Assessing the strengths of motoneuron inputs: different anatomical and physiological approaches compared.
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Animals↗
Biomedical subjects
G Holstege
Publications and source records attributed to G Holstege.
The central control of micturition and continence: implications for urology.
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Animals↗
Three times as many lamina I neurons project to the periaqueductal gray than to the thalamus: a retrograde tracing study in the cat.
The number and distribution of lamina I neurons projecting to the periaqueductal gray (PAG) were examined by a retrograde tracing study in the cat. WGA-HRP injections in the intermediate and caudal PAG resulted in as much as 1600 labeled lamina I neurons throughout the length of the spinal cord, counted in a 1:4 series of sections. The lamina I-PAG projection was predominantly contralateral and most labeled lamina I neurons were found in the enlargements. Comparing these results with the number of lamina I-thalamic neurons leads to the conclusion that in the cat about three times as many lamina I neurons project to the PAG than to the thalamus. Considering this, one can conclude that the spino-PAG system is a virtually neglected area in pain research.
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Electrical stimulation of the sacral dorsal gray commissure evokes relaxation of the external urethral sphincter in the cat.
Stimulation of the pontine micturition center (PMC) results in micturition, i.e. an immediate relaxation of the urethral sphincter and a contraction of the detrusor muscle of the bladder. The PMC generates the bladder contraction by way of a direct excitatory pathway to the parasympathetic bladder motoneurons in the sacral cord. The idea is that the PMC produces the relaxation of the urethral sphincter via direct projections to GABAergic neurons in the dorsal gray commissure (DGC), which, in turn, inhibit the urethral sphincter motoneurons. According to this hypothesis, electrical stimulation in the DGC in three cats should result in relaxation of the urethral sphincter. The results were in total agreement with this concept. During DGC stimulation a sharp decrease of the urethral pressure was found, the strength of which depended completely on the amplitude of the electrical stimulation.
Animals↗
Estrogen receptor-alpha-immunoreactive neurons in the periaqueductal gray of the adult ovariectomized female cat.
Anatomical and physiological studies in rodent and cat have shown that distinct parts of the midbrain periaqueductal gray (PAG) are important for the estrogen dependent, female reproductive behavior. The present study gives a detailed overview of the estrogen receptor-alpha-immunoreactive (ER-IR) neurons in the PAG in the cat. ER-IR neurons were found throughout the rostrocaudal extent of the PAG and laterally adjacent tegmentum, but were most numerous at caudal levels. The lateral and dorsal PAG contained most ER-IR neurons, whereas moderate numbers were found dorsolaterally. In these areas, only very few ER-IR neurons were found near the border of the ependymal layer. Except for the rostral dorsal raphe nucleus, the ventral PAG contained only few ER-IR neurons.
Animals↗
The anatomy of the central control of posture: consistency and plasticity.
Posture is usually thought to be steered by brainstem and cortical structures that have access to the motoneurons and their premotor interneurons of the axial and neck muscles. The present paper describes these pathways and their relation with gaze control structures. All these systems belong to the medial component of the so-called voluntary motor system. On the other hand, in the cat there also exist several postures that are not steered by the somatic, but by the emotional motor system. Examples are arching of the back and mating postures. The pathways thought to be involved in these behaviours are described. They belong to the lateral component of the emotional motor system and, especially in case of mating postures, are extremely plastic. They have been demonstrated to be almost 10 times as strong in oestrus than in non-oestrus cats.
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The emotional motor system in relation to the supraspinal control of micturition and mating behavior.
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Animals↗
Premature ejaculation and serotonergic antidepressants-induced delayed ejaculation: the involvement of the serotonergic system.
Premature ejaculation has generally been considered a psychosexual disorder with psychogenic aetiology. Although still mainly treated by behavioural therapy, in recent years double-blind studies have indicated the beneficial effects of some of the serotonergic antidepressants (SSRIs) in delaying ejaculation. We describe here the neurophysiology and the peripheral neuroanatomy of ejaculation and provide a review of the involvement of serotonin in the central nervous system in relation to serotonergic nuclei and their projections. A hypothesis of the role of 5-HT1A and 5-HT2C receptors in premature ejaculation is postulated.
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The central nervous system control of micturition in cats and humans.
