An efference copy which is modified by reafferent input.

In electric fish of the mormyrid family, an efference copy is present in the brain region that receives afferent input from ampullary electroreceptors. The efference copy is elicited by the motor command to fire the electric organ. Its effect is always opposite that the ampullary afferents responding to the electric organ discharge, and it changes to match variations in this afferent input. It probably reduces the central effects of activity in ampullary receptors evoked by the electric organ discharge.

Reversible associative depression and nonassociative potentiation at a parallel fiber synapse.

The electrosensory lobe (ELL) of mormyrid electric fish is one of several cerebellum-like sensory structures in fish that remove predictable features of the sensory inflow. This adaptive process obeys anti-Hebbian rules and appears to be mediated by associative depression at the synapses between parallel fibers and Purkinje-like cells of ELL. We show here that there is also a nonassociative potentiation at this synapse that depends only on the repeated occurrence of the EPSP. The depression can be reversed by the potentiation and vice versa. Finally, we show that the associative depression requires NMDA receptor activation, changes in postsynaptic calcium, and the occurrence of a postsynaptic dendritic spike within a few milliseconds following EPSP onset.

Memory-based expectations in electrosensory systems.

Adaptive processing of electrosensory information occurs in the cerebellum-like structures of three distinct groups of fish. Associations within each of these structures result in the generation of negative images of predictable features of the sensory inflow. Addition of these negative images to the actual inflow removes the predictable features, allowing the unpredictable, information-rich sensory signals to stand out. Evidence from all three groups of fish indicates that the negative images are mediated by plasticity at parallel fiber synapses.

Central distribution of octavolateral afferents and efferents in a teleost (Mormyridae).

The central distribution of afferents from individual eight nerve branches (N VIII) and mechanical lateral line end organs in mormyrid fish are described. Afferents were labeled with horseradish peroxidase (HRP) placed on the cut ends of the different N VIII branches and the anterior and posterior lateral line nerves. Descending, tangential, and magnocellular nuclei receive input almost exclusively from the utriculus and canals. Nucleus octavius receives afferents from the lateral line nerves and all N VIII branches, with one part receiving exclusive and bilateral input from the sacculus. Afferents from both lateral line nerves and all N VII branches, except the sacculus, end in eminentia granularis. Afferents from each of the two lateral line nerves and from each of three otolith branches of N VIII end in different regions of the anterior lateral line lobe, with some areas of overlap. Behavioral studies in other families of fish indicate that the utriculus and canals are critical for postural control, whereas the sacculus and possibly the lagena are concerned with hearing. Such findings, together with the results of this study, suggest that mormyrids and perhaps other fish possess separate auditory and vestibular centers within the octavolateral area. The HRP method also shows the cell bodies and axons of octavolateral efferents. N VIII and lateral line efferents arise from a common nucleus, and the central course of their axons parallels that of facial motoneurons. Axons of efferent cells divide to supply two or more branches of N VIII and some axons supply both lateral line and N VIII end organs.

Termination of electroreceptor and mechanical lateral line afferents in the mormyrid acousticolateral area.

The projection regions of electroreceptor and mechanical lateral line afferents in electric fish of the mormyridae family are described. Electroreceptor afferents from the posterior dorsal skin run in the dorsal branch of the posterior lateral line nerve. Electroreceptor afferents from ventral skin and mechanical lateral line afferents and efferents run in the ventral branch of the nerve. Horseradish peroxidase (HRP) injections into each branch resulted in filling of its central terminals with the marker enzyme. The method yields a Golgi-like staining of afferent terminals, allowing some aspects of their morphology to be described. Comparison of results from dorsal and ventral branch injections shows the separate medullary regions to which electroreceptor and mechanical afferents project, and also demonstrates four separate somatotopic maps within the electroreceptor region. Mechanical afferents end predominantly ipsilaterally in nucleus anterior and eminentia granularis as has been suggested by others. Ipsilateral endings in nucleus octavius are also seen. Electroreceptor afferents end exclusively in the cortex and nucleus of posterior lateral line lobe (PLLL). Within the cortex there are three distinct maps of the skin surface which are separated from each other by discontinuities in the cellular layers. Somatotopic mapping is also present in the nucleus of PLLL though it is less precise than in the cortical zones. Large club endings of the cells of this nucleus are filled with HRP. Labeled cells are seen within a small midline nucleus located at the level of the eighth nerve just above the medial longitudinal fasciculus. These are probably the cell bodies of lateral line efferents.

