THE COOLING POWER OF THE PIGEON HEAD

Resting pigeons preheated to a stable core temperature of 43.2 °C, which is within the range of body temperatures recorded during flight, were able to cool their body at high rates if their head and upper neck were exposed to an air stream at 23.5 °C. The heat dissipation capacity of the head and neck, estimated from measurements made at a wind speed (100 km h-1) corresponding to fast flight, was 9.8 W, or 4.5 times the resting heat production. Since the greater part of this capacity, about 8 W, was attributable to the inner surfaces of the mouth, ram ventilation of the buccal cavity appears to be an important mechanism for increasing evaporative heat loss during flight. Accordingly, wind-assisted mouth cooling should be utilized by resting pigeons, since exposure to a slight breeze (approximately 10 km h-1) could augment their dissipating power by an amount equivalent to their resting metabolic rate. It is concluded that beak opening, together with a source of convection other than panting and gular flutter, is required to exploit fully the heat dissipation capacity of the buccopharyngeal mucosa of birds.

Beneficial effect of exercise training on cardiac long-chain acylcarnitine levels in diabetic rats

Long-chain acylcarnitines are markedly elevated in the diabetic rat heart. This could be associated with the increased rate of fatty acid metabolism in this tissue seen in the diabetic animal. The effect of exercise training on this carnitine derivative in the diabetic rat, however, has received little attention. We therefore examined the effect of exercise training on this derivative as well as other carnitine esters in hearts of diabetic rats. Four groups of male Wistar rats were used: sedentary-control (SC), trained-control (TC), sedentary-diabetic (SD), and trained-diabetic (TD). Diabetes was induced by the I.V. injection of streptozotocin at the dose of 50 mg/kg. Training was performed on a motor-driven treadmill according to a 10-week program. Sixty hours after the last bout of exercise, the rats were killed by decapitation and the hearts were quickly excised and placed in liquid nitrogen for measurement of total carnitine and its acyl derivatives. SD and TD had significantly lower levels of total (p less than 0.001) and free carnitine (p less than 0.01) compared to the respective control groups. Exercise had no effect on total and free carnitine levels in both control and diabetic groups. Short-chain acylcarnitine levels were neither altered by training nor diabetes. Heart tissue levels of long-chain acylcarnitine were increased (p less than 0.01) in SD compared to SC. However, exercise training resulted in a significant (p less than 0.05) reduction in long-chain acylcarnitines in diabetic rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Characterization of Aeromonas salmonicida mesophilic isolates from Alberta (Canada) allows the development of a more sensitive Dictyostelium discoideum predation test

Aeromonas salmonicida is studied using Dictyostelium discoideum as a model host, with predation resistance measured as a key parameter. Aeromonas salmonicida mesophilic isolates exhibit inconclusive results with the amoebic model. This study focuses on new mesophilic isolates (S24-S38, S26-S10, and S28-S20) from Alberta, Canada, and introduces an improved predation test method. Phylogenetic analysis reveals two subgroups, with S24-S38 and S26-S10 clustering with the subspecies pectinolytica from Argentina, and S28-S20 with strains from India (Y567) and Spain (AJ83), showcasing surprising mesophilic strain diversity across geographic locations. Predation tests were carried out with various mesophilic and psychrophilic strains of A. salmonicida, including Alberta isolates. The amoeba cell lines used were DH1-10 and AX2. Although the mesophilic isolates were very resistant to predation by the amoeba DH1-10, some lost this resistance to the AX2 strain, which appeared more voracious in the conditions tested. In addition, when diluting the culture medium used in a predation test with AX2, a loss of the capacity to predation resistance was observed for all the mesophilic isolates, including the highly resistant S28-S20 isolate. This study provides insights into the predation resistance of A. salmonicida isolates and offers avenues for better characterizing mesophilic isolates.

Beneficial effect of exercise training on cardiac long-chain acylcarnitine levels in diabetic rats

Long-chain acylcarnitines are markedly elevated in the diabetic rat heart. This could be associated with the increased rate of fatty acid metabolism in this tissue seen in the diabetic animal. The effect of exercise training on this carnitine derivative in the diabetic rat, however, has received very little attention. We therefore examined the effect of exercise training on this derivative as well as other carnitine esters in hearts of diabetic rats. Four groups of male Wistar rats were used: sedentary-control (SC), trained-control (TC), sedentary-diabetic (SD), and trained-diabetic (TD). Diabetes was induced by the I.V. injection of streptozotocin at the dose of 50 mg/kg. Training was performed on a motor-driven treadmill according to a ten-week program. 60 hr after the last bout of exercise, the rats were killed by decapitation and the hearts were quickly excised and placed in liquid nitrogen for measurement of total carnitine and its acyl derivatives. SD and TD had significantly lower levels of total (p less than 0.001) and free carnitine (p less than 0.01) compared to the respective control groups. Exercise had no effect on total and free carnitine levels in both control and diabetic groups. Short-chain acylcarnitine levels were neither altered by training nor diabetes. Heart tissue levels of long-chain acylcarnitine were increased (p less than 0.01) in SD compared to SC. However, exercise training resulted in a significant (p less than 0.05) reduction in long-chain acylcarnitines in diabetic rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Impact of Predation by Ciliate Tetrahymena borealis on Conjugation in Aeromonas salmonicida subsp. salmonicida

BACKGROUND/OBJECTIVES

Antibiotic resistance gene (ARG) spread is driven by horizontal gene transfer (HGT). Ciliated protozoa may contribute to this process, as their predation has been shown to facilitate HGT in certain bacteria. Here, this phenomenon was further investigated using A. salmonicida subsp. salmonicida. This fish pathogen bears an extensive and dynamic plasmidome, suggesting a high potential for HGT.

METHODS

A. salmonicida strains carrying one of three conjugative plasmids bearing ARGs (pSN254b, pRAS1b or pAsa4b) were cocultured with a recipient, either A. salmonicida, E. coli or A. hydrophila. Conjugation rates were assessed in the presence and absence of the ciliate Tetrahymena borealis. PCR genotyping confirmed the acquisition of the conjugative plasmids and was used to verify the mobilization of other plasmids.

RESULTS

The basal rate of conjugation observed was high. Under the conditions studied, ciliate predation did not appear to influence the conjugation rate, except at higher proportions of ciliates, which typically hampered conjugation. Microscopy revealed that most bacteria were digested in these conditions. PCR screening demonstrated that small mobilizable plasmids from A. salmonicida (pAsa1, pAsa2, pAsa3, and pAsal1) were acquired by the recipients along with the conjugative plasmids, with a slight effect of the ciliates in some donor/recipient cell combination.

CONCLUSIONS

These results highlight how A. salmonicida can conjugate efficiently with different species and how complex its relationship with ciliates is.