Quantitative determination of neuronal size and density using flow cytometry.

BACKGROUND: Recent anthropomorphic disturbances are occurring at an increasing rate leading to organisms facing a variety of challenges. This change is testing the information processing capacity (IPC) of all animals. Brain function is widely accepted to be influenced by a variety of factors, including relative size, number of neurons and neuronal densities. Therefore, in order to understand what drives an animals IPC, a methodological approach to analyze these factors must be established. NEW METHOD: Here we created a protocol that allowed for high-throughput, non-biased quantification of neuronal density and size across six regions of the brain. We used the Isotropic Fractionator method in combination with flow cytometry to identify neuronal and non-neuronal cells in the brains of adult rats. COMPARISON WITH EXISTING METHODS: The results obtained were comparable to those identified using stereological counting methods. RESULTS: By employing this new method, the number of nuclei in a specific brain region can be compared between replicate animals within an experiment. By calibrating the forward scatter channel of the flow cytometer with size standard beads, neuronal and non-neuronal nuclear sizes can be estimated simultaneously with nuclei enumeration. These techniques for nuclear counting and size estimation are technically and biologically reproducible. CONCLUSION: Use of flow cytometry provides a methodological approach that allows for consistency in research, so that information on brain morphology, and subsequent function, will become comparable across taxa.

The influence of testosterone on territorial defence and parental behavior in male free-living rufous whistlers, Pachycephala rufiventris.

We studied a population of rufous whistlers, Pachycephala rufiventris, throughout a single breeding season in central New South Wales, Australia. We evaluated the relation between plasma testosterone (T) and reproductive behaviors using both simulated territorial intrusions (STIs) and subcutaneous T implants. We compared circulating T values to aggression levels of males (using STI) during pair bond and territory establishment and again during incubation. Although plasma T levels were significantly lower in the latter period, male responsiveness to STI, in terms of proximity to decoy, call rate, and number of attacks on the decoy, was indistinguishable between the two breeding stages. T levels of males exposed to STI were not different from the levels of unexposed free-living males at the same breeding stage. The effect of exogenous T on parental behavior was examined by comparing duration of incubation bouts of males and their mates prior to and after T treatment. T males significantly reduced the amount of time they incubated following implantation, whereas Control males maintained their incubation effort. After cessation of breeding activities, T males displayed significantly higher call rates due to increased use of the primary intersexual advertisement call in this species. The reduction of incubation behavior following T implantation emphasises the functional significance of the rapid decline in T in free-living males during incubation. The results from both experiments suggest that intersexual advertisement, rather than territorial aggression, may be dependent on high T levels in this species.

Influence of ethnicity and gender on cardiovascular responses to active coping and inhibitory-passive coping challenges.

OBJECTIVE: The goal of this study was to evaluate how black and white men and women responded physiologically to specific laboratory challenges. METHODS: Hemodynamic responses to an active coping (evaluated speaking) and two inhibitory-passive coping (mirror tracing, cold pressor) tasks were examined in 138 black and white men and women. RESULTS: Significant ethnicity by gender interactions occurred for the evaluated speaking task. Black men responded with lower blood pressure, cardiac output or heart rate, or both, than black women, white men, and white women, who did not differ from each other. Black men, relative to the other subgroups, also reported more inhibitory-passive coping, hostility, and pessimism, and less social support. Whites also responded with greater increases in systolic blood pressure during mirror tracing than blacks. CONCLUSIONS: These findings indicate that black-white differences in physiological responsivity obtained for men may have limited generalizability for women. The results also suggest that environmental and social factors rather than genetic or constitutional factors may play a role in black-white reactivity differences.

Effects of oestradiol-17beta, oestradiol benzoate and the synthetic oestrogen RU 2858 on sexual differentiation in the neonatal female rat.

Groups of neonatal female rats were treated for the first 5 days of life with oestradiol-17beta, oestradiol benzoate or a synthetic oestrogen, 11beta-methoxy-17-ethynyl-1,3,5(10)-oestratriene-3,17beta-diol (RU 2858), in daily doses ranging from 0-5 to 1000 ng. Oestradiol-17beta had no effect on adult ovarian cyclicity or sexual receptivity after ovariectomy and oestrogen+ progesterone treatment. Ovarian cyclicity was prevented by 100 ng or more oestradiol benzoate/day, and by all doses of RU 2858. Only rats receiving 50 ng oestradiol benzoate/day or 0-5 ng RU 2858/day showed normal receptivity. The defeminizing action of RU 2858 was at least 100 times greater than that of oestradiol benzoate; it is suggested that this greater potency is due to the low affinity of RU 2858 for the oestradiol-binding protein in the plasma of neonatal rats. These results indicate that defeminization of the neonatal rat brain can be induced by physiological amounts of oestrogen, and are discussed with reference to the action of testosterone.

Sexual behavior: Extreme reduction of postejaculatory refractory period by midbrain lesions in male rats.

The refractory period that characteristically follows ejaculation was abolished or significantly reduced by rostral midbrain lesions in male rats. The postejaculatory vocalization was also abolished or reduced, but other aspects of copulatory performance were unaffected. The results were attributed to disruption of biogenic amine pathways that pass from the ventral part of the rostral midbrain into the posterior hypothalamus.

Effect of serotonin and progesterone on induced ovulation in immature rats.

Serotonin (50 and 100 mg/kg), given subcutaneously, inhibited induced ovulation in immature rats treated with pregnant mare serum gonadotrophin (PMSG). A single injection was effective if given 52-55 h after the PMSG, i.e. in the 3 h period after the critical period before ovulation. The injection of serotonin inhibited the release of luteinizing hormone (LH) from the pituitary since the pituitary levels were higher than in the control animals and there was complete inhibition of the plasma LH surge. The anti-ovulatory effect was reversed by administration of progesterone and endogenous plasma progesterone levels were reduced in the late evening after serontonin treatment. The site of action of serotonin appeared to be peripheral since it inhibited induced ovulation in hypophysectomized rats but was without effect in intact rats treated intraventricularly. It is suggested that progesterone is essential for the occurrence of induced ovulation and serotonin inhibits either its secretion at the ovarian level or its passage away from the ovary.