Ultrastructural detection of neuronally transported choleragenoid by postembedding immunocytochemistry in freeze-substituted Lowicryl HM20 embedded tissue

Choleragenoid (cholera toxin B-fragment; CTB) is an anterograde, retrograde and transganglionic neuronal tracer. We describe a method for detecting CTB-labeled neuronal cell bodies, neurites and boutons at the ultrastructural level, using postembedding immunogold techniques on freeze-substituted Lowicryl HM20 embedded nervous tissue. Primary afferents and motoneurons were labeled by injection of CTB in the dorsal ramus of the C2 spinal nerve of the rat. Following fixation with paraformaldehyde (4%) and glutaraldehyde (0.25%), tissue sections from the spinal cord C2 segment were freeze-substituted and embedded in Lowicryl HM20 and subsequently processed with postembedding immunocytochemistry for CTB and glutamate. Immunogold particles indicating CTB immunoreactivity were found over primary afferents and motoneurons. In primary afferents in the central cervical nucleus (CCN) and motor nuclei, immunogold labeling was seen in boutons over vesicle-containing axoplasm and to a lesser extent over axoplasm devoid of vesicles, but not over mitochondria or axolemma. In motoneurons, immunogold particles were seen over the Golgi apparatus in the soma and over lysosomes in both soma and dendrites. Quantification of glutamate-like immunoreactivity in 20 CTB-labeled and 20 CTB-negative boutons in the neuropil was found similar, indicating that CTB does not interfere with the immunocytochemical detection of neuronal epitopes such as the transmitter substance glutamate.

Distribution of glutamate-, glycine- and GABA-immunoreactive nerve terminals on dendrites in the cat spinal motor nucleus

The dendritic tree constitutes more than 93% of the receptive membrane area of a spinal motoneuron, yet little is known about its synaptic inputs. In this study we examined the distribution of glutamate-, GABA- and glycine-like immunoreactivity in boutons apposing dendrites in the L7 spinal cord motor nucleus, by use of postembedding immunohistochemistry on serial sections. We examined 799 boutons apposing 401 cross-sectioned dendrites of different calibre (range 0.2-15 microm), and 14 first-order (stem) dendrites. Thirty-five percent (35%) of the boutons were immunopositive for glutamate and 59% for GABA and/or glycine. Among the latter, 30% showed glycine immunoreactivity only and 24% were immunoreactive for both GABA and glycine. Very few were immunoreactive only for GABA (5%). As few as 6% of the boutons were judged as not enriched for any amino acid analysed. The fine structural characteristics of the boutons were in accordance with previous descriptions. The sample of dendrites was arranged in calibre bins in order to facilitate distribution analysis. Stem dendrites differed from the other bins, with a high total bouton covering (61%) and a high bouton density. Sixty-nine percent of the membrane covering was by glycine- and/or GABA-immunoreactive boutons, whereas 18% was covered by boutons enriched in glutamate. For non-stem dendrites, bouton covering fell from 33% to 12% with decreasing calibre. However, bouton apposition length decreased in parallel, yielding a fairly uniform bouton density among dendrites of different calibre. The lack of correlation between packing density and dendrite calibre was also evident when the sample of dendrites was broken down into subsamples based on content of amino acid immunoreactivity. The latter analysis also revealed that both the relative covering and density of boutons containing inhibitory amino acids (57%; glycine and/or GABA) and glutamate (38%), respectively, did not vary systematically with dendrite calibre. Combined, the data indicate that in non-stem dendrites the proportion of excitatory and inhibition inputs does not change systematically throughout the dendritic arborizations of spinal alpha-motoneurons. Thus, spinal motoneurons can, with respect to the general synaptic architecture, be divided into two main compartments, i.e. the proximal soma-juxtasomatic compartment (including stem dendrites) and the distal dendritic compartment. The proximal domain is under a powerful glycine and/or GABA influence. Finally, based on the data presented here and previously published data, it was calculated that spinal alpha-motoneurons receive in the range of 50-140 x 10(3) synaptic boutons.

Alterations in mystacial pad innervation in the aged rat

It is well established that sensory perception becomes impaired with advancing age and that, in parallel, dystrophy and degeneration of axons occur in sensory pathways. In this study, the impact of aging was examined in the mystacial pad, which receives a large variety of sensory nerve endings organized in a highly predictable pattern. Mystacial pad specimens from aged (30 months old) and young adult (2-3 months old) female Sprague-Dawley rats were processed, in parallel, for immunohistochemical analyses with antibodies against human neuronal cytoplasmic protein (protein gene product 9.5), transmitter enzymes, and several neuropeptides. Several changes in cutaneous innervation including both degenerative and regenerative processes were evident in the aged rat: (1) the Merkel endings and lanceolate endings that emanate from large-caliber afferents in the whisker follicles were reduced and showed signs of degeneration. Furthermore, a reduction of piloneural complexes at the intervibrissal hairs were evident, but only in aged rats that showed more severe behavioral sensorimotor disturbances. In contrast, Ruffini endings as well as mechanoreceptors emanating from medium-caliber axons, i.e., transverse lanceolate and reticular endings, appeared normal. (2) A reduction was evident among two sets of unmyelinated epidermal endings; however, the epidermal innervation affiliated with the intervibrissal hairs appeared normal in the aged rat. (3) A loss of sympathetic neuropeptide tyrosine (NPY) or tyrosine hydroxylase-immunoreactive (IR) and somatosensory Calcitonin gene-related peptide (CGRP)-IR perivascular axons was paralleled by an increase in presumed parasympathetic NPY/CGRP-IR axons. (4) Two "novel" networks of fine-caliber axons were observed in the outer and inner root sheaths of the whisker follicles in the aged rat. (5) NPY was present in a population of small-caliber, somatosensory CGRP-IR axons in the aged rat. This may represent a de novo synthesis, since, normally, NPY-like immunoreactivity is not observed in this set of axons. Our results suggest that the sensory impairments occurring with advancing age are part of a peripheral process instigated by changes in nerve-target interactions and/or incapacitation of the neuronal machinery to sustain the axonal integrity.

Fluorescence lifetime measurements in confocal microscopy of neurons labeled with multiple fluorophores

In order to resolve multiple fluorophores by their lifetimes in discrete tissue domains, the labeling intensity must be sufficiently strong and the intensity-difference between the labels must not be too large, the rate of fading should be similar for all fluorophores, and the lifetimes of the fluorophores should be sufficiently discrete. We could readily distinguish Cyanine-3.18 (Cy-3), Lissamine Rhodamine (LRSC), and Texas Red when they were not colocalized in tissue profiles. Colocalization of Cy-3 and LRSC, as well as Cy3 and Texas Red, could also be distinguished, while the combination of LRSC and Texas Red was more difficult. We have used fluorescence lifetime recordings in confocal microscopy to detect different neuropeptides in neurons. We demonstrate that somatostatin and galanin are colocalized in axon profiles of the spinal cord dorsal horn.

Neuropeptides and neurotrophin receptor mRNAs in primary sensory neurons of aged rats

Neuropeptides and neurotrophin receptors are regulated in primary sensory neurons in response to axonal injury, and axonal lesions are characteristic stigmata of aging primary sensory neurons. We have therefore examined the expression of neuropeptides and neurotrophin receptor mRNAs in 30-month-old (median survival age) Sprague-Dawley rats to see if similar adaptive mechanisms operate in senescence. The content of neuropeptides was examined with immunohistochemistry (IHC) and in situ hybridization (ISH), and the cellular mRNA expression of neurotrophin receptors was studied with ISH. All of the aged rats had symptoms of hind limb incapacity (posterior paralysis), but fore limbs did not seem affected. The size-distribution of neuronal profiles in cervical and lumbar dorsal root ganglia (DRGs) was similar in aged and young adult (2-3 months old) rats. In aged rats, the DRG neurons showed an increase in both immunolabelling and mRNA content of neuropeptide tyrosine (NPY), as well as an increased cellular expression of galanin mRNA. In the same animals, there were decreased cellular levels of calcitonin gene-related peptide (CGRP; IHC and ISH) and substance P (SP; IHC and ISH), while the difference in neuronal somatostatin (IHC and ISH) was small. The distribution of neuropeptide immunoreactivities in the dorsal horn of the corresponding spinal cord segments revealed a decreased labelling for CGRP-, SP-, and somatostatin-like immunoreactivities (LI) in the aged rats at both cervical and lumbar levels. NPY- and galanin-LI had a similar distribution in aged and young adult rats. NPY-immunoreactive fibers were also encountered in the dorsal column of aged but not young adult rats. ISH revealed that most of the primary sensory neurons express mRNA for the p75 low-affinity neurotrophin receptor (p75-LANR) and that there was no discernible difference between young adult and aged rats. The labelling intensity for mRNA encoding high-affinity tyrosine kinase receptors (TrkA, TrkB, and TrkC) was decreased in aged rat DRG neurons, while the percentage of neuronal profiles expressing mRNA for TrkA/B/C was similar in young adult and aged rats. The changed pattern of neuropeptide expression in primary sensory neurons of aged rats resembled that seen in young adult rats subjected to axonal injury of peripheral sensory nerves and may, thus, indicate aging-related lesions of sensory fibers. Since NPY is primarily present in large and galanin in small DRG neurons, the stronger effect on NPY as compared to galanin expression may indicate that aging preferentially affects neurons associated with mechanoreception (A alpha and A beta fibers) as compared to nociceptive units (A delta and C fibers). Furthermore, the observed changes in neuropeptide expression were most pronounced in lumbar DRGs, that harbors the sensory neurons supplying the affected hindlimbs of the rats.

