Mood alterations and sleep

We have reviewed literatures about neurobiological aspect of mood disorders in the light of abnormalities of REM sleep. A shortened REM latency is a consistent finding in depressed patients and may be considered a biological marker for depression. Most depressed patients with shortened REM latency also show non-suppression on dexamethasone-suppression test (DST). The commonly used antidepressant drugs cause a significant reduction in REM sleep. Patients with abnormal DST show a better response to sleep deprivation than those with normal DST. Recent studies indicated that borderline patients, primary dysthymic patients and obsessive-compulsive patients (OCD) have shortened REM latency. Farthermore, patients with OCD have a fairly good response to antidepressant clomipramine. Diagnostic and therapeutic strategies can conceivably be related on the examination of sleep patterns of psychiatric patients.

Studies on neurotransmitter markers and striatal neuronal cell density in Huntington's disease and dentatorubropallidoluysian atrophy

Neurotransmitter abnormalities in the basal ganglia of individual "choreic" patients (9 cases of Huntington's disease-HD and 3 cases of dentatorubropallidoluysian atrophy-DRPLA) and 14 normal controls were investigated. Choline acetyltransferase activity in the striatum was decreased in approximately half the "choreic" patients. GABA concentration in the substantia nigra or in the globus pallidus was decreased in all "choreic" cases except one case of DRPLA. Substance P concentration was also reduced in the same nuclei as GABA except in one case of HD. These findings imply: cholinergic, GABAergic or substance P-related markers found in the basal ganglia of HD are not disease-specific but also found in the other "choreic" disorder, i.e. DRPLA; most prominent biochemical changes in HD would be a decrease of GABA in the basal ganglia. Correlation analysis of the markers in the basal ganglia and the striatal neurone densities of "choreic" patients (5 cases of HD and 3 cases of DRPLA) and 7 normal controls yielded positive correlation between GABA concentration in the substantia nigra and the globus pallidus, and the neuronal cell density in "small" cells in the striatum of normal control and HD. Positive correlation between substance P concentration and the striatal neurone density was only found in the substantia nigra. Choline acetyltransferase activity in the striatum was found to be positively correlated with the density of "large" cells in the striatum rather than that of "small" cells. In DRPLA there was no direct correlation between the values of the markers in the basal ganglia and the striatal neurone density. The decrease of transmitter markers without striatal cell loss in this particular choreic disorder could be regarded as a sequence of "biochemical degeneration" of striatal neurones. Based on these findings, the underlying mechanisms of choreic involuntary movements were briefly discussed.

Gene diversity in finite populations

DNA sequence comparison among homologous genes sampled at random from one or two populations allows one to estimate the ultimate amount of genetic variation maintained in a population and to construct the gene genealogy within and between populations. Moreover, if we use the finding of the molecular clock (Zuckerkandl & Pauling, 1965), it is also possible to estimate the divergence time of populations examined. Such an estimated divergence time is, however, intricately affected by samples and stochastic forces occurring in the course of evolution.

Metabolic and histologic changes in the ischemic muscles of replanted dog legs

The sequential and histologic changes occurring in muscles from ischemia were investigated in dogs. The left hind limbs were amputated, and recirculation was established after preserving them either in ice water or at room temperature for six to 12 hours. Slight leakage of the muscle enzymes creatine phosphokinase (CPK), mitochondrial glutamic oxaloacetic transaminase (GOT-m), and lactate dehydrogenase (LDH) into the recirculated venous blood occurred in specimens preserved in ice water for six hours, but there was a marked increase in enzyme leakage in the other groups. Histologic muscle changes consisted of cell swelling and separation of the sarcoplasm from the endomysium. Electron microscopy revealed widening of the myofibrillar spaces, a virtual absence of glycogen granules, and degeneration of mitochondria. These results support the clinical practice that the amputated extremities must be preserved in ice water and that blood recirculation should be initiated within six hours of amputation.

Gene genealogy and variance of interpopulational nucleotide differences

A mathematical theory is developed for computing the probability that m genes sampled from one population (species) and n genes sampled from another are derived from l genes that existed at the time of population splitting. The expected time of divergence between the two most closely related genes sampled from two different populations and the time of divergence (coalescence) of all genes sampled are studied by using this theory. It is shown that the time of divergence between the two most closely related genes can be used as an approximate estimate of the time of population splitting (T) only when T identical to t/(2N) is small, where t and N are the number of generations and the effective population size, respectively. The variance of Nei and Li's estimate (d) of the number of net nucleotide differences between two populations is also studied. It is shown that the standard error (Sd) of d is larger than the mean when T is small (T much less than 1). In this case, Sd is reduced considerably by increasing sample size. When T is large (T greater than 1), however, a large proportion of the variance of d is caused by stochastic factors, and increase in the sample size does not help to reduce Sd. To reduce the stochastic variance of d, one must use data from many independent unlinked gene loci.

