Basis for the specificity of anti-5-HT-like antisera in immunocytochemistry applied to the central nervous system

Nicotinamide adenine dinucleotide phosphate/neuronal nitric oxide synthase-positive neurons in the trigeminal subnucleus caudalis involved in tooth pulp nociception

Sensory information on facial structures, including teeth pulp, periodontium, and gingiva, is relayed in the trigeminal complex. Tooth pulp inflammation constitutes a common clinical problem, and this peripheral injury can induce neuroplastic changes in trigeminal nociceptive neurons. There is considerable evidence that the trigeminal subnucleus caudalis (Vc) is the principal relay for trigeminal nociceptive information as well as modulation of the painful stimuli. Glutamatergic primary afferents innervating the tooth pulp project to the most superficial laminae of the Vc. N-methyl-D-aspartate receptor stimulation leads to the activation of the enzyme nitric oxide synthase (NOS), which synthesizes the free radical nitric oxide (NO). This enzyme is expressed mainly in lamina II interneurons, and in a small number of cells in lamina I as well as in deep laminae projection neurons of Vc. In the present study, we analyzed the temporal changes in neuronal NOS (nNOS) in Vc local circuitries after unilateral intermediate molar pulp injury. Our results demonstrate that a peripheral dental pulp injury leads to neuroplastic changes in the relative amount and activity of nNOS enzyme. Moreover, after a period of time, the nitrergic system shifts to the initial values, independently of the persistence of inflammation in the pulp tissues.

Darkness induced neuroplastic changes in the serotoninergic system of the chick retina

Sensory experience is critical for the formation of neuronal circuits and it is well known that neuronal activity plays a crucial role in the formation and maintenance of synapses. In the vertebrate retina, exposure to different environmental conditions results in structural, physiological, neurochemical and pharmacological changes. Serotoninergic (5HT) amacrine cells of the chicken retina are bistratified interneurons whose primary dendrites descend through the inner nuclear layer (INL) to branch in the inner plexiform layer (IPL) forming two plexi, an outer network, localized to sublamina 1, and an inner network, localized to sublamina 4 and 5 of the IPL. Their development is temporally correlated with the establishment of synapses in the retina and with the emergence of the typical adult electroretinogram. It is unknown, however, which role these cells play in processing visual information and whether visual deprivation modifies their phenotype. Here, we show that, in the chicken, red-light rearing from hatching to postnatal day 12 significantly alters the stratification pattern of 5HT amacrine cells, inhibiting their age-dependent pruning measured with morphometric and densitometric procedures; as well as increasing serotonin immunoreactivity measured as relative optical density. This change in dendritic arborization, accompanied by an increase in serotonin concentration in dark adapted conditions, may decrease visual threshold, thus increasing visual sensitivity.

Morphological study of 5-HT neurons and astroglial cells on brain of adult rats perinatal or chronically exposed to 2,4-dichlorophenoxyacetic acid

2,4-D is a chlorophenoxyherbicide used worldwide. We have studied the morphological alterations of 5-HT neurons and glial cells in the mesencephalic nuclei of adult rats exposed to 2,4-D both perinatally (during pregnancy and lactation) and chronically (during pregnancy, lactation and after weaning) with quantitative methods. Pregnant rats were daily exposed to 70 mg/kg of 2,4-D from gestation day (GD) 16 to post-natal day (PND) 23 through diet. After weaning, pups were assigned to one of two sub-groups: T1 (fed with untreated diet until PND 90) and T2 (maintained with 2,4-D diet until PND 90). Brain sections were immunocytochemically stained using polyclonal anti-5-HT, anti-GFAP and anti-S-100 protein antibodies as cells markers. 2,4-D exposure during pregnancy and lactancy (T1 group) produced an increase in 5-HT neuronal area and immunoreactivity (IR) in the mesencephalic nuclei studied. However, with the chronical 2,4-D exposure (T2 group) only the 5-HT neuronal area from the dorsal raphe nucleus (DRN) was increased, suggesting an adaptable response of 5-HT neurons in median raphe nucleus (MRN). The presence of reactive astrocytes in mesencephalic nuclei and in hippocampus were also different for the two 2,4-D exposure designs, showing the existence of a correspondence between neuronal changes and astrogliosis. Results support evidences that 2,4-D alters the serotoninergic system and that 5-HT neurons of each mesencephalic nuclei show different responses to the 2,4-D exposure designs which are parallel to astrogliosis.

