Phosphoinositide hydrolysis linked 5-HT2 receptors in fibroblasts from choroid plexus.

A serotonin (5-HT)-mediated phosphoinositide hydrolysis response was characterized in fibroblasts cultured from rabbit choroid plexus. 5-HT elicited a maximum 8-fold increase in [3H]inositol-phosphate ([3H]IP) formation, while the partial agonists, (+)-lysergic acid diethylamide and (-)-1-(4-bromo-2,5-dimethyoxyphenyl)-2-aminopropane caused 2- and 5-fold increases, respectively. Mianserin, ketanserin, and spiperone were equipotent at blocking the 5-HT-mediated response. Thus, agonist and antagonist profiles indicate interactions with 5-HT2 receptors.     

Serotonin 5-HT1C receptors are expressed at high density on choroid plexus tumors from transgenic mice

Choroid plexus tumors develop spontaneously in adult transgenic mice carrying integrated copies of SV40 early region genes. In this communication, we report that these tumors exhibit the highest density of serotonin receptors (6600 fmol/mg protein) found in any tissue. ¹²⁵I-LSD binding to choroid plexus tumors displays a pharmacological profile that matches the properties of 5-HT_1C receptors in normal choroid plexus tissue. Autoradiographic localization of ¹²⁵I-LSD binding in brain sections from transgenic mice shows high levels of labelling in the tumors, in correlation with immunohistochemical staining for SV40 large T antigen expression. Choroid plexus tumors from these transgenic mice provide an excellent model system for the study of serotonin 5-HT_1C receptors.     

Denervation supersensitivity of 5-HT-1c receptors in rat choroid plexus

Serotonin (5-HT)-stimulated phosphoinositide hydrolysis in the choroid plexus is mediated by the 5-HT-1c receptor. The current study demonstrates that treatment of rats with the serotonergic neurotoxin, 5,7-dihydroxytryptamine, caused a marked depletion of 5-HT and a supersensitive 5-HT-1c mediated phosphoinositide hydrolysis response. These data suggest that the 5-HT-1c site in choroid plexus receives tonic serotonergic input.     

Expression of 5-HT2A, 5-HT2B and 5-HT2C receptors in the mouse embryo

Expression patterns of 5-HT(2A), 5-HT(2B) and 5-HT(2C) receptors during mouse embryogenesis were investigated using highly specific monoclonal antibodies. Differential and overlapping spatio-temporal patterns of 5-HT(2A), 5-HT(2B) and 5-HT(2C) receptor immunoreactivity were observed during active phases of morphogenesis of a variety of embryonic tissues, including neuroepithelia of brain and spinal cord, notochord, somites, cranial neural crest, craniofacial mesenchyme and epithelia, heart myocardium and endocardial cushions, tooth germs, whisker follicles, cartilage and striated muscle. The functional significance of these receptors was tested by exposing headfold stage mouse embryos to different subtype-selective 5-HT(2) receptor antagonists for 2 days in whole embryo culture. The most potent was the pan 5-HT(2) receptor antagonist ritanserin, which has high affinity for the 5-HT(2B) receptor. Ritanserin caused 100% malformed embryos at a dose of 1 microM. The 5-HT(2A/2C) receptor antagonist mianserin also caused a significant number of malformed embryos, but only when used at a 10 fold higher dose (10 microM). Ketanserin, which primarily targets 5-HT(2A) receptors, did not cause a significant number of malformed embryos at any dose tested. Together with previous evidence that 5-HT acts as an important morphoregulatory signal during mouse embryogenesis, present evidence for the early and continued expression of functional 5-HT(2) receptors throughout gestation raises the possibility that psychotropic drugs taken during pregnancy could interfere with developmental actions of 5-HT during prenatal development of neural and non-neural tissues.     

