Musculotopic organization of the motor neurons supplying the mouse hindlimb muscles: a quantitative study using Fluoro-Gold retrograde tracing

We have mapped the motor neurons (MNs) supplying the major hindlimb muscles of transgenic (C57/BL6J-ChAT-EGFP) and wild-type (C57/BL6J) mice. The fluorescent retrograde tracer Fluoro-Gold was injected into 19 hindlimb muscles. Consecutive transverse spinal cord sections were harvested, the MNs counted, and the MN columns reconstructed in 3D. Three longitudinal MN columns were identified. The dorsolateral column extends from L4 to L6 and consists of MNs innervating the crural muscles and the foot. The ventrolateral column extends from L1 to L6 and accommodates MNs supplying the iliopsoas, gluteal, and quadriceps femoris muscles. The middle part of the ventral horn hosts the central MN column, which extends between L2–L6 and consists of MNs for the thigh adductor, hamstring, and quadratus femoris muscles. Within these longitudinal columns, the arrangement of the different MN groups reflects their somatotopic organization. MNs innervating muscles developing from the dorsal (e.g., quadriceps) and ventral muscle mass (e.g., hamstring) are situated in the lateral and medial part of the ventral gray, respectively.MN pools belonging to proximal muscles (e.g., quadratus femoris and iliopsoas) are situatedventral to those supplying more distal ones (e.g., plantar muscles). Finally, MNs innervatingflexors (e.g., posterior crural muscles) are more medial than those belonging to extensors ofthe same joint (e.g., anterior crural muscles). These data extend and modify the MN maps in the recently published atlas of the mouse spinal cord and may help when assessing neuronal loss associated with MN diseases

Nucleus retroambiguus-spinal pathway in the mouse:Localization, gender differences, and effects of estrogen treatment

Nucleus retroambiguus (NRA)-motoneuronal projections are species-specific and serve expiration, Valsalva maneuvers, vocalization, and sexual behavior. In cat and monkey, estrogen induces sprouting of NRA-spinal axons. This pathway may thus serve as a model to study mechanisms through which estrogen induces neuronal plasticity. In this study, NRA-spinal projections are described in adult mice by using anterograde and retrograde tracing techniques, with attention to gender, strain (CD-1 and C57BL/6), and estrogen-induced changes (in ovariectomized females). Labeled NRA-spinal neurons at the level of the decussation of the corticospinal tract were most numerous after tracer injections into the thoracic and upper lumbar cord. They were medium-sized and had axons that descended through the contralateral cord. A group of small neurons was labeled in the NRA immediately rostral to the decussation of the corticospinal tract after cervical and thoracic, but not after lumbar injections. This group projected mainly via an ipsilateral pathway. The main projections from the caudal NRA involved motoneurons in the thoracic and upper-lumbar cord that supply abdominal wall and cremaster muscles. Pelvic floor motoneurons did not receive substantial input. NRA-spinal projections, especially those involving the upper lumbar cord, were sexually dimorphic, being more extensive in males than in females. Moreover, they were more distinct in estrogen-treated females than in control females. Strain differences were not observed. The unique features of the caudal NRA-spinal pathway in the mouse are discussed in the framework of possible functions of this system, such as mating behavior and related social behaviors, parturition, thermoregulation, and control of balance. (c) 2005 Wiley-Liss, Inc

Nucleus retroambiguous projections to lumbosacral motoneuronal cell groups in the male cat

Recently, in the female cat, nucleus retroambiguus (NRA) projections have been described as distinct motoneuronal cell groups in the lumbar enlargement, possibly involved in lordosis behavior. The present study deals with the NRA-lumbosacral pathway in the male cat, Lumbosacral injections of wheat germ agglutinin-horseradish peroxidase (WGA-HRP) were made to localize and quantify retrogradely labeled neurons in the caudal medulla. These injections were preceded by spinal hemisections to distinguish between neurons with ipsi- and contralaterally descending axons. The NRA-lumbosacral fibers descended almost exclusively contralaterally, but neurons in areas surrounding the NRA projected mainly ipsilaterally. Injections of WGA-HRP were made in the region of the NRA to determine its targets in the lumbosacral cord. To distinguish between the contralateral NRA pathways and the ipsilateral projections from neurons in the adjoining lateral tegmentum, the injections were preceded by ipsilateral hemisections in C2. A new scaling method was used to compare the results of the different cases, despite variations in size and segmental organization. The results show that the distribution pattern of anterogradely labeled fibers in the lumbosacral cord matched precisely the location of certain motoneuronal cell groups. The NRA projected densely to the abdominal wall and pelvic floor motoneurons in Onuf's nucleus, moderately to adductor longus, semimembranosus, and biceps femoris anterior motoneuronal cell groups, and only sparsely to iliopsoas and semitendinosus motoneuronal cell groups. Compared with the findings in the female, the NRA in the male cat projects more heavily to the biceps anterior and adductor longus and only sparsely to the iliopsoas and semitendinosus motoneuronal cell groups. These male-female differences are discussed. (C) 1997 Wiley-Liss. Inc

