Leonora J. Mouton

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.

Emotional Motor System

This chapter focuses on the emotional motor system. It also discusses the somatic motor system in order to point out the similarities and differences between the two systems. The idea of the existence of an emotional motor system is primarily based on anatomical organization. The pathways of the somatic and emotional motor system are always separate until their termination on premotor interneurons or motoneurons. The function of the somatic and emotional motor system pathways is different. The emotional motor pathways play a role in basic survival behavior. The somatic or voluntary motor system, and especially its cortical parts, starts operating only after a relatively long time of processing environmental data, combined with information from the extensive memory banks in the various regions around the primary cortices. Moreover, the behavioral differences between animals and humans are not located in the emotional, but in the somatic motor system, which, as pointed out earlier, is nothing more than a tool of the emotional, or limbic system to fulfill its needs. In that respect, humans differ only slightly from other animals.

The Periaqueductal Gray In The Cat Projects To Lamina Viii And The Medial Part Of Lamina Vii Throughout The Length Of The Spinal Card.

The periaqueductal gray (PAG) plays an important role in analgesia as well as in motor activities, such as vocalization, cardiovascular changes, and movements of the neck, back, and hind limbs. Although the anatomical pathways for vocalization and cardiovascular control are rather well understood, this is not the case for the pathways controlling the neck, back, and hind limb movements. This led us to study the direct projections from the PAG to the spinal cord in the cat. In a retrograde tracing study horseradish peroxidase (HRP) was injected into different spinal levels, which resulted in large HRP-labeled neurons in the lateral and ventrolateral PAG and the adjacent mesencephalic tegmentum. Even after an injection in the S2 spinal segment a few of these large neurons were found in the PAG. Wheat germ agglutinin-conjugated HRP injections in the ventrolateral and lateral PAG resulted in anterogradely labeled fibers descending through the ventromedial, ventral, and lateral funiculi. These fibers terminated in lamina VIII and the medial part of lamina VII of the caudal cervical, thoracic, lumbar, and sacral spinal cord. Interneurons in these laminae have been demonstrated to project to axial and proximal muscle motoneurons. The strongest PAG-spinal projections were to the upper cervical cord, where the fibers terminated in the lateral parts of the intermediate zone (laminae V, VII, and the dorsal part of lamina VIII). These laminae contain the premotor interneurons of the neck muscles. This distribution pattern suggests that the PAG-spinal pathway is involved in the control of neck and back movements. Comparing the location of the PAG-spinal neurons with the results of stimulation experiments leads to the supposition that the PAG-spinal neurons play a role in the control of the axial musculature during threat display.

Segmental and laminar organization of the spinal neurons projecting to the periaqueductal gray (PAG) in the cat suggests the existence of at least five separate clusters of spino-PAG neurons.

The present retrograde tracing study in the cat describes the spinal cord projections to the periaqueductal gray (PAG), taking into account different regions of the PAG and all spinal segments. Results show that injecting different parts of the PAG leads to different laminar and segmental distributions of labeled spinal neurons. The impression was gained that at least five separate clusters of spinal neurons exist. Cluster I neurons are found in laminae I and V throughout the length of the cord and are probably involved in relaying nociceptive information to the PAG. Cluster II neurons lie in the ventrolateral part of laminae VI–VII of the C1–C4 spinal cord and were labeled by injecting the ventrolateral or lateral part of the rostrocaudal PAG or the deep tectum. Cluster III neurons are located in lamina X of the thoracic and upper lumbar cord and seem to target the PAG and the deep tectum. Cluster IV neurons are located in the medial part of laminae VI–VII of the lumbosacral cord and seem to project predominantly to the lateral and ventrolateral caudal PAG. These neurons may play a role in conveying tactile stimuli to the PAG during mating behavior. Neurons of cluster V are located in the lateral part of lamina I of L6–S2 and in laminae V–VII and X of S1–S3. They are labeled only after injections into the central portion of the lateral and ventrolateral caudal PAG and probably relay information concerning micturition and mating behavior. J. Comp. Neurol. 428:389–410, 2000.

Afferent projections to the pontine micturition center in the cat

The pontine micturition center (PMC) or Barringtons nucleus controls micturition by way of its descending projections to the sacral spinal cord. However, little is known about the afferents to the PMC that control its function and may be responsible for dysfunction in patients with urge‐incontinence and overactive bladder. In five female cats, wheatgerm agglutinin‐conjugated horseradish peroxidase (WGA‐HRP) injections were made in the PMC and adjoining dorsolateral pontine tegmentum. Retrogradely labeled neurons were found in a large area, including the medullary and pontine medial and lateral tegmental field; dorsomedial, lateral, and ventrolateral periaqueductal gray matter (PAG); posterior hypothalamus; medial preoptic area (MPO); bed nucleus of the stria terminalis; central nucleus of the amygdala; and infralimbic, prelimbic, and insular cortices. To verify whether these areas indeed project specifically to the PMC or perhaps only to adjacent structures in the pontine tegmentum, in 67 cats 3H‐leucine or WGA‐HRP injections were made in each of these regions. Five cell groups appeared to have direct connections to the PMC, the ventromedial pontomedullary tegmental field, the ventrolateral and dorsomedial PAG, the MPO, and the posterior hypothalamus. The possible functions of these projections are discussed. These results indicate that all other parts of the brain that influence micturition have no direct connection with the PMC. J. Comp. Neurol. 494:36–53, 2006.

