RFamide Peptides in the Leech, Hirudo medicinalis

RFamide peptides have been localized to a number of neuronsof the CNS of the leech, Hirudo medicinalis, using immunocytochemicaltechniques. The majority of this immunoreactivity appears tobe due to the peptide FMRFamide. Most of the identified RFamideimmunoreactive cells are cholinergic motor neurons, though someare interneurons. Superfused FMRFamide is active on the targetsof these identified neurons; in a few well studied cases, ithas been possible to show that FMRFamide mimics a specific physiologicalaction of an identified neuron on its target. In the leech as in other phyla where they occur, RFamide peptidesare widely distributed in neurons, and are neuromodulators withdiverse physiological effects.     

Type specimens in the Vidal Herbarium at the Real Jardín Botánico,Madrid

Ninety eight type specimens collected by Sebastián Vidal in the Philippines, and kept at the Real Jardín Botánico Herbarium, Madrid (MA), are compiled. Most of these specimens are types of Vidal's names. Only a few are names of other authors (Hoogland, Merrill, and Rolfe). A list of specimens, as well as the indicatio locotypica and number in MA, is presented. © 2009 The Linnean Society of London, Botanical Journal of the Linnean Society, 2009, 159 , 292–299.     

Modeling a Neural Oscillator that Paces Heartbeat in the Medicinal Leech

SYNOPSIS. Heartbeat in the medicinal leech is paced by a neuraloscillator comprising two elemental oscillators whose activityis coordinated intersegmental coordinating fibers. The elementaloscillators each consist of a bilateral pair of heart interneuronslinked by reciprocal inhibitory synapses. The activity cycleof each elemental oscillator consists of alternating burstsof action potentials (plateau/burst phase) and periods inhibition(inactive phase). Oscillation ensues in the reciprocally inhibitorypairs because each neuron is able to escape from the inhibitionits contralateral partner and thus move on to the plateau/burstphase. We have identified and described membrane currents thatcontribute to oscillation and studied graded synaptic transmissionbetween the neurons, using discontinuous current clamp and switchingsingle electrode voltage clamp techniques. A hyperpolarization-activatedinward current, Ih, plays a major role in escape from inhibition,and Ca²⁺ currents produce plateau potentials that support burstformation and mediate graded synaptic transmission. To consolidate our knowledge and guide future research, we haveconstructed a first generation computer model of a neural oscillatorbased on reciprocal inhibition, using Hodgkin-Huxley equationsand a synaptic transfer model, derived from our biophysicalstudies, with Nodus software (De Schutter, 1989). This modelhas confirmed an important role for I_h in sustaining oscillationand has implicated a similarly important role for outward currents(particularly I_A), which remain to be studied. Neural oscillatorsbased on reciprocal inhibition appear to be ubiquitous, andour studies, biophysical and computational, provide insightsinto how they may operate.     

Neural Generation of the Peristaltic and Non-Peristaltic Heartbeat Coordination Modes in the Leech, Hirudo Medicinalis

The bilateral paired heart tubes of the leech Hirudo medicinalisare controlled, via excitatory synapses, by a set of bilaterallypaired segmental heart motor neurons (HE cells) which are inturn controlled, via inhibitory synapses, by a set of bilaterallypaired segmental heart interneurons (HN cells). The HE cellsproduce rhythmic impulse bursts because their inherent steadydischarge is periodically inhibited by the HN cells, most ofwhich produce impulse bursts endogenously. The known synapticinteractions among the HN cells and HE cells can account wellfor the observed behavior of the hearts. The HE cells are coordinatedby the HN cells such that the segmental heart tube sectionson one side constrict in a caudorostral sequence (peristalsis),while the segmental heart tube sections on the other side constrictnearly synchronously (non-peristalsis). This difference in thecoordination modes of the two hearts is not permanent; reciprocalcoordination mode transitions occur every 10–50 heartbeatcycles. Only one member of HN(5) cell pair (the HN cells ofthe fifth segmental ganglion) is rhythmically active at a time,the other being completely inactive. By coordinating the frontand rear HN cells the active HN(5) cell produces non-peristalsisipsilaterally and peristalsis contralaterally. Reciprocal changesin the activity-inactivity pattern of the HN(5) cell pair areresponsible for the reciprocal changes in the coordination mode.     

Stimulation of Growth of Peppermint (Mentha piperita) by Phosfon, a Growth Retardant

The shoot growth and fresh weight of Mentha piperita grown in soil were stimulated at concentrations of 1.26 × 10^?5M to 7.77 × 10^?4M phosfon (2,4-dichlorobenzyl tributyl phosphonium chloride) while higher concentrations resulted in retardation of growth. Concentrations of 6.30 × 10^?7M to 3.78 × 10^?5M caused retardation of growth in mineral nutrient solution, and even death at the highest concentrations. However, when the M. piperita plants were grown in mineral nutrient solutions at concentrations of phosfon which had been sequentially lowered from 2.52 × 10^?8M to 2.52 × 10^?12M, the shoot growth and fresh weight were stimulated as in the case of plants grown in phosfon treated soil.