Kathy Poole

Effects of photoperiod on the circadian timing of pheromone response in male Trichoplusia ni: Relationship to the modulatory action of octopamine

Abstract The pheromone-mediated upwind flight of male cabbage looper moths was measured throughout the scotophase in a series of photoperiods, to determine the phase-relationship between the time of peak response to pheromone during the dark and the photoperiod cues. Male upwind flight and source contact was measured to a low dose of pheromone, one that would best reveal the presence of a temporal peak in male sensitivity. Results failed to support the idea that there is a narrow ‘window’ of maximal sensitivity during the dark that is phase-regulated by either the lights off, or lights on signal. Rather, there was a clear relationship between the lights off signal and the time (2–3h) to reach maximal response levels, regardless of the duration of the dark. Once the point of maximal response was reached, response levels displayed relatively constant levels until the very end of the dark period. Experiments involving shifts in the time of lights off or lights on also supported the idea that the lights off cue is critical for expression and timing of the response rhythm. Other experiments confirmed that a circadian oscillator is involved, evidenced by the rhythmic expression of male behavior mirroring the duration of expected dark periods in two photoperiods when males were tested in constant dark conditions. Also, constant dark and light conditions significantly affected the pattern of change in levels of octopamine observed in the brain in a light:dark regime. Of particular interest, the pattern of decrease in octopamine levels correlated well with the pattern of response to sex pheromone over the dark, supporting an earlier hypothesis that octopamine modulates neural pathways involved in perception of the odor signal, and that this action is triggered by the lights off cue. The results support the conclusion that the lights off photoperiod cue is a critical time in which a number of physiological process are initiated that will affect male response thresholds for a number of behaviors during the dark, including our previously demonstrated modulatory action of octopamine on the sensitivity of male moths to sex pheromone.

Studies on biogenic amines and their metabolites in nervous tissue and hemolymph of adult male cabbage looper moths—I. Quantitation of photoperiod changes

Abstract HPLC with electrochemical detection was used to quantify levels of 5-hydroxytryptamine, octopamine, dopamine, tryptophan, tyramine, tyrosine, 5-hydroxytryptophan, 5-hydroxyindolacetic acid, 3,4-dihydroxyphenylacetic acid, N -acetyl-5-hydroxytryptamine, N -acetyloctopamine, and N -acetyldopamine in optic lobes, corpora allata/corpora cardiaca compex, thoracic ganglia, supraesophageal-subesophageal ganglion complex (or brain) and hemolymph in individual male cabbage looper moths, Trichoplusia ni , at five times in the photoperiod. Levels of amines remained unchanged throughout the photophase, but decreased in some tissues during scotophase. In the hemolymph, levels of octopamine increased during the initial part of the dark period, whereas levels of dopamine remained unchanged, and 5-hydroxytryptamine was not detected. Levels of tryptophan, tyrosine, 5-hydroxytrytophan and tyramine did not change significantly over the photoperiod. Levels of N -acetyloctopamine, N -acetylserotonin and N -acetyldopamine in each tissue increased corresponding to the observed decreases in octopamine, 5-hydroxytryptamine, or dopamine. No evidence was found for catabolic activity involving monoamine oxidase. Within individuals, there was no correlation between decreased levels of octopamine and 5-hydroxytryptamine in the brain, or with levels of either of these amines in the thoracic ganglia. However, decreases in octopamine in the thoracic ganglia paralleded decreases in dopamine. The results are discussed with respect to the proposed modulatory action of amines on male moth locomotor activity and response to sex pheromone.

