Veronique G.J.M. VanderHorst

Organization of lumbosacral motoneuronal cell groups innervating hindlimb, pelvic floor, and axial muscles in the cat

In a study on descending pathways from the nucleus retroambiguus (NRA) to hindlimb motoneurons (see accompanying paper), it appeared impossible, using data from the literature, to precisely determine which muscles were innervated by the motoneurons receiving the NRA fibers. This lack of data made it necessary to produce a detailed map of the lumbosacral motoneuronal cell groups in the cat. Therefore, 50 different muscles or muscle compartments of hindlimb, pelvic floor and lower back were injected with horseradish peroxidase (HRP) in 135 cases. The respective muscles were divided into ten groups: I, sartorius and iliopsoas; II, quadriceps; III, adductors; IV, hamstrings; V, gluteal and other proximal muscles of the hip; VI, posterior compartment of the distal hindlimb; VII, anterior compartment of the distal hindlimb; VIII, long flexors and intrinsic muscles of the foot; IX, pelvic floor muscles; and X, extensors of the lower back and tail. The L4‐S2 segments were cut and incubated, and labeled motoneurons were counted and plotted. A new method was developed that made it possible, despite variations in size and segmental organization between the different cases, to compare the results of different cases. The results show that the spatial interrelationship between the hindlimb and pelvic floor lumbosacral motoneuronal cell groups remains constant. This finding enabled the authors to compose an accurate overall map of the location of lumbosacral motoneuronal cell groups. The general distribution of the motoneuronal cell groups is also discussed in respect to their dorsoventral, mediolateral, and rostrocaudal position within the lumbosacral ventral horn. J. Comp. Neurol. 382:46‐76, 1997.

Distinct Cell Groups In The Lumbosacral Cord Of The Cat Project To Different Areas In The Periaqueductal Gray.

The periaqueductal gray (PAG) is involved in aggressive and defensive behavior, micturition, and lordosis. Especially for the latter two functions, PAG afferents from the lumbosacral cord are of vital importance because, in addition to information regarding homeostasis and thermoregulation, they convey information from the pelvic viscera and sex organs. In the present retro‐ and antero‐grade tracing study, the projection patterns of different lumbosacral cell groups in the PAG were determined. In the retrograde study, wheatgerm agglutinin‐horseradish peroxidase (WGA‐HRP) injections were made in the PAG and/or adjacent tegmentum, and in the anterograde study, WGA‐HRP was injected in different lumbosacral segments.

Estrogen receptor‐α and ‐β immunoreactive neurons in the brainstem and spinal cord of male and female mice: Relationships to monoaminergic, cholinergic, and spinal projection systems

For many populations of estrogen‐sensitive neurons it remains unknown how they are associated with central nervous system circuitries that mediate estrogen‐induced modulation of behavioral components. With the use of double‐labeling immunohistochemistry and tracing techniques, the relationships of estrogen receptor (ER)‐α‐ and ER‐β‐immunoreactive (IR) neurons in the mouse brainstem and spinal cord to monoaminergic, cholinergic, and spinal projection systems are explored. Similar distributions of ER‐IR neurons were present in females and males, with differences in labeling intensity of ER‐α immunoreactivity among males and estrogen‐, and oil‐treated females. Barringtons nucleus, the ventrolateral medulla, and the nucleus of the solitary tract contained spinal‐projecting ER‐α‐IR neurons, whereas ER‐α‐IR neurons in the periaqueductal gray, parabrachial nucleus, and catecholaminergic A1 cell group received spinal input. Numerous tyrosine hydroxylase (TH)‐IR ER‐α‐IR neurons were present in the ventral periaqueductal gray, nucleus of the solitary tract, A1 cell group, and lumbosacral cord. The dorsal raphe nucleus contained ER‐α‐IR and ER‐β‐IR neurons that colocalized with serotonin (5HT), and the reticulotegmental nucleus contained 5HT‐IR ER‐α‐IR neurons. Fibers IR for vesicular acetylcholine transporter (VAChT), TH, and 5HT were located among ER‐α‐IR neurons in the dorsal horn and spinal autonomic regions. Robust staining for TH and VAChT, but not 5HT, was present among ER‐α‐IR neurons in the lumbosacral lateral collateral pathway. Possible modulatory actions of estrogen on each of these ER‐IR populations are discussed in the context of their specific function, including micturition, sexual behavior, ejaculation, cardiovascular and respiratory control, tactile and nociceptive sensory processing, anti‐nociception, endocrine regulation, and feeding. J. Comp. Neurol. 488:152–179, 2005.

