicosities form a dense plexus in laminae I, IIo, the reticulated region of lamina V, and in the region of the central canal. The intervaricose fibers consistently measured 1 micron or less in diameter suggesting a population of finely myelinated or unmyelinated fibers. At the electron microscopic level, two types of terminals were labeled: a glomerular type where one CGRP-labeled profile was indented by several unlabeled postsynaptic profiles and an axodendritic type with one or sometimes two postsynaptic elements. The most noteworthy cytologic feature of CGRP-labeled profiles was the presence of many relatively large vesicles with dense cores. These findings are steps towards understanding the synaptic interactions of CGRP in the monkey dorsal horn.

Animals↗
PubMed1987

Intraspinal sprouting of rat primary afferents after deafferentation.

To test intraspinal sprouting of primary afferent fibers, unilateral chronic, followed by contralateral acute, dorsal rhizotomies were done 3 segments above and below a spared segment (T9) in rats. Following perfusion with 4% paraformaldehyde, T9 spinal cord segments were frozen, sectioned and reacted by a modified Gomori procedure for fluoride-resistant acid phosphatase (FRAP) enzyme activity, a marker for primary afferent terminals. As determined by light microscopy, there was greater and extended FRAP reaction product in laminae I and II on the chronically denervated side than on the contralateral acutely denervated side. These data support the hypothesis of axonal sprouting and synaptogenesis of primary afferent fibers after spinal cord deafferentation.

Afferent Pathways↗
PubMed1987

Peripheral pathways for neuropeptide Y- and cholecystokinin-8-immunoreactive nerves innervating the rat ovary.

The superior ovarian nerve (SON) or plexus nerve (PN) innervating the rat ovary was transected separately or in combination and the effects of these nerve lesions on intra-ovarian NPY- or CCK-8-immunoreactive nerve fibers was evaluated. Transection of the SON did not affect NPY or CCK-8-immunoreactive nerve fibers. In contrast, section of the PN eliminated nerve fibers immunoreactive for these neuropeptides. This study demonstrates that both NPY- and CCK-8-immunoreactive nerve fibers reach the ovary via the PN.

Animals↗
PubMed1987

Neuropeptides in sensory perikarya projecting to the rat ovary.

Afferent perikarya in dorsal root ganglia (DRG) at the T13 and L1 segmental levels projecting to the rat ovary were identified by utilizing the fluorescent retrograde tracer true blue (TB). Subsequently, TB-labeled ovarian afferent perikarya in DRG were examined for vasoactive intestinal polypeptide (VIP), substance P (SP), cholecystokinin-8 (CCK-8), neuropeptide Y (NPY), and somatostatin (SOM) immunoreactivity and for the presence of fluoride-resistant acid phosphatase (FRAP) enzyme activity. Of the ovarian afferent perikarya at the T13 and L1 segmental levels, 20.5% displayed VIP immunoreactivity, 23.8% displayed SP immunoreactivity, and 43.1% were immunoreactive for CCK-8. No ovarian afferent perikarya contained SOM or NYP immunoreactivity or FRAP activity. It is suggested that different neuropeptides may participate in modulation of specific ovarian functions.

Acid Phosphatase↗
PubMed1986

Convergence of sensory processes from the heart and left ulnar nerve onto a single afferent perikaryon: a neuroanatomical study in the rat employing fluorescent tracers.

After injection of true blue (TB) into the pericardial sac and nuclear yellow (NY) into the left ulnar nerve of rats, most perikarya in the left eighth cervical and first thoracic dorsal root ganglia are single-labeled with either TB or NY. However, 7.1-14.7% of the sensory perikarya from the cardiac area labeled with TB are simultaneously labeled with NY. This finding indicates that some primary sensory perikarya receive processes from both the left arm and the heart. In addition to other mechanisms that may be operative in the referral of pain of cardiac origin to the medial left arm, these results suggest that sensory neurons with dichotomizing somatic and visceral peripheral processes may also contribute to this phenomenon.

Afferent Pathways↗
PubMed1986

Utilization of a polyethylene enclosure for nerve tracing studies in the rat ovary.

