Developmental neuroethology of insect metamorphosis.

During metamorphosis, the insect nervous system must change to accomodate alterations in body form and behavior. Studies primarily on moths have shown that these changes involve the death of some larval neurons, the conservation and remodeling of others, and the maturation of new, adult-specific cells. The motor and sensory sides of the adult CNS vary in this regard with the former being constructed primarily from remodeled larval components, whereas the latter arises primarily from new neurons. Neuronal remodeling has received considerable attention. Larval-specific dendritic fields are pruned back during the larval-pupal transition, followed by the sprouting of adult-specific dendrites. Simple reflexes have been used to correlate these neuronal changes with the acquisition or loss of particular behaviors. The loss of the proleg retraction reflex is associated with the regression of the dendritic arbors of the proleg motoneurons. By contrast, expansion of axon arbors of the gin-trap afferents is necessary, but not sufficient, for the assembly of the gin-trap reflex in the pupal stage. The stretch receptor reflex provides a third example in which a new dendritic field in the adult form of a neuron is associated with new adult-specific connections. Interestingly, these connections are masked by persisting larval contacts until the emergence of the adult moth. For the metamorphosis of more complex behavioral circuits, some, such as that for flight behavior, seem to be assembled de novo, whereas others, like that for adult ecdysis behavior, show conservation of some circuit elements from the larval stage but with the superposition of some adult-specific components.     

Hemispheric specialization for global and local processing: the effect of stimulus category.

Neuropsychological evidence indicates that the global aspect of complex visual scenes is preferentially processed by the right hemisphere, and local aspects are preferentially processed by the left hemisphere. Using letter-based hierarchical stimuli (Navon figures), we recently demonstrated, in a directed-attention task, lateralized neural activity (assessed by positron emission tomography) in the left prestriate cortex during local processing, and in the right prestriate cortex during global processing. Furthermore, temporal-parietal cortex was critically activated bilaterally in a divided-attention task that involved varying the number of target switches between local and global levels of letter-based hierarchical stimuli. Little is known about whether such stimulus categories influence such hemispheric lateralization. We now present data on brain activity, derived from positron emission tomography, in normal subjects scanned during either local or global processing of object-based hierarchical stimuli. We again observe attentional modulation of neural activity in prestriate cortex. There is now greater right-sided activation for local processing and greater left-sided activation for global processing, which is the opposite of that seen with letter-based stimuli. The results suggest that the relative differential hemispheric activations in the prestriate areas during global and local processing are modified by stimulus category.     

The neuroethology of C. elegans escape

Escape behaviors are crucial to survive predator encounters. Touch to the head of Caenorhabditis elegans induces an escape response where the animal rapidly backs away from the stimulus and suppresses foraging head movements. The coordination of head and body movements facilitates escape from predacious fungi that cohabitate with nematodes in organic debris. An appreciation of the natural habitat of laboratory organisms, like C. elegans, enables a comprehensive neuroethological analysis of behavior. In this review we discuss the neuronal mechanisms and the ecological significance of the C. elegans touch response.     

Parallel versus sequential processing of relational stimulus structures

Organisms are often faced with sets of stimuli bearing specifiable relationships to each other. Experimental data suggest that even animals not suspected of being particularly rational can solve problems involving consistent linear relationships. We examine the information processing required to cope with these and related stimulus structures from a theoretical point of view. We show that both a parallel processing neural network model and a serially processing Turing machine model require minimal complexities to process linear hierarchical structures. When dealing with other relational stimulus structures, the models need differing, greater minimal complexities. Siemann and Delius (1994) report experimental results indicating that both pigeons and humans appear to operate according to the parallel, neural network model we propose here. Further experiments likely to be diagnostic are proposed.     

History of developmental neuroethology: early contributions from ethology.

Ethology has its roots in the natural history of animal behavior. Questions of causation and function have historically been complementary, and each has rested upon a prior appreciation of the behavior of animals in nature. It is thus difficult to place a single time or place where ethology was born. Early evolutionary interests hinted at developmental constraints that continue to guide much research. It has only been relatively recently, however, that the explicit analysis of neural mechanisms in behavior has received the attention it deserves in developmental analyses. A mature developmental neuroethology will require a synthesis of the broad insights of ethology with refined neurobiological technique. Fundamental, however, is the primary focus upon behavior as it normally occurs.     

Modulation of the crayfish escape reflex--physiology and neuroethology

We review here factors that control the excitability of thegiant neuron-mediated tail-flip escape behavior in crayfish,focusing especially on recent findings concerning serotonergicmodulation. Serotonin can either facilitate or inhibit escapedepending on concentration and pattern of application. Low concentrationsfacilitate while high ones inhibit; however, if high concentrationsarise gradually they facilitate instead of inhibiting. The effectsof serotonin can also be altered by social experience, withapplication regimens that cause facilitation in social isolatescoming to produce inhibition after an extended period of livingas a subordinate. Attempts to understand both the possible physiologicalbasis of some of these complexities and their possible functionare discussed. Neuroethological investigations indicate thatgiant neuron-mediated escape is inhibited during the initialfights that establish social relationships and is facilitatedin their immediate aftermath. Once the relationship of a pairis well-established, the presence of the dominant tends to suppressgiant neuron-mediated escape (but not tail-flip escape mediatedby non-giant circuitry) in the subordinate, but the presenceof the subordinate has relatively little effect on the dominant.These patterns of modulation can be seen as consistent withthe known variations in serotonin's effect as a function ofconcentration and social experience and may provide a biologicalreason for these variations.     