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-1 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 B4 group, reticulotegmental nucleus (B9 group), lateral paragigantocellular nucleus and raphe magnus nucleus (B3 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.

Evidence for a periaqueductal gray–nucleus retroambiguus–spinal cord pathway in the rat

The nucleus retroambiguus in the cat has been shown to receive strong projections from the periaqueductal gray and to send fibres to distinct motoneuronal cell groups in brainstem and spinal cord. The nucleus retroambiguus plays a role in the production of vocalization and possibly copulatory (lordosis and mounting) behaviour. The question arises of whether a periaqueductal gray nucleus retroambiguus-spinal cord projection also exists in the rat. In the present study, using the retrograde wheatgerm agglutinin-horseradish peroxidase tracing technique, the nucleus retroambiguus was defined as the area in the caudal medulla oblongata (1.0-2.0 mm caudal to the obex) which sends its fibres mainly through the contralateral spinal cord. Further retrograde tracing experiments demonstrated that a relatively large number of neurons in the lateral and ventral periaqueductal gray and immediately adjacent tegmentum projects to the caudal medullary lateral tegmentum. Anterograde wheatgerm agglutinin-horseradish peroxidase tracing studies finally showed that neurons in the lateral periaqueductal gray and immediately adjoining tegmentum project specifically to the nucleus retroambiguus and not to the lateral tegmentum in general, which seems to be the case for the neurons in the ventral periaqueductal gray. The results indicate that in the rat a periaqueductal gray nucleus retroambiguus spinal cord projection also exists, which may be of crucial importance for the study of the anatomical and physiological framework of respiration, vocalization, and female and male reproductive behaviour in this animal.

Spinal projections of the A5, A6 (locus coeruleus), and A7 noradrenergic cell groups in rats.

The pontine noradrenergic cell groups, A5, A6 (locus coeruleus), and A7, provide the only noradrenergic innervation of the spinal cord, but the individual contribution of each of these populations to the regional innervation of the spinal cord remains controversial. We used an adeno‐associated viral (AAV) vector encoding green fluorescent protein under an artificial dopamine beta‐hydroxylase (PRSx8) promoter to trace the spinal projections from the A5, A6, and A7 groups. Projections from all three groups travel through the spinal cord in both the lateral and ventral funiculi and in the dorsal surface of the dorsal horn, but A6 axons take predominantly the dorsal and ventral routes, whereas A5 axons take mainly a lateral and A7 axons a ventral route. The A6 group provides the densest innervation at all levels, and includes all parts of the spinal gray matter, but it is particularly dense in the dorsal horn. The A7 group provides the next most dense innervation, again including all parts of the spinal cord, but is it denser in the ventral horn. The A5 group supplies only sparse innervation to the dorsal and ventral horns and to the cervical and lumbosacral levels, but provides the densest innervation to the thoracic intermediolateral cell column, and in particular to the sympathetic preganglionic neurons. Thus, the pontine noradrenergic cell groups project in a roughly topographic and complementary fashion onto the spinal cord. The pattern of spinal projections observed suggests that the locus coeruleus might have the greatest effect on somatosensory transmission, the A7 group on motor function, and the A5 group on sympathetic function. J. Comp. Neurol. 520:1985–2001, 2012.

Monosynaptic projections from the lateral periaqueductal gray to the nucleus retroambiguus in the rhesus monkey: Implications for vocalization and reproductive behavior

