Expression of D1 receptor mRNA in projections from the forebrain to the ventral tegmental area

In situ hybridization was combined with Fluoro-Gold retrograde labeling to determine if cells projecting from the forebrain to the ventral tegmental area (VTA) express D₁ receptor mRNA. Cell counts were made in the prefrontal cortex, shell of the nucleus accumbens, and ventral pallidum to estimate the percentage of neurons projecting to the VTA that express D₁ receptor mRNA. Retrogradely labeled cells were observed in the infralimbic and prelimbic regions of the prefrontal cortex, and up to 37% of the retrogradely labeled cells expressed D₁ receptor mRNA. Double-labeled cells constituted up to 89% of retrogradely labeled neurons in the rostral shell and up to 68% in the caudal shell of the nucleus accumbens. The number of retrogradely labeled cells in the ventral pallidum that were double-labeled ranged from 13% in the rostral to less than 10% in the caudal portions. These data provide anatomical support for a role of D₁ receptors in the reciprocal innervation between the forebrain and VTA. Synapse 25:205–214, 1997. © 1997 Wiley-Liss, Inc.     

Projections of neurons in the ventromedial medulla to pontine catecholamine cell groups involved in the modulation of nociception

Stimulation of neurons in the nucleus raphe magnus (RMg) or the adjacent gigantocellular nucleus pars alpha (Gi) and paragigantocellular nucleus (PGi) produces antinociception which is partially mediated by bulbospinal noradrenergic neurons. Since no norepinephrine-containing neurons are located in either the RMg or the Gi/PGi, it is likely that neurons located in these nuclei have axonal connections with the spinally-projecting catecholamine neurons located in the A5, A6 (locus coeruleus), or A7 catecholamine cell groups. To provide evidence for such connections, the anterograde tracer, Phaseolus vulgaris-leucoagglutinin (PHA-L), was injected into the RMg or Gi/PGi and labeled axons were identified near catecholamine-containing neurons labeled with dopamine-β-hydroxylase-immunoreactivity (DβH-ir). A dense field of PHA-L-positive terminals was seen within the A7 cell group which was mainly ipsilateral to PHA-L injections made into either the RMg or the Gi/PGi. Many PHA-L-positive terminals were closely apposed to DβH-ir A7 perikarya or proximal dendrites. A modest number of terminals was seen within the A5 and LC cell groups. In the second experiment, a unilateral injection of the retrograde tracer, Fluoro-Gold, was made into the A7 cell group and brainstem sections were processed for serotonin (5-HT) immunocytochemistry. Many neurons retrogradely labeled with Fluoro-Gold were seen in the RMg, but a much larger number were found in the Gi/PGi. Less than 5% of these Fluoro-Gold-labeled cells contained 5-HT-immunoreactivity. The results of these experiments indicate that the RMg and Gi/PGi have a substantial population of non-serotonergic neurons which project to the A7 noradrenergic cell group.     

Axonal projections between fetal spinal cord transplants and the adult rat spinal cord: a neuroanatomical tracing study of local interactions.

Three neuroanatomical tracers have been employed to map the axonal projections formed between transplants of fetal spinal cord tissue and the surrounding host spinal cord in adult rats. Solid pieces of embryonic day 14 (E14) rat spinal cord were placed into hemisection aspiration cavities in the lumbar spinal cord. Injections of either (1) a mixture of horseradish peroxidase and wheat germ agglutinin- conjugated horseradish peroxidase, (2) Fluoro-Gold, or (3) Phaseolus vulgaris leucoagglutinin (PHA-L) were made into the transplants or the neighboring segments of the host spinal cord at 6 weeks to 14 months post-transplantation. Injections of anterograde and retrograde tracers into the transplants revealed extensive intrinsic projections that often spanned the length of the grafts. Axons arising from the transplants extended into the host spinal cord as far as 5 mm from the host-graft interface, as best revealed by retrograde labeling with Fluoro-Gold. Consistent with these observations, iontophoretic injections of PHA-L into the transplants also produced labeled axonal profiles at comparable distances in the host spinal cord, and in some instances elaborate terminals fields were observed surrounding host neurons. The majority of these efferent fibers labeled with PHA-L, however, were confined to the immediate vicinity of the host-graft boundary, and no fibers were seen traversing cellular partitions between host and transplant tissues. Host afferents to the transplants were also revealed by these tracing methods. For example, the injection of Fluoro-Gold into the grafts resulted in labeling of host neurons within the spinal cord and nearby dorsal root ganglia. In most cases, retrogradely labeled neurons in spinal gray matter were located within 0.5 mm of the graft site, although some were seen as far as 4-6 mm away. The distance and relative density of ingrowth exhibited by host axons into the grafts, however, appeared modest based upon the results of HRP and Fluoro-Gold retrograde labeling. This was further confirmed with the PHA-L anterograde method. Whereas some host fibers were seen extending into the transplants, the majority of PHA-L containing axons formed terminal-like profiles at or within 0.5 mm of the host-graft interface. The comprehensive view of intrinsic connectivity and host-graft projections obtained in these studies indicates that intraspinal grafts of fetal spinal cord tissue can establish a short-range intersegmental circuitry in the injured, adult spinal cord. These observations are consistent with the view that such grafts may contribute to the formation of a functional relay between separated segments of the spinal cord after injury.(ABSTRACT TRUNCATED AT 400 WORDS)     