Recent findings concerning the central control of micturition in cats are compared to findings obtained from dynamic imaging studies in humans. In the cat, three areas in the brainstem and diencephalon are specifically implicated in the control of micturition: (1) Barrington's nucleus or the pontine micturition center in the dorsomedial pontine tegmentum directly excites bladder motoneurons and indirectly inhibits, via inhibitory interneurons in the medial sacral cord, urethral sphincter motoneurons; (2) the periaqueductal grey receiving bladder filling information; and (3) the pre-optic area of the hypothalamus possibly involved in determining the beginning of micturition. According to PET-scan studies, in humans the same supraspinal regions are active during micturition. In the cat another area, located in the ventrolateral pontine tegmentum and is called the L-region, which controls the motoneurons of the pelvic floor, including the external urethral sphincter. This region might be considered as the pontine storage center. In humans the L-region is especially active in volunteers who tried but did not succeed to micturate. The results suggest that in cats and humans at the brainstem and diencephalic levels micturition is organized in the same way.
Animals↗
Sensory and motor components of reproductive behavior: pathways and plasticity.
Reproductive behavior in most mammalian species consists of a highly stereotyped pattern of movements, is elicited by specific sensory stimuli and is sex steroid dependent. The present paper describes a concept of the pathways in the midbrain, brainstem and spinal cord which control the receptive posture of the female cat. The midbrain periaqueductal gray (PAG), which is an important structure in the Emotional Motor System (EMS), receives direct input from a distinct group of neurons in the dorsal horn of the lumbosacral cord. This cell group overlaps with the location of pelvic and to lesser extent, pudendal nerve primary afferents, which convey information from the pelvic viscera and sex organs to the central nervous system. The PAG, in turn, controls various motor components of female receptive behavior using different pathways. For example, immobility, which is one of the characteristics of receptive behavior, might be mediated by a diffuse pathway from the PAG, via the ventral part of the medial medullary tegmentum, to all parts of the spinal ventral horn. More specific components, such as hindlimb treading, lateral deviation of the tail and elevation of the lower back, are thought to be controlled by a circumscribed projection from the PAG to the nucleus retroambiguus (NRA). The NRA is a group of interneurons at the transition between brainstem and spinal cord and projects directly to distinct lumbosacral motoneuronal cell groups, which innervate muscles that are likely to be involved in the female receptive posture. Estrogen induces axonal sprouting of the NRA-lumbosacral pathway in adult female cats, which explains why female cats only display receptive behavior when estrogen levels are high.
Adult↗
Brain activation during micturition in women.
Experiments in the cat have led to a concept of how the CNS controls micturition. In a previous study this concept was tested in a PET study in male volunteers. It was demonstrated that specific brainstem and forebrain areas are activated during micturition. It was unfortunate that this study did not involve women, because such results are important for understanding urge incontinence, which occurs more frequently in women than in men. Therefore, a similar study was done in 18 right-handed women, who were scanned during the following four conditions: (i) 15 min prior to micturition (urine withholding); (ii) during micturition; (iii) 15 min after micturition; and (iv) 30 min after micturition. Of the 18 volunteers, 10 were able to micturate during scanning and eight were not, despite trying vigorously. Micturition appeared to be associated with significantly increased blood flow in the right dorsal pontine tegmentum and the right inferior frontal gyrus. Decreased blood flow was found in the right anterior cingulate gyrus during urine withholding. The eight volunteers who were not able to micturate during scanning did not show significantly increased regional cerebral blood flow in the right dorsal, but did so in the right ventral pontine tegmentum. In the cat this region controls the motor neurons of the pelvic floor. In the same unsuccessful micturition group, increased blood flow was also found in the right inferior frontal gyrus. In all 18 volunteers, decreased blood flow in the right anterior cingulate gyrus was found during the period when they had to withhold their urine prior to the micturition condition. The results suggest that in women and in men the same specific nuclei exist in the pontine tegmentum responsible for the control of micturition. The results also indicate that the cortical and pontine micturition sites are more active on the right than on the left side.
Adult↗
A PET study on cortical and subcortical control of pelvic floor musculature in women.