The periaqueductal gray (PAG) is known to be essential for vocalization and reproductive behavior. The PAG controls components of these behaviors by means of projections to the nucleus retroambiguus (NRA), a group of premotor neurons in the caudal medulla oblongata. In the accompanying study (VanderHorst et al., 2000 [accompanying study]), the NRA and its lumbosacral projections have been identified in the rhesus monkey. The present light and electron microscopical tracing study describes the PAG‐NRA pathway in primates. To locate midbrain neurons projecting to the NRA, wheat germ agglutinin horseradish peroxidase (WGA‐HRP) was injected into the NRA in six monkeys. To determine the distribution pattern of PAG axons in the medulla oblongata, WGA‐HRP was injected into the PAG and adjacent tegmentum in three additional monkeys. In one of these three monkeys, biotinylated dextran amine and cholera toxin subunit b were injected into the lumbosacral cord to retrogradely identify NRA neurons. The results show that a compact group of neurons in the medial part of the lateral PAG at the intercollicular level sends a dense projection to the NRA. The projection is bilateral with a clear ipsilateral predominance. At the ultrastructural level, there are monosynaptic contacts between PAG fibers and NRA neurons, including NRA neurons that project to the lumbosacral cord. The synaptic contacts were primarily asymmetrical and the labeled terminal profiles contained spherical and dense core vesicles. It is concluded that there exists a strong and direct PAG‐NRA pathway in the rhesus monkey. Because NRA neurons projecting to the lower lumbar cord are included, the PAG‐NRA projection is likely to be involved not only in vocalization but also in other behaviors, such as receptive posture. J. Comp. Neurol. 424:251–268, 2000.

Monosynaptic projections from the nucleus retroambiguus to motoneurons supplying the abdominal wall, axial, hindlimb, and pelvic floor muscles in the female rhesus monkey

The nucleus retroambiguus (NRA) consists of premotor neurons in the caudal medulla. It is involved in expiration, vomiting, vocalization, and probably reproductive behavior by means of projections to distinct motoneuronal cell groups. Because no information is available about the NRA and its efferent pathways in primates, the present study examines NRA projections to the lumbosacral spinal cord in female rhesus monkeys. To identify the NRA, wheat germ agglutinin‐horseradish peroxidase (WGA‐HRP) was injected into the lumbosacral cord in three monkeys. To study the distribution of NRA axons in the lumbosacral cord, WGA‐HRP injections were made into the NRA in seven monkeys. To identify motoneuronal cell groups receiving input from the NRA, the same seven monkeys also received cholera toxin subunit b (CTb) injections into different hindlimb, axial, and pelvic floor muscles. The results show that NRA neurons projecting to the lumbosacral cord are mainly located between 1 to 4 mm caudal to the obex. They send numerous axons to external oblique and pelvic floor motoneurons, whereas projections to iliopsoas and axial motoneurons are less numerous. The projections are bilateral, but show a clear contralateral predominance in the iliopsoas, axial, and pelvic floor motoneuronal cell groups. At the ultrastructural level, NRA‐terminal profiles make asymmetrical contacts with labeled and unlabeled dendrites in these motoneuronal cell groups and contain large amounts of spherical and a few dense core vesicles. It is concluded that the NRA is well developed in the monkey and that there exists a direct pathway from the NRA to lumbosacral motoneurons in this species. The finding that the NRA projects to a somewhat different set of motoneuronal cell groups compared with other species fits the concept that it is not only involved in expiration‐related activities but also in species specific receptive and submissive behavior. J. Comp. Neurol. 424:233–250, 2000.

A concept for the final common pathway of vocalization and lordosis behavior in the cat

Publisher Summary Periaqueductal gray matter (PAG) integrates the autonomic and somatic components of survival and mating behavior. For example, PAG stimulation has been demonstrated to produce simultaneous changes in nociception and blood pressure, vocalization, jumping, arching of the back, micturition, and lordosis. This chapter discusses the projections from the PAG to the nucleus retroambiguus (NRA), especially the projections from the NRA to motoneurons not so much in the framework of vocalization but in the framework of lordosis behavior. NRA neurons also project directly to motoneurons, bypassing the spinal interneurons. The NRA neurons play the role of premotor interneurons, similar to the ones in the spinal intermediate zone. Premotor interneurons usually receive peripheral Ia afferents or input from cortico- and rubrospinal tracts, but this is not the case for the premotor interneurons in the NRA. A probable explanation is that the NRA interneurons have a special function that is, activating a set of motoneuronal cell groups located throughout the lower brainstem and entire spinal cord, totally independent of voluntary input or spinal reflexes. In this context, the NRA receives afferents from other sources such as the PAG and respiration related brainstem nuclei.

Nucleus retroambiguus 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 Onufs 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. J. Comp. Neurol. 382:77‐88, 1997.