IMMUNOCYTOCHEMICAL LOCALIZATION OF SEROTONIN (5-HT) IN THE NERVOUS-SYSTEM OF THE HYDATID ORGANISM, ECHINOCOCCUS-GRANULOSUS (CESTODA, CYCLOPHYLLIDEA)

The localization and distribution of the serotoninergic components of the nervous system in the hydatid organism, Echinococcus granulosus, were determined by immunocytochemical techniques in conjunction with confocal scanning laser microscopy (CSLM). The distribution of serotonin immunoreactivity (IR) paralleled that previously described for cholinesterase activity, although it was more widespread. Nerve cell bodies and nerve fibres immunoreactive for 5-HT were present throughout the central nervous system (CNS), occurring in the paired lateral, posterior lateral and rostellar ganglia, their connecting commissures and nerve rings in the scolex and in the ten longitudinal nerve cords that run posteriorly throughout the body of the worm. A large population of nerve cell bodies was associated with the lateral nerve cords. In the peripheral nervous system (PNS), immunoreactive nerve fibres occurred in well-developed nerve plexuses innervating the somatic musculature and the musculature of the rostellum and suckers. The genital atrium and associated reproductive ducts were richly innervated with serotoninergic nerve cell bodies and nerve fibres.

CYTOCHEMICAL OBSERVATIONS ON CHOLINERGIC, SEROTONINERGIC AND PEPTIDERGIC NEURONAL PATHWAYS IN CEPHALOCHLAMYS-NAMAQUENSIS

The localization and distribution of cholinergic, serotoninergic (5-HT, serotonin) and peptidergic components of the nervous system of adult Cephalochlamys namaquensis (Cestoda: Pseudophyllidea) have been determined using enzyme histochemical and immunocytochemical techniques interfaced with light and confocal scanning laser microscopy. All three classes of neuroactive substance showed a similar pattern of staining, occurring extensively throughout the central and peripheral nervous systems of the parasite. There were some minor regional differences in staining, suggesting specific roles for certain classes of neurone, and nerve cell bodies were most evident following immunostaining for serotonin. The general overlap in the distribution of staining may be indicative of som co-localization of neurotransmitter and/or neuromodulatory substances.

CYTOCHEMICAL DEMONSTRATION OF CHOLINERGIC, SEROTONINERGIC AND PEPTIDERGIC NERVE ELEMENTS IN GORGODERINA-VITELLILOBA (TREMATODA, DIGENEA)

Standard enzyme cytochemical and indirect immunocytochemical techniques have been used in conjunction with light and confocal scanning laser microscopy (CSLM) to visualize cholinergic, serotoninergic and peptidergic nerve elements in whole-mount preparations of the amphibian urinary-bladder fluke, Gorgoderina vitelliloba. Cholinesterase (ChE) activity was localized in paired anterior ganglia, a connecting dorsal commissure and in the origins of the ventral nerve cords. Cholinergic ganglia were also evident in shelled embryos in the uterus. Serotonin-immunoreactivity (IR) was more extensive than ChE activity and was identified in both the central and peripheral nervous systems. Serotoninergic nerve fibres were associated with the somatic musculature and female reproductive ducts. Antisera to nine mammalian peptides and one invertebrate (FMRFamide) peptide have been used to investigate the peptidergic nervous system in the parasite. Immunoreactivity was obtained to five peptides, namely pancreatic polypeptide (PP), peptide YY (PYY), neuropeptide Y (NPY), substance P (SP) and FMRFamide. Peptidergic nerve fibres were found to be more abundant than demonstrable cholinergic or serotoninergic nerve fibres. NPY-IR was identified only in the main components of the central nervous system. However, PP- and PYY-IR occurred in the anterior ganglia, dorsal commissure, main nerve cords and in numerous small varicose fibres that ramified throughout the worm. Additionally, PP-immunoreactive nerve fibres were found to innervate the musculature of the female reproductive tracts. Six sites of IR were found in the acetabulum, using antisera directed towards the C-terminal end of PP and PYY, and these matched with the distribution of six non-ciliated rosette-like papillae observed by scanning electron microscopy. SP- and FMRFamide-IR were identified in the CNS, and FMRFamide-immunopositive nerve fibres were also evident in association with the gonopore/cirrus region and with the terminal excretory pore. Results are discussed with respect to possible roles for each of the neurochemical types.

