Immune function in lines of mice selected for high or low degrees of behavioral asymmetry

What's left in asymmetry?

Left-right patterning is a fascinating problem of morphogenesis, linking evolutionary and cellular signaling mechanisms across many levels of organization. In the past 15 years, enormous progress has been made in elucidating the molecular details of this process in embryos of several model species. While many outside the field seem to believe that the fundamental aspects of this pathway are now solved, workers on asymmetry are faced with considerable uncertainties over the details of specific mechanisms, a lack of conceptual unity of mechanisms across phyla, and important questions that are not being pursued in any of the popular model systems. Here, we suggest that data from clinical syndromes, cryptic asymmetries, and bilateral gynandromorphs, while not figuring prominently in the mainstream work on LR asymmetry, point to crucial and fundamental gaps of knowledge about asymmetry. We identify 12 big questions that provide exciting opportunities for fundamental new advances in this field.

Brain behavior and immunity: twenty years of T cells

During the period from 1987 to 2007, our understanding of nervous system-T lymphocyte bi-directional communication advanced exponentially. Progress in exploring these relationships was aided by the constant development of new, cutting-edge technologies, and by a steady growth in interest, and number, of scientists who recognized the need to conduct cross-disciplinary research. In this brief review of 20 years of Brain, Behavior, and Immunity (BBI), we highlight just a small number of the important studies published in the journal that collectively have provided the foundation for our current understanding of brain, behavior, and, specifically, T cells.

Differential immune responses in mice with left- and right-turning preference

Humoral and cell-mediated immune responses of inbred BALB/c male mice were assayed for differential reactivities associated with behavioral sidedness, which was evaluated by spontaneous rotational behavior in a circular cage model system. Mice with left-turning preference had lower in vivo primary IgM and IgG anti-Keyhole Limpet Hemocyanin (KLH) antibody responses, delayed-type hypersensitivity (DTH) responses, and host-resistance against the intracellular bacteria, Listeria monocytogenes, than mice with right-turning preference. The only immune parameter not shown to be associated with turning preference was the secondary humoral immune response to KLH. The weak innate immune response of left-turners for clearance of Listeria showed close intercorrelation with elevated serum IL-6 levels. Serum corticosterone and splenic norepinephrine levels were differentially increased and decreased by infection, respectively. We suggest that the observed differential immune reactivities of individual animals with same age, gender, and genetic background are associated with functional asymmetries within the brain, that the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic innervation are involved in the regulatory brain: immune interconnection after infection, and that the HPA axis and sympathetic nervous system are involved in the brain laterality effects on immune responses.

Stress influence on development of hepatocellular tumors in transgenic mice overexpressing TGF alpha

We investigated whether stress increases tumorigenesis in male transgenic mice that overexpress the gene encoding human transforming growth factor alpha (TGF alpha). At the age of 10-15 months, these mice begin to develop spontaneous hepatocellular carcinomas at high incidence. The male TGF alpha mice were housed with their siblings (non-stressful environment), housed in social isolation, or housed with aggressive non-siblings (stressful environment). Some animals in each group were exposed once a week to a second stressor (swim stress), beginning at the age of 7 months. Housing with aggressive non-siblings increased neoplastic growth in the male TGF alpha mice: the incidence and multiplicity of liver tumors, and tumor burden were higher in these animals than in the sibling-housed mice. Among the isolated TGF alpha mice, only the tumor burden was increased, when compared with the sibling-housed TGF alpha mice. Swim stress significantly increased the incidence of liver tumors and tumor burden in the sibling-housed TGF alpha mice. Plasma levels of 17 beta-estradiol (E2) that are elevated in the TGF alpha mice, were modestly but significantly higher in the non-sibling housed transgenic mice than in the sibling-housed. Natural killer (NK) cell activity, reduced in these mice, was not affected by housing environment. These data suggest that stress promotes the growth of hepatocellular tumors in the male TGF alpha mice. Whether estrogens are involved in mediating this association remains to be determined.

