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PubMed1998

A reexamination of the synaptic connection between neuron L7 of the abdominal ganglion and neurons of the branchial ganglion in Aplysia californica, A. kurodai and A. juliana.

The presence of a synaptic connection between neuron L7 of the abdominal ganglion and branchial ganglionic neurons (BGNs) was reexamined by means of electrophysiology and fluorescent microscopy using three Aplysia species. We succeeded in recording excitatory postsynaptic potentials produced in a BGN, which followed impulses of L7 one-to-one with a constant latency, even in A. californica as well as in A. kurodai and A. juliana. Dye-injection revealed that fine collaterals extended from a major branch of L7 to the branchial ganglion and arborized in neuropil of the ganglion. The results show that L7 in the three species has a dual function as a motor neuron and as an interneuron for the gill.

Animals↗
PubMed1981

Electrophysiological evidence for connections between septal neurones and the supraoptic nucleus of the hypothalamus of the rat.

In order to see whether septal neurones are connected to the hypothalamic neurones secreting vasopressin or oxytocin, neurones in different regions of the septum were recorded during electrical stimulation of the supraoptic nucleus. The position of the stimulating electrode within the latter was verified using lactating rats in which milk ejections could be induced by a train of electrical pulses applied to the nucleus. The responses of septal neurones to single pulse stimulation were then analysed by post-stimulus time histograms. In the septum ipsilateral to the site of stimulation, 42% of the neurones were antidromically invaded, 20% were orthodromically excited and 21% were inhibited following suraoptic stimulation. In the contralateral septum, 2% of the cells tested were antidromically invaded, 3% were excited and 16% inhibited. In the medial septum, 14% of the neurones were orthodromically excited, and 48% were inhibited. These results provide electrophysiological evidence for direct connections between septal neurones and the ipsilateral supraoptic nucleus of the hypothalamus, and give further support to the hypothesis of a septal influence on the activity of vasopressin- or oxytocin-releasing cells in the magnocellular system.

Animals↗
PubMed1998

Axonal connections of the high vocal center and surrounding cortical regions in juvenile and adult male zebra finches.

Neuronal connections of the High Vocal Center (HVC), a cortical nucleus of songbirds necessary for learned vocal behavior, and the region adjacent to HVC called paraHVC (pHVC), were studied in adult and juvenile male zebra finches. Extremely small injections of fluorescent dextran amines or biocytin were made within subregions of HVC and pHVC to define the precise nature and development of these pathways. In adults, all HVC injections produced an even, nontopographic distribution of retrograde label throughout the medial magnocellular nucleus of the anterior neostriatum (mMAN), the interfacial nucleus (NIf), and the uvaeform nucleus of the thalamus (Uva) and an even distribution of anterograde label within area X of the striatum and the robust nucleus of the archistriatum (RA). These same patterns of projections were present in juvenile birds 20-23 days of age, including the projection from HVC to RA, which has previously been reported to develop only after 25-30 days of age. Results also establish a novel efferent projection from HVC to pHVC in both juvenile and adult birds. Injections into pHVC indicate that this region receives afferent input from song control areas HVC, mMAN, medial regions of the parvicellular shell of lateral MAN, NIf, and Uva and projects to Area X, caudomedial regions of striatum, and regions of the caudomedial neostriatum (NCM). Thus, neuronal connections of pHVC are highly integrated with circuitry important for vocal behavior and are distinct from those of HVC. Such differences establish HVC and pHVC as separate brain areas and suggest that each may serve a different function in vocal behavior. Control injections in both juveniles and adults produced specific patterns of projections from areas outside of HVC to areas outside of RA, illustrating an overall spatial organization of projections from HVC and neighboring cortical areas. Further, although neuronal connections of HVC are not topographic, projections of HVC, pHVC, and surrounding areas demonstrate a broad spatial organization of efferents to striatum and regions surrounding RA, thus defining a level of organization beyond that of individual song control nuclei.

Afferent Pathways↗
PubMed1985

Connections of neurons in the region of the nucleus tractus solitarius with the hypothalamic paraventricular nucleus: their possible involvement in neural control of the cardiovascular system in rats.

Extracellular recordings were made from 607 spontaneously firing neurons within the nucleus tractus solitarius (NTS) and its vicinity in urethane-anesthetized male rats. Following electrical stimulation of the hypothalamic paraventricular nucleus (PVN) area, 21% of the neurons were orthodromically excited, 6% were inhibited and 2.5% were antidromically activated. The antidromic spike latencies were 22-64 ms. Among those orthodromically responding neurons, 81 neurons were tested by pressure pulse stimulation of the isolated carotid sinus. The pressure stimulation produced excitation in 7 and inhibition in 13 neurons. Of the 8 tested neurons which were antidromically activated, one neuron was excited and another neuron inhibited by the pressure pulse stimulation. These results provide electrophysiological evidence for reciprocal connections between neurons in the NTS region and the PVN, and give support to the hypothesis that the PVN is involved in the neural control of the cardiovascular system.

