Multifunctional interneurons in behavioral circuits of the medicinal leech

Summary We are using the medicinal leech to study the neuronal basis of behavioral choice. In particular, we are recording from neurons, both extracellularly and intracellularly, in preparations that can express three different behaviors: the shortening reflex, crawling and swimming. We have found that particular mechanosensory neurons can elicit any of the behaviors, and that the movements are produced by just four sets of muscles, each controlled by a small number of motor neurons. Hence, there must be three different pattern-generating neuronal circuits, each of which can be activated by the same set of sensory neurons. We are studying how the choice is made among the three behaviors by recording, while one behavior is being performed, from neurons known to be involved in the initiation of the other two. We have found that an interneuron, cell 204, which is known to initiate and maintain swimming, is also active during shortening and crawling. The activity level in this interneuron can influence whether a mechanosensory stimulus produces shortening or swimming. The neuronal mechanisms by which this choice is normally effected awaits further elucidation of the circuits that elicit and generate shortening and crawling.     

A study on discharge features of interneuron in the hippocampal network

The firing of neurons in the hippocampal network has a close relationship with human memory and learning. In this paper, a numerical simulation of interneurons in the hippocampal network has been operated. It analyzes the influence of external stimulation on firing rhythms. The diversity of firing pattern, especially the circle of unit firing pattern, is shown by ISI.     

Analysis of synaptic integration using the laser photoinactivation technique

Summary Crickets (and many other insects) have two antenna-like appendages at the rear of their abdomen, each of which is covered with hundreds of filiform hairs resembling the bristles on a bottle brush. Deflection of these filiform hairs by wind currents activates mechanosensory neurons at the base of the hairs. The axons from these sensory neurons project into the terminal abdominal ganglion to form a topographic representation (or map) containing information about the direction, velocity and acceleration of wind currents around the animal. Information is extracted from this map by primary sensory interneurons that are also located within the terminal abdominal ganglion. In this paper, we review the progress that has been made toward understanding the mechanisms underlying directional sensitivity of an identified sensory interneuron in the cricket,Acheta domesticus. The response properties of the cell have been found to depend to a large extent upon the structure of its dendritic branches, which determines its synaptic connectivity with the sensory afferents in the map of wind space and the relative efficacy of its different synaptic inputs.     

Threshold and directional sensitivity of air-current-sensitive giant interneurons of a cricket

Summary Some of the directional characteristics of air-current-sensitive giant interneurons (GIs) of a cricket were investigated by using an exactly defined unidirectional air-current stimulus. In each GI, the velocity thresholds for the stimulating air-current in two different directions were measured, using various time-courses of the velocity change (frequency). Each GI showed identical velocity threshold curves, depending on the stimulus direction.     

Dogma and dreams: experimental lessons for epilepsy mechanism chasers

Epilepsy mechanism chasers face one major difficulty. Since we don’t know how the normal brain works, we can’t start to understand how the diseased brain fails. Most of today’s hypotheses are based on what we think about ‘normal’ brain function, which may lead to misconceptions, as will be developed here. Furthermore, since there are many different types of epilepsies, some mechanisms may only be relevant to some epilepsies. Here, I shall focus on temporal lobe epilepsy (TLE) the most common form of partial epilepsy in adults. TLE is often drug resistant, as are 30–40% of all forms of epilepsies. The failure of drug-treatments most likely reflects our lack of knowledge of the underlying mechanisms.Received 10 January 2005; received after revision 3 March 2005; accepted 23 March 2005     

面神经核神经纤维联系及功能

面神经核作为一个传统意义上的运动性神经核团,在咀嚼、吞咽、吸吮、表情和发音等方面发挥重要作用.近年来的研究表明,面神经核内除了有运动性神经元外,还有形态较小的非运动性神经元,它们可能参与机体呼吸等其他功能活动的调节.本文主要介绍面神经核的形态结构,纤维联系及功能,以便更深入、全面的认识面神经核.