Medial Lamina Research Articles

Antidromic field potentials recorded from cell groups of S2 spinal cord segment with axons in the opposite Th13 dorsolateral funiculus in the cat

Location of cell groups within gray matter of S2 spinal cord segment, whose axons are running in the opposite Th13 dorsolateral funiculus, were studied by means of antidromic field potentials recorded in chloralose anaesthetized cats. The cell bodies are forming six separate groups occupying medial laminae II and III, medial laminae IV and V, medial lamina VII, medial lamina VIII, lateral laminae V and VI and lateral laminae VIII and IX. Properties of main components in antidromic field potentials recorded in each of areas have been described. The presumable termination sites of axons of investigated cellular groups are considered.

NADPH-diaphorase histochemistry provides evidence for a bilateral, somatotopically inappropriate response to unilateral hindpaw inflammation in the rat

Unilateral hindpaw inflammation produces several neurochemical changes in the ipsilateral spinal dorsal horn that have been interpreted as contributing to the associated hyperalgesia. NADPH-diaphorase histochemical staining was used to examine the response of a population of neurons 1, 2, 6 or 24 h following injection of 6 mg carrageenan into the left hindpaw of the rat. The resulting unilateral hindpaw inflammation produced a bilateral, time-dependent, reversible increase in the number of NADPH-diaphorase stained neurons in the lumbar spinal cord that peaked at 6 h. In laminae I–III, there was a significant increase in the number of NADPH-diaphorase stained neurons both ipsilateral (25.9 ± 2.3) and contralateral (26.3 ± 1.3) to the inflamed hindpaw relative to uninflamed, control animals (18.6 ± 1.7, 17.4 ± 1.7, respectively). A smaller but significant increase was observed in laminae IV–VII and X. Under dark field illumination, an increase in the number of densely stained neurons in laminae I–III was also observed to peak at 6 h. A greater percentage of the neurons observed under bright field illumination were visible under dark field illumination at 6 h (47%) compared to control (18%), suggesting an increase in the enzymatic activity of neurons in laminae I–III in addition to the increase in the number of neurons with threshold levels of NADPH-diaphorase activity. There was no consistent increase in this ratio over time in laminae IV–VII or X. Six hours following carrageenan, there was a bilateral 50% increase in the density of NADPH-diaphorase staining in the neuropil in the medial laminae I–III. Both spinal neurons and primary afferent axons contributed to this bilateral increase in staining as the number of NADPH-diaphorase stained dorsal root ganglion cell bodies increased 47% over control. In addition to the increase in staining in the lumbar spinal cord, at 6 h post carrageenan, there was a bilateral 23% increase over control in the number of stained neurons in the cervical dorsal spinal cord. For comparative purposes, the distribution of Fos-immunoreactive nuclei was compared to NADPH-diaphorase 6 h post carrageenan. The distribution of Fos-immunoreactive nuclei differed from the NADPH-diaphorase stained neurons, suggesting that two separate populations of neurons were stained. Unilateral hindpaw inflammation did not result in an increase in NADPH-diaphorase activity in the periaqueductal gray or the ventroposteriolateral thalamic nucleus. The relationship of NADPH-diaphorase to nitric oxide is discussed and it is concluded that NADPH-diaphorase, while labeling nitric oxide-producing neurons, is not an exclusive marker for nitric oxide synthase following unilateral hindpaw inflammation. A role for NADPH-diaphorase in general excitatory mechanisms in the spinal cord is proposed.

Microflap vocal fold cover excisional biopsy for atypia and microinvasive glottic cancer

Microflap dissection and resection are an effective strategy for the management of premalignant and microinvasive neoplastic glottic epithelium. It provides for an en bloc excisional biopsy while affording precise diagnostic information by means of serial section histopathologic analysis of the specimen. The medial lamina propria is not violated, resulting in less scarring of the vocal fold cover to the vocal ligament. The approach may be repeated and preserves other cancer treatment options for more advanced disease. Finally, it is cost-effective and may be performed as outpatient surgery.

