Urine release in freely moving catheterised lobsters (Homarus americanus) with reference to feeding and social activities.

Previous studies suggest that urine-borne pheromones play an important role in lobster agonistic and sexual behaviour. This paper investigates the pattern of urine release in catheterised, but otherwise freely moving, adult lobsters with respect to feeding, social and non-social activities. Lobsters on average released 4.1 ml (1 % of body mass) of urine over a 12 h period; this more than doubled to 10.6 ml over the 12 h period after feeding. Hourly monitoring revealed that most urine was released in the first hour after feeding (2.84 ml). With the exception of the first hours after feeding, urine release was intermittent, with pauses lasting up to 17 h. The probability of urine release per hour in unfed lobsters was 0.34 (median); this value increased during agonistic interactions elicited by the introduction of a conspecific (median 0. 63) and during activity initiated by non-social disturbance (median 0.56). Mean urine volume during output hours in unfed lobsters amounted to 1.09 ml h-1. This volume was significantly increased by the presence of a conspecific (1.88 ml h-1) and decreased during activity initiated by non-social disturbances (0.56 ml h-1). No sex-specific differences in urine release were found. The data demonstrate that lobsters control their urine release in a manner dependent on behavioural context. This supports recent findings suggesting the use of urine for chemical signalling in agonistic interactions.

Temporal resolution in olfaction II: time course of recovery from adaptation in lobster chemoreceptor cells.

1. Adaptation and disadaptation rates determine the temporal response properties of sensory receptor cells. In chemoreception, temporal filter properties of receptor cells are poorly understood. We studied the time course of disadaptation in lobster antennular chemoreceptor cells by using in situ high-resolution stimulus measurement and extracellularly recorded spike responses. Fifteen receptor cells were each tested with two series (one at 10 microM, one at 100 microM) of three odor (hydroxyproline) pulses: a 200-ms test pulse, a 5-s adapting pulse, and a 200-ms probe pulse after time intervals ranging from 1 to 60 s. After complete adaptation by the adapting pulse, individual cells recovered at different rates. After 1 s, a third of the cells responded with a mean response of 3 spikes/cell, representing approximately 20% recovery. All cells fully recovered between 10 and 30 s. Mean full recovery was within 25 s, with a time constant of 14 s, independent of stimulus concentration.

Chemical signals in the marine environment: dispersal, detection, and temporal signal analysis.

Chemical signals connect most of life's processes, including interorganismal relationships. Detection of chemical signals involves not only recognition of a spectrum of unique compounds or mixtures of compounds but also their spatial and temporal distribution. Both spectral and temporal signal processing determine what is a signal and what is background noise. Each animal extracts its unique information from the chemical world and uniquely contributes to it. Lobsters have provided important information on temporal signal processing. Marine chemical signals can be measured with high spatio-temporal resolution giving us a novel view of the lobster's environment. Lobster chemoreceptor cells have flicker fusion frequencies of 4 Hz and can integrate stimuli over 200 ms, closely corresponding to odor sampling behavior with 4-Hz "sniffs." Using this information, spatial odor gradients can be determined from temporal analysis of odor patches typical of turbulent dispersal. Lobsters appear to use this information to locate odor sources. Lobster social behavior depends greatly on chemical signals. Urine carries important information for courtship, dominance, and individual recognition. A novel gland in the nephropore is strategically located to release its products into the urine. Urine, in turn, is injected into the gill current, which jets water 1-2 m ahead of the animal. Lobsters control three different currents that carry chemical signals to and from them. The study of odor dynamics has only just begun. It will be exciting to see how signal dispersal, receptor temporal tuning, neural processing, and animal behavior interact to enhance signals for communication and detection and to reduce signals for chemical camouflage.

Across-fiber patterns may contain a sensory code for stimulus intensity.

Various models for sensory coding have used statistical approaches based on the assumption that the stimulus intensity parameter is represented in the afferent neurons as mean firing frequency. In this paper we question the assumption that this is the only code for intensity. We show that in lobster olfactory receptors narrowly tuned to hydroxyproline, an across-fiber pattern (AFP) code distinguished more concentration levels over a 5 log step range than a response magnitude code and, unlike the latter, was unaffected by response summation time. AFP discrimination of stimulus intensity appears to be based on high inter-cell response variability and low intra-cell response variability.

