Use of recombinant inbred strains to assess vulnerability to drug abuse at the genetic level

The use of Recombinant Inbred mouse Strains (RIS) to derive information about the complexity of the genetic architecture underlying various traits is increasing in popularity. Behaviors measured to index sensitivity to drug effects and vulnerability to drug abuse are considered here. Potential uses of RIS are identification of major gene effects, mapping of traits to particular chromosomal sites, determining genetic correlations between characters, and identifying behaviorally extreme genotypes. This approach has led to identification of a major gene moderating alcohol acceptance in mice and has revealed a more complex polygenic system influencing morphine consumption.

Genetic analyses of the biphasic nature of the alcohol dose-response curve

Ethanol (ETOH)-induced locomotor activation and depression were studied in 23 genotypes of mice. This included a diallel cross of four inbred strains tested with a range of ETOH doses from 0 to 2.75 g/kg. The diversity in shapes of the biphasic ETOH dose-response curves was both qualitative and quantitative, and additive gene action characterized the genetic control of the dose-response curve. Small dominance effects were typically directional in the direction of more activation, or resistance to sedation. No evidence was found for maternal effects, sex linkage, or epistasis. Sex differences were seen in the increased susceptibility of male mice to locomotor sedation at higher ETOH doses. In the diallel cross, there was no correlation between the degree of activation produced by low ETOH doses and sedation produced by higher doses. This indicates that while considerable genetic influences exist for both activational and sedative domains of ETOH effects, these genetic influences are relatively independent.

Locomotor activity responses to ethanol in selectively bred long- and short-sleep mice, two inbred mouse strains, and their F1 hybrids

Locomotor activity responses to sub-hypnotic doses of ethanol (ETOH) were assessed in selected lines of mice (LS and SS), inbred strains, and their F1 hybrids. Data were obtained as photocell beam interruptions in a 15-min test for a dose range of 0 to 2.75 or 3.5 g/kg for LS and SS mice, respectively. Biphasic dose-response curves were obtained for LS and SS mice with the SS mice showing a sedative limb of the dose-response curve shifted to the right. The effects of 2.0 g/kg ETOH were also assessed in a diallel cross of the selected LS/SS lines and C57BL/6Abg and MOLD/RkAbg inbred strains. The 2.0 g/kg dose produced a wide range of responses, from sedation in C57BL/6Abg mice to extreme activation in SS and MOLD/RkAbg mice, and no effect in LS mice. The responses of F1 hybrids reflected a typical pattern of partial dominance, with heterosis in some crosses. When present, dominance was in the direction of greater locomotor activation. These patterns were confirmed by biometrical genetic analysis of the 4 x 4 diallel cross of the two lines and the two inbred strains. The data indicate that loci in addition to those responsible for selection for sedative sensitivity in LS and SS mice can influence locomotor activation produced by sub-hypnotic ETOH doses, and that SS and MOLD mice show locomotor activation for different genetic reasons.

Use of recombinant inbred strains to identify quantitative trait loci in psychopharmacology

Unlike simple Mendelian characteristics, individual differences in complex quantitative phenotypes studied in psychopharmacology are generally distributed continuously and are likely to be influenced by many genes. Recombinant inbred (RI) strains are valuable not only for their traditional use of detecting major gene segregation and linkage but also for identifying associations between quantitative traits and quantitative trait loci (QTL) that account for relatively small amounts of variation in phenotypes as well as loci that account for greater amounts of variation. When applied to published data on genetic markers and on amphetamine, alcohol, and morphine responses in BXD RI strains (RI strains developed from the cross between C57BL/6J and DBA/2J progenitor inbred strains), the RI QTL approach identified several significant associations beyond known major gene effects. Together, significant associations explain more than half of the genetic variance for these measures. The RI QTL approach is especially valuable for investigating the QTL underpinnings of genetic correlations among measures. It is recommended that psychopharmacogenetic research focus on the BXD RI strains. The cumulative and integrative nature of such a program of research is the major benefit of the RI QTL association approach for molecular genetic analysis of psychopharmacological processes, their physiological infrastructure, and their interface with other behavioral and biological systems.