Introgression of extranuclear genomes in finite populations: nucleo-cytoplasmic incompatibility

A ‘two locus two allele’ model is developed with special reference to the introgression of extranuclear genomes between two species of finite size. The model assumes that one locus, coded by a nuclear genome, causes the reproductive barrier while the other locus, coded by an extranuclear genome, causes nucleo-cytoplasmic incompatibility in particular genotypes. To fully study this model, simulations are conducted, and a diffusion equation is derived when introgression or extranuclear gene flow occurs in one direction. It is shown that although selection against the nuclear genome can reduce the levels of extranuclear gene flow and retard the introgression process, the dynamics are very similar to those without such selection. In contrast, the nucleo-cytoplasmic incompatibility directly affects the dynamics of introgressing extranuclear genomes: in large populations the ability of incompatibility to overcome extranuclear gene flow is conspicuous, but in small populations it is overshadowed by random sampling drift. Paternal leakage of extranuclear genomes, if present, is of evolutionary importance only when the male's migration rate is much larger than the female's. When the sizes of two populations are unequal, the introgression is most likely to occur from the larger population to the smaller one in the absence of mating preferences of backcross progeny. Recent observations on interspecific mitochondrial transfer in various species do not support the ubiquitousness of nucleo-cytoplasmic incompatibility as an efficient reproductive barrier.

EXTRANUCLEAR DIFFERENTIATION AND GENE FLOW IN THE FINITE ISLAND MODEL

Use of sequence information from extranuclear genomes to examine deme structure in natural populations has been hampered by lack of clear linkage between sequence relatedness and rates of mutation and migration among demes. Here, we approach this problem in two complementary ways. First, we develop a model of extranuclear genomes in a population divided into a finite number of demes. Sex-dependent migration, neutral mutation, unequal genetic contribution of separate sexes and random genetic drift in each deme are incorporated for generality. From this model, we derive the relationship between gene identity probabilities (between and within demes) and migration rate, mutation rate and effective deme size. Second, we show how within- and between-deme identity probabilities may be calculated from restriction maps of mitochondrial (mt) DNA. These results, when coupled with our results on gene flow and genetic differentiation, allow estimation of relative interdeme gene flow when deme sizes are constant and genetic variants are selectively neutral. We illustrate use of our results by reanalyzing published data on mtDNA in mouse populations from around the world and show that their geographic differentiation is consistent with an island model of deme structure.

Mitochondrial gene flow

To account for the transmission of mitochondrial DNA between conspecific species Drosophila pseudoobscura and D. persimilis in sympatry reported by J.R. Powell [Powell, J.R. (1983) Proc. Natl. Acad. Sci. USA 80, 492-495], a simple model of gene flow and selection in infinite populations is analyzed. The model assumes two alleles at each of two loci, one of which is coded by an autosome and the other by mitochondrial DNA. Viability selection is presumed to be underdominant--i.e., heterozygous inferiority to the homozygotes--at an autosomal locus, and neutral or deleterious at a mitochondrial locus, with the combined action being multiplicative. Extremely strong selection against heterozygotes may prevent the transmission of mitochondrial DNA between two species, but otherwise the transmission can easily occur over species boundaries. The rate of approach to equilibrium is determined by the level of gene flow and is not affected much by selection against an autosomal locus. The divergence of the nuclear genomes of the two species is reexamined. Based on published data on enzyme loci, we conclude that there has been mitochondrial gene flow between these species for a long enough time that several nuclear loci examined could diverge because of accumulation of neutral mutations.

GENE IDENTITY AND GENETIC DIFFERENTIATION OF POPULATIONS IN THE FINITE ISLAND MODEL

A formula for the variance of gene identity (homozygosity) was derived for the case of neutral mutations using diffusion approximations for the changes of gene frequencies in a subdivided population. It is shown that when gene flow is extremely small, the variance of gene identity for the entire population at equilibrium is smaller than that of the panmictic population with the same mean gene identity. On the other hand, although a large amount of gene flow makes a subdivided population equivalent to a panmictic population, there is an intermediate range of gene flow in which population subdivision can increase the variance. This increase results from the increased variance between colonies. In such a case, each colony has a predominant allele, but the predominant type may differ from colony to colony. The formula for obtaining the variance allows us to study such statistics as the coefficient of gene differentiation and the correlation of heterozygosity. Computer simulations were conducted to study the distribution of gene identity as well as to check the validity of the analytical formulas. Effects of selection were also studied by simulations.