Development of nitric oxide neurons in the chick embryo retina

Nitric oxide (NO) is a gas involved in neurotransmission in the central nervous system (CNS) and in vertebrate retinas. This paper describes five types of nitrergic neurons in developing and adult chick retina using the nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) reaction. Three of them, nitrergic types 1, 2 and 3, were observed in the inner nuclear layer, while nitrergic type 4 was observed in the ganglion cell layer; nitrergic type 5 were the retinal photoreceptors. Cell processes formed four nitrergic networks, which could be observed in the inner plexiform layer (IPL), at sublayers 1, 3a, 3b and 4. Another nitrergic network was observed in the outer plexiform layer (OPL). From hatching, the dendritic branches were completely developed in the IPL and in the OPL, forming the mentioned networks. Current evidence suggests that NO is coexpressed with other neurotransmitters in neurons of the CNS. Double-staining procedures, using NADPHd and 5HT immunohistochemistry in chicken retina, in a sequential or in an alternative manner, did not reveal the coexistence of these two neurotransmitters in the same neurons, but their networks matched in sublayers 1 and 4 of the IPL.

Immunofluorescence and glutaraldehyde fixation. A new procedure based on the Schiff-quenching method

The immunofluorescence technique is one of the most useful methods for localizing antigens in several tissues, including the central nervous system. For immunohistochemical procedures, especially immunofluorescence methods, formaldehyde is commonly used as a fixative agent. But for some protocols, mainly in neurobiology, glutaraldehyde is necessary to recognize a number of small molecules (haptens) whose antisera have been raised using glutaraldehyde as the cross-linking agent. This is a severe limitation because glutaraldehyde gives rise to a strong autofluorescence on tissue that precludes the observation of specific immunofluorescence staining. In this paper we present a new method that allows the use of immunofluorescence techniques on glutaraldehyde-fixed tissues. The new method consists of a treatment of tissue sections with the Schiffs reagent (leucobasic fuchsin) followed by a reduction of the Schiff-dye with sodium borohydride. This reduced dye produces a quenching of glutaraldehyde-induced fluorescence on the tissue. The goal of the new method is to make possible the use of a great number of available glutaraldehyde-raised antisera for immunofluorescence techniques, a useful tool in both basic and clinical research.

Development of serotonergic innervation of the chick embryo tectum opticum

This paper describes the development of the serotonergic innervation of the chick tectum opticum as revealed by an immunohistochemical methodology. The development of this innervation was previously described simply as the formation of an irregular network of serotonergic fibers that gradually invades the organ and increases in density. Our results show that the developmental pattern of serotonergic innervation differs significantly through the distinct tectal layers and that it progresses through a characteristic temporospatial pattern related to the lamination process. These findings support the idea that the concept of laminar segregation can be applied to describe the development of the serotonergic innervation. On the other hand, it is clear that the existence of a typical ordered developmental pattern of innervation makes it possible to detect embryonic or post-hatching alterations. Thus, the tectal serotonergic innervation could be used as a suitable model to investigate possible plastic changes in experimental conditions.