Pathways of the electric organ discharge command and its corollary discharges in mormyrid fish.

The motoneurons which innervate the mormyrid electric organ are driven by a descending volley from the medullary relay nucleus. This nucleus does not initiate the electric organ discharge (EOD) but is driven in an obligatory manner by another center, a command nucleus. One goal of the present study was to identify this command nucleus anatomically. A second goal was to determine the pathways by which corollary discharges of the EOD motor command exert their effects on sensory input to the electroreceptive lateral line lobe. Horseradish peroxidase (HRP) was injected into the medullary relay nucleus and other EOD command-related centers. Placement was guided by recording the electrical activity preceding the EOD. A nucleus of smaller cells is found immediately beneath the large cells of the medullary relay nucleus. This nucleus, nucleus C, projects densely to the medullary relay nucleus and is hypothesized here to be the command nucleus. Nucleus C appears to receive input from the mesencephalon and from unspecified sources of input to the nearby reticular formation. Nucleus C projects to the medullary relay nucleus and to a lateral nucleus, the bulbar command-associated nucleus. This nucleus is probably the source of the corollary discharge signals. It projects to the medullary relay nucleus and to the paratrigeminal and mesencephalic command-associated nuclei. The latter two nuclei project to separate regions which in turn project to the electroreceptive lateral line lobe. There are thus at least two different paths by which the presumed EOD command nucleus, nucleus C, can affect the electroreceptive lateral line lobe.

Mormyromast electroreceptor organs and their afferent fibers in mormyrid fish: I. Morphology.

Mormyromast electroreceptor organs are the most numerous type of electroreceptor organs in mormyrid electric fish and provide the sensory information necessary for active electrolocation. Mormyromast organs and their primary afferent fibers have not been studied very extensively. Both morphological and physiological questions remain to be answered before the neural basis of active electrolocation in mormyrids can be understood. This paper examines four different aspects of the morphology of mormyromast organs and afferent fibers: 1) Mormyromast organs in the skin. The innervation patterns for the two types of separately innervated sensory cells in the mormyromast organ are described on the basis of silver-stained whole mounts of skin. The number of sensory cells per mormyromast organ increases linearly with fish growth for both types of sensory cells. 2) Relation between peripheral sensory cell innervated and central zone of termination for mormyromast afferent fibers. The afferent fibers arising from the two types of sensory cell in the mormyromast organ project to separate zones of the electrosensory lateral line lobe, as shown by using retrograde labeling with horseradish peroxidase. 3) Central trajectories and terminal arbors of mormyromast afferent fibers. These aspects of mormyromast fibers are described by using intracellular staining of individual fibers as well as whole nerve staining of an electrosensory nerve. 4) Fine structure of mormyromast afferent terminals in the electrosensory lateral line lobe. Afferent fibers make various synaptic contacts, including contacts of a mixed type, gap junction-chemical, onto a restricted class of granule cells. The fine structure is described based on electron microscopy of horseradish-peroxidase-labeled fibers. The results provide an anatomical base for current physiological studies on mormyromast afferent fibers.

Morphology and physiology of the brainstem nuclei controlling the electric organ discharge in mormyrid fish.

The motoneurons to the mormyrid electric organ are driven from the medullary relay nucleus. This nucleus is in turn innervated by an adjacent cell group, nucleus C. The goals of this study were to characterize the morphology and physiology of neurons in these two nuclei, and to test the hypothesis that nucleus C is the command nucleus responsible for initiating the electric organ discharge. Medullary relay neurons and nucleus C neurons were recorded intracellularly and labeled with horseradish peroxidase. Medullary relay neurons have a richly branched dendritic arborization, confined mainly to the nucleus itself, and somatosomatic, dendrosomatic, and presynaptic dendro-axonal gap junctions have been observed. Medullary relay neuron axons descend to the spinal cord without branching. Nucleus C dendrites extend far into the ventral reticular formation. Axons of nucleus C neurons have one branch that ramifies densely within the medullary relay nucleus, forming large club endings on the medullary relay neuron soma. Two additional branches project bilaterally toward the bulbar command associated nuclei. Both medullary relay neurons and nucleus C neurons fire a double action potential that precedes each electric organ discharge. Activity in nucleus C precedes that in the medullary relay nucleus by 100-300 microseconds. Postsynaptic activity is recorded in nucleus C neurons but not in medullary relay neurons. Hyperpolarization of a single nucleus C neuron can lower the frequency of the electric organ discharge. Both morphological and physiological data indicate that nucleus C is an integrating center where the electric organ command is initiated.

