Harold Koopowitz

The primitive brains of platyhelminthes

Abstract The study of polyclad flatworms promises new insight into the organization and role of the brain during the evolution of Metazoa. Behavioral, physiological and anatomical studies are revealing that much, if not most, of the basic neuronal machinery seen in complex vertebrate central nervous systems, as well as higher invertebrates, is already present in extant flatworms.

The ultrastructure of neuromuscular systems in Notoplana acticola, a free-living polyclad flatworm

SummaryNeuromuscular junctions in the marine polyclad flatworm, Notoplana acticola were studied with the electron microscope. Synapses were found between nerve endings and specialized extensions of the muscle cells. Characteristically these processes contained clear cytoplasm with a basal mitochondrion and numerous microtubules aligned parallel to the long axis of the extension. Sarcoplasmic diverticuli which contained the nucleus had granular cytoplasm with an assortment of membranes and organelles. We have proposed the term sarconeural junction to describe synapses between long sarcoplasmic extensions and nerve cells in flatworms as well as other animals.Tight junctions between adjacent contractile portions of muscle cells were common. As groups of cells appeared to be connected by tight junctions or shared common nerve terminals we conjectured that these formed discrete functional motor-units.

Primitive nervous systems. Control and recovery of feeding behavior in the polyclad flatworm, Notoplana acticola.

1. Feeding behavior in Notoplana acticola involves a series of local responses which are under central control. Behavior involves recognizing food, gripping with the tail and turning towards the prey. Food is then conveyed to the mouth and swallowed.2. Worms are still able to ingest food in the absence of the brain using local reflexes.3. Central control is abolished in areas posterior to cuts through the body wall.4. Functional recovery of behavior occurs in a minimum of 8 hr following closure of the wound.5. Anatomical fusion of cut nerves occurs and conduction of potentials can be demonstrated across the healed cut regions of major nerves.6. Recovery of function also occurs in approximately 36 to 48 hr if the cut is not allowed to heal suggesting that new or normally unused pathways can be recruited.

On the evolution of central nervous systems: Implications from polyclad turbellarian neurobiology

The nervous system of the polyclad turbellarian Notoplana acticola consists of a series of nerve plexuses and a central ganglion, the brain. The brain contains a variety of cell types including multipolar heteropolar and bipolar neurons. These cell types are rare in other invertebrate ganglia. Individual neurons also contain a variety of different ion channels. both spiking and nonspiking neurons are found. Some neurons are multimodal interneurons. Habituation appears to be a postsynaptic phenomenon. Sensitization and long-term potentiation have not been demonstrated. Polyclads appear to represent a stage in the evolution of centralized nervous systems where much of the neuronal machinery underlying behavior occurs in the peripheral nervous system and the brains main functions are the coordination and sequencing of peripherally placed reflexes. Even at this stage, however, the brain already contains cells that seem as advanced as those found in higher organisms.

Ionic bases of action potentials in identified flatworm neurones

SummaryThe ionic bases for generation of action potentials in three types of identified multimodal neurones of the brain ofNotoplana acticola, a polyclad flatworm, were studied. The action potentials were generated spontaneously, in response to water-borne vibrations, or by intracellularly injected current pulses. At least three components comprise the depolarizing excitable phase of the action potentials: (a) a rapidly inactivating TTXsensitive Na+ component (Fig. 2); (b) a Ca++ component that is unmasked by intracellular TEA+ (Figs. 4, 6, 7); (c) a TTX-resistant Na+ component (Fig. 8). Two K+ currents appear to account for the repolarization phase of the action potentials: (a) a rapid K+ current that is blocked by intracellular TEA+ (Figs. 4, 7, 8) and (b) a Ca++ -activated K+ conductance that is blocked by Ca++ and Ba++ (Fig. 6). Ionic mechanisms in the generation of action potentials in the central multimodal neurones ofNotoplana pharmacologically resemble those in higher metazoans.

