A developmental study of substance-P, somatostatin, enkephalin, and serotonin immunoreactive elements in the spinal cord of the North American opossum

Monoaminergic systems in the brainstem and spinal cord of the turtlePseudemys scripta elegansas revealed by antibodies against serotonin and tyrosine hydroxylase

With the aim of gaining more insight into the monoaminergic regulation of spinal motor systems in the turtle, we have studied the distribution of 5-HT (5-HTir) and tyrosine hydroxylase immunoreactivity (THir) in the brainstem and spinal cord of Pseudemys scripta elegans. 5-HTir cell bodies were located in the midline in nucleus raphe inferior, nucleus raphe superior, and laterally in nuclei reticularis superior and inferior and nucleus reticularis isthmi. THir cell bodies were located in the commissural nucleus, nucleus tractus solitarii, the locus coeruleus-subcoeruleus complex, nuclei reticularis superior and inferior, the pretectal area, and substantia nigra. 5-HTir and THir tracts were found in lateral and ventral bundles superficially in the brainstem. 5-HTir fibers in the spinal cord were located in a large dorsolateral and a smaller ventrolateral tract. In the gray matter, a high concentration of 5-HTir fibers were observed in areas I-IV and in the lateral motor column of cervical and lumbar enlargements. Areas V-VIII and area X were less intensively innervated, with the lowest fibre concentration in areas VII-VIII and area X. Throughout the spinal cord, THir nerve fibres were located in the same areas but with a lower density. Small bipolar 5-HTir and THir cell bodies were found ventromedially to the central canal especially in cervical and lumbosacral segments. Large THir cells were found in area IX in the caudal sacral and coccygeal spinal cord. THir cerebrospinal fluid-contacting cells were also found in the most caudal part of the brainstem and the upper cervical spinal cord. The well developed spinal 5-HT system and the less developed THir system provides an anatomical explanation for the monoaminergic modulation of turtle motoneuron membrane properties, which has been observed in electrophysiological experiments.

Ontogeny of descending serotonergic innervation and evidence for intraspinal 5-HT neurons in the mouse spinal cord

Neuronal networks in the mouse spinal cord express serotonin (5-HT)-induced rhythmic motor activity at early developmental stages (embryonic day (E) 12.5). Later in development, by post-natal day (P) 10, the 5-HT-evoked rhythmic motor activity matures and acquires an adult locomotor-like pattern. With the view to establishing a relationship between the ontogeny of locomotor networks and the maturation of spinal 5-HT systems, we have traced 5-HT immunoreactivity in the mouse spinal cord from E12.5 to PN10. By E12.5, descending 5-HT immunoreactive (5-HT-ir) fibers that likely originate from raphe nuclei were detected in the ventral and lateral funiculi, at anterior cervical spinal levels, but not at more caudal levels. Descending 5-HT-ir axons reached thoracic levels at E14.5 and lumbar levels at E16.5. Some 5-HT-ir fibers could be detected in the ventral and intermediate gray matter by E16.5, whereas the dorsal gray matter was not invaded before PN0. At PN10, a dense serotonergic innervation was restricted to the gray matter with a high concentration of 5-HT-ir fibers in three areas: dorsal horn, ventral horn (where motoneurons are located) and intermediate area. Surprisingly, from E16.5 to PN10, 5-HT-ir intraspinal neurons were found, exclusively at sacral levels. Their somata lay in the gray matter around the central canal and preferentially in the ventro-median part of the ventral horn. The functional significance of these sacral 5-HT-ir neurons is discussed.

The role of serotonin in reflex modulation and locomotor rhythm production in the mammalian spinal cord

Over the past 40 years, much has been learned about the role of serotonin in spinal cord reflex modulation and locomotor pattern generation. This review presents an historical overview and current perspective of this literature. The primary focus is on the mammalian nervous system. However, where relevant, major insights provided by lower vertebrate models are presented. Recent studies suggest that serotonin-sensitive locomotor network components are distributed throughout the spinal cord and the supralumbar regions are of particular importance. In addition, different serotonin receptor subtypes appear to have different rostrocaudal distributions within the locomotor network. It is speculated that serotonin may influence pattern generation at the cellular level through modulation of plateau properties, an interplay with N-methyl-D-aspartate receptor actions, and afterhyperpolarization regulation. This review also summarizes the origin and maturation of bulbospinal serotonergic projections, serotonin receptor distribution in the spinal cord, the complex actions of serotonin on segmental neurons and reflex pathways, the potential role of serotonergic systems in promoting spinal cord maturation, and evidence suggesting serotonin may influence functional recovery after spinal cord injury.

Serotonergic systems in the spinal cord of the amphibian urodele Pleurodeles waltl

The role of the monoamine serotonin (5-HT) in modulating the neural networks underlying axial locomotor movements was studied in an adult amphibian urodele, Pleurodeles waltl. 5-HT was applied to an in vitro brainstem-spinal cord preparation of P. waltl, which displayed fictive axial locomotor patterns following bath application of N-methyl-D-aspartate (5 microM) with D-serine (10 microM). Our results showed that 5-HT (1-25 microM) produces a reversible increase in the cycle duration and the duration of rhythmic bursting activity recorded extracellularly from ventral roots innervating the axial musculature. When applied alone, 5-HT does not trigger axial locomotor activity. The distribution pattern of 5-HT immunoreactive (5-HT-ir) cells along the spinal cord was investigated both in intact and in chronic spinal animals. The number of 5-HT-ir cell bodies is higher at brachial levels and decreases through crural levels. Sparse oval or fusiform 5-HT-ir somata are present within the gray matter, just ventrolateral to the central canal. Longitudinal fibers were detected throughout the entire white matter, except in the medial part of the dorsal funiculi. Two columns of intensely labeled and profusely branching thick and thin fibers associated with numerous varicosities run continuously along the ventrolateral surface of the spinal cord. Three weeks following full spinal cord transection at the level of the second spinal root, all longitudinal processes had disappeared, indicating their supraspinal origin, whereas the ventrolateral plexes remained, suggesting that they originated from intraspinal 5-HT-ir cell bodies. Our data showing that spinal 5-HT is organized according to a rostrocaudal gradient suggest that the 5-HT systems of P. waltl are not related to the presence of limb motor pools but more likely are related to axial central pattern generators (CPGs) networks down the length of the spinal cord. The possible involvement of these two sources (descending vs. intraspinal) of 5-HT innervation in the modulation of the axial CPGs is discussed.

Three-dimensional visualization of the distribution, growth, and regeneration of monoaminergic neurons in whole mounts of immature mammalian CNS

At birth, the opossum, Monodelphis domestica, corresponds roughly to a 14-day-old mouse embryo. The aim of these experiments was to compare the distribution of monoaminergic neurons in the two preparations during development and to follow their regeneration after injury. Procedures that allowed antibody staining to be visible in transparent whole mounts of the entire central nervous system (CNS) were devised. Neurons throughout the brain and spinal cord were stained for tyrosine hydroxylase (TH) and for serotonin (5-HT). At birth, patterns of monoaminergic cells in opossum CNS resembled those found in 14-day mouse embryos and other eutherian mammals. By postnatal day 5, immunoreactive cell bodies were clustered in appropriate regions of the midbrain and hindbrain, and numerous axons were already present throughout the spinal cord. Differences found in the opossum were the earlier presence of TH neurons in the olfactory bulb and of 5-HT neuronal perikarya in the spinal cord. Most, if not all, monoaminergic neurons in opossum were already postmitotic at birth. To study regeneration, crushes were made in cervical cords in culture. By 5 days, 8% of all TH-labeled axons and 14% of serotonergic axons had grown beyond lesions. Distal segments of monoaminergic axons degenerated. In CNS preparations from opossums older than 11 days, no regeneration of monoaminergic fibers occurred. Isolated embryonic mouse CNS also showed regeneration across spinal cord lesions, providing the possibility of using knockout and transgenic animals. Our procedures for whole-mount observation of identified cell bodies and their axons obviates the need for serial reconstructions and allows direct comparison of events occurring during development and regeneration.