Estrogen induces axonal outgrowth in the nucleus retroambiguus-lumbosacral motoneuronal pathway in the adult female cat

In 1995, we discovered a new pathway in the cat, which originates from the nucleus retroambiguus (NRA) and terminates in a distinct set of lumbosacral hindlimb, axial, and pelvic floor motoneuronal cell groups [VanderHorst VG.JM, Holstege G (1995) Caudal medullary pathways to lumbosacral motoneuronal cell groups in the cat: evidence for direct projections possibly representing the final common pathway for lordosis. J Comp Neurol 359:457-475]. The NRA is a compact group of interneurons located laterally in the caudal medulla oblongata. Its projection to lumbosacral moloneurons is thought to represent the final common pathway for male mounting and for female receptive or lordosis behavior. However, females only display lordosis behavior when they are in estrus, which suggests that the NRA-lumbosacral pathway is only active during estrus. This raised the question of whether estrogen affects this pathway. The effect of estrogen on the NRA-lumbosacral projection was studied light microscopically, using wheat-germ agglutinin horseradish peroxidase (WGA-HRP) as a tracer. The rubrospinal pathway served as control. The density of labeled NRA fibers in their target hindlimb motoneuronal cell groups appeared abundant in estrous and very weak in nonestrous cats. Such differences were not found in the rubrospinal pathway. For electron microscopical study, the NRA projection to the semimembranosus motoneuronal cell group was selected. In this cell group, an almost ninefold increase of labeled profiles was found in estrous versus nonestrous cats. Moreover, the semimembranous motoneuronal cell group contained labeled growth cones in estrous, but not in nonestrous, cats. The present study is the first to show that estrogen induces axonal outgrowth of a precisely identified pathway in the adult mammalian central nervous system. The possible mechanisms underlying this outgrowth are discussed

The organization of the brainstem and spinal cord of the mouse: Relationships between monoaminergic, cholinergic, and spinal projection systems

Information regarding the organization of the CNS in terms of neurotransmitter systems and spinal connections in the mouse is sparse, especially at the level of the brainstem. An overview is presented of monoaminergic and cholinergic systems in the brainstem and spinal cord that were visualized immunohistochemically in inbred C57BL/6 and outbred CD-I mice. This information is complemented with data on spinal cord-projecting systems that were characterized using retrograde tracing, spinal hemisections, and double labeling techniques. Attention is given to differences in these systems related to spinal levels. The data are discussed with reference to studies in the rat, and to standardized information as provided in the atlas of the mouse brain. Although the overall organization of these systems in the mouse is largely similar to those in the rat, species differences are present in relative location, size and/or connectivity of cell groups. For example, catecholaminergic neurons in the (ventro)lateral pons (A5 and A7 cell groups) in the mouse project to the spinal cord mainly via contralateral, and not ipsilateral, pathways. The data further supplement information as provided in standardized brainstem. sections of the C57BL/6 mouse [Paxinos, G., Franklin, K.B.J., 2001. The mouse brain in stereotaxic coordinates. Academic Press, San Diego], especially with respect to the size and/or location of the catecholaminergic retrorubral field (A8 group), A5, A1, and C1 cell groups, and the serotonergic 134 group, reticulotegmental nucleus (139 group), lateral paragigantocellular nucleus and raphe magnus nucleus (133 group). Altogether this study provides a comprehensive overview of the spatial relationships of neurochemically and anatomically defined neuronal systems in the mouse brainstem, and spinal cord. (c) 2005 Elsevier B.V. All rights reserved

Industrial Resources: Logan County

Resources for the Economic Development: Logan County prepared by the Kentucky Department of Business Development, Division of Research and Planning in cooperation with the Russellville-Logan County Chamber of Commerce and the Cities of Adairville, Auburn and Lewisburg, 1988. The report includes, but is not limited to, information about: population, labor market, local manufacturing, transportation, utilities, fuel, water, industrial sites, local government and services, taxes, educational and health facilities, housing, communication, recreation, natural resources, markets, and climate

Projections from estrogen receptor-alpha immunoreactive neurons in the periaqueductal gray to the lateral medulla oblongata in the rhesus monkey