Monoclonal antibody against the glutaraldehyde-conjugated polyamine, spermine

We developed a mouse monoclonal antibody (ASPM-29, mAb) against spermine (Spm) conjugated to human serum albumin (HSA) using glutaraldehyde-sodium borohydride, for applications in immunocytochemistry (ICC). The antibody specificity was evaluated by an enzyme-linked immunosorbent assay (ELISA) binding test, simulating the ICC of tissue sections. ASPM-29 showed an almost equal immunoreactivity to Spm and spermidine (Spd) but no reactivity to any of the other polyamine (PA)-related compounds tested. By use of this antibody, indirect immunoperoxidase staining was observed in different tissues fixed with glutaraldehyde in combination with borohydride reduction. In contrast, immunoreactivity was quite low in tissues fixed only with glutaraldehyde. Absorption controls indicated that the immunostaining could be completely inhibited by 50 micrograms/ml of Spm or Spd and partially inhibited by N-acetylspermine (Ac-Spm), N1-acetylspermidine (N1-Ac-Spd), or N8-acetylspermidine (N8-Ac-Spd), but was hardly inhibited at all by other PA-related compounds or amino acids. The reactivity of the antibody with Spm conjugated on wells in an ELISA plate was inhibited by micromolar concentrations of Spm, Spd, Ac-Spm, N1-Ac-Spd, or N8-Ac-Spd, in decreasing order, but not by other small molecules. Dense ICC staining was observed in the paranuclear and basal cytoplasm of acinar cells of rat pancreas, submandibular gland and paratid gland, these results being in complete agreement with our recent ICC methods using other mAbs produced against N-(gamma-male-imidobutyryloxy) succinimide-conjugated Spm.

Changes in serotonin-immunoreactivity in the dorsal and median raphe nuclei of rats exposed to 2,4-dichlorophenoxyacetic acid through lactation

Comparison of serotonin-immunoreactive (SER-IR) neurons in nucleus raphe dorsalis (NRD) and median raphe nucleus (MRN) of 25-d-old rat pups exposed to 70 mg/kg/d 2,4-dichloro-phenoxyacetic acid through mothers milk and control pups was made using an immunohistochemical analysis. Significant 2,4-D-treatment-related increase in size and density of SER-IR neuronal somata as well as in fiber length were observed. We postulate that exposure to 2,4-dichlorophenoxyacetic acid on the first day of life would modify the synthesis of 5-HT or the maturation of the brain serotonergic system.

Serotonin innervation of enkephalin containing neurones in the rat spinal trigeminal nucleus

Light and electron microscopic immunocytochemistry was used to examine the serotonin (5-HT) innervation of the rat spinal trigeminal subnucleus caudalis. 5-HT-immunoreactive fibres form a dense plexus in lamina I and outer lamina II and synapse with the cell bodies and proximal dendrites of local neurones. Light microscopic double labelling revealed that the 5-HT axons contact enkephalin immunoreactive neurones in both laminae. The 5-fHT electron microscopic results indicate that at least some of these contacts are likely to be synapses. 5-HT axons are therefore in a position to exert a direct action on enkephalinergic interneurones and this may contribute to the analgesic actions of the 5-HT system.

Differential expression of serotonin and [Met]enkephalin-Arg6-Gly7-Leu8 in neurons of the rat brain stem

The hypothesis that serotonin (5-HT) and [Met]enkephalin-Arg6-Gly7-Leu8 (MEAGL) coexist in the rat brain stem raphe nuclei was tested by a technique combining histofluorescence with immunocytochemistry, after treatment with colchicine and nialamide. In midbrain and pons serotonergic cell groups (B5-B9), no coexistence of 5-HT and MEAGL was detected. In serotonergic cell groups of the medulla oblongata (B1-B3), only 0.3-1.5% of 5-HT-fluorescent cells were MEAGL-immunoreactive. These findings suggest that putative 5-HT and MEAGL are mostly expressed in different populations of neurons in the rat raphe nuclei.