Spatial organization of inner hair cell synapses and cochlear spiral ganglion neurons

The morphological organization of the central projections of the cat cochlear spiral ganglion into the cochlear nucleus was previously investigated by creating restricted lesions in the anteroventral cochlear nucleus (AVCN) to ablate selectively either the lateral or the medial aspect of isofrequency projection laminae. Such lesions resulted in highly selective retrograde degeneration of spiral ganglion cells. Ablation of the lateral part of the AVCN caused degeneration of cells within the scala tympani part of the ganglion, whereas medial ablations within the AVCN induced degeneration of the scala vestibuli aspect of the ganglion. The peripheral axons also degenerated and this fiber loss exhibited selective topographies that paralleled the cell loss within the spiral ganglion, although this phenomenon was more prominent in the proximal part of the osseous spiral lamina near the ganglion and less obvious more distally near the habenula perforata. In this investigation, inner hair cells (IHCs) from these selective lesion cases were evaluated by electron microscopy of serial sections through the basal synaptic regions. Results demonstrated differential degeneration of afferent synapses, with greater (but not completely selective) loss of pillar synapses after lateral AVCN lesions and greater loss of modiolar synapses after medial lesions. Because auditory nerve fibers of different spontaneous discharge rates (SRs) have different spatial distributions on the IHC (Liberman, Science 216:1239, 1982), our results suggest that this SR-based organization is maintained in a topographic organization across the vertical (scala tympani-to-scala vestibuli) dimension of the spiral ganglion cell cluster and carried into the ventral cochlear nuclei (VCN). Thus, in addition to the spiral frequency organization represented by the dorsal-to-ventral frequency map in the VCN, there is also an orderly organization of inputs from high- and low-SR fibers across the lateral-to-medial dimension of the VCN such that the lateral isofrequency laminae receive a proportionately greater input from high-SR fibers, whereas medial isofrequency laminae receive preferential input from low- and medium-SR fibers.

Elastin at the Hinge Portion of the Eustachian Tube Cartilage in Specimens from Normal Subjects and Those with Cleft Palate

The density of elastin in the intermediate portion between the lateral lamina and the medial lamina of human eustachian tube (ET) cartilage was examined in six normal adults, seven normal children, and six children with cleft palate (CP) in order to obtain information about how the physical properties of the ET cartilage differ as a function of age and presence of CP. Cross sections of the midcartilaginous portions of the ETs that had been stained with Weigert's elastin stain were photographed at uniform magnification, the area for study was projected, and the meshlike are of the ET cartilage that stained elastin-positive was represented on paper by lines. A digitizer was used to measure the total length of all the lines representing elastin in each photomicrograph, and the mean was determined for each of the three groups. The mean density of elastin was significantly greater in normal adults than in normal children (Student's t test, t = 2.781; p less than .02). It was also significantly greater in normal children than in CP children (Wilcoxon t = 24.0; p less than .05). These results appear to indicate that CP children have poorer elasticity in this area of the ET cartilage, which might cause functional obstruction (floppiness) of the ET in those children.

Calbindin-D28K (CaBP28k)-like Immunoreactivity in Ascending Projections.

