Neuronal mechanisms of habituation and dishabituation of the gill-withdrawal reflex in Aplysia

The cellular mechanisms of habituation and dishabituation of the gill-withdrawal reflex in Aplysia were studied with an isolated abdominal ganglion connected to a piece of skin from the tactile receptive field of the reflex. By obtaining simultaneous intracellular recordings from both the sensory neurons and one of the main identified motor neurons, we have been able to reduce the reflex to its monosynaptic components. The monosynaptic excitatory postsynaptic potentials showed a profound low-frequency depression when repeatedly elicited and showed heterosynaptic facilitation after application of a strong stimulus to another pathway. Thus, both habituation and dishabituation can be explained in part and perhaps entirely by changes in the efficacy of specific excitatory synapses.     

Long-term habituation of a defensive withdrawal reflex in aplysia

A tactile stimulus to the siphon of Aplysia produces a defensive withdrawal reflex consisting of contraction of the siphon, the gill, and the mantle shelf. We studied long-term habituation of this reflex using two types of preparations, one focusing on the siphon component and the other on the gill component of the reflex. Siphon withdrawal, studied in unrestrained animals, showed marked habituation within a single ten-trial training session. Five daily training sessions produced habituaton that built up across days and lasted for at least 3 weeks. Furthermore, spaced training produced significantly longer lasting habituation than massed training. Gill withdrawal, studied in a restrained animal, also showed long-term retention of habituation. Since the neural circuitry of gill withdrawal is relatively well understood, it may be possible to study the cellular mechanisms underlying a long-term behavioral modification.     

Habituation and dishabituation: interactions between peripheral and central nervous systems in Aplysia

The withdrawal response of the isolated siphon of Aplysia habituates to a light stimulus and dishabituates to a tactile stimulus, and vice versa, with or without connections to the central nervous system. The peripheral nervous system can dishabituate or enhance the response mediated by the central nervous system and vice versa. Normally the adaptive siphon withdrawal response of the intact animal must be mediated by the integrated activity of the peripheral and central nervous systems.     

Differential classical conditioning of a defensive withdrawal reflex in Aplysia californica

The defensive siphon and gill withdrawal reflex of Aplysia is a simple reflex mediated by a well-defined neural circuit. This reflex exhibits classical conditioning when a weak tactile stimulus to the siphon is used as a conditioned stimulus and a strong shock to the tail is used as an unconditioned stimulus. The siphon withdrawal component of this reflex can be differentially conditioned when stimuli applied to two different sites on the mantle skin (the mantle shelf and the siphon) are used as discriminative stimuli. The differential conditioning can be acquired in a single trial, is retained for more than 24 hours, and increases in strength with increased trials. Differential conditioning can also be produced within the field of innervation of a single cluster of sensory neurons (the LE cluster) since two separate sites on the siphon skin can serve as discriminative stimuli. The finding that two independent afferent inputs that activate a common set of interneurons and motor neurons can be differentially conditioned restricts the possible cellular loci involved in the associative learning.     

Initiation of behavior by single neurons: the role of behavioral context

Flying crickets avoid sources of ultrasound, possibly echolocating bats, by making rapid steering movements that turn them away from the stimulus. Electrical stimulation of a single, identified sensory interneuron (Int-1) elicits avoidance steering; depressing its response to ultrasound abolishes avoidance steering. Int-1 is necessary and sufficient for this behavior but only while the cricket is in flight. Thus, the sufficiency of Int-1 for eliciting this behavior is contingent on behavioral context.     

Neuronal correlates of habituation and dishabituation of the gill-withdrawal reflex in Aplysia

We have examinived the nieural correlates of habittuatiotn atid dishabitiuation of tlhe gill-withdrwal reflex in Aplysia. We obtained intracelllular recordings from identified gill motor neurons in the abdominal ganglionz of a semi-intact preparation of Aplysia wlhile we simultaneously recorded behavior responises of the gill. Habituation and dishabituation were not due to peripheral changes in either the sensory receptors or the gill musculature butt were caused by changes in the amplitlude of the excitatory synaptic potentials produced at the gill motor neurons.     

A critical period for macromolecular synthesis in long-term heterosynaptic facilitation in Aplysia

Both long-term and short-term sensitization of the gill and siphon withdrawal reflex in Aplysia involve facilitation of the monosynaptic connections between the sensory and motor neurons. To analyze the relationship between these two forms of synaptic facilitation at the cellular and molecular level, this monosynaptic sensorimotor component of the gill-withdrawal reflex of Aplysia can be reconstituted in dissociated cell culture. Whereas one brief application of 1 microM serotonin produced short-term facilitation in the sensorimotor connection that lasted minutes, five applications over 1.5 hours resulted in long-term facilitation that lasted more than 24 hours. Inhibitors of protein synthesis or RNA synthesis selectively blocked long-term facilitation, but not short-term facilitation, indicating that long-term facilitation requires the expression of gene products not essential for short-term facilitation. Moreover, the inhibitors only blocked long-term facilitation when given during the serotonin applications; the inhibitors did not block the facilitation when given either before or after serotonin application. These results parallel those for behavioral performance in vertebrates and indicate that the critical time window characteristic of the requirement for macromolecular synthesis in long-term heterosynaptic facilitation is not a property of complex circuitry, but an intrinsic characteristic of specific nerve cells and synaptic connections involved in the long-term storage of information.     

