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Query: UMLS:C0011570 (depression)
 172,036 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

1. Habituation of the lateral giant fibre escape response in the crayfish to repetitive tactile stimuli is believed to result from homosynaptic depression at the first synapse of the reflex, between tactile afferents and interneurones. Normally, habituation of escape responses to repeated innocuous stimuli is presumed to be adaptive. Experiments reported here were undertaken to determine whether habituation would occur under circumstances when it would presumably be maladaptive - in particular, when tactile receptors are stimulated by an animal's own tail-flip movements.2. Experiments were carried out on the crayfish isolated abdominal nerve cord, which contains the lateral giant reflex pathway.3. Compound e.p.s.p.s elicited in the lateral giant by electrical stimulation of tactile afferents decline by from 25 to 36% over a series of eleven trials at 1/5 sec (control series).4. To determine whether such a decline would occur when sensory afferents are stimulated during a ;tail-flip', stimuli were given as in the control series but each stimulus occurred 20 msec after direct electrical stimulation of a medial giant or lateral giant escape-command fibre at which time tail flexion movements of an intact animal would be in progress. Under these conditions% e.p.s.p. decline over 11 trials at 1/5 sec was only 16-45% of that occurring on the control series.5. This protective effect starts at about 10 msec after escape command neurone firing, is maximal at 20 msec, and thereafter declines, remaining weakly detectable at 100 msec. This time course is commensurate with that required for execution of a tail-flip movement. Thus, sensory afferent-to-lateral giant transmission is protected from depression if stimuli occur when a tail-flip movement is or should be occurring.6. Giant fibre spikes do not superimpose facilitation upon a depressed reflex pathway, nor accelerate rate of recovery from depression; rather, protection is attributable to actual prevention of development of the depressed state.7. Protection was also examined at the first synapse of the reflex, where the depression responsible for habituation is believed to occur, by recording intracellularly in the largest of the first-order interneurones (interneurone A) of the pathway. In absence of protection, ten stimuli presented at 1/4 sec caused a mean decline of 32% in the e.p.s.p. in interneurone A. When such stimuli followed directly evoked escape command neurone firing by 20 msec this decline was reduced by 59-100%.8. We suggest that protection serves to prevent crayfish from habituating to stimuli produced by their own tail-flip movements.
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PMID:Protection from habituation of the crayfish lateral giant fibre escape response. 20 Jul 34

Medically ill patients who show signs of depression may have problems with traditional antidepressant therapy, because of the side effect profile and the delayed onset of action of these agents. Psychostimulants such as methylphenidate and dextroamphetamine are another treatment option. The beneficial effects of these drugs are usually noted within 36 hours, and drug habituation is generally not a problem. The primary obstacle to the use of these agents for depression in medically ill patients is the hesitancy of physicians to prescribe them.
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PMID:Psychostimulants for depression in the medically ill. 185 97

The authors reviewed the efficacy and safety of stimulant drugs in the treatment of depression. Although uncontrolled studies were generally positive, the 10 placebo-controlled studies of stimulant drugs in primary depression, with one exception, indicated little advantage of drug over placebo. Although several of these studies were methodologically unsophisticated, they were comparable with and performed during the same period as studies establishing the efficacy of imipramine. Controlled studies of stimulants in apathetic or depressed geriatric patients were more likely to be positive, but outcome frequently consisted of partial improvement. Studies in medically ill patients with depression were promising but uncontrolled. Side effects have not been severe, and these drugs may pose less of a risk than tricyclics in the medically ill or elderly. Habituation is suggested, but there are no placebo-controlled studies to confirm this. In short, the stimulant drugs do not appear to be as effective as the conventional antidepressants in primary depression, but may be of value in refractory cases or in special cases, such as those involving the medically ill patient. Placebo-controlled trials are needed to explore these questions.
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PMID:Stimulants in the treatment of depression: a critical overview. 256 30

