Neurological and endocrine phenotypes of fragile X carrier women

Women who carry fragile X mental retardation 1 (FMR1)gene premutation expansions frequently report neurological or endocrine symptoms and prior studies have predominantly focused on questionnaire report of medical issues. Premutation carrier (PMC) women (n = 33) and non-carrier controls (n = 13) were recruited and evaluated by a neurologist, neuropsychologist, and endocrinologist. Blood and skin biopsies were collected for molecular measures. Scales for movement disorders, neuropathy, cognitive function, psychiatric symptoms, sleep, and quality of life were completed. The average age of the women was 51 years (n = 46) and average CGG repeat size was 91 ± 24.9 in the FMR1 PMC women. Seventy percent of the PMC women had an abnormal neurological examination. PMC women had significantly higher scores on the Fragile X-Associated Tremor Ataxia Syndrome (FXTAS) rating scale, more neuropathy, and difficulty with tandem gait compared to controls. Central sensitivity syndromes, a neuroticism profile on the NEO Personality Profile, and sleep disorders were also prevalent. Discrepancies between subject report and examination findings were also seen. This pilot study suggests that women with the FMR1 premutation may have a phenotype that overlaps with that seen in FXTAS. Additional research with larger sample sizes is warranted to better delineate the clinical features.

A comparative study of the performance of individuals with fragile X syndrome and Fmr1 knockout mice on Hebb-Williams mazes

Fragile X syndrome (FXS) is the most prevalent form of heritable mental retardation. It arises from a mutation in the FMR1 gene on the X chromosome that interferes with expression of fragile X mental retardation protein (FMRP) and leads to a wide range of behavioural and cognitive deficits. Previous studies have shown a deficit in basic visual perceptual processing as well as spatial abilities in FXS. How such a deficit may impact spatial navigation remains unknown. The current study extended previous research by evaluating spatial learning and memory using both virtual and physical versions of Hebb-Williams mazes, which allows for testing of humans and animals under comparable conditions. We compared the performance of individuals affected by FXS to typically developing individuals of equivalent mental age as well as the performance of Fmr1 knockout mice to wild-type control mice on the same maze problems. In human participants, performance of the comparison group improved across trials, showing expected significant decreases in both errors and latency. In contrast, the performance of the fragile X group remained at similar levels across trials. Although wild-type control mice made significantly fewer errors than the Fmr1 knockout mice, latencies were not statistically different between the groups. These findings suggest that affected humans and mice show similar spatial learning deficits attributable to the lack of FMRP. The implications of these data are discussed including the notion that Hebb-Williams mazes may represent a useful tool to examine the impact of pharmacological interventions on mitigating or reversing the symptoms associated with FXS.

A comparative neuropsychological test battery differentiates cognitive signatures of Fragile X and Down syndrome

BACKGROUND

Standardised neuropsychological and cognitive measures present some limitations in their applicability and generalisability to individuals with intellectual disability (ID). Alternative approaches to defining the cognitive signatures of various forms of ID are needed to advance our understanding of the profiles of strengths and weaknesses as well as the affected brain areas.

AIM

To evaluate the utility and feasibility of six non-verbal comparative neuropsychological (CN) tasks administered in a modified version of the Wisconsin General Test Apparatus (WGTA) to confirm and extend our knowledge of unique cognitive signatures of Fragile X syndrome (FXS) and Down syndrome (DS).

METHOD

A test battery of CN tasks adapted from the animal literature was administered in a modified WGTA. Tasks were selected that have established or emerging brain-behaviour relationships in the domains of visual-perceptual, visual-spatial, working memory and inhibition.

RESULTS

Despite the fact that these tasks revealed cognitive signatures for the two ID groups, only some hypotheses were supported. Results suggest that whereas individuals with DS were relatively impaired on visual-perceptual and visual-spatial reversal learning tasks they showed strengths in egocentric spatial learning and object discrimination tasks. Individuals with FXS were relatively impaired on object discrimination learning and reversal tasks, which was attributable to side preferences. In contrast, these same individuals exhibited strengths in egocentric spatial learning and reversal tasks as well as on an object recognition memory task. Both ID groups demonstrated relatively poor performance for a visual-spatial working memory task.

CONCLUSION

Performance on the modified WGTA tasks differentiated cognitive signatures between two of the most common forms of ID. Results are discussed in the context of the literature on the cognitive and neurobiological features of FXS and DS.

A pilot open label, single dose trial of fenobam in adults with fragile X syndrome

Objective:

A pilot open label, single dose trial of fenobam, an mGluR5 antagonist, was conducted to provide an initial evaluation of safety and pharmacokinetics in adult males and females with fragile X syndrome (FXS).

Methods:

Twelve subjects, recruited from two fragile X clinics, received a single oral dose of 50–150 mg of fenobam. Blood for pharmacokinetic testing, vital signs and side effect screening was obtained at baseline and numerous time points for 6 h after dosing. Outcome measures included prepulse inhibition (PPI) and a continuous performance test (CPT) obtained before and after dosing to explore the effects of fenobam on core phenotypic measures of sensory gating, attention and inhibition.

Results:

There were no significant adverse reactions to fenobam administration. Pharmacokinetic analysis showed that fenobam concentrations were dose dependent but variable, with mean (SEM) peak values of 39.7 (18.4) ng/ml at 180 min after the 150 mg dose. PPI met a response criterion of an improvement of at least 20% over baseline in 6 of 12 individuals (4/6 males and 2/6 females). The CPT did not display improvement with treatment due to ceiling effects.

Conclusions:

Clinically significant adverse effects were not identified in this study of single dose fenobam across the range of dosages utilised. The positive effects seen in animal models of FXS treated with fenobam or other mGluR5 antagonists, the apparent lack of clinically significant adverse effects, and the potential beneficial clinical effects seen in this pilot trial support further study of the compound in adults with FXS.

FMR1 CGG repeat length predicts motor dysfunction in premutation carriers

BACKGROUND

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a recently described, underrecognized neurodegenerative disorder of aging fragile X mental retardation 1 (FMR1) premutation carriers, particularly men. Core motor features are action tremor, gait ataxia, and parkinsonism. Carriers have expanded CGG repeats (55 to 200); larger expansions cause fragile X syndrome, the most common heritable cause of mental retardation and autism. This study determines whether CGG repeat length correlates with severity and type of motor dysfunction in premutation carriers.