Analysis of two measures of paw preference in a large population of inbred mice

Two measures of lateralized forelimb usage, the Collins paw preference test and the Lateral Paw Preference test (LPP), were tested in 693 mice of 29 inbred strains and F1 crosses, and 2 embryo transfer groups. These strains included NZB, SM, and the NXSM recombinant inbred (RI) strains; RF and the NXRF RI strains; BXSB and the Y-consomic BXSB-Yaa+; DBA/2 and F1s of DBA/2 and BXSB and BXSB-Yaa; and NZB x NZW F1s. The findings indicated that (1) the Collins and LPP tests were independent in terms of direction of lateralization, (2) there were significant population biases of 60.96% rightward on the LPP test, and 54.39% leftward on the Collins test, (3) there were significant strain differences on measures of absolute asymmetry on both tests, (4) there were strain differences for direction of asymmetry on the Collins test, but not on LPP, (5) on the basis of the NXSM RI strains, 3 genetic loci contribute to strength of laterality on the LPP test, and (6) there was a strong correlation among strain means for strength of lateralization on the two tests. These results extend previous findings on the strength and direction of laterality, showing that two independent systems for direction of laterality may depend on the same mechanism for magnitude, and establish that multiple factors of handedness, previously identified in humans and other primates, also exist in mice.

Genetic and behavioral tests of the McManus hypothesis relating response to selection for lateralization of handedness in mice to degree of heterozygosity

McManus advanced a genetic hypothesis to explain differences of lateralization between HI and LO lines of mice selectively bred for degree of handedness. It states that lateralization is a function of heterozygosity. Specifically it predicts that (a) the HI line will be more heterozygous than the LO line and (b) populations with a greater average heterozygosity (AH) will be more strongly lateralized. Both genetic and behavioral predictions were tested here. Results using coat color and biochemical variants show that AH in the HI line is somewhat less (not greater) than that in the LO line. The handedness of HET control mice and HI by LO reciprocal hybrids, where AH is greater than that of the HI line, exhibits lessened (not greater) lateralization. Results reject the heterozygosity hypothesis. A model for the inheritance of human handedness that accounts for difficulty in detecting heritable differences in degree of asymmetry is presented.

Alterations in behavior, steroid hormones and natural killer cell activity in male transgenic TGF alpha mice

The expression of transforming growth factor alpha (TGF alpha) is widely distributed throughout many normal and neoplastic tissues, but its physiological significance remains unclear. We have utilized male transgenic mice overexpressing the gene encoding human TGF alpha in multiple tissues to further identify those functions which are influenced by this protein. Male TGF alpha mice develop hepatocellular carcinoma at the age of 10-15 months. At the age of 2-3 months these mice, compared to age matched CD-1 controls, spent significantly longer times immobile in Porsolt's swim test, a model of stress and depressive behavior, and exhibiting aggressive behavior in the resident-intruder test. In contrast, the transgenic TGF alpha mice did not differ from the controls in either the plusmaze test of anxiety, or in their voluntary alcohol intake. Significantly, the TGF alpha mice exhibited a 25% lower Natural Killer (NK) cell activity and a four-fold increase in the plasma levels of 17-beta-estradiol (E2) than the controls. No significant changes in plasma testosterone or corticosterone levels were noted. The results indicate that transgenic male mice overexpressing TGF alpha exhibit behaviors characteristic of both an impaired ability to cope with stress and an increased aggressivity. The TGF alpha mice also show reduced NK cell activity and increased plasma estradiol concentrations. The present data suggest that TGF alpha may be important in influencing behavioral, immunological and hormonal systems prior to the onset of tumors. It remains to be determined whether hepatocarcinoma is associated with the direct proliferative and transforming effects of TGF alpha and/or indirect effects mediated through immune, hormonal and behavioral mechanisms.

Reimpressed selective breeding for lateralization of handedness in mice

Eleven generations of bidirectional selection for lateralization produced 2 lines of mice that differ markedly in degree of asymmetry for hand preference. The foundation population was derived from 6 distantly related inbred strains and 2 stocks of wild mice, M. castaneus. HI line matings were made using mice that exhibited consistent right or left paw use in a food reaching task and LO line matings were made using mice with little overall paw preference. All matings were made without regard to the expressed directions of asymmetry. Line differences emerged at the third generation and increased thereafter. Selection was relaxed at generation 12 and the lines were maintained by random within-line mating. At generation 28 selective breeding was reimpressed for 3 generations. Results indicated that between-line divergence in degree of lateralization had remained high during 17 generations of relaxed selection. Mice of the HI line are more strongly lateralized than mice of the unselected HET population. Mice of the LO line are more weakly lateralized than controls. The selected lines may provide a useful mammalian genetic resource for studying the neurobiology of cerebral lateralization.