This study concerns the involvement of calbindin-D28K (CaBP28k)-containing neurons in ascending spinal projections to the brainstem (nucleus of the solitary tract, lateral reticular nucleus area), pontine (parabrachial area) and mesencephalic (periaqueductal grey) structures. All these central structures are important in the processing of visceroception and visceronociception and all are targets for spinal efferents from similar areas. CaBP28k controls the excitability of cells by acting on intrinsic calcium metabolism. Results refer to the caudal spinal areas where the visceroceptive regions are concentrated. Experiments were performed through a double labelling approach that combined the retrograde transport of a protein - gold complex to identify the projection cells and immunohistochemistry to identify the CaBP28k-positive cells. The caudal spinal cord is rich in both CaBP28k-containing and projection cells. Cells colocalizing the protein and the retrograde tracer were quite numerous, with a particularly high concentration in the superficial layers of the dorsal horn (laminae I and outer II) and the lateral spinal nucleus. The other spinal areas containing immunoreactive projection cells were the reticular part of the neck of the dorsal horn, the medial laminae VII and VIII, lamina X and the sacral parasympathetic nucleus. The superficial layers and the neck of the dorsal horn are targets for nociceptive, visceroceptive and thermal inputs; the sacral parasympathetic column and lamina X are involved in visceroceptive integration. A functional role for the lateral spinal nucleus has not yet been established. Quite similar results were obtained for each of the ascending pathways under study. The high incidence of CaBP28k in spinal pathways suggests that calbindin has a major role in controlling the excitability of spinal cells subserving the processing of visceroception and/or visceronociception information to supraspinal levels. The participation of CaBP28k-immunoreactive cells in spinal ascending tract cells largely outnumbers those previously reported for various neuropeptides (Leah et al., Neuroscience, 24, 195 - 207, 1988)

Abnormalities of Lateral Cartilaginous Lamina and Lumen of Eustachian Tube in Cases of Cleft Palate

Development of the lateral lamina (LL) of the eustachian tube (ET) cartilage was investigated in cleft palate (CP) cases and controls by measuring the areas of the LL and medial lamina (ML) of the ET cartilage in histologic cross section, and comparing the ratio of the area of LL to that of ML (LL/ML) in CP cases and controls. The degree to which the ET lumen appeared straight or C-shaped in cross section was also measured. Thirty temporal bones with the entire ET--10 CP cases and 20 controls--were studied. The ratio of the areas of the ET cartilage was significantly smaller (t = 2.903, p less than .01) and the curvature of the ET lumen was significantly less (t = 2.080, p less than .05; chi 2 = 3.936, p less than .05) in CP cases than in controls. In addition, in all 30 CP cases and controls, the ratio of the areas of cartilage was significantly less in specimens with straight ET lumens than in those with C-shaped lumens (t = 2.713, p less than .02). The results appear to show that the ET cartilages and lumens are anomalous in CP cases. These anomalies are considered to be important factors in active ventilatory dysfunction of the ET.

Cells of origin of avian postsynaptic dorsal column pathways

Whereas in the cervical spinal cord of pigeons lamina IV and medial lamina V neurons are at the origin of postsynaptic pathways to the dorsal column nuclei, lumbar lamina IV neurons do not project substantially beyond the cervical enlargement. There is, however a distinct group of medially located lumbar lamina V neurons which projects ipsilaterally to the dorsal column nuclei.

Scanning electron microscopic studies of tissue elastin components exposed by a KOH-collagenase or simple KOH digestion method.

A KOH-collagenase or simple KOH digestion method was employed for scanning electron microscope (SEM) studies of elastin components in the rat thoracic aorta, mouse urinary bladder, and human ductus deferens. Immersion of the fixed tissues in 30% KOH solution for 8-10 min at 60 degrees C, with or without subsequent collagenase treatment, successfully removed collagen fibrils and basal laminae while leaving cellular and elastin elements unchanged at their original shapes and locations. The internal elastic lamina of the rat aorta appeared as a solid sheet formed by elastin fibrils 0.1-0.2 microns thick, while the medial elastic laminae were more fibrous because of the presence of numerous fine elastin fibers on their surface. Adventitial elastin fibers were of a cord-like shape complicatedly entangled among the adventitial fibroblasts. These fibers were seen as bundles of fibrils 0.1-0.2 microns thick. In the mouse urinary bladder, elastin formed a thin lace-like sheet just beneath the serosal covering of the peritoneum. This sheet was composed of small bundles of fine (0.1-0.2 microns thick) fibrils. The external connective tissue of the human ductus deferens was made up of a three-dimensional loose network of elastin fibers 0.1-1.5 microns thick. These fibers also appeared as bundles of the fine fibrils. These findings indicate that the present method is useful for SEM studies of elastin as well as cellular components in various tissues and organs. This study also maintains that elastin fibers and laminae are basically composed of unit fibrils of 0.1-0.2 microns thickness. As elastin components are arranged specific to individual organs and tissues, it is reasonable that these components are concerned in the characteristic mechanical properties of these tissues and organs.