METHODS

Persons aged >or=50 years with a family history of fragile X syndrome underwent structured videotaping. Movement disorder neurologists, blinded to carrier status, scored the tapes using modified standardized rating scales. CGG repeat length analyses for women incorporated the activation ratio, which measures the percentage of normal active chromosome X alleles.

RESULTS

Male carriers (n = 54) had significantly worse total motor scores, especially in tremor and ataxia, than age-matched male noncarriers (n = 51). There was a trend toward a difference between women carriers (n = 82) and noncarriers (n = 39). In men, increasing CGG repeat correlated with greater impairment in all motor signs. In women, when activation ratio was considered, increasing CGG correlated with greater ataxia.

CONCLUSIONS

CGG repeat size is significantly associated with overall motor impairment in premutation carriers. Whereas this association is most pronounced for men and covers overall motor impairment-tremor, ataxia, and parkinsonism-the association exists for ataxia among women carriers. This is the first report of a significant correlation between the premutation status and a motor feature of fragile X-associated tremor/ataxia syndrome in women.

Initial diagnoses given to persons with the fragile X associated tremor/ataxia syndrome (FXTAS)

Fragile X-associated tremor/ataxia syndrome (FXTAS) is a newly described disorder that occurs in premutation carriers of the fragile X mental retardation 1 (FMR1) gene. Fifty-six patients with FXTAS were given 98 prior diagnoses: most were in the categories of parkinsonism, tremor, ataxia, dementia, or stroke. Data from this study and others were used to develop guidelines for FMR1 diagnostic testing for FXTAS.

Amyloid mediates the association of apolipoprotein E e4 allele to cognitive function in older people

BACKGROUND

The neurobiological changes underlying the association of the apolipoprotein E (APOE) e4 allele with level of cognition are poorly understood.

OBJECTIVE

To test the hypothesis that amyloid load can account for (mediate) the association of the APOE e4 allele with level of cognition assessed proximate to death.

METHODS

There were 44 subjects with clinically diagnosed Alzheimer's disease and 50 without dementia, who had participated in the Religious Orders Study. They underwent determination of APOE allele status, had comprehensive cognitive testing in the last year of life, and brain autopsy at death. The percentage area of cortex occupied by amyloid beta and the density of tau positive neurofibrillary tangles were quantified from six brain regions and averaged to yield summary measures of amyloid load and neurofibrillary tangles. Multiple regression analyses were used to examine whether amyloid load could account for the effect of allele status on level of cognition, controlling for age, sex, and education.

RESULTS

Possession of at least one APOE e4 allele was associated with lower level of cognitive function proximate to death (p = 0.04). The effect of the e4 allele was reduced by nearly 60% and was no longer significant after controlling for the effect of amyloid load, whereas there was a robust inverse association between amyloid and cognition (p = 0.001). Because prior work had suggested that neurofibrillary tangles could account for the association of amyloid on cognition, we next examined whether amyloid could account for the effect of allele status on tangles. In a series of regression analyses, e4 was associated with density of tangles (p = 0.002), but the effect of the e4 allele was reduced by more than 50% and was no longer significant after controlling for the effect of amyloid load.

CONCLUSION

These findings are consistent with a sequence of events whereby the e4 allele works through amyloid deposition and subsequent tangle formation to cause cognitive impairment.

The apolipoprotein E epsilon4 allele increases the odds of chronic cerebral infarction [corrected] detected at autopsy in older persons

BACKGROUND AND PURPOSE

Studies investigating the relation of the apolipoprotein E (apoE) epsilon4 allele to clinical stroke and to vascular changes on magnetic resonance imaging have been conflicting. Little data are available regarding the relation of apoE epsilon4 to cerebral infarctions documented on postmortem examination.

METHODS

We studied the apoE epsilon4 allele in 214 deceased members of the Religious Orders Study, a longitudinal clinical-pathologic study of aging and Alzheimer disease. The apoE genotype was determined using DNA from lymphocytes. Brains were removed a median of 5 hours (interquartile range, 5.5) after death. At postmortem examination, age, location, and size of macroscopic chronic cerebral infarctions were recorded from 1-cm coronal slabs after paraformaldehyde fixation. We also examined 20-microm paraffin-embedded sections of midfrontal and calcarine cortex for amyloid angiopathy on a scale of 1 to 4.

RESULTS

Subjects included 96 males and 118 females with a mean age at death of 86 years (SD, 7). Sixty-five subjects (30.4%) had at least 1 apoE epsilon4 allele and 76 (35.5%) exhibited cerebral infarctions. More than 74% of the subjects exhibited amyloid angiopathy with a mean score of 1.4+/-1.2. After controlling for age and sex, apoE epsilon4 increased the odds of cerebral infarction by 2.3-fold (95% CI, 1.2 to 4.2). apoE epsilon4 increased the odds of cortical 3.2-fold (95% CI, 1.3 to 7.7) and subcortical infarctions 2.3-fold (95% CI, 1.2 to 4.5). The effect was unchanged after accounting for amyloid angiopathy.

CONCLUSIONS

apoE epsilon4 increases the odds of chronic cerebral infarction detected at autopsy in older persons.

Filamin A mutations cause periventricular heterotopia with Ehlers-Danlos syndrome

OBJECTIVE

To define the clinical, radiologic, and genetic features of periventricular heterotopia (PH) with Ehlers-Danlos syndrome (EDS).

METHODS

Exonic sequencing and single stranded conformational polymorphism (SSCP) analysis was performed on affected individuals. Linkage analysis using microsatellite markers on the X-chromosome was performed on a single pedigree. Western blotting evaluated for loss of filamin A (FLNA) protein and Southern blotting assessed for any potential chromosome rearrangement in this region.

RESULTS

The authors report two familial cases and nine additional sporadic cases of the EDS-variant form of PH, which is characterized by nodular brain heterotopia, joint hypermobility, and development of aortic dilatation in early adulthood. MRI typically demonstrated bilateral nodular PH, indistinguishable from PH due to FLNA mutations. Exonic sequencing or SSCP analyses of FLNA revealed a 2762 delG single base pair deletion in one affected female. Another affected female harbored a C116 single point mutation, resulting in an A39G change. A third affected female had a 4147 delG single base pair deletion. One pedigree with no detectable exonic mutation demonstrated positive linkage to the FLNA locus Xq28, an affected individual in this family also had no detectable FLNA protein, but no chromosomal rearrangement was detected.

CONCLUSION

These results suggest that the Ehlers-Danlos variant of periventricular heterotopia (PH), in part, represents an overlapping syndrome with X-linked dominant PH due to filamin A mutations.