5-HYDROXYTRYPTAMINE (SEROTONIN)-IMMUNOREACTIVITY IN THE NERVOUS-SYSTEM OF MESOCESTOIDES-CORTI TETRATHYRIDIA (CESTODA, CYCLOPHYLLIDEA)

An indirect immunocytochemical technique has been interfaced with confocal scanning laser microscopy to investigate the occurrence and distribution of serotoninergic (5-HT) nerve elements in Mesocestoides corti tetrathyridia. Cell bodies and nerve fibers immunoreactive to 5-HT were found concentrated in the innervation around the 4 suckers and associated commissures and in the 5 pairs of longitudinal nerve cords and their cross-connectives. Immunoreactivity was evident also in the extensive, peripheral network of fine fibers of the subtegumental region and in the plexus of varicose fibers that innervate the muscle in each of the suckers. In dividing stages of the tetrathyridium, the immunoreactive lateral nerve cords of adjoining progeny were in continuity around the base of the division cleft.

A CYTOCHEMICAL STUDY OF THE NERVOUS-SYSTEM OF THE PROTEOCEPHALIDEAN CESTODE, PROTEOCEPHALUS-POLLANICOLA

The localization and distribution of cholinergic, serotoninergic and peptidergic nerve elements in the proteocephalidean tapeworm, Proteocephalus pollanicola, have been investigated by enzyme histochemistry, and by an indirect immunofluorescence technique interfaced with confocal scanning laser microscopy. Cholinesterase (ChE) activity was localized in the major components of the central nervous system (CNS) and the peripheral nervous system (PNS), including the innervation of the reproductive structures of the worm. Serotoninergic (5-HT) nerves were found in the paired cerebral ganglia, transverse commissure and in the 10 longitudinal nerve cords. Antisera to 17 mammalian regulatory peptides and the invertebrate peptide FMRFamide have been used to explore the peptidergic nervous system of the worm. The most extensive immunostaining occurred with antisera raised to members of the neuropeptide Y superfamily, namely neuropeptide Y (NPY), peptide YY (PYY) and pancreatic polypeptide (PP). In all cases, intense immunoreactivity was found in numerous cell bodies and fibres of both the CNS and PNS, including the innervation of the reproductive apparatus. FMRFamide antisera stained the same structures to a comparable degree as those raised to the NPY superfamily. Cholinergic and peptidergic elements were much more prevalent within the CNS, while the serotoninergic nerve fibres tended to dominate in the PNS. The overlap obtained in staining patterns for the peptidergic and cholinergic components suggests that there may be a certain amount of co-localization of peptides with small-molecule transmitter substances in the same neurone. Weak staining for the tachykinin, substance P and for calcitonin gene-related peptide(CGRP) was confined to the major longitudinal nerve cords.

Dysfunction of Cortical Dendritic Integration in Neuropathic Pain Reversed by Serotoninergic Neuromodulation

Neuropathic pain is caused by long-term modifications of neuronal function in the peripheral nervous system, the spinal cord, and supraspinal areas. Although functional changes in the forebrain are thought to contribute to the development of persistent pain, their significance and precise subcellular nature remain unexplored. Using somatic and dendritic whole-cell patch-clamp recordings from neurons in the anterior cingulate cortex, we discovered that sciatic nerve injury caused an activity-dependent dysfunction of hyperpolarization-activated cyclic nucleotide-regulated (HCN) channels in the dendrites of layer 5 pyramidal neurons resulting in enhanced integration of excitatory postsynaptic inputs and increased neuronal firing. Specific activation of the serotonin receptor type 7 (5-HT7R) alleviated the lesion-induced pathology by increasing HCN channel function, restoring normal dendritic integration, and reducing mechanical pain hypersensitivity in nerve-injured animals in vivo. Thus, serotoninergic neuromodulation at the forebrain level can reverse the dendritic dysfunction induced by neuropathic pain and may represent a potential therapeutical target.