The Morphometry and Three-Dimensional Structure of the Adult Eustachian Tube: Implications for Function

An accurate description of the functioning Eustachian tube (ET) requires a thorough knowledge of the anatomic relationships of its components. To this end, 15 "normal" adult ETs were obtained, sectioned, and stained with hemotoxylin-eosin. Descriptive and quantitative data of ET structures and their relationships were obtained. Eustachian tube length was normalized and comparisons between specimens made. This analysis suggests (1) in its midsection the cartilage is loosely attached to the cranial base; (2) the deep portion of the tensor veli palatini (TVP) originates from the lateral lamina and the fibrous portion of the lateral membraneous wall; and (3) the levator veli palatini (LVP) can interact with the ET primarily via the elongated medial lamina in the anterior portion of the ET. These observations suggest the ET is opened by a medial rotation of cartilage effected primarily by the TVP, but aided anteriorly by the LVP.

Afferents to the cerebellar nuclei from the cervical enlargement in the rat, as demonstrated with the Phaseolus vulgaris leucoagglutinin method

Injections of Phaseolus vulgaris leucoagglutinin into the cervical enlargement labeled spinocerebellar fibers in the rat cerebellar nuclei. Immunoreactive terminal axons and terminals were distributed in the medial nucleus, and the anterior interpositus and the posterior interpositus nucleus. The present study suggests that spinocerebellar neurons in the cervical enlargement (the medial lamina VI and the central lamina VII groups) project to the cerebellar nuclei.

A spinomedullary projection terminating in the dorsal reticular nucleus of the rat

Spinal afferents to the medullary dorsal reticular nucleus were studied using the following retrograde tracers: horseradish peroxidase (diluted in dimethylsulfoxide), wheat germ agglutinin conjugated with horseradish peroxidase, and cholera toxin subunit B. Spinal cord cells projecting to that medullary region were located predominantly in medial lamina I and lamina X. Cell labelling was moderate in the medial part of laminae II–IV and sparse throughout laminae V–VII. Labelling was predominantly ipsilateral in the dorsal horn and bilateral in laminae VII and X. After mechanical lesions of the dorsal white matter which severed most of the ipsilateral cuneate fasciculus, the numbers of superficial dorsal horn cells that were labelled from the dorsal reticular nucleus were considerably decreased caudal to the lesion, which suggests that their axons utilize mostly the cuneate fasciculus. Since the medullary dorsal reticular nucleus of the rat has a predominant population of nociceptive specific neurons, it is suggested that this spino-dorsomedullary reticular pathway is involved in pain processing.

Posterior cervical interspinous compression wiring and fusion for mid to low cervical spinal injuries.

A technique of posterior cervical interspinous compression wiring and fusion, which offers significant immediate stability, is presented. Its efficacy in 50 consecutive cases illustrates its utility. The technique involves the passage of an interspinous cerclage wire. Rather than placement of onlay laminar and facet grafts, a split-thickness tricortical iliac-crest graft is compressed against the involved medial laminae and spinous processes bilaterally. These grafts are held in place by a compression wire, which encircles the grafts and thus sandwiches the spinous processes between them. This virtually ensures subsequent bone fusion and offers substantial acute stability. The compression wire offers an added advantage of encircling the cerclage wire, thus pulling it dorsally. This significantly diminishes translational mobility at the unstable segment. It also minimizes hyperextension at the unstable segment via medial compression of the grafts into the interspinous space. The fusion of a minimal number of spinal segments is emphasized. This substantially diminishes the chance of flexible kyphosis and degenerative changes, both above and below the fusion site. A three- or four-level fusion was performed in only 11 patients. The remaining 39 patients underwent two-level fusion. A solid bone fusion was achieved in all cases, with a follow-up period of at least 6 months. In one patient, the spinous process fractured, necessitating an anterior fusion procedure. The technique presented here appears to acutely offer a very stable construct and, in addition, is a simple and straightforward procedure for the treatment of the unstable cervical spine.