Aging in Individuals With the FMR1 Mutation

Individuals with fragile X mental retardation 1 (FMR1) premutation (55 to 200 CGG repeats) are typically unaffected by fragile X syndrome. However, a subgroup of older males with the premutation have developed a neurological syndrome, which usually begins between 50 and 70 years and is associated with a progressive intention tremor and/or ataxia manifested by balance problems, frequent falling, and Parkinsonian symptoms, such as masked facies, intermittent resting tremor, and mild rigidity. This finding has been termed the fragile X-associated tremor/ataxia syndrome (FXTAS) and has brought focus to the aging process in individuals with the FMR1 mutation. The premutation is associated with elevated messenger RNA levels leading to the formation of intranuclear inclusions in neurons and astrocytes associated with FXTAS. This review is a summary of our experience with FXTAS in male carriers of the premutation.

Apolipoprotein E epsilon4 allele, AD pathology, and the clinical expression of Alzheimer's disease

OBJECTIVE

To test the hypothesis that the APOE epsilon4 allele is associated with the clinical manifestations of AD through an association with the pathologic hallmarks of disease.

METHODS

Participants were older Catholic nuns, priests, and brothers who agreed to annual neurologic and neuropsychological evaluation for AD and other common neurologic conditions and brain autopsy at the time of death. There were 77 persons without dementia and 51 with probable AD; 38 participants had one or more epsilon4 alleles.

RESULTS

In logistic regression analyses, controlling for age, sex, and education, the epsilon4 allele was strongly associated with the likelihood of clinical AD (odds = 3.46, 95% CI = 1.44 to 8.33). However, controlling for the effect of AD pathology, the association of the epsilon allele with clinical AD was reduced by >50% and was no longer significant (odds = 1.58, 95% CI = 0.56 to 4.43). Similarly, in linear regression analyses, controlling for age, sex, and education, the epsilon4 allele was strongly associated with level of cognitive function proximate to death (regression coefficient = -0.477, p = 0.005). However, after controlling for the effect of AD pathology, the association of the epsilon4 allele with level of cognition was reduced by >80% and was no longer significant (regression coefficient = -0.093). Similar results were found in analyses using separate measures of neuritic plaques, diffuse plaques, and neurofibrillary tangles, and in analyses of five different cognitive systems (episodic memory, semantic memory, working memory, perceptual speed, and visuospatial ability).

CONCLUSIONS

The APOE epsilon4 allele appears to be associated with the clinical manifestations of AD through an association with the pathologic hallmarks of AD rather than another mechanism.

The apolipoprotein E epsilon 2 allele and decline in episodic memory

OBJECTIVES

The apolipoprotein E (apoE) epsilon 4 allele is related to decline in multiple cognitive domains, especially episodic memory, but the effect of the epsilon 2 allele on change in different forms of cognitive function has been difficult to establish.

METHODS

Participants are from the Religious Orders Study. At baseline, they were at least 65 years old and free of clinical evidence of dementia. For up to eight years, they underwent annual clinical evaluations that included detailed cognitive function assessment from which previously established summary measures of episodic memory, semantic memory, working memory, perceptual speed, and visuospatial ability were derived. Growth curve models were used to assess change in each measure and its relation to apoE genotype, controlling for age, sex, education, and baseline level of cognition. Follow up data were available in 669 persons (98% of those eligible). We treated those with the epsilon 3/3 genotype as the reference group (n=425), which was contrasted with epsilon 2 ( epsilon 2/2, epsilon 2/3; n=86), and epsilon 4 ( epsilon 3/4, epsilon 4/4; n=158) subgroups.

RESULTS

Rate of episodic memory change in the three subgroups significantly differed, with an average annual increase of 0.016 units in the epsilon 2 subgroup and annual decreases of 0.022 units in those with epsilon 3/3 and of 0.073 units in the epsilon 4 subgroup. The epsilon 2 subgroup did not differ from those with epsilon 3/3 in rate of decline in other cognitive systems. The epsilon 4 subgroup declined more rapidly than those with epsilon 3/3 in semantic memory and perceptual speed but not in working memory or visuospatial ability.

CONCLUSION

Possession of one or more apoE epsilon 2 alleles is associated with reduced decline in episodic memory in older persons.

Carnitine levels and the ketogenic diet

PURPOSE

To determine the long-term effect of the ketogenic diet (KD) on carnitine levels and whether carnitine depletion is a significant cause of clinical complications during KD initiation or treatment.

METHODS

Carnitine levels at 0, 1, 6, 12, and 24 months of diet treatment, carnitine antiepileptic drug (AED) history, lowest blood glucose and time to achieve ketosis during diet initiation, and diet complications were analyzed for 38 consecutive patients who initiated the KD from May 1997 to March 2000. Carnitine levels at follow-up were analyzed for eight patients started on the diet before to May 1997.

RESULTS

Total carnitine (TC) at diet initiation correlated negatively with the number of AEDs at diet initiation but not with number of past AEDs, lowest blood glucose, or time to ketosis. TC decreased in the first months of diet treatment and then stabilized or increased slightly with long term treatment. Only 19% of patients were supplemented with carnitine for low TC. No patient showed clinical signs of carnitine deficiency.

CONCLUSIONS

Multiple AED exposure lowers TC, but actual TC deficiency in patients initiating the KD is not common, and TC levels do not appear to predict hypoglycemia or problems achieving ketosis. Mild carnitine depletion may occur early in KD treatment and occasionally TC decreases out of the normal range, without clinical symptoms. TC stabilizes or increases back toward baseline with long-term treatment, and most patients do not require carnitine supplementation.

Genetic variation analysis in parkinson disease patients with and without hallucinations: case-control study

BACKGROUND

Visual hallucinations in Parkinson disease (PD) occur in approximately one third of patients treated long-term with dopaminergic medications. In Alzheimer disease, hallucinations and psychosis have been linked to increased representations of B2/B2 homozyogotes for the dopamine receptor gene DRD1 and 1/1 or 2/2 homozygotes for DRD3. In addition, a previous study of PD patients with and without hallucinations did not show differences in D2 and D3 polymorphisms, although careful case-control matching was not performed. Another study linked the apolipoprotein E4 (APOE4) allele to hallucinations in PD.

OBJECTIVE

To determine whether the frequency of dopamine receptor genetic variants and APOE alleles in patients with PD with and without chronic visual hallucinations resembles the pattern previously documented in patients with Alzheimer disease.