We have explored the morphological basis of the synaptic depression that underlies short-term habituation of the gill-withdrawal reflex in Aplysia by examining the fine structure of the presynaptic terminals of identified sensory neurons--a critical site of plasticity for the biochemical and biophysical changes that underlie this elementary form of learning. The structure of sensory neuron synapses from control (unstimulated) cells was compared with that of sensory neuron synapses from cells in which synaptic transmission had been depressed by repeated activation. We focused our analysis, as we had in an earlier study of long-term memory (Bailey and Chen, 1983), on the morphology of active zones at sensory neuron synapses. We found that both the incidence and size of serially reconstructed active zones were not changed in cells exposed to short-term habituation. This contrasts sharply with the reduction in both the frequency and surface area of sensory neuron active zones that accompanies long-term habituation, and suggests that modulation of active zone number and size may be an anatomical correlate that lies in the long-term domain. A quantitative analysis of the relationship between the active zone and nearby vesicle populations revealed a possible morphological substrate for the homosynaptic depression that underlies short-term habituation. Habituation leads to a depletion of synaptic vesicles immediately adjacent to the active zone. The ratio of this readily releasable pool of vesicles to the total population of vesicles associated with the active zone is 28% for control terminals, but only 11.5% for habituated terminals.(ABSTRACT TRUNCATED AT 250 WORDS)
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PMID:Morphological basis of short-term habituation in Aplysia. 324 36

Before treatment 49 obsessive-compulsive (o-c) ritualizers were presented with two series of brief stimuli--15,100db tones (brief neutral) and 15 presentations of a ritual-evoking object (brief aversive). Habituation of skin conductance (SC) responses to the tones was reduced compared with that previously found in normal subjects. Neither habituation rates to tones nor aversive stimuli were related to coexisting anxiety or depression or to the severity of o-c symptoms. The increased arousal induced by the aversive stimuli was sustained, that induced by the tones was short-lived and SC level and subjective anxiety had returned to resting levels by the end of the tone series. Concordance between SC activity and subjective anxiety was much greater during and after the presentations of ritual evoking stimuli than of tones. There were few correlations between SC and clinical measures, though patients who strongly resisted and were able to control their compulsive urges were more aroused.
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PMID:Relationship of skin conductance activity to clinical features in obsessive-compulsive ritualizers. 343 65

Habituation of acoustically evoked heart rate responses and retention of this habituation was studied in functionally decorticate rats. An improved technique to induce cortical spreading depression (CSD) resulted in a pronounced and continuous depression of electroencephalographic activity. In Experiment 1, short-term habituation (STH) was demonstrated in decorticate rats and surgical controls; long-term habituation (LTH, 24 hr) occurred only in intact animals. In Experiment 2, only CSD groups were used. As in the first experiment, STH but not LTH was obtained under CSD. However, there was clear evidence that habituation could be retained subcortically for 30 min. It is concluded that the rat's cortex is not necessary for habituation of acoustically evoked heart rate responses and retention of this habituation over a moderately long interval. However, the results suggest that the cortex is involved in LTH and that the neuronal substrates of STH and LTH are, in significant part, different.
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PMID:Habituation of heart rate in functionally decorticate rats. 384 25

Habituation, one of the simplest behavioral paradigms for studying memory, has recently been examined on the cellular level in the gill-withdrawal reflex in the mollusc Aplysia and in the escape response in cray-fish. In both cases short-term habituation involved a decrease in excitatory synaptic transmission at the synapses between the sensory neurons and their central target cells. To analyze the mechanisms of the synaptic depression in Aplysia, we applied a quantal analysis to synaptic transmission between the sensory and motor neurons of the gill-withdrawal reflex. Our results indicate that short-term habituation results from a presynaptic mechanism: a decrease in the number of transmitter quanta released per impulse. The sensitivity of the postsynaptic receptor remains unaltered.
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PMID:A quantal analysis of the synaptic depression underlying habituation of the gill-withdrawal reflex in Aplysia. 437 38