Postsynaptic dorsal column neurons in the cat: a study with retrograde transport of horseradish peroxidase.

The numbers, laminar position, perikaryal and dendritic morphology, and axonal trajectories of postsynaptic cells ascending the dorsal column have been studied after implantation of HRP pellets in either the dorsal columns or dorsal column nuclei after destruction of the dorsolateral fascicle on one side. Observations made throughout the spinal cord gave estimated figures of 800-1000 and 1700-2000 cells in lumbosarcal and brachial enlargements respectively on the side of the implant. The commonest type (C), centred on lamina IV, had dendritic trees greatly extended rostrocaudally and restricted mediolaterally in the lateral dorsal horn, the extension and restriction diminishing for more medial cells. Type B cells differed dramatically, with large straight dendrites in the transverse plane and large perikarya in medial lamina V. Type A cells, distinguished by both rostrocaudal and mediolateral restriction in dendritic trees, were only found medially in laminae III and IV. Outside the enlargements, in high lumbar and thoracic cord, many fewer cells were found, corresponding to Type C but with dendrites much elongated rostrocaudally and little mediolateral variation. Many small fusiform cells were found in medial lamina VI in the upper cervical cord, distinct from any of the above. A few cells were found in the cord enlargements in lamina VII of the contralateral ventral horn, with axons crossing through the ventral commissure. The axons of all cell types were tortuous, and some entered the dorsolateral fascicle before crossing into the dorsal column: collaterals were often seen but could not be followed far. A complementary study of cells with axons ascending in the dorsolateral fascicle is reported in the following paper.

Ascending projections of long descending propriospinal tract (LDPT) neurons

Ascending projections of long descending propriospinal tract (LDPT) cells were investigated using the technique of double retrograde labeling. In rat, injection of one fluorescent dye was made into either the reticular formation or the cerebellum and a second dye was injected into the lumbosacral enlargement (LSE). In cat, injections were made into the reticular formation and into the lumbosacral enlargement. Using fluorescence microscopy, observation of neurons in the cervical enlargement (CE) revealed single- and double-labeled cells which were either spinoreticular or spinocerebellar tract cells and/or LDPT cells. In both cat and rat, the locations of double-labeled LDPT-spinoreticular cells were in the ventromedial spinal gray matter of the CE and were coextensive with single-labeled LDPT and spinoreticular cells. The locations of double-labeled LDPT-spinocerebellar cells in rat were in the ventromedial gray and were coextensive with single-labeled LDPT cells, but not with single-labeled spinocerebellar cells. The latter group was located in central lamina VII and medial laminae V and VI. Overall, the mean number of double-labeled cells was 40% of rat and 7% of cat LDPT cells, indicating projections to either the brainstem reticular formation or cerebellum as well as to the lumbosacral enlargement. Thus, a subpopulation of LDPT cells apparently also serves as a spinoreticular (SR) and spinocerebellar (SC) projection system.

Effects of muscle and cutaneous hindlimb afferents on L4 neurons whose activity is modulated by neck rotation.