METHODS

We conducted a case-control study of 44 patients with PD and chronic hallucinations and 44 patients with PD who had never hallucinated. Cases and controls were matched for current age and medications. DNA was isolated from blood samples and assayed for DRD1, DRD2, DRD3, DRD4, and APOE polymorphisms. Receptor polymorphisms were genotyped by polymerase chain reaction. Genotypes in hallucinators and nonhallucinators were compared using Mantel-Haenszel tests stratified by pair, and allele frequencies were compared using Wilcoxon signed rank tests within pairs.

RESULTS

Neither D1 receptor genotypes (P =.37) nor allele frequencies (P =.38) differed, and there was no predominance of B2/B2 homozygotes in the hallucinators. For D3, there was a higher frequency of allele 2 (P =.047), but there was no significant difference between frequencies of homozygotes vs heterozygotes (P =.39) as reported in Alzheimer disease. D4 receptor distribution of long and short alleles did not differ between the 2 patient groups, and there were too few C alleles (3 of 86) to compare D2 allele genotypes or frequencies. For APOE, 12 cases and 12 controls carried E4 alleles (P>.99).

CONCLUSIONS

With careful case-control matching, visual hallucinations in PD are not associated with the pattern seen for patients with Alzheimer disease and visual hallucinations. Furthermore, there was no association between hallucinations and APOE. Similar methods using larger sample sizes might be adapted to test whether specific dopaminergic receptor genetic variants are associated with visual hallucinations in PD. Based on our data, the DRD3 allele 2 may merit further study.

Bruising and the ketogenic diet: evidence for diet-induced changes in platelet function

Excessive bruising is a symptom noted by parents of some children treated with the ketogenic diet for epilepsy control, although this side effect is not reported in the literature. We evaluated our cohort of current and past diet-treated patients for symptoms of bruising or bleeding through chart review and prospective screening at clinic follow-up visits. A significant increase in bruising or other minor bleeding was reported and/or observed in 16 of 51 patients (31.4%). There were no differences in sex distribution or number of anticonvulsants used between patients with bruising/bleeding and those without this symptom, although the group with bruising/bleeding was significantly younger. No specific anticonvulsant was associated with bruising/bleeding. Six patients with diet-induced bruising/bleeding underwent an investigation for bleeding diathesis. Five of these patients had prolonged bleeding times and all had diminished responsiveness to various platelet aggregating agents, with no evidence of a release defect. The abnormalities all normalized in the 1 patient tested after ceasing the diet. No patients had serious hemorrhage. One patient had mild von Willebrand disease, which had been asymptomatic before diet initiation. Some patients were Stimate responsive, suggesting a treatment for more severe bouts of symptoms. These data suggest that a ketogenic diet-related bleeding tendency occurs in about one third of treated patients owing to preexisting factors defining susceptibility in combination with diet-induced depression of platelet responsiveness, possibly related to changes in platelet membrane lipid composition and/or concentration and resultant effects on function of membrane-embedded proteins. Patients on the diet undergoing anticoagulation or surgery should be evaluated carefully for symptoms of bleeding tendency.

Cognitive and visual processing skills and their relationship to mutation size in full and premutation female fragile X carriers

BACKGROUND

The fragile X gene contains an unstable trinucleotide (CGG) repeat that expands as it is passed from female carriers to the affected offspring. Obligate female carriers may have a premutation or full mutation genotype.

METHODS

In this study, fragile X premutation and full mutation female carriers were compared on three tasks of visual processing and cognitive skills.

RESULTS

In each case, there were significant differences between premutation and full mutation carriers on a number of the subtests or the full test scores. Specifically, full mutation female carriers performed more poorly in visual-motor processing and analysis-synthesis on the Woodcock-Johnson Psycho-Educational Battery-Revised, The Developmental Test of Visual Motor Integration, and on five of the seven subtests of the Test of Visual-Perceptual Skills. Regression analyses revealed significant negative correlations between mutation size and cognitive ability.

CONCLUSIONS

These findings have implications in educational planning decisions for full mutation carriers who may present with specific cognitive deficits.

Prenatal testing for late infantile neuronal ceroid lipofuscinosis

Classic late infantile neuronal ceroid lipofuscinosis (LINCL) is a neurodegenerative disease in which autofluorescent "curvilinear" storage bodies accumulate in tissues from affected patients. Recently, the LINCL gene (CLN2) has been found to code for a pepstatin-insensitive lysosomal protease whose activity is deficient in LINCL specimens. We report the first 2 cases of successful prenatal testing for LINCL by using DNA and enzyme-based methods on amniocytes, and describe a new private mutation in one of the families analyzed. These approaches allow definitive prenatal diagnosis and represent a significant improvement over previous pathological methods.

X-linked lissencephaly with absent corpus callosum and ambiguous genitalia

Lissencephaly has been described in over 10 distinct malformation syndromes. Recently, we have recognized 5 children from four unrelated families with an almost identical disorder comprising lissencephaly with a posterior-to-anterior gradient and only moderate increase in thickness of the cortex, absent corpus callosum, neonatal-onset epilepsy, hypothalamic dysfunction including deficient temperature regulation, and ambiguous genitalia in genotypic males. Our observation of 5 affected males in one of these families is consistent with an X-linked pattern of inheritance. However, it differs in many regards from the X-linked form of isolated lissencephaly sequence that is associated with mutations of the XLIS (DCX) gene. Therefore, we propose that this disorder comprises a new X-linked malformation syndrome, which we refer to as X-linked lissencephaly with ambiguous genitalia (XLA-G).

