Efficacy of fluorescence-based PCR-SSCP for detection of point mutations

We assessed the efficiency of fluorescence-based PCR single-strand conformation polymorphism analysis (PCR-SSCP) using an automated DNA sequencer and analysis software. We evaluated 48 point mutations in a 191-bp stretch of mouse beta-globin. The mutations included 10 transversions and 38 transitions; and both types of mutation were compared at six different locations in the PCR fragment. Mobilities of the red dye-labeled internal standard fragments were non-proportional to size but highly reproducible and were used to normalize or correct minor differences in apparent electrophoretic mobility between lanes. Forty-six of forty-eight mutants (96%) were distinguished from wild type when run in separate lanes using one set of conditions. Co-electrophoresis of wild type and mutant in the same lane resolved 100% of 45 mutants from wild type. Under conditions of this study, the magnitude of mobility shifts resulting from the globin mutations were largely determined by position of the mutation, rather than by the nature of the substitution (transition vs. transversion). However, examination of paired mutations at the same position revealed that some substitutions cause greater mobility shifts than others.

Analysis of the 5-HT1C receptor and the serotonin uptake site in fawn-hooded rat brain

Both the 5-HT1C receptor and the 5-HT uptake binding sites were measured in Fawn-Hooded, Sprague-Dawley and Wistar rats. Five brain regions were examined: frontal cortex, hippocampus, striatum, hypothalamus, and brainstem. We found significant differences in the Bmax and Kd values in various brain regions comparing Fawn-Hooded rats, with Sprague-Dawley and Wistar animals. The regional differences in receptor number and affinity in both the 5-HT1C receptor and the 5-HT uptake site in the Fawn-Hooded strain, relative to Wistar and Sprague-Dawley animals, provide support for the use of the Fawn-Hooded rat in serotonin dysfunction studies.

Diurnal rhythms of 5-HT1A and 5-HT2 receptor binding in euthermic and torpor prone deermice, Peromyscus maniculatus

Deermice display both spontaneous and induced daily torpor bouts, attaining minimum body temperatures of 15-20 degrees C. There is evidence that brain serotonin may be involved in the initiation and/or maintenance of torpor. Inhibition of serotonin [5-hydroxytryptamine (5-HT)] synthesis markedly reduces the duration and depth of torpor. Because a certain percentage of deermice will not enter torpor under any circumstances, we were able to compare 5-HT receptor subtypes in deermice that readily enter into torpor (TP) and in non-torpor prone (NTP) animals. Deermice were trapped in the wild and subjected to food rationing and low ambient temperature and then sacrificed either in a normothermic or torpid state at 11:00 p.m. or 11:00 a.m. Whole brain was assayed for 5-HT1A and 5-HT2 receptor differences using [3H]8-OH-DPAT and [3H]ketanserin, respectively. The Bmax values for 5-HT1A receptors were significantly greater in both TP and NTP animals sacrificed at 11:00 p.m. compared to animals sacrificed at 11:00 a.m. In contrast, the density of 5-HT2 receptors was significantly greater in animals sacrificed at 11:00 a.m. compared to animals sacrificed at 11:00 p.m. This is consistent with the opposing functions of these receptors in the regulation of temperature and sleep. The affinity (Kd) of each receptor was unchanged. A comparison of TP and NTP animals sacrificed at the same time of day revealed no significant differences in either Bmax or in Kd values, indicating that differences in 5-HT1A and 5-HT2 receptors may not explain the heterogeneity of deermice in their ability to enter torpor.(ABSTRACT TRUNCATED AT 250 WORDS)

Cues intrinsic to the retina induce nAChR gene expression during development

Recent studies of optic nerve regeneration in goldfish have indicated that the optic tectum plays an important role in modulating the induction of nicotinic acetylcholine receptor (nAChR) gene expression in regenerating retinal ganglion cells (Heiber, Agranoff, and Goldman, 1992, J. Neurochem. 58:1009-1015). These observations suggest that induction of these genes is regulated by brain target regions. The appearance of nAChR mRNA in the developing rat retina coincides with a time when ganglion cells are sending axons to their brain targets (Hoover and Goldman, 1992, Exp. Eye Res. 54:561-571). Might a mechanism similar to that seen during goldfish optic nerve regeneration also mediate induction of nAChR gene expression during development of the mammalian retina? This possibility was tested by either transplanting embryonic rat retina to different brain regions, or explanting it to organ culture and assaying for nAChR gene expression. These studies showed that induction of the nAChR genes in developing rat retina is independent of the environment in which the retina develops. These results indicate that either the retinal microenvironment or a signal intrinsic to the retinal ganglion cell is responsible for this induction.