We recorded extracellularly, in decerebrate, labyrinthectomized cats, from spontaneously active L4 neurons whose activity was modulated by head rotation, and studied the effects of stimulation of ipsilateral hindlimb nerves. Rotation of the head about the longitudinal (roll) axis was more effective than rotation about the transverse (pitch) axis or vertical (yaw) axis for this group of neurons. Most units received convergent excitatory or inhibitory inputs from several nerves, with excitation being more prominent. The most effective muscle nerves were quadriceps (37/43 neurons), sartorius (19/21) and tibialis anterior (17/35); stimulation of biceps posterior-semitendinosus, biceps anterior-semimembranosus, or gastrocnemius rarely influenced the firing of the neurons. Group I effects were present in only a small fraction of neurons; however, short latency (central latency less than or equal to 5 ms) group II effects were observed in almost one-third. Longer latency group II as well as group III inputs were also common. All neurons received inputs from mixed and cutaneous nerves which usually had low thresholds and central latencies greater than 5 ms. Most recording sites were in medial lamina VII or lamina VIII; some of the units were identified by antidromic stimulation as propriospinal neurons which projected to the lumbar enlargement.

Spinal and supraspinal terminations of primary afferent fibers from the gastrocnemius-soleus muscle in the cat

The central distribution of the terminations of primary afferent fibers from the gastrocnemiussoleus muscle in the cat was examined with the method of transganglionic transport of horseradish peroxidase. At the segmental level, the main projection areas were found to be laminae I and V–VII; in the rostrocaudal direction, the terminations extended from the third sacral segment to nucleus Z. A 40% solution of horseradish peroxidase in 2% dimethylsulfoxide was applied to the central cut ends of the muscle nerves in an open pool for several hours and subsequently was removed. A capsule of tracer solution applied during the survival period of the animals was found to result in additional labeling due to peripheral leakage. The tissue sections were processed with tetramethylbenzidine. Termination fields were consistently observed ipsilaterally in: lamina I from the L4 through S3 segments, being most dense in L6 and S1; lateral lamina V in L6 and S1–3; medial laminae VI–VII from L5 through S3; medial Clarke's column from L1 through L4; the ventral aspect of the gracile nucleus; and, nucleus Z. Little or no labeling was found in laminae II–IV in experiments in which peripheral leakage of tracer solution was prevented. The distribution of reaction product in laminae VI–VII and Clarke's column corresponds to the projections of large-diameter afferent fibers from the gastrocnemius-soleus muscle. The projections to laminae I and V, which are attributed to small-diameter sensory fibers, indicate involvement of these laminae in sensory modalities mediated by slowly conducting muscle afferent fibers, e.g. deep nociception. This pattern contrasts strongly with the central projections of cutaneous fibers, which terminate heavily in laminae II–IV, but resembles the central distribution of fibers from tooth pulp and viscera.

Histopathologic Study of Eustachian Tube in Cleft Palate Patients

We studied eight temporal bones from eight individuals with cleft palates (CPs) and eight age-matched control temporal bone specimens from our collection. We used the eustachian tube (ET) and its surrounding structures in serial vertical histologic sections. The findings observed in CP specimens were as follows: 1) the angle between axial lines through the tensor veli palatini (TVP) muscle and the superior portion of the ET lumen was narrow, 2) the angle between axial lines through the lateral lamina and the medial lamina of the cartilage was wide, 3) the angle between axial lines through the TVP muscle and the lateral lamina of the cartilage was narrow, and 4) the angle between axial lines through the superior part and the inferior part of the ET lumen was wide. From these findings, we assume that the ET dysfunction that occurs in individuals with CP is the result of abnormalities of the ET and its cartilage and of abnormal anatomic relationships of these structures to the TVP muscle.

Spinocerebellar projections from the cervical enlargement in the cat, as studied by anterograde transport of wheat germ agglutinin-horseradish peroxidase.