Response to selection for ethanol-induced locomotor activation: genetic analyses and selection response characterization

Selectively bred FAST mice are highly susceptible, while SLOW mice are less susceptible, to the locomotor stimulant effects of ethanol. Heritability estimates indicate that approximately 15% of the variance in the FAST lines is of additive genetic origin, while low susceptibility is ostensibly nonheritable. Inbreeding has increased at the rate of 2% per generation, but fertility has been unaffected. Measurement reliability for sensitivity to this ethanol effect was high when measured in both circular (r = 0.6) and square (r = 0.7) open-fields. In addition, our results indicate that we have selected for differences in sensitivity to ethanol rather than for differences in habituation to the test environment. The difference in response to ethanol between FAST and SLOW mice extended to tests varying in duration, and to a range of ethanol doses. We conclude that the divergence between FAST and SLOW mice generalizes to related test parameters, and speculate that the genetic architecture underlying the locomotor stimulant response may be simpler than previously proposed.

Cultured epidermal autografts and allografts: a study of differentiation and allograft survival

Cultured epidermal sheets were examined before and at various times after grafting on skin ulcer beds. Before grafting, the sheet consisted of four to five layers of keratinocytes with incomplete differentiation. Ten days after grafting, graft recipient sites showed compact hyperkeratosis, a normal-appearing epidermis, and a flat dermoepidermal junction. At 6 months, the stratum corneum had a basket-weave appearance but the dermoepidermal junction remained flat. Monoclonal antibodies to keratins 14 and 10 showed normal basal and suprabasal localization, respectively. Electron microscopy showed a normal basement membrane with anchoring fibrils. LH7:2, a monoclonal antibody that binds to the type VII collagen molecule, stained the dermoepidermal junction in all biopsy specimens. AE-1, an antibody that stains suprabasal cells in hyperproliferative skin, was expressed suprabasally for up to 12 weeks after healing (16 weeks after grafting), but expression was confined to the basal layer at 18 weeks after healing (6 months after grafting). Anti-involucrin staining was found in the deeper layers of the epidermis up to 12 weeks after healing (16 weeks after grafting) but had receded to a normal distribution in upper spinous and granular layers at 18 weeks (6 months after grafting). Overall, the histologic patterns observed in recipient sites during the first 4 months after grafting resembled those observed for 10 to 14 days in newly healed epidermis and in hyperproliferative states such as psoriasis. In four sex-mismatched graft sites, specimens were reacted with a biotinylated probe to the Y chromosome by in situ hybridization. Lack of Y chromosome-positive cells suggested that host keratinocytes had replaced the allografts. Multilocus DNA analysis in one patient confirmed this observation. Our data suggest that an altered state of epithelial maturation persists for several months after culture grafting, with restoration of the normal pattern by 6 months. No differences were detected between autografted and allografted sites.

Response to selection for sensitivity to ethanol hypothermia: genetic analyses

Selective breeding has been used to produce lines of mice differing in sensitivity to the hypothermic effects of ethanol (EtOH). Two genetically independent HOT (insensitive) and two COLD (sensitive) lines are maintained along with two nonselected control (CON) lines. The breeding program is currently in selected generation 14, and HOT and COLD mice differ by about 4 degrees C in selected hypothermic response. Estimates of heritability indicate that approximately 20% of the variance in EtOH-induced hypothermic response in mice is of additive genetic origin. Inbreeding has increased at a rate of about 1.7% per generation and no fertility problems have been detected as a result of selection. Projects designed to evaluate apparent correlated responses to selection are discussed.