Animals↗
PubMed2000

Optimal sizes of dendritic and axonal arbors in a topographic projection.

I consider a topographic projection between two neuronal layers with different densities of neurons. Given the number of output neurons connected to each input neuron (divergence) and the number of input neurons synapsing on each output neuron (convergence), I determine the widths of axonal and dendritic arbors which minimize the total volume of axons and dendrites. Analytical results for one-dimensional and two-dimensional projections can be summarized qualitatively in the following rule: neurons of the sparser layer should have arbors wider than those of the denser layer. This agrees with the anatomic data for retinal, cerebellar, olfactory bulb, and neocortical neurons the morphology and connectivity of which are known. The rule may be used to infer connectivity of neurons from their morphology.

Animals↗
PubMed1999

[Not Available].

With the increasing application of imaging techniques, characteristic changes in the structure and functional activity of certain neuronal networks and transmitter Systems have been discovered in the brains of patients suffering from various psychiatric disorders. These findings have often been assumed to support biological concepts of the genetic background and causation of these disorders. However, several lines of research are converging to indicate that the initially established genetically programmed neuronal Connectivity is further elaborated, fine tuned and modified by usedependent neuronal and synaptic plasticity. In all socially organized species in general and in human subjects in particular, psychosocial experiences appear to represent the most important trigger of use-dependent adjustments of neuronal Connectivity through the facilitation, modification and reorganization of neuronal networks. In experimental animals, changes in psychosocial rearing conditions were shown to cause profound and persistent changes in the cytoarchitecture, dendritic arborization and synapse formation in individual brain regions as well as in the maturation of monoaminergic afferences. Based on these findings, the mechanisms of the biological affixation of psychosocial experiences are described and the implications of experience dependent neuronal and synaptic plasticity in the prevention and the therapy of mental disorders are outlined.

Attachment↗
PubMed1995

Localisation and association of pathomorphological changes at the brainstem in Alzheimer's disease.

The brainstems of ten patients with Alzheimer's disease were examined with specific silver impregnations for beta-amyloid deposits, neurofibrillary tangles, neuropil threads and neuritic plaques. The results show a selective and focal involvement of brainstem nuclei, which are diffusely connected to the cortex or are neuronally connected with other damaged subcortical and cortical regions. Therefore, it is concluded that neuronal connectivity plays an important role in the pathogenesis of Alzheimer's disease lesions. This may be due to the intraneuronal transport of beta-amyloid precursor protein. There was a local association between neurofibrillary tangles and neuropil threads, but not between beta-amyloid structures on the one hand and neurofibrillary structures on the other hand. Neuritic plaques were rarely found.

Aged↗
PubMed1997

Types of neurons, synaptic connections and chemical characteristics of cells immunoreactive for calbindin-D28K, parvalbumin and calretinin in the neocortex.

This article provides a general account of types of neurons, synaptic connections and chemical characteristics (colocalization studies) of cells immunoreactive for the three main calcium-binding proteins found in the neocortex, namely, calbindin-D28K, parvalbumin and calretinin. The main conclusion is two-fold. First, all, or the majority, of calbindin-, parvalbumin- and calretinin-immunoreactive cells are smooth nonpyramidal neurons (interneurons) which participate in a variety of complex cortical circuits that may differ depending on the species, cortical area or layer where they are located. Second, in general, different types of nonpyramidal neurons are stained for each of these calcium-binding proteins and display different chemical characteristics regarding a variety of neurotransmitters (or related compounds), cell surface markers and receptors. However, a certain overlap exits, which also shows regional and species differences.

Adult↗
PubMedDate not supplied

Loss of interhemispheric connectivity in patients with lacunar infarction reflected by diffusion-weighted MR imaging and single-photon emission CT.

BACKGROUND AND PURPOSE: Although decreased neuronal connectivity in white matter has been reported to be a key mechanism of vascular dementia, assessment of white matter changes by diffusion-weighted MR imaging in relation to measures of associative function has not been previously addressed. We evaluated the loss of interhemispheric neuronal connectivity in vascular dementia by measuring diffusional anisotropy of the corpus callosum and determining its relationship to the regional cortical activity as reflected by cortical perfusion. METHODS: Nine patients with multiple lacunar infarction and six healthy volunteers (25-35 years old) were examined. We developed a method to determine the active cortical volume (ACV) by masking iodine-123 iodoamphetamine SPECT scans to eliminate the effect of brain atrophy. The anisotropic rate (AR) was calculated as a ratio of two perpendicular diffusion coefficients in diffusion-weighted MR imaging. RESULTS: Compared with the ACVs of the healthy volunteers, there were significant decreases in the ACVs in the frontal associative areas in the patients, and these were significantly correlated with cognitive scores. The frontal ACVs showed good correlations with the AR of the anterior corpus callosum among all participants; however, only insignificant trends toward correlation were observed between these two parameters within the patient group. CONCLUSION: A possible relationship between diffusional anisotropy of the anterior corpus callosum and frontal associative function was suggested; however, an estimation of the decrease in neuronal connectivity in patients with multiple lacunar infarction in terms of the deterioration in diffusional anisotropy requires further documentation.

