Acute and chronic effects of ferret odor exposure in Sprague-Dawley rats

Abstract

This manuscript describes several behavioral and functional studies evaluating the capacity of ferret odors to elicit a number of acute and long-term responses in male Sprague-Dawley rats. Acute presentation elicits multiple responses, suggesting that ferret odor, likely from skin gland secretions, provides an anxiogenic-like stimulus in this strain of rats. Compared to cat odor, however, ferret odor did not produce rapid fear conditioning, a result perhaps attributable to methodological factors. Inactivation of the olfactory system and medial nucleus of the amygdala, combined with induction of the immediate-early gene c-fos, suggest the necessity of the accessory olfactory system in mediating the effects of ferret odor. Repeated exposures to ferret odor produce variable habituation of neuroendocrine and behavioral responses, perhaps indicative of the lack of control over the exact individual origin or concentration of ferret odor. Ferret odor induces rapid and long-term body weight regulation, thymic involution, adrenal hyperplasia and facilitation of the neuroendocrine response to additional challenges. It is argued that the use of such odors is exquisitely suited to investigate the brain regions coordinating anxiety-like responses and the long-term changes elicited by such stimuli.

Fig. 1

Defensive withdrawal apparatus, as seen from above (camera angle). The black rectangle inside the apparatus depicts the hide box, with the X representing the opening on the side of the box. The small white square diagonally opposite the hide box represents the location where the ferret or control odor towels are taped down.

Fig. 2

(A) Mean plasma levels of corticosterone (CORT; ±S.E.M.) for rats exposed to ferret odor (n = 4), control odor (n = 4), isopentyl acetate (n = 4), or butyric acid (n = 4) for 30 min at the trough of the circadian cycle. (B) Mean plasma levels of adrenocorticotropin hormone (ACTH; ±S.E.M.) for the same rats as in (A). Asterisks indicate a significant difference from all other groups (p < 0.05).

Fig. 3

(A) Mean heart rate (beat per min ±S.E.M.) and (B) core body temperature (degree C ±S.E.M.) of rats exposed to ferret (rhombus shape) or strawberry (square shape) odors for 30 min (grey bars).

Fig. 4

Effect of control (strawberry—STR) or ferret (FER) odor in rats sustaining either complete bilateral medial amygdala ibotenic acid (IBO) cell loss or sham (SHAM) lesions on mean time (±S.E.M.) spent in the towel corner (A), in the hide chamber (B), or the number of visits to the towel corner (C). Note that the IBO/FER rats respond in a way more similar to rats presented with control (IBO/STR, SHAM/STR) than normal rats presented with ferret odor (SHAM/FER). *p < 0.05 compared to all other groups (Tukey post hoc multiple means comparisons).

Fig. 5

Immunohistochemical detection of the neuronal specific marker NeuN indicates the extent of neuron loss in the region of the medial amygdaloid nucleus (MeA—black arrow, right) following ibotenic acid injection, compared to an injection of ACSF (left).

Fig. 6

Effect of control (strawberry—STR) or ferret (FER) odor in rats sustaining either complete bilateral medial amygdala ibotenic acid (IBO) cell loss or sham (SHAM) lesions on mean levels of plasma corticosterone (A) and ACTH (B). Note that the IBO/FER rats respond in a way more similar to rats presented with control (IBO/STR, SHAM/STR) than normal rats presented with ferret odor (SHAM/FER). *p < 0.05 compared to all other groups (Tukey post hoc multiple means comparisons).

Fig. 7

(A) Mean circulating plasma corticosterone (μg/dl ±S.E.M.) in response to ferret (FER) or control (clean towel—CON) odor following intranasal saline (SAL) or a 10% solution of zinc sulfate (10%) in male rats (n = 8 for SAL/FER, n = 13 for 10% ZnSu, n = 6’s for both SAL/CON and 10%/CON, respectively). There was no statistical difference between the SAL/FER and 10%/FER groups. (B) c-fos mRNA induction at the level of the olfactory bulb in control (saline) or 10% zinc sulfate (ZnSu)-treated rats in response to ferret odor. Note the c-fos mRNA induction greatly limited to the accessory olfactory bulb (AOB) in ZnSu-treated rats as compared to a much larger induction throughout the main olfactory bulb (MOB) of saline-treated rats.

Fig. 8

Reliable plasma corticosterone (A) and ACTH (B) response habituation (respective ANOVAs over time, reliable group × time effect, p < 0.05) to 11 consecutive 30 min daily exposures to ferret or control odor towels hung in the home cages (n = 8 per group).