Inhibition of mating in Aplysia fasciata by food stimuli in the environment, but not by post-ingestion stimuli causing satiation

Aplysia mating is inhibited when animals have steady-state access to food. We examined which stimuli provided by food inhibit mating. Pre-feeding animals to satiation caused a decrease in mating immediately after the meal. This effect could be mimicked by placing food into the water for the length of time of a meal just before the animals were allowed to mate, but not by filling the gut with non-nutritive bulk, which inhibits feeding. The presence of food in the water while animals were allowed to mate caused a stronger inhibition of mating. When food was maintained in the water for 24 h, animals adapted to this stimulus, indicating that the maintained presence of food could not alone account for the inhibition of mating in steady-state conditions of access to food. However, food in the water for 24 h, coupled with an occasional touch of food to the lips while animals had access to mates, caused strong inhibition of mating. We tested the hypothesis that food initiates a state of food arousal, which competes with sexual arousal, and thereby inhibits mating. If this hypothesis is correct, gut fill should facilitate mating, by inhibiting food arousal. However, this effect was not observed. The data support the hypothesis that food stimuli directly inhibit sexual arousal, rather than acting via an excitation of food arousal. Accepted: 14 June 1997     

Pheromones linked to sexual behaviors excite the appetitive phase of feeding behavior of Aplysia fasciata. I. Modulation and excitation of appetitive behaviors

Pheromones presumably secreted by mating conspecifics – as well as homogenates containing tissue that is homologous with the atrial gland – increase the time that Aplysia fasciata spend feeding. This effect is caused by increasing the number of feeding episodes initiated in response to food, whereas the duration of a feeding bout remains unchanged. The increase in the number of feeding episodes is related to increases in head waving and crawling, i.e., appetitive movements that bring the animal into contact with food, as well as an increase in the responsiveness to food after it is contacted. Releasing a homogenate containing atrial gland tissue, or egg laying hormone, in the water near the animal elicited head lifting similar to that seen when animals are food aroused. The data indicate that the facilitation of Aplysia feeding caused by pheromones arises in part by an excitation of appetitive behaviors. These findings suggest that neurons generating appetitive behaviors will be affected by pheromones. Accepted: 28 November 1997     

Control of gill reflex habituation and the rate of EPSP decrement of L7 by a common source in the CNS of Aplysia

It was found in older Aplysia that the rate of decrement of the EPSP evoked in L₇ by repeated tactile stimulation of the gill was dependent on the strength of the applied stimulus and that the rate of decrement paralleled the rate of gill reflex habituation. As the stimulus intensity was increased both rates slowed. In contrast, it was found in young Aplysia that the rate of EPSP decrement and the rate of gill reflex habituation were independent of the strength of the stimulus applied to the gill. Neither rate changed as the stimulus intensity was changed. Moreover, L₇'s of young animals are more responsive to tactile stimuli applied to the gill than are L₇'s of older animals and the difference in excitability is not due to any differences in passive membrane properties between the L₇'s in young and older Aplysia. These findings are fully consistent with and supportive of the proposal that a common neuronal source in the parieto-visceral ganglion of Aplysia controls the rate of gill reflex habituation, the synaptic input to L₇, and the rate of decrement of this input, evoked by repeated tactile stimulation of the gill. Additinally, it was proposed that this common source is developed in completely in the young. As a consequence of this incomplete development, young Aplysia exhibit less adaptability to changing stimulus conditions and, in general, less ability to suppress their behavior. It may thus be possible to study directly developmental changes in the nervous system which act to transform juvenile behavior to adult behavior.     