Aged↗
PubMed2002

Functional connectivity between neurons generating resting discharge in renal sympathetic neurons in the rabbit.

In anaesthetised rabbits, we analysed the cross-correlations of resting discharges in pairs of simultaneously recorded renal neurons. The study of 428 significant cross-correlations showed three pure types of neuronal co-ordination and two combined effects. Pure shared input was observed in 202 pairs of neurons (47.2%). The width of cross-correlogram peak was 222.9 +/- 7.2 ms. The peak height of shared input was 4.8 +/- 0.2 spikes s(-1) and was significantly related with correlogram width. Pure excitatory connection was found in 24 neuronal pairs (5.6%). Its peak width was 7.9 +/- 1.9 ms and it was shifted from time zero by 13.3 +/- 3.4 ms. The amplitude of the peak was 19.6 +/- 4.6 spikes s(-1). In 165 pairs of neurons (38.6%), excitatory connection was combined with shared input component. Pure reciprocal activation was seen in only 5 pairs of neurons (1.1%) while in 32 pairs (7.5%) it was accompanied by shared input co-ordination. The distance between narrow peaks measured in the combined type of co-ordination was 32.5 +/- 3.5 ms and the mean peak height was 4.1 +/- 0.7 spikes s(-1). Shared input in pure form and that accompanying both excitatory connection and reciprocal activation were significantly related to the frequency of discharge of neurons contributing to the cross-correlogram. The incidence and basic properties of the encountered types of neural coordination may indicate a pattern of interconnections between cells generating vasomotor tone in renal sympathetic neurons.

Action Potentials↗
PubMed1974

Plasticity in small neuronal assemblies.

When spike activity of two or more individual neurons is simultaneously recorded, it is possible to detect various types of neuronal connections to and between the observed neurons by making appropriate statistical analysis of the data. Such methods are reviewed. This approach is particularly useful in seeking changes of neuronal connectivity associated with behavioral plasticity. Examples from experiments with Aplysia and crayfish are given.

Animals↗
PubMed2003

Are hypothalamic neurons transsynaptically connected to porcine adipose tissue?

Specific anatomical sites and pathways responsible for mediating metabolic and neuroendocrine effects of leptin are still poorly understood. Therefore, we examined distribution of leptin receptor-containing neurons transsynaptically connected with the porcine fat tissue by means of combined viral transneuronal tracing and immunohistochemical staining method. Pseudorabies virus (PRV) was injected into the perirenal fat tissue in pigs, and after survival periods of 3, 5, 7, 9, and 11 days, hypothalami were processed immunohistochemically with primary antisera against PRV and leptin receptor (OBR). PRV labeled neurons were found in paraventricular nucleus (PVN), ventromedial nucleus (VMN), anterior hypothalamic area (AHA), preoptic area (PA), arcuate nucleus (ARC), and supraoptic nucleus (SON) by nine days after injection of the virus. Double-labeling immunofluorescence demonstrated that OBR were co-localized in nearly all virus-infected neurons. The present results provide the first morphological data demonstrating a multisynaptic circuit of neurons of CNS origin which innervates porcine fat tissue.

Adipose Tissue↗
PubMed2004

Firing properties and connectivity of neurons in the rat lateral central nucleus of the amygdala.