Selective constraint in protein polymorphism: study of the effectively neutral mutation model by using an improved pseudosampling method

To investigate the pattern of allelic distribution in enzyme polymorphism, with special reference to the relationship between the mean (H) and the variance (V(H)) of heterozygosity, we used the model of effectively neutral mutations involving multiple alleles in which selective disadvantage of mutant alleles follows a Gamma distribution. A simulation method was developed that enables us to study efficiently the process of random drift in a multiallelic genetic system and that saves a great deal of computer time. It is an improved version of the pseudosampling-variable (PSV) method [Kimura, M. (1980) Proc. Natl. Acad. Sci. USA 77, 522-526] previously used to simulate random drift in a diallelic system. This method will be useful for simulating many models of population genetics that involve behavior of multiple alleles in a finite population. By using this method, it was shown that, as compared with the model of strictly neutral mutations, the present model gives the reduction of both H and V(H) and an excess of rare variant alleles. The results were discussed in the light of recent observations on protein polymorphism with special reference to the functional constraint of proteins involved.

A model of evolutionary base substitutions and its application with special reference to rapid change of pseudogenes

A model of evolutionary base substitutions that can incorporate different substitutional rates between the four bases and that takes into account unequal composition of bases in DNA sequences is proposed. Using this model, we derived formulae that enable us to estimate the evolutionary distances in terms of the number of nucleotide substitutions through comparative studies of nucleotide sequences. In order to check the validity of various formulae, Monte Carlo experiments were performed. These formulae were applied to analyze data on DNA sequences from diverse organisms. Particular attention was paid to problems concerning a globin pseudogene in the mouse and the time of its origin through duplication. We obtained a result suggesting that the evolutionary rates of substitution in the first and second codon positions of the pseudogene were roughly 10 times faster than those in the normal globin genes; whereas, the rate in the third position remained almost unchanged. Application of our formulae to histone genes H2B and H3 of the sea urchin showed that, in each of these genes, the rate in the third codon position is tremendously higher than that in the second position. All of these observations can easily and consistently be interpreted by the neutral theory of molecular evolution.

GENETIC VARIABILITY AND RATE OF GENE SUBSTITUTION IN A FINITE POPULATION UNDER MUTATION AND FLUCTUATING SELECTION

By using a numerical method of solving stochastic difference equations, the level of genetic variability maintained in a finite population and the rate of gene substitution under several models of fluctuating selection intensities were studied. It is shown that mutation and random genetic drift both play an important role in determining genetic variability and the rate of gene substitution. Compared with the case of neutral mutations, the fluctuation of selection intensity caused by temporal and spatial heterogeneity of environments generally increases the rate of gene substitution, but the level of genetic variability may be increased or decreased, depending upon the model and the parameters used. Although such a type of selection per se can not be ruled out, when mutation is taken into account, it is difficult to explain both the observed amount of genetic variability and the rough constancy of evolutionary rate within a framework of fluctuating selection models.

Estimating evolutionary distance from restriction maps of mitochondrial DNA with arbitrary G+C content

We develop a mathematical model for estimating evolutionary distance from restriction enzyme maps, which incorporate non-uniformity of the rate of base substitution into the theory and allows for an arbitrary G+C content at equilibrium. When the G+C content differs significantly from 1/2, the traditional model of base changes can introduce a systematic bias which depends upon the base composition of the restriction site. In addition, the accuracy of estimated evolutionary distance depends heavily upon the choice of restriction enzyme in that the expected number of sites is also affected. Monte Carlo experiments are conducted to check the validity of the present theoretical treatment and from which we draw several cautionary notes on estimation. An application is made to the available data on restriction enzyme maps of human mitochondrial DNA where the G+C content is approximately 1/3.

Composite stepwise mutation model under the neutral mutation hypothesis

As an extension of the conventional ("Ohta-Kimura") stepwise mutation model, a new model is proposed. In this model, it is assumed that each charge state ("electromorph") is represented by K alleles and that a mutation changes an allele either by one step in the charge space or to one of the other members of the identical electromorph. It is shown that the net genetic variability within a population is similar to that predicted by the infinite-allele model ("Kimura-Crow" model) rather than to that predicted by the stepwise mutation model, and the K-dependence of genetic variability is rather weak when K greater than or equal to 2 and the effective population size is not much greater than the reciprocal of mutation rate. The results are compared with the recent observations at the xanthine dehydrogenase locus in Drosophila pseudoobscura.

