Ann Jane Tierney

Structure and function of invertebrate 5-HT receptors: a review.

Over the last decade, knowledge of invertebrate serotonin receptors has expanded greatly. The first 5-HT receptor from Drosophila was cloned 10 years ago, and subsequently, 11 additional receptor genes have been cloned from Drosophila, molluscs (Lymnaea and Aplysia) and nematodes (Caenorhabditis and Ascaris). Information has also accumulated from physiological and biochemical studies that have used vertebrate serotonergic ligands to characterize endogenous invertebrate receptors. Although the endogenous receptors are often classified according to mammalian-based categories, in many cases the pharmacological properties of vertebrate and invertebrate receptors differ significantly and the actual identity of the latter is questionable. By providing information on the gene structure and amino acid sequence, molecular cloning studies offer a more definitive way to identify and classify invertebrate 5-HT receptors. This review summarizes information on the pharmacological and transductional properties of cloned invertebrate 5-HT receptors, and considers recent studies of endogenous receptors in the light of this new data.

The evolution of learned and innate behavior: contributions from genetics and neurobiology to a theory of behavioral evolution

In recent years, ethologists and psychologists have become increasingly interested in the evolution of the ability to learn and in the relationship between innate and learned behavior. However, recent discussions of behavioral evolution have not adequately incorporated contemporary knowledge of nervous system development and structure. Most discussions are based on the following assumptions: (1) That innate behaviors are programmed by specific genes; (2) that learning requires a larger, more flexible nervous system than does innate behavior; and (3) that the ability to learn is phylogenetically more recent than innate behavior. This paper reviews information about nervous system development and the neurobiology of plasticity and learning that questions the validity of these assumptions. It is hypothesized that behavioral flexibility is phylogenetically primitive and that learned behavioral adaptations may commonly precede innate forms of the same behaviors. The role of genetic assimilation in behavioral evolution is discussed.

Effects of serotonin and serotonin analogs on posture and agonistic behavior in crayfish.

Abstract. Exogenous serotonin has been shown to induce an elevated, flexed posture in crustaceans and has also been hypothesized to enhance aggressive behavior. We conducted three experiments to further investigate the effects of serotonin and serotonin analogs on posture and agonistic behavior in the crayfish Procambarus clarkii. In the first experiment, we recorded behavioral responses to five different concentrations of serotonin injected into the ventral hemolymph sinus. The amine elicited a series of behaviors including the characteristic high, flexed posture, but none were clearly associated with aggression. In our second experiment, we tested serotonin and four serotonin receptor agonists [1-(3-chlorophenyl)piperazine dihydrochloride, 2-methyl-5-hydroxytryptamine maleate, 5-carboxamidotryptamine maleate and α-methyl-5-hydroxytryptamine maleate] and measured the ability of each agonist to mimic the actions of the amine. High concentrations of 1-(3-chlorophenyl)piperazine dihydrochloride most closely mimicked the actions of serotonin; 5-carboxamidotryptamine maleate induced a high stance, but did not otherwise induce effects similar to serotonin. In our third experiment, we conducted an analysis of fighting behavior between pairs of crayfish that had received injections of control saline, serotonin, or 5-carboxamidotryptamine maleate. Serotonin generally reduced the level of aggression between opponents, whereas 5-carboxamidotryptamine maleate enhanced the performance of several agonistic behaviors.

Chemical Communication in the Reproductive Isolation of the Crayfishes Orconectes Propinquus and Orconectes Virilis (Decapoda, Cambaridae)

ABSTRACT Laboratory experiments demonstrate that chemical cues are important in species recognition in the crayfishes Orconectes propinquus and Orconectes virilis. Males and females of both species can perceive the chemicals released from their own and the other species and are attracted only to the chemicals of conspecifics of the opposite sex.

Behavioral responses of crayfish (Orconectes virilis andOrconectes rusticus) to chemical feeding stimulants.

We conducted two experiments to assess how chemical stimuli affect feeding behavior, grooming, and walking in the crayfishesOrconectes virilis andOrconectes rusticus. In the first experiment,O. virilis was tested with 29 amino acids; in the second experiment,0. rusticus was tested with 12 amino acids, 13 additional single compounds, and two six-compound mixtures. InO. virilis, the following amino acids, in order of potency, elicited feeding movements:l-isoleucine, glycine, hydroxy-l-proline,l-glutamate,l-valine, and B-alanine. Grooming increased in response tol-phenylalanine,l-tryptophan,l-tyrosine,l-leucine,l-methionine, and D-aspartate. InO. rusticus, both mixtures and the following single compounds, in order of potency, elicited feeding movements: cellobiose, sucrose, glycine, maltose, glycogen, nicotinic acid methyl ester, putrescine, andl-glutamate. Grooming increased in response to putrescine only, and walking increased in response to glycogen only. The responsiveness of these crayfishes to a wide variety of chemicals may reflect the omnivorous foraging habits of these crustaceans.