Antibodies as molecular probes in neurobiology. Identification of chemically defined neurons and synapses in tissues and tissue cultures

Immunocytochemical localization of 5-hydroxytryptamine (5-HT) in the nervous system and aggregate tissue cultures was performed employing an antibody to 6-OH-1,2,3,4-tetrahydro-beta-carboline. A number of immunochemical and biochemical tests with the antigen and the antibody and some procedural changes in the methodology applied for immunolocalization revealed the anti-5-HT-like affinity of the antibody, if applied in paraformaldehyde-fixed tissues. Studies in the hypothalamus, striatum, brainstem, spinal cord, and pineal gland show the complexities of the serotoninergic system. Ultrastructural immunocytochemistry with the preembedding technique reveals that 5-HT synapses are of the asymmetric type. The presynaptic element contains clear, round, small vesicles, with some large dense-core vesicles. The contacts are made with the somata and primary, secondary dendrites or with spines of non-5-HT neurons. Presynaptic dendrites are found in the n. raphe dorsalis, contacting non-5-HT dendrites. Double immunocytochemical methods demonstrated contacts of 5-HT fibers on enkephalin containing neurons of the spinal trigeminal nucleus and on somatostatin containing neurons of the medullary reticular formation. In vitro studies of cultured mesencephalic neurons were performed with the method of aggregating cultures. Such development of a miniature organized nerve tissue was followed up to 35 d in culture. Organization of the neuropil and synaptogenesis was studied using standard electron microscopy. The differentiation of neurons and astrocytes was studied using antibodies to 5-HT and GFAP. Serotonin immunoreactivity could be observed in neuronal bodies and processes at light microscope level as early as the fourth day of culture.(ABSTRACT TRUNCATED AT 250 WORDS)

Serotoninergic reinnervation of regenerating tentacular sensory organs in a pulmonate snail, Cryptomphalus aspersa

Several ontogenetic studies performed in different species suggest a developmental role for 5-HT neurons. The 5-HT system interconnecting the CNS and the tentacular sensory organs in pulmonates is a suitable model for studying the postulated developmental role of 5-HT neurons. In this paper we describe the behavior of the 5-HT fibers during the early stages of blastema reinnervation, primordium formation and differentiation of regenerating tentacular sensory organs in the pulmonate snail Cryptomphalus aspersa. Our results show that the regeneration process allows the development of a normal pattern of 5-HT innervation of the regenerated sensory organs and suggest that 5-HT could be involved in reciprocal developmental interactions with regenerating tentacular tissues.

Enkephalin and serotonin innervation of somatostatin-immunoreactive medullary reticular formation neurones

Somatostatin cells in the rat medullary reticular formation (Md) have been studied using peroxidase-antiperoxidase immunocytochemistry. Large fusiform and multipolar somatostatin immunoreactive cells were observed in the ventral subnucleus (MdV) running in a band close to the border with the dorsal subnucleus (MdD). In the same region somatostatin-, serotonin- and enkephalin-immunoreactive fibres occur and double staining revealed that these all contact the somatostatin-immunoreactive cells, with enkephalin making a particularly dense innervation.

[Apparent immunoreactivity of CRF in the tentacles of the mollusk Helix pomatia]

In the Gastropod Mollusc Helix pomatia (Pulmonata: Stylommatophora), an antiserum raised against ovine CRF 41 reveals a neuropeptide in some primary sensory neurons distributed beneath the epithelium of the higher tentacles (optic) and the lower tentacles. The collar cells and the lateral cells of both kinds of tentacles are innervated by some CRF immunoreactive fibers. Considering the given results, these processes probably originate in the central ganglia, but also in the tentacular sensory neurons. The neuropeptide revealed by our immunserum would be involved in the regulation of the exocrine secretion of the collar and lateral cells. It may also take part in the regulation of the endocrine secretion of collar cells in both sorts of tentacles.

