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PubMedDate not supplied

Silent synapses in neural plasticity: current evidence.

Silent synapses, defined as structural specializations for neurotransmission that do not produce a physiological response in the receiving cell, may occur frequently in neural circuits. Their recruitment to physiological effectiveness may be an important component of circuit modification. In several nervous systems, evidence from electrophysiological and optophysiological measurements has established a strong case for the existence of silent synapses and for their emergence as active synapses with appropriate stimulation. During normal development and aging, synapses of individual neurons change in number, and many of these may be functionally silent at certain stages of their developmental trajectory. Changes in their status may contribute to shaping the properties of neural pathways during development, often in response to neural activity. In general, it is often difficult to distinguish physiological emergence of pre-established silent synapses from developmental maturation or de novo formation of new synapses. Several possible mechanisms for silent synapses and their recruitment are reviewed. These include incompletely assembled synapses that lack structural components, insufficient availability of key presynaptic proteins, and nonfunctional postsynaptic receptors, or presence of receptors that do not mediate a postsynaptic response except under specific conditions (conditionally silent synapses). The available silent synapses can often be rapidly activated, and conversely, active synapses appear to be rapidly silenced in many instances. These properties enable silent synapses to participate in short-term facilitation and depression. In addition, they may contribute to long-term facilitation and potentiation, especially during development.

Animals↗

PubMed1984

Confirmatory evidence for a direct parasympathetic pathway to internal eye structures.

The hypothesis that a direct neural pathway exists between the midbrain and the intrinsic musculature was investigated. Wheat germ agglutinin labeled with HRP and WG-HRP were injected intraocularly into the ciliary muscle of rabbits and cynomolgus monkeys, and their retrograde movement was monitored. Sparse, but definite labeling was found in the AM nuclei, the EW nuclei, and Perlia's nucleus of the monkey, confirming the existence of a nonsynapsing pathway between intraocular structures and the midbrain in the primate.

Animals↗

PubMed1980

Suppression of sexual receptivity in the female hamster: neuroanatomical projections from preoptic and anterior hypothalamic electrode sites.

Electrical stimulation (ES) through fine-wire electrodes chronically implanted in the preoptic area and anterior hypothalamus suppressed the lordosis response in freely moving hormone-primed female hamsters. ES at these sites never induced or facilitated lordosis. When behavioral testing was completed small lesions were made at the tips of the electrodes, and the Fink-Heimer method was used to trace degenerating axons away from the sites of ES. This was done in an effort to determine the neural pathways important for the modulation of this behavior. The hypothalamic distribution of the stria terminalis was also charted for the hamster and was found to be similar to that in the rat, including projections to both the shell and core of the ventromedial nucleus (VMN). No single pattern of degeneration was common to all females showing ES-produced lordosis suppression. These data demonstrate that stimulation of several different pathways can produce behavioral states that are incompatible with the lordosis response. We suggest that ES in the medial preoptic-medial anterior hypothalamic continuum suppresses sexual receptivity by influencing neurons in the VMN region, while ES through more laterally placed electrodes suppresses receptivity by producing an incompatible state of behavioral activation, without directly influencing VMN region neural activity.

Amygdala↗

PubMed2001

Neuronal activity in the globus pallidus in chorea caused by striatal lacunar infarction.

Pallidotomy was performed in a patient with hemichorea caused by lacunar infarction in the striatum. Chorea in the lower limb was reduced after a neurosurgical lesion in the medial portion of the sensorimotor territory of the internal segment of the globus pallidus, and chorea in the upper limb disappeared after an additional lesion in the lateral portion of that same area. Intraoperative neuronal recording revealed that mean firing rates were low, and that firing was irregular in the globus pallidus compared with off-state parkinsonian patients. These results suggest that chorea with striatal infarction is driven by phasic neuronal activity with a low firing rate in the globus pallidus and that the neural pathway of chorea has a functional somatotopical organization in the globus pallidus.

Action Potentials↗

PubMed1980

Vestibular inputs to the fastigial nucleus; evidence of convergence of macular and ampullar inputs.

1. Experiments have been undertaken on 11 decerebrate cats to investigate the effects of natural vestibular stimulation on the activity of cerebellar fastigial neurons. 2. From recordings in the rostral portion of the nucleus during sinusoidal lateral (roll) and horizontal (yaw) rotation, distinctive patterns of response were observed. 3. The majority of neurons sensitive to vestibular stimulation showed responses to a single modality of vestibular activation. During lateral tilt some neurones showed positional sensititivy, others gave responses related tothe velocity of movement. Other neurones responded in phase with the velocity of movement in the horizontal plane. 4. Aside from these neuronal responses, others provided indications of a convergence of inputs from different sets of vestibular receptors. In particular, several neurons showed a pattern of response that indicated tht they received inputs from otolith receptors and ampullar receptors of the vertical canal. At low velocities of movement their response was positional but with inreasing velocity the magnitude of the response increased and there was a marked phase shift of the discharge towards head velocity. 5. Neurons responding to horizontal rotation often showed positional responses during lateral tilt. There were also indications of a convergence of ampullar inputs from both vertical and horizontal canals. 6. The neural pathways mediating these resonses are discussed in consideration of previous neuroanatomical and neurophysiological data. We consider it likely that several pathways may act to evoke the patterns of response observed, and a role of the cerebellar cortex is indicated.

