Comparative study of alpha2-adrenoceptors in Fischer 344 and Lewis rats. Evidence for clonidine-induced place aversion

Noradrenergic modulation of play in Sprague-Dawley and F344 rats

RATIONALE

For many mammals, engaging in social play behavior as a juvenile is important for cognitive, social, and emotional health as an adult. A playful phenotype reflects a dynamic interplay between genetic framework and experiences that operate on hard-wired brain systems so the relative lack of play in an otherwise playful species may be useful for identifying neural substrates that modulate play behavior. The inbred F344 rat has been identified as a strain that is consistently less playful than other strains commonly used in behavioral research. Norepinephrine (NE) acting on alpha-2 receptors has an inhibitory effect on play and F344 rats differ from a number of other strains in NE functioning. As such, the F344 rat may be particularly useful for gaining insight into NE involvement in play.

OBJECTIVE

The objective of this study was to determine whether the F344 rat is differentially sensitive to compounds that affect NE functioning and that are known to affect play behavior.

METHODS

Using pouncing and pinning to quantify play, the effects of the NE reuptake inhibitor atomoxetine, the NE alpha-2 receptor agonist guanfacine, and the NE alpha-2 receptor antagonist RX821002 on play behavior were assessed in juvenile Sprague-Dawley (SD) and F344 rats.

RESULTS

Atomoxetine and guanfacine reduced play in both SD and F344 rats. RX821002 increased pinning to a comparable extent in both strains but F344 rats were more sensitive to the play-enhancing effects of RX821002 on pounces.

CONCLUSIONS

Strain differences in NE alpha-2 receptor dynamics may contribute to the lower levels of play in F344 rats.

Opiate-agonist induced taste aversion learning in the Fischer 344 and Lewis inbred rat strains: evidence for differential mu opioid receptor activation

The Fischer 344 (F344) and Lewis (LEW) inbred rat strains react differently to morphine in a number of behavioral and physiological preparations, including the acquisition of aversions induced by this compound. The present experiment tested the ability of various compounds with relative selectivity at kappa, delta and mu receptor subtypes to assess the relative roles of these subtypes in mediating the differential aversive effects of morphine in the two strains. In the assessment of the role of the kappa receptor in morphine-induced aversions, animals in both strains were given access to saccharin followed by varying doses of the kappa agonist (-)-U50,488H (0.0, 0.28, 0.90 and 1.60 mg/kg). Although (-)-U50,488H induced aversions in both strains, no strain differences emerged. A separate subset of subjects was trained with the selective delta opioid agonist, SNC80 (0.0, 5.6, 10.0 and 18.0 mg/kg), and again although SNC80 induced aversions, there were no strain differences. Finally, a third subset of subjects was trained with heroin (0.0, 3.2, 5.6 and 10.0 mg/kg), a compound with activity at all three opiate receptor subtypes. Although heroin induced aversions in both strains, the aversions were significantly greater in the F344 strain, suggesting that differential activation of the mu opioid receptor likely mediates the reported strain differences in morphine-induced aversion learning. These data were discussed in terms of strain differences in opioid system functioning and the implications of such differences for other morphine-induced behavioral effects reported in F344 and LEW rats.