Decreased expression of TrkB and TrkC mRNAs in spinal motoneurons of aged rats

Several studies have indicated that a decrease in availability and/or responsiveness to neurotrophin(s) may be of importance in ageing and disease-related neurodegeneration. Using in situ hybridization we have studied the mRNA expression of the full-length neurotrophin receptors TrkB and TrkC in spinal cord motoneurons of aged rats (30 months old) with symptoms of hindlimb incapacity and in young adult rats (2-3 months old). The labelling intensity for TrkB of the individual cell profile was decreased by 25% (P < 0.001) in both the cervical and lumbar motor nuclei of aged rats. In thoracic motoneurons of aged and young adult rats the difference in expression of TrkB mRNA was smaller (down by 15%; P < 0.05). The labelling for TrkC mRNA was much weaker than that for TrkB in both aged and young adult rats, but TrkC mRNA expression also seemed to decrease. Comparison of the different motor nuclei along the spinal cord axis revealed that the motoneurons of the L6/S1 nuclei showed the strongest hybridization signal for the two Trk receptors in both aged and young adult rats. The possibility that a decrease in TrkB mRNA may contribute to age-related motor disturbances is discussed.

Qualitative and quantitative analysis of glycine- and GABA-immunoreactive nerve terminals on motoneuron cell bodies in the cat spinal cord: a postembedding electron microscopic study

The distribution of glycine- and gamma-aminobutyric acid (GABA)-like immunoreactivity (LI) in nerve terminals on the cell soma of motoneurons in the aldehyde-fixed cat L7 spinal cord was examined using postembedding immunogold histochemistry in serial ultrathin sections. Quantitative examination of 405 terminals on eight neurons of alpha-motoneuron size in the L7 motor nuclei from one animal was performed. A majority of the terminals (69%) were immunoreactive to glycine and/or GABA. These terminals contained flat or oval synaptic vesicles, thus classifying them as F type or as C type in one case. In no case was a type-F terminal unlabeled for both glycine and GABA. Most of the immunolabeled terminals were immunoreactive to glycine only (62.5%), whereas 35.4% contained both glycine- and GABA-LI. A very small number of immunolabeled terminals (2%) were immunoreactive to GABA only. In those terminals, where glycine- and GABA-LI coexisted, the gold particle density for each amino acid was only half of that seen in boutons containing only one of the two amino acids. The involvement of glycine and GABA in postsynaptic inhibition of spinal alpha-motoneurons is discussed, with particular reference to the possibility that these two inhibitory amino acids may be coreleased from a significant proportion of the nerve terminals impinging on the cell bodies.

Ia boutons to CCN neurones and motoneurones are enriched with glutamate-like immunoreactivity

The monosynaptic connection between muscle spindle Ia afferents and motoneurones is one of the most extensively studied reflex pathways in the central nervous system. Physiological evidence has pointed to glutamate as the fast transmitter in this synaptic connection. In this study of the spinal cord segment C2, we used dual labelling with cholera toxin subunit B-horseradish peroxidase (B-HRP) and postembedding immunohistochemistry to show that group Ia primary afferent boutons synapsing on retrogradely labelled central cervical nucleus (CCN) neurones and motoneurones are enriched in glutamate-like immunoreactivity (LI). All double-labelled Ia terminals studied could be classified as S-type (CCN neurones and motoneurones) or M-type (motoneurones) boutons.

Increased expression of serotonin transporter messenger RNA in raphe neurons of the aged rat

The action of serotonin (5-hydroxytryptamine; 5HT) in the nervous system is terminated by reuptake of the neurotransmitter into the presynaptic nerve terminal via a plasma membrane-bound transporter protein. Recently, cDNAs encoding serotonin transporter protein were cloned. Using in situ hybridization we have studied the expression of serotonin transporter mRNA in the bulbospinal 5HT system of adult (2-3 months) and aged (30 months) rats. In adult rats, serotonin transporter mRNA labelled neurons were detected in the nucleus raphe obscurus, pallidus and magnus. In all aged rats, the optical density of the serotonin transporter mRNA labelling of individual cell profiles was increased by 20-30% (P < 0.001) when compared with adult rats. Five of the six aged rats studied had various degrees of hindlimb motor dysfunctions. In rats with the most pronounced signs of hindlimb motor dysfunction the number of labelled neurons was increased by 25-75% (P < 0.01) when compared with young adult rats. It is concluded that an increased serotonin transporter gene expression is present in the bulbospinal 5HT system of aged animals.

Increase in alpha-CGRP and GAP-43 in aged motoneurons: a study of peptides, growth factors, and ChAT mRNA in the lumbar spinal cord of senescent rats with symptoms of hindlimb incapacities

Sprague-Dawley rats develop progressive motor dysfunctions during the third year of life. We use this as a model to examine possible neuronal mechanism(s) that may cause motor impairments occuring during aging. In this study we have used indirect immunofluorescence histochemistry (IF) and in situ hybridization histochemistry (ISH) to study quantitatively and qualitatively the staining pattern and mRNA expression of calcitonin gene-related peptide (alpha-CGRP), growth-associated protein 43 (GAP-43), and acidic fibroblast growth factor (aFGF) in spinal lumbar motoneurons of young adult (2-3 months) and aged (30 months) Sprague-Dawley rats. In addition, mRNAs encoding choline acetyltransferase (ChAT), beta-CGRP, and cholecystokinin (CCK) were analyzed. All aged rats used in this study disclosed symptoms of hindlimb incapacity, ranging from mild weight-bearing insufficiency to paralysis of the hind limbs. The symptoms were confined to the musculature of the hindlimb and hip regions. Only a small number (approximately 15%) of the large motoneurons that innervate the hindlimb muscles were lost in those aged rats that had clinical symptoms of hindlimb motor incapacities. The remaining motoneurons expressed ChAT mRNA at levels similar to those of young adult rats. The vast majority of these motoneurons showed increased mRNA levels for alpha-CGRP and GAP-43. Aged motoneurons contained more CGRP like immunoreactivity (LI), but the number of immunoreactive neurons was smaller than in adult rats. GAP-43-LI could be detected in motoneurons in aged, but not in adult, rats. GAP-43-LI was always colocalized with CGRP-LI in aged motoneurons. Studies of individual aged rats revealed that the increase of GAP-43 mRNA-positive cell bodies occurred in cases with the most severe clinical symptoms, whereas the increase in alpha-CGRP was even evident in rats with mild symptoms. No alterations in content of aFGF-LI or aFGF mRNA could be detected in the aged rat, and the content of CCK and beta-CGRP mRNAs was also normal. The usefulness of this rat model for studies of neuromuscular aging and possible functional roles for GAP-43 and CGRP in plastic and regenerative processes during aging are discussed.

Spectra and fluorescence lifetimes of lissamine rhodamine, tetramethylrhodamine isothiocyanate, texas red, and cyanine 3.18 fluorophores: influences of some environmental factors recorded with a confocal laser scanning microscope

We report on the spectra and fluorescence lifetimes of four commonly used fluorophores: lissamine rhodamine (LRSC); tetramethyl rhodamine isothiocyanate (TRITC); Texas Red; and cyanine 3.18 (Cy-3). Fluorescence lifetime recordings revealed that these spectrally overlapping fluorophores can be individually detected by their lifetimes, indicating that at least four fluorophores can be individually identified in discrete tissue domains by confocal microscopy. A further advantage of lifetime recordings is that fluorophores that emit light within the same wavelength band can be used and chromatic aberrations are therefore circumvented, thereby improving the spatial accuracy in imaging of multiple fluorophores. Low and high pH, respectively, tended to influence fluorophore emission spectra and fluorescence lifetime. IgG conjugation of the fluorophores tended to shift the spectra towards longer wavelengths and to change the fluorescence lifetimes. The IgG-conjugated form of the fluorophores may, when applied to tissue specimens, change the emission spectrum and lifetime. In addition, different tissue embedding procedures may influence fluorescence lifetime. These observations emphasize the importance of spectral and lifetime characterization of fluorescent probes within the chemical context in which they will be used experimentally. Changes in spectra and fluorescence lifetimes may be a useful tool to gain information about the chemical environment of the fluorophores.

Improved fluorophore separation with IMS confocal microscopy

Some of the most extensively used fluorophores for multicolour fluorescence labelling of tissue, such as Lucifer yellow, fluorescein, Cyanine-3.18 and rhodamine, all have the disadvantage of being difficult to separate spectrally due to their broad and overlapping emission spectra. With the intensity-modulated multiple-beam scanning (IMS) technique, cross-talk between labels can be reduced to a fraction of that seen using conventional excitation and detection technique. Thus, cross-talk to the 'red' channel decreased with about one order of magnitude for the 'green' fluorophores Lucifer yellow and FITC. For the tested 'red' fluorophores, the amount of cross-talk to the green channel was reduced by 60-90%.

Enkephalin-, thyrotropin-releasing hormone- and substance P-immunoreactive axonal innervation of the ventrolateral dendritic bundle in the cat sacral spinal cord: an ultrastructural study

The distribution and synaptic arrangement of thyrotropin-releasing hormone-, substance P- and enkephalin-immunoreactive axonal boutons have been studied in the ventrolateral nucleus (Onuf's nucleus) of the upper sacral spinal cord segments in the cat. For this purpose, the peroxidase-antiperoxidase immunohistochemical technique was used. Immunoreactive axonal boutons were traced in complete series of sections in order to reveal synaptic contacts with the bundled dendrites of the ventrolateral nucleus. As judged from the cross-sectional diameter of the postsynaptic dendrites, the distribution of immunoreactive boutons was non-random. Enkephalin-immunoreactive axonal boutons, presumed to be mostly of segmental origin, displayed a rather restricted distribution to mainly (> 80%) medium-to-large dendrites. Thyrotropin-releasing hormone-immunoreactive boutons, that derive from supraspinal levels, were also found to impinge on medium-to-large dendrites (> 80%), indicating a proximal location within the dendritic trees. The skewness toward large postsynaptic dendrites was even more marked for thyrotropin-releasing hormone- than for enkephalin-immunoreactive boutons. Substance P-immunoreactive boutons, that are of either supraspinal or spinal origin, showed a more even distribution throughout the dendritic trees, including both thin distal branches and thick proximal dendrites. In view of the well-known fact that virtually all thyrotropin-releasing hormone-immunoreactive boutons in the ventral horn co-contain substance P (and serotonin) it was assumed that substance P-immunoreactive boutons in synaptic contact with the finest-calibre dendrites as well as most of those with a very proximal juxtasomatic location on the dendritic trees were of segmental origin, while those impinging on medium-to-large dendrites could be of either spinal or supraspinal origin. Fine-calibre dendrites (< 1 micron) represent about 25% of the dendritic branches in the ventrolateral nucleus, but receive, with the exception of substance P (8%), very little (< 3%) peptidergic or GABAergic (Ramírez-León and Ulfhake, 1993) input, although the degree of dendritic membrane covering by bouton profiles in the ventrolateral nucleus does not seem to vary much with the calibre of the postsynaptic dendrite (Ramírez-León and Ulfhake, 1993). Both substance P- and enkephalin-immunoreactive axonal boutons established synaptic contact with more than one dendrite. Furthermore, one and the same bouton could be found in contact with two dendrites that were coupled to each other by a dendro-dendritic contact of desmosomal or puncta adherentia type.(ABSTRACT TRUNCATED AT 400 WORDS)