Acoustic Maculae↗

PubMed2005

Neural mechanisms of freezing and passive aversive behaviors.

Cues that predict aversive outcomes often produce marked inhibitions of behavior known as freezing, but it is unknown exactly what neural pathways cause this inhibition. The amygdala and bed nucleus of the stria terminalis, along with their projections to the periaqueductal gray, are strongly implicated in freezing, but it is not known how these structures inhibit motor output. The median raphe nucleus (MRN), which contains a major population of serotonin neurons, has also been implicated in freezing, but the serotonin neurons themselves do not seem to be involved, leaving it uncertain which neurons in this area promote freezing. Our recent work suggests that GABAergic neurons just lateral to the MRN, but not within the MRN, regulate freezing via projections to midbrain dopamine neurons. Because freezing pathways may control a variety of other passive aversive behaviors, their elucidation may help understand the mechanisms of addictions and compulsions, which involve a failure of aversive outcomes to inhibit behavior.

Amygdala↗

PubMed1978

Hypothalamic-pituitary responses to intracranial self-stimulation in the rat.

The effects on pituitary and adrenal hormones of intracranial self-stimulation (ISS) and forced stimulation in rewarding (PS) and non-rewarding (NSS) sites were investigated in adult male rats. Growth hormone (GH) was suppressed during periods of ISS and PS and rose sharply to a peak within 15 min of cessation. The interval between GH secretory episodes was significantly shortened during all 3 types of stimulation when compared to the normal rhythmic discharge observed in freely behaving baseline (BL) sampled rats. ISS, PS and NSS resulted in a rapid rise in prolactin (Prl), which returned to normal by the end of each hourly period of stimulation. There was a significant reduction of Prl elevation in the second and third periods of stimulation, suggesting that the first exposure to ISS had a greater stimulatory effect than subsequent stimulations. There was a rapid and sustained release of corticosterone (CS) during ISS and PS. As with Prl, the initial period of either ISS or PS caused a greater effect that subsequent periods. These studies provide data to compare the relationship between ISS and neuroendocrine responses. The hormonal responses, with minor exceptions, were similar under all experimental conditions, and could not be clearly dissociated from previously described stress responses. Neural pathways and substrates involved in GH, Prl and CS secretion are discussed in relation to pathways activated by LH-MFB stimulation. Potential differential functions of monoamines and hypothalamic neuropeptides in behavioral and neuroendocrine regulation are hypothesized.

Animals↗

PubMed2002

Enhancement of electrically evoked startle-like responses by tetanic stimulation of the superior colliculus.

Single-pulse unilateral electrical stimulation of either the amygdala or the inferior colliculus elicited startle-like responses in chloral hydrate anesthetized rats. EMG responses to intracranial stimulation were recorded from the anterior biceps femoris muscles. The EMG responses were generally enhanced following unilateral tetanic stimulation of the deep layers of the superior colliculus, but the enhancement was stronger for amygdala sites than inferior colliculus sites. The enhancement of EMG responses to ipsilateral amygdala stimulation was much larger than that for contralateral amygdala stimulation and that for ipsilateral inferior colliculus stimulation. The enhancement of EMG responses to contralateral inferior colliculus stimulation was not significant. The present study provides a motor-output model for studying plasticity in the neural pathways mediating startle facilitation.

Amygdala↗

PubMed2005

Itching for progress.

The study of itch remains a neglected field, with a number of barriers limiting satisfactory therapy in the majority of instances. We review recent advances, focusing on the identification of the neural pathways, distinct from pain, that signal itch; methods to measure itch as scratch in humans; and the identification of a role for H4 receptors in mediating itch (in the mouse).

Animals↗

PubMed1987

Efferent projections from posteroventral cochlear nucleus to lateral superior olive in guinea pig.

Phaseolus vulgaris leucoagglutinin (PHA-L), a kidney bean lectin used as an anterograde tracer, was iontophoretically injected into the posteroventral cochlear nucleus (PVCN) of guinea pigs. PHA-L-labeled fiber segments and their terminal specializations were observed within the ipsilateral lateral superior olive (LSO) thereby establishing the existence of an efferent neural pathway from PVCN to this nucleus. Furthermore, the pathway is topographically organized with dorsal regions of PVCN projecting to the medial limb and ventral regions projecting to the lateral limb of LSO.