Estimation of genetic correlation: interpretation of experiments using selectively bred and inbred animals

There is increasing interest in determining the extent to which multiple characters related to drug sensitivity are influenced by common genes. The principal method for testing for the existence of such genetic correlations has been examination of pairs of mouse or rat lines selectively bred for sensitivity or resistance to a single behavioral effect of a drug. When a pair of selected lines is found to differ significantly on some trait other than the one on which they were selected, it is commonly concluded that significant genetic correlation between the traits exists, implying the action of a common set of genes on the two responses. In addition, results from comparisons of lines of animals selected for trait X and tested for trait Y may be compared with results from lines selected for trait Y and tested for trait X. As the number of correlated responses in selected lines increases, it becomes more important to adhere to sensible, consensual guidelines for interpreting such line differences. The principles underlying phenotypic and genotypic correlational analyses with selected lines are discussed. A scheme is presented to allow standardization across laboratories of inferences about the relative strength of genetic association from experiments with selected lines. Statistical and practical experimental issues are addressed. Estimates of genetic correlations may also be derived from the correlation of mean trait values across a panel of inbred strains. Existing data have sometimes found estimates of genetic correlations made with one approach to be inconsistent with those estimated in other ways. Possible reasons for this are discussed. Finally, the relationship between phenotypic correlations and genetic correlations is discussed. Phenotypic and genetic correlations for a pair of traits may differ widely, and may even be opposite in sign. Both are characteristic of the population from which they are sampled. Phenotypic correlations estimated within selected lines may change over time, as the additive genetic variance in the selected trait is exhausted. A specific example of this phenomenon is given.

Distinctions among sedative, disinhibitory, and ataxic properties of ethanol in inbred and selectively bred mice

Three different domains of behavioral action of ethanol (ETOH) were examined in a battery of seven inbred strains and in the selectively bred Long-Sleep (LS) and Short-Sleep (SS) mice. Sedative effects were examined with the loss of the righting reflex test at 3.8 g/kg. The variation among inbred strains was only half the size of the difference between LS and SS mice which were selectively bred for extremes in this phenotype; such a result is expected for phenotypes controlled polygenically. Blood ETOH levels at waking from the narcosis also showed a range of differences among the inbred strains that was less than the LS/SS difference. Ataxia was measured with the grid test, and the inbred strains fell into two groups, resembling the highly ataxic LS line, and the less ataxic SS line. Biphasic effects of ETOH on locomotor activity were strongly genotype dependent. Variation in degree of activation/disinhibition produced by doses up to 1.5 g/kg (IP) ranged from no activation, in the C57BL/6Abg strain which was larger than that seen for SS mice. The patterns of strain differences for both ataxia and activation were highly different from the duration of loss of righting reflex measure, suggesting multiple independent genetically based "sensitivities" to ETOH.

Cultured allogenic keratinocyte grafts in the management of wound healing: prognostic factors

Cultured allografts derived from neonatal foreskin provide a potent stimulus to wound healing in a wide variety of wounds. Their application is a simple outpatient procedure involving no discomfort for the patient. In contrast to autografting, no biopsy is necessary, and growth of newborn keratinocytes in cultures is more rapid than that of adult cells. Use of cultured allogeneic cells offers immediate graft availability and the possibility of stockpiling and preserving the graft for future use. Cultured epidermal allografts may be valuable in accelerating healing by second intention in surgical wounds, as well as being a helpful addition to chronic ulcer management. In venous disease, the outcome is at least comparable to other forms of skin grafting. Ulcers due to connective tissue disorders fared less well and deep chronic ulcers (down to fascia or tendon) were not significantly improved by cultured allograft application. Surprisingly, patient age did not influence outcome.