Synaptic and nonsynaptic monoaminergic neuron systems in the lamprey spinal cord

In the lamprey spinal cord, dopamine- (DA) and 5-hydroxytryptamine-(5-HT) containing cells appear to play an important role in controlling the firing properties of motoneurons and interneurons and, thereby, in modulating the efferent motor pattern. To determine the detailed morphology and synaptic connectivity of the intraspinal DA and 5-HT systems in Lampetra fluviatilis and Ichthyomyzon unicuspis, DA and 5-HT antisera were used in light and electron microscopic immunocytochemical experiments. Two main groups of labeled cells were distinguished: DA-containing liquor-contacting (LC) cells distributed along the central canal, and 5-HT+DA-containing multipolar cells located near the midline ventral to the central canal. Both types were synaptically connected with other neuronal elements. The DA-immunoreactive LC cells, which extended a ciliated process into the central canal, received symmetrical synapses from unlabeled terminals containing small synaptic vesicles. The distal process of the LC cells could be traced to the lateral cell column, to the ventral aspect of the dorsal column, or to the ventromedial area. Ultrastructural analysis of DA fibers in these regions showed the presence of labeled terminals containing numerous small synaptic vesicles and a few dense-core vesicles. These terminals formed symmetrical synapses with unlabeled cell bodies and dendrites, with GABA-immunopositive LC cells, and with the multipolar DA+5-HT cells. The multipolar DA+5-HT cells also received input from unlabeled synapses. Intracellular recording from these cells showed that they received excitatory postsynaptic potentials in response to stimulation of fibers in the ventromedial tracts and dorsal roots. The terminals of the multipolar DA+5-HT neurons in the ventromedial spinal cord contained numerous dense-core vesicles and small synaptic vesicles, but no synaptic specializations could be detected. In addition, a small number of larger DA-immunoreactive cells were observed in the lateral cell column at rostral levels. The lamprey spinal cord thus contains distinct populations of synaptically interconnected monoaminergic neurons. Dopamine-containing LC cells synapse onto DA+5-HT-containing multipolar cells, in addition to GABAergic LC cells and unidentified spinal neurons. In contrast, the multipolar cells appear to exert their influence by nonsynaptic mechanisms.

Brain growth and neocortical development in the opossum

General brain growth and differentiation of the neocortex have been studied in the marsupial, Didelphis virginiana from the 10.5 day embryo through adulthood. Didelphis is born after a short gestation period of about 12.5 days, at a time when the telencephalic wall consists only of two layers and is considered to be at an embryonic stage of development. The cortical plate does not appear until late in the first postnatal week, thus neocortical development is totally a postnatal phenomenon in Didelphis as has been shown in other marsupial species examined to date. The general pattern of development and the establishment of the six-layered adult neocortex in Didelphis is similar to that described in eutherian mammals. Signs of cortical lamination can be seen as early as postnatal day 35 and the cytoarchitecture of a typical mammalian neocortex is well defined by postnatal day 60 in Didelphis prior to the onset of weaning.

Postnatal changes in the dorsal root reflex in the isolated spinal cord of the hamster, Mesocricetus auratus

Spontaneous activity has been demonstrated in the lumbar dorsal roots of isolated spinal cord preparations taken from animals ranging in age from 2 to 65 days. Peaks of activity were recorded at 2 and 5 weeks of age, with mean firing frequencies of 33 Hz and 28 Hz respectively. The firing frequency in weeks 3 and 4 was lower (15 Hz) as was the frequency in cords taken from animals older than 6 weeks. The pattern of the spontaneous dorsal root activity changed during the first 5 weeks of life. In cords taken from animals less than 10 days old, the roots fired single action potentials, producing a single broad peak in Inter Spike Interval plots (ISI). Dorsal root recordings made from cords taken from animals in weeks 2 and 3 of life exhibited both single spikes and bursts of action potentials. By the end of the third week of life, individual spike activity had declined and the bursts of action potentials characteristic of the adult pattern had become dominant, producing a bimodal ISI plot. Cross correlation analysis of dorsal root and dorsal horn activity in lumbar segments up to five segments apart, revealed an increasing degree of correlation developing over the first 4 weeks of postnatal life. Dorsal horn responses to dorsal root stimulation in cords taken from young animals were prolonged, lasting in excess of 250 msec. In the third week of life, the duration of the excitatory component of the response was reduced to approximately 50 msec by the development of an inhibitory phase.

Development of radial glia and astrocytes in the spinal cord of the North American opossum (Didelphis virginiana): an immunohistochemical study using anti-vimentin and anti-glial fibrillary acidic protein

We have shown previously that rubrospinal axons grow around a lesion of their pathway in developing opossums and that a critical period exists for that plasticity. As a first step toward addressing the possibility that glial maturation and/or the development of an astrocytic response to lesioning contribute to loss of rubrospinal plasticity, we have studied the normal development of radial glia and astrocytes in the spinal cord of the opossum by immunostaining for vimentin (Vim) and glial fibrillary acidic protein (GFAP). Vim-like immunoreactivity (Vim-LI) was present in radial glia throughout the spinal cord at birth (12 days after conception), whereas GFAP-like immunoreactivity (GFAP-LI) was limited to cells of comparable morphology in the ventral part of the cervical cord. The subsequent appearance of GFAP-LI followed ventral to dorsal and rostral to caudal gradients and by postnatal day (PD) 15, it was found in radial glia throughout the cord. At the same age, processes immunostained by either antibody had lost their radial orientation in the ventral horn of the cervical cord. The subsequent transformation from radial glia to astrocytes also followed ventral to dorsal and rostral to caudal gradients. By PD30, mature appearing astrocytes were immunostained by both antibodies at thoracic levels of the spinal cord, the levels lesioned in the plasticity experiments referred to above, and by PD41, they were found at all levels of the cord.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of descending fibers to the rat embryonic spinal cord

Onset and development of descending pathways to the rat embryonic spinal cord was examined by the use of retrograde transport of horseradish peroxidase (HRP). HRP was injected in the lower thoracic segments of the spinal cord of embryos ranging in age from embryonic day (E)14.5 to E20.5. A small number of labelled cells were found in the brain stem nuclei on E14.5: they were located in medullary as well as pontine reticular formation, lateral vestibular nucleus and interstitial nucleus of the medial longitudinal fasciculus. By E15.5 labelled cells were observed in the reticular formation of the caudal part of the medulla oblongata, medullary raphe nuclei, locus coeruleus, subcoeruleus nucleus, Barrington's nucleus and central gray of the midbrain. Cells in the red nucleus and in the nucleus of the solitary tract were labelled by E 16.5 and E17.5, respectively. Thereafter, labelled cells were first found in a few other nuclei: the gracile nucleus on E19.5 and the paraventricular nucleus on E20.5. The present study demonstrated that all the major supraspinal inputs except corticospinal fibers project to the lower thoracic spinal cord by E20.5.

The origins of descending projections to the lumbar spinal cord at different stages of development in the North American opossum

We have employed the retrograde transport of fast blue (FB) to identify the origins of descending projections to the lumbar cord of the opossum from postnatal day (PD)1, 12-13 days after conception, to maturity. When FB injections were made into the lumbar cord at PD1, supraspinal labeling was sparse and limited to the hypothalamus, the reticular formation, the coeruleus complex, the caudal raphe, and, in one case, the interstitial nucleus of the medial longitudinal fasciculus and the lateral vestibular nucleus. Only a few propriospinal neurons were labeled at cervical and thoracic levels. By PD3, however, supraspinal and propriospinal labeling was abundant and present in most of the areas labeled in the adult animal. A notable exception was the red nucleus which was not labeled until approximately PD10. Our results have been compared with those described in other species and discussed in light of their relevance to the development of descending control over hindlimb movement and developmental plasticity of descending spinal pathways.