Quantitative and qualitative aspects on the distribution of 5-HT and its coexistence with substance P and TRH in cat ventral medullary neurons

By use of the indirect immunofluorescence technique the distributions of 5-hydroxytryptamine (5-HT)-, substance P- and thyrotropin-releasing hormone (TRH)-immunoreactive (IR) neurons have been studied in the midline raphe nuclei and nucleus reticularis lateralis of the caudal brainstem (levels P18.3-P8.5; according to Berman (1968), in the cat, after treatment with colchicine. In addition, by use of the double-labelling technique, the coexistence between 5-HT-, substance P- and TRH-like immunoreactivity (LI) in these neurons was analysed. The results show that cell bodies in the midline raphe nuclei and nucleus reticularis lateralis contain 5-HT-, substance P- and TRH-LI. 5-HT-IR cells were more abundant than peptidergic neurons in all areas analysed. Quantitative estimations indicated that the total number of 5-HT-IR cells in the regions studied was about 17 x 10(3), while the corresponding numbers for substance P- and TRH-IR cells were 11 x 10(3) and 12 x 10(3), respectively. From double-labelled sections it was concluded that the vast majority of peptidergic cells also contained 5-HT-LI (87-100%). However, a subpopulation of 5-HT-IR neurons lacked peptide-LI (10-55%). The degree of coexistence varied with the brainstem level, in that neurons at more rostral locations showed a lower incidence of coexistence between 5-HT and peptide(s). The presence of all three compounds in one and the same cell body could also be demonstrated. In summary, 5-HT-, substance P- and TRH-IR cell bodies were encountered in medullary nuclei known to contain neurons with projection to the spinal cord. A high degree of coexistence between the compounds was demonstrated in these nuclei. The obtained results fit well with earlier studies on the patterns of distribution and peptide colocalization of 5-HT fibres in the spinal cord. The existence of biochemically distinct neuronal subpopulations within the 5-HT bulbospinal pathway is discussed.

Serotoninergic, peptidergic and GABAergic innervation of the ventrolateral and dorsolateral motor nuclei in the cat S1/S2 segments: an immunofluorescence study

Indirect single- and double-staining immunofluorescence techniques were used to study the serotoninergic, peptidergic and GABAergic innervation of the ventrolateral (Onuf's nucleus) and dorsolateral (innervating intrinsic foot sole muscles) nuclei, located in the S1/S2 segments of the cat spinal cord. The relative density of 5-hydroxytryptamine-, thyrotropin-releasing hormone-, substance P- and gamma-aminobutyric acid-immunoreactive axonal varicosities was similar in both nuclei. The highest relative density was recorded for varicosities immunoreactive to gamma-aminobutyric acid, while those immunoreactive to 5-hydroxytryptamine or thyrotropin-releasing hormone yielded the lowest values. The density of enkephalin-immunoreactive varicosities was higher in the ventrolateral than in the dorsolateral nucleus. Calcitonin gene-related peptide-like immunoreactivity could be seen in neurons of the ventrolateral and dorsolateral nuclei. Occasionally, calcitonin gene-related peptide-immunoreactive axonal fibers were also encountered in these nuclei. Virtually all thyrotropin-releasing hormone-immunoreactive varicosities in the ventrolateral and dorsolateral nuclei also contained 5-hydroxytryptamine-like immunoreactivity, while a somewhat smaller number of them were co-localized with substance P. About 5-10% of the 5-hydroxytryptamine-immunoreactive varicosities were devoid of peptide-like immunoreactivity, and the number of 5-hydroxytryptamine-immunoreactive varicosities lacking thyrotropin-releasing hormone-like immunoreactivity was higher in the dorsolateral than in the ventrolateral nucleus. Finally, the free fraction of substance P-immunoreactive varicosities, i.e., those lacking both 5-hydroxytryptamine and thyrotropin-releasing hormone, was about 39% in the ventrolateral and 26% in the dorsolateral nucleus. Spinal cord transection at the lower thoracic level induced a depletion of 5-hydroxytryptamine and thyrotropin-releasing hormone-immunoreactive fibers from the ventrolateral and dorsolateral nuclei, indicating an exclusive supraspinal origin for these fibers. A reduction in substance P-like immunoreactivity following spinal cord transection alone or spinal cord transection combined with unilateral dorsal rhizotomy was also detected in both nuclei, suggesting a dual origin for substance P-immunoreactive fibers, i.e., both supra- and intraspinal. The decrease in number of substance P-immunoreactive fibers was however smaller than expected from the analysis of the fraction of substance P-immunoreactive fibers co-localized with 5-hydroxytryptamine, indicating thus that the experimental lesions may have triggered a sprouting of substance P-immunoreactive axons originating from spinal cord sources. The distribution of gamma-aminobutyric acid in the ventrolateral and dorsolateral nuclei was not affected by the different lesion paradigms. It is therefore assumed that these inputs are intrinsic to the spinal cord.(ABSTRACT TRUNCATED AT 250 WORDS)

GABA-like immunoreactive innervation and dendro-dendritic contacts in the ventrolateral dendritic bundle in the cat S1 spinal cord segment: an electron microscopic study

The motoneurons (MNs) in the ventrolateral nucleus (VLN) of the upper sacral spinal cord segments in the cat supply the external sphincters and the ischiocavernosii muscles. The dendrites of the MNs in the VLN are arranged into rostro-caudally oriented bundles (ventrolateral dendritic bundle, VLB). In this study we describe the distribution and synaptic arrangement of gamma-aminobutyric acid-immunoreactive (GABA-IR) axonal bouton profiles innervating the VLB. This was accomplished using the peroxidase-antiperoxidase technique and a polyclonal antibody raised against glutaraldehyde-conjugated GABA. The VLN receives an extensive innervation of GABA-IR axonal bouton profiles that surround both cell bodies and dendrites. Twenty-five per cent of the total number of vesicle-containing axonal profiles in the VLN neuropil were estimated to be GABA-IR. On cell bodies in the alpha-motoneuron size-range, the membrane covering of GABA-IR bouton profiles was about 18% and they constituted about 29% of the total membrane covering of axonal bouton profiles. Quantitative analysis of GABA-IR bouton profiles on dendrites revealed membrane covering figures rather similar to those on the cell bodies. They were not randomly distributed within the dendritic arborisations. Instead, they were very infrequent (2.5% of the covering) on small calibre dendrites (< 1 microns) as compared to larger dendrites (> 1 microns, 14-18.5% of the covering), although the total membrane covering of axonal bouton profiles was rather similar for all dendrites (42-52%). The data on membrane covering by GABA-IR boutons presented here may be low estimates due to technical limitations, indicating that the GABAergic input to this region might be even more extensive. A frequent finding was that one and the same GABA-IR bouton made synaptic contact with two to three adjacent dendrites. This type of synaptic arrangement among the VLN MNs indicates a divergence of the GABAergic input at the terminal level. In addition, the postsynaptic dendrites involved in such arrangements often disclosed dendro-dendritic contacts. In total, 44% of the bundled dendrites in the VLN disclosed direct dendro-dendritic contact regions. These contacts were most often of the puncta adherentia type, while desmosome-type contacts were less frequent. None of the dendro-dendritic contacts studies had the characteristics of a gap junction. Taken together, the present results indicate that GABA may be a transmitter substance in a large fraction of the synaptic input to the VLN MNs.(ABSTRACT TRUNCATED AT 400 WORDS)

Immunocytochemical localization of amino acid neurotransmitter candidates in the ventral horn of the cat spinal cord: a light microscopic study

The distribution of immunoreactivities to six amino acids, possibly related to synaptic function, was investigated in the motor nucleus of the cat L7 spinal cord (laminae VII and IX) using a postembedding peroxidase-antiperoxidase technique. Consecutive 0.5 micron transverse sections of plastic-embedded tissue were incubated with antisera raised against protein-glutaraldehyde conjugates of gamma-aminobutyric acid (GABA), glycine, aspartate, glutamate, homocysteate, and taurine. This method allowed localization of the different immunoreactivities in individual cell profiles. The results showed that all these amino acids, except homocysteate, could be clearly detected in either neuronal or glial elements in the ventral horn. In cell bodies of neurons in lamina VII, immunoreactivity was observed for aspartate, glutamate, GABA, and glycine. Adjacent section analysis revealed that combinations of immunoreactivity for glycine/glutamate/aspartate, GABA/glycine/glutamate/aspartate and glutamate/aspartate, respectively, may occur in one and the same cell. In the motor nuclei (lamina IX), immunoreactivity to amino acids was observed in two types of neuron. Large cells, probably representing alpha-motoneurons, were harboring immunoreactivity to both glutamate and aspartate, while a few small neurons in this area displayed a colocalization of glycine, glutamate, and aspartate. Dendrites and axons in the motor nuclei contained glycine/glutamate/aspartate, GABA/glycine/glutamate/aspartate, and glutamate/aspartate immunoreactivities. In both laminae VII and IX, taurine-like immunoreactivity was absent in neuronal cell bodies, but highly concentrated in perivascular cells and small cells with a morphology resembling that of glial cells. A punctate immunolabeling, in all probability representing labeling of nerve terminals, could be demonstrated in the ventral horn for GABA, glycine, and glutamate, but not with certainty for aspartate or taurine. A quantitative estimate of the covering of cell bodies of alpha-motoneuron size by immunoreactive puncta revealed that glycine immunoreactive terminal-like structures were most abundant (covering 26-42% of the somatic membrane), while glutamate immunoreactive terminals were seen least frequently (5-9% covering). GABA-immunoreactive terminals covered from 10 to 24% of the soma surface.(ABSTRACT TRUNCATED AT 400 WORDS)