Differential calbindin-immunoreactivity in dopamine neurons projecting to the rat striatal complex

The calcium-binding protein calbindin-D28K is an anatomical marker that has been associated with resistance to neurodegeneration and with the electrophysiological characteristics of neurons. In this study, we compared the presence of calbindin in dopamine neurons projecting to three distinct functional regions of the striatal complex: the striatum, and the core and the shell of the nucleus accumbens. After iontophoretic injections of Fluoro-Gold in the dopaminergic terminal fields, the presence of tyrosine hydroxylase and calbindin were immunohistochemically assessed in the mesencephalon. It was found that the proportion of cells expressing calbindin was highest in the dopamine cells projecting to the core (72%), intermediate in the cells projecting to the shell (51%) and lowest in the cells projecting to the dorsolateral striatum (2.6%). These results do not support the idea that calbindin is a sufficient condition to confer resistance to neurodegeneration because shell-projecting neurons seem the most resistant to it. The present data also raise the question of the role of calbindin in the differences in firing characteristics among dopamine neurons projecting to the striatal complex.     

The centrally projecting Edinger–Westphal nucleus—I: Efferents in the rat brain

The oculomotor accessory nucleus, often referred to as the Edinger–Westphal nucleus [EW], was first identified in the 17th century. Although its most well known function is the control of pupil diameter, some controversy has arisen regarding the exact location of these preganglionic neurons. Currently, the EW is thought to consist of two different parts. The first part [termed the preganglionic EW—EWpg], which controls lens accommodation, choroidal blood flow and pupillary constriction, primarily consists of cholinergic cells that project to the ciliary ganglion. The second part [termed the centrally projecting EW—EWcp], which is involved in non-ocular functions such as feeding behavior, stress responses, addiction and pain, consists of peptidergic neurons that project to the brainstem, the spinal cord and prosencephalic regions. However, in the literature, we found few reports related to either ascending or descending projections from the EWcp that are compatible with its currently described functions. Therefore, the objective of the present study was to systematically investigate the ascending and descending projections of the EW in the rat brain. We injected the anterograde tracer biotinylated dextran amine into the EW or the retrograde tracer cholera toxin subunit B into multiple EW targets as controls. Additionally, we investigated the potential EW-mediated innervation of neuronal populations with known neurochemical signatures, such as melanin-concentrating hormone in the lateral hypothalamic area [LHA] and corticotropin-releasing factor in the central nucleus of the amygdala [CeM]. We observed anterogradely labeled fibers in the LHA, the reuniens thalamic nucleus, the oval part of the bed nucleus of the stria terminalis, the medial part of the central nucleus of the amygdala, and the zona incerta. We confirmed our EW–LHA and EW–CeM connections using retrograde tracers. We also observed moderate EW-mediated innervation of the paraventricular nucleus of the hypothalamus and the posterior hypothalamus. Our findings provide anatomical bases for previously unrecognized roles of the EW in the modulation of several physiologic systems.     

Observations on the projection from the perihypoglossal nuclei to the cerebellar cortex and nuclei in the cat