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.

Distribution of somatostatin immunoreactivity in the forebrain of the squirrel monkey: Basal ganglia and amygdala

The distribution of somatostatin immunoreactivity in the basal ganglia and amygdala of the squirrel monkey (Saimiri sciureus) was studied with specific polyclonal antibodies directed against somatostatin-28 and somatostatin-28(1-12). Both antibodies gave similar results with regard to the distribution of somatostatin-immunoreactive neuronal profiles. A moderately dense and highly heterogeneous network of somatostatin-positive fibers was observed throughout the striatum. A dorsoventral gradient of increasing immunoreactivity was noted in the striatum and the caudate nucleus was found to strain generally less intensely than the putamen. The immunoreactive fibers within the striatum were mostly thin and varicose and formed patches corresponding to the striosomes, as visualized on adjacent sections immunostained for calbindin. Although some somatostatin cell bodies rimmed the striosomes, most of the positive cells were rather uniformly scattered in the striatum. These medium-sized cells were significantly smaller in the caudate nucleus (93 microns2, S.D. = 26 microns2) than in the putamen (122 microns2, S.D. = 39 microns2), but their density was significantly higher in the caudate nucleus (29.7 cells/mm2, S.D. = 8.8 cells/mm2) than in the putamen (20.5 cells/mm2, S.D. = 7.0 cells/mm2). The nucleus accumbens stained moderately and positive cell bodies were evenly dispersed throughout this structure. In contrast, the olfactory tubercle displayed a heavily stained neuropil but positive neurons were encountered only in its polymorph layer. In the sublenticular region, dense fiber plexuses appeared in register with nonreactive cell clusters of the nucleus basalis of Meynert and of the nucleus of the anterior commissure. More caudally, a dense bundle of positive fibers was observed at the level of the ansa lenticularis, the inferior thalamic peduncle, and the adjoining bed nucleus of the stria terminalis. Several fibers contributing to this bundle were of the woolly type. Woolly fibers also coursed in the substantia innominata between the ventral aspect of the globus pallidus and the optic tract, and ascended in the internal medullary lamina separating the internal and external segments of the globus pallidus. Somatostatin-immunoreactive cell bodies were uniformly scattered throughout the substantia innominata. The various nuclei of the amygdala showed a wide range of immunoreactivity. The central nucleus was lightly reactive, whereas the intercalated masses displayed a moderate staining. A dorsoventral gradient of immunostaining was noted in the ventrolateral portion of the amygdala, the lateral nucleus being moderately to densely stained and the basal nucleus very lightly to lightly immunoreactive.(ABSTRACT TRUNCATED AT 400 WORDS)

Anatomical evidence for interactions between somatostatin neurites in lamina II of the rat spinal cord

Light microscopic analysis of adult and 10-14-day-old rat spinal cords suggested that somatostatin-immunoreactive (SOM-I) fibers apposed SOM-I cell bodies in lamina (L) II. Electron microscopic analysis of these relationships at both ages showed the presence of direct appositions between SOM-I fibers and SOM-I cells. However, synapse formation between SOM-I fibers and cells was observed only in the young rat. Similarly, synapses between SOM-I fibers and SOM negative cell bodies were only found in the young animal. Adjacent SOM-I perikarya directly contacted each other, but, again, membrane specializations were evident only in the young rat. Within L I of the adult dorsal horn, a SOM-I fiber directly apposed an unlabeled cell body. Despite analysis of serial sections through the apposition, no synaptic contacts were observed.

Developmental changes in the serotoninergic innervation of hindlimb extensor motoneurons in neonatal rats

The postnatal development of quadriceps femoris motoneurons (Q-MNs) and serotonin (5-HT) nerve terminals in rat spinal cord were studied using retrograde neurotracing techniques combined with 5-HT immunohistochemistry. We attempted to elucidate the 5-HT-ergic innervation to the Q-MNs by counting the number of 5-HT-immunoreactive varicosities that were in close apposition to the Q-MNs. The following results were obtained: (1) Q-MNs possessed, at birth, few if any very short dendrites. The size of these somata was relatively uniform and small. During postnatal periods lasting from 1 to 30 days, the mean cell size of Q-MNs increased with the development of dendrites. From 5 to 14 days after birth, in particular, cell size increased markedly. (2) 5-HT-immunopositive fibers were, at birth, already observed in the ventral horn of the lumbar spinal cord. The density of these fibers increased gradually with age. (3) At birth, only a few 5-HT terminals and varicosities showed close apposition with about half the Q-MNs examined. At 5-days postnatally, such close apposition was found in all Q-MNs. By the first two postnatal weeks, Q-MNs grew quickly and the 5-HT innervation to the Q-MNs appeared to have been established. Based on these results, the significance of 5-HT innervation to developing Q-MNs is discussed in relation to the postnatal development of motor function.

Development of serotoninergic system in the brain and spinal cord of the chick

(1) Development of serotonin positive cells and fibers was immunohistochemically studied by the use of an antibody against serotonin. (2) Serotoninergic neurons were first observed in the immature rohmbencephalon raphe nuclei on embryonic day (E)4, where two clusters of serotonin positive neurons were located: one observed at the rostral part of the rohmbencephalon corresponding to the dorsal raphe nuclei had many serotonin positive cells: the other located at the caudal part of the rohmbencephalon corresponding to the medullary raphe nuclei of the adult animals had only a small number of serotoninergic cells. (3) By E8 the number of serotonin positive cells in the brain stem increased, and virtually all the raphe nuclei found in an adult animal were located. (4) Serotonin positive fibers in the marginal layer reached up to the diencephalon and telencephalon on E6 and E8, respectively. (5) Serotonin positive cells were found beside the midline regions in the ventral part of the spinal cord of the embryonic as well as posthatching chick. (6) Because almost all the serotoninergic fibers in the spinal cord originated from the brain stem raphe nuclei, propriospinal serotonin positive cells were considered as phylogenetic vestiges. (7) Serotoninergic fibers were first found in the marginal layer of the cervical and lumbar spinal cord on E6 and E8, respectively. (8) There was a waiting period of a few days before they penetrated into the mantle layer. (9) Terminal arbolization of the serotoninergic fibers started from late embryonic periods (E16 less than), and was maximized within one week of hatching. (10) Thereafter the density of serotonin positive fibers decreased in all the regions of the spinal cord. (11) Developmental changes of the density of serotonin determined with a high performance liquid chromatography were the same as those determined through immunohistochemistry. Namely the density of serotonin increased linearly from E6 to hatching period, and reached the maximum value one week posthatching. (12( The density of the serotonin in the adult spinal cord was about half of the maximum value. (13) It is to say that the densities of serotonin and serotoninergic fibers transiently increased around one week posthatching. (14) Following the transient increase serotoninergic fibers were eliminated from the neuropil, the fibers were localized in the specific regions of the motor nucleus: motor neuron pools of extensor muscles of the hip joint in the lumbosacral spinal cord.(ABSTRACT TRUNCATED AT 400 WORDS)

Transient expression of opioid receptors in defined regions of developing brain: are embryonic receptors selective?