Neuronal input contributes to sequence of Aplysia egg laying behaviors

Egg laying in Aplysia is controlled by the bag cell neuroendocrine system, which releases multiple peptides during a long-lasting electrical discharge. Following the discharge, a fixed sequence of head and neck movements is performed in which two phases can be distinguished: an appetitive or preparatory phase, in which the substrate is prepared, and a consummatory phase, when the egg string is deposited. During egg laying, feeding responses are suppressed. In this study, Aplysia fasciata was used. When the movement of the egg string through the genital groove was prevented by ligation, lesions of the nerve innervating the genital pore completely abolished the consummatory egg-laying behaviors. This shows that a nervous connection between the genital pore area and the central nervous system is important for the consummatory egg-laying behaviors.We found that suppression of feeding responses to seaweed occurred only during the consummatory phase of egg laying in controls, but animals with ligated genital grooves continued to show normal responses to food. It is hypothesized that a neuronal feedback, possibly together with the bag cell peptides, is critical for the temporal organization of egg-laying behavior in Aplysia.Abbreviations CNS central nervous system - ELH egg laying hormone     

A note on the effect of the full moon on the activity of wild maned wolves, Chrysocyon brachyurus

It is well established in the scientific literature that animal prey species reduce their activity at times of high predation risk. In the case of nocturnal animals this occurs when there is a full moon; however, the response of predators to the changes in their prey behaviour is relatively unknown. Two responses are possible: (1) increase in search effort to maintain food intake; or (2) decrease in distance travelled due to either: (a) an effort to conserve energy or (b) increased kill efficiency. Using GPS tracking collars we monitored the distances travelled (which is representative of search effort) by three maned wolves during the night of the full and new moon for five lunar cycles (during the dry season). A Wilcoxon matched-paired test showed that the maned wolves travelled significantly less during the full compared to the new moon (p < 0.05). On average, during the 10 h of darkness during a full moon maned wolves travelled 1.88 km less than on a new moon. These data suggest that maned wolves respond to temporally reduced prey availability by reducing their distance travelled.     

Pattern of integration of conflicting stimuli by the crab Heterozius rotundifrons

When an animal receives several stimuli that could evoke conflicting behaviours they can either show a response to just one stimulus or show a gradation of responses to the multiple stimuli. It has been proposed [Hazlett BA. 2000. Responses to single and multiple sources of chemical cues by New Zealand crustaceans. Mar Freshw Behav Physiol. 34:1–20] that a graded response will be seen if the animals have an alternative response to one behavioural category of stimuli (the alternative-behaviour-gradual-change rule). The crab Heterozius rotundifrons has two alternative patterns of predation avoidance, either assumption of a rigid limb-extended posture for several minutes or a short period of limb extension and then rapid locomotion. We presented crabs with full strength input in one category (food stimulus) and one of seven intensities of input in a conflicting category (either chemical or visual cues associated with increased predation risk). In both cases, as the intensity of the danger signal gradually increased, there was a gradual increase in the duration of the limb-extended posture.     

Risk assessment and avoidance in juvenile golden hamsters exposed to repeated stress

Juvenile hamsters are typically less vulnerable to social subjugation than adults, although they will avoid aggressive individuals in some situations. The purpose of this study was to determine the extent to which social subjugation stimulates fear- or anxiety-like behavior in juvenile hamsters in both social and non-social contexts. Social context testing was conducted in a Y-maze while the non-social context apparatus consisted of an open field arena and a lat-maze. In the Y-maze, subjects were exposed to an unfamiliar aggressive adult hamster. Compared with non-subjugated controls, subjugated juveniles spent significantly more time in the area furthest from the aggressive adult stimulus. In addition, socially stressed animals were more likely to avoid the arm of the maze containing the social stimulus. When they did walk in the arm containing the social stimulus, subjugated individuals were more likely to ambulate slowly. Subjugated hamsters also performed fewer olfactory investigations in the proximity of the unfamiliar aggressive individual. Despite these behavioral differences detected between groups during testing in a social context, we observed no differences between groups in the open field and lat-maze. This suggests that the effects of subjugation observed in the Y-maze are specific to exposure to a social context and that social subjugation in juvenile hamsters does not result in a generalized state of fear. Instead, subjugated juveniles learned to avoid adult males and were otherwise behaviorally similar to non-subjugated controls.     

