Sexual differences in the distribution of substance P immunoreactive fibers in the ventral horn of the rat lumbar spinal cord

Early appearance of acetylcholinergic, serotoninergic, and peptidergic neurons and fibers in the developing human central nervous system

Animal experiments have already shown that neurotransmitters and neuropeptides are not only important for normal functioning of the adult central nervous system (CNS) but are also crucial to its development. However, information on the spatio-temporal distribution of these endogenous substances in the developing human CNS is still scarce. With the use of immunocytochemical staining and a constant supply of properly fixed human abortuses from southern China, an early appearance of acetylcholinesterase, enkephalin, and substance P immunoreactivities was detected first in the spinal cord (weeks 5 to 7 of gestation), then in the brainstem nuclei (weeks 11 to 12). Their overlapping localizations in many regions of the CNS suggest possible interactions among neurons containing these substances, which are in turn important for the proper establishment of the neuronal circuitry. Immunoreactivity for neuropeptide Y appeared initially in the lateral region of upper segments of the spinal cord at week 12 of gestation, then spread latero-medially and cranio-caudally to the sacral region. In the hippocampus, neuropeptide Y neurons appeared from week 15 onwards. Serotoninergic neurons were found in the dorsal raphe nucleus at week 10 and then decreased in number as the fetus grew older. Somatostatin releasing inhibitory factor, vasopressin, and oxytocin were detected in the hypothalamus from weeks 12 to 14 onwards, and monoamine oxidase, succinic dehydrogenase, parvalbumin, calbindin D28K, and vasoactive intestinal peptide were found in the visual cortex at midgestation. The early appearance and the abundance of the neurotransmitters and neuropeptides in the developing CNS indicate that they may play a key role in neuronal differentiation.

5-HT1A receptor mRNA expressions differ in the embryonic spinal cord of male and female rats

During critical periods of development, the effects of testosterone (T) on promoting androgenization of the central nervous system (CNS) are reflected not only by behavior, morphology, and hormone secretion but also by gene expression. The mechanisms involved in sexual differentiation of the CNS, however, remain incompletely defined. The current set of experiments examined with in situ hybridization the dimorphism in 5-HT1A receptor mRNA expression in the embryonic rat spinal cord and the possible role of T in the dimorphism. We found sex-related differences in expression of 5-HT1A mRNA in the spinal cord, which were altered by a single injection of T. The results suggest that this gonadal steroid is responsible for the sexual dimorphism in 5-HT1A mRNA expression occurring during the critical period.

Distribution of dopamine immunoreactivity in the rat, cat and monkey spinal cord

In the present study, the distribution of dopamine (DA) was identified light microscopically in all segments of the rat, cat, and monkey spinal cord by using immunocytochemistry with antibodies directed against dopamine. Only fibers and (presumed) terminals were found to be immunoreactive for DA. Strongest DA labeling was present in the sympathetic intermediolateral cell column (IML). Strong DA labeling, consisting of many varicose fibers, was found in all laminae of the dorsal horn, including the central canal area (region X), but with the exception of the substantia gelatinosa, which was only sparsely labeled, especially in rat and monkey. In the motoneuronal cell groups DA labeling was also strong and showed a fine granular appearance. The sexually dimorphic cremaster nucleus and Onuf's nucleus (or its homologue) showed a much stronger labeling than the surrounding somatic motoneurons. In the parasympathetic area at sacral levels, labeling was moderate. The remaining areas, like the intermediate zone (laminae VI-VIII), were only sparsely innervated. The dorsal nucleus (column of Clarke) showed the fewest DA fibers, as did the central cervical nucleus, suggesting that cerebellar projecting cells were avoided by the DA projection. In all species, the descending fibers were located mostly in the dorsolateral funiculus, but laminae I and III also contained many rostrocaudally oriented fibers. It is concluded that DA is widely distributed within the spinal cord, with few differences between species, emphasizing that DA plays an important role as one of the monoamines that influences sensory input as well as autonomic and motor output at the spinal level.