The developmental profile of opioid receptors was studied in rat and guinea pig striatum and hippocampus. The two brain regions show different receptor profiles during development, which are characteristic for each animal. Yet, both tissues and animal species share one common feature; the binding of the universal opioid ligand [3H]diprenorphine per milligram of protein is high at the early embryonic period, it decreases toward birth, and then gradually increases to the adult levels. This apparent transient expression of the receptors during the early developmental stage was manifested in the guinea pig as an actual decrease in the total receptor number. As an attempt to characterize the receptors involved in this process, the binding of the selective mu-opioid ligand [3H]Tyr-D-Ala-Gly-MePhe-NH(CH2)OH [( 3H]DAGO) was studied in striatal membranes of young (P1) and adult (P60) rats. Competition between [3H]DAGO and the delta-selective peptide Tyr-D-Pen-Gly-Phe-D-Pen (DPDPE) shows higher affinity of the delta opioid to P1 membranes than to P60 membranes, though the number of delta receptors in P1 membranes is very small. This observation is in line with a previous study suggesting that opioid receptors in embryonic striatum and hippocampus are less selective to various opioids than those of adult brain. An additional difference between adult and embryonic tissue was observed on Scatchard analysis of [3H]DAGO binding; striatum P60 membranes exhibit one binding site with a KD of 0.8 +/- 0.1 nM and Hill coefficient of 0.96, whereas striatum P1 membranes bind the peptide in an apparent cooperative fashion with an overall Hill coefficient of 1.30.(ABSTRACT TRUNCATED AT 250 WORDS)

The origin of serotoninergic projections to the lumbosacral spinal cord at different stages of development in the North American opossum

We have employed immunohistochemistry and the retrograde transport of Fast blue to study the origin of serotoninergic projections to the lumbosacral spinal cord at different stages of development in the North American opossum. A few serotoninergic axons are present in the lumbosacral cord at birth, 12 days after conception, and serotoninergic neurons are numerous in the brainstem where they are present in most, if not all, of the areas which contain them in the adult animals. A few neurons of the caudal raphe and adjacent reticular formation were labeled by lumbar injections of Fast blue on postnatal day 1, and by postnatal day 3, labeled neurons were numerous within all areas which provide serotoninergic projections to the lumbosacral cord in adult animals. By postnatal day 11, it was possible to combine Fast blue labeling with immunofluorescence to show that some of the labeled neurons were serotoninergic. By postnatal day 24, neurons which provide serotoninergic projections to the lumbosacral cord were especially numerous and some of them were found in areas which do not provide comparable projections in adult animals. In developing and adult animals, few, if any, neurons were labeled in the dorsal raphe or superior central nuclei. We have shown previously that serotoninergic axons do not innervate laminae I and II of the lumbosacral cord until approximately postnatal day 50, although they are present in the marginal zone at birth and have grown into laminae III-X by postnatal day 15. Since serotoninergic axons which project to laminae I and II originate within the raphe magnus and adjacent reticular formation, and those areas provide serotoninergic projections to the spinal cord well before postnatal day 50, it is possible that serotoninergic innervation of laminae I and II is provided by late growth of collaterals from axons that have been present in the marginal zone for some time.

Origins and terminations of bulbospinal axons that contain serotonin and either enkephalin or substance-P in the North American opossum

We have shown previously that some enkephalin, substance-P, and serotoninergic neurons in the medullary raphe and adjacent reticular formation project to the spinal cord in the opossum. In the present study we have combined the retrograde transport of True Blue and immunofluorescence histochemistry to determine whether methionine enkephalin or substance-P containing bulbospinal neurons are serotoninergic. Furthermore, we have used the same immunofluorescence protocol to determine whether spinal axons contain the same substances. Neurons that immunostained for both enkephalin and serotonin were observed in many brainstem nuclei. However, those that projected to the spinal cord were limited to the nuclei raphe magnus and obscurus, and the ventral part of nucleus reticularis gigantocellularis, pars ventralis. Neurons that immunostained for both substance P and serotonin were fewer in number, but some of the ones in the above nuclei and within the nucleus raphe pallidus, projected to the spinal cord. Spinal axons exhibiting both enkephalin- and serotonin-like immunoreactivity were observed in the superficial laminae of the dorsal horn, lamina X, and the intermediolateral cell column, whereas those showing both substance-P and serotonin-like immunoreactivity were seen primarily in lamina X, the intermediolateral cell column, and the ventral horn. Some of the axons in the ventral horn were in close apposition to presumed motoneurons. Comparison of the above results with those obtained from previous studies of bulbospinal projections has allowed us to infer the origins of axons that innervate different spinal targets.

Distribution of axons showing both enkephalin- and serotonin-like immunoreactivities in the lumbar cord segments of the Japanese monkey (Macaca fuscata)

Axons exhibiting both enkephalin- and serotonin-like immunoreactivities were observed by the double immunofluorescence method in the lumbar cord segments of the Japanese monkey. Double-labeled axons were seen almost exclusively in the dorsal horn, particularly in lamina I, lamina IIa and the lateral part of lamina V. After thoracic cordotomy, almost all of the double-labeled axons disappeared from the lumbar cord segments.

Developmental changes in serotonin levels in the chick spinal cord and brain

Developmental changes in 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA) in the developing chick spinal cord and brain were examined using high-performance liquid chromatography with electrochemical detection and immunohistochemistry. On embryonic day (E)6 only small amounts of 5-HT (0.086 ng) and 5-HIAA (0.0144 ng) were found in the spinal cord. By contrast, large amounts of 5-HT (x30) and 5-HIAA (x60) were detected in non-neuronal tissue outside the spinal cord; a similar distribution of 5-HT was also detected by immunohistochemistry. Up to E10, the highest concentrations of 5-HT in the spinal cord were found in the cervical region, followed by the thoracic and lumbar regions. In embryos older than E16, as well as in posthatched chicks, however, the highest and lowest concentrations of 5-HT were found in the lumbar and thoracic spinal cord, respectively. The concentration of spinal cord 5-HT reached maximal values on posthatching day (P)7, after which there was a marked decrease. By P120, 5-HT levels in the spinal cord decreased to the same level as on E10-E16. Concentrations in the brain, however, gradually increased with development. The basic pattern of development of 5-HIAA was similar to that of 5-HT.

Ontogenesis of enkephalinergic afferent systems in the opossum cerebellum

Enkephalin (ENK) immunoreactive climbing fibers, mossy fibers and a beaded plexus of axons are present in the adult opossum's cerebellar cortex. We have used the indirect antibody peroxidase-antiperoxidase technique to study the ontogeny of enkephalinergic axons in the cerebellum of pouch young opossums from postnatal day (PD) 1 to PD 83. On PD 1, ENK axons are present in the intermediate layer of the cerebellar anlage. At PD 18, after a period of 'waiting', ENK fibers form clusters throughout the cerebellar cortex primarily within the nascent Purkinje cell layer. By PD 40, axon terminals with a climbing fiber phenotype circumscribe Purkinje cells; immature mossy fiber rosettes are present within the internal granule cell layer. A third axon phenotype, beaded ENK fibers can be distinguished on PD 68. Between PD 40 and PD 68, the distributions of ENK climbing and mossy fibers overlap in vermal lobules II-VIII and X, whereas in the hemispheres climbing fibers predominate. However, by PD 83, ENK positive climbing fibers are no longer evident in lateral folia. These results indicate that early arriving ENK axons are present before the differentiation of their cellular targets. Further, a transient appearance of ENK in discrete populations of developing climbing fibers suggests several developmental events: (1) cell death in the inferior olive, (2) collateral regression, or (3) a transient expression of this peptide, that may be characteristic of this chemically defined system of axons.

The early development of major projections to the dorsal striatum in the North American opossum

We have employed immunocytochemical and axonal transport techniques to study the development of major projections to the dorsal striatum of the North American opossum. The opossum is born in a very immature state, 12-13 days after conception, and climbs into an external pouch where it remains attached to a nipple for several months. Its immaturity at birth and its protracted postnatal development make the opossum a good model for developmental studies. Although tyrosine hydroxylase-like immunoreactive (TH-LI), presumably dopaminergic, neurons were present in the ventral mesencephalon at birth (the presumptive substantia nigra and ventral tegmental area), there was no evidence for TH-LI axons in the striatal anlage. By postnatal day (PD)6, a few immunostained axons were found within the putamen. The subsequent growth of TH-LI axons into the striatum followed general caudal to rostral and ventrolateral to dorsomedial gradients and, at any age, they were most numerous in the areas exhibiting the greatest cytodifferentiation. By estimated (E)PD45, TH-LI axons were present in most, if not all, areas of the striatum. Serotoninergic (5-HT)-LI axons were found lateral to the presumptive striatum at birth but not within it. By PD7, however, a few 5-HT-LI axons could be identified in the putamen. The growth of 5-HT-LI axons into the striatum generally followed the same gradients described for TH-LI axons although at all ages their density was much less. Using the orthograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP), evidence was obtained for the existence of thalamostriatal projections by PD5 and for corticostriatal projections by PD10. Crossed corticostriatal projections were present by EPD23. Our results suggest that the development of major projections to the striatum occurs postnatally in the opossum, rather than prenatally as in placental animals. The timetable for striatal innervation is discussed in light of the developmental sequences established for other motor circuits.