Physical Fitness in People After Burn Injury: A Systematic Review

OBJECTIVE To gain insight into the physical fitness of people after burn injury compared with healthy subjects, and to present an overview of the effectiveness of exercise training programs in improving physical fitness in people after burn injury. DATA SOURCES Electronic databases EMBASE, PubMed, and Web of Science were searched for relevant publications. Additionally, references from retrieved publications were checked. STUDY SELECTION The review includes studies that provide quantitative data from objective measures of physical fitness of both the intervention group and the control group. DATA EXTRACTION Characteristics of each study such as study design, institution, and intervention are reported, as well as mean ages and burn sizes of the subjects. Results are divided into 5 components of physical fitness-muscular strength, muscular endurance, body composition, cardiorespiratory endurance, and flexibility-and reported for each component separately. DATA SYNTHESIS Eleven studies met the inclusion criteria, and their methodological quality was assessed using the PEDro score and a modified Sackett scale. Six studies were used for the comparison of physical fitness in burned and nonburned subjects, and 9 studies for evaluating the effectiveness of exercise training programs. CONCLUSIONS Physical fitness is affected in people with extensive burns, and exercise training programs can bring on relevant improvements in all components. However, because of the great similarities in the subjects and protocols used in the included studies, the current knowledge is incomplete. Future research should include people of all ages with a broad range of burn sizes, for both short-term and long-term outcomes.

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.

Two parts of the nucleus prepositus hypoglossi project to two different subdivisions of the dorsolateral periaqueductal gray in cat

The dorsolateral column of the mesencephalic periaqueductal gray (PAG) is a separate part of the PAG. Its afferent sources, efferent targets, and neurochemical properties differ from the adjacent PAG columns. The dorsolateral PAG is thought to be associated with aversive behaviors, but it is not yet understood how these behaviors are brought about. To elucidate the function of the PAG further, in the present study we investigated which brainstem regions project to the dorsolateral PAG. Wheat germ agglutinin‐horseradish peroxidase (WGA‐HRP) injections involving the dorsolateral PAG, but extending into the lateral part, resulted in many retrogradely labeled cells in the pontine and medullary tegmentum bilaterally. However, it was concluded that these neurons were labeled from the lateral PAG, because no anterograde labeling was found in the dorsolateral PAG after a large injection into the tegmentum. Retrogradely labeled cells were also found in the nucleus prepositus hypoglossi (PPH), mainly contralaterally. Injections of [3H]leucine or WGA‐HRP in the PPH resulted in anterogradely labeled fibers in the dorsolateral PAG. Two separate distribution patterns were found. The caudal and intermediate PPH projected to a small region on the dorsolateral edge of the dorsolateral column, whereas the supragenual PPH distributed labeled fibers to all other parts of the dorsolateral PAG, except the area on the dorsolateral edge. These separate PPH projections suggest that two subdivisions exist within the dorsolateral PAG. The present findings suggest a role for the dorsolateral PAG in the oculomotor system. J. Comp. Neurol. 492:303–322, 2005.

Lamina I-periaqueductal gray (PAG) projections represent only a limited part of the total spinal and caudal medullary input to the PAG in the cat.

The periaqueductal gray is well known for its involvement in nociception control, but it also plays an important role in the emotional motor system. To accomplish these functions the periaqueductal gray receives input from the limbic system and from the caudal brainstem and spinal cord. Earlier studies gave the impression that the majority of the periaqueductal gray projecting cells in caudal brainstem and spinal cord are located in the contralateral lamina I, which is involved in nociception. The present study in the cat, however, demonstrates that of all periaqueductal gray projecting neurons in the contralateral caudal medulla less than 7% was located in lamina I. Of the spinal periaqueductal gray projecting neurons less than 29% was located in lamina I. However, within the spinal cord large segmental differences exist: in few segments of the enlargements the lamina I-periaqueductal gray projecting neurons represent a majority. In conclusion, although the lamina I-periaqueductal gray projection is a very important nociceptive pathway, it constitutes only a limited part of the total projection from the caudal medulla and spinal cord to the periaqueductal gray. These results suggest that a large portion of the medullo- and spino-periaqueductal gray pathways conveys information other than nociception.

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.