The periaqueductal gray (PAG) contains numerous estrogen receptor-alpha immunoreactive (ER-alpha IR) neurons that are distributed in a species-specific way. These neurons might modulate different types of behavior that are mediated by the PAG such as active and passive coping responses, analgesia, and reproductive behavior. In primates, it is not known whether ER-c, IR PAG neurons represent local interneurons and/or neurons that project to brainstem areas that control these behaviors. In this double labeling study, we asked whether ER-alpha IR neurons in the PAG of the rhesus monkey project to the nucleus retroambiguus (NRA), an area in the ventrolateral caudal medulla oblongata that is involved in expiration, vocalization, and reproductive behavior. Tracer was injected into the caudal lateral medulla oblongata to retrogradely label PAG neurons, and ER-alpha was visualized immunohistochemically. Although ER-alpha IR neurons and NRA-projection neurons were present at similar levels of the PAG, their distributions hardly overlapped. ER-alpha IR PAG neurons that project to the lateral caudal medulla represented less than 2% of ER-alpha IR PAG neurons. These double-labeled neurons were mainly located in the ipsilateral caudal PAG. The cluster of neurons in the medial part of the lateral PAG that projects specifically to the NRA-region did not contain double-labeled cells. The results indicate that only a few ER-alpha IR PAG neurons project to the NRA-region. This might be related to the modest effects of estrogen on mating-related behavior in primates compared most other mammalian species. Remaining ER-alpha. IR PAG neurons might act locally on other PAG neurons, or they might represent neurons that project to other areas. Furthermore, the finding that the distributions of ER-alpha IR neurons and neurons that project to premotor neurons in the NRA-region scarcely overlap illustrates that the PAG in primates is very highly organized into anatomically distinct regions compared with other species. (C) 2004 IBRO. Published by Elsevier Ltd. All rights reserved

Estrogen receptor-alpha immunoreactive neurons in the ventrolateral periaqueductal gray receive monosynaptic input from the lumbosacral cord in the rhesus monkey

Estrogen affects female sexual behavior, analgesia, and micturition in mammals. One of the possible sites at which estrogen might exert its effect on these functions is the periaqueductal gray (PAG). The PAG is involved in each of these functions, it receives sensory input relevant to these functions from the lumbosacral cord, and contains estrogen receptor-alpha immunoreactive (ER-alpha IR) neurons. The present light (LM) and electron microscopic (EM) study seeks to determine whether there are monosynaptic projections from the lumbosacral cord to ER-alpha IR neurons in the PAG of the female rhesus monkey. Tracer was injected into the lumbosacral cord to visualize the lumbosacral-PAG projection, and the distribution of ER-alpha IR neurons in the PAG was studied immunohistochemically. The medial part of the ventrolateral caudal PAG received the densest projection from the lumbosacral cord. Another prominent projection was found in the lateral PAG at the intercollicular level. Although ER-alpha IR neurons were widely distributed throughout the PAG, approximately 40%, of ER-alpha IR PAG neurons were located as a distinct cluster in the medial portion of the ventrolateral, caudal PAG. Double labeling experiments showed that the location of this cluster precisely overlapped with the densest lumbosacral-PAG projection. EM revealed that axons from the lumbosacral cord made asymmetrical synaptic contacts with unlabeled dendrites and ER-alpha IR neuronal somata in the ventrolateral PAG. It is concluded that there exists a specific, monosynaptic pathway from lumbosacral neurons to ER-alpha expressing PAG neurons in the rhesus monkey. This pathway might be involved in the mechanism of analgesia, blood pressure, mating behavior, and micturition. J. Comp. Neurol. 443:27-42, 2002. (C) 2002 Wiley-Liss, Inc

Axonal sprouting of a brainstem-spinal pathway after estrogen administration in the adult female rhesus monkey

The nucleus retroambiguus (NRA) is located in the caudal medulla oblongata and contains premotor neurons that project to motoneuronal cell groups in the brainstem and spinal cord. NRA projections to the lumbosacral cord are species specific and might be involved in mating behavior. In the female cat, this behavior is estrogen dependent, and estrogen induces axonal sprouting in the NRA-lumbosacral pathway. Because female receptive behavior in primates is not fully dependent on estrogen, the question arises as to whether the capacity of estrogen-induced sprouting is preserved in primates. The effect of estrogen was studied on the NRA-lumbosacral projection with the use of wheat germ agglutinin conjugated to horseradish peroxidase as a tracer in six adult ovariectomized rhesus monkeys with or without estrogen priming (three controls and three treated with 20 mug/day of estradiol benzoate subcutaneously for 14 days). Light microscopy showed that the density of arborizing labeled NRA axons in the lumbosacral cord was greater in estrogen-treated than in control animals. Ultrastructurally, labeled NRA terminal profiles were quantified in motoneuron pools that supply muscles of the abdominal wall, axial, and pelvic floor. After estrogen treatment, the average number of labeled terminal profiles per area of the abdominal wall, axial, and pelvic floor motoneuron pool increased 1.5-, 3.3-, and 2.8-fold, respectively. In the estrogen-treated cases, 8.9% of labeled terminal profiles showed characteristics of growth cones. In controls, such profiles were rarely observed. The results showed that estrogen induces axonal sprouting in a brainstem-spinal pathway in the adult female rhesus monkey. These findings supported the concept that the NRA-lumbosacral pathway may be involved in sexual behavior. Moreover, they demonstrated that a long descending brainstem-spinal tract in adult nonhuman primates retains the capacity for axonal sprouting. (C) 2002 Wiley-Liss, Inc