Summary The origin and distribution of cerebellar cortical and nuclear afferents from the perihypoglossal nuclei have been studied by means of retrograde transport after implants and injections of the wheat germ agglutinin-horse-radish peroxidase complex in the cat. The projection reaches all the cerebellar nuclei as well as vermal, intermediate and lateral parts of the cerebellar cortex. It is bilateral with an ipsilateral predominance and originates from all the perihypoglossal nuclei. The majority of the projecting neurons are situated caudally in the nucleus prepositus, while smaller numbers of projecting neurons are located in the rostral part of this nucleus, in the rostral nucleus intercalatus and in the nucleus of Roller. Small and medium-sized spindle-shaped to round cells located throughout the nucleus prepositus and in the rostral nucleus intercalatus have widespread projections, reaching all parts of the cerebellar cortex and nuclei, whereas large multipolar cells located in the caudal ventromedial part of the nucleus prepositus and in the nucleus of Roller have projections only to the flocculus and nodulus and the lateral and intermediate cortices.Retrograde fluorescent double-labelling experiments were made to investigate possible axonal branching of the perihypoglosso-cerebellar fibres. In experiments with injections of rhodamine-B-isothiocyanate (RITC) in the left cerebellar hemisphere and implants of crystalline Fluoro-Gold in the right hemisphere, single- and double-labelled cells were found intermingled throughout the perihypoglossal nuclei. Experiments with cerebellar cortical injections of RITC and implants of crystalline Fluoro-Gold in the underlying nucleus, demonstrated single- and double-labelled cells in the nucleus prepositus and the rostral nucleus intercalatus, while only single-labelled RITC neurons were seen in the group of large neurons in the ventromedial part of the nucleus prepositus and the nucleus of Roller. After injections of RITC in the cerebellar cortex and implants of crystalline Fluoro-Gold in the abducent nucleus on the same side, double-labelled neurons were found only in the rostral nucleus prepositus.     

Axotomized,adult basal forebrain neurons can innervate fetal frontal cortex grafts: A double fluorescent tracer study in the rat

Summary The ability of axonal regeneration of identified adult basal forebrain (BFB) neurons was examined after homotopic grafting of fetal neocortical tissue to a lesion cavity in the frontal neocortex. Using a four step experimental procedure, adult rats first received an injection of the fluorescent dye Fluoro-Gold (FG) into the sensorimotor cortex in order to label those neurons with projections to the area by retrograde axonal transport. After one week the injection area was removed by aspiration, leaving a cavity in the neocortex. One week later a block of fetal (E14) frontal cortical tissue was placed in the cavity. The animals were then allowed to survive for 6 weeks before a second fluorescent tracer, Nuclear Yellow (NY), was injected into the transplant. The animals were sacrificed 24 h later and analyzed by fluorescence microscopy. Both single labeled, FG and NY containing neurons and double labeled neurons containing both tracers were found in the BFB. The results demonstrate that adult BFB neurons can reestablish cortical projections into fetal cortical grafts (double labeled neurons), and they suggest that other BFB neurons, not initially innervating the lesioned cortical area, have sprouted into the transplant (NY labeled neurons).     

Estradiol-concentrating forebrain and midbrain neurons project directly to the medulla

The location and number of estradiol (E2)-concentrating neurons afferent to the dorsal medulla were determined by combining retrograde fluorescent tract tracing with steroid hormone autoradiography. Injections of Fluro-Gold were made into the medulla of 80 day old, ovariectomized, and adrenalectomized female rats. After 7 days survival to allow for retrograde transport, females were injected with [3H]estradiol; they were then perfused and their brains processed for steroid hormone autoradiography. Following a 4-12 month exposure period, autoradiograms were developed and microscopically analyzed for the presence of E2-concentrating neurons that project to the medulla. Numerous E2-concentrating neurons were identified that send axons directly to the medulla; the majority were found in the bed nucleus of the stria terminalis, paraventricular nucleus of the hypothalamus, central nucleus of the amygdala, and the central gray. Of the E2-concentrating neurons in the bed nucleus of the stria terminalis, 12.7% also projected to the medulla. E2-concentrating neurons that sent axons to the medulla were also identified in and ventromedial to the lateral parvicellular subdivision in the caudal half of the paraventricular nucleus of the hypothalamus (69.4%). Over one-third of the E2-concentrating neurons found in the central nucleus of the amygdala coursed to the medulla. The central gray was the only mesencephalic brain region that contained E2-concentrating neurons that projected to the medulla (41.9%). The medulla-bound E2-concentrating forebrain and midbrain neurons identified in the present study may influence autonomic tone via direct projections.     

神经示踪定位SD大鼠长下行脊髓固有神经元胞体及其轴突投射的解剖位置

目的 利用神经示踪技术探讨SD大鼠长下行脊髓固有神经元及其轴突投射的解剖位置.方法 将荧光金(FG)注射入第1腰髓(L1)节段逆行标记大鼠下行脊髓固有神经元(DPNs)胞体;将顺行神经示踪剂生物素葡聚糖胺(BDA)注射到脊髓第3和第4颈髓处标记此处的DPNs胞体及其长下行脊髓固有束(LDPT).固定取材与切片染色后,检...