The pelvic floor musculature plays an important role in behaviors such as defecation, micturition, mating behavior, and vomiting. A recent positron emission tomography (PET) study revealed that structures belonging to the emotional motor system are involved in the control of the pelvic floor during micturition. However, there also exist brain structures involved in the voluntary motor control of the pelvic floor, and the present PET study was designed to identify these structures. Six adult female volunteers were scanned with the bolus injection of H2(15)O during the following four conditions: (1) rest, (2) repetitive pelvic floor straining, (3) sustained pelvic floor straining, and (4) sustained abdominal straining. The results revealed that the superomedial precentral gyrus, the most medial portion of the motor cortex, is activated during pelvic floor contraction and the superolateral precentral gyrus during contraction of the abdominal musculature. In these conditions, significant activations were also found in the cerebellum, supplementary motor cortex, and thalamus. The right anterior cingulate gyrus was activated during sustained pelvic floor straining. No activations were found in subcortical structures belonging to the emotional motor system. The results are discussed in light of the existing literature on human control of the pelvic floor and micturition.
Abdominal Muscles↗
Large segmental differences in the spinal projections to the periaqueductal gray in the cat.
The periaqueductal gray (PAG) is involved in motor activities, such as movements of the neck, back and hind limbs, cardiovascular regulation, micturition, vocalization, and mating behavior, as well as in nociception control. To accomplish these functions the PAG uses information from other parts of the limbic system, from the lower brainstem, and from the spinal cord. To study the ascending projections from the spinal cord to the PAG, tracer was injected in different parts of the PAG, and the number of retrogradely labeled neurons were counted for each spinal segment. Results show that large segmental differences exist in the number of PAG projecting neurons throughout the length of the spinal cord and that different parts of the spinal cord project to specific areas in the PAG.
Afferent Pathways↗
The lumbar cord location of the motoneurons innervating psoas and iliacus muscles: a single and double labeling study in the female Syrian golden hamster.
The spinal cord location of the motoneurons innervating the psoas and iliacus muscles was determined in the golden hamster. The results of single and double labeling studies, using the retrograde tracers horseradish peroxidase (HRP) and cholera toxin B-subunit (CTB), showed that both psoas and iliacus motoneurons were present ventrolaterally in the ventral horn in the caudal L1 to rostral L5 lumbar spinal segments with their motoneurons intermingled in one cell group. Further retrograde tracing studies demonstrated abdominal muscle motoneurons ventrolaterally in the ventral horn of the L1 and upper L2 segments. Double labeling experiments revealed that at these levels (caudal L1 and rostral L2), the abdominal muscle motoneurons were located dorsomedial to the psoas and iliacus motoneurons.
Abdominal Muscles↗
Estrogen receptor-immunoreactive neurons in the lumbosacral cord projecting to the periaqueductal gray in the ovariectomized female cat.
The periaqueductal gray (PAG) plays a crucial role in reproductive behavior. The present study investigates whether lumbosacral PAG-projecting neurons contain estrogen receptors. In four ovariectomized adult female cats, injections with cholera toxin subunit (CTb) were made into the PAG to retrogradely label PAG projecting neurons in the lumbosacral cord. Estrogen receptor immunoreactive ER-IR neurons in the lumbosacral cord were identified immunohistochemically using the antibody H222. PAG-projecting neurons that were immunoreactive for the estrogen receptor were very scarce, and predominantly present in the medial part of the ventral horn. The results indicate that only very few of the neurons relaying information from the urogenital organs to the PAG contain estrogen receptors.
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The pontine micturition center projects to sacral cord GABA immunoreactive neurons in the cat.
Stimulation of the pontine micturition center (PMC) results in micturition, i.e. an immediate relaxation of the bladder sphincter and a contraction of the detrusor muscle of the bladder. Earlier studies have shown that the bladder contraction is brought about by a direct excitatory pathway from the PMC to the parasympathetic bladder motoneurons in the sacral cord. How the PMC produces the inhibition of the bladder sphincter is not known. The present study in two adult male cats demonstrates at the ultrastructural level a direct pathway from the PMC to the dorsal gray commissure of the sacral cord. More than half (55%) of these terminals made contact with gamma amino butyric acid (GABA) immunoreactive neurons or somata, the others with non-GABA immunoreactive profiles. The PMC terminals contained many round vesicles, some dense cored vesicles and exclusively asymmetric synaptic clefts, which correspond with an excitatory pathway. A concept is put forward in which this pathway produces the relaxation of the bladder sphincter during micturition.
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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 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.
Afferent Pathways↗
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.
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