Selected mouse lines, alcohol and behavior

The technique of selective breeding has been employed to develop a number of mouse lines differing in genetic sensitivity to specific effects of ethanol. Genetic animal models for sensitivity to the hypnotic, thermoregulatory, excitatory, and dependence-producing effects of alcohol have been developed. These genetic animal models have been utilized in numerous studies to assess the bases for those genetic differences, and to determine the specific neurochemical and neurophysiological bases for ethanol's actions. Work with these lines has challenged some long-held beliefs about ethanol's mechanisms of action. For example, lines genetically sensitive to one effect of ethanol are not necessarily sensitive to others, which demonstrates that no single set of genes modulates all ethanol effects. LS mice, selected for sensitivity to ethanol anesthesia, are not similarly sensitive to all anesthetic drugs, which demonstrates that all such drugs cannot have a common mechanism of action. On the other hand, WSP mice, genetically susceptible to the development of severe ethanol withdrawal, show a similar predisposition to diazepam and phenobarbital withdrawal, which suggests that there may be a common set of genes underlying drug dependencies. Studies with these models have also revealed important new directions for future mechanism-oriented research. Several studies implicate brain gamma-aminobutyric acid and dopamine systems as potentially important mediators of susceptibility to alcohol intoxication. The stability of the genetic animal models across laboratories and generations will continue to increase their power as analytic tools.

Treatment of skin ulcers with cultured epidermal allografts

Thirty-six skin ulcers in 23 patients were treated with cultured allogeneic epidermal sheets derived from neonatal foreskin. In 73% of ulcers, there was complete healing within 8 weeks, with a mean healing time of 3.3 weeks. In the other 27%, there was reduction in ulcer size of 35% to 93% by 8 weeks after grafting. In 30 painful ulcers, pain was markedly relieved within 24 hours of grafting. The healing pattern suggested that the cultured epidermal sheets acted by stimulation of host keratinocytes to divide and migrate rather than by permanent acceptance of the allograft. Of the 26 ulcers that healed within 8 weeks, 23 (88.5%) remained healed for follow-up periods of 10 to 18 months (mean 13.7 months), with an overall mean duration of healing of 13 months.

Cutaneous effects and therapeutic uses of heat with emphasis on infrared radiation

The adverse effects and therapeutic benefits of heat, specifically infrared radiation, on skin have received little attention. In this review we discuss the evidence indicating that heat and infrared radiation are not totally harmless, but that they may be involved in both photoaging and photocarcinogenesis. We also review the clinical syndrome thought to be caused by infrared radiation and the therapeutic uses of both local heat and infrared radiation.

Genotype-dependent effects of GABAergic agents on sedative properties of ethanol

Two lines of mice, selectively bred for differential sensitivity to the soporific effects of ethanol (ETOH), were administered GABAergic drugs in an effort to evaluate a role for GABA in ETOH sensitivity. ETOH sensitive Long-Sleep mice (LS) showed potentiated ETOH sedation when administered bicuculline, muscimol and aminooxyacetic acid (AOAA). ETOH-insensitive SS mice exhibited reduced ETOH sedation in the presence of the antagonists, bicuculline and picrotoxin, and potentiated sedation in the presence of muscimol and AOAA. These changes in narcosis duration were interpreted as central effects, since blood ethanol levels at waking from ETOH sedation varied with GABAergic drug treatment. Picrotoxin antagonized pentobarbital-induced narcosis in both lines, but to a greater extent in SS mice. These and other experiments with a genetically heterogeneous stock suggest GABA involvement in genotype-dependent ETOH sensitivity, but do not support a simple role of GABA receptor involvement.

Convulsant properties of GABA antagonists and anticonvulsant properties of ethanol in selectively bred long- and short-sleep mice

The convulsant potency of bicuculline, a GABA antagonist, was shown to be greater in Short-Sleep (SS) mice than in Long-Sleep (LS) mice. LS mice, selectively bred for lengthy ethanol-induced narcosis, had longer latencies to myoclonus and clonus following administration of bicuculline and picrotoxin than did ethanol-resistant SS mice. SS mice were also more susceptible to pentylenetetrazol-induced myoclonus, but not clonus. F1 hybrids showed bicuculline seizure sensitivity intermediate to the two parent lines. Ethanol weakly inhibited bicuculline-induced myoclonus in both LS and SS mice. Clonus was clearly antagonized by ethanol in both lines, but to a similar degree. These data provide evidence for a GABAergic role in genotype-dependent sensitivity to ethanol.