GAP-43, aFGF, CCK and alpha- and beta-CGRP in rat spinal motoneurons subjected to axotomy and/or dorsal root severance

The mRNA levels for growth-associated protein 43 (GAP-43), acidic fibroblast growth factor (aFGF), alpha- and beta-calcitonin gene-related peptide (CGRP), cholecystokinin (CCK) and choline acetyltransferase (ChAT) in rat lumbar spinal motoneurons were studied by in situ hybridization 1, 5 and 21 days and 20 weeks following unilateral peripheral nerve sectioning, ventral rhizotomy or dorsal rhizotomy. Furthermore, CGRP- and aFGF-like immunoreactivities in the ventral horn were studied using immunohistochemistry. One to 21 days after axotomy, GAP-43 and alpha-CGRP mRNAs increased in lesioned motoneurons, while the aFGF mRNA levels were marginally higher in motoneurons on the lesion side as compared to the control side. beta-CGRP, CCK and ChAT mRNA levels, on the other hand, decreased during the short-term response (1-21 days) to axotomy. After ventral rhizotomy, but not peripheral axotomy, there was complete disappearance of aFGF-like immunoreactivity in the ventral root proximal to the lesion. In animals subjected to long-term survival (20 weeks) after peripheral axotomy, the expression of all studied substances had returned to normal levels. Unilateral dorsal rhizotomy did not induce any substantial short- or long-term shifts in the cellular expression of the GAP-43, aFGF, CGRP and CCK peptides or their mRNAs in motoneurons of lesioned segments. These results indicate that peptides/proteins in motoneurons are expressed differentially after axotomy. Whereas alpha-CGRP and GAP-43 are up-regulated, CCK and beta-CGRP become down-regulated and aFGF is largely unaffected.

The serotoninergic bulbospinal system and brainstem-spinal cord content of serotonin-, TRH-, and substance P-like immunoreactivity in the aged rat with special reference to the spinal cord motor nucleus

The 5-hydroxytryptamine (5HT) containing bulbospinal pathway was studied with immunohistochemical (IF) and chemical techniques in 2-3 and 30 months old male Sprague-Dawley rats. The coexisting neuropeptides substance P (SP), thyrotropin-releasing hormone (TRH) and galanin were also analysed. Furthermore, the expression of mRNA encoding aromatic L-amino acid decarboxylase (AADC), prepro-TRH, and preprotachykinin (prepro-SP) was analysed with in situ hybridization (ISH) in the midline raphé nuclei inthe lower brainstem. The results showed a decreased number of axonal 5HT fibers with a normal morphology in the ventral horn of the aged rat lumbosacral spinal cord, and several 5HT immunoreactive (IR) fibers with an aberrant morphology, suggestive of axonal degeneration, were intermingled. This was evident in both the dorsal and ventral horn of the spinal cord. The 5HT-IR fibers with an aberrant morphology usually also contained TRH-and/or SP- and/or galanin-like immunoreactivity (LI) in the ventral horn. These signs of degeneration were clearly less evident in the thoracic and cervical spinal cord segments. Moreover, these changes varied between aged litter-mates. This was in agreement with behavioural signs of motor disturbances, present in about 40% of the aged rats and which in all cases were confined to the hindlimbs. Chemical analyses disclosed significantly lower levels of TRH-LI and, in particular, SP-LI in both the ventral and dorsal quandrants of the spinal cord in the aged rat compared to young adults. The differences were largest in the lumbar regions of the spinal cord. Corresponding analysis of 5HT and 5-hydroxyindoleacetic acid (5HIAA) in the same tissue specimens revealed largely unaltered levels of 5HT and a slight increase in 5HIAA, indicating the possibility of an increased 5HT turnover in the aged rat spinal cord. Neurons in nucleus raphé obscurus and nucleus raphé pallidus were immunoreactive to 5HT, and after pretreatment with colchicine to TRH-, SP-, and galanin-LI as well. There was no obvious difference in number of labeled cells, or labeling intensity, between colchicine-treated young adult and aged rats, although, in the corresponding region of medulla oblongata, chemical analysis disclosed significantly lower levels of 5HT, TRH, and, in particular, SP in untreated aged rats. In contrast, in situ hybridization analysis revealed increased mRNA levels encoding prepro-TRH and prepro-SP in old rats, while mRNA content encoding AADC mRNA was similar in young adult and aged rats.(ABSTRACT TRUNCATED AT 400 WORDS)

The peptidergic motoneurone

Acetylcholine is the classic transmitter in the spinal cord motoneurone. Recent studies have shown that motoneurones also contain calcitonin-gene related peptide (CGRP) and other peptides. In addition to transmitter-like effects, CGRP may also exert trophic actions, as suggested by changes in CGRP expression in motoneurones during development and following experimental perturbations.

Expression of GAP-43 mRNA in the adult mammalian spinal cord under normal conditions and after different types of lesions, with special reference to motoneurons

In situ hybridization histochemistry was used to detect cell bodies expressing mRNA encoding for the phosphoprotein GAP-43 in the lumbosacral spinal cord of the adult rat, cat and monkey under normal conditions and, in the cat and rat, also after different types of lesions. In the normal spinal cord, a large number of neurons throughout the spinal cord gray matter were found to express GAP-43 mRNA. All neurons, both large and small, in the motor nucleus (Rexed's lamina IX) appeared labeled, indicating that both alpha and gamma motoneurons express GAP-43 mRNA under normal conditions. After axotomy by an incision in the ventral funiculus or a transection of ventral roots or peripheral nerves, GAP-43 mRNA was clearly upregulated in axotomized motoneurons, including both alpha and gamma motoneurons. An increase in GAP-43 mRNA expression was already detectable 24 h postoperatively in lumbar motoneurons both after a transection of the sciatic nerve at knee level and after a transection of ventral roots. At this time, a stronger response was seen in the motoneurons which had been subjected to the distal sciatic nerve transection than was apparent for the more proximal ventral root lesion. An upregulation of GAP-43 mRNA could also be found in intact motoneurons located on the side contralateral to the lesion, but only after a peripheral nerve transection, indicating that the concomitant influence of dorsal root afferents may play a role in GAP-43 mRNA regulation. However, a dorsal root transection alone did not seem to have any detectable influence on the expression of GAP-43 mRNA in spinal motoneurons, while the neurons located in the superficial laminae of the dorsal horn responded with an upregulation of GAP-43 mRNA. The presence of high levels of GAP-43 in neurons has been correlated with periods of axonal growth during both development and regeneration. The role for GAP-43 in neurons under normal conditions is not clear, but it may be linked with events underlying remodelling of synaptic relationships or transmitter release. Our findings provide an anatomical substrate to support such a hypothesis in the normal spinal cord, and indicate a potential role for GAP-43 in axon regeneration of the motoneurons, since GAP-43 mRNA levels was strongly upregulated following both peripheral axotomy and axotomy within the spinal cord.(ABSTRACT TRUNCATED AT 400 WORDS)

Thyrotropin-releasing hormone (TRH)-like immunoreactivity in the grey monkey (Macaca fascicularis) spinal cord and medulla oblongata with special emphasis on the bulbospinal tract

The distribution of thyrotropin-releasing hormone (TRH)-like immunoreactivity (LI) has been studied in the grey monkey (Macaca fascicularis) spinal cord and medulla oblongata by the use of indirect immunofluorescence and the peroxidase-antiperoxidase (PAP) technique. Furthermore, double-labeling experiments were performed in order to study colocalization of 5-hydroxytryptamine (5-HT)- and substance P-LI. A dense innervation of TRH-immunoreactive (IR) varicose fibers was found in the ventral horn motor nuclei, in the region surrounding the central canal, in the intermediolateral cell column, and in the dorsal horn laminae II and III. In addition, cell bodies harboring TRH-LI were found in the dorsal horn laminae II-IV. In the ventral horn, many of the large cell bodies and their proximal dendrites were totally encapsulated by TRH-IR fibers. From double-labeled sections a high degree of coexistence could be established between TRH-/5-HT-LI, TRH-/substance P-LI, and 5-HT-/substance P-LI in fibers in the motor nuclei; as a consequence, a large proportion of these fibers should harbor TRH-/5-HT-/substance P-LI. A coexistence between TRH-/5-HT-LI could also be demonstrated in the intermediolateral cell column. However, no unequivocal coexistence could be found between TRH-/substance P-LI and 5-HT-/substance P-LI in this region. In the dorsal horn, no clear coexistence could be encountered for any of the above indicated combinations. Electron microscopic analysis of material from the lumbar lateral motor nucleus demonstrated TRH-IR terminals making synapses with large cell bodies and dendrites. In addition, contacts lacking synaptic specializations could also be verified. In the medulla oblongata, with the use of the PAP technique, a large number of cell bodies containing TRH-LI were encountered in the midline raphe nuclei and in nucleus reticularis lateralis. A similar distribution pattern could be found for 5-HT-LI, but no cell bodies containing substance P-LI could be seen in these regions. Chemical analysis of specimens from cervical, thoracic, and lumbar spinal cord revealed higher concentrations of TRH- and 5-HT-LI in the ventral quadrants, whereas substance P-LI dominated in the dorsal quadrants. Thus, the concentrations of TRH-, 5-HT-, and substance P-LI was in accordance with the observed regional variation in density of IR-fibers and varicosities found in the spinal cord. We have shown that TRH-LI has a distribution in the monkey spinal cord and medulla oblongata similar to that previously demonstrated in other species.(ABSTRACT TRUNCATED AT 400 WORDS)

Reappearance of calcitonin gene-related peptide-like immunoreactivity in the dorsal horn in the long-term dorsal root transected rat

Calcitonin gene-related peptide (CGRP)-immunoreactive (IR) fibers in the rat dorsal horn superficial laminae vanish almost completely 3 weeks following unilateral dorsal rhizotomy. After a prolonged survival (20 weeks) of dorsal rhizotomy there is, however, a reappearance of CGRP-IR fibers in the corresponding laminae of the dorsal horn. The density of such IR fibres showed a clear gradient with the lowest number found in the midlesion region and an increase in density towards the neighboring, intact segments. In normal as well as lesioned rats, no neurons intrinsic to the dorsal horn contained detectable levels of CGRP-like immunoreactivity (LI). Furthermore, no cells could, by use of in situ hybridization, be demonstrated to contain detectable levels of mRNA encoding for CGRP in the dorsal horn. Based on these findings, we suggest that the CGRP-IR fibers observed following long-term survival of dorsal rhizotomy derive from proliferating collateral branches of primary afferents of neighboring intact segments.