Roles of steroid hormones and their receptors in structural organization in the nervous system

Due to their chemical properties, steroid hormones cross the blood-brain barrier where they have profound effects on neuronal development and reorganization both in invertebrates and vertebrates, including humans mediated through their receptors. Steroids play a crucial role in the organizational actions of cellular differentiation representing sexual dimorphism and apoptosis, and in the activational effects of phenotypic changes in association with structural plasticity. Their sites of action are primarily the genes themselves but some are coupled with membrane-bound receptor/ion channels. The effects of steroid hormones on gene transcription are not direct, and other cellular components interfere with their receptors through cross-talk and convergence of the signaling pathways in neurons. These genomic and non-genomic actions account for the divergent effects of steroid hormones on brain function as well as on their structure. This review looks again at and updates the tremendous advances made in recent decades on the study of the role of steroid (gonadal and adrenal) hormones and their receptors on developmental processes and plastic changes in the nervous system.

Galanin immunoreactivity in rat spinal lamina IX: emphasis on sexually dimorphic regions

Fibers and puncta that contained galanin-like immunoreactivity (GAL-LI) were distributed within lamina IX in a heterogeneous fashion. In cervical spinal segments, GAL-LI was almost absent except for the phrenic nucleus, which received the most robust GAL-LI innervation in lamina IX. In high and mid-thoracic segments, GAL-LI was found in moderate amounts, but the number of GAL-LI fibers gradually diminished in a caudal fashion, so that in low thoracic segments GAL-LI was sparse. Throughout all thoracic segments, GAL-LI fibers surrounded some clusters of motoneurons, while other groups of motoneurons were devoid of GAL-LI fibers. In lumbar segments, three sexually dimorphic nuclei received sparse to moderate amounts of GAL-LI, while GAL-LI in the remainder of lumbar lamina IX was very sparse. In sacral spinal segments, GAL-LI was very sparse. These data indicate that fibers and puncta that contain GAL-LI preferentially surround motoneurons that innervate muscles associated with the axial skeleton, while motoneurons that innervate appendicular or tail-associated skeletal muscles only have an occasional GAL-LI fiber associated with them.

Acetylcholinesterase-containing neurons, substance P and enkephalin fibers in the ventral horns of developing human embryos and fetuses

The presence of the acetylcholinesterase neurons and substance P-like and enkephalin-like fibers in the various nuclear columns of the ventral horns of the spinal cords was studied in the developing human by acetylcholinesterase histochemistry and substance P and enkephalin immunohistochemistry. Acetylcholinesterase-positive neurons initially appeared in the lateral neuronal columns and eventually were also observed in the medial columns as well as the median columns at various levels of the spinal cord by 10 weeks' gestation. Acetylcholinesterase-positive neurons in the lower sacral levels were not detected until 11-12 weeks' gestation. Diffused substance P- and enkephalin-like fibers were demonstrated as early as 10 weeks' gestation but did not align with any particular nuclear column until after 15 weeks' gestation. These fibers further increased in length and adopted reticular branching patterns and many of these tended to surround the cell bodies of the nuclear columns. Possible interaction of acetylcholinesterase neurons and substance P and enkephalin fibers would commence by 15 weeks' gestation.

Serotoninergic, noradrenergic, and peptidergic innervation of Onuf's nucleus of normal and transected spinal cords of baboons (Papio papio)

We have investigated with light and electron microscope immunocytochemistry the aminergic and peptidergic innervation of Onuf's nucleus in adult baboons. This nucleus, located in the ventrolateral part of the sacral spinal cord (S2 and S3), is considered to control urethral and anal sphincters and penile muscles. By comparison of intact and transected spinal cords, we have found that serotoninergic innervation has two origins: first, supraspinal, innervating the whole nucleus, with a possible predominance in the dorsal half; and second, intraspinal, corresponding to the ventral half of the nucleus. Thyrotropin-releasing hormone innervation appears largely coincident with serotonin, both in intact and transected spinal cords. Noradrenaline is exclusively of supraspinal origin, as attested by its disappearance below the level of the section. Substance P, calcitonin gene-related peptide, and Leu- and Met-enkephalin, which profusely innervate Onuf's nucleus, are on the contrary not affected by the transection. They most likely originate from the cord itself or the dorsal root ganglia. Thus, Onuf's nucleus innervation in the baboon arises both from supraspinal and intraspinal sources. The present study provides an anatomical basis for both voluntary and reflex controls of excretory and sexual functions in a primate. The same neurotransmitter (serotonin) according to its cell origin and discrete topography could exert different influences upon the same effector system.

