Parasites differentially impact crayfish personality in different contexts

The expression of an individual animal’s behaviour can be placed along many different personality spectra. Parasite load can alter animal behaviour and, thus, fitness. The personality traits of rusty crayfish, Faxonius rusticus, were analysed in three different behavioural contexts: foraging, exploration, and threatened. Each crayfish was tested in each context 3 times, giving a total of 9 assays per crayfish. After assays were completed, crayfish were dissected, and the hepatopancreas of each crayfish was photo analysed to determine the parasite load of the trematode, Microphallus spp. A composite personality score for each assay and parasite load was loaded into a PCA. The PCA model showed that as parasite load increased, crayfish became bolder in threatening contexts and less exploratory in novel environments, whether or not a food stimulus was present. Thus, parasite load alters the placement of crayfish on different personality spectra, but this change is context specific.

Electrophysiological and Behavioral Analysis of Lip Touch as a Component of the Food Stimulus in the SnailLymnaea

Electrophysiological and behavioral analysis of lip touch as a component of the food stimulus in the snail Lymnaea. Electrophysiological and video recording methods were used to investigate the function of lip touch in feeding ingestion behavior of the pond snail Lymnaea stagnalis. Although this stimulus was used successfully as a conditioning stimulus (CS) in appetitive learning experiments, the detailed role of lip touch as a component of the sensory stimulus provided by food in unconditioned feeding behavior was never ascertained. Synaptic responses to lip touch in identified feeding motoneurons, central pattern generator interneurons, and modulatory interneurons were recorded by intracellular electrodes in a semi-intact preparation. We showed that touch evoked a complex but characteristic sequence of synaptic inputs on each neuron type. Touch never simply activated feeding cycles but provided different types of synaptic input, determined by the feeding phase in which the neuron was normally active in the rhythmic feeding cycle. The tactile stimulus evoked mainly inhibitory synaptic inputs in protraction-phase neurons and excitation in rasp-phase neurons. Swallow-phase neurons were also excited after some delay, suggesting that touch first reinforces the rasp then swallow phase. Video analysis of freely feeding animals demonstrated that during normal ingestion of a solid food flake the food is drawn across the lips throughout the rasp phase and swallow phase and therefore provides a tactile stimulus during both these retraction phases of the feeding cycle. The tactile component of the food stimulus is strongest during the rasp phase when the lips are actively pressed onto the substrate that is being moved across them by the radula. By using a semi-intact preparation we demonstrated that application of touch to the lips during the rasp phase of a sucrose-driven fictive feeding rhythm increases both the regularity and frequency of rasp-phase motoneuron firing compared with sucrose applied alone.

Cephalic phase insulin release in normal weight males: verification and reliability

The existence and reliability of cephalic phase insulin release (CPIR) were tested in 20 normal weight males. Each subject was challenged three times with the same food stimulus over a 5-day period. Four baseline blood samples were taken at 5-min intervals before food ingestion and then every 2 min for 16 min postingestion. Significant increases in plasma insulin were found at 4 min postingestion on each trial day. CPIR was found to be highly reproducible between trials (r = 0.83; P less than 0.001). Fifty percent of the subjects exhibited a significant increase of plasma insulin above their own baseline mean on the first trial, whereas 75 and 72% exhibited increases on trials 2 and 3, respectively. Only two subjects (10%) did not demonstrate a response on any trial. A significant decline in plasma glucose was observed at 4 min postingestion on trials 2 and 3. No significant changes in plasma glucagon were found during any trial day. This study confirms a reliable CPIR in normal weight males.

Tegumental glands in the paragnaths of Palaemon serratus (Crustacea: Natantia)

The three lobed paragnath of Palaemon serratus (Pennant) contains numerous rosette-type tegumental glands often arranged in clusters of up to ten glands. Each gland is made up of around ten cells most of which stain deeply with toluidine blue and whose contents have a reticulate appearance in electron micrographs. One, or occasionally two, cells stain faintly and have a fine granular appearance in electron micrographs. The central region of each gland contains the main drainage duct together with feeder canals from the vesicular storage areas. The actively secreting region of each cell is peripheral and typified by abundant rough endoplasmic reticulum and Golgi apparatus. There are nerves adjacent to the glands and their contents are probably discharged in response to a food stimulus. The structure and possible function of the glands are discussed in relation to those of other species The secretions could act as a lubricant and as a binding agent to aid in the ingestion of particulate food. There is no evidence for any direct digestive function.

Pancreatic glucagon and cholecystokinin synergistically inhibit sham feeding in rats

Pancreatic glucagon (PG) elicits satiety in normally feeding rats but fails to inhibit sham feeding in rats with open gastric cannulas. This suggests that a gastric or postgastric food stimulus is necessary for PG's satiating action. To determine whether bombesin or cholecystokinin might provide such a stimulus, sham-feeding rats received simultaneous intraperitoneal injections of 100-800 micrograms/kg of PG and doses of bombesin or cholecystokinin (CCK) that were near the threshold for inhibition of sham feeding. PG and 0.15-to 0.30-micrograms/kg CCK combinations inhibited sham feeding potently (37.6 +/- 7.0 and 62.0 +/- 9.4%, respectively). In contrast, PG and 0.25- to 0.50-microgram/kg bombesin combinations did not significantly affect sham feeding. Behavioral observations indicated that the inhibition of sham feeding by PG plus CCK did not disrupt the normal postprandial satiety sequence of behavior, PG, 400 micrograms/kg, plus 0.15 micrograms/kg of CCK did not inhibit sham drinking in 18-h water-deprived rats. PG, 400 micrograms/kg, plus 0.30 microgram/kg of CCK did inhibit sham drinking, although the effect (34.6 +/- 6.6%) was significantly less than the effect on sham feeding (75.5 +/- 9.7%) in the same rats. These data indicate that CCK is a sufficient food stimulus to permit PG to inhibit sham feeding. Furthermore, this inhibitory effect appears to result from a functional synergism of PG and CCK.