Using whole cell recordings from acute slices of the rat amygdala, we have examined the physiological properties of and synaptic connectivity to neurons in the lateral sector of the central amygdala (CeA). Based on their response to depolarizing current injections, CeA neurons could be divided into three types. Adapting neurons fired action potentials at the start of the current injections at high frequency and then showed complete spike-frequency adaptation with only six to seven action potentials evoked with suprathreshold current injections. Late-firing neurons fired action potentials with a prolonged delay at threshold but then discharged continuously with larger current injections. Repetitive firers discharged at the start of the current injection at threshold and then discharged continuously with larger current injections. All three cells showed prolonged afterhyperpolarizations (AHPs) that followed trains of action potentials. The AHP was longer lasting with a larger slow component in adapting neurons. The AHP in all cell types contained a fast component that was inhibited by the SK channel blocker UCL1848. The slow component, not blocked by UCL1848, was blocked by isoprenaline and was significantly larger in adapting neurons. Blockade of SK channels increased the discharge frequency in late firers and regular-spiking neurons but had no effect on adapting neurons. Blockade of the slow AHP with isoprenaline had no effect on any cell type. All cells received a mixed glutamatergic and GABAergic input from a medial pathway. Electrical stimulation of the lateral (LA) and basolateral (BLA) nuclei evoked a large monosynaptic glutamatergic response followed by a disynaptic inhibitory postsynaptic potential. Activation of neurons in the LA and BLA by puffer application of glutamate evoked a small monosynaptic response in 13 of 55 CeA neurons. Local application of glutamate to the CeL evoked a GABAergic response in all cells. These results show that at least three types of neurons are present in the CeA that can be distinguished on their firing properties. The firing frequency of two of these cell types is determined by activation of SK channels. Cells receive a small input from the LA and BLA but may receive inputs that course through these nuclei en route to the CeA.

Action Potentials↗
PubMed1989

Simultaneous recording of presynaptic spikes and excitatory postsynaptic potentials from monosynaptically connected hippocampal neurons.

A technique has been devised to activate single granule cells in the hippocampus, and to record simultaneously spikes from the particular granule cell and excitatory postsynaptic potentials from a monosynaptically connected CA3 neuron. The unitary excitatory postsynaptic potentials (EPSPs) sustained for long observation periods, and increased in size with increases in stimulus frequency and in external Ca2+ concentration. This technique may be useful for quantal analysis of transmission through the synapse between mossy fibers and CA3 neurons.

Action Potentials↗
PubMed2003

Loss of dendritic connectivity in CA1, CA2, and CA3 neurons in hippocampus in rat under aluminum toxicity: antidotal effect of pyridoxine.

Aluminum chloride (AlCl(3); 4 mg/kg) was injected into the cerebrospinal fluid of adult rats as a one time dose. Rapid Golgi stained sections of hippocampus were examined for detailed histology of neurons in CA1, CA2, and CA3 areas. The axonal length and number of dendritic branches were seen reduced 30 days later in aluminum (Al)-injected group when compared to vehicle-injected controls. Of these perturbations, dendritic branches were seen reduced significantly. Al toxicity apparently affects neuronal connectivity in hippocampus. These perturbations are reversed by supplementing the feed with pyridoxine (8 mg/kg) for 30 days. As the loss of synaptic connectivity is a predominant feature of neurodegenerative disorders such as Alzheimer disease, this study may have implications in such disorders. Pyridoxine may be considered as a potent antidote to Al toxicity and neurodegenerative disorders such as Alzheimer disease.

Aluminum Chloride↗
PubMed2002

Electrophysiological and morphological characterization of the medulla bilateral neurons that connect bilateral optic lobes in the cricket, Gryllus bimaculatus.

The medulla bilateral neurons (MBNs) in the cricket brain directly connect two optic lobes and have been suggested to be involved in mutual coupling between the bilateral optic lobe circadian pacemakers. Single unit analysis with intracellular recording and staining with Lucifer Yellow was carried out to reveal morphology and physiology of the MBNs. Neurons having a receptive field in the rostral part of the compound eye showed greater response and a higher sensitivity to light than those having receptive fields in the ventro-caudal or dorsal portions. The MBN showed diurnal change in their responsiveness to light; the light-induced response in the night was about 1.3, 5 and 2 times of that in the day in MBN-1s, -3s and -4s, respectively. These results suggest that the MBNs mainly encode the temporal information by the magnitude of light-induced responses. The differences in magnitude of light-induced responses and of daily change in photo-responsiveness among MBNs may suggest that each group of MBNs plays different functional role in visual and/or circadian systems.

Journal Article↗
PubMed1986

Insect optic lobe neurons identifiable with monoclonal antibodies to GABA.

Five monoclonal antibodies against GABA were tested on glutaraldehyde fixed sections of optic lobes of three insect species, blowflies, houseflies and worker bees. The specificity of these antibodies was analyzed in several tests and compared with commercially available anti-GABA antiserum. A very large number of GABA-like immunoreactive neurons innervate all the neuropil regions of these optic lobes. Immunoreactive processes are found in different layers of the neuropils. The immunoreactive neurons are amacrines and columnar or noncolumnar neurons connecting the optic lobe neuropils. In addition some large immunoreactive neurons connect the optic lobes with centers of the brain. Some neuron types could be matched with neurons previously identified with other methods. The connections of a few of these neuron types are partly known from electron microscopy or electrophysiology and a possible role of GABA in certain neural circuits can be discussed.

Animals↗