Expression of EAAT-1 distinguishes choroid plexus tumors from normal and reactive choroid plexus epithelium

Microscopic distinction of normal choroid plexus (CP) from choroid plexus tumors (CPT) may be difficult, especially in small samples of well-differentiated CP papillomas. So far, there are no established markers that reliably distinguish normal and neoplastic CP epithelium. Recently, a correlation between expression/function of glial glutamate transporters EAAT-1 (GLAST) and EAAT-2 (Glt-1) and tumor proliferation has been reported. Furthermore, we previously found that CPTs frequently express EAAT-1, but not EAAT-2. We now compared expression of EAAT-1, EAAT-2 and GFAP in non-neoplastic CP (n = 68) and CPT (n = 79) by immunohistochemistry. Tissue of normal CP was obtained from 50 autopsy cases (20 normal and 30 pathologic brains) and 18 neurosurgical specimens that included 17 fetal, 21 pediatric and 30 adult cases. In non-neoplastic postnatal CP (n = 51), focal expression of EAAT-1 was found in only two pediatric cases (4%). In CPT, expression of EAAT-1 was found in 64 of 79 (81%) tumor samples and was significantly age-dependent (P < 0.0001). Hence, EAAT-1 expression distinguishes neoplastic from normal CP, both in children (P = 0.0032) and in adults (P < 0.0001). Immunostaining for EAAT-2 in selected samples from cases of different ages showed that normal CP (n = 15) or CPT (n = 16) lacked EAAT-2 expression. GFAP expression was found in 3 of 32 (10%) normal CP and in 28 of 73 (38%) tumor samples. In conclusion, in contrast to neoplastic CP samples, expression of EAAT-1 is exceptionally rare in non-neoplastic CP. Thus, EAAT-1 is superior to GFAP as a helpful diagnostic tool in CP samples.     

DOI disrupts prepulse inhibition of startle in rats via 5-HT2A receptors in the ventral pallidum

Serotonin (5-HT)_2A receptors are known to be involved in prepulse inhibition of the startle response (PPI), a measure of sensorimotor inhibition that is deficient in schizophrenia, Huntington's disease, and obsessive compulsive disorder. In the present studies, the localization of the 5-HT_2A receptors responsible for modulating PPI was investigated using central injections of the hallucinogenic 5-HT₂ agonist DOI and the novel 5-HT_2A antagonist MDL 100,907. 5-HT_2A receptors are densely localized in the nucleus accumbens (NAC) and the ventral pallidum (VP), areas known to be important components of neural circuitry that mediates the ventral forebrain modulation of PPI. In the present studies, it was found that the infusion of DOI (0.0–5.0 μg/0.5 μl) into the VP disrupted PPI without having effects on startle reactivity. In contrast, similar infusions into the NAC had no effect on PPI or startle reactivity. The infusion of MDL 100,907 into the VP was found to increase PPI by itself and to attenuate the PPI-disruptive effects of systemically administered DOI. It is concluded that 5-HT_2A receptors within the VP are important for the modulation of PPI, presumably through interactions at intrinsic GABAergic or cholinergic interneurons.     

Cationic modulation of 5-HT2 and 5-HT3 receptors in rat sensory neurons: the role of K, Ca and Mg