Immunocytochemical study of the postnatal development of 5-HT-containing neurons and fibers in the cerebroid ganglia of Cryptomphalus aspersa

In this work we have studied the organization of the serotonergic system in new-hatched snails and the developmental changes that occur postnatally. The serotonergic system of the new-hatched snail is not completely developed. Tracts previously described in the adult were already present at hatching; however immunoreactivity of these tracts was somewhat less intense than that in adults, but, their location was practically the same. At hatch the pro- and postcerebral serotonergic plexi were poorly developed, while the mesocerebral one was nearly absent. The procerebral plexus occupied only the caudal half of the procerebral neuropile. Growth cone profiles were found in all plexi. The paired giant dorsal serotonergic neurons were the only stained neurons constantly found at hatching; they were symmetrically located. The paired medium-sized neurons were not found in all brains examined. Sometimes only one of them was present at hatching; it was located either in the right or in the left ganglion. The small neurons were absent in most cases. They gradually appeared during the first three postnatal months. Following hatching the procerebral plexus had undergone an intense growth. By the third postnatal month it innervated completely the procerebral neuropile. At hatching the area innervated by the procerebral plexus was 4500 micron 2, by the third month this area was about 58,000 micron 2 and in the adult was 80,000 micron 2. The postnatal development of the procerebral serotonergic plexus proceeds through two different modalities of neuritic growth: expansive growth is mediated by centrifugal elongation of terminal branches while the increase in fiber density within the plexus results from lateral sprouting.(ABSTRACT TRUNCATED AT 250 WORDS)

The serotoninergic system in Cryptomphalus aspersa. Immunocytochemical study with an anti-5-HT antiserum

This immunocytochemical study of 5-HT neurons and fibers in the nervous system of C. aspersa corroborate previous findings and describe new 5-HT neurons and their connections, mainly between the central nervous system and the tentacular sensory organs. We found a number of networks, fascicles, and neurons that show constant and symmetrical location. Three networks were found at the tip of the posterior tentacle: underlying the olfactory epithelium, in the neuropil of the tentacular ganglion (TG), and in the ocular capsule. The TG also contains a ventral 5-HT fascicle. A group of 30-40 serotoninergic fibers run through the tentacular connective from the postcerebrum to the tentacular ganglion. This 5-HT fascicle has a lateral position in the postcerebrum (lateral fascicle of the postcerebrum) and a subcortical location in the procerebrum (subcortical fascicle of the procerebrum). The optic nerve also has a small group of 5-HT fibers. Seven serotoninergic neurons were found in each cerebral ganglion: two giant neurons, one medium-sized, and four small neurons. Three different types of fascicles are in the postcerebrum: fascicles proceeding from the suboesophageal connectives, a lateral fascicle, and a commisural fascicle. Each cerebral ganglion region (pro-, meso- and postcerebrum) has a 5-HT network with a particular pattern of distribution and morphology. The suboesophageal ganglia show the highest concentration of 5-HT neurons (large, medium-sized, and small neurons).

Serotonin immunoreactivity in the nervous system of the dragonfly nymph

Serotonin-like immunoreactivity was mapped using an antiserotonin antibody in wholemounts of the ventral nerve cord from dragonfly nymphs (Epitheca sp. and Pachydiplax longipennis). In both species, an immunoreactive cell ventral to each connective tract and an immunoreactive median cell cluster on the ganglion ventral surface were found in the unfused abdominal ganglia. Axon(s) from the median cell cluster branch in the anterior unpaired median nerve. Posterolaterally, in all of the ganglia examined, two or more intensely immunoreactive, bilaterally symmetric pairs of neurons were seen. Comparison of these posterolateral neurons, which appear to be serially homologous, with similar antiserotonin immunoreactive neurons described in other insects suggests that these neuron pairs may have cross-species homology as well.