Acquisition and retention of long-term habituation in Aplysia: correlation of behavioral and cellular processes

To examine the cellular mechanisms responsible for transition from a short-term to a long-term behavioral modification, a rapid training procedure was developed for producing long-term habituation of the defensive withdrawal of gill and siphon in Aplysia. Four ten-trial training sessions, with 1(1/2)-hour intersession intervals, produced habituation that was retained for more than 1 week. This 5-hour procedure could be applied to a test system in the isolated abdominal ganglion where the cellular changes accompanying the acquisition of long-term habituation can be examined. During acquisition, intracellular recordings were obtained from L7, a major gill and siphon motor neuron, and the pattern of stimulation used in the behavioral experiments was applied to an afferent nerve. Acquisition was associated with a progressive decrease in the complex excitatory synaptic potential produced in L7 by afferent nerve stimulation. When retention was tested 24 hours later, the synaptic decrement was still evident. Thus, a behaviorally meaningful stimulus sequence, consisting of only 40 patterned stimuli, leads to changes in synaptic effectiveness lasting one or more days in a neural pathway involved in short-term habituation of this reflex.     

Auditory frequency-following response: neural or artifact?

An electrical response which reproduces the waveform and frequency of the sound stimulus can be recorded from the central neural pathway for audition. Controversy has existed for some years over whether this frequency-following response (FFR) is neural or an artifact such as remote pickup of the cochlear microphonic or cross talk in the recording system. Two experiments resolve this issue by demonstrating that the frequency-following response depends upon functionally intact neural pathways. The frequency-following response, as well as auditory evoked potentials, is abolished by section of the eighth nerve; it is reversibly abolished by cooling of the cochlear nucleus.     

Long-term sensitization of a defensive withdrawal reflex in Aplysia

When a weak tactile stimulus is applied to the siphon of Aplysia californica, the animal withdraws the siphon between the parapodia. This defensive withdrawal reflex can be facilitated (sensitized) if the animal is previously given 4 days of training, consisting of four brief noxious stimuli each day. The sensitization of this reflex can last for up to 3 weeks after training and is mediated by the abdominal ganglion which also mediates long-term habituation. This preparation may provide a system for analyzing the neural mechanism of long-term behavioral modifications of complexity which is intermediate between habituation and associative learning.     

Habituation and dishabituation in the absence of a central nervous system

Habituation and dishabituation have been observed in a semi-intact Aplysia preparation in which the central nervous system is removed. The amplitude of withdrawal responses in the gill decreases in proportion to the rate of water drops applied (one drop per 0.5 minute to one drop per 2.5 minutes at 15 degrees C). The effects of habituation last for at least 2 hours. A dishabituated response is elicited by stopping the water drops or electrically stimulating the preparation. Furthermore, the gill contains nerve cell bodies, and habituation and dishabituation appear to be properties of these peripheral neurons.     

Action potential and contraction of Dionaea muscipula (Venus flytrap)

Observation of the action potential and contraction of the leaf of Dionaea muscipula Ellis revealed several interesting phenomena. Two successive stimuli are generally necessary to cause contraction. The first and ineffective stimulus is associated with slow depolarization. The second stimulus has much more rapid depolarization and initiates contraction.     

RseB影响溶藻弧菌感染花鲈的能力

为了研究Rse基因缺失对溶藻弧菌感染花鲈能力的影响，评估了花鲈感染后的LD50、定殖能力和免疫响应，结果显示，溶藻弧菌野生株LD50为2.013×105CFU/ml，RseB缺失溶藻弧菌LD50为5.526×105CFU/ml，RseB缺失溶藻弧菌毒力下降2.75倍；溶藻弧菌主要在花鲈的鳃部、肠道、皮肤定殖，RseB缺失溶藻弧菌定殖肠空泡化程度更低，鳃组织结构的损坏程度更低；分别对野生株与RseB缺失溶藻弧菌感染的花鲈头肾组织进行转录组测序，发现与免疫相关的差异表达基因一共有236个，其中包括了122个显著上调的免疫基因和114个显著下调的免疫基因，这些基因大部分显著富集在Th1和Th2细胞分化、B细胞受体信号通路、T细胞受体信号通路等特异性免疫通路上，部分基因显著富集在与细胞凋亡相关的通路以及与炎症相关的NF-kappa B信号通路中。综上结果表明RseB缺失溶藻弧菌能引起宿主细胞的免疫反应且毒力有所降低。     