The effects of changes in external K⁺, Ca²⁺, and Mg²⁺ concentrations on 5-HT₂- and 5-HT₃ receptor-mediated depolarizations of the resting membrane potential in rat dorsal root ganglion (DRG) cells was studied. In cells exhibiting a 5-HT₂-mediated response, 5-HT and α-methyl 5-HT depolarized the resting membrane potential (RMP) and increased the slope of the current–voltage (I/V) relationship. The equilibrium potential (E_r) for the depolarization was linearly related to the logarithm of the [K⁺]_o, indicating the depolarization resulted from a decrease in resting K⁺ conductance. In a subpopulation of large-diameter acutely dissociated DRG neurons recorded from using the whole-cell patch-clamp configuration, 5-HT produced an inward shift in the current required to hold cells at −60 mV. This inward shift in holding current was associated with a reduction in membrane conductance and reversed near E_k. This data suggests that the 5-HT₂ receptor-mediated depolarization and increase in R_in seen in intact DRG preparation is produced by blockade of an outward K⁺ leak current. Increases in [K⁺]_o reduced the increase in R_in and depolarization induced by 5-HT with 50% inhibition of the depolarization occurring at 8.3 mM of [K⁺]_o. Half-normal Ca²⁺ (1.2 mM) produced a downward shift of the 5-HT concentration–response curve, reducing the maximal response by 40%, with minimal effect on the half-maximal response. Mg²⁺ ions did not affect this 5-HT response. In cells exhibiting a 5-HT₃ receptor response, 5-HT and 2-methyl-5-HT produced depolarization with decreased R_in. The E_r for this depolarizing response (−30.2±1.8 mV) became less negative (−11.5 mV) in 10 mM [K⁺]_o with minimal effect on the amplitude of the depolarization. In Na⁺-free superfusate, the 5-HT-induced depolarization was converted to hyperpolarization. This indicated the 5-HT₃ response increased a mixed Na⁺/K⁺ conductance. Elevated Ca²⁺ or Mg²⁺ markedly reduced the 5-HT₃ response. Incubation with 3.5 mM Ca²⁺ shifted the 5-HT concentration–response curve downward and to the right, decreasing the maximal response by 49% and increasing the EC₅₀ by 10-fold. Elevated Mg²⁺ produced similar effects. In cells where both 5-HT₂- and 5-HT₃-mediated responses could be demonstrated, the elevation of K⁺ or the reduction of Ca²⁺ converted a 5-HT₂ response to a 5-HT₃ response. The above data suggest that elevation of [K⁺]_o or reduction of [Ca²⁺]_o produced by rapid firing rates of sensory neurons will favor the expression of 5-HT₃ responses over 5-HT₂ responses.     

Immunohistochemical evidence of endothelin-1 in human choroid plexus

Summary An immunohistochemical investigation was carried out on 17 specimens of human choroid plexus obtained post mortem, 1 biopsy of normal choroid plexus including part of the lateral ventricle and 1 papilloma of the choroid plexus removed surgically. The material was fixed in formalin. Paraffin and cryostat sections were used. A polyclonal antiserum to endothelin-1 served as a primary antibody. The avidin-biotin-peroxidase method was applied to demonstrate the immunoreaction. The epithelial cells of the choroid plexuses, the choroid papilloma and most ependymal cells of the lateral ventricle showed a distinct brown reaction product in their cytoplasm indicating antigenic sites to endothelin-1. The reaction was of lesser intensity in the ependymal cells. The connective tissue in choroid plexus was unstained. A positive immunoreaction was present in the walls of some vessels in the choroid plexus in cryostat sections. This is the first report on the presence of antigenic sites to endothelin-1 in the epithelial cells of the human choroid plexus. The role of endothelin in these cells should be investigated to ascertain if the cells synthesize this biologically active peptide or if it is merely bound to receptors in them.Supported by grants from Swedish Medical Research Council, project 03020, 1987 Års stiftelse för strokeforskning, Selanders stiftelse, Åhlen-stiftelsen and Stiftelsen Gamla Tjänarinnor, Stockholm Sweden     

The role of endoscopic choroid plexus coagulation in the surgical management of bilateral choroid plexuses hyperplasia

Background Bilateral choroid plexus hyperplasia is a rare condition often associated with cerebrospinal fluid (CSF) overproduction. CSF overproduction is usually so high that the placement of a CSF ventriculoperitoneal shunt almost always results in progressive ascites leading to the necessity of removing the inserted shunt device. A direct surgical treatment of the hyperplastic choroid plexuses is then mandatory. Endoscopic coagulation of the choroid plexuses has been recently proposed as an alternative to open surgical plexectomy. However, the effectiveness of the procedure in controlling CSF overproduction is still debated.Technique We report a case of bilateral choroid plexus hyperplasia in which an extensive bilateral endoscopic coagulation of the choroid plexuses failed to reduce the CSF formation rate sufficiently. A one-stage bilateral open surgical plexectomy was performed.Results The procedure succeeded to control CSF overproduction. Intraoperative blood loss during the surgical removal of the choroid plexuses was significantly reduced due to the previous coagulation of their surface.Conclusion On these grounds, we suggest that endoscopic choroid plexuses coagulation, even when failing to normalize CSF production, may still be considered as a valid adjuvant procedure in the management of this condition.     