Mosaic trisomy 16 ascertained through amniocentesis: evaluation of 11 new cases

Trisomy 16, once thought to result uniformly in early pregnancy loss, has been detected in chorionic villus samples (CVS) from on-going pregnancies and was initially ascribed to a second, nonviable pregnancy. Prenatally detected trisomy 16 in CVS and its resolution to disomy has led to the reexamination of the viability of trisomy 16. This study evaluates 11 cases of mosaic trisomy 16 detected through second trimester amniocentesis. In 9 of the 11 cases, amniocenteses were performed in women under the age of 35 because of abnormal levels of maternal serum alpha-fetoprotein (MSAFP) or maternal serum human chorionic gonadotropin (MShCG). The other two amniocenteses were performed for advanced maternal age. Five of the 11 pregnancies resulted in liveborn infants, and six pregnancies were electively terminated. The liveborn infants all had some combination of intrauterine growth retardation (IUGR), congenital heart defects (CHD), or minor anomalies. Two of them died neonatally because of complications of severe congenital heart defects. The three surviving children have variable growth retardation, developmental delay, congenital anomalies, and/or minor anomalies. In the terminated pregnancies, the four fetuses evaluated by ultrasound or autopsy demonstrated various congenital anomalies and/or IUGR. Cytogenetic and fluorescent in situ hybridization studies identified true mosaicism in 5 of 10 cases examined, although the abnormal cell line was never seen in more than 1% of cultured lymphocytes. Placental mosaicism was seen in all placentas examined and was associated with IUGR in four of seven cases. Maternal uniparental disomy was identified in three cases. Mosaic trisomy 16 detected through amniocentesis is not a benign finding but associated with a high risk of abnormal outcome, most commonly IUGR, CHD, developmental delay, and minor anomalies. The various outcomes may reflect the diversity of mechanisms involved in the resolution of this abnormality. As 80% of these patients were ascertained because of the presence of abnormal levels of MSAFP or MShCG, the increased use of maternal serum screening should bring more such cases to clinical attention.

Overexpression of fragile X gene (FMR-1) transcripts increases cAMP production in neural cells

Fragile X syndrome results from amplification of an unstable trinucleotide (CGG) repeat in the first exon of FMR-1, the "fragile X gene." This mutation silences the gene, resulting in loss of expression of the FMR proteins (FMRP), a series of RNA-binding proteins generated by alternative splicing of FMR-1 transcripts. We have shown that cAMP production is diminished in cells from patients with fragile X syndrome. To establish a direct relationship between FMR-1 expression and cAMP metabolism, FMRP isoforms 1 and 7 were overexpressed in the neurotumor hybrid cell line HN2. Cyclic AMP production in clonal HN2 lines overexpressing FMRP was significantly higher than in nonoverexpressing control lines and increased with increasing total FMR-1 mRNA on Northern blots and FMRP signal on Western blots. These data support a role for FMRP in the regulation of cAMP signal transduction by increasing intracellular cAMP, perhaps through a mechanism involving binding and enhanced translation of mRNA(s) for cAMP cascade proteins. Diminished cAMP production in the absence of FMR-1 may provide one neurochemical mechanism through which FMR-1 influences cognitive function.

Stable expression and heterologous coupling of the kappa opioid receptor in cell lines of neural and nonneural origin

Signal transduction cascades initiated by the neuronal kappa opioid receptor were studied following transfection of a neuronal (hippocampal) line, HN2, and the non-neural CHOs. Retinoic-acid mediated differentiation resulted in intense staining of the HN2 cells with a neurofilament protein antibody SMI 33 but not with an antibody to GFAP, thus establishing neuronal characteristics of the HN2 cell line. The kappa opioid receptor was stably expressed in the two cell lines by electroporation mediated transfer of a Cytomegalovirus-promoter driven construct, pCMV-kappa, harboring the kappa-opioid receptor cDNA. Positive clones (HN2 kappa 24 and CHO kappa 18) from both lines showed high expression of the kappa opioid receptor, as identified by [3H] U-69,593 binding to membranes prepared from HN2 kappa 24 and CHO kappa 18. Scatchard analysis revealed the presence of high affinity kappa opioid receptors in both engineered cell lines (KD=1.3 nM for HN2 kappa 24 and 2.1 nM for CHO kappa 18). Functional coupling to adenylate cyclase was displayed by 1 microM U-69,593 mediated inhibition (55-63%) of prostaglandin E1-stimulated intracellular cAMP levels. A major difference between the two clones was observed in functional coupling of the expressed kappa opioid receptor to phospholipases C (PL-C) and D (PL-D). U-69,593 (1 microM) treatment stimulated PL-C, but not PL-D, in HN2 kappa 24 cells, whereas PL-D, but not PL-C, was stimulated following such treatment of CHO kappa 18 cells. Our results using the model neuronal system, HN2 kappa 24, demonstrate cell-type specific, positive coupling of the kappa opioid receptor to the major Ca2+ mobilizing system, the PL-C cascade, which regulates neuronal firing.

Reduced cyclic AMP production in fragile X syndrome: cytogenetic and molecular correlations

The cAMP cascade is an intracellular signal transduction system thought to be important for neuronal regulation and information storage. cAMP production is reduced in platelets from patients with fragile X syndrome. In the present study we assayed cAMP metabolism, Xq27.3 fragile site percentages, size of amplification mutation in fragile X mental retardation-1 gene (FMR-1), and FMR-1 mRNA levels in 21 lymphoblastoid cell lines (LCL) from fragile X patients. cAMP production was diminished in fragile X LCL relative to controls (n = 20) when cells were assayed in prostaglandin E1 (74%, p < 0.02) and in forskolin (64%, p < 0.1) although the difference was statistically significant only in prostaglandin E1. The length of the FMR-1 amplification mutation correlated with measures of cAMP production which were unassociated with receptor activation (r = -0.53, p = 0.02, and r = -0.48, p = 0.03, for unstimulated and forskolin-stimulated cAMP production, respectively). In fragile X LCL, fragile site percentages did not correlate with any measure of cAMP production. All fragile X LCL showed absence of FMR-1 mRNA. These data suggest that diminished cAMP production in fragile X tissues may be linked to the fragile X amplification mutation, either as a result of influences of the mutation on FMR-1 expression or on transcription of other genes downstream from FMR-1.

Fragile X syndrome in a normal IQ male with learning and emotional problems

The present case study features an adult male who was diagnosed with fragile X syndrome after the identification of this syndrome in his more affected brother. The patient presented with a Full Scale IQ within the broad range of normal and has been diagnosed with a schizotypal personality disorder. He shows significant deficits in the social and emotional aspects of daily life, but has striking cognitive strengths relating to reading and vocabulary as compared to most males affected with fragile X syndrome. DNA testing of blood leukocytes revealed that he has a fully expanded FMR1 CGG repeat mutation associated with almost complete lack of methylation. Protein studies demonstrate a limited production of FMRP, the protein produced by the FMR1 gene. It is believed that the near absence of methylation of the fully expanded mutation and the resultant expression of the FMR1 protein is responsible for the strong cognitive abilities of this fragile X patient.