PRIMITIVE NERVOUS SYSTEMS. A SENSORY NERVE-NET IN THE POLYCLAD FLATWORM NOTOPLANA ACTICOLA

(1). The response to mechanical stimuli in the polyclad flatworm, Notoplana acticola, is the initiation of ditaxic locomotion. The response to electrical stimuli is local contraction.(2). Animals will respond to mechanical stimuli with ditaxic movements even if a series of cuts are made so that the stimulus must be propagated around lesions as in a nerve-net.(3). Only the sensory side of the system is organized as a diffusely conducted system; motor control involves direct connections to the brain.(4). Sensory stimuli that convey information about the location of a stimulus on the body also require direct routes.

Behavior of the rhabdocoel flatworm Mesostoma ehrenbergii in prey capture and feeding

The prey-capture and feeding behavior of the rhabdocoel flatworm Mesostoma ehrenbergii (Focke, 1836) was analyzed using a variety of live and dead prey, including Daphnia, mosquito larvae, and tubifex annelids. Prey-capture behavior was broken down into its individual components. Mesostoma could accommodate to and change its behavior depending on the size and type of prey. Mechanical rather than chemical cues were effective in inducing prey-capture behavior. No evidence for a special chemical paralysis as suggested by other workers was found. The apparent paralysis observed in cladocera such as Daphnia and mosquito larvae was, in part a behavioral response of the prey in ‘playing possum’ and also in part due to immobilization of the prey by the flatworm with mucous threads.

Viability of Disa uniflora Berg (Orchidaceae) seeds under variable storage conditions: Is orchid gene-banking possible?

Earlier attempts to store orchid seeds for extended periods of time using conventional subfreezing methods have not been successful. In this paper we examine the storage biology of Disa uniflora seeds at a range of temperatures and under a variety of conditions. Viability of seeds increased with decreases in both temperature and moisture content. After 10 weeks, seeds stored at 6°C with desiccant had 90% of their original viability while those stored at 45°C retained only 40% of their viability. Seeds stored for ten weeks without desiccant at 6°C and 45°C retained 73% and 25% of the original viability, respectively. Seedling vigor followed similar patterns of decline with increasing storage times, temperatures and moisture contents. Over a course of twenty freeze-thaw cycles viability dropped to 88% of the control value. First- and second-order regressions were used to fit the storage time and viability data to extrapolate survival times at subfreezing temperatures. A first-order regression indicates limited storage capability under the temperature regimes used for agricultural seeds (−18°C), an observation that could explain earlier failures. Below −70°C, orchid seeds should retain 50% viability for a minimum of two centuries, thus allowing gene-banking.

Multimodal interneurones in the polyclad flatworm,Alloeoplana californica

SummaryTwo morphological types of interneurones were found in the brainof Alloeoplana californica (Figs. 1, 2). Both respond to water vibration and to light offset (Fig. 3). These responses are blocked by Mg++ or Cd++ (Fig. 4), and habituate to repetitive stimuli (Figs. 6, 10). Even when the light response is habituated, light offset will dishabituate the vibration response (Figs. 7, 10); no other regime tested produced dishabituation of either response. These neurones receive higher-order sensory input, and make subthreshold excitatory synapses on motor pathways; intracellular tetraethylammonium lengthens the time course of the spikes (Fig. 5), and each such spike elicits a contraction in the anterior margin of the animal. We believe that they form part of the neuronal circuitry underlying arousal.

Global climate change is confounding species conservation strategies

Most organisms face similar problems with respect to their conservation in the face of global climate change. Here, we examine probable effects of climate change on the hyperdiverse plant family Orchidaceae. In the 20th century, the major concerns for orchid conservation revolved around unsustainable harvest for the orchid trade and, more importantly, land conversion from natural ecosystems to those unable to support wild orchid populations. Land conversion included logging, fire regimes and forest conversions to agricultural systems. Although those forms of degradation continue, an additional suite of threats has emerged, fueled by global climate change. Global climate change involves more than responses of orchid populations to increases in ambient temperature. Increasing temperature induces secondary effects that can be more significant than simple changes in temperature. Among these new threats are extended and prolonged fire seasons, rising sea levels, increases in cyclonic storms, seasonal climate shifts, changes in orthographic wind dew point and increased drought. The long-term outlook for orchid biodiversity in the wild is dismal, as it is for many animal groups, and we need to start rethinking strategies for conservation in a rapidly changing world.