Olfaction evaluation in dogs with sudden acquired retinal degeneration syndrome.

Abstract

PURPOSE: To evaluate olfaction in dogs with sudden acquired retinal degeneration syndrome (SARDS) compared with sighted dogs and blind dogs without SARDS as control groups. ANIMALS STUDIED: Forty client-owned dogs. PROCEDURE: Olfactory threshold testing was performed on three groups: SARDS, sighted, and blind/non-SARDS using eugenol as the test odorant. The olfactory threshold was determined when subjects indicated the detection of a specific eugenol concentration with behavioral responses. Olfactory threshold, age, body weight, and environmental room factors were evaluated. RESULTS: Sixteen dogs with SARDS, 12 sighted dogs, and 12 blind/non-SARDS dogs demonstrated mean olfactory threshold pen numbers of 2.8 (SD&#x2009;=&#x2009;1.4), 13.8 (SD&#x2009;=&#x2009;1.4), and 13.4 (SD&#x2009;=&#x2009;1.1), respectively, which correspond to actual mean concentrations of 0.017&#x2009;g/mL, 1.7&#x2009;&#xd7;&#x2009;10&#x2009;g/mL and 4.26&#x2009;&#xd7;&#x2009;10&#x2009;g/mL, respectively. Dogs with SARDS had significantly poorer olfactory threshold scores compared with the two control groups (p&#x2009;<&#x2009;.001), with no difference between the control groups (p&#x2009;=&#x2009;.5). Age, weight, and room environment did not differ between the three groups. CONCLUSIONS: Dogs with SARDS have severely decreased olfaction capabilities compared with sighted dogs and blind/non-SARDS dogs. This finding supports the suspicion that SARDS is a systemic disease causing blindness, endocrinopathy, and hyposmia. Since the molecular pathways are similar in photoreceptors, olfactory receptors, and steroidogenesis with all using G-protein coupled receptors in the cell membrane, the cause of SARDS may exist at the G-protein associated interactions with intracellular cyclic nucleotides. Further investigations into G-protein coupled receptors pathway and canine olfactory receptor genes in SARDS patients may be valuable in revealing the cause of SARDS.