X-linked pachygyria and agenesis of the corpus callosum: evidence for an X chromosome lissencephaly locus

A family of 5 affected male infants in 2 generations with an X-linked pattern of inheritance is described. All affected infants manifested intractable seizures, severe psychomotor retardation, growth failure, microphallus, and death during infancy. Three of the affected patients had radiological studies that demonstrated findings consistent with pachygyria-agyria and agenesis of the corpus callosum. We believe that this family represents a form of X-linked pachygyria-agyria (lissencephaly) that has not been described previously and suggests a locus for lissencephaly on the X chromosome.

Preferential beta-hexosaminidase (Hex) A (alpha beta) formation in the absence of beta-Hex B (beta beta) due to heterozygous point mutations present in beta-Hex beta-chain alleles of a motor neuron disease patient

Deficiency of the lysosomal enzyme beta-hexosaminidase B (beta-Hex B) (a homodimer, beta beta), caused by a defect in the HEX B gene encoding the beta-chain, is usually accompanied by an absence of beta-Hex A (a heterodimer, alpha beta), thereby causing Sandhoff disease. However, we have earlier demonstrated the presence of partial beta-Hex A (30-50% of normal) even in the absence of beta-Hex B in an adult with motor neuron disease. The patient is a compound heterozygote with normal beta-chain message and one HEX B point mutation originating from each asymptomatic parent. Since the non-expression of beta-Hex B was post-transcriptional, we transfected COS-7 cells to understand the effect of each mutation on beta-Hex B activity. Transfection of the A1367-->C mutant (maternal allele) construct produced no overexpressed beta-Hex B, indicating that the encoded Tyr456-->Ser beta-chain was non-functional. Chou-Fasman analysis predicted that the Tyr456-->Ser mutation would cause a dramatic change in beta-chain folding (which often inhibits formation of functional dimers). This explains the complete lack of beta-Hex B in the transfectants and a partial deficiency of beta-Hex A and B (50% of normal) in the patient's mother. Since immunoprecipitated beta-Hex A (alpha beta) protein from patient fibroblasts showed the presence of mature beta-chains even though there was no beta-Hex B (beta beta) protein, the mutant beta-chain inherited from the father (who has normal beta-Hex A and B) must undergo preferential association with the normal alpha-chains in the patient, thus producing only beta-Hex A. Transient expression of the A619-->G mutant (paternal allele) construct produced beta-Hex B activity comparable to the wild type (approximately 10-20-fold over mock-transfected) whereas stable expression produced normal message but no beta-Hex B activity (wild type beta-Hex B expression: only 2-fold over mock-transfected). The lack of increased beta-Hex B after stable expression of the Ile207-->Val beta-chains at a lower copy number indicates the absence of self-association at low concentrations of Ile207-->Val beta-chain. In the patient who also has a non-functional Tyr456-->Ser allele, the effective concentration of beta-chains is reduced to 50% of normal and the remaining Ile207-->Val beta-chains fail to self-associate but can still dimerize with the abundant normal alpha-chains thus producing partial beta-Hex A and no beta-Hex B.

Two patients with overlapping de novo duplications of the long arm of chromosome 9, including one case with Di George sequence

Duplications of chromosome 9q are rare. We describe the cytogenetic and phenotypic findings in 2 patients, one with a large duplication covering most of 9q(q12-q33.2) and one with a smaller duplication (q21.12-q22.1) who had Di George sequence (DGS). The chromosome 9 origin of the extra material in the second case was confirmed by fluorescence in situ hybridization (FISH) analysis with a whole chromosome 9 paint. Microdeletions of chromosome 22 are common in DGS and have been reported in CHARGE association. This is the first report of an association of a chromosome 9 abnormality with DGS in the absence of a chromosome 22 abnormality and the seventh report of a patient with a duplication of a large portion of 9q (q11-q13 to q32-q33).

Heterologous expression of the serotonin 5-HT1A receptor in neural and non-neural cell lines

Stable expression of neuronal receptors in cell lines of neural origin is important for studies of neurotransmitter mediated signal transduction. We have achieved this for the first time in three cell lines which are derived from various tissues of neural origin (hippocampus, HN2; chinese hamster brain explant, NCB-20; rat dorsal root ganglion, F-11). Following electroporation assisted transfer of a construct containing the hippocampal serotonin 5-HT1A receptor (5-HT1AR) DNA, one neural cell line, NG-108-15 (murine neuroblastoma x C6 glioma), failed to express the transfected activity, while three others as well as the non-neural CHO (chinese hamster ovary) cells expressed high levels of the receptor. Upon normalization to coexpressed human beta-hexosaminidase B activity, it was found that the human 5-HT1AR, which is normally concentrated in the hippocampus and at a lesser density in the brain, was expressed at the highest level (15.7 x 10(4) receptors/cell) in the HN2 followed by the NCB-20 (8.3 x 10(4) receptors/cell), F-11 (4.4 x 10(4) receptors/cell) and lastly the non-neuronal CHO (4.2 x 10(4) receptors/cell) cells. Ten-twelve days after passage, a striking increase in expression of the receptor was observed only in the cell lines of neural origin. By contrast, there was no appreciable increase in expression of the transfected 5-HT1AR in the non-neural CHO cells over time. This late increase in expression was eliminated in cells which had been maintained in low glucose (1 g/L) for the first two days after passage, thus establishing a vital role of glucose in expression of the transfected 5-HT1AR in cell lines of neural origin. In all cases the 5-HT1AR was negatively coupled to adenylate cyclase, as evidenced by an agonist mediated decrease in prostaglandin E1 stimulated cyclic AMP levels.

Demonstration of abnormal cyclic AMP production in platelets from patients with fragile X syndrome

Cyclic AMP production was studied in platelets from 31 patients with fragile X syndrome, 16 patients with mental retardation, 4 patients with autistic disorder, and 57 control individuals. 1-isobutyl-3-methylxanthine (IBMX) was used to inhibit phosphodiesterase; prostaglandin E1 (PGE1), to stimulate cAMP production via a receptor-dependent mechanism, and forskolin (FSK), to directly activate the catalytic subunit. Cyclic AMP production in IBMX, PGE1 + IBMX, and FSK + IBMX was 50% (P < 0.05), 65% (P = 0.001), and 53% (P = 0.001), respectively, in fragile X platelets relative to controls. Cyclic AMP production was not statistically different from controls in patients with mental retardation or autistic disorder. There was no effect of age or sex on cAMP production. Dose response curves suggested that abnormal cAMP production was due to diminished maximal response rather than altered potency of stimulating agents. The data presented here demonstrate that diminished cAMP production exists in platelets from patients with fragile X syndrome. Thus, defective functioning of cAMP-mediated regulatory signalling pathways in fragile X brain may contribute to the mental deficiency in these patients.