Adaptation in chemoreceptor cells. I. Self-adapting backgrounds determine threshold and cause parallel shift of response function.

1. The self-adapting effects of chemical backgrounds on the response of primary chemoreceptor cells to superimposed stimuli were studied using lobster (Homarus americanus) NH4 receptor cells. 2. These receptors responded for several seconds to the onset of the backgrounds, and then returned to their initial level of spontaneous activity (usually zero). The strongest response always occurred only during the steepest concentration change; the response then decayed back to zero or to the earlier spontaneous firing level, while the background concentration was still rising, and remained silent during the entire time that the background was maintained constant (20-30 min) 3. Exposure to constant self-adapting backgrounds eliminated the response of NH4 receptor cells to stimuli of concentration lower than the background, and reduced the responses to all higher stimulus concentrations tested by a nearly equal amount. This resulted in a parallel shift of the stimulus-response function to the right along the abscissa. 4. Since the response threshold was completely re-set by adaptation to backgrounds, NH4 receptors seem to function mostly as detectors of relative rather than absolute stimulus intensity across their entire dynamic range: the response to a given stimulus-to-background ratio remained the same over 3 log step increases of background concentration. 5. As in other sensory modalities, a parallel shift of response functions appears to be an important property of chemoreceptor cells, allowing for this sensory system to function over a wider stimulus intensity range than the instantaneous dynamic range of individual receptor cells.

The role of narrowly tuned taste cell populations in lobster (Homarus americanus) feeding behavior.

A whole-animal behavioral assay was developed to measure responses to chemical stimulation of the walking leg (taste) receptors of lobsters. Lesions of only the taste receptors abolished the dactyl clasping response, a result demonstrating that such receptors are necessary to elicit this response. Then the stimulatory effectiveness of natural and synthetic mixtures was determined, particularly of 6 single compounds (glutamate, glutamine, NH4Cl, betaine, aspartate, and taurine) for which the legs have prominent, narrowly tuned receptor cell populations. The results showed that a synthetic mixture of the 22 principal amino acids and amines present in mussel tissue is as powerful a stimulus as either a homogenate of such tissue or its purified extract. Of the single compounds, only NH4Cl was stimulatory at the behavioral level; glutamate was not despite the fact that glutamate receptors are the predominant cell population known in lobster legs. Even a mixture of the 6 single compounds in their natural mixture ratio was not very stimulatory (it was even less stimulatory than the sum of the responses to each single compound), a result suggesting the occurrence of suppressive interactions. The complementary mixture, that is, the synthetic mixture without the 6 single compounds, was equally unstimulatory. It is unlikely that mixture suppression alone is responsible for the poor behavioral responses to single compounds such as glutamate, and to the partial mixtures that were tested. Full response to the more complex mixture of 22 compounds demonstrates that special mixture combinations can "override" mixture suppression. Such signal mixtures may represent the lobster leg's picture of food.

Chemoreception in the sea: adaptations of chemoreceptors and behaviour to aquatic stimulus conditions.

The chemical stimulus environment is pulsed in nature. Mixtures can identify an odour source with great specificity, and (hence) most chemical signals are mixtures, even when initial research may seem to indicate that single compounds are sufficient to release complete behaviour. Information currents are often necessary to receive chemical stimuli. Receptor cell physiology reflects the microenvironment in which the receptor organ operates. Receptor cells interface with the stimulus environment in such a way as to enhance signal-to-noise ratios and to cover the naturally occurring dynamic stimulus range. Different chemoreceptor organs are designed to perform a number of different behavioural tasks. This is equally true for aquatic species that sample one (aqueous) medium as for terrestrial species that sample air and aqueous media. Hence, most of these principles are not unique to aquatic chemoreception.

Narrow-spectrum chemoreceptor cells in the antennules of the American lobster, Homarus americanus.

The present study shows that smell (antennular) receptor cells are as narrowly tuned to single compounds as taste (leg) receptor cells in the lobster. Antennular receptors responded best to hydroxy-L-proline (57% of the 30 cells sampled) and taurine (24%). In the presence of 14 other compounds in equimolar concentrations, the hydroxy-L-proline and taurine receptors showed a suppressed response to their best stimulus. Other cells had best responses to ammonium chloride, betaine, L-glutamate or L-proline. The results have implications for molecular receptor processes and for the neural basis of feeding behavior.