Serotonergic effects on carbonic anhydrase activity in the choroid plexus

The carbonic anhydrase (CA) activities in the choroid plexus of dogs were investigated by electron microscopy, and the effects of 5-hydroxytryptophan (5-HTP) on them were examined to elucidate the participation of serotonin in the production of cerebrospinal fluid. The reaction products yielded by the method employed proved to be CA activity by elimination tests using acetazolamide (Diamox). Following administration of 5-HTP, the CA activities fell to 43.3% of the control value, that is, approximately 56% of the CA activities in the choroid plexus were affected by serotonin. When tetrabenazine (TBZ) was administered, the CA activities in the choroid plexus decreased to 22.4% of the control value. These results suggest that the CA activity in the choroid plexus is remarkably suppressed when nervous control of the choroid plexus is disturbed by the administration of a monoamine denervator such as TBZ. The present data indicate that the serotonergic inhibitory effect on the CA activity in the choroid plexus may be less predominant than that of TBZ and acetazolamide.     

Autoradiographic mapping of 5-HT1, 5-HT1A, 5-HT1B and 5-HT2 receptors in the rat spinal cord

The distribution of 5-HT₁, 5-HT_1A, 5-HT_1B and 5-HT₂ receptors in the rat spinal cord was investigated with quantitative autoradiography. Receptors were labeled respectively with [³H]serotonin (5-[³H]HT],8-hydroxy-2-[N-dipropylamino-³H]tetralin (8-OH-[³H]DPAT), [¹²⁵I]iodocyanopindolol and [³H]ketanserin. It is shown that 5-HT₁, 5-HT_1A and 5-HT_1B receptors are distributed within the spinal cord according to a rostro-caudal gradient. Both 5-HT₁ and 5-HT_1A receptors are mainly present in the dorsal horn and 5-HT_1B is present throughout the spinal cord, exhibiting high densities in the caudal-most part of the dorsal in lamina X and in the sacral parasympathetic area. On the other hand, 5-HT₂ receptors are shown mostly in the thoracic sympathetic area and in the thoracic ventral horn; the dorsal horn exhibits few 5-HT₂ receptors. The differential involvement of 5-Ht through different receptors in nociception, autonomous nervous system control and motility are discussed.     

Clinicopathologic correlations in epithelial choroid plexus neoplasms: a study of 52 cases

Summary Sixty-seven tumor specimens of epithelial choroid plexus neoplasms obtained by 60 biopsies and 7 autopsies from 52 patients were investigated. Diagnoses of the first operations were choroid plexus papilloma (PP; 32 cases), choroid plexus papilloma with histological atypies (atypical PP; 6 cases), and choroid plexus carcinoma (PC; 14 cases). Carcinoembryonic antigen was expressed by 2 of the 3 biopsies autoptically recognized as metastatic carcinomas and by 2 autopsy cases of PC, while it was absent in all biopsies of true choroid plexus tumors. Tumor cells positive for transthyretin (TTR, prealbumin), S-100 protein (S100), and glial fibrillary acidic protein (GFAP) were detected in 39, 46 and 13, respectively, of the 49 cases of true choroid plexus tumors. Fourth ventricle tumors expressed more S100 (number of positive tumor cells) than lateral ventricle tumors, PP more S100 and TTR than atypical PP/PC. Tumors from patients 20 years of age and older expressed more GFAP and TTR than tumors from younger patients. Of the 30 patients with complete follow-up 19 were alive 2 to 11 years after surgery, including 7 recurrencies. Eleven died from the tumor 4 months to 7 years after surgery. The following histopathologic features (in order of decreasing significance) were correlated with poor prognosis (recurrency or fatal outcome): less than 50% of the tumor cells heavily positive for S100, presence of mitoses, absence of TTR-positive cells, brain invasion by cell nests, absence of marked stromal edema, and presence of necrotic areas. Our results indicate that some histologic features correlate significantly with poor prognosis and that immunohistochemical results correlate with tumor localization, age, and malignancy.     