Seaweed extract stimuli in plant science and agriculture

Both micro- and macroalgae have long been used to augment plant productivity and food production in various regions of the world through their beneficial effects when applied to soils. Interactions of algae with the soil community undoubtedly are complex and benefits are dependent on the crop and the local environmental conditions. This has resulted in much speculation as to mechanisms involved as well as the validity of the results reported. It is now 60 years since the first commercial seaweed extract was manufactured for agricultural use. These aqueous extracts allowed for the first time the direct application of soluble seaweed constituents to specific plant organs such as leaves and roots. The earlier concept that benefits of seaweeds and their extracts were due mainly to their manurial value or to their micronutrient suites is no longer tenable. Seaweeds likewise have been used for millennia as fodder supplements to improve animal nutrition and productivity. Recent research is focusing on their mode of action, specific health benefits, and the mechanisms of action in animals. Improved analytical techniques and instrumentation coupled with the use of molecular genetic tools are establishing that seaweed extracts can modify plant and animal responses at a fundamental level. It therefore seems appropriate to review key developments over the years and to remark on novel findings. A new and exciting vista has opened for seaweed extracts in both plant and animal applications.     

Variables Controlling Entry into and Exit from the Steady-State,One of Two Modes of Feeding in Aplysia

Background

Aplysia feeding is a model system for examining the neural mechanisms by which changes in motivational state control behavior. When food is intermittently present, Aplysia eat large meals controlled by a balance between food stimuli exciting feeding and gut stimuli inhibiting feeding. However, when food is continuously present animals are in a state in which feeding is relatively inhibited and animals eat little. We examined which stimuli provided by food and feeding initiate steady-state inhibition of feeding, and which stimuli maintain the inhibition.

Results

Multiple stimuli were found to control entry into the steady-state inhibition, and its maintenance. The major variable governing entry into the steady-state is fill of the gut with bulk provided by food, but this stimulus cannot alone cause entry into the steady-state. Food odor and nutritional stimuli such as increased hemolymph glucose and L-arginine concentrations also contribute to inhibition of feeding leading to entry into the steady-state. Although food odor can alone cause some inhibition of feeding, it does not amplify the effect of gut fill. By contrast, neither increased hemolymph glucose nor L-arginine alone inhibits feeding in hungry animals, but both amplify the inhibitory effects of food odor, and increased glucose also amplifies the effect of gut fill. The major variable maintaining the steady-state is the continued presence of food odor, which can alone maintain the steady-state for 48–72 hrs. Neither increased glucose nor L-arginine can alone preserve the steady-state, although they partially preserve it. Glucose and arginine partially extend the effect of food odor after 72 hrs.

Conclusions

These findings show that control of Aplysia feeding is more complex than was previously thought, in that multiple inhibitory factors interact in its control.     

The reactions of the Norway lobster,Nephrops norvegicus (L.), to water currents

Observations were made on the reactions of the Norway lobster, Nephrops norvegicus, to water currents in a sea‐water flume tank. Blind animals were used to prevent visually‐guided behaviour. Nephrops adopted a downstream orientation, and usually walked downstream, in response to water current speeds in the range of 0.07 to 0.20 ms^?1. Patterns of water flow around the body revealed that it was most effectively streamlined when the animal adopted a downstream orientation. Direct measurements of the forces acting on the body revealed that animals with a downstream orientation experienced the least hydrodynamic drag and the greatest downforce.     

A Multinucleated Marine Amoeba Which Digests Seaweeds1

Marine amoebae were isolated during a search for organisms which degrade cell walls of seaweed. One of the isolates, a multinucleated amoeba (referred to here as Amoeba-I-7 or Am-I-7) was isolated from live tissues of the brown seaweed Sargassum muticum. It digested a variety of brown and red seaweeds including their walls and cuticles. Axenic clone cultures were isolated from cells that migrated on agar. Cultures were grown on agar or in liquid media. Seaweeds, seaweed wall extracts, and unicellular algae were tested as food sources.     