A commonly used technique for mapping neuronal connections in the peripheral nervous system involves the injection of a tracer substance into a peripheral organ. The tracer is taken up by nerve terminals at the injection site and transported retrogradely to motor or sensory perikarya where it can be visualized. One of the pitfalls of this technique is that tracer may leak from the injection site, enter nerve terminals adjacent to the injection area and thus cause erroneous interpretations. Similarly, some tracers may enter blood vessels and be taken up by nerve cell bodies indiscriminately. In order to circumvent these potential problems in studies on the innervation of the rat ovary, a polyethylene enclosure for the organ was fabricated from a BEEM capsule. The retrograde tracer, True blue, was then applied topically on the ovarian surface inside the enclosure. In chronic experiments, specifically labeled ovarian nerve cell bodies were identified in dorsal root and preaortic ganglia. Utilization of this simple and effective enclosure eliminates the false-positive and non-specific labeling of perikarya due to diffusion and blood-borne transport of the tracer from the injection area.

Animals↗
PubMed1986

Neuropeptide Y and somatostatin immunoreactive perikarya in preaortic ganglia projecting to the rat ovary.

Postganglionic perikarya in preaortic ganglia projecting to the ovary of the rat were identified utilizing the retrograde fluorescent tracer, true blue. Ovarian perikarya were subsequently examined for neuropeptide Y and somatostatin immunoreactivity. True blue-labelled ovarian postganglionic perikarya were distributed in the coeliac ganglion and in smaller ganglia located at the origins of the renal and ovarian arteries. In the coeliac ganglia, 74.4 +/- 18.8% of true blue-labelled ovarian perikarya were immunoreactive to neuropeptide Y while 37.4 +/- 9.6% were immunoreactive to somatostatin. In the inferior smaller ganglia, 72.2 +/- 18.7% and 2.2 +/- 2.2% of the true blue-labelled ovarian perikarya were immunoreactive to neuropeptide Y and somatostatin respectively. It is suggested that neuropeptide Y and somatostatin participate in the modulation of ovarian function.

Animals↗
PubMed1984

An immunocytochemical study of the pancreatic islet system of the channel catfish.

The endocrine pancreas of the channel catfish is segregated into a large primary islet and numerous smaller secondary islets. In view of cell distribution differences in mammalian islets of ventral and dorsal primordia, we have determined the percentage volumes of insulin-, glucagon-, and somatostatin-containing cells in primary and secondary catfish islets to ascertain if these islets correlated with those derived from ventral and dorsal primordia in mammals. Islets were immunocytochemically stained using antisera to anglerfish insulin, porcine glucagon, and synthetic somatostatin and volume densities were quantified on light micrographs by point-counting procedures. In both primary and secondary islets the insulin-, glucagon-, and somatostatin-containing cells comprised approximately 32%, 23%, and 38% of the endocrine cell volumes, respectively. Therefore, the cell populations did not reflect any embryological differences between the two groups of islets. In this study, the volume densities of insulin-reactive cells in the primary islet were less than previously reported, and the overall insulin staining was about one-half of that seen in mammals. The volume density of somatostatin-reactive cells in primary islets was greater than previously reported. Based on these data, primary and secondary islets of the catfish do not appear to have a similar development to the ventral and dorsal islets of the mammalian system.

Animals↗
PubMedDate not supplied

Calcitonin gene-related peptide in the rat uterus: presence in nerves and effects on uterine contraction.

The influence of calcitonin gene-related peptide (CGRP) on rat uterine activity was examined in concert with the anatomical distribution of CGRP-like immunoreactivity in the uterus. CGRP-like immunoreactivity was localized in nerve fibers; these peptide-containing nerves were abundant throughout the mesometrium of the uterine horn and appeared to innervate mesometrial smooth muscle and vascular smooth muscle. In the uterine wall, CGRP-like immunoreactive fibers were prevalent in the myometrium, endometrium and the endocervix. Fibers in the endometrium and endocervix appeared to form a plexus subjacent to the epithelium and some fibers penetrated the epithelium as an intraepithelial plexus. The action of CGRP (10(-9) to 10(-6) M) on acetylcholine (10(-6) or 10(-5) M)-stimulated uterine activity was examined in vitro. Exogenously applied CGRP induced a dose-dependent relaxation of acetylcholine-stimulated uterine contractions. CGRP had no effect on basal uterine tension. The localization of CGRP-like immunoreactivity in nerves and the relaxing effect of CGRP suggests a role for CGRP-containing nerve fibers in the regulation of uterine activity.

Animals↗