Cyclic AMP metabolism in fragile X syndrome

Cyclic AMP (cAMP) metabolism was studied in platelets from a series of 14 patients with fragile X syndrome (fra X) and 21 control individuals. 1-Isobutyl-3-methylxanthine was used to inhibit phosphodiesterase and thus measure cAMP production, prostaglandin E1 was used to assess receptor-mediated cAMP accumulation, and forskolin was used to directly stimulate the catalytic subunit. In patients with fra X, basal production was 63% of that of control subjects (p = 0.019). Prostaglandin E1- and forskolin-stimulated production were 61% (p = 0.039) and 56% (p = 0.012) of that of control subjects, respectively. cAMP production in 8 patients with fra X overlapped the control range, whereas measures of production in 6 patients formed a cluster with values lower than any of the 21 control subjects assayed, suggesting possible biochemical heterogeneity within patients with fra X. Results obtained from the group of patients with fra X suggest possible abnormal function or regulation of the catalytic subunit of adenylate cyclase in at least a subgroup of patients with fra X. Variability of biochemical findings in patients with fra X may reflect the known high variability of the clinical syndrome.

Neuromodulator-mediated phosphorylation of specific proteins in a neurotumor hybrid cell line (NCB-20)

Mouse neuroblastoma X embryonic Chinese hamster brain explant hybrid cell line (NCB-20) forms functional synapses when intracellular cyclic AMP levels are elevated for a prolonged period of time. NCB-20 cells were labeled with [32P]orthophosphate under conditions where 2-chloroadenosine gave maximum increases of 32P incorporation into tyrosine hydroxylase in nerve growth factor dibutyryl cyclic AMP-differentiated PC12 (pheochromocytoma) cells. When NCB-20 cells were exposed to activators [5-hydroxytryptamine (5-HT), prostaglandin E1, or forskolin], resulting in activation of cyclic AMP-dependent protein kinase, increased 32P incorporation into two major proteins [130 kilodaltons (kDa) and 90 kDa] occurred. 5-HT (in the presence of phosphodiesterase inhibitor, isobutylmethylxanthine) gave a three- to fourfold increase, and forskolin a four- to sevenfold increase in 32P incorporation into the 90-kDa protein. [D-Ala2,D-Leu5]-enkephalin, which decreased cyclic AMP levels and reversed the 2-chloroadenosine-stimulated phosphorylation of tyrosine hydroxylase in differentiated PC12 cells, also reversed the stimulation of phosphorylation of the 90-kDa protein in NCB-20 cells. Pretreatment of NCB-20 cells with a calcium ionophore, A23187, gave increased phosphorylation of the 90- and 130-kDa proteins, but phorbol esters such as 12-O-tetradecanoylphorbol 13-acetate (tumor promoting agent), cell depolarization with high K+, or pretreatment with dibutyryl cyclic GMP had no effect on phosphorylation of these proteins. In contrast, phosphorylation of an 80-kDa protein was decreased by forskolin, but increased following activation of the calcium/phospholipid-dependent kinase with tumor promoting agent. Neither the 90-kDa nor the 80-kDa protein showed any immunological cross-reactivity with synapsin, a major synaptic protein known to be phosphorylated by cyclic AMP-dependent protein kinase and calcium/calmodulin-dependent protein kinase, but not calcium/phospholipid-dependent protein kinase. This suggests that in NCB-20 cells, several unique proteins can be phosphorylated by cyclic AMP-dependent protein kinase in response to hormonal elevation of cyclic AMP levels. In contrast, an 80-kDa protein is the primary substrate for calcium/phospholipid-dependent protein kinase, and its phosphorylation is inhibited by agents that elevate cyclic AMP levels and thereby activate cyclic AMP-dependent protein kinase.

Differential regulation of multiple neuroreceptors in a somatic cell hybrid by inhibitors of glycoprotein processing

Specific binding of [3H][D-Ala2,D-Leu5]enkephalin, [3H]ethylketocyclazocine, 5-[3H]hydroxytryptamine, and [3H]spiperone was examined in neuroblastoma-brain hybrid cell line NCB-20 following exposure to inhibitors of N-linked protein glycosylation (tunicamycin, TM) and oligosaccharide processing (swainsonine, SW). TM treatment reduced ligand binding at delta- and sigma-opiate receptors and neuroleptic binding sites (20 to 50% of control), with no discernible effect on the binding properties of 5HT1-serotonin receptors. In contrast, exposure to SW resulted in a three-fold increase in binding capacity of sigma-receptors, while decreasing receptor affinity for ligand. SW treatment did not alter ligand interactions with either sigma-receptors or neuroleptic binding sites, but did reduce specific binding of serotonin to 5HT1-receptors. The effects of TM and SW on distinct receptor subpopulations were further demonstrated by attenuation of opiate and serotonin-mediated regulation of intracellular cyclic AMP.

Possible role of gangliosides in regulating an adenylate cyclase-linked 5-hydroxytryptamine (5-HT1) receptor

Cultured NCB-20 hybrid cells express adenylate cyclase-coupled receptors for 5-hydroxytryptamine (5-HT) that correspond biochemically and pharmacologically to 5-HT1 receptors in rodent brain membrane preparations, apart from a much-reduced affinity for 5-HT (160 nM compared to less than 5 nM in brain). Since NCB-20 cells also differ from rodent brain both qualitatively and quantitatively in their ganglioside composition, the effects of exogenously added gangliosides on the affinity of the 5-HT1 receptor for 5-HT were tested. Both GM1 ganglioside (the cholera toxin receptor) and tetrasialoganglioside GQ1b produced a 10-fold increase in receptor affinity for [3H]5-HT, measured by binding studies. All gangliosides, at submicromolar concentrations, resulted in significantly reduced EC50 values for 5-HT-mediated elevation of intracellular cyclic AMP levels. GQ1b had the capacity to most dramatically enhance the potency of 5-HT in mediating increases in cyclic AMP levels. Gangliosides had no effect on the potency of DADLE or 3,4-dihydroxyphenylethylamine (dopamine)-mediated depression of cyclic AMP levels, suggesting some specificity for 5-HT. Our data are interpreted as implying a specific role for polysialogangliosides in modulating the affinity of the 5-HT1 receptor and the coupling of the 5-HT1 receptor-guanine nucleotide binding protein adenylate cyclase complex.