The projection fields of spinocerebellar tracts arising from the cervical enlargement were studied by the anterograde transport of wheat germ agglutinin conjugated to horseradish peroxidase (WGA-HRP) in the cat. Following injections of WGA-HRP into the C5-C8 or T1 segments, labeled terminals were seen in lobule I to sublobule Vf of the anterior lobe, and lobule VI, sublobule VIIb, lobules VIII and IX, the simple lobule, crus II, and the paramedian lobule of the posterior lobe. In the sagittal plane of sublobules Ib-Vf and sublobules VIf and VId, the labeled terminals were distributed mainly in the superficial two thirds of the apicobasal extent. The labeled terminals in the anterior lobe accounted for about 70% of the total labeled terminals; the great majority were in lobule IV (17-20%) and lobule V (40%). The labeled terminals in the posterior lobe accounted for 30% of the total labeled terminals; the majority were in sublobules VIf (11-15%) and VId (6%). In the mediolateral extent, more than 50% of the total labeled terminals in each lobule were concentrated within 1.0 mm from the midline (the vermis) and 70-80% within 2.0 mm from the midline (the vermis and the medial part of the intermediate regions). A smaller number were also present in the intermediate region. Cases with lateral cordotomies revealed that the projections were bilateral but predominantly ipsilateral to the cells or origin and that the quantity of the ipsilateral projection was 66.5-75% of the total in each of sublobules IVb, Va, and VIf. The projection to the paramedian lobule was also predominantly ipsilateral. Projection fields in the horizontal plane were reconstructed from a series of transverse sections through each lobule. In sublobules Va-VIf labeled terminals were distributed in three areas: area 1 located within 0.25 mm from the midline in zone A1 of Voogd; area 2 located between 0.5 and 0.75 mm lateral to the midline in zones A1 and A2; and area 3, which appeared to be located between 0.75 and 1.5 mm lateral to the midline in zones A2-B. These areas extended longitudinally in the apical two thirds of the lobules. From the present and previous retrograde HRP studies it was suggested that the neuronal groups in the cervical enlargement (the medial lamina VI group and the central lamina VII group) project to lobules I-V of the anterior lobe and lobule VI, sublobule VIIb, and lobule VIII of the posterior lobe. They have strong projections to caudal lobules of the anterior lobe (lobules III-Va) and lobules facing the primary fissure (sublobules Vd-Vf and sublobules VIf and VId).

Several morphological types of terminal arborizations of primary afferents in laminae I‐II of the rat spinal cord, as shown after HRP labeling and golgi impregnation

The morphology of the terminal arborizations in laminae I-II of primary afferent fibers was studied in sections stained by the heavy metal (nickel and cobalt) intensification of diaminobenzidine (DAB) after crushing one dorsal root with horseradish peroxidase (HRP) crystals, and with the mixed Golgi method which duplicated the staining provided by the first method. Besides the flame-shaped arbors located in deep lamina IIi as an extension of the arbors of lamina III, which were derived from 1.7-micron thick stem fibers (probably A alpha beta fibers), six types of terminal arbors, all rostrocaudally oriented, arising from fine stem fibers and having preferential locations, were disclosed. The lateral third of laminae I-II contained a longitudinal plexus of parallel 0.8-micron thick stem fibers (C fibers) with longitudinal side branches generating many boutons en passant. Laminae I and IIo, in their middle third, contained dichotomizing longitudinal fibers with elongated boutons, arising from 1-micron thick stem fibers (C or A delta), and, in the medial third, a dense plexus with terminal networks carrying large boutons, which arose from 1.3-micron thick stem fibers (A delta). Fibers ending in terminal bouquets and issuing from 1-micron thick stem fibers (C or A delta) occupied the dorsal part of middle and medial lamina IIi, while the intermediate part contained clusters (swarms) of ultrafine boutons arising from extremely fine fibers. The whole medial lamina IIi also contained fine undulating fibers arising from 0.3 micron-thick stem fibers (C fibers) with large boutons near their ends. The functional meaning of this multiplicity of morphological types and locations is still unclear. It may be clarified when single unit analysis of HRP-injected fine fibers is made possible, or immunocytochemical stainings disclose the neurotransmitters utilized by each fiber type.