Modification of ethanol effects by bicuculline: genotype-dependent responses and inheritance

Genetic influences on the interaction between ethanol (ETOH) and gamma-aminobutyric acid (GABA) neurotransmitter systems were evaluated with a survey of responses to coadministration of ETOH and a GABA antagonist, bicuculline, in a battery of inbred mouse strains. The selectively bred ETOH-sensitive Long-Sleep (LS) mice, the relatively ETOH-resistant Short-Sleep (SS) mice, and a genetically heterogeneous stock (GHS) were also evaluated. The effect of bicuculline on ETOH-induced sedation, hypothermia, and blood ethanol content upon recovery from sedation was assessed. Inheritance of these responses was also examined using F1 hybrids. The effect of bicuculline on ETOH-produced narcosis varied widely among stocks and included antagonism, potentiation, and no effect. Changes in ETOH-induced narcosis produced by bicuculline were accompanied by changes in blood ethanol concentrations consistent with an hypothesis of altered central nervous system sensitivity to ETOH. Knowledge of a strain's seizure susceptibility to the GABA antagonist or of its sensitivity to the hypnotic effects of ETOH were of no predictive value in estimating the outcome of coadministration studies, suggesting at least partially separate genetic influences on each phenotype. In cross-breeding studies there was commonly dominance toward a profile of bicuculline antagonism of ETOH narcosis but different patterns of dominance were observed for seizure susceptibility, again indicating separate genetic control. The results suggest considerable complexity of GABAergic involvement in genotype-dependent ETOH sensitivity.

Treatment of chronic venous ulcers with sheets of cultured allogenic keratinocytes

Cultured keratinocytes were used as allografts to treat 51 patients with chronic venous ulceration or rheumatoid ulcers unresponsive to all previous conventional treatments including split skin grafts. Although early epithelialization could be seen in the centre of some ulcers, a major effect appeared to be healing from the previously indolent edge. This treatment appears to provide some clinical benefit in healing of chronic ulceration.

Dermatomyositis and pulmonary fibrosis associated with anti-Jo-1 antibody

Although fibrosing alveolitis is a rare complication of dermatomyositis, early detection and treatment are important in preventing pulmonary fibrosis. Anti-Jo-1 antibody, an antibody to the cellular enzyme histidyl-t-RNA synthetase, has been found to correlate closely with the subset of dermatomyositis/polymyositis associated with fibrosing alveolitis. This association is well known to rheumatologists but has received little attention in the dermatologic literature. We wish to alert dermatologists to the importance of the association of anti-Jo-1 antibody in patients with dermatomyositis and present a patient with anti-Jo-1 antibody who had Raynaud's phenomenon and mild arthritis in association with dermatomyositis and pulmonary fibrosis. We suggest screening patients with polymyositis/dermatomyositis for this antibody, to detect the population at high risk of developing pulmonary complications.

Pulmonary complications following methotrexate therapy

Methotrexate is frequently used in the treatment of severe psoriasis, and its hepatotoxicity has long been recognized by dermatologists. Pulmonary complications resulting from use of the drug are uncommon but should be considered in any patient on methotrexate who develops pulmonary symptoms in the absence of infection. We describe two patients, one who developed an acute pneumonitis and one with progressive pulmonary fibrosis following long-term, low-dose methotrexate for psoriasis. Early recognition of these complications by lung function testing and withdrawal of the drug, when necessary, may arrest or reverse methotrexate-induced lung disease.

Pulmonary function in patients on long-term, low-dose methotrexate

We have made a detailed study of pulmonary function in patients receiving long-term, low-dose methotrexate for psoriasis. We were unable to detect any changes indicative of early pulmonary damage.

Disseminated superficial actinic porokeratosis. Coexistence with other porokeratotic variants

The coexistence of disseminated superficial actinic porokeratosis (DSAP) with other variants of porokeratosis is rare. We report three such cases: DSAP with porokeratosis of Mibelli; DSAP with linear porokeratosis; and DSAP occurring in the mother of a girl with linear porokeratosis. Although different areas of skin and different family members usually express the same morphological variant, we suggest that the simultaneous expression of two closely linked gene loci could explain the coexistence of different porokeratotic variants.