Applications of video mixing and digital overlay to neuroethology

Neuroethological experiments often require video images of animal behavior and recordings of physiological data to be acquired simultaneously, synchronized with each other, stored, and analyzed together. The use of inexpensive multimedia computers offers new possibilities for mixing video images, analog voltages, and computer data, storing these combined signals to videotape, and extracting quantitative data for analysis. In this paper, we summarize methods for mixing images from multiple video cameras and a Macintosh computer display to facilitate manipulation of data generated during our neurophysiological and behavioral research. These technologies enhance accuracy, speed, and flexibility during experiments, and facilitate selecting and extracting quantitative data from the videotape for further analysis. Three applications are presented: (A) we used an analog video mixer to synchronize neurophysiological recordings with ongoing behaviors of freely moving rats; (B) we used a chroma keyed digital overlay to generate positional data for the rat's face during drinking behavior; and (C) we combined a computer model of a rat's head and whiskers with videos of exploratory behaviors to better track and quantify movements in three dimensions. Although the applications described here are specific to our neuroethological work, these methods will be useful to anyone wishing to combine the signals from multiple video sources into a single image or to extract series of positional or movement data from video frames without frame grabbing.     

Selective amplification of stimulus differences during categorical processing of speech

The brain's perceptual stimuli are constantly changing: some of these changes are treated as invariances and are suppressed, whereas others are selectively amplified, giving emphasis to the distinctions that matter most. The starkest form of such amplification is categorical perception. In speech, for example, a continuum of phonetic stimuli gets carved into perceptually distinct categories. We used fMRI to measure the degree to which this process of selective amplification takes place. The most categorically processing area was the left supramarginal gyrus: stimuli from different phonetic categories, when presented together in a contrasting pair, were neurally amplified more than two-fold. Low-level auditory cortical areas, however, showed comparatively little amplification of changes that crossed category boundaries. Selective amplification serves to emphasize key stimulus differences, thereby shaping perceptual categories. The approach presented here provides a quantitative way to measure the degree to which such processing is taking place.     

Song learning: the interface between behaviour and neuroethology

The high degree of developmental plasticity displayed by the songs of oscine birds makes them appropriate subjects for research on the etiology and neurobiology of vocal learning. Strong individual differences and learned local dialects are common. The readiness to acquire new songs appears to persist throughout life in some species and is restricted to relatively short sensitive periods in others. Learning can occur with remarkably few exposures to song. Mimicry of other species occurs but, given a choice, there is a tendency to favour conspecific songs. Evidence is presented for two kinds of vocal learning, one 'memory-based', the other 'action-based.' Subsong and 'plastic song' phases of motor development appear to be obligatory steps in the ontogeny of learned songs. A case is made that acquisition and production should be viewed as distinct phenomena with different physiological correlates. Research on behavioural development is closely associated with studies of the physiology of development. The two are mutually synergistic, and the synergism is well displayed in research on song learning in birds. This review of some of the characteristics of avian vocal learning as derived from behavioural studies, indicates lacunae in our knowledge about the ethology of song learning, and suggests how the comparative study of vocal development can pave the way for new insights into the underlying neurobiology.     

Fluidized bed design parameters affecting novel lactic Acid downstream processing.

Lactic acid purification was directly done from fermentation utilizing a fluidized bed column refilled with a strong anionic exchange resin. The purpose of this work was to study the influence of two important design parameters, bed-diameter (D) and bed-height (H), in the lactic acid binding and elution capacity of the matrix. By changing the settled bed height from 2.5 to 5 cm for each diameter of column analyzed it was possible to obtain an 50% increase in the binding capacity of the resin in all experiments. This fact was attributed to a higher contact time between the culture broth and the anionic resin produced by the increase of back mixing and lactic acid residence time.     

Structure requirements for anaerobe processing of azo compounds: Implications for prodrug design

This Letter generalizes the metabolism of the azo class of compounds by Clostridium perfringens, an anaerobe found in the human colon. A recently reported 5-aminosalicylic acid-based prednisolone prodrug was shown to release the drug when incubated with the bacteria, while the para-aminobenzoic acid (PABA) based analogue did not. Instead, it showed a new HPLC peak with a relatively close retention time to the parent which was identified by LCMS as the partially reduced hydrazine product. This Letter investigates azoreduction across a panel of substrates with varying degrees of electronic and steric similarity to the PABA-based compound. Azo compounds with an electron donating group on the azo-containing aromatic ring showed immediate disproportionation to their parent amines without any detection of hydrazine intermediates by HPLC. Compounds containing only electron withdrawing groups are partially and reversibly reduced to produce a stable detectable hydrazine. They do not disproportionate to their parent amines, but regenerate the parent azo compound. This incomplete reduction is relevant to the design of azo-based prodrugs and the toxicology of azo-based dyes.