Mormyrid electrosensory lobe in vitro: morphology of cells and circuits.

The electrosensory lobe (ELL) of mormyrid electric fish is a cerebellum-like brainstem structure that receives the primary afferent fibers from electroreceptors in the skin. The ELL and similar sensory structures in other fish receive extensive input from other central sources in addition to the peripheral input. The responses to some of these central inputs are adaptive and serve to minimize the effects of predictable sensory inputs. Understanding the interaction between peripheral and central inputs to the mormyrid ELL requires knowledge of its functional circuitry, and this paper examines this circuitry in the in vitro slice preparation and describes the axonal and dendritic morphology of major ELL cell types based on intracellular labeling with biocytin. The cells described include medium ganglion cells, large ganglion cells, large fusiform cells, thick-smooth dendrite cells, small fusiform cells, granule cells, and primary afferent fibers. The medium ganglion cells are Purkinje-like interneurons that terminate on the two types of efferent cells, i.e., large ganglion and large fusiform cells, as well as on each other. These medium ganglion cells fall into two morphologically distinct types based on the distributions of basal dendrites and axons. These distributions suggest hypotheses about the basic circuit of the ELL that have important functional consequences, such as enhancement of contrast between "on" elements that are excited by increased afferent activity and "off" elements that are inhibited.

Myelinated dendrites in the mormyrid electrosensory lobe.

This is the third paper in a series on the morphology, immunohistochemistry, and synaptology of the mormyrid electrosensory lateral line lobe (ELL). The ELL is a highly laminated, cerebellum-like structure in the rhombencephalon that subserves an active electric sense: Objects in the nearby environment are detected on the basis of changes in the reafferent electrosensory signals that are generated by the animal's own electric organ discharge. This paper concentrates on the intermediate (cell and fiber) layer of the medial zone of the ELL and pays particular attention to the large multipolar neurons of this layer (LMI cells). LMI cells are gamma-aminobutyric acid (GABA)ergic and have one axon and three to seven proximal dendrites that all become myelinated after their last proximal branching point. The axon projects to the contralateral homotopic region and has ipsilateral collaterals. Both ipsilaterally and contralaterally, it terminates in the deep and superficial granular layers. The myelinated dendrites end in the deep granular layer, where they most likely do not make postsynaptic specializations, but do make presynaptic specializations, similar to those of the LMI axons. Because it is not possible to distinguish between axonal and dendritic LMI terminals in the granular layer, the authors refer to both as LMI terminals. These are densely filled with small, flattened vesicles and form large appositions with ELL granular cell somata and dendrites with symmetric synaptic membrane specializations. LMI cells do not receive direct electrosensory input on their somata, but electrophysiological recordings suggest that they nevertheless respond strongly to electrosensory signals (Bell [1990] J. Neurophysiol. 63:303-318). Consequently, the authors speculate that the myelinated dendrites of LMI cells are excited ephaptically (i.e., by electric field effects) by granular cells, which, in turn, are excited via mixed synapses by mormyromast primary afferents. The authors suggest that this ephaptic activation of the GABAergic presynaptic terminals of the myelinated dendrites may trigger immediate synaptic release of GABA and, thus, may provide a very fast local feedback inhibition of the excited granular cells in the center of the electrosensory receptive field. Subsequent propagation of the dendritic excitation down the myelinated dendrites to the somata and axon hillocks of LMI cells probably generates somatic action potentials, resulting in the spread of inhibition through axonal terminals to a wide region around the receptive field center and in the contralateral ELL. Similar presynaptic myelinated dendrites that subserve feedback inhibition, until now, have not been described elsewhere in the brain of vertebrates.