Sexually dimorphic distribution of a galanin-like peptide in the central nervous system of the teleost fish Poecilia latipinna

Immunohistochemical techniques were used to visualize areas of the brain and spinal cord containing a galanin-like peptide in the teleost fish, the sailfin molly. Galanin-like immunoreactivity (GAL-LI) in both males and females was identified in neurons in the nucleus preopticus periventricularis, nucleus lateralis tuberis, and nucleus commissuralis. GAL-LI fibers had a comparable distribution in the forebrain, preoptic, hypothalamic, and visceral sensory areas of both sexes. In striking contrast to these areas, the optic tectum, torus semicircularis, brainstem tegmentum, and spinal cord of the male contained much higher levels of GAL-LI than the female. GAL-LI in these dimorphic areas in the female was limited to single fiber bundles in the ventromedial tegmentum and in the trigeminal system. Additionally, a population of neurons in the preoptic nucleus was found to contain GAL-LI in the male only. Sexual dimorphism was especially prominent in the spinal cord, where extensive GAL-LI fibers were found in the male only. These fibers were oriented in the longitudinal plane and confined largely to the gray matter. Comparative studies were performed on the goldfish spinal cord, in which GAL-LI was localized solely in the dorsal horn and exhibited no sexual dimorphism. Further, examination of spinal cord material from neonatal mollies revealed a lack of spinal GAL-LI at this developmental stage. As the extent of GAL-LI in the male molly spinal cord differs from both the goldfish and from that reported for the mammalian spinal cord, and a prominent sexual dimorphism in GAL-LI extends from the diencephalon to the caudal spinal cord, it is suggested that a galanin-like peptide may play a unique, sex-specific role in this species.

Peptidergic innervation of the cremaster nucleus. I. A sexually dimorphic population of substance P-containing intraspinal neurons exists in the substance P pathway to the rat cremaster nucleus

The cremaster nucleus (CN) lies in the lumbar spinal cord and is sexually dimorphic: the male CN contains three times as many motoneurons as the female. The substance P (SP) innervation of the CN is also sexually dimorphic with males receiving a very prominent innervation which is greatly diminished in females. These investigations examined SP-containing neurons located in the ventral half of lamina IV and the lateral aspects of laminae V, VII, and IX, in lumbar spinal levels 1,2. SP-containing intraspinal neurons in these laminae are at least three times as numerous in males than females. This provides the first demonstration of a sexually dimorphic population of spinal neurons which is not motor or preganglionic in nature. These SP-containing interneurons are found within, or adjacent to, the SP-containing fibers which constitute the massive SP pathway to the male CN. Processes of these SP-containing neurons were observed to contribute to the formation of the SP pathway to the male CN. The immunohistochemically demonstrable presence of these lumbar 1,2, laminae IV-IX, SP-containing neurons validates former studies which suggested their existence (Gibson et al., Brain Research, 301 (1984) 243-251; Uda et al., Neurosci. Lett., 57 (1985) 185-190).

Calcitonin gene-related peptide and somatostatin immunoreactivities in the rat lumbar spinal cord: sexually dimorphic aspects