Paternal and maternal genetic and environmental contributions to cerebrospinal fluid monoamine metabolites in rhesus monkeys (Macaca mulatta)

BACKGROUND

To study genetic and environmental contributions to cerebrospinal fluid (CSF) monoamine concentrations, 55 young rhesus monkeys (Macaca mulatta) were reared apart from their 10 fathers to perform a paternal half-sibling analysis.

METHODS

To study maternal genetic contributions, 23 infants were reared with their mothers, 23 infants were removed from their mothers at birth and fostered to unrelated lactating female monkeys, and 24 infants were removed from their mothers at birth and reared with age-matched peers. When the monkeys reached age 6 months, CSF samples were obtained via cisternal puncture prior to and during a series of social separations.

RESULTS

When the results were statistically pooled according to the biological father, comparisons using analysis of variance indicated that both CSF 5-hydroxyindoleacetic acid (5-HIAA) and homovanillic acid (HVA) concentrations showed significant heritable (h2) effects (h2 > 0.5) for both sons and daughters, whereas 3-methoxy-4-hydroxyphenylglycol (MHPG) showed a nearly significant paternal genetic effect only for sons (h2 > 0.5). In addition, there were substantial maternal genetic influences on the young monkeys' CSF MHPG and 5-HIAA (h2 > 0.5) levels. Structural equation analyses indicated a maternal genetic contribution without a maternal environmental contribution to CSF 5-HIAA concentration; on the other hand, there was both a maternal genetic and environmental contribution to MHPG.

CONCLUSIONS

These findings suggest that a significant portion of the variance in the turnover of the monoamine neurotransmitters is determined by genetic mechanisms.

Regional analysis of 5-HT1A receptors in two species of Peromyscus

Two species of deer-mice, Peromyscus maniculatus (P. man) and Peromyscus leucopus (P. leu), were compared for differences in 5-hydroxytryptamine1A (5-HT1A) receptor number and affinity. Both species enter into torpor; however, P. man enters spontaneous torpor with a higher frequency and for a longer duration than P. leu. Further, compared to P. leu a higher percentage of P. man exhibit daily torpor. Deer mice can be induced to enter torpor by a reduction in food supply, shortened photoperiods, and decreasing ambient temperature. Under these conditions, P. man enters into torpor more frequently, for longer durations, and with a higher percentage of individuals as compared to P. leu. [3H]8-OH-DPAT was used to label 5-HT1A brain receptors in three brain regions: the frontal cortex, brainstem, and striatum. In addition, the hypothalamus and hippocampus were examined for 5-HT1A receptor differences; however, no measurable specific binding could be determined in these regions. In the frontal cortex, the Bmax values were significantly lower in P. man compared to P. leu. There were no significant differences in the Bmax values in the striatum and brainstem between P. man and P. leu. Further, there were no significant differences in the Kd values between the two species in any of the brain regions examined. The absence of any difference in receptor number or affinity in any of the brain regions examined, except the cortex, suggests that the 5-HT1A receptor is most likely not involved in a more efficient pathway to torpor.

The A1 allele at the D2 dopamine receptor gene and alcoholism. A reappraisal

OBJECTIVE

An allelic association between the TaqI "A" system A1 allele at the D2 dopamine receptor locus (DRD2) and either alcoholism or severe alcoholism has been proposed. Our purpose was to evaluate whether, based on all of the accumulated evidence, this association could be considered to be proven.