Postnatal ontogeny of enkephalin fibers in spinal sympathetic nuclei

The postnatal distribution of enkephalin (Enk) fibers is described in preganglionic containing sympathetic nuclei in the rat thoracolumbar spinal cord. In high thoracic spinal cord, at birth, Enk fibers are present in moderate numbers in the intermediolateralis nucleus, pars principalis (ILp), and nucleus intercalatus spinalis (IC). Enkephalin fibers first appear in the dorsal commissural nucleus (dcn) on postnatal day 2. Postnatal day 6 represents a pivotal timepoint when the basic Enk innervation pattern is established. From postnatal day 11 through day 20 there is a gradual accumulation of Enk fibers within each of the sympathetic nuclei such that the density and distribution of immunoreactive fibers approaches the adult appearance by postnatal day 20. An adult pattern is achieved by postnatal day 30. There is a rostral-caudal gradient in the developmental appearance of Enk fibers in sympathetic nuclei such that the ILp nucleus contains Enk fibers on postnatal day 0 in the high thoracic spinal levels compared to postnatal day 6 in low thoracic-high lumbar spinal levels. Examination of the location of Enk fibers during ontogeny highlighted several additional features of the distribution of Enk fibers in the adult animal. Enkephalin fibers delineate two subdivisions of the IC nucleus; a thin dense core of Enk fibers contained within a broader band of moderate numbers of Enk fibers. We also report variations in the general overall pattern of the Enk fiber distribution in high thoracic, middle thoracic, and lwo thoracic-high lumbar spinal cord levels.

Convergence of serotonin-, enkephalin- and substance P-like immunoreactive afferent fibers on single pudendal motoneurons in Onuf's nucleus of the cat: a light microscope study combining the triple immunocytochemical staining technique with the retrograde HRP-tracing method

Convergence of serotonin (5-HT)-, enkephalin (ENK)-, and substance P (SP)-like immunoreactive (LI) afferent fibers on single pudendal motoneurons within Onuf's nucleus was demonstrated: pudendal motoneurons were retrogradely labeled with horseradish peroxidase applied to the pudendal nerve. Subsequently, 5-HT-LI fibers were stained by the immunoperoxidase method, and then ENK- and SP-LI fibers were stained by the double immunofluorescence method.

Immunohistochemical distribution of serotonin in spinal autonomic nuclei: I. Fiber patterns in the adult rat

The differential distribution of serotonin (5HT) fibers in spinal laminae VII and X is described for the adult rat. The results indicate that descending 5HT fibers preferentially innervate those regions of lamina VII that contain sympathetic and parasympathetic neurons. In lamina X, especially the dorsal commissural nucleus, large numbers of 5HT fibers are observed throughout the spinal cord. Moreover, sympathetic nuclei are more richly innervated with 5HT than the spinal parasympathetic nuclei. Spinal cord hemisections reveal that spinal autonomic nuclei are differentially innervated: ipsilateral serotoninergic projections to the intermediolateral cell column are preferentially interrupted. In addition, a large crossed 5HT projection exists throughout the length of the spinal cord that decussates five to six spinal segments rostral to its termination. Both crossed and uncrossed 5HT fibers span many spinal segments and have large numbers of collaterals. Spinal cord transections show that the vast majority of spinal 5HT descends from the brainstem but that some 5HT fibers are of intrinsic origin.

Immunohistochemical distribution of serotonin in spinal autonomic nuclei: II. Early and late postnatal ontogeny in the rat

These studies reveal that the postnatal ontogeny of serotonin (5HT) in the sympathetic nuclei of the rat spinal cord is protracted; the adult complement of 5HT-immunoreactive fibers is not achieved until at least 60 days of age. As descending serotonin fibers innervate and demarcate the distribution of preganglionic sympathetic nuclei, rostral-caudal and temporal gradients exist. Additionally, a heterogeneous segmental 5HT ontogenetic pattern is observed in sympathetic nuclei. Most serotonin fibers in laminae VII and X are unorganized at birth except for some sympathetic nuclei in high thoracic regions where the 5HT sympathetic pattern is being initiated. By postnatal day 6 the framework of the 5HT pattern is established in all sympathetic nuclei, and by postnatal day 16 a pattern is formed, which develops into the compact adult state by postnatal day 60. The protracted period of sympathetic 5HT development corresponds with the length of time it takes for the autonomic nervous system to mature. In addition, 5HT intraspinal cell bodies are observed at all time points examined, except for the day of birth, and are found in the same regions as adult 5HT neurons, i.e., dorsal or lateral to the central canal in laminae VII and X and in all spinal segments except cervical levels. Many of the 5HT neurons are pericanalicular and bipolar in appearance. Multipolar 5HT neurons are first observed on postnatal day 45.

Release of immunoreactive somatostatin in the spinal dorsal horn of the cat

Antibody microprobes were used to investigate the possible release of immunoreactive somatostatin (irSS) within the lumbar spinal cord of anaesthetized cats. A basal release of irSS was detected in the region of the substantia gelatinosa of the dorsal horn. By comparison with in vitro standards the concentration of SS detected in this region was estimated at 10(-7) M. This release of irSS was not significantly altered by electrical stimulation of large myelinated primary afferent fibres but was increased when unmyelinated afferents were additionally stimulated. Release of irSS was also detected at the spinal cord surface. The results support a role for somatostatin in nociceptive transmission in the spinal cord.

Development and distribution of enkephalin-immunoreactive elements in the chicken spinal cord

The development and distribution of methionine-enkephalin-immunoreactive elements were studied in the chicken spinal cord with the indirect immunofluorescence method. Methionine-enkephalin-like immunoreactivity was first detected in the chick spinal cord at embryonic stages 29-30 (incubation day 6). Before stage 35 (day 9), it was mainly observed in fibres almost throughout the white matter. Subsequently, fibres containing the peptide appeared in the ventral half of the gray matter, but mostly in the lateral portion of the neck of the dorsal horn. From stage 40 (day 13 or 14), fibres were especially noticed in laminae 1 and 2, and in the area dorsal to the central canal. In particular, many enkephalin-immunoreactive perikarya were observed in several spinal areas during this period. Such a distribution of both enkephalin-immunoreactive fibres and perikarya remained visible at later embryonic stages, but labelled cells gradually decreased in number and disappeared after hatching. With colchicine treatment, however, a similar distribution of the peptide was found in the spinal cord of adult chickens. As in the embryo, enkephalin-immunoreactive perikarya were mainly observed in the lateral portion of the neck of the dorsal horn, in lamina 1, and in the nucleus of the dorsolateral funiculus throughout the spinal cord. At the thoracic level, many were also located ventral to the central canal. Enkephalin-immunoreactive fibres increased notably in the gray matter of adult chickens. They mainly occurred in laminae 1 and 2, in the lateral portion of the neck of the dorsal horn, and in the area around, especially dorsal to, the central canal. In contrast, enkephalin-immunoreactive fibres decreased in the white matter and they were mainly observed in the dorsolateral funiculus, in Lissauer's tract, and in the lateral funiculus adjacent to the gray. The distribution of enkephalin-immunoreactive fibres was generally comparable at all spinal levels examined. In addition, examination of post-hatched chickens showed virtually the same results as in the adult.