The immunohistochemical distribution of calcitonin gene-related peptide and somatostatin in rat lumbar spinal laminae VII-X was investigated using the peroxidase-antiperoxidase technique. Within L1,2 laminae VII and X, calcitonin gene-related peptide and somatostatin fibers demarcate the location of preganglionic sympathetic neurons in a similar fashion in either sex but somatostatin is distributed in a sexually dimorphic manner in the lumbosacral (L5-S2) spinal cord with the male rat containing more somatostatin fibers and neurons than females. Within the ventral horn (lamina IX), calcitonin gene-related peptide has a sexually dimorphic distribution. Calcitonin gene-related peptide varicose fibers are found within the sexually dimorphic male cremaster nucleus but are virtually absent in the female cremaster nucleus. Calcitonin gene-related peptide varicose fibers are nearly absent in the remainder of the male and female lamina IX: this area includes the other two known sexually dimorphic spinal motonuclei: the dorsomedial and dorsolateral nuclei. Virtually all motoneurons in the lumbosacral spinal cord which are not sexually dimorphic contain calcitonin gene-related peptide. However, calcitonin gene-related peptide containing motoneurons have a heterogeneous distribution within sexually dimorphic nuclei. Calcitonin gene-related peptide containing motoneurons within the male and female cremaster nucleus are extremely rare. Some motoneurons within the male and female dorsomedial and dorsolateral nuclei contain calcitonin gene-related peptide with the female dorsomedial and dorsolateral nuclei containing a greater percentage of calcitonin gene-related peptide-containing motoneurons (c. 50%) than males (c. 20%). Somatostatin fibers are preferentially located in sexually dimorphic nuclei of either sex and are distributed in a sexually dimorphic manner within these nuclei with males containing a greater amount of somatostatin fibers than females. The amount of somatostatin immunoreactivity is most dense in the medial aspect of the dorsolateral nucleus, dense in the dorsomedial nucleus, moderate in the cremaster nucleus, and sparse in the lateral portion of the dorsolateral nucleus. In addition, a small column of motoneurons, between the dorsomedial and dorsolateral nuclei at the L5 level, is outlined by somatostatin fibers in females but is absent in males. Somatostatin containing motoneurons were not observed within the lumbar sexually dimorphic nuclei of either sex.

The ontogeny of substance P- and serotonin-like immunoreactivities in the sexually dimorphic cremaster nucleus of the rat spinal cord

This study investigates the ontogeny of two transmitter systems which innervate the sexually dimorphic cremaster nucleus (CN). Since these transmitter systems arise from separate extra- and intraspinal sources, their ontological sequences differ. In males, substance P (SP) innervates CN motoneurons on postnatal day (P) 0, while serotonin (5-HT) is first observed on P2. SP reaches a mature innervation pattern on P20, while 5-HT maturation is prolonged to P40-60. It is suggested that part of the reason for the differing rates of development of 5-HT and SP within CN is due to the source of the innervating fibers; 5-HT descends from the brainstem while SP is of intraspinal origin. On P6, the SP innervation of the dorsal processes of the male CN is so advanced that the spinal cord may be 'sexed' according to the male presence, or the female 'absence', of this SP pattern. In developing and adult females, the 5-HT innervation of the CN is greater than the SP innervation. In addition, the 5-HT and SP innervation of the female CN is greater than the surrounding motor columns. Compared to surrounding ventral gray horn motor nuclei, the CN receives a slightly delayed SP and 5-HT innervation and this may be a reflection of the postnatal formation of the cremaster muscle.

Target regulation of the serotonin and substance P innervation of the sexually dimorphic cremaster nucleus

The effects of perinatal castrations on the serotonin (5-HT) and substance P (SP) innervation patterns of the adult male cremaster nucleus (CN) were examined in Sprague-Dawley rats. These investigations reveal that day-of-birth bilateral castration precludes cremaster muscle formation, significantly reduces CN motoneuron number, and dramatically reduces the 5-HT and SP innervation of the adult male CN. Day-of-birth castration reduces the adult CN SP innervation pattern to a greater degree than the 5-HT pattern and this may be attributed to a substantial loss of primary afferent information to the dorsal horn of the spinal cord. Furthermore, day-of-birth unilateral castration causes an ipsilateral reduction in the adult 5-HT and SP immunostaining patterns. This may be correlated with the failure of the ipsilateral cremaster muscle to form with a subsequent ipsilateral reduction of CN motoneuron number. On the contralateral side the intact testis is accompanied by normal cremaster muscle gross morphology, CN motoneuron number, and CN immunostaining. Together these observations suggest that the sexually dimorphic 5-HT and SP innervation of the male CN is predominantly under target control vs androgen control. Castration during adulthood does not alter the 5-HT and SP innervation patterns of CN; thus, a time-dependent period, probably initiated by cremaster muscle formation, underlies these target organ regulatory effects.