Distribution of enkephalin and its relation to serotonin in cat and monkey spinal cord and brain stem

The distribution of enkephalin (ENK)-like immunoreactivity (LI) in spinal cord and medulla oblongata of cat and gray monkey (Macaca fascicularis) was studied by use of immunofluorescence and peroxidase antiperoxidase (PAP) techniques. Possible coexistence between ENK- and 5-hydroxytryptamine (5-HT)-LI was also analyzed with double labeling immunofluorescence. Furthermore, in situ hybridization was used to demonstrate cell bodies in the brain stem expressing mRNA encoding for ENK. ENK-immunoreactive (IR) axonal varicosities and fibers were demonstrated throughout the spinal cord gray matter, with the highest density in the superficial dorsal horn, the area around the central canal, the intermediolateral cell column, the sacral parasympathetic nucleus, and in Onuf's nucleus. In the monkey ventral horn, ENK-IR varicose fibers could in some cases be demonstrated in very close apposition to cell bodies. A low degree of co-localization between ENK- and 5-HT-LI was seen in the spinal cord of both species. Still, fibers containing both compounds could as a rule be demonstrated in every section studied. The highest degree of coexistence was encountered in the motor nucleus of the ventral horn. Six weeks after a low thoracic spinal cord transection a decreased staining for ENK-LI was demonstrated in the ventral horn motor nucleus, whereas other parts of the spinal cord appeared unaffected. In the brain stem of cats after colchicine treatment, ENK-LI was found in a majority of the 5-HT-IR cell bodies in the raphe nuclei (nucleus raphe magnus, pallidus and obscurus) and in the lateral reticular nucleus (rostroventrolateral reticular nucleus). In cat not pretreated with colchicine, a few weakly stained ENK-IR cell bodies could be found in the midline raphe nuclei and in the lateral reticular nucleus with the PAP technique. In the monkey brain stem without colchicine treatment, using the PAP technique, heavily stained ENK-IR cell bodies could be seen in the lateral reticular nucleus whereas, as in the cat, only a few, weakly stained ENK-IR cell bodies could be seen in the midline raphe nuclei. Using in situ hybridization technique, ENK mRNA expressing cells were demonstrated in the lateral reticular nucleus while no convincing mRNA signal could be found over cell bodies in the raphe nuclei. It is concluded that part of the ENKergic innervation of the cord in both species derives from supraspinal or suprasegmental levels.(ABSTRACT TRUNCATED AT 400 WORDS)

A parsimonious description of motoneuron dendritic morphology using computer simulation

Most quantitative descriptions of neuronal dendrite morphology involve tabulations of measurements and correlations among them. The present work is an attempt to extract from such data a parsimonious set of parameters that are sufficient to describe the quantitative features of individual and pooled dendrites, including their statistical variability. A relatively simple stochastic (Monte Carlo) model was devised to simulate branching dendritic trees. The necessary parameters were then derived directly from measurements of 64 completely reconstructed dendrites belonging to six gastrocnemius alpha-motoneurons, labeled by intracellular injection of HRP. Comparison of actual and simulated dendrites was used to guide the process of parameter extraction. The model included only two processes, one to generate individual branches given their starting diameters and the second to select starting diameters for the daughter branches produced at dichotomous branching points. The stochastic process for branch generation was controlled by probability functions for branching (Pbr) and for terminating (Ptrm), together with a constant rate of branch taper. All model parameters were fixed by motoneuron measurements except for branch taper rate, which was allowed to vary within limits consistent with observed taper rates in order to generate the appropriate total number of branches. The simplest model (model 1), in which Pbr and Ptrm depended only on local branch diameter, produced simulated dendrites that fit many, but not all, characteristics of actual motoneuron dendrites. Two additional properties produced significant improvements in the fit: (1) a small but significant dependence of daughter diameters on the normalized starting diameter of the parent branch, and (2) a dependence of Pbr and Ptrm on distance from the soma as well as on local branch diameter. The process of developing this model revealed unsuspected relations in the original data that suggest the existence of fundamental mechanisms for morphological control. The final model succinctly describes a large amount of data and will enable quantitative comparisons between the dendritic structures of different types of neurons, regardless of their relative sizes.

Galanin- and CGRP-like immunoreactivity coexist in rat spinal motoneurons

We can report, that by the use of indirect immunofluorescence techniques, that rat spinal motoneurons contain galanin-like immunoreactivity (LI). Furthermore, that galanin and calcitonin gene-related peptide (CGRP)-LI coexist in a number of spinal motoneurons. Co-localization could be demonstrated as thoracic, lumbar as well as sacral spinal cord levels in individual neurons by studying adjacent sections each stained by one of the two antisera, as well as by double labelling experiments. Small neurons, within the gamma-motoneuron and interneuron size-range, were also positive for galanin-LI.

Distribution of calbindin D28k-like immunoreactivity (LI) in the monkey ventral horn: do Renshaw cells contain calbindin D28k-LI?

By use of indirect immunofluorescence and peroxidase-antiperoxidase immunohistochemistry, we show that the monkey (Macaca fascicularis) ventral horn harbors small- to medium-sized neurons in lamina VII as well as a dense network of fibers in laminae IX and VII that contain calbindin D28k (calbindin)-like immunoreactivity. The highest frequency of immunoreactive (IR) cell bodies was found at the levels of the cervical and lumbar intumescences. Furthermore, rostrocaudally oriented calbindin-IR fibers were encountered in the ventral and ventrolateral funiculi throughout the whole length of the cord, with the highest density at cervical and lumbar intumescences. Analysis at the EM level revealed calbindin-IR terminals in contact preferentially with dendrites of variable size and occasionally also large cell bodies, presumably belonging to motoneurons, in the lateral motor nucleus. The location of calbindin-IR neurons, as well as the distribution and ultrastructural characteristics of the calbindin-IR axonal system, makes it highly likely that these neurons are Renshaw cells that mediate recurrent inhibition to motoneurons.

Anatomy of dendrites in motoneurons supplying the intrinsic muscles of the foot sole in the aged cat: evidence for dendritic growth and neo-synaptogenesis

Motoneurons (MNs) supplying the intrinsic muscles of the foot sole (IFS) were studied in the aged cat (greater than 15y). Axon conduction velocity of IFS MNs was 30-40% slower in the aged than in young adult cats. IFS MNs that appeared intact during intracellular recordings and labeling with horseradish peroxidase (HRP) were subjected to anatomical investigation of their dendrites. The results were compared with corresponding data from young adult (less than 3y) cats. The average number of dendrites per IFS MN was twelve in both the aged and young adults. However, the branching was significantly more extensive in the aged cat, thus indicating that proliferation of dendritic branches may occur during the later part of life. Topological analysis revealed a significant difference in the frequency distributions of nodal vertices between young adult and aged cats. In the young adult, the dendritic branching pattern was compatible with trees generated by outgrowth from terminal segments, while in the aged there was a clear indication of collateral outgrowth of branches. The dendritic path distance and the length of terminal branches were similar in young adults and aged. The length of preterminal branches was shorter in the aged, while the combined dendritic length of a dendrite was larger compared to young adults. These data are consistent with the topological data, and add further evidence that the proliferation of branches in the aged cat may also take place from preterminal branches. Light microscopic analysis revealed the presence of "growth cone-like" extensions in the dendrites of the aged cats. Such profiles were not encountered in dendrites from young adults. Electron microscopic observations showed that these "growth cone-like" formations were not artifacts and that they were apposed by numerous axonal boutons, of which a number made synaptic contact. A distinct feature of the extensions was their rich content of mitochondria and membranous elements. It was suggested that these "growth cone-like" formations were sites at which novel synaptic connections are established, and that they may represent the initial stage of an outgrowth of new dendritic branches in the aged cat. Local dendritic branch diameter related closely to the amount of dendritic membrane area located distally in both young adults and aged. Curve fitting disclosed that this relationship was quite similar for both age groups, despite concurrent differences in combined dendritic length and branching degree.