DATA SOURCES

We considered data from all published reports of DRD2 allele frequency in alcoholics, controls, or both.

STUDY SELECTION

We concentrated on the issue of replication. We therefore considered all data reported (on white samples, because DRD2 allele frequency varies by race and ethnicity) since the first report by Blum et al in 1990.

DATA SYNTHESIS

We analyzed the set of data for differences in allele frequencies between alcoholics and controls, and for heterogeneity among samples. We also investigated the influence of the data from the first group to report an association (including a subsequent report from that group) on the findings. Our analysis shows that, when all studies subsequent to the original study are considered, there is no significant difference in DRD2 A1 allele frequency between alcoholics and controls, there is significant heterogeneity among reported alcoholics and reported controls, and there is no significant difference in DRD2 A1 allele frequency between severe and not severe alcoholics. Also, the two reports of Blum et al account for all of the (nonsignificant) differences seen between controls, alcoholics, and severe alcoholics.

CONCLUSIONS

In general, heterogeneity among studies (for alcoholics or controls) is considerably greater than differences between alcoholics and controls overall. The findings to date can best be explained by more conservative interpretations than a confirmed physiologically important allelic association between DRD2 alleles and alcoholism. These other possibilities include sampling error and ethnic variation in those studies that individually showed a large effect.

DRD2 dopamine receptor genotype, linkage disequilibrium, and alcoholism in American Indians and other populations

We defined interpopulation differences in the frequency of the dopamine D2 receptor DRD2/Taq1 A1 allele, which has previously been associated with alcoholism. Frequencies of the A1 allele in unrelated subjects were 0.18 to 0.20 (se = 0.02 to 0.03) in several Caucasian populations previously assessed, 0.38 (+/- 0.05) in American Blacks (n = 44), 0.63 (+/- 0.07) in Jemez Pueblo Indians (n = 23), and 0.80 (+/- 0.04) in Cheyenne Indians (n = 52). The existence of large interpopulation differences in the frequency of the Taq1 alleles suggests that associations to disease status could readily be generated or masked if disease and control groups were uneven in ethnic composition. To address the possibility that the 4-fold higher frequency of the A1 allele in Cheyenne Indians was related to an increased vulnerability to alcoholism in that population, 47 Cheyenne Indians were psychiatrically interviewed and blind-rated. However, there was no significant difference between interviewed controls (0.73 +/- 0.06, n = 24), subjects with alcoholism and/or drug abuse (0.74 +/- 0.06, n = 23) and noninterviewed population controls (0.87 +/- 0.05, n = 20). Legitimate association of the DRD2/Taq1 allele to alcoholism would presumably require it to be in linkage disequilibrium (nonrandom association) with a functional mutation at DRD2 or elsewhere. The level of disequilibrium would vary between populations and could place an upper bound on the strength of an association.(ABSTRACT TRUNCATED AT 250 WORDS)

Genomic imprinting: implications for behavioral genetics

In recent years it has become apparent that the parental origin of genetic material has an impact on gene expression and this effect has become known as genomic imprinting. The evidence for the influence of genomic imprinting on behavior and in the etiology of certain neurobehavioral disorders is discussed. The possibilities for a role for genomic imprinting in the inheritance of behaviors related to alcohol abuse and alcoholism and in the paternal alcohol syndrome are also explored.

Identification of tryptophan 2,3-dioxygenase RNA in rodent brain

The gene for tryptophan 2,3-dioxygenase (TDO) heretofore was believed to be expressed only in liver. The data presented here demonstrate that RNA encoding TDO is present in rodent brain. Oligonucleotide primers based on the rat liver TDO cDNA sequence were synthesized and used to amplify RNA derived from mouse whole brain and liver and rat brain regions by the RNA-PCR. Reaction products were purified and subjected to DNA sequencing. Identical sequences were obtained when mouse whole brain and liver RNAs were amplified, and these sequences were shown to be 96% identical to the published rat liver tryptophan TDO cDNA sequence. In addition, TDO sequences were found in RNA derived from rat brainstem, cerebellum, cortex, hypothalamus, and the remainder of the brain.

