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Reproductive techniques

Optimal physicochemical conditions for the manipulation and short-term preservation of koala (Phascolarctos cinereus) spermatozoa

Johnston, SD, McGowan, MR, Phillips, NJ & O’Callaghan, P 2000, Journal of Reproduction and Fertility, vol. 118, no. 1, pp. 273-281.

Under the same physical and chemical conditions in short-term liquid storage, koala spermatozoa respond similarly to eutherian mammal spermatozoa, except that koala spermatozoa are more resilient to exposure to rapid changes in temperature.

  To determine the most suitable physical and chemical conditions for the short-term storage of koala sperm, five separate experiments were conducted to test the effects on sperm motility of repeated dilution, rapid temperature shock, diluent pH, diluent osmolality, and diluent buffer type. Repeatedly diluting the sperm sample reduced both the percentage of forwardly motile spermatozoa and the rate of sperm movement. While exposure to temperatures of 15OC or 25OC did not affect spermatozoa motility when compared to the control sample held at 35OC, exposure to the more extreme temperatures of 5OC or 45OC significantly reduced motility. When tested in a range of diluents with varying pH levels, sperm motility was observed to be highest when the diluent pH was within the range of pH 6.5 – 8.1, with a significant reduction in sperm movement and motility within the pH range 4.7 – 5.9. As the osmolality of the diluent was altered, sperm motility was greater in hyper-osmotic conditions than hypo-osmotic conditions. From comparisons of sperm motility when diluted using Tris-citrate-glucose or Phosphate Buffered Saline, Tris-citrate-glucose was far better for preserving spermatozoa motility across all incubation temperatures trialled.

  Serial dilution is thought to reduce sperm motility by eroding sperm surface components and altering the permeability of sperm membranes. Temperature shock has not previously been reported for marsupial spermatozoa, making the findings of this particular experiment unique. The reason for this variance may relate to differences in the phospholipid structures of the sperm membrane. Regarding the effects of changes to diluent pH and osmolality, koala spermatozoa were found to respond in a manner that was consistent with that of eutherian mammal spermatozoa. These findings are novel as previously only limited information was available about the conditions under which we can most effectively preserve marsupial spermatozoa.

  Studies investigating the resilience of koala spermatozoa under different physicochemical conditions are beneficial for developing effective preservation protocols for artificial insemination programs. In particular, short-term liquid storage may prove to be a suitable alternative to the preferred method, cryopreservation, while protocols for the latter are still being established.

 

Summarised by Joanna Horsfall

 

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