The total neuron population of the superficial dorsal horn (SDH), i.e., laminae I and II, was quantitated in Nissl preparations of spinal segment L1 in the rat. Subpopulations of the SDH, defined by axon projection, were quantitated following strategic intraspinal injections of dual retrograde tracers (Fluoro-Gold and true blue). These methods were used in conjunction with [3H]thymidine (delivered in utero) autoradiography for neurogenic pattern analysis. Following stereological correction, each dorsal horn in spinal segment L1 contained 11 neurons in lamina I and 42.6 neurons in lamina II per 10-microm transverse section. Neurons with long projections, i.e., neurons with projections rostral to spinal segment T5, were only slightly more numerous in lamina I than in lamina II. These neurons made up 34% of the total neuron population in lamina I and 7.0% in lamina II. Most of these neurons did not demonstrate descending connections, and many (presumed supraspinal projection neurons) did not demonstrate short, ascending, intersegmental connections. Neurons with short propriospinal projections, i.e., neurons with connections caudal to spinal segment T5, made up approximately half of the total neuron population in both lamina I and lamina II: 55% and 52%, respectively. Of these, 79% had both short ascending and descending projections; the remaining 21% had only descending projections. Neurons that were not labeled with retrograde tracers (presumed local circuit cells) represented 11% of the neurons in lamina I and 41% in lamina II. Neurogenesis in the SDH proceeded along an axon-length gradient, whereby neurons with the longest axons completed neurogenesis first, and those with the shortest completed neurogenesis last. The generation of both propriospinal and supraspinal projection neurons began on embryonic day 13 (E13). Nearly equal numbers of neurons in this group were generated in laminae I and II through E14. On E15, neuron production slowed in lamina I and accelerated in lamina II as local circuit neurons and the remaining propriospinal neurons were generated. Neuron production ceased simultaneously in both lamina I and lamina II on E16.

Dual retrograde axonal tracers, Fluoro-Gold (FG) and true blue (TB), were used in conjunction with [3H]thymidine autoradiography to determine the number and neurogenic pattern of neurons with supraspinal projections in the superficial dorsal horn (SDH), i.e., laminae I and II, in spinal segment L1 of the rat. FG was injected into rostral brain centers (dorsal thalamus and midbrain), and TB was injected into the caudal brainstem (medulla) in young adult rats previously administered [3H]thymidine in utero. Following stereological correction, each dorsal horn had an average of 1.22 neurons in lamina I and 0.24 neurons in lamina II that had supraspinal projections per 10-microm transverse section. In the SDH, 52% of the neurons with supraspinal projections were found to project to rostral brain centers alone, 3.0% only to the caudal brainstem, and 45% to both areas. There was no significant difference in the percentage distribution of each of the three groups of neurons between lamina I and lamina II. Cell counts in the present study, in conjunction with previous observations in the literature, suggest that the majority of supraspinal projection neurons in the SDH fall into two groups: 1) spinomesencephalic neurons with collaterals to the medulla and 2) spinothalamic neurons with collaterals to the midbrain. The neurogenesis of supraspinal projection neurons in the SDH proceeded along an axon-length gradient, whereby neurons with the longest axons, those with projections to rostral brain centers, completed neurogenesis prior to neurons with shorter axons, those with projections only to the caudal brainstem. The generation of all SDH neurons with supraspinal projections was completed on embryonic day 14 (E14), 2 days prior to the completion of neurogenesis for SDH neurons with intraspinal projections.

The nerve cells of the gelatinosal complex (laminae I1 and 111) were examined in various planes of section in Golgi and Nissl preparations of the lumbosacral spinal cord of the adult monkey. An attempt was made to characterize the neurons based on morphological variations and establish criteria for consolidation or separation of laminae I1 and 111. In Nissl preparations the laminae essentially conform to Rexed's ('52) description for the cat. In Golgi preparations impregnated neurons of the gelatinosal complex show a spectrum of morphological variation. These variations, however, are not restricted by Rexed's border between laminae I1 and 111. In either lamina the cells vary in size from small (12 p m x 8 pm) to medium (30 p m x 25 pm) and in shape from fusiform to polygonal. Polygonal neurons are prevalent in the dorsal part of lamina I1 (Rexed's outer zone) and some have craggy contours.Axons of the cells of the gelatinosal complex vary in diameter, but most measure around 1.0 p m with some up to 2.0 pm. Their course is often a meandering one which cannot be followed. Those from cells in the outer zone of lamina I1 are different. They issue collaterals to lamina I then immediately enter the overlying white matter. Golgi type I1 (short axoned) cells were not definitively demonstrated. Nonetheless, the neurons of the gelatinosal complex display stalked dendritic appendages and axon-like processes which are similar to those described on Golgi type I1 interneurons elsewhere in the central nervous system. For this reason, in spite of the long axons and relatively large dimensions of the neurons of the gelatinosal complex, their circuitry is suspected to be similar to that of local circuit interneurons.The dendritic arbor of the cells of the gelatinosal complex, as viewed in horizontal sections, generally extends longitudinally with little mediolateral spread. In sagittal sections a stratified pattern of dendritic arborization divides the gelatinosal complex into three regions: (1) an outer region which corresponds to Rexed's ('52) outer zone of lamina 11, (2) a middle region composed of the remainder of lamina I1 and the dorsal portion of lamina 111, and (3) an inner region or ventral part of lamina 111. A large portion of the dendritic arbors of cells in the outer region spread ventrally a t oblique angles while those from the inner region spread dorsally. Dendrites arising from cells in the middle region, on the other hand, extend almost exclusively in the longitudinal plane, are often of considerable lengths, and give rise to unique recurrent branches. The dendritic arborization is discussed in relation to the primary afferents to the gelatinosal complex.The substantia gelatinosa of the dorsal horn gions. The dorsal region, which contains large was first recognized and named by Roland0 in nerve cells with Nissl bodies, was designated 1824 and later divided by Lissauer (1886) and the marginal zone of Waldeyer, while the Waldeyer (1888) into dorsal and ventral re-ventral region was called the substantia