Individual discrimination in the big-clawed snapping shrimp,Alpheus heterochelis

Rahman et al. (Rahman, N., Dunham, D.W. and Govind, C.K. (). Mate recognition and pairing in the big-clawed snapping shrimp, Alpheus herterochelis. Mar. Fresh. Behav. Physiol., 34, 213–226.) demonstrated discrimination by snapping shrimp between former mates and unfamiliar conspecifics, but did not test individual discrimination. In the present study, snapping shrimp showed discrimination between familiar and unfamiliar same-sex conspecifics by preferentially entering that arm of a Y-maze leading to familiar individuals. Furthermore, after being exposed to water from the home tanks of unknown individuals, they later showed an elevated response to this water, if the direction from which the water came into their tank was changed to be novel. This indicates that test subjects associated a familiar chemical stimulus with its location in the environment. This discrimination could only have been made if that chemical signature were recognised as different from that of another chemically familiar individual. This result also demonstrates that the water surrounding an individual contains sufficient (chemical) information to allow discrimination of one individual from another.     

Selective and divided attention in animals

This article reviews some of the research on attentional processes in animals. In the traditional approach to selective attention, it is proposed that in addition to specific response attachments, animals also learn something about the dimension along which the stimuli fall (e.g., hue, brightness, or line orientation). More recently, there has been an attempt to find animal analogs to methodologies originally applied to research with humans. One line of research has been directed to the question of whether animals can locate a target among distracters faster if they are prepared for the presentation of the target (search image and priming). In the study of search image, the target is typically a food item and the cue consists of previous trials on which the same target is presented. In research on priming effects, the cue is typically different from the target but is a good predictor of its occurrence. The study of preattentive processes shows that perceptually, certain stimuli stand out from distracters better than others, depending not only on characteristics of the target relative to the distracters, but also on relations among the distracters. Research on divided attention is examined with the goal of determining whether an animal can process two elements of a compound sample with the same efficiency as one. Taken together, the reviewed research indicates that animals are capable of centrally (not just peripherally) attending to selective aspects of a stimulus display.     

Attractivity of pheromone surpassed by time-patterned application of two nonpheromone compounds

Strong support is given to the thesis that an unmodulated level of pheromone does not evoke orientation toward the source in male silkmoth Bombyx morieven if the concentration is high. The bombykol-related compound (Z,E)-4,6-hexadecadiene, which is known to elicit a firing of bombykol receptors that is maintained for many minutes after the removal of the stimulus, was used for the tests, together with linalool, which inhibits the response of the bombykol cells. Neither hexadecadiene nor linalool is known to release the typical behavior of orientation in these moths. The experiments, however, show that if the uniform firing after a hexadecadiene stimulus is modulated by a suitable sequence of linalool pulses, the males immediately display orientation behavior and approach the source even faster and more directed than with pulsed bombykol.     

Spontaneous light or dark preference in albino mice?

The present experiment examined spontaneous visual choice behaviour and acquisition of a positively reinforced visual discrimination task in Swiss albino mice. In experiment I animals were given 4 consecutive trials in which they could freely enter either a dimly illuminated or a darkened arm of a Y-maze; the position of the light stimulus was randomized across trials. D groups and L groups were tested during the dark and the light period of the day respectively. Results revealed a significant spontaneous preference for the illuminated arm of the maze, independent of the testing period. It is suggested that the dim light has a reinforcing value because it provides additional information about a novel environment. In a second experiment an appetitive visual discrimination task was carried out in the same Y-maze. After a pretraining period, half the animals were reinforced in the illuminated arm and half were reinforced in the darkened one, on five consecutive days. On the first test session all groups of animals chose the illuminated arm significantly more frequently, whereas light/dark choices reached chance level on the last test session. Discrimination learning was not acquired and a behavioural analysis revealed an increasing tendency to a side preference across testing.     

Multi‐directional sensitivity of statocyst receptor cells of the opisthobranch gastropod Aplysia limacina

The electrical activity in the static nerves of Aplysia limacina was studied in relation to the spatial orientation of the animal. Each sense cell shows a multi‐directional sensitivity. Hence, it responds during full‐circle rotations about all horizontal axes but only within a limited angular range. The statocyst receptor cells are found to be gravity receptors only, and their electrical behaviour suggests that main information about the spatial orientation of Aplysia is contained in the pattern of responding cells, i.e. which of the 13 cells are active at any one time, and not in their absolute discharge frequencies. Furthermore, evidence is given to a similar function of the statocysts of opisthobranch and pulmonate gastropods.     