Coupling muscle electrical activity to gene expression via a cAMP-dependent second messenger system

Embryonic-type nicotinic acetylcholine receptor (nAChR) gene expression is regulated by muscle activity. The mechanism by which this activity is transduced to the genome is not known. We have addressed this issue by using a rat primary muscle cell culture system that mimics the in vivo effects of muscle activity on nAChR expression. We report here that the suppression of nAChR gene expression by muscle activity can be reversed by increasing intracellular cAMP levels. This effect is specific to the embryonic-type receptor genes. Electrically insensitive genes such as those encoding the adult-type nAChR epsilon-subunit and creatine kinase are not up-regulated by cAMP. In addition, muscle inactivity caused either by tetrodotoxin or denervation increases cAMP levels and protein kinase A activity, consistent with their proposed role in mediating nAChR gene expression. Finally, we report that this same mechanism appears to regulate other genes, such as those encoding the tetrodotoxin-insensitive sodium channel, MyoD, and myogenin which, like the nAChR, are regulated by muscle electrical activity. Based on these results it is proposed that muscle electrical activity is coupled to gene expression via a cAMP-dependent second messenger system.

Genetic mapping of the human tryptophan hydroxylase gene on chromosome 11, using an intronic conformational polymorphism

The identification of polymorphic alleles at loci coding for functional genes is crucial for genetic association and linkage studies. Since the tryptophan hydroxylase (TPH) gene codes for the rate-limiting enzyme in the biosynthesis of the neurotransmitter serotonin, it would be advantageous to identify a polymorphism in this gene. By examining introns of the human TPH gene by PCR amplification and analysis by the single-strand conformational polymorphism (SSCP) technique, an SSCP was revealed with two alleles that occur with frequencies of .40 and .60 in unrelated Caucasians. DNAs from 24 informative CEPH families were typed for the TPH intron polymorphism and analyzed with respect to 10 linked markers on chromosome 11, between p13 and p15, with the result that TPH was placed between D11S151 and D11S134. This region contains loci for several important genes, including those for Beckwith-Wiedemann syndrome and tyrosine hydroxylase.

Regional analysis of 5-HT1A and 5-HT2 receptors in the fawn-hooded rat

The Fawn-Hooded strain of rats exhibits a hemorrhagic disorder, known as platelet storage pool deficiency. In addition to the platelet dysfunction, there is an altered response to certain serotonin drugs. To assess the characteristics of the binding to 5-HT1A and 5-HT2 receptors in this strain, regions of the brain from Fawn-Hooded, Sprague-Dawley and Wistar male rats were examined. The drug [3H]8-OH-DPAT was used to label 5-HT1A receptors and the Kd values for frontal cortex, hippocampus, striatum, hypothalamus and brainstem were similar in all three strains of rat. As with the 5-HT1A receptors, no differences were observed in the Kd values for 5-HT2 receptors, in any of the regions examined, among the three strains. However, the Bmax for the binding of [3H]8-OH-DPAT in the striatum and brainstem of Fawn-Hooded rats was less than in the Sprague-Dawley and Wistar animals. Furthermore, 5-HT2 receptors displayed a greater Bmax value in the striatum and in the frontal cortex of Fawn-Hooded animals, compared to Sprague-Dawley and Wistar rats. These differences in receptors are consistent with previous studies in which Fawn-Hooded rats were found to have altered serotonergic function, relative to Wistar and Sprague-Dawley animals.

D2 dopamine receptor genotype and cerebrospinal fluid homovanillic acid, 5-hydroxyindoleacetic acid and 3-methoxy-4-hydroxyphenylglycol in alcoholics in Finland and the United States