关于模糊收缩列拟阵的研究

首先从普通拟阵、子拟阵、对偶拟阵和子集套出发,利用模糊拟阵的导出拟阵的序列分解和合成性质,生成了模糊收缩列拟阵和模糊约束列拟阵.再通过对某些模糊拟阵的导出拟阵序列取对偶,构造了模糊上对偶拟阵.然后,在研究模糊收缩列拟阵性质的基础上,找到了模糊拟阵是模糊收缩列拟阵的一个充要条件,同时,证明了所有模糊收缩列拟阵都是闭正规模糊拟阵.随后,证明了:所有准模糊图拟阵都有模糊上对偶拟阵,并且利用模糊收缩列拟阵和模糊上对偶拟阵的性质描述了闭模糊拟阵是准模糊图拟阵的充要条件.最后,证实了:在模糊拟阵中,模糊上对偶拟阵、模糊约束列拟阵和模糊收缩列拟阵之间的关联关系类似于在拟阵中,对偶拟阵、约束拟阵和收缩拟阵之间的关联关系.     

Neuronal controls of a behavioral response mediated by the abdominal ganglion of Aplysia

Tactile stimulation of the siphon and mantle shelf in Aplysia causes a characteristic withdrawal response of the external organs of the mantle cavity. A similar response also occurs spontaneously. Both responses are mediated by the abdominal ganglion and therefore provide an opportunity for correlating cellular functioning and behavior in a relatively simple and well-studied neuronal system. The withdrawal responses are controlled by five identified motor cells which receive two types of synaptic inputs. One set of excitatory connections, activated by tactile stimulation of the siphon and mantle shelf, mediates the defensive withdrawal reflex. A second set of connections is activated by a spontaneous burst of activity in a group of closely coupled interneurons which are excitatory to some of the motor cells and inhibitory to the others. This second set of connections mediates the spontaneous withdrawal response. These two inputs can therefore switch the same population of motor cells from a simple reflex to a more complex, internally organized response.     

Effect of deafferentation on a conditioned avoidance response

To determine whether peripheral afferent pathways could be bypassed in the performance of purposive movement, a group of monkeys was trained to avoid shock by flexing a forelimb in response to an auditory stimulus. The dorsal roots of the responding limb were then sectioned. Postoperatively it was found that the affected limb could be reconditioned.     

The latency of pathways containing the site of motor learning in the monkey vestibulo-ocular reflex

The vestibulo-ocular reflex helps to stabilize retinal images by generating smooth eye movements that are equal to and opposite each rotatory head movement. It is well known that the reflex undergoes adaptive plasticity or "motor learning" whenever there is persistent image motion during head turns: the resulting changes in the reflex occur gradually and help to restore image stability. A new approach makes it possible to identify the pathways containing the site of motor learning according to their total latency in response to natural vestibular stimuli. The fastest pathways required 14 milliseconds to initiate a vestibulo-ocular reflex, but the site of motor learning was in pathways having latencies of at least 19 milliseconds.     

Optical imaging of a tactile illusion in area 3b of the primary somatosensory cortex

In the tactile funneling illusion, the simultaneous presentation of brief stimuli at multiple points on the skin produces a single focal sensation at the center of the stimulus pattern even when no physical stimulus occurs at that site. Consistent with the funneling percept, we show with optical imaging in area 3b of the primary somatosensory cortex (SI) that simultaneous stimulation of two fingertips produces a single focal cortical activation between the single fingertip activation regions. Thus, in contrast to traditional views of the body map, topographic representation in the SI reflects the perceived rather than the physical location of peripheral stimulation.     

Response decrements in the cochlear nucleus of decerebrate cats during repeated acoustic stimulation

In the cochlear nucleus of decerebrate, paralyzed cats, multiple-unit responses to an acoustic stimulus showed significant decrements when the stimulus was repeatedly presented once every 5 seconds. These decrements developed in the absence of peripheral receptor adaptation. The responses recovered to the level prior to stimulation when stimulation was withheld for 5 to 10 minutes. Dishabituation by somatic stimulation of the forepaw, however, was less effective than in the intact cat. The continued development of response decrements after strychnine blockade of peripheral olivocochlear influences and central postsynaptic inhibition suggests a mechanism of decreased synaptic effectiveness, which has previously been postulated for neuronal habituation in brainstem and spinal cord.     

cAMP evokes long-term facilitation in Aplysia sensory neurons that requires new protein synthesis

Behavioral sensitization leads to both short- and long-term enhancement of synaptic transmission between the sensory and motor neurons of the gill-withdrawal reflex in Aplysia. Serotonin (5-HT), a transmitter important for short-term sensitization, can evoke long-term enhancement of synaptic strength detected 1 day later. Because 5-HT mediates short-term facilitation through adenosine 3',5'-monophosphate (cAMP)-dependent protein phosphorylation, the role of cAMP in the long-term modulation of this identified synapse was examined. Like 5-HT, cAMP can also evoke long-term facilitation lasting 24 hours. Unlike the short-term change, the long-lasting change is blocked by anisomycin, a reversible inhibitor of protein synthesis, and therefore must involve the synthesis of gene products not required for the short-term change.