A new case for a presynaptic role of dendrites: an immunocytochemical study of the n. raphé dorsalis

The distribution of serotonin (5-HT) was determined by the application of the preembedding peroxidase-anti-peroxidase (PAP) technique in vibratome and ultrathin sections of the brain stem. The antiserum stained the neuronal groups B1 to B9. Somata, dendrites and axons of multipolar and bipolar neurons were recognized in the usual locations. The most commonly found profiles in the area of the n. raphe dorsalis were dendrites. The search for axon terminals was unsuccessful. The labeled dendrites appear in synaptic contact with unlabeled endings containing round or pleomorphic vesicles, and occasionally some large dense core vesicles. Contacts between two labeled dendrites or processes were not found. Occasionally a dendrodendritic junction between a 5-HT labeled dendrite and an unlabeled dendrite has been found. There are areas of the dendritic membrane free of synaptic junctions and free of glial insulation. Results are discussed in relation with the previously proposed presynaptic role of the dendrites in the neuronal circuitry of the n. raphé dorsalis.

Aromatic L-amino acid decarboxylase in the rat brain: immunocytochemical localization during prenatal development

Immunocytochemically labeled cells containing the enzyme aromatic L-amino acid decarboxylase were localized in the brain of rat embryos at gestational age E15-E19. Cell groups that contained aromatic L-amino acid decarboxylase but lacked either the enzyme tyrosine hydroxylase or the indolamine serotonin were referred to as "D" groups. Anatomical landmarks, cytoarchitectonic structure and histochemical staining for acetylcholinesterase were used to delineate the position of "D" groups. In the E15 embryo three "D" groups existed. The first to appear, named D1, was located in the spinal cord and had been demonstrated before. A large "D" cell cluster was found in the walls of the central forebrain deep to the hypothalamic sulcus. This group distributed dorsally in the ventral dorsal thalamic region and ventrally in the dorsal hypothalamus. The rostral-most "D" group, D14, occurred in the ventral telencephalon just medial to fibers of the nigrostriatal projection. D14 was the smallest of the early groups. In E16 and E17 embryos dorsal di- and mesencephalic "D" groups were first detected. During the course of ontogeny a considerable increase of immunoreactive cells occurred and segregation of the large central forebrain cluster into several rostrally and laterally distributed "D" groups took place. Some "D" groups that occur in the adult brain were not present in the E19 embryo. This study provides a first report of the localization of several unique cell groups in the brain of rat embryos and their appearance at different stages of gestation. It also gives further support to the notion that variations of aromatic L-amino acid decarboxylase staining intensities may be characteristic of different monoamine neurons.

Further evidence for the specificity of anti-5-HT (serotonin)-like antisera in immunocytochemistry. Existence of cyclic secondary amino groups in the immunogen

The serotonin antigen (5-HT-BSA formaldehyde conjugate) used for obtaining anti-5-HT antibodies was studied to obtain additional data concerning the nature of its immunogen. Dialysis against 0.1 M acetic acid and then against distilled water proved to be the best way of removing 5-HT condensation products not bound to BSA. The hapten has the configuration of a tetrahydro-beta-carboline (THBC) ring structure that is coupled to protein most probably via the carbon(s) ortho to the phenolic hydroxyl group and the indole nitrogen. The cyclic secondary amine of the THBC remained unsubstituted and was not involved in the bridging to BSA. This functional group was effectively blocked by acetylation and was unreactive to glutaraldehyde. On the other hand, in 5-HT conjugates synthesized using glutaraldehyde as the coupling agent, no cyclization to THBC occurred, and the amino groups were blocked. The chemical reactivity of the secondary amino group of the hapten in the synthesized conjugates was compared to the immunoreactivity of 5-HT conjugates formed in tissues. Immunostaining of formaldehyde-fixed serotoninergic neurons of the raphe of rats was suppressed by acetylation and the use of glutaraldehyde as the primary fixative, but the staining was unaffected when glutaraldehyde was reacted with formaldehyde-fixed 5-HT neurons. It is concluded that the cyclic secondary amine of the THBC structure is not conjugated to protein and forms part of the 5-HT-antibody-binding site in immunogens formed in vitro and in tissues.