Evidence for [D-Ala2,D-Leu5]enkephalin-induced supersensitivity to 5-hydroxytryptamine in a neurotumor x brain hybrid cell line (NCB-20)

A neuroblastoma X Chinese hamster embryonic brain explant hybrid cell line (NCB-20) expressed 5-hydroxytryptamine (5-HT1) receptors, linked to adenylate cyclase, which closely resembled 5-HT1 receptors previously characterized in central nervous tissue. However, the affinity of the receptors for 5-HT was only 150 nM compared to 5 nM in membranes prepared from cerebral cortex. The elevation of cyclic AMP levels in NCB-20 cells produced by 5-HT was found additive to that produced by cholera toxin but synergistic with that produced by either prostaglandin E1 (PGE1) or forskolin, suggesting that these latter two agents elevate cyclic AMP levels by a different mechanism than 5-HT. The elevation of cyclic AMP levels by either 5-HT or PGE1 was reversed by [D-Ala2,D-Leu5]enkephalin (DADLE), morphine, clonidine, and 3,4-dihydroxyphenylethylamine (dopamine) on a short (30 min) time scale. However, continued exposure to DADLE resulted in loss of the initial inhibitory effects of DADLE after 6 h and return of cyclic AMP levels to that seen with either 5-HT or PGE1 alone. When the DADLE exposure time was increased to 48 h, 5-HT produced a further twofold increase in cyclic AMP levels, but there was no increase in the responsiveness of the cells to PGE1 unless naloxone was added 1 h prior to treatment with PGE1. Scatchard analysis showed that the increased potency of 5-HT resulted from an increase in receptor affinity for 5-HT (from a KD of 150 +/- 20 nM to one of 20 +/- 7 nM), with a reduction in the number of apparent binding sites. The 5-HT supersensitivity observed in NCB-20 cells may be a good model for neurotransmitter interactions that produce desensitization or facilitation in the intact nervous system.

Specific receptor-mediated inhibition of cyclic AMP synthesis by dopamine in a neuroblastoma X brain hybrid cell line NCB-20

Dopamine and dopamine receptor agonists were found to inhibit adenylate cyclase activity dose-dependently in a neuroblastoma X Chinese hamster brain explant hybrid cell line NCB-20. Apomorphine (with an IC50 value of 10 nM) was the most effective inhibitor, followed by 2-amino-6,7-dihydroxy-1,2,3,4-tetrahydronaphthaline (ADTN), dopamine, and N-dipropyldopamine. The inhibition was potently reversed by sulpiride, butaclamol, and flupenthixol in a stereospecific manner, but was unaffected by yohimbine, except at high concentrations. Clonidine also inhibited adenylate cyclase activity in these cells and this was reversed by the alpha 2-adrenoreceptor antagonist yohimbine, but not by sulpiride. [D-Ala2, D-Leu5] Enkephalin inhibited adenylate cyclase activity in NCB-20 cells at nanomolar concentrations; this was reversed by naloxone. All three inhibitory neurotransmitters were able to reverse the stimulation of cyclic AMP synthesis by serotonin or prostaglandin E1. The dopamine receptor that modulates cyclic AMP synthesis in NCB-20 cells is pharmacologically quite distinct from a high-affinity spiperone binding site identified in these cells, but shows the pharmacologic specificity of the "D2" receptor previously described in mammalian brain.

Gangliosides as modulators of the coupling of neurotransmitters to adenylate cyclase

Cultured NCB-20 mouse neuroblastoma X Chinese hamster brain clonal hybrid cells express an adenylate cyclase-coupled receptor for serotonin (5HT) which corresponds pharmacologically to the 5HT1 receptor in whole brain, except for its much lower affinity for serotonin. Studies showed that the affinity of the NCB-20 receptor could be increased to near that of the whole brain receptor and the potency of 5HT in elevating cyclic AMP levels increased by pre-incubating NCB-20 cells for at least 3 hours with submicromolar concentrations of brain gangliosides. Tetrasialoganglioside (GQ1b) was found to be the most potent ganglioside tested, producing a ten-fold increase in affinity. However, the actual 5HT binding site is a protein and we have obtained no evidence that serotonin binds directly to gangliosides at the concentrations at which it labels the receptor. The receptor-mediated inhibition of adenylate cyclase by biogenic amines such as dopamine and clonidine through dopamine (D2) and alpha-adrenoreceptors was unaffected by pre-incubation of the NCB-20 cells with gangliosides. Enkephalin was also found to acutely supress both the ability of 5HT to stimulate adenylate cyclase activity and the synthesis of polysialogangliosides in NCB-20 cells. After 6 hours of exposure, the cells became tolerant to enkephalin and after 36 hours the cells became supersensitive to 5HT in terms of adenylate cyclase activation and 5HT binding. The affinity of the receptor for 5HT increased the same 10-fold magnitude as achieved by GQ1b pre-incubation in comparison with untreated cells. This increase in receptor affinity appeared to coincide chronologically with the increase in ganglioside synthesis observed in enkephalin tolerant cells, further suggesting an important role of polysialogangliosides in the function of the serotonin (5HT1) receptor.

Characterization of an adenylate cyclase-linked serotonin (5-HT1) receptor in a neuroblastoma X brain explant hybrid cell line (NCB-20)

Clonal cell line NCB-20 (a hybrid of mouse neuroblastoma N18TG2 and Chinese hamster 18-day embryonic brain explant) expressed both high- (KD 180 nM) and low-affinity (greater than 3000 nM) binding sites for [3H]serotonin (5-HT) which were absent from the parent neuroblastoma. The low-affinity binding site was eliminated by 1 microM spiperone. The order of drug potency for inhibition of high-affinity [3H]5-HT binding was consistent with a 5-HT1 receptor (5,6 - dihydroxytryptamine = 5-HT = methysergide = 5-methoxytryptamine greater than cyproheptadine = clozapine = mianserin greater than spiperone greater than dopamine = morphine = ketanserin = norepinephrine). [3H]5-HT binding was inhibited by guanine nucleotides (e.g., GTP and Gpp(NH)p), whereas antagonist binding was not; ascorbate was also inhibitory. A 30-min exposure of cells to 1-2 microM 5-HT or other agonists produced a three- to fivefold stimulation of cyclic AMP levels. The order of potency for 5-HT agonist stimulation of basal cyclic AMP levels and 5-HT antagonist reversal of agonist-stimulated levels was the same as the order of drug potency for inhibition of high-affinity [3H]5-HT binding, suggesting linkage of the 5-HT1 receptor to adenylate cyclase in NCB-20 cells.