Immunohistochemical localization of substance P, somatostatin, enkephalin, and serotonin in the spinal cord of the northern leopard frog, Rana pipiens

Using the indirect antibody peroxidase-antiperoxidase method of Sternberger, we localized substance P (SP), somatostatin (SOM), enkephalin (ENK), and serotonin (5HT, 5-hydroxytryptamine) in the spinal cord of Rana pipiens. This is the first study to demonstrate all four substances in adjacent sections of frog spinal cord. The distribution patterns of ENK, SP, SOM, and 5HT in our study differ from that described for laminae I and II in amniotes. A high density of ENK, SP, and SOM fibers is present in a band ventral to the dorsal terminal field of cutaneous primary afferent fibers and slightly overlapping the ventral terminal field of muscle primary afferent fibers. However, a high density of 5HT fibers is present in the dorsal terminal field.

Somatostatin immunoreactive structures in the developing rat spinal cord

Somatostatin immunoreactive (SOM-I) perikarya were first observed in the ventral horn at E12, in the presumptive intermediate gray area at E14, and in the alar plate of the rostral spinal cord at E14. In general, after their initial appearance, their density increased and then decreased during development. A moderate density of SOM-I varicosities became obvious in the superficial laminae of the E20 dorsal horn. By E12 a few SOM-I perikarya, interpreted to be dorsal root ganglia, were observed lateral to the spinal cord, and by E13, SOM immunoreactivity was visualized within the central and peripheral processes of dorsal root ganglion axons. In the marginal zone, SOM-I fibers were first demonstrable in the ventral funiculus at E14, and in the lateral funiculus at E15. After their initial appearance, their density increased and then decreased with age, with the exception of the dorsal part of the lateral funiculus where it increased at the early stages of development to an apparently stable level. The early detection of SOM immunoreactivity in specific spinal regions corresponds well with the birth dates of cells in those regions. This indicates that the SOM-I cells are capable of synthesizing the substance at least as early as they have entered their final cell division.

Effects of neonatal spinal cord serotonin depletion on opiate-induced analgesia in tests of thermal and mechanical pain

There is considerable evidence that serotonin (5-HT) is involved in the analgesic actions of various opiates. However, it is less clear which opioid receptor types interact with these descending systems and whether the various monoaminergic pathways are specific for different types of nociceptive signals. In the present study we lesioned the spinal cord serotonin pathways by neonatal spinal injections of 5,7-dihydroxytryptamine (5,7-DHT) and tested the analgesic effects of morphine and ketocyclazocine one and two weeks later using both mechanical and thermal noxious stimuli. The treatment depleted spinal cord serotonin by more than 90% while not affecting norepinephrine levels. The effects of morphine were greatly attenuated in the depleted animals when the thermal noxious stimulus was applied. The analgesic actions of morphine were only slightly affected when the mechanical stimulus was applied. The effects of ketocyclazocine were not reduced by the treatment. The results further buttress the conclusion that at least part of morphine's analgesic effects are mediated by descending serotonin systems and that these systems are primarily effective against a thermal stimulus. The data suggest that non-5-HT brainstem system(s) are involved in morphine-induced analgesia to a mechanical noxious stimulus.

Immunohistochemical studies of cholecystokininlike peptides and their relation to 5-HT, CGRP, and bombesin immunoreactivities in the brainstem and spinal cord of lampreys

The distribution of cholecystokinin (CCK)-like immunoreactivity in the brainstem and spinal cord of lampreys was studied by using CCK antisera with different properties. In the spinal cord, three separate systems reacted with CCK antisera: (1) A ventral and lateral fiber system descending from a group of neurons in the posterior reticular nucleus of the rhombencephalon was labeled by both a C-terminal-directed CCK antiserum and a monoclonal CCK antibody. (2) A dorsal root-dorsal column system of fibers originating from cell bodies in the dorsal root ganglia was labeled only by the C-terminal CCK antiserum. This CCK immunoreactivity could be abolished by preabsorption with calcitonin-gene-related peptide (CGRP), suggesting that it was due to cross-reactivity with a CGRP-like peptide. This system also contained 5-hydroxytryptamine (5-HT)-, bombesin-, and CGRP-like immunoreactivities. (3) An intraspinal system of 5-HT neurons was labeled with an antiserum to the midportion of CCK-33 but not by the other CCK antisera. The CCK labeling of this system was difficult to reduce by preabsorption with CCK peptide and thus appeared to be nonspecific. Groups of cell bodies in the middle reticular nucleus of the rhombencephalon, the reticular nucleus of the mesencephalon, and the hypothalamus were labeled by both the C-terminal and the monoclonal CCK antisera. The gut contained two types of CCK-like immunoreactivity, one of which appeared to be due to cross-reactivity with CGRP. A biochemical analysis showed that the content of CCK was low in the spinal cord compared to the brain, and these results agreed with the immunohistochemical findings.

The morphology and distribution of rat serotoninergic intraspinal neurons: an immunohistochemical study

An immunohistochemically derived morphological description of a diverse population of rat lamina VII and X intraspinal 5HT neurons is provided. These bipolar or multipolar neurons occur most frequently in lamina X, dorsal or dorsolateral to the central canal, in thoracolumbar, sacral, and coccygeal spinal segments. These 5HT intraspinal neurons are found in normal rat spinal cords as well as in spinal cords that have been hemisected or transected 60 days prior to serotonin immunostaining. Therefore, 5HT intraspinal neurons are the probable source of the biochemically detectable 5HT that remains in the spinal cord distal to a spinal transection. In the rat, serotonin intraspinal neurons are most often associated with spinal autonomic nuclei but it is unknown if they are preganglionic in nature.

Distribution of axons exhibiting both enkephalin- and serotonin-like immunoreactivities in the lumbar cord segments: an immunohistochemical study in the cat

Axons exhibiting both enkephalin- and serotonin-like immunoreactivities were observed by the double immunofluorescence method in the lumbar cord segments of the cat. Double-labeled axons were seen most frequently in laminae I, IIa and the lateral part of lamina V. They were also distributed in other parts of the dorsal horn and lamina X (especially in the dorsal part), but rarely found in laminae VII, VIII and IX. After cervical hemicordotomy the vast majority of double-labeled axons disappeared from the spinal gray ipsilateral to the lesion.

Developmental changes in density and distribution of serotoninergic fibers in the chick spinal cord

Developmental changes of serotoninergic innervation in the chick spinal cord (third lumbosacral segment) were examined with an immunohistochemical technique using an antiserum to serotonin. In the 1-day-old hatched chick, serotoninergic fibers were located in laminae I, II, VII, IX, and X. A large number of serotonin-positive fibers and terminals were found around somal profiles of large neurons and in the neuropil of the medial and lateral parts of the lateral motor column (LMC). In the 1-week-old chick, the density of serotoninergic fibers was greatly increased in the posterior columns, and serotoninergic fibers were most densely aggregated in the dorsolateral part of the LMC. In the 2-week-old chick, a considerable decrease in the density of serotoninergic fibers was observed in the lateral funiculus and the gray matter (laminae I, II, VII, IX, and X). In the LMC, serotonin-positive fibers and terminals were largely absent from the neuropil, but were found preferentially around the somal profiles of large neurons. Between 1 and 2 weeks after hatching the density of varicosities and terminals in the neuropil of the dorsolateral and medial parts of the LMC decreased by 33% and 56%, respectively. In the 3-month-old chick, the density of serotoninergic fibers in laminae I, II, V, VII, and X had increased compared to younger ages. Serotonin-positive fibers were not evenly distributed in the LMC of the adult chicken; rather, they were densely aggregated around the soma and proximal dendrites of motoneurons in the dorsolateral LMC. Many neuronal soma in the medial and intermediate regions of the LMC lacked serotoninergic fibers.