Correspondence between 5-HT2 receptors and serotonergic axons in rat neocortex

The anatomic relationship between serotonergic (5-HT) axons and 5-HT₂ receptors in the rat forebrain was determined by a combined analysis of transmitter immunocytochemistry and receptor autoradiography. High densities of 5-HT₂ receptors, localized by the ligand N1-methyl-2-¹²⁵I-LSD (¹²⁵I-MIL), are found in neocortex and striatum; these regions also receive a dense serotonergic innervation. Regional variations in the density of 5-HT₂ receptors and 5-HT axons correspond closely in most, but not all, areas of the forebrain. In somatosensory cortex (SI), the laminar distribution of 5-HT₂ receptors closely matches that of 5-HT axons: in particular, a dense band of 5-HT₂ receptors in layer V_a of SI is in precise register with a dense plexus of fine 5-HT axons. We have also observed a close spatial relationship between 5-HT₂ receptors and fine axons in other areas of the forebrain, suggesting that 5-HT₂ receptors may be selectively linked to a particular type of 5-HT axon terminal. Since fine axons of this type have been reported to arise from the dorsal raphe nucleus, it appears likely that 5-HT₂ receptors may mediate the effects of dorsal but not median raphe projections.     

5-HT1A/1B, 5-HT6, and 5-HT7 serotonergic receptors recruitment in tonic-clonic seizure-induced antinociception: Role of dorsal raphe nucleus

Pharmacological studies have been focused on the involvement of different neural pathways in the organization of antinociception that follows tonic-clonic seizures, including 5-hydroxytryptamine (5-HT)-, norepinephrine-, acetylcholine- and endogenous opioid peptide-mediated mechanisms, giving rise to more in-depth comprehension of this interesting post-ictal antinociceptive phenomenon. The present work investigated the involvement of 5-HT_1A/1B, 5-HT₆, and 5-HT₇ serotonergic receptors through peripheral pretreatment with methiothepin at doses of 0.5, 1.0, 2.0 and 3.0 mg/kg in the organization of the post-ictal antinociception elicited by pharmacologically (with pentylenetetrazole at 64 mg/kg)-induced tonic-clonic seizures. Methiothepin at 1.0 mg/kg blocked the post-ictal antinociception recorded after the end of seizures, whereas doses of 2.0 and 3.0 mg/kg potentiated the post-ictal antinociception. The nociceptive thresholds were kept higher than those of the control group. However, when the same 5-hydroxytryptamine receptors antagonist was microinjected (at 1.0, 3.0 and 5.0 μg/0.2 μL) in the dorsal raphe nucleus, a mesencephalic structure rich in serotonergic neurons and 5-HT receptors, the post-ictal hypo-analgesia was consistently antagonized. The present findings suggest a dual effect of methiothepin, characterized by a disinhibitory effect on the post-ictal antinociception when peripherally administered (possibly due to an antagonism of pre-synaptic 5-HT_1A serotonergic autoreceptors in the pain endogenous inhibitory system) and an inhibitory effect (possibly due to a DRN post-synaptic 5-HT_1B, 5-HT₆, and 5-HT₇ serotonergic receptors blockade) when centrally administered. The present data also suggest that serotonin-mediated mechanisms of the dorsal raphe nucleus exert a key-role in the modulation of the post-ictal antinociception.     

Focal ependymal differentiation in choroid plexus papillomas

Summary Choroid plexus papillomas are usually easily distinguishable from papillary ependymomas by their delicate fibrovascular stroma and their cytologic similarity to normal choroid plexus epithelium. Exceptionally, however, examples are met which give rise to diagnostic difficulty. We therefore tested 22 choroid plexus papillomas for the presence of glial fibrillary acidic (GFA) protein using the immunoperoxidase technique. Positivity for the protein was found focally in epithelial tumor cells in nine of the 22 papillomas. All were in adults ranging from 19–66 years of age. Eight of the nine tumors originated in the 4th ventricle or from one of its lateral recesses. In six papillomas showing GFA protein in the cells, intracellular fibrils were found in a small number of elongated epithelial cells with the PTAH and/or Masson trichrome stains; in all these six cases, the GFA protein-positive cells were considerably more numerous than cells containing fibrils. Normal choroid plexus epithelium lacks GFA protein, but pathologically altered ependymal cells are often GFA protein-positive. Our findings therefore suggest that focal divergent glial (presumably ependymal) differentiation may be expressed in neoplastic choroid plexus epithelium, consistent with the origin of this epithelium from primitive neuroepithelial (ventricular) cells.This work was supported in part by Research Grant CA-11689 from the National Cancer Institute, USPHS     

