The effects of early olfactory experience and inter-species cross-fostering on the sexual preferences of mice

This study on the effects of early experience in mice consists of two different sets of experiments. The first part is an investigation on the role of odours in the ontogeny of sexual preferences. It is preceeded by a review of the state of our knowledge of the role of odours in the social behaviour of rodents. MAINARDI et al. found in 1965 that female mice, reared with artificially perfumed parents, spent more time with males scented with the same perfume when sexually mature. The aims of my study were to repeat these investigations using better. controlled conditions and with a new experimental set-up, and to extend' the research by testing the hypothesis of "sensitive periods" for olfactory stimuli in mice. Two strains were used ~ Balb/C and c₅₇ /Black. Experimental animals were scented by daily spraying with geraniol (c₁₀H₁₈O) on the mother, litter and nest using an aerosol spray. A first group was scented from birth till the 10th day of life, a second from day 11 to day 20, a third from day 21 to day 30. The animals were tested for their preference between normal conspecifics and a geraniol- scented one, when they were between 3 and 4 months of age. The improvements on MAINARDI's Technique consisted of, 1°) a more reliable apparatus which offered a wider range of choice between 5 stimulus animals, 2°) better control of the "spontanous response of the mice towards the experimental odour, 3°) a control of the spontaneous responses of the mice in choice of compartments within the apparatus itself and towards the individual stimulus mice without the presence of geraniol, 4°) the use of two strains as control for genetic variability. I have not been able to replicate MAINARDI's results. Two alternative conclusions are suggested. First there is nd effect of early experience on the attitude of these strains towards geraniol. The odour is mildly aversive to them and remains so even if they are exposed to it early in life. Secondly, if taking a trend into account: exposure to geraniol for the first 10 days of life accentuates aversiveness in adult life. The second ,part of the experimental work consists of an investigation of the effects of cross-fostering mice (Balb/C) and voles (Clethrionomys glareolus britan, nicus). Two control groups were employed, one of mice and voles reared normally, the others of mice and voles cross-fostered within the ir own species. All vole pups fostered to mice died but 55% of the mice fostered to voles survived although they were significantly lighter than controls at weaning. Intraspecific fostering of mice did not affect their mortality rate or body weight. The following code will be used: control (normal) Balb (NB), Balb-fostered Balbs (BFB), vole-fostered Balbs (VFB), control voles (NV), vole-fostered voles (VFV). The animals were submitted to various tests. 1) Small field test (between day 21 and 28): recording of various activities in a small breeding cage. The general trend in the fostered animals was an increase of more "sedentary" activities (grooming, pausing, chewing) and digging, and a corresponding decrease of activities such as sniffing/walking and rearing. 2) Open field test (between day 45 and 52): the main trend was a drop in ambulation in BFB and VFB compared to NB, and in VFV compared to NV. The rearing scores for the open field showed less significant differences, but the trends were the same as in the ambulation scores. Urination, defecation and grooming seemed to be unaffected by fostering. The test demonstrates that changes produced are mainly due to the act of fostering itself. 3) Emergence test (various ages): this test measures the time taken to emerge from a hide beneath which the animals could shelter. BFB and VFB males are significantly more reluctant to leave the hide than NB. The females showed no significant differences. 4) Social preference test (between day 60 and 67): NB prefer Balbs, NV prefer voles, and VFB prefer voles (their foster-species). However, BFB and VFV show a strong drop in their preference for their own species, revealing again an effect due to the act of fostering itself, and thus forcing one to qualify a simple interpretation in terms of sexual imprinting for the changed behaviour of VFB

How polyelectrolyte adsorption depends on history: A combined Fourier transform infrared spectroscopy in attenuated total reflection and surface forces study

We present a systematic study of how adsorption history affects the thickness, surface forces, and interfacial rheology of a model cationic polymer. The polymer was quaternized poly-4-vinylpyridine, QPVP (weight-average degree of polymerization n(w) = 325 and 98% quaternized with ethyl bromide). The main comparisons concerned one-step adsorption from solution at a variable salt concentration up to 0.5 M NaCl, versus two-step adsorption (initial adsorption from buffer solution without added salt, then NaCl added later). The aqueous solutions were buffered at pH = 9.2 such that the surfaces (mica in the case of surfaces forces (SFA) experiments, oxidized silicon in the case of in situ infrared (FTIR-ATR) experiments) in each case carried a large negative charge. The SFA and FTIR-ATR experiments gave consistent estimates of the amount of polymer adsorbed, confirming the expectation that adsorption should be driven by electrostatic attraction to the surface of large opposite charge. The adsorbed amount showed little dependence on path, validating the common assumption of equilibration in this respect. However the layer thickness measured by surface forces, the shear nanorheology response at a given surface force, and the dichroism of pendant side groups of the polymer all showed a pronounced dependence on the path to reach the adsorbed state. We interpret the measurements to suggest that two-step adsorption produces an inhomogeneous layer comprised of a dense layer of segments closest to the solid surface and a sparse outer layer. In particular, two-step adsorption produced thicker layers and a greater tendency to decouple shear forces from those that resist compression in the normal direction, thereby lessening the shear forces at a given level of normal force