Imaging of fluorescent neurons labelled with fluoro-gold and fluorescent axon terminals labelled with AMCA (7-amino-4-methylcoumarine-3-acetic acid) conjugated antiserum using a UV-laser confocal scanning microscope

This paper describes the implementation of an ultraviolet (UV) laser (Spectra Physics 171-18 with 3 lines: 334, 351 and 364 nm in UV) as light source for fluorescence confocal scanning microscopy. With this instrument it is possible to use fluorophores not previously available for confocal laser microscopical imaging of fluorophores such as fluoro-gold and AMCA. In the study we show confocal laser microscopical imaging of fluorescent motoneurons labelled by retrograde transport of fluoro-gold and AMCA-fluorescent axon terminals labelled with antisera against immunogenes as thyrotropin-releasing hormone (TRH) and calcitonin gene-related peptide (CGRP). These two fluorophores may be recorded simultaneously or separately by using a filter that suppresses the emission of one of the fluorophores. The described instrument should also be useful in applications involving detection of monoamines by the Falck-Hillarp technique, as well as measurements of cytosolic free calcium by indicators such as Fura-2 and Indo-1. Measurements performed in reflected and fluorescence light indicated that the resolution along the optical axis improved by about 25% when UV (351 nm) is used instead of visible light (514 nm). This figure is close to that expected on theoretical basis. There are, however, also serious problems related to the use of UV excitation. Firstly, objectives must be selected based on their UV transmission properties. Secondly, chromatic aberration may cause a substantial focal shift between illuminating and emitted light, calling for a flexible instrumental design in order to allow for compensation. As shown here, this problem can be circumvented by using reflecting objectives but at a price of lower resolution compared with high-aperture refracting objectives.

Postnatal development of cat hind limb motoneurons supplying the intrinsic muscles of the foot sole

The postnatal development of dendrite anatomy in alpha-motoneurons intracellularly labeled with horseradish peroxidase (HRP), innervating the intrinsic muscles of the sole of the foot (IFS MNs) in the cat, was investigated. The number of dendrites per neuron was about 11 and did not change from birth to adult. The number of branches per dendrite decreased during the same period by 20-25%. The net elimination of dendritic branches appeared to occur at distal branching points, as revealed by topological analysis. The dendritic branching pattern tended to be asymmetric at birth and the net decrease in dendritic branching postnatally did not alter this pattern. The length of preterminal branches (PTB) increased by a factor of 2, while terminal branch (TB) length increased by a factor of 3.3 postnatally. The large increase in TB length was attributed to both longitudinal growth and an apparent lengthening caused by resorption of distal branches during development. Dendritic length in the transverse spinal cord plane increased in parallel with the overall growth of the parent spinal cord segment, while dendritic growth along the rostro-caudal axis exceeded, by about one order of magnitude, dendritic growth in the transverse plane. Average branch diameter doubled from birth to adult. The decrease in branch diameter across branching points did not obey satisfactorily to the 'power rule' of Rall. However, the 1.5 power ratio of daughters-to-parents branch dropped from 1.18 to 1.08 between 3 weeks of age and adult. Tapering was evident in both PTBs and TBs. The rate of taper did not change postnatally. From birth onwards, 'local' branch diameter correlated closely with amount of membrane area and combined length of the dendritic branches located distal to the 'supporting' parent branch. These relations were similar in all age groups and are suggested to be properties intrinsic to the IFS MNs. The local branch diameter also co-varied with the number of distal dendritic branches, but in this case there was a systematic shift in the relationship with increasing postnatal age. It appears that the local diameter in IFS MN dendrites is a key indicator of the size of the distal dendritic arborization.

Calcitonin gene-related peptide in monkey spinal cord and medulla oblongata

The distribution of calcitonin gene-related peptide (CGRP)-immunoreactive (IR) fibers and cell bodies was studied in the spinal cord and the medulla oblongata of the grey monkey (Macaca fascicularis) using peroxidase-antiperoxidase (PAP) immunohistochemistry. At all levels of the spinal cord many CGRP-IR motoneurons and fibers were seen in the motor nuclei. In the medulla, CGRP-IR cell bodies were encountered in nucleus raphe obscurus, nucleus raphe pallidus and nucleus raphe magnus, nucleus reticularis lateralis as well as in the area dorsal to the inferior olive. Bulbar motoneurons were much more intensely stained than spinal cord motoneurons, indicating higher levels of CGRP-like immunoreactivity (LI) at the medullary level. The concentration of CGRP-LI measured by radioimmunoassay showed higher levels in the dorsal quadrants as compared to the ventral quadrants, but the dorsal/ventral ratio was lower than has previously been reported from the rat. The present results demonstrate that using the PAP technique CGRP-LI can be visualized in a larger number of spinal cord motoneurons of the monkey than earlier revealed by immunofluorescence. Moreover, the finding supports the view that the CGRP-IR nerve endings in the spinal motor nuclei originate from cell bodies in the medullary raphe nuclei.

Distribution of 125I-galanin binding sites, immunoreactive galanin, and its coexistence with 5-hydroxytryptamine in the cat spinal cord: biochemical, histochemical, and experimental studies at the light and electron microscopic level

The distribution of galanin-like immunoreactivity (GAL-LI) in the spinal cord of the cat was studied by use of indirect histochemistry and the peroxidase-antiperoxidase (PAP) technique. In the ventral horn GAL-immunoreactive (IR) axonal fibers and terminals were most frequent in the ventral part of the motor nucleus. The GAL-IR axons also contained 5-hydroxytryptamine (5-HT)-LI, and they disappeared after spinal cord transection. It was concluded that these GAL-IR fibers belong to the serotoninergic bublospinal pathway. In the medulla oblongata from normal cats, scattered GAL-IR cell bodies were encountered within the nucleus raphe obscurus and nucleus raphe pallidus. Electron microscopic observations revealed that the fine structure of the GAL-IR axonal boutons in the motor nucleus was similar to that of 5-HT-IR boutons with a varying number of immunoreactive large dense core vesicles. The postsynaptic element in all cases studied was a dendrite. A dense GAL-IR axonal plexus was found in the superficial laminae I-II of the dorsal horn. Coexistence was found between the GAL- and substance P-LI in fibers within the dorsal horn plexus. Spinal cord transection did not alter the pattern of GAL-LI in the dorsal horn, while the vast majority of GAL-IR axonal swellings disappeared following dorsal root sectioning. Electron microscopic observations in lamina II (substantia gelatinosa) revealed that the GAL-IR axonal terminals could be divided into two main groups. One with small to medium-sized axonal boutons formed synaptic contacts with both dendritic and axonal profiles. The other formed the central axon terminals of glomeruli, suggesting that GAL-LI may be present in C-type primary afferents. Numerous small GAL-IR cell bodies were encountered in laminae II and III. GAL-IR cell bodies were also observed in lamina X. The dorsal root ganglia contained a low but consistent number of small to medium-sized GAL-IR cell bodies, which all contained immunoreactive calcitonin gene-related peptide (CGRP). Following peripheral sciatic nerve transection, the number and the labeling intensity of GAL-IR cell bodies in the corresponding dorsal root ganglia showed a moderate increase. Radioimmunoassay revealed that the concentration of GAL-LI increased along the rostrocaudal axis of the normal spinal cord, and was about three times higher in the dorsal than in the ventral regions. The concentration in the dorsal root ganglia was intermediate to those seen in the corresponding dorsal and ventral cord regions.(ABSTRACT TRUNCATED AT 400 WORDS)

Changes in size and shape during histochemical preparation for light and electron microscopy of neurons intracellularly labelled with horseradish peroxidase

In this study we show that neurons labelled intracellularly with horseradish peroxidase react differently from surrounding unlabelled neurons in vibratome sections during histological preparations for light and electron microscopy. The diameters and cross-sectional area of the cell bodies of intracellularly horseradish peroxidase-labelled neurons increased by about 6 and 11% respectively, while the surrounding unlabelled neurons decreased by the same amount. Also, the caliber of the proximal dendrites of horseradish peroxidase-labelled neurons increased during the histological preparation while dendritic path lengths remained unchanged. Since the surrounding tissue shrunk, the dendritic path shapes became more tortuous during histological processing. The demonstrated reaction of horseradish peroxidase-labelled neurons is suggested to be caused by the horseradish peroxidase reaction product.

Enkephalin-like immunoreactivity levels increase in the motor nucleus after an intramedullar axotomy of motoneurons in the adult cat spinal cord

Neuropeptide- and serotonin-like immunoreactivities were studied in the lumbar spinal cord of the cat after a longitudinal incision in the ventral funiculus. This lesion, which accomplishes a central axotomy of motoneurons, was accompanied by increased level of Met-enkephalin-like immunoreactivity in nerve endings in those parts of the motor nucleus (lamina IX) which harbored severed motoneurons. This increase, which was evident in the fluorescence microscope, could be verified photometrically by use of a confocal scanning laser microscope.

Evidence for coexistence between calcitonin gene-related peptide and serotonin in the bulbospinal pathway in the monkey

By the use of the indirect immunofluorescence and in situ hybridization techniques, the distribution of calcitonin gene-related peptide (CGRP)-like immunoreactivity (LI) and CGRP mRNA was studied in the spinal cord as well as in the midline raphe nuclei and the hypoglossal nucleus in the medulla oblongata of the monkey (Macaca fascicularis). In the spinal cord only a few large neurons in the motor nucleus contained CGRP-LI, while a majority of the neurons in the hypoglossal nucleus contained CGRP-LI. A relatively dense innervation by CGRP-immunoreactive (IR) fibers was also seen close to cell bodies and proximal dendrites of large neurons in the motor nucleus, especially in its ventral part. 5-Hydroxytryptamine (5-HT)-, substance P- and thyrotropin-releasing hormone (TRH)-IR varicosities were also observed in a similar position around large neurons in the motor nucleus. Double labeling disclosed that the majority of CGRP-IR axon terminals also contained 5-HT-LI. Expression of CGRP mRNA was found in neurons in the medullary midline raphe nuclei and in large neurons in the motor nucleus at the cervical spinal cord level. In adjacent sections of the medulla oblongata, CGRP-labeled neurons in the midline raphe nuclei also expressed preprotachykinin mRNA. The present results show that CGRP- and 5-HT-LI coexist in fibers within the motor nucleus of the monkey spinal cord and that this coexistence is probably due to the presence of CGRP in the descending bulbospinal, serotonergic pathway.