Circadian changes in melatonin in the nervous system and hemolymph of the cabbage looper moth, Trichoplusia ni

Quantitative levels of melatonin and 5-hydroxytryptamine were measured over the scotophase in the protocerebrum, subesophageal ganglion, optic lobes, thoracic ganglia, and hemolymph of adult male cabbage looper moths, Trichoplusia ni, using HPLC with electrochemical detection. Melatonin levels were very low (s < 1 pmol) or undetectable during the photophase, but increased in all tissues during the dark. Lowest mean levels in the dark were observed in the optic lobes (0.3 to 0.7 pmols). Maximal mean levels in the protocerebrum (5.2 pmols) occurred in the early part of the scotophase, but in all other tissues (2.8 in the subesophageal ganglion; 9.5 in thoracic ganglia) and hemolymph (18 pg/μl) maximal mean levels were observed later in the dark. Levels of 5-hydroxytryptamine in each tissue, in contrast, were higher than melatonin levels in the photophase, and in the protocerebrum and thoracic ganglia decreased during the dark, but in the optic lobes and subesophageal ganglion remained unchanged. Further, decreases in 5-hydroxytryptamine during the dark were significantly lower than the increased levels of melatonin, suggesting that active synthesis of 5-hydroxytryptamine was occurring. In a second experiment, when measured from individuals in three different photoperiods (6∶18, 12∶12, 18∶6 light∶dark) maximum mean melatonin levels in the brain (protocerebral and subesophageal ganglia) peaked within the first 1.5 h of the dark and remained at measurable levels for the duration of the dark. In a third experiment, levels of melatonin in the brain and thoracic ganglia displayed rhythmicity in continuous dark conditions but not in continuous light, when compared with profiles obtained in a normal light ∶ dark regime.

Studies on biogenic amines and metabolites in nervous tissue and hemolymph of male cabbage looper moths. III: Fate of injected octopamine, 5-hydroxytryptamine and dopamine

Abstract Adult male cabbage looper moths, Trichoplusia ni, were injected with two dosages of octopamine, or 5-hydroxytryptamine, or dopamine. The dosages were 1 and 10 μg, the latter a dosage that was previously shown to induce changes in nocturnal locomotor activity (5-hydroxytryptamine) and sensitivity to sex pheromone (octopamine). Injections were made into the hemolymph in the head capsule dorsal to the supraesophageal ganglion. Males were injected 1 hr prior to the onset of scotophase, and then brains + optic lobes, thoracic ganglia and hemolymph were analyzed at five time intervals over the following 6 hr. Levels of the three amines and their N-acetylated metabolites were quantified using HPLC with electrochemical detection. With the 1 μg dosage of the three amines, there was a significant increase in hemolymph values, but no changes in levels in the nervous system. With the 10 μg dosage, significant increases in each amine were found in the hemolymph, thoracic ganglia and brain + optic lobes. Levels of injected amines then rapidly decreased from hemolymph and nervous tissue. Within 2.5 hr following injections, levels of octopamine and dopamine in the brain + optic lobes and thoracic ganglia stabilized at twice the level in saline injected controls, 5-hydroxytryptamine levels were below control levels and hemolymph levels of each amine were not significantly different from controls. Decreases in amine levels were accompanied by significant increases in the N-acetylated form of each amine. In no instance did we observe a measurable peak for metabolites that would suggest the presence of MAO activity.

PHEROMONE-BLEND DISCRIMINATION BY EUROPEAN CORN BORER MOTHS WITH INTER-RACE AND INTER-SEX ANTENNAL TRANSPLANTS

Abstract Transplantation of larval antennal imaginal disks between the pheromone races of the European corn borer moth produced males and females of one race with male antennal phenotypes of the race using the opposite pheromone blend. All of the adults with transplanted antennal disks that exhibited a pheromone-mediated response in the flight tunnel did so with the pheromone blend of the recipients race, even though the respective males and females possessed male antennae of the opposite race. Our results support the conclusion that male antennal response type is not a determining factor in pheromone-blend discrimination in male moths.

Studies on biogenic amines and their metabolites in nervous tissue and hemolymph of male cabbage looper moths - II. Photoperiod changes relative to random locomotor activity and pheromone-response thresholds