If a genetic association between the D2 dopamine receptor genotype and alcoholism is mediated by altered dopamine function, then a stronger association might be found in alcoholics who are deviant in indices of dopamine function and by comparing alcoholics to nonalcoholics matched for ethnic origin. Therefore, we evaluated the D2/TaqI polymorphism in 29 impulsive violent alcoholic Finns, 17 nonimpulsive violent alcoholic Finns and 36 Finnish controls free of mental disorders, alcoholism and substance abuse. In 37 of the alcoholics, we measured cerebrospinal fluid (CSF) homovanillic acid (HVA), 5-hydroxyindoleacetic acid (5-HIAA) and 3-methoxy-4-hydroxyphenylglycol. There was no relationship between D2/Taq 1 genotype and concentrations of these monoamine metabolites in this group, which exhibits lower CSF HVA and 5-HIAA as compared to controls. There was also no genotypic difference between Finnish alcoholics and nonalcoholic controls. The lack of relationship between D2/Taq1 genotype and HVA concentration was replicated in 24 Caucasian alcoholics in the United States.

Quantitative autoradiography of 3H-paroxetine binding sites in rat brain

The use of 3H-paroxetine as a ligand for quantitative autoradiography of serotonin (5-HT) transport sites was optimized, and the distribution of 3H-paroxetine binding sites in rat brain was studied. Under the conditions described, 3H-paroxetine binding in forebrain sections was of high affinity and saturable, with a Kd of 0.18 +/- 0.02 nM (mean +/- SEM) and Bmax of 268 +/- 12 fmol/mg of protein (n = 3). Nonspecific binding was 10.7% +/- 1.0 of the total binding (n = 8). The distribution of 3H-paroxetine binding sites closely matched the regional distribution of 5-HT nerve terminals and cell bodies. The highest concentrations of 3H-paroxetine binding sites were found in the dorsal raphe nucleus (563 +/- 55 fmol/mg tissue, n = 4), and high densities of binding were also found in the locus coeruleus, medial forebrain bundle, substantia nigra, several limbic structures (amygdala, hippocampus, hypothalamus, olfactory tubercle, septum, and thalamus), and components of the visual relay system (superior colliculus and the lateral geniculate body). Although lesioning of 5-HT neurons with p-chloroamphetamine (PCA) drastically eliminated 3H-paroxetine binding in most regions of the rat brain, significant binding remained in the raphe nuclei and medial forebrain bundle suggesting that 3H-paroxetine binding in these regions was to presynaptic sites on cell bodies or axons relatively resistant to PCA.

A 102 base pair sequence of the nicotinic acetylcholine receptor delta-subunit gene confers regulation by muscle electrical activity

Muscle electrical activity suppresses expression of the embryonic-type (alpha, beta, gamma, and delta) nicotinic acetylcholine receptor (nAChR) genes. The molecular mechanism by which electrical activity regulates these genes is not known. One approach to this problem is to identify regions of the nAChR genes that mediate electrical regulation. Here we report results from such a study of the nAChR delta-subunit gene. We cloned the rat delta-subunit promoter region and created an expression vector in which this DNA controlled the expression of a down-stream luciferase structural gene. The effect that muscle electrical activity had on the expression from this promoter was assayed by introducing this expression vector into electrically stimulated and tetrodotoxin (TTX)-treated rat primary myotubes, and assaying for luciferase activity. These myotubes, when stimulated with extracellular electrodes, suppressed endogenous embryonic-type nAChR gene expression compared to those treated with TTX. Transfection of these cells with delta-promoter-luciferase expression vectors resulted in the delta-promoter conferring electrical regulation on luciferase expression. Additional experiments using deletions from the 5′ end of the delta-promoter region have identified an element between −677 and −550 bp that suppressed delta-promoter activity and a minimal 102 bp sequence that promotes and regulates luciferase expression in response to muscle electrical activity. This latter sequence also contains all the necessary elements to confer tissue and developmental stage-specific expression.

Bizarre delusions and DSM-III-R schizophrenia

OBJECTIVE

Bizarre delusions are assigned greater weight relative to other delusions in the DSM-III-R diagnosis of schizophrenia. The decision to emphasize bizarre delusions was based largely on historical tradition rather than empirical evidence. This study examined 1) the extent to which a history of bizarre delusions contributes to the diagnosis of schizophrenia and 2) whether schizophrenic patients with bizarre delusions constitute a clinically distinguishable subgroup.