First report of occurrence of choroid plexus papilloma and medulloblastoma in the same patient

Introduction Choroid plexus papilloma is a benign epithelial brain tumour showing a striking predilection for infants and occurring most frequently in the lateral and fourth ventricles. Medulloblastoma, on the other hand, is a primitive neuroectodermal tumour and is the most frequent malignant brain tumour of the posterior fossa in children. In this study, we report a metachronous occurrence of choroid plexus papilloma and medulloblastoma in the same patient, which has not been reported before to the best of our knowledge. Case report The authors describe the case of a girl who presented with an atypical choroid plexus papilloma on the posterior wall of the left lateral ventricle at 3 months of age that was resected completely. She was followed up regularly after surgery and made good progress with normal development. At 8 years of age, she presented with right cerebellar medulloblastoma. Discussion The authors review literature for incidence and aetiology of the two tumours.     

Alteration of atrial natriuretic peptide receptors in the choroid plexus of rats with induced or congenital hydrocephalus

Specific binding sites for atrial natriuretic peptide (ANP) in the choroid plexus of rats with induced or congenital hydrocephalus were examined using in vitro quantitative receptor autoradiographic methods. The number of¹²⁵I-ANP binding sites in the choroid plexus of rats with kaolin-induced hydrocephalus was significantly higher as compared to findings in the control rats, whereas no differences in the binding affinity were observed 3 days and 3 weeks after the intracisternal injection of kaolin. Conversely, rats with congenital hydrocephalus (LEW-HYR and HTX rats) had a small number of binding sites for¹²⁵I-ANP in the choroid plexus, as compared to findings in the control rats. These alterations may relate to the pathophysiology of hydrocephalus. The possibility that atrial natriuretic peptide may be involved in the regulation of cerebrospinal fluid production in the choroid plexus must be considered.     

Antinociceptive effect of ketanserin in mice: involvement of supraspinal 5-HT2 receptors in nociceptive transmission

The involvement of 5-HT₂ receptors in pain transmission was investigated in mice. Subcutaneous administration of the selective 5-HT₂ receptor antagonist ketanserin produced dose-dependent antinociception in the hot-plate and acetic acid-induced writhing tests withED₅₀ values (95% confidence limit) of 1.51 (1.13–1.89) and 0.62 (0.10–1.40) mg/kg, respectively, but was without any significant effect on the tail-flick test. Pretreatment with the catecholamine depletors 6-hydroxydopamine (2.5 μg, i.c.v.) orα-methyl-p-tyrosine (200 mg/kg, s.c.), or the serotonin synthesis inhibitorp-chlorophenylalanine methylester (200 mg/kg, s.c.), resulted in a significant decrease in the antinociceptive effect of ketanserin. Likewise, intrathecal (i.t.) administration of 1 μg/mouse of idazoxan (anα₂-antagonist), methysergide (mixed 5-HT₁, and 5-HT₂ antagonist) or ketanserin also reversed the antinociceptive effect of s.c. administered ketanserin. The results of this work indicate that 5-HT₂ receptors located supraspinally may inhibit descending nociceptive neurotransmission. In addition, these studies suggest that 5-HT₂ receptors located at the spinal level modulate nociception.     

Usefulness of synaptophysin immunohistochemistry in an adult case of choroid plexus carcinoma

Abstract

Choroid plexus carcinoma in an adult case is a very rare tumor and difficult to differentiate from metastatic tumors. The authors report a case of a 49-year-old female with choroid plexus carcinoma who previously had multiple carcinomas. In this case, synaptophysin immunohistochemistry proved to be extremely helpful for the histological diagnosis. [Neurol Res 2000; 22: 478-480]