Activation of the sensory current in salamander olfactory receptor neurons depends on a G protein-mediated cAMP second messenger system.

Olfactory receptor neurons respond to odor stimulation with an inward cationic current. Under whole-cell patch clamp, individual, isolated olfactory receptors were exposed to pharmacological agents known to interact with distinct enzymes in a putative second messenger cascade, and their response to odors was measured. IBMX prolonged the odor-evoked current and also reduced its amplitude. cAMP and cGMP induced a current electrically identical to the odor current, but the current showed desensitization only with cAMP. GTP-gamma-s prolonged and GDP-beta-s interfered with the odor-evoked current. The long latency seen in the odor response appears to be mainly due to the loading of the G protein and secondarily to the requirement for cAMP accumulation. The main source of the response decay appears to be cyclic nucleotide hydrolysis.     

Influence of a collector-filterer caddisfly (Trichoptera :Hydropsyche betteni Ross) on leaf processing rates in an artificial stream

A 2 × 6 unbalanced fixed effects factorial treatment design was used to examine the effects of a collector-filterer on leaf processing rates of American Cottonwood (Populus deltoides Bartr.) in an artificial stream over a six week period. Pre-leached leaves were placed into 30 small enclosures; collector-filterer caddisflies (Hydropsyche betteni Ross) were added to 18 enclosures resulting in two treatment factors (leaves with and without caddisflies). Changes in leaf dry-weight and caddisfly biomass were determined at weekly sampling intervals. Leaf processing rates were significantly different between treatments over time, with enclosures without caddisflies exhibiting a greater weight loss (higher k value) than enclosures with caddisflies (p < 0.01). The reduction in processing rates of the leaves due to the presence of caddisflies was attributed to the construction of retreats by these collector-filterers. Under the influence of the caddisfly, leaf material may be able to remain as a viable food resource for a longer period in the stream.