Animals↗

PubMed1984

Brain monoaminergic control of male reproductive behavior. III. Norepinephrine and the post-ejaculatory refractory period.

The present study was performed to examine the role of brain norepinephrine in the control of copulation and the post-ejaculatory refractory period in the male rat. Disruption of central noradrenergic systems was achieved by (1) selective electrolytic lesion of noradrenergic cell bodies in the locus coeruleus or (2) administration of specific inhibitors of norepinephrine synthesis, sodium diethyldithiocarbamate (DDC) or 1-phenyl-3-(2-thiazolyl)-2 thiourea (U-14, 624). Electrolytic lesions of the locus coeruleus produced a significant increase in the duration of the post-ejaculatory refractory period and its concomitant 22-kHz ultrasonic vocalization. Administration of norepinephrine synthesis inhibitors significantly increased both mount and intromission latencies and caused a dramatic increase in the length of the post-ejaculatory refractory period. These findings support the hypothesis that norepinephrine-containing neural pathways are involved in the control of sexual arousal and suggest that a functional noradrenergic system is essential to the integrity of normal masculine copulatory behavior.

Animals↗

PubMed1997

Behavioral and functional analysis of mouse phenotype: SHIRPA, a proposed protocol for comprehensive phenotype assessment.

For an understanding of the aberrant biology seen in mouse mutations and identification of more subtle phenotype variation, there is a need for a full clinical and pathological characterization of the animals. Although there has been some use of sophisticated techniques, the majority of behavioral and functional analyses in mice have been qualitative rather than quantitative in nature. There is, however, no comprehensive routine screening and testing protocol designed to identify and characterize phenotype variation or disorders associated with the mouse genome. We have developed the SHIRPA procedure to characterize the phenotype of mice in three stages. The primary screen utilizes standard methods to provide a behavioral and functional profile by observational assessment. The secondary screen involves a comprehensive behavioral assessment battery and pathological analysis. These protocols provide the framework for a general phenotype assessment that is suitable for a wide range of applications, including the characterization of spontaneous and induced mutants, the analysis of transgenic and gene-targeted phenotypes, and the definition of variation between strains. The tertiary screening stage described is tailored to the assessment of existing or potential models of neurological disease, as well as the assessment of phenotypic variability that may be the result of unknown genetic influences. SHIRPA utilizes standardized protocols for behavioral and functional assessment that provide a sensitive measure for quantifying phenotype expression in the mouse. These paradigms can be refined to test the function of specific neural pathways, which will, in turn, contribute to a greater understanding of neurological disorders.

Animals↗

PubMed1978

Differential display of hippocampal and amygdaloid influences on hypothalamic evoked potentials.

Adult female rabbits with bipolar electrodes chronically implanted in the brain were employed to study the changes of the evoked potentials (EP) in the medial basal hypothalamus including the median eminence (ME), elicited by single hippocampal (HPC) or amygdaloid (AMYG) stimulus during EEG afterdischarge induced by electrical stimulation of the lattter two areas. In HPC seizures, the ME-EP from the HPC stimulation was extensively influenced in amplitude and peak-latency, the former decreased and the latter lengthened remarkably. On the other hand, the ME-EP from the AMYG stimulation did not show any noticeable changes either in amplitude or in peak-latency. During an AMYG seizure, the ME-EP from either the HPC or AMYG stimulation did not show any significant changes in amplitude or peak-latency. The results suggest that electrical activity of the neural pathways from the HPC to ME are very dependent on the excitability of the HPC, whereas those from the AMYG to ME seem variable, depending on the activity of the AMYG.

Amygdala↗

PubMed1989

Age sensitivity of osmoregulation and of its neural correlates in Aplysia.

Osmoregulation was studied in the marine mollusc Aplysia californica in young, mature, and old adults. To monitor volume and osmoregulation, we measured body weight, hemolymph osmolality, and chloride concentration. These parameters were measured at regular intervals with animals in 90% artificial seawater (90% ASW) for up to 36 h. They showed that the rates at which Aplysia osmo- and volume regulate were significantly slowed with increased age. However, no age effect was found in osmoregulation when the hemolymph was diluted to 90% of control in animals without an external stress, i.e., by injection of distilled H2O and keeping animals in 100% ASW. Because the dilution bypassed the sensory receptors that detect external changes of osmolality, this finding suggested that the slowed osmoregulation involved age-impaired functioning of the neural pathway mediating osmoregulation. Other evidence was from mature adults whose osmoreceptive organ, the osphradium, was lesioned; they mimicked osmoregulation measured in old adults. In preparations containing a portion of the osmoregulatory pathway, the osphradium was stimulated by 90% ASW, and the responsiveness of neuron R15, which putatively regulates antidiuresis, was tested. The stimulus inhibited spiking in R15 from mature adults but not in R15 from old adults or from osphradiallesioned mature ones. In old Aplysia the refractoriness of R15 to osphradial stimulation demonstrated that the effecacy of the pathway was impaired with increased age; it helped explain the slower rate of osmoregulation. Possible changes of osmoregulatory mechanisms and behavior compensating for the age sensitivity of osmoregulation are discussed.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗

PubMed1998

Pilot study of functional MRI to assess cerebral activation of motor function after poststroke hemiparesis.

BACKGROUND AND PURPOSE: Studies of cerebral activation of motor function after ischemic stroke may enhance our understanding of the underlying mechanisms of motor functional recovery, including the role of the noninfarcted hemisphere. METHODS: Eight right-handed recovering hemiparetic or hemiplegic patients were studied using functional MRI. Results were evaluated for each patient to consider individual variability in original functional organization, neuroanatomy, infarct size and extent, treatment, age, and sex. The results were also pooled as a group for comparison with a control group of eight right-handed normal subjects. RESULTS: In six of eight stroke patients, extended activation in ipsilateral sensorimotor cortex was observed during paretic hand movements. Bilateral activation of the primary sensorimotor cortex was recorded in three of these six patients; ipsilateral activation alone was recorded in the remaining three patients. Only two patients had mild synkinesia. Furthermore, in two male patients, the paretic hand movements activated extended areas of ipsilateral premotor and dorsolateral prefrontal cortex, when compared with normal subjects. In two patients with left frontal infarction, profound activation in the right supramarginal gyrus and in the right premotor cortex was observed during the ipsilateral paretic hand movements. CONCLUSIONS: Synkinesia alone cannot explain the extent of ipsilateral activation in primary sensorimotor cortex. The explanation offered for our findings is that preexisting uncrossed motor neural pathways may be accessed or recruited to compensate for damage to the crossed motor pathways after ischemic stroke.

Adult↗

PubMed1993

Hypothalamic angiotensin release in response to AII or glutamic acid stimulation of the SFO in rats.

Recent evidence from our laboratory suggests that angiotensin II (AII) is synthesized, stored within cells in the paraventricular nucleus (PVN) of the hypothalamus, and upon appropriate stimulation, released and rapidly converted to angiotensin III (AIII). The present investigation extends these observations by first employing a retrograde tracer to confirm a direct connection from the subfornical organ (SFO) to the PVN, and then showing that microinfusion of AII or glutamic acid into the SFO provokes release of endogenous angiotensin within the PVN. Potentially it is this release that contributes to the elevations in blood pressure and drinking that have been reported to occur with electrical and chemical stimulation of the SFO. These results represent the first evidence of releasable angiotensin provoked by the chemical activation of a neural pathway that has been histochemically demonstrated to link the SFO with the PVN and brain stem structures concerned with cardiovascular functioning.

Angiotensin II↗

PubMed1991

Monoclonal antibodies recognize localized antigens in the eye and central nervous system of the marine snail Bulla gouldiana.

The eyes of the marine snail Bulla gouldiana act as circadian pacemakers. The eyes exhibit a circadian variation in spontaneous optic nerve compound action potential frequency in constant darkness, and are involved in controlling circadian rhythms in behavioral activity expressed by the animal. To initiate an investigation of the molecular aspects of circadian rhythmicity in the Bulla eye and to identify specific molecular markers in the nervous system, we raised monoclonal antibodies (MAb) to the eye and screened them for specific patterns of staining in the eye and brain. Several MAb recognize antigens specific to groups of neurons in the brain, whereas others stain antigens found only in the eye. In addition, some antigens are shared by the eye and the brain. The antigens described here include molecules that mark the lens, retina, neural pathways between the eye and the brain, specific groups of neurons within the central ganglia, and an antigen that is shared by basal retinal neurons (putative ocular circadian pacemaker cells) and glia. These molecular markers may have utility in identifying functionally related groups of neurons, elucidating molecular specializations of the retina, and highlighting pathways used in transmission of information between the retina and the brain.

Animals↗

PubMed2005

Functional significance of the innervation of the gonads.

Gonadal functions are governed by the hypothalamohypophysial system. Recent studies have demonstrated the existence of a multisynaptic neural pathway between the brain and the gonads. This review summarizes the morphological and physiological data that suggest the role of the brain-gonadal circuitry in the control of gonadal functions and discusses relevant clinical observations.

Animals↗