Habituation of the Aplysia gill-withdrawal reflex (and siphon-withdrawal reflex) has been attributed to low-frequency homosynaptic depression at central sensory-motor synapses. The recent demonstration that transfer of habituation between stimulation sites occurs in this model system has prompted the hypothesis that heterosynaptic inhibitory pathways also play a role in the mediation of habituation behavior. To test this hypothesis, the sites and mechanisms of neural plasticity which underlie transfer of habituation in Aplysia were examined. Transfer of habituation is a reduction in the reflex evoked at one stimulation site (siphon) due to repeated presentation of a stimulus to a second site (gill). Centrally mediated transfer of habituation, measured in a preparation lacking the siphon-gill peripheral nervous system (PNS), was associated with a reduced excitatory response in central motor neurons. Repeated tactile stimulation of the gill did not attenuate the gill response evoked by electrical stimulation of the branchial nerve nor the mechanoreceptor response recorded in LE sensory neurons. In contrast, repeated stimulation of siphon or gill at a site which was "off" the sensory field of a specific mechanoreceptor led to a diminution in synaptic transmission between that sensory neuron and its followers (motor neurons and inter-neurons). These data demonstrate that centrally mediated transfer of habituation results from heterosynaptic modulation of synaptic transmission at the sensory-motor (and sensory-interneuron) synapses. Therefore, habituation behavior in Aplysia is mediated through the conjoint action of homosynaptic and heterosynaptic inhibitory processes.
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PMID:Transfer of habituation in Aplysia: contribution of heterosynaptic pathways in habituation of the gill-withdrawal reflex. 609 42

The tentacle withdrawal reflex of the snail Helix aspersa exhibits a complex combination of habituation and sensitization consistent with the dual-process theory of plasticity. Habituation, sensitization, or a combination of both were elicited by varying stimulation parameters and lesion condition. Analysis of response plasticity shows that the late phase of the response is selectively enhanced by sensitization, whereas all phases are decreased by habituation. Previous data have shown that tentacle withdrawal is mediated conjointly by parallel monosynaptic and polysynaptic pathways. The former mediates the early phase, whereas the latter mediates the late phase of the response. Plastic loci were identified by stimulating and recording at different points within the neural circuit, in combination with selective lesions. Results indicate that depression occurs at an upstream locus, before circuit divergence, and is therefore expressed in all pathways, whereas facilitation requires downstream facilitatory neurons and is selectively expressed in polysynaptic pathways. Differential expression of plasticity between pathways helps explain the behavioral manifestation of depression and facilitation. A simple mathematical model is used to show how serial positioning of depression and facilitation can explain the kinetics of dual-process learning. These results illustrate how the position of cellular plasticity in the network affects behavioral change and how forms of plasticity can interact to determine the kinetics of the net changes.
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PMID:Sites of plasticity in the neural circuit mediating tentacle withdrawal in the snail Helix aspersa: implications for behavioral change and learning kinetics. 1050 7

Prenatal development of the primary visual cortex leads to simple cells with spatially distinct and oriented ON and OFF subregions. These simple cells are organized into spatial maps of orientation and ocular dominance that exhibit singularities, fractures, and linear zones. On a finer spatial scale, simple cells occur that are sensitive to similar orientations but opposite contrast polarities, and exhibit both even-symmetric and odd-symmetric receptive fields. Pooling of outputs from oppositely polarized simple cells leads to complex cells that respond to both contrast polarities. A neural network model is described which simulates how simple and complex cells self-organize starting from unsegregated and unoriented geniculocortical inputs during prenatal development. Neighboring simple cells that are sensitive to opposite contrast polarities develop from a combination of spatially short-range inhibition and high-gain recurrent habituative excitation between cells that obey membrane equations. Habituation, or depression, of synapses controls reset of cell activations both through enhanced ON responses and OFF antagonistic rebounds. Orientation and ocular dominance maps form when high-gain medium-range recurrent excitation and long-range inhibition interact with the short-range mechanisms. The resulting structure clarifies how simple and complex cells contribute to perceptual processes such as texture segregation and perceptual grouping.
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PMID:A neural network model for the development of simple and complex cell receptive fields within cortical maps of orientation and ocular dominance. 1266 31


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