Computerized quantification of immunofluorescence-labeled axon terminals and analysis of co-localization of neurochemicals in axon terminals with a confocal scanning laser microscope

The confocal scanning laser microscope (CSLM) offers improved optical resolution and contrast, high photometric precision, and the ability to make optical sections. These benefits were explored for use in quantitative analysis of immunofluorescence-labeled axon terminals. Guidelines were obtained for adjustments of the CSLM parameters. In the present applications, bleaching of the fluorescence did not represent a serious obstacle to analysis with the CSLM. A method was developed to distinguish the background fluorescence from the specific fluorescence labeling. This procedure made way for the development of automated quantification of immunolabeled axon terminals. The automated procedures substantially reduced the man-hour expenditure for analysis and provided highly reproducible quantifications compared with manual methods. The increased resolution and contrast of the CSLM allowed measurements of the fluorescence signal strength of individual axon terminals. The CSLM also allowed detection of co-localized neurochemicals in axon terminals.

Peripheral nerve section induces increased levels of calcitonin gene-related peptide (CGRP)-like immunoreactivity in axotomized motoneurons

By use of fluorescence immunohistochemistry it is shown that sciatic nerve section in cat and rat induces increased levels of immunoreactive calcitonin gene-related peptide (CGRP) in axotomized motoneurons. In the rat, this effect was clearly seen at 2-5 days postoperatively, but could not be demonstrated after 11-21 days. These findings are discussed in relation to previously proposed roles for CGRP in motoneurons.

5-Hydroxytryptamine, substance P, and thyrotropin-releasing hormone in the adult cat spinal cord segment L7: immunohistochemical and chemical studies

The terminal projections of the descending 5-hydroxytryptamine (5-HT) bulbospinal pathway and the coexistence among 5-HT-, substance P (SP)-, and thyrotropin-releasing hormone (TRH)-like immunoreactivities (LI) in fibers innervating the L7 segment in the cat spinal cord were studied quantitatively and semiquantitatively by use of the indirect double-staining immunofluorescence technique. The content of 5-HT, SP, and TRH in different parts of the spinal cord was determined by use of radioimmunoassay (RIA) (SP and TRH) and high-performance liquid chromatography with electrochemical detection (HPLC-ECD) (5-HT). For all three substances studied, immunoreactive (IR) axon terminals were found in all parts of the gray matter, but with clear regional variation in the density of innervation. Thus, all three substances showed a dense innervation in the motor nucleus, particularly in the ventral part of the nucleus, while the superficial dorsal horn was very densely innervated by SP-IR fibers (laminae I and II) and TRH-IR fibers (laminae II and III). In the motor nucleus, the studied substances coexisted to a very high degree, but some 5-HT-IR fibers (about 10%) lacked peptide-LI and some SP-IR fibers (about 10%) lacked 5-HT-LI while virtually all TRH-IR fibers also contained 5-HT-LI. In the superficial dorsal horn (laminae I-III), no coexistence was detected, while other parts of the gray matter displayed various degrees of coexistence in between those found in the motor nucleus and laminae I-III. The quantitative analysis of IR varicosities in the motor nucleus suggested that the unilateral L7 motor nucleus is innervated by about 55-110 x 10(6) 5-HT-IR nerve terminals, which may indicate as many as 4,000 boutons per descending 5-HT cell body in the brain stem only with this restricted projection. When combing these results with the biochemical data, it could be calculated that the concentration of 5-HT in IR varicosities is about 3-6 x 10(-3) M, while the corresponding figures for SP and TRH was 0.3-0.5 x 10(-3) M and 0.1-0.2 x 10(-3) M, respectively. In cats subjected to spinal cord transection at the lower thoracic level, all 5-HT-IR fibers in the L7 segment had disappeared 44 days after the lesion, indicating a strict suprasegmental origin of 5-HT-IR fibers in this segment.(ABSTRACT TRUNCATED AT 400 WORDS)

Anatomy of soleus alpha-motoneurone dendrites in normal cats and in cats subjected to chronic postnatal tenotomy or overload of the soleus muscle

The anatomy of intracellularly HRP-labeled soleus alpha-motoneurone dendrites was studied both in normal adult cats ("normal soleus", NS) and in adult cats which at a postnatal age of 5-7 days had been subjected to chronic tenotomy of either the soleus muscle ("tenotomized soleus", TS), or all the soleus synergists contributing to the achilles tendon ("overloaded soleus", OS). A set of "structural rules" seemed to govern the architecture of normal soleus alpha-motoneurone dendrites. Thus, the dendrites branched dichotomously and the number of daughter branches originating from a preterminal branch was proportional to the diameter of that parent branch. Branch diameter decreased across branching points according to the "3/2 power rule" of Rall (1959). Branching occurred down to a preterminal branch diameter of about 0.8 micron. Through all branch orders there existed a quite precise relation between the diameter of a preterminal branch and the membrane area of its distal dendritic arborization. The average dendritic path distance from soma to termination was not closely related to the diameter of the stem dendrite, since thick stem dendrites rather generated more profusely branched arborizations than thin stem dendrites. As a corollary of these characteristics close relations existed between the dendritic stem diameter on one hand, and the total number of branches, combined dendritic length, total dendritic membrane area and total volume, on the other. In the OS material, the dendrites were not different from those of normal soleus motoneurone dendrites. In the TS material, the dendrites were less branched and had greater dendritic path lengths, although the relations between various size-parameters within the dendrites were not significantly altered compared with normal dendrites. It was concluded that the change in branching pattern was due to a net elimination of dendritic branches following the muscle tenotomy.

Altered levels of calcitonin gene-related peptide (CGRP)-like immunoreactivity of cat lumbar motoneurons after chronic spinal cord transection

In cats subjected to total spinal cord transection at the lower thoracic level, the calcitonin gene-related peptide (CGRP)-like immunoreactivity (LI) was studied in motoneuron cell bodies in the L6-L7 segments. In transected animals, the CGRP-immunoreactive labeling of the motoneurons was virtually absent. When combining the spinal cord transection with a unilateral rhizotomy of all dorsal roots below the transection, however, an apparently normal labelling pattern of CGRP-LI of the motoneurons was displayed on both sides. Thus, surgical interventions which affect afferent pathways to the motoneurons may have influence on the levels of CGRP-LI in otherwise intact motoneurons.

Distribution of TRH-like immunoreactivity with special reference to coexistence with other neuroactive compounds

During the last years, several important advancements have been made that are of importance for our understanding of the distribution and localization of neurons and cells producing TRH-LI. As detailed in other chapters in this volume, the precursor for TRH has been characterized that has allowed production of antibodies raised against specific sequences of this precursor. This, in turn, has provided new tools for the immunohistochemical elucidation of TRH systems in the CNS. The TRH precursor has also been cloned, leading to possibilities for studying the localization of TRH mRNA with in situ hybridization. Finally, as shown in this paper, improvement of the fixation technique has made it possible to visualize extensive TRH-immunoreactive cell body and fiber systems with antiserum raised against the TRH tripeptide. The results from the latter studies and those with antisera directed to the TRH precursor and in situ hybridization are in good agreement, with some minor exceptions. It should be pointed out that some of the systems described here, for example TRH positive-cell bodies in cortical areas and the hippocampal formation, contain only a very weak immunoreactivity. As always with immunohistochemical techniques, the possibility of crossreactivity with TRH-like peptides or TRH-like sequences within larger proteins must be considered. The present results confirm the presence of TRH-LI in the insulin-producing beta cells of the pancreas, which with the improved technique can be demonstrated also in early adulthood in rats and guinea pigs. Moreover, it could be established that TRH-LI is present in neurons in the gastrointestinal tract as well as in a population of endocrine cells in the antrum of the stomach of the guinea pig. These cells seem at least partly to be identical to the well-known gastrin-producing cells. TRH-LI has been observed to occur in neurons already containing a classical transmitter and/or other peptides. Of particular importance here seems to be a descending bulbospinal system that in addition to TRH co-contains 5-HT, substance P-LI, galanin-LI, human growth hormone immunoreactive material, and proctolin-like material. The significance of this coexistence is not well understood, but interesting interactions have been observed. Attempts to manipulate the TRH phenotype in these medullary neurons by transplantation to other sites in the brain has so far shown that the expression of this peptide seems fairly stable.(ABSTRACT TRUNCATED AT 400 WORDS)

Motoneurons reinnervate skeletal muscle after ventral root implantation into the spinal cord of the cat

By use of intracellular recording and staining with horseradish peroxidase it was found that alpha and probably also gamma motoneurons were able to reinnervate ventral root implants after an avulsion of ventral roots at the spinal cord surface in the cat. The reinnervation of the implant was achieved after an initial growth of new axons in central nervous system tissue. Reinnervating neurons could be excited or inhibited by segmental reflex activity and their axons could conduct nerve impulses. The character of muscle twitch responses elicited by electrical stimulation of implanted roots strongly indicated that denervated muscles were reinnervated by new motor axons via the implant.

Nerve fibre regeneration across the PNS-CNS interface at the root-spinal cord junction

Root-spinal cord regeneration was investigated in immature and adult rats. The elongation in the dorsal root of regrowing dorsal root axons, rerouted ventral root nerve fibres (cholinergic neurons) or hypogastric nerve fibres (catecholaminergic neurons) is impeded as they meet the astrocyte dominated CNS tissue of the root. The establishment of synaptoid nerve terminals as the regrowing axons encounter astrocytes indicates a mechanism for growth inhibition other than a physical impediment in the CNS environment. The glial cells of the CNS segment in the root are influenced by the type of regenerating nerve fibres in terms of maintenance, multiplication and phenotypic expression. After a dorsal root lesion in the neonatal rat several root axons may reinnervate the spinal cord. In these rats, the normal establishment of a CNS root segment has been disrupted and the PNS-CNS border is situated central to the root-spinal cord junction. Implantation of cut dorsal roots into the spinal cord of adult rats results in the extension of processes from intrinsic spinal cord neurons out into the root. After implantation of avulsed ventral roots into the ventro-lateral aspect of the cord, axonal regrowth and functional restitution of alpha-motoneurons could be demonstrated by intracellular recordings and injections with horseradish peroxidase. These results show that regeneration can occur across a PNS-CNS interface that has been established secondary to a trauma in the mature animal and in the immature animal before the astrocyte-rich CNS root segment has been developed.