Evolutionary implications of neural circuit structure and function.

Recent physiological studies of neural circuits have shown that single circuits can produce more than one behavior, and that different circuits can combine to produce a single, new behavior. Because neural circuits are multifunctional and highly integrated, they are expected to evolve relatively slowly. Comparative studies of invertebrates and vertebrates have confirmed this expectation, as circuit structure and motor pattern output are generally conserved relative to peripheral morphological structures. These findings suggest that behavioral evolution may also be relatively conservative. Information about neural circuit structure and function also has implications for our understanding of morphological and brain evolution. In particular, the conserved nature of neural circuits may contribute to evolutionary change in peripheral structures, and to the gradual increase in nervous system size over evolutionary time.

Serotonin-like immunoreactivity in the stomatogastric nervous systems of crayfishes from four genera.

Abstract We used whole-mount immunocytochemistry to characterize the distribution of serotonin in the stomatogastric nervous systems of seven species of crayfish representing three genera from the family Cambaridae (Orconectes, Cambarus, and Procambarus) and one from the family Astacidae (Pacifastacus). In all species, we observed serotonin-like immunoreactivity in four gastropyloric receptor (GPR) neurons located in the lateral ventricular nerves, with one pair of neurons in each nerve. As in other crustaceans, the GPR axons project to the stomatogastric ganglion and to the bilateral commissural ganglia. In three crayfishes, we observed the GPR axons crossing the commissural ganglia, and extending toward the thoracic nervous system. This feature was most clearly and consistently seen in Pacifastacusleniusculus. The number of stained somata in the commissural ganglia varied among crayfish species from two (in Procambarusclarkii) to five (in Pacifastacusleniusculus). The largest soma (the L cell) displayed both serotonin- and tyrosine hydroxylase-like immunoreactivity in all species, suggesting that serotonin and dopamine are cotransmitters in this cell. The inferior esophageal nerve and a branch of this nerve (the inner labral nerve) contained several axons with serotonin-like immunoreactivity. These axons were clearly present in only one species (Procambarusclarkii). Serotonin acts as a neuromodulator of rhythms produced by circuits in the crab and lobster stomatogastric ganglion, and is likely to play a similar role in crayfish. Differences are apparent in the distribution of serotonin among crayfish species and between crayfish and other crustaceans, and could result in differences in the physiological action of this modulator.

Amino acid chemoreception effects of ph on receptors and stimuli

A current model of amino acid chemoreception has generated the idea that pH affects the efficiency of stimulus-receptor binding by altering the charge distribution on stimulus molecules. The model suggests that amino acids are maximally stimulatory near their isoelectric points. We point out that, within a broad range of pH values, changes in stimulant amino acids cannot account for altered chemoresponsiveness. We suggest instead that pH-induced changes in chemoreception are a result of changes in charge distribution on the protein receptor.

Egas Moniz and the Origins of Psychosurgery: A Review Commemorating the 50th Anniversary of Moniz's Nobel Prize

Modern psychosurgery began in 1936 with the work of the Portuguese neurologist, Egas Moniz, who attempted to treat the symptoms of mental illness by severing neural tracts in the frontal lobes. This procedure eventually became widespread and applied to thousands of institutionalized, psychotic patients in the United States and other countries. Despite serious side effects associated with psychosurgery, the apparent importance and validity of the treatment was recognized in 1949 when Moniz received the Nobel Prize for his innovation. Psychosurgery was largely replaced by anti-psychotic drugs in the mid-1950s, and the procedure and its practitioners rapidly fell into disrepute. This article reviews Monizs career, the factors that led up to his first clinical trials of frontal lobe surgery, and the circumstances that allowed psychosurgery to flourish in the 1940s, eventually leading to Monizs Nobel Prize.

Effects of acidification on the behavioral response of crayfishes (Orconectes virilis and Procambarus acutus) to chemical stimuli

Abstract We conducted laboratory experiments to determine how crayfish respond to differing concentrations of food-relevant chemicals under low pH conditions. At pH 5.8 the crayfishes Orconectes virilis and Procambarus acutus responded to an amino acid mixture with antennule and feeding movements. Response intensity increased with stimulus intensity. These responses were significantly reduced in both species when the animals were held for 48 h in acidified (pH 4.5 and 3.5) water; the lower the pH, the lower the responsiveness. General activity and amount of food actually consumed, however, were not affected by acidification. O. virilis was generally more sensitive to acidification than P. acutus. These results indicate that acid exposure may interfere specifically and quantitatively with chemoreceptive processes in aquatic crustaceans.