Utilizing the Golgi technique, the present study provides a structural analysis of primate marginal (lamina I) neurons in the lumbosacral spinal cord. Marginal neurons are classified on the basis of major structural differences in dendritic conformation, distribution, and specialization. Cell size and shape alone were not found to be reliable criteria. Marginal cells can be divided into four major groups. Group I (Aspiny Neurons with Thick, Blunt Dendrites) consists of neurons with relatively thick dendrites which have an abrupt, blunt termination and few spines. This heterogeneous group includes large, medium, and small neurons of various shapes. Group II cells (Large to Medium Spiny Neurons) can be subdivided into two distinct groups: Group IIA neurons, which have longitudinal spiny dendritic arbors, and Group IIB cells, which have a moderately spiny, fan-shaped dendritic arbor which spreads across the lateral portion of the dorsal marginal zone. Both Groups A and B exhibit several types of spines. Group III (Aspiny Neurons with Thin, Tapering Dendrites) consists of small to medium size neurons which can be further divided into two groups: Group IIIA, which is characterized by oval- to fusiform-shaped neurons with tortuous, fine, tapered dendrites which ramify in the dorsolateral fasciculus and the lateral funiculus, and Group IIIB, which is composed of fusiform-pyramidal-and polygonal-shaped neurons with fine, tapering dendrites confined to lamina I. Group IV (Small Spiny Neurons) are characterized by a small fusiform- to pyramidal-shaped cell body and delicate longitudinal dendrites with small, short-necked pedunculated spines. This group is subdivided into Group IVA cells, which are found within lamina I proper and Group IVB cells, which are located in the dorsolateral fasciculus and have unmyelinated axons. The present study demonstrates considerably more structural diversity within the marginal zone than has been previously reported, and offers sufficient variation to correlate with functional differences described from laminal I neurons.

The purpose of the present study was to determine the relationship between the duration of a spinal neuron's neurogenic period and the length of its axon or level of projection. Spinal segment L1 was chosen for examination and neurons were divided into four projection groups: 1) supraspinal projection (SSp), 2) long ascending propriospinal (LAPr), 3) short ascending propriospinal (SAPr), and 4) descending propriospinal (DPr). To determine the duration of the neurogenic period for each group, 3H-thymidine was administered to fetal rats during the proliferative period for spinal neuroblasts on one of embryonic (E) days E13 through E16. Between 50 and 100 days after birth neurons in each group were labeled with the retrograde fluorescent tracer Fluoro-Gold. To demonstrate nerve cells with SSp projections, spinal cords were hemisected at spinal segment C3 in one group of animals and Fluoro-Gold was applied to the sectioned surface of the cord. Three additional sets of animals were used to label nerve cells with LAPr, SAPr, and DPr projections by injecting Fluoro-Gold into the gray matter at spinal segments C6, T12, and L5, respectively. Neurons labeled with both Fluoro-Gold and 3H-thymidine and neurons labeled with Fluoro-Gold alone in each animal in each group were counted and the data statistically analyzed. Results showed that within each spinal lamina neurons with different projections were generated, i.e., completed cell division, at significantly different rates. Neurons with the longest axons, those with SSP projections, were generated first. These were followed by those with LAPr projections, and finally those with SAPr and DPr projections. In most laminate there was no significant difference between the neurogenic periods of rostrally projecting short propriospinal (SAPr) neurons versus caudally projecting short propriospinal (DPr) neurons. It was concluded that the duration of the neurogenic period for a given group of neurons within each spinal lamina is inversely related to the distance between the nerve cell and its projection site regardless of the direction of its projection.

Cryostat- and vibratome-cut rat kidney secretions were singly or doubly labeled to visualize immunoreactive calcitonin-gene-related peptide (CGRPI) and substance P (SPI). Rats were perfused with 2-4% paraformaldehyde + 0.15% picric acid then rinsed with buffer. Horseradish peroxidase (HRP) was used to visualize CGRP in vibratome sections, and combined HRP and fluorophore were used to visualize the two peptides simultaneously in cryostat sections. There is a complex, multilayered plexus of CGRP nerves on the renal pelvis and a less dense, single-layered plexus on the major branches of the renal artery and on interlobar arteries and veins. A few axons innervate finer branches of the arterial tree and other intrarenal structures. Results of double immunolabeling suggest that SPI axons comprise a subpopulation of the CGRP axon population in the rat kidney. There was no evidence for a separate population of SPI axons.

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