METHOD

Two hundred fourteen consecutively admitted psychotic inpatients were assessed for bizarre delusions according to the DSM-III-R criteria. Clinical and demographic correlates of bizarre delusions were examined in subsets of patients diagnosed as schizophrenic according to DSM-III-R who also received CT scans and neuropsychological testing.

RESULTS

With the base prevalence rate for schizophrenia of 0.71, bizarre delusions had a sensitivity of 0.79, a specificity of 0.56, and a positive predictive power of 0.82 for the diagnosis of schizophrenia (N = 152) relative to other psychotic disorders (N = 62). Clinical, neurobehavioral, CT scan, and premorbid adjustment data on the schizophrenic patients indicated that beyond manifesting more severe positive symptoms, patients with bizarre delusions did not otherwise constitute a clinically distinguishable subgroup.

CONCLUSIONS

The data suggest that criterion A for the diagnosis of schizophrenia in DSM-IV could be improved by removing the special emphasis that was placed on bizarre delusions in DSM-III-R.

Temporally correlated expression of nAChR genes during development of the mammalian retina

In situ hybridizations and RNase protection assays have been used to characterize nicotinic acetylcholine receptor (nAChR) gene expression in the developing and adult rat retina. At the earliest time examined (embryonic day 13) a low level of alpha-3 and beta-4 gene expression could be detected. During the next 48 hr there was a dramatic induction of the alpha-3, alpha-4, beta-2, beta-3 and beta-4 genes in the recently differentiated retinal ganglion cells. By post-natal day 4 we detected nAChR gene expression in the inner nuclear layer. In the adult retina, in situ hybridizations showed these genes are expressed by cells residing in the ganglion and inner nuclear layers. These results suggest a common regulatory mechanism for the induction of nAChR expression in retinal ganglion cells during development. In addition, the variety of nAChR genes expressed in the retina imply a relatively large number of different types of nAChRs can be expressed by these cells.

Target-dependent regulation of retinal nicotinic acetylcholine receptor and tubulin RNAs during optic nerve regeneration in goldfish

A fundamental issue in central nervous system development regards the effect of target tissue on the differentiation of innervating neurons. We address this issue by characterizing the role the retinal ganglion cell target, i.e., the optic tectum, plays in regulating expression of tubulin and nicotinic acetylcholine receptor genes in regenerating retinal ganglion cells. Tubulins are involved in axonal growth, whereas nicotinic acetylcholine receptors mediate communication across synapses. Retinal ganglion cell axons were induced to regenerate by crushing the optic nerve. Following crush, there was a rapid increase in alpha-tubulin RNAs (3 days), which preceded the increase in nicotinic acetylcholine receptor RNAs (10-15 days). Both classes of RNAs approached control levels by the time retinotectal synapses and functional recovery were restored (4-6 weeks). If the optic nerve was repeatedly crushed or its target ablated, tubulin RNAs remained elevated, and the increase in receptor RNAs that would otherwise be seen 2 weeks after a single nerve crush did not occur. The interaction of retinal ganglion cell axons with their targets in the optic tectum appears, then, to exert a suppressive effect on the RNA encoding a cytoskeletal protein, tubulin, and an inductive effect on RNAs encoding nicotinic acetylcholine receptors involved in synaptic communication.

Expression of Size-Selected RNA Encoding Brain Serotonin Transporter in Xenopus laevis Oocytes

The mRNA that encodes a serotonin transporter was expressed using the Xenopus laevis oocyte expression system. Poly(A)+ RNA isolated from mouse brainstem was injected into Xenopus laevis oocytes, and the ability of oocytes to take up serotonin was measured 3 days postinjection. RNA-dependent serotonin uptake was sensitive to citalopram, a specific inhibitor of serotonin uptake, whereas background levels of serotonin uptake were not citalopram sensitive. Two RNA size fractions, 4.0 and 4.5 kb, were most efficient in stimulating uptake. Injection into Xenopus laevis oocytes of the 4.5-kb size fraction of mouse brainstem RNA resulted in threefold more serotonin uptake than did injection of unfractionated poly(A)+ RNA.