Ontogeny of somatostatin-like immunoreactivity in the human fetus and infant spinal cord

The localization and distribution of somatostatin like-immunoreactivity (SSLI) in postmortem human fetus and infant spinal cord and dorsal root ganglia were studied by using the indirect immunofluorescence technique. SSLI, which was mostly located within varicose fibers and terminal-like structures, occasionally within cell bodies, was detected during early fetal life (on gestational week 9 and beyond). The changes occurring from the early to the late fetal and infant stages mainly resulted in a progressive increase in the number of somatostatin-like immunoreactive fibers within most of the gray areas. On the whole the majority of immunolabelled fibers and terminal-like structures were observed over the superficial layers of the dorsal gray including the marginal zone and the substantia gelatinosa. Other regions displaying a moderate number of somatostatin-like immunoreactive fibers were the intermediate gray and the gray commissure area around the central canal. A few scattered immunofluorescent fibers were unevenly distributed over the white matter especially in the lateral and ventral funiculus areas and near the ventral motor nuclei. A few somatostatin-like immunoreactive cell bodies were occasionally found in the superficial layers of the dorsal gray and in the intermediolateral gray. Immunolabelled cells were further usually visualized in dorsal root ganglia. Although the distribution patterns of somatostatin-like immunoreactive structures were similar throughout the entire spinal cord, the highest density of immunolabeled fibers, however, was seen at the lumbosacral level. Our results indicate that in the human spinal cord SSLI is already widespread before birth. It is further suggested that somatostatin ontogenesis in human spinal cord and dorsal root ganglia begins early in fetal life.

Development and distribution of substance P in the spinal cord and ganglia of embryonic and newly hatched chick: an immunofluorescence study

The development and distribution of substance P (SP) immunoreactivity were studied in the spinal cord and ganglia of embryonic and newly hatched chick by using the indirect immunofluorescence method. Substance P immunoreactivity was first detected in the spinal cord at embryonic stages 18-20 (incubation day 3). Before stage 32 (day 7), it was mainly found in regions corresponding to the dorsolateral funiculus and Lissauer's tract. Subsequently, SP fibers appeared in the dorsal horn. By stage 38 (day 11), they were demonstrated almost throughout the gray matter, but mostly in laminae I and II. During this period, however, many SP-positive cells were found just ventral to the central canal at the thoracic level, although a few were also detected in other areas throughout the cord. In the white matter, very dense longitudinal SP fibers were observed in Lissauer's tract and the dorsolateral funiculus, where extremely dense plexuses of SP immunoreactivity were also detected around a group of nonimmunoreactive cell bodies. At later stages, no remarkable differences were noticed in the distribution of SP fibers, but the SP-positive cells decreased gradually in number and disappeared after hatching. However, they reappeared following colchicine treatment. In the spinal ganglia, SP immunoreactivity appeared initially at stage 25 (day 4). It was mostly located in small neurons of the mediodorsal region. These cells also decreased in number from later stages but increased by colchicine treatment after hatching. The development and distribution of SP immunoreactivity in the spinal cord and ganglia were generally comparable at all levels examined, except where indicated.

Development of serotonin immunoreactivity in the rat spinal cord and its plasticity after neonatal spinal cord lesions

The postnatal maturation of spinal pathways may account for the gradual time course of postnatal development of behavior and also account for the greater anatomical reorganization which often follows damage to the developing CNS compared to the mature CNS. The purpose of the current study was to examine (1) the prenatal and postnatal development of the descending serotonergic (5-HT) projection to the spinal cord and (2) the effects of a neonatal spinal cord lesion on this development. In addition, we wished to determine (3) whether transplants of fetal spinal cord tissue placed into the neonatal lesion site alter the plasticity of the 5-HT projection to the cord. Peroxidase-antiperoxidase immunocytochemical techniques were used. At embryonic day 14 (E14), no 5-HT immunoreactive fibers could be identified at any spinal cord level. By E18 the first axons were identified in the white matter only at all spinal cord levels. At birth, 5-HT immunoreactive fibers were present both in the white matter and in the gray matter at all cord levels. The projection within the gray matter was diffuse and considerably less dense than in the adult. The postnatal maturation of the 5-HT projection within the gray matter of the spinal cord followed rostral to caudal and ventral to dorsal gradients. During the first weeks postnatal, the 5-HT immunoreactivity within the cord increased to attain an adult pattern and density by 14 days in the cervical cord and 21 days in the thoracic and lumbar cord. The effect of a spinal cord hemisection at birth on the anatomical reorganization of the descending serotonergic innervation of the cord was compared with the effect of the same lesion in the adult. In the adult animal, mid-thoracic hemisection decreased the 5-HT content of the ventral horn of the lumbar spinal cord caudal and ipsilateral to the lesion to 8% of that on the intact side. When this same lesion was made in the newborn animal, the innervation was 43% of that on the intact side. When a transplant of fetal spinal cord tissue was inserted into the lesion site in the newborn animals, there was even greater 5-HT innervation caudal to the lesion, 83% of that on the intact side. These results indicate that there is considerable postnatal development and plasticity of the descending serotonergic projection to the spinal cord, and this plasticity is enhanced by the presence of a spinal cord transplant at the site of the lesion.

Development of brainstem and cerebellar projections to the diencephalon with notes on thalamocortical projections: studies in the North American opossum

The North American opossum is born in a very immature state, 12 days after conception, and climbs into an external pouch where it remains attached to a nipple for an extended period of time. We have taken advantage of the opossum's embryology to study the development of brainstem and cerebellar projections to the diencephalon as well as the timing of diencephalic projections to somatosensory motor areas of neocortex. The techniques employed included immunocytochemistry for serotonin, the retrograde and orthograde transport of wheat germ agglutinin conjugated to horseradish peroxidase, and the selective impregnation of degenerating axons. Our results suggest that serotoninergic axons, presumably from the dorsal raphe and superior central nuclei, are present in the diencephalon at birth. Axons from the bulbar reticular formation, the vestibular complex, the trigeminal sensory nuclei, and the dorsal column nuclei reach at least mesencephalic (and probably diencephalic) levels by postnatal day (PND) 3, whereas those from the cerebellar nuclei may not grow into comparable levels until PND 5. The dorsal column and cerebellar nuclei innervate the ventral nuclei of the thalamus by estimated postnatal day (EPND) 17 and all of the diencephalic nuclei supplied in the adult animal by EPND 26. Diencephalic axons enter ventrolateral (face) areas of presumptive somatosensory motor cortex by PND 12, but do not reach dorsomedial (limb) regions until EPND 21. At both ages, diencephalic axons are limited to the cortical subplate and marginal zone; they do not innervate an identifiable internal granular layer until considerably later. Our results suggest that axons from the brainstem and cerebellum grow into the diencephalon early in development, but that they do not influence the cerebral cortex until relatively late. When the results of the present study are compared with those reported previously on the development of ascending spinal (Martin et al., '83) and corticofugal (Martin et al., '80; Cabana and Martin, '85b,c) projections, it appears that specific components of major somatosensory and motor circuits develop according to different timetables.

Immunohistochemical study on the development of serotoninergic neurons in the chick: II. Distribution of cell bodies and fibers in the spinal cord

Developmental changes of serotonin (5-hydroxytryptamine) neurons and fibers in the spinal cord of the embryo and posthatching chick were studied with immunohistochemical techniques with the aid of an antibody against serotonin. The first serotonin-immunoreactive fibers were found in the marginal layer of the cervical and lumbar spinal cord on embryonic days 6 and 8, respectively. There was a time lag of a few days between the first appearance of serotonin fibers in the marginal layer (embryonic days 6-8) and the time of penetration of serotonin fibers into the mantle layer (embryonic day 8 or older). The developments of serotonin innervation in the rostral parts of the spinal cord precedes that of caudal regions. Serotonin fibers penetrating into the mantle layer of the lumbar spinal cord were first found in lamina VII on embryonic day 8, whereas there were no serotonin-immunoreactive fibers in lamina IX by embryonic day 10. Large differences were found between embryonic day 16 and posthatching day 5 with regard to the density of serotonin varicosities and fibers in lamina IX, where profiles of soma and large-sized dendrites were heavily covered with varicosities. Laminae I and II first received serotonin fibers on embryonic day 16 and had a much denser innervation by posthatching day 5. There were no traces of serotonin fibers in lamina III in the stages examined up to posthatching day 5. Serotonin fibers were located in the lateral and ventral marginal layers in all specimens examined; only a few fibers were found in the dorsal marginal layer. Although few, serotonin-immunoreactive cell bodies were found in an area around the central canal of all animals from embryonic day 8 to adult. Some of these were located in the ependymal layer and sent processes toward the central canal; there were a small number of cells with long, fine processes. Serotonin-immunoreactive fibers in the spinal cord were not altered in regions rostral to the spinal transection, whereas all the serotoninergic fibers of the supraspinal origin were eliminated in the spinal cord caudal to the gap.