Levels of octopamine, 5-hydroxytryptamine, dopamine and their metabolites were measured in brain, corpora cardiaca/corpora allata complex, thoracic ganglia and optic lobes from individual male cabbage looper moths, Trichoplusia ni, using HPLC with electrochemical detection. Measurements were made from individuals in late photophase and compared with levels from individuals at mid-scotophase. Individuals at mid-scotophase had been observed for locomotor activity throughout the dark period and then assayed in the sustained-flight tunnel with a low, threshold, dose of sex pheromone prior to dissection. Individuals were selected for dissection if they exhibited a complete upwind flight to the pheromone source, or if they did not respond at all. Mid-scotophase levels of octopamine in the brain and thoracic ganglia, dopamine in the thoracic ganglia, and 5-hydroxytryptamine in the brain and thoracic ganglia were all significantly lower than photophase levels. Scotophase levels of octopamine in individuals that responded to a low dose of pheromone were significantly lower than levels from males that did not respond. Levels of random locomotor activity over the scotophase were not correlated with the probability of a male responding to the threshold dose of pheromone. There also was no correlation between brain mid-scotophase levels of amines and the degree of locomotor activity exhibited, but there was a strong correlation between decreased levels of octopamine and dopamine in the thoracic ganglia and high levels of locomotor activity. Decreased levels of octopamine in the brain and thoracic ganglia over the dark period were correlated with increased levels of N-acetyloctopamine, suggesting that utilization of the amines occurs within the tissues over this time period. Mid-scotophase levels of N-acetyldopamine were significantly greater than photophase levels, suggesting increased metabolism of this amine as well. Our results indicate that changes in amine levels within specific tissues can be correlated with behaviors exhibited by individual insects. The results support the hypothesis that octopamine, dopamine and 5-hydroxytryptamine exert modulatory or transmitter roles in the central nervous system of the cabbage looper moth.

Plasticity in central olfactory processing and pheromone blend discrimination following interspecies antennal imaginal disc transplantation.

The antennal imaginal disc was transplanted between premetamorphic male larvae of two different Lepidopteran moth species. Following adult eclosion, electrophysiological recordings were made from 33 central olfactory neurons in the antennal lobes of both Helicoverpa zea donor to Heliothis virescens recipient (Z‐V) and reciprocal (V‐Z) transplants. Under the influence of sensory neuron input derived from the transplanted antennal imaginal disc, most antennal lobe projection neurons (29/33) were classified as belonging to physiological categories encountered previously in donor species males. Furthermore, when stained many of these neurons had dendritic arbors restricted to donor‐induced glomerular locations predicted by their physiology. However, some neurons with unexpected physiological profiles were also identified (4/33), but only in V‐Z transplants. These profiles help to explain why some V‐Z bilateral transplants were able to respond to both pheromone blends in flight tunnel bioassays, an unforeseen result counter to the assumption that a donor antenna develops a normal donor antennal olfactory receptor neuron complement. Stainings of several neurons in V‐Z transplant males also revealed unusual morphological features including multiglomerular dendritic arbors and “incorrect” glomerular locations. These results indicate a developmental plasticity in the final dendritic arborization pattern of central olfactory neurons, including an ability to colonize and integrate inputs across topographically novel donor glomeruli, different from those found in the normal recipient antennal lobe. J. Comp. Neurol. 491:141–156, 2005.

Transplant Antennae and Host Brain Interact to Shape Odor Perceptual Space in Male Moths.

Behavioral responses to odors rely first upon their accurate detection by peripheral sensory organs followed by subsequent processing within the brain’s olfactory system and higher centers. These processes allow the animal to form a unified impression of the odor environment and recognize combinations of odorants as single entities. To investigate how interactions between peripheral and central olfactory pathways shape odor perception, we transplanted antennal imaginal discs between larval males of two species of moth Heliothis virescens and Heliothis subflexa that utilize distinct pheromone blends. During metamorphic development olfactory receptor neurons originating from transplanted discs formed connections with host brain neurons within olfactory glomeruli of the adult antennal lobe. The normal antennal receptor repertoire exhibited by males of each species reflects the differences in the pheromone blends that these species employ. Behavioral assays of adult transplant males revealed high response levels to two odor blends that were dissimilar from those that attract normal males of either species. Neurophysiological analyses of peripheral receptor neurons and central olfactory neurons revealed that these behavioral responses were a result of: 1. the specificity of H. virescens donor olfactory receptor neurons for odorants unique to the donor pheromone blend and, 2. central odor recognition by the H. subflexa host brain, which typically requires peripheral receptor input across 3 distinct odor channels in order to elicit behavioral responses.