The mormyrid brainstem--II. The medullary electromotor relay nucleus: an ultrastructural horseradish peroxidase study.

The medullary relay nucleus of the mormyrid weakly electric fish Gnathonemus petersii is a stage in the command pathway for the electric organ discharge. It receives input from the presumed command or pacemaker nucleus and projects to the electromotoneurons in the spinal cord. Its fine structure and synaptology were investigated by electron microscopy. The origin of the terminals contacting the cell membrane of the neurons of this nucleus was determined by horseradish peroxidase (HRP) injections into different brain structures, namely into the bulbar command- and mesencephalic command-associated nuclei. Twenty-five to thirty large cells of about 45 micron in diameter constitute the medullary electromotor relay. Each cell has a kidney-shaped, lobulated nucleus, a large myelinated axon with a short initial segment and several long, richly arborizing primary dendrites. Many, if not all, cells are interconnected with large somatosomatic or dendrosomatic, dendrodendritic and dendroaxonic gap junctions. These junctions often occur in serial or triadic arrangements. The relay cells receive large club endings as well as small boutons. The club endings are found mainly on the soma and primary dendrites and are morphologically mixed synapses. The boutons are characterized by synapses which are only chemical and are distributed all over the cell membrane, but with a definitely higher frequency on secondary dendrites and more distal parts of dendritic processes. Horseradish peroxidase injections into the mesencephalic command-associated nucleus reveal a large number of labelled boutons on the secondary dendrites of the relay cells. Injections into the bulbar command-associated nucleus label the same type of boutons as mesencephalic injections, but also label club endings on relay cell soma and primary dendrites. The results support the conclusion made on the basis of previous light microscopical observations that boutons originate from the bulbar command-associated nucleus, whereas the club endings issue from the presumed pacemaker nucleus (nucleus c). The club endings of the bifurcating axons of this nucleus are labelled by retro- and anterograde transport of horseradish peroxidase; the bifurcating axons project simultaneously to the bulbar command-associated nucleus and the medullary relay nucleus.

Activity of adenosine deaminase in the sleep regulatory areas of the rat CNS.

There are data to support the notion that adenosine (ADO), a neuromodulator in the CNS, is an important regulator of sleep homeostasis. It has been demonstrated that ADO agonists and antagonists strongly impact upon sleep. In addition, the level of adenosine varies across the sleep/wake cycle and increases following sleep deprivation. Adenosine deaminase (ADA) is a key enzyme involved in the metabolism of ADO. We questioned, therefore, whether there are differences in adenosine deaminase activity in brain regions relevant to sleep regulation. We found that ADA exhibits a characteristic spatial pattern of activity in the rat CNS with the lowest activity in the parietal cortex and highest in the region of the tuberomammillary nucleus (15.0+/-4.8 and 63.4+/-28.0 nmoles/mg protein/15 min, mean+/-S.D., respectively). There were significant differences among the brain regions by one-way ANOVA (F=31.33, df=6, 123, P=0.0001). The regional differences in ADA activity correlate with variations in the level of its mRNA. This suggests that spatial differences in ADA activity are the result of changes in the expression of the ADA gene. We postulate that adenosine deaminase plays an important role in the mechanism that controls regional concentration of adenosine in the brain and thus, it is a part of the sleep-wake regulatory mechanism.

Duration of plastic change in a modifiable efference copy.

A modifiable efference copy associated with the motor command that elicits an electric organ discharge (EOD) is found in mormyrid electric fish. It is a negative image of the expected effect of the afferent input that follows the EOD. A change in the afferent input pattern causes, over time, a corresponding change in the efference copy. The negative image is retained for at least one half-hour when the motor command is artificially silenced.

Effect of electric organ discharge on ampullary receptors in a mormyrid.