Patterned jaw movements and the motor neuron activity during rejection of seaweed in Aplysia kurodai

Japanese Aplysia kurodai feeds well on Ulva. In the present experiments we collected several species of seaweed at a location with many animals and initially explored the preference behavior for them. The animals rejected Grateloupia, Pachydictyon, Gelidium and Laurencia with rhythmic jaw and radula movements (active rejection). The animals sometimes bit off a piece of them (biting-off response). Recording activity of muscles contributing to jaw-opening and jaw-closing in freely moving animals showed that the onset of the jaw-closing activity, which always started later than the jaw-opening activity during each cycle of ingestion of Ulva, was advanced toward that of the jaw-opening activity during each cycle of the active rejection. Semi-intact experiments also showed that application of Pachydictyon or Gelidium extract to the lip region advanced the firing onset of the jaw-closing motor neurons at the radula-retraction phase. Video analysis showed that during the Ulva response the jaws opened at the radula-protraction phase and remained half-open at the earlier radula-retraction phase, while the jaws opened similarly at the radula-protraction phase but immediately closed at the radula-retraction phase during the Pachydictyon or Gelidium response. Accepted: 8 October 1997     

Physiological and behavioral effects of chemoreceptors located in different body parts of the swimming crab Callinectes danae

By perfusing their branchial chambers with filtered seawater, we have developed a preparation that allows us to maintain the swimming crab Callinectes danae outside water without any major effects on its cardiac activity. This in turn allowed us to selectively stimulate chemoreceptors located in different body parts, and specifically to discriminate between the receptors located in the branchial chambers and those located in the oral region (mainly in the mouthparts, antennules and antennae). We show that a taurine solution can evoke bradycardia when applied to the oral region or to a combination of the oral region and the branchial chambers. Although the precise localization of the oral region receptors involved remains to be determined, ablation experiments show that the olfactory organs (i.e., the antennules) are not involved. Finally, we show that although stimulating the pereiopods has no effect on the animals' cardiac activity it causes the animals to move, putatively to try to grasp a piece of food, a reaction not evoked by stimulating the gills or the oral regions. Our results lend support to the idea that chemoreceptors located in different parts of the body play different functional roles in decapod crustaceans.     

Fish blood as a chemical signal for Antarctic marine invertebrates

Chemical cues released from dead or injured organisms constitute important signals informing nearby animals about a feeding possibility. The ability to detect the signal, evaluate its meaning and locate its source can help organisms to exploit food resources efficiently, which is especially important to animals living in environments with limited food supply. Experiments were carried out to study the behavioral responses of several Antarctic benthic invertebrates to fish (Notothenia corriceps) blood. Necrophagous species such as sea stars Odontaster validus and Lysasterias sp., amphipod Waldeckia obesa and nemertean Parborlasia corrugatus responded to fish blood with changes in their behavior. The behavior common to all these species was locomotion directed towards the stimulus source. Behavioral components consistent with food consumption were observed in O. validus and P. corrugatus. The reaction of herbivorous limpets Nacella concinna to fish blood depended on the animal size. Large (>10 mm) limpets showed no behavioral response, whereas small ones (<10 mm) reacted to the stimulus by moving a short distance away. These results indicate that blood released from the tissues of injured or dead animals may be an important chemical signal for organisms belonging to different taxa.     

Cooling as Reinforcing Stimulus in Aplysia

An experiment was carried out to investigate the role of temperaturein the previously reported reinforcing effect of an increasein sea water level in Aplysia. In the present experiment, itwas found that the reinforcing effect of water level changeon rod-pressing behavior in Aplysia depends on a decrease intemperature associated with water level change. In order studymodification of rod pressing behavior produced by contingentincrease in water level and decrease in temperature, the rateand latency of rod-press responses in experimental animals wherecompared with those of yoked control animals exposed to non-contingentwater level and temperature change. Higher response rates andshorter response latencies were obtained from experimental overyoked control animals but only the shorter latencies of experimentalanimals were attributed to a behavioral change resulting fromcontingent water level and temperature reinforcement.