Polymorphism and loss of duplicate gene expression: a theoretical study with application of tetraploid fish

We studied the fixation of null alleles at independent duplicate loci, assuming that wild-type active alleles mutate irreversibly to nonfunctional null alleles and that the population is finite and panmictic. Solving the two-dimensional Kolmogorov backward equation numerically, we obtained the rate at which one of the active genes is lost and the amount of heterozygosity at specified times. Previously harmful genes, including recessive lethals, can be fixed at one of the duplicate loci, which would not happen with a single locus. Examination of data from several fish families showed that the rate of fixation of null alleles is too slow and the amount of heterozygosity too small to be compatible with complete recessivity at all loci. Our conclusion differs in this regard from that of Bailey et al. [Bailey, G.S., Poulter, R. T. M. & Stockwell, P. A. (1978) Proc. Natl. Acad. Sci. USA 75, 5575--5579]. They also reported that the time taken for 50% of the loci to be fixed for null alleles is approximately 15N + v-3/4, in which N and v are the effective population sizgote is lethal. We found that the fixation rate depends not only on N, but also on Nv.

Pontine infarction with diffuse myelin destruction

A 57-year-old man with clinical symptoms of dementia and spastic paraplegia revealed pathologically scattered cerebral arteriosclerotic changes and diffuse myelin destruction in the basis pontis. The latter was characterized by comcomitances with an eminent fibrous gliosis and a neuronal as well as an axonal loss. Pontine infarction and the following fibrous gliosis possibly caused a wide area of myelin destruction resembling cpm.

An experimental study on "replantation toxemia". The effect of hypothermia on an amputated limb

Hind legs of dogs were amputated at the middle of the thigh and preserved in three different conditions: in ice water, in a refrigerator, and at room temperature. After 6 or 12 hours of ischemia, recirculation was established. The survival rate of the animals was observed and measurement of limb edema, potassium, pH, and lactate in the blood was performed to study the effects of hypothermia on prevention of "replantation toxemia." Cooling of the amputated limb was effective for prevention of toxemia, and the cooling effect was greater in ice water than in a refrigerator. However, when cooled in ice water, some animals died due to toxemia when the time of ischemia was prolonged to 12 hours. In the dead animals, a close relationship was observed between the developement of toxemia and metabolic acidosis due to the increase in lactate.

Familial chorea and myoclonus epilepsy

A familial disorder was characterized by chorea, ataxia, myoclonus, convulsions, dementia, and mental retardation. In five cases, the main lesion affected cerebellar dentate nuclei, with nerve cell loss, gliosis, chromatolysis, and grumose degeneration. Fibrous glial cell proliferation was detected in the globus pallidus.

HLA and Japanese MS

Determination of HLA-A, -B and -C types in 43 Japanese patients with multiple sclerosis (MS) and of DR type in 25 MS patients was carried out using antisera from the 7th International Histocompatibility Workshop. The results were compared with 46 controls typed simultaneously. Twenty-three patients were also tested for HLA-Dw2. The conclusions were: 1) There were no significantly higher occurrences of HLA-A3, B7, Dw2 or DRw2 in Japanese MS. 2) Japanese MS might nevertheless be associated with the human major histocompatibility complex, because HLA-B40 was significantly less frequent in MS and two anti HLA-DRw sera, 7w008 and 034, reacted positively more often against lymphocytes from MS patients.

Chronic brainstem encephalitis with mental symptoms and ataxia: report of three cases with necropsy

Three necropsied cases of chronic, sporadic brainstem encephalitis of unknown aetiology are presented. Since their outstanding symptoms were dementia and ataxia of a progressive nature, a noninflammatory disease of the central nervous system was suspected. Neuropathological studies showed chronic inflammatory changes mainly in the brainstem without the presence of inclusion bodies or viral particles. Compared to cases previously reported as brainstem encephalitis, the clinical and pathological findings observed in these cases have rather peculiar characteristics.

Electron microscopic studies on the cerebral lesions of rats in experimental chronic disulfiram poisoning

Following chronic administration of disulfiram to rats, changes of the brain were examined electron-microscopically. Pathological findings were observed in the nerve cells of the cerebral cortex and hypothalamus at later stage and synaptic changes in the hypothalamus from initial stage. On the other hand, changes of myelinated fibers, neuroglias and capillaries were very slight. It was considered that neurons were affected more predominantly than other neuronal elements by the cytotoxic action of the drug, and that the synaptic changes of the hypothalamus might reveal chronic disturbance of noradrenergic transmission by inhibition of dopamine-beta-hydroxylase. These ultrastructural findings might relate to the pathogenic mechanism of the disulfiram psychosis.