(1) Afferents from ampullary receptors were shown to be strongly affected by the electric organ discharge (EOD) in the mormyrid Gnathonemus petersii. (2) Over a broad range of resistivities (4-60 komegacm) the response to the EOD was similar to the response to a brief (50-200 microsec) outside positive pulse, i.e. an initial acceleration of the discharge rate followed by a deceleration. (3) Brief biphasic positive-negative or negative-positive pulses where both phases were of equal amplitude and duration had no effect on ampullary afferents. Each phase had an effect, however, when given in isolation. These results suggest that a DC component in the EOD may cause the response in the ampullary afferent. (4) The response of ampullary afferents decreased sharply as resistivity was lowered below 10komegacm. Responses to the EOD in mormyromast afferents also decreased. These effects were probably due to loading of the EOD at low resistivities and to a more rapid spatial decay of EOD voltage. (5) Responses of ampullary afferents to the EOD were much less affected by external non-conducting objects than were the responses of mormyromasts. These observations plus other considerations indicate that mormyromasts must still be held to play the major role in active electrolocation. Unresponsiveness of ampullary afferents to the EOD can not be taken as a reason for this, however.

Basic research and community collaboration: necessary ingredients for the development of a family-based HIV prevention program.

This article describes the development of a family-based, longitudinal HIV prevention program targeting urban, African American fourth- and fifth-grade children and their families living in areas with high rates of HIV infection. The intervention is based on the research findings of the Chicago HIV Prevention and Adolescent Mental Health Family Study, a longitudinal study of 315 urban, African American families with preadolescent children (Paikoff, 1997). Results from this study informed the development of a 12-week, family-based preventive intervention-the Chicago HIV-Prevention and Adolescent Mental Health Project (CHAMP) Family Program. The development and implementation of the program also was guided by a collaborative partnership between university researchers and community members (parents and school staff). A description of the process by which collaboration influenced the development of the intervention is provided. This article is meant to serve as a model for the integration of empirical findings and community collaboration into the development of HIV prevention programs.

Cultivating resiliency in youth.

This paper highlights characteristics of resiliency and the importance of strengthening resiliency and how to build it. The neuropsychiatry of traumatic stress is underscored and more esoteric resiliency-building activities are discussed.

Adolescent suicide.

This article reviews the origin of youth suicide. Theoretic suicide risk factors and empirically observed suicide risk factors are discussed along with proposed resiliency factors that prevent suicide. Finally, suicide prevention and intervention strategies are covered, and a call for better studies on suicide prevention is heralded.

Issues in the psychiatric treatment of African Americans.

African Americans constitute about 12 percent of the United States population. Sixty percent of African Americans live in urban areas, and 25 percent have incomes below the poverty level. Issues in the psychiatric assessment and evaluation of African-American patients include diagnostic bias that has resulted in overdiagnosis of schizophrenia. Use of screening instruments can help standardize assessment, but appropriate screening instruments that have been evaluated and found reliable in this population must be used. Issues in treatment and outcome for African Americans include challenges in establishing rapport in interethnic situations, racial identity as a focus in psychotherapy, and awareness of biological characteristics that affect response to medications. Many African Americans live in high-crime areas where high rates of drug abuse and violence create chronic stresses. Patients with dual diagnoses of chronic mental illness and substance use or abuse need targeted interventions. Strategies for prevention and treatment of the effects of having experienced or witnessed violence have been proposed. Additional research is needed to clarify the true prevalence of specific mental disorders among African Americans and to determine the most effective combinations of treatment strategies for various disorders.

Using sports to strengthen resiliency in children. Training heart.

This article describes how sports can cultivate resiliency. Encouraging the development of heart in youth is highlighted. The concept is a simple one. By encouraging children and adolescents to go the extra mile in a sports context, youth practice calling up emotional reserves until they trust that they have a stockpile of conviction. The authors believe building heart in youth is a preventive public health strategy that can inoculate against the potentially negative effects of stress and trauma. It is hoped that heart will become an essential tool in the primary prevention of stress-related disorders in youth and a critical skill that promotes having an optimal life. In addition, the authors believe that heart can be developed after exposure to traumatic stress. Heart is critical to overcoming the sense of devastation and helplessness that develops from traumatic experiences.

Assessment and management of the violent patient.

This article provides guidance on how to manage the unavoidable challenge of aggression in psychiatric relationships. Accordingly, this article addresses issues of personal safety and how to manage potentially violent patients, defuse situations that threaten imminent violence, and manage emergent violence. In addition, a useful chart is highlighted that differentiates different types of violence.