Metabolic (oxygen consumption) rate, opercular abduction rate and tail beat frequency were determined in two strains of diploid and triploid female brook trout (Salvelinus fontinalis) while these fish swam at 0.37±0.02 body lengths per sec in a Blazka respirometer. Total blood hemoglobin level was also measured and opercular condition examined. Total blood hemoglobin levels in diploids and triploids were equal. The opercular abduction rate was the same in diploids and triploids (regardless of whether triploid opercular condition was good or poor) yet triploids had a lower oxygen consumption rate than diploids, indicating that triploids take up less oxygen than diploids per opercular cycle. Tail beat frequency, an indicator of swimming effort, was the same in diploids and triploids, suggesting that triploids require less oxygen than diploids for a similar swimming effort.

No abstract

No significant difference was found in the critical swimming velocity of diploid and triploid brook trout Salvelinus fontinalis, suggesting that the triploid state is not associated with a reduced aerobic capacity. 1997 The Fisheries Society of the British Isles

Induction oflong-term potentiation, a putative substrate for behavioral plasticity, appears to be dependent on NMDA receptor activation. Blockade ofNMDA receptor activity has been shown to impair both classical conditioning and spatial cognition. The present study evaluated the effects of NMDA-receptor blockade by MK801 on latent inhibition of the classically conditioned nictitating membrane response in rabbits. Nonreinforced preexposure to a tone conditioned stimulus retarded acquisition rates in subjects pretreated with either saline or MK8010 Thus, latent inhibition does not appear to be mediated by or dependent on NMDA activity or related NMDAdependent long-term potentiation. Findings are discussed in relation to potential substrates for latent inhibition.Long-tenn potentiation (LTP) of synaptic transmission is a prominent candidate for a neurobiological mechanism underlying behavioral plasticity. LTP occurs in brain systems known to playa significant role in learning, such as the hippocampus (Bliss & Gardner-Medwin, 1973), and LTP-like changes develop as a consequence of stimulus pairings during associative learning (Berger, Alger, & Thompson, 1976;G. B. Robinson, 1992;Weisz, Clark, & Thompson, 1984). Moreover, prior potentiation of hippocampal synapses has been shown to facilitate acquisition of conditioned responses (CRs) (Berger, 1984;G. B. Robinson, Port, & Berger, 1989). The induction of L TP at both hippocampal CAl and dentate granule cell synapses appears to be dependent on N-methyl-n-aspartate (NMDA) receptors (Collingridge, Kehl, & McLennan, 1983;Harris, Ganong, & Cotman, 1984). Antagonists of NMDA-mediated activity have been reported to impair both LTP (G. B. Robinson & Reed, 1992) and classical conditioning (G. B. Robinson, 1993) in the rabbit, as well as perfonnance on the Morris milk maze (Heale & Harley, 1990), spontaneous alternation (Walker & Gold, 1991), and operant conditioning with differential reinforcement oflow rates of responding (Tonkiss, Morris, & Rawlins, 1988) in rats.The research reported here was supported by grants from the Natural Sciences and Engineering Research Council of Canada (G.B.R.). We would like to thank Marni Turnbull for her expert assistance with portions of these experiments. Requests for reprints should be addressed to G.