Postnatal development of cat hind limb motoneurons. II: In vivo morphology of dendritic growth cones and the maturation of dendrite morphology

The maturation of dendrite morphology was studied by light and electron microscopy in cat spinal alpha-motoneurons intracellularly labeled with horseradish peroxidase. Alpha-motoneurons supplying the triceps surae (TS) and the intrinsic foot sole (SP) muscles were investigated in kittens from birth to 44-46 days of postnatal (d.p.n.) age. At birth, a large number of dendritic branches displayed growth cones, filopodia, and fusiform processes. The growth cones were of lamellipodial and filopodial types, but intermediate forms also occurred. The growth cones shared several morphological features with the neuritic growth cones studied in vitro. It was suggested that the occurrence of different types of growth cones--even in the same dendrite--may reflect their transformation from one type to the other and the level of growth activity could be inferred from the number and form of the growth cones. About 50-70% of the terminal branches in the dendrites of newborn kittens possessed growth cones, filopodia, and/or fusiform processes. The corresponding figure for preterminal branches was 20-30%, with a clear decrease in incidence when approaching the soma. During the period under study, most of these growth-associated processes disappeared from the dendrites so that at 44-46 d.p.n. of age only about 10% of the terminal and less than 1% of the preterminal branches had growth-associated processes. Analysis of the three-dimensional distribution of dendritic branches with such processes disclosed that they were relatively more frequent in the medial, rostral, and caudal dendritic territories. It was concluded that the pattern of distribution and disappearance of growth cones, filopodia, and fusiform processes coincided with postnatal longitudinal dendritic growth and the development of the adult dendritic territories described in a preceding paper (Ulfhake et al., '88). Dendritic growth, with respect to length and caliber, also occurred in the absence of growth cones and filopodia. It is suggested that the important role of these processes may be to act as a steering device in establishing the adult distribution and synaptology of the dendrites. Comparison of TS and SP alpha-motoneuron dendrite morphology at birth and at 22-24 d.p.n. age showed that the SP neurons lagged in the maturation process. Light and electron microscopic observations indicated that postnatally direct contacts might exist between dendrites and fine blood vessels in the neuropil without any interposing glial sheath. The number of such suspected contacts diminished during the period under study, indicating that the glial ensheathment of the blood vessel takes place, in part, postnatally.

Postnatal development of cat hind limb motoneurons. I: Changes in length, branching structure, and spatial distribution of dendrites of cat triceps surae motoneurons

The postnatal development of length, branching structure, and spatial distribution of dendrites of triceps surae motoneurons, intracellularly stained with horseradish peroxidase, was studied from birth up to 44-46 days of postnatal (d.p.n.) age in kittens and compared with corresponding data from adult cats. The number of dendrites of a triceps surae motoneuron was about 12, and the arborization of each dendrite generated an average of 12-15 terminal branches. There was no net change in the number of dendrites of a neuron or in the degree of branching of the dendrites despite the occurrence of both a transient remodeling of the dendritic branching structure and changes of the spatial distribution of the dendritic branches during postnatal development. The perisomatic territory in the transverse plane occupied by the dendritic branches of a motoneuron increased in parallel with the overall growth of the spinal cord. Thus, the relative size of the dendritic territory in this plane was kept almost constant, whereas dendritic branches projecting in the rostrocaudal direction grew much faster than the spinal cord and also became more numerous. At birth the rostro-caudal dendritic span of individual motoneurons bridged 1:6 to 1:5 of the L7 spinal cord segment length; this figure was 1:3 at 22-24 d.p.n. Hence, in this direction, the growing dendritic branches invaded novel dendritic territories. The change in dendritic branch length from birth to 6 weeks of age corresponded to an average growth rate of 2 to 4 microns per dendritic branch and day, which implies that the total increase in length of the dendrites of a neuron could amount to 1 mm/day. The increase in branch length did not occur in a uniform or random manner; instead, it followed a spatiotemporal pattern with three phases: From birth to 22-24 d.p.n., growth was particularly prominent in greater than or equal to 3rd order preterminal and 2nd through 6th order terminal branches. From 22-24 to 44-46 d.p.n., a large increase in branch length confined to terminal branches of greater than or equal to 3rd branch orders was observed. As indicated by topological analysis, this length increase was probably due in part to a resorption of peripheral dendritic branches during this stage of development. From 44-46 d.p.n. to maturity, the increase of dendritic branch length was restricted to preterminal branches of low (less than or equal to 4th) branch order.(ABSTRACT TRUNCATED AT 400 WORDS)

Postnatal development of cat hind limb motoneurons. III: Changes in size of motoneurons supplying the triceps surae muscle

The postnatal changes of neuronal dimensions were studied in cat triceps surae motoneurons intracellularly labeled with horseradish peroxidase. Systematic correlations were observed in the analysis of single dendrites at each studied stage, from birth to 44-46 days post natum (d.p.n.) age, between size parameters intrinsic to the dendrites as the diameter of a 1st-order dendrite, the combined dendritic length, the dendritic membrane area, and the degree of branching. Some variability among samples was evident in each studied age group. The correlations were, however, sufficiently close to permit indirect estimations of both combined dendritic length and dendritic membrane area for larger samples of neurons from data on dendritic stem caliber. The total postnatal increase in dendritic membrane area was, on the average, 400%, i.e., from close to 100 X 10(3) microns2 to about 500 X 10(3) microns2. The corresponding increase in soma area amounted to 100%. Analysis revealed that there was a time lag between the increase in somatic and dendritic size. Thus, adult somatic dimensions were attained at age 44-46 d.p.n.; however, at this stage, the mean total dendritic membrane area was only about half of the adult value. The postnatal increase in size appeared to vary among neurons, yielding a wider neuronal size spectrum in the adult cat than that observed in kittens. The measured increase in size corresponded to a calculated average addition of dendritic membrane area of 3700 microns2/day from birth to 22-24 d.p.n. and from that stage to 44-46 d.p.n. of 2700 microns2 per day. Likewise, the increase in combined dendritic length could initially be as large as 1 mm/day down to 0.4 mm/day between 22-24 and 44-46 d.p.n., with a mean growth during the first 44-46 d.p.n. of 0.5 to 0.6 mm/day. The ratios of daughters to parent branch diameters (sigmadd1.5: dp1.5) and the dendritic trunk parameter (sigma d1.5) recorded along the proximodistal dendritic path distance revealed transient changes that might impact on the electrotonic properties of the dendrites during postnatal development. Computations from the measured changes in dendritic branch lengths and calibers indicated that if membrane and internal resistivity remain unaltered during postnatal development, the dendritic domain is electrotonically more compact in the newborn kitten than in the adult cat.(ABSTRACT TRUNCATED AT 400 WORDS)

The effects of tenotomy and overload on the postnatal development of muscle fibre histochemistry in the cat triceps surae

Five to seven day-old kittens were subjected to partial tenotomy of the Achilles (triceps surae) tendon. The effects of tenotomy and overload on the development of muscle fibre histochemistry and fibre sizes were investigated when the cats had reached the adult stage. The examined muscles were the uniform soleus and the mixed medial gastrocnemius. Tenotomized muscles of both types had lower weights than their controls. Tenotomized soleus showed a redistribution of succinic dehydrogenase (SDH) activity, together with signs of muscle fibre death. Tenotomized medial gastrocnemius muscles displayed more severe degenerative signs than the soleus, together with signs of fibre death. The fibre death seemed to affect mainly fibres of type IIb. Moreover, a less distinct differentiation in histochemical staining pattern between muscle fibre types was found in these muscles. Overloaded soleus muscles had greater weights than their controls, while no difference could be shown for the overloaded medial gastrocnemius. The overloaded medial gastrocnemius showed a uniform hypertrophy of all fibre types. Also, overloaded soleus showed a uniform hypertrophy. Both types of muscle showed a normal histology as well as normal staining characteristics (SDH and AcATPase). It is concluded that both soleus and medial gastrocnemius are sensitive to loss of muscle tension during development. The basic features of muscle morphology and histochemistry were normal, though, and it is suggested that other factors account for most of the normally occurring development and differentiation.

An ultrastructural study of 5-hydroxytryptamine-, thyrotropin-releasing hormone- and substance P-immunoreactive axonal boutons in the motor nucleus of spinal cord segments L7-S1 in the adult cat

The distribution and fine structure of 5-hydroxytryptamine-, thyrotropin-releasing hormone- and substance P-immunoreactive synaptic boutons and varicosities were studied in the motor nucleus of the spinal cord segments L7-S1 in the cat, using the peroxidase-antiperoxidase immunohistochemical technique and analysis of ultrathin serial sections. The 5-hydroxytryptamine-, thyrotropin-releasing hormone- and substance P-immunoreactive boutons had a similar ultrastructural appearance as judged from serial section analysis. The boutons could be classified into two types on the basis of their vesicular content, with one type containing a large number of small agranular vesicles together with only a few, if any large granular vesicles, while the other type contained a large number of large granular vesicles in addition to small agranular vesicles. The vesicles were spherical or spherical-to-pleomorphic. Postsynaptic dense bodies (Taxi bodies) were occasionally observed in relation to all three types of immunoreactive boutons, which almost invariably formed synaptic junctions with dendrites. Judged by the calibre of the postsynaptic dendrites, the boutons were preferentially distributed to the proximal dendritic domains of motoneurons. In one case, a substance P-immunoreactive bouton formed an axosomatic synaptic contact. In addition to synaptic boutons, 5-hydroxytryptamine-, thyrotropin-releasing hormone- and substance P-immunoreactive axonal varicosities containing a large number of large granular and small agranular vesicles but lacking any form of conventional synaptic contact were observed. Such varicosities were either directly apposing surrounding neuronal elements or separated from the neurons by thin glial processes. The origin of the immunoreactive boutons was not traced, but it was thought likely that the main source of the boutons was neurons with their cell bodies located in the medullary raphe nuclei.