Development of projections from somatic motor-sensory areas of neocortex to the diencephalon and brainstem in the North American opossum

The development of projections from somatic motor-sensory areas of neocortex to the diencephalon and brainstem was studied by using the orthograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) in a series of pouch-young opossums. The opossum was chosen for study because it is born in a very immature state, 12 days after conception, and has a protracted postnatal development. Cortical axons form a cerebral peduncle by at least postnatal day (PD) 10, a medullary pyramid by estimated PD (EPD) 17, a pyramidal decussation by EPD 26, and reach the first cervical segment of the spinal cord by EPD 29. Cortical axons innervate diencephalic nuclei and perhaps the substantia nigra by EPD 17, but do not grow into more caudal brainstem nuclei until EPD 26. The first brainstem areas innervated by cortical axons are the mesencephalic and rostral pontine tegmentum and parts of the pontine gray adjacent to the pyramidal tract (EPD 29). By EPD 31, cortical axons project to additional areas of the pontine gray, the gigantocellular reticular formation, the medial accessory olive, and the cuneate nucleus. Cortical innervation of the red nucleus and superior colliculus begins at EPD 31 but is not well developed until EPD 35. Cortical axons do not innervate the parvicellular reticular formation or the sensory trigeminal nuclei until EPD 35. Evidence for transient cerebrocerebellar axons was also found.

Analysis of the change in number of serotonergic neurons in the chick spinal cord during embryonic development

The existence of serotonin (5-HT)-containing neurons in the spinal cord of the chick embryo was examined by anti-5-HT immunocytochemistry. The first immunoreactive cells were observed in embryos at 7 days of incubation (E7) and were initially located within the floor plate of the early spinal cord. By E9, immunostained cells occurred throughout the length of the spinal cord and were frequently encountered in most transverse sections of the cord. When examined at later embryonic ages of E12, 17 and at hatching (E21 or 22), the 5-HT cells became progressively more difficult to find with the advancing age of the embryos. To determine if this population of spinal cord 5-HT neurons actually diminished during development, a detailed quantitative analysis was undertaken to estimate the number of 5-HT cells in the cord of chick embryos at different ages. The results of this investigation demonstrated that the size of the 5-HT neuronal population rose rapidly from E7 and plateaued (at approximately 3500 neurons) between E9 and E12. As anticipated, the number of 5-HT cells at E17 decreased at all cord levels. Surprisingly, however, the number of spinal cord 5-HT neurons at hatching increased (depending on the cord level) either back to, or above, the counts estimated for the earlier ages of E9 and E12. Therefore, cells expressing the 5-HT phenotype in the spinal cord of the chick embryo persist throughout the period of embryonic development, rather than appear transiently.(ABSTRACT TRUNCATED AT 250 WORDS)

Intrinsic 5HT-immunoreactive neurons in the spinal cord of the fetal non-human primate

Serotonin (5HT) immunoreactive neurons were identified in the late-term fetal spinal cord of normal non-human primates. These neurons were distributed throughout the spinal cord, being concentrated in lamina X and the subjacent ventral median fissure, while their immunoreactive fibers and terminals innervated the zone surrounding the central canal and the ventral spinal artery. Even at this late fetal stage, the dorsal and ventral spinal gray matter was virtually devoid of any positive 5HT immunoreactivity, in contrast to that seen in the adult primate. These findings suggest that the intrinsic 5HT neurons of the primate during development may modulate CSF composition or provide cues for spinal cord differentiation rather than regulate sensorimotor functions as they do in the adult.

Immunohistochemical demonstration of serotonin neurons in autonomic regions of the rat spinal cord

The immunohistochemical distribution of serotonin neurons in normal and transected spinal cords of rats was examined. Intraspinal serotonin neurons were immunostained as far rostral and caudal as T3 and Co1, respectively. All serotonin neurons were located in lamina VII and X, and most were located in spinal autonomic areas. Both bipolar and multipolar neurons were observed with many of the neurons oriented longitudinally to the long axis of the cord. Spinal neurons immunostained for serotonin were visible with and without L-tryptophan and monoamine oxidase inhibitor pretreatment.

A spinal projection of 5-hydroxytryptamine neurons in the lamprey brainstem; evidence from combined retrograde tracing and immunohistochemistry

To investigate whether there is a descending contribution to the spinal 5-hydroxytryptamine (5-HT) innervation in the lamprey, a primitive vertebrate, a study using retrograde transport of the fluorescent tracer Fast blue combined with 5-HT immunohistochemistry was conducted. Two to 4 weeks after an injection of Fast blue into the rostral spinal cord, retrogradely labelled cells were seen throughout the brainstem. Two groups of these cells, one within the posterior reticular nucleus of the rhombencephalon and another rostral to the trigeminal motor nucleus, were labelled after incubation with 5-HT antiserum. These findings suggest that in addition to the well-described local intraspinal 5-HT system, there is also, as in higher vertebrates, a descending 5-HT projection from the brainstem which extends at least 20 segments into the spinal cord.

The development of serotonergic raphespinal projections in Xenopus laevis

The development of serotonin-immunoreactive neurons in the central nervous system of Xenopus laevis larvae has been studied with special emphasis on the development of the raphe nuclei and raphespinal projections. The first serotonergic neurons were observed in the rostral part of the brain stem at stage 25, only 28 hr after fertilization. By stage 28 some 20 serotonin-immunoreactive neurons were found in the rostral part of the brain stem, bearing small protrusions on the ventromedial side of the soma. These initial axonal outgrowths reach the rostral part of the spinal cord at stage 32. By stage 35/36 the growth cones of the descending serotonergic axons in the spinal cord have reached the level of the anus (10th to 15th myotome). Up to stage 45 the majority of the descending serotonergic axons was found in the dorsolateral part of the marginal zone of the spinal cord. After stage 45 some serotonergic axons were also found scattered over other parts of the spinal marginal zone. Collateral branches were first observed in the caudal part of the brain stem at stage 35/36. Later they occurred also in the rostral (stage 43) and caudal (stage 50) spinal cord, usually on fibers in the ventral half of the spinal cord. The number of serotonergic neurons in the central nervous system (brain stem and hypothalamus) increased steadily throughout development until stage 45. After that the total number of serotonergic neurons in the central nervous system increased about two times faster than the number of serotonergic neurons in the raphe nuclei, due to a massive increase of serotonergic neurons in the hypothalamus. The present study shows that young, just differentiated raphe neurons already contain serotonin. The generation of these neurons appears to take place in the ventricular zone (matrix) of the brain stem between the caudal border of the mesencephalon and the entrance of the nervus octavus. From here these neurons seem to migrate to their final destination. The distribution of serotonin-immunoreactive neurons in the brain stem suggests that a superior (not described so far in Anura) and an inferior raphe nucleus can be distinguished in Xenopus. A rostrocaudal gradient seems to be present in the production of serotonergic neurons which project to the spinal cord. Spinal projections from the raphe nuclei are particularly extensive from the nucleus raphes inferior and gradually decrease rostralwards. In the rostral part of the nucleus raphes superior almost no neurons projecting to the spinal cord are found.