Inhibitory and activatory effects of dopamine on neurons in slices of the compact zone of theSubstantia nigra of rats

Effects of dopamine on the background spike activity of functionally (according to their electrophysiological characteristics) identified dopaminergic (DA) or non-dopaminergic (non-DA) neurons of the compact zone of thesubstantia nigra were studied on slices of the midbrain of adult rats. In the majority of DA neurons, dopamine suppressed the background activity in a dose-dependent manner. Sensitivity of these cells to dopamine varied within a wide range: IC₅₀, the concentration providing the 50% maximum effect, equalled from 3 to 3,000 µM in different units. A part of DA neurons responded to dopamine with an increase in their activity. Mixed responses, in which an initial suppression of impulsation was replaced by a slow-developing activation, was observed in some neurons. Non-DA neurons usually responded to dopamine by an enhancement of impulsation; yet, the cells with inhibitory or mixed responses similar to those of DA neurons could be found in this population as well. Sensitivity of non-DA neurons to dopamine was about the same as that of DA-cells, without the dependence on the direction of responses. S(–)-suipiride, a blocker of D₂ receptors, decreased the inhibitory component of all tested responses to dopamine both in DA and non-DA neurons and evoked no changes in the excitatory component. At the same time, R(+)-SCH 23390 HC1, a blocker of D₁ receptors, suppressed the activatory component of responses with no effect on the inhibitory component. We conclude that both types of DA receptors, D₂ and D₁ receptors, can be present on the DA and non-DA neurons. Dopamine, influencing these receptors, suppresses or facilitates, respectively, the spike activity of these cells. The relative amount of such receptors is the main factor determining the pattern and dynamics of the integral response to dopamine application. The possible functional role of the presence of both D₁ and D₂ receptors on the membrane of a single neuron is discussed.Neirofiziologiya/Neurophysiology, Vol. 27, No. 4, pp. 268–277, July–August, 1995.     

Effects of substantia nigra stimulation on high- and low-threshold response in reticular neurons

The effects of electrical stimulation of the substantia nigra (NS) pars compacta on somatosensory response in pontine neurons (from n. reticularis pontis caudalis) and reticular cells (n. reticularis gigantocellularis) were investigated in chloralosed cats. These effects were found to be inhibitory and tended mainly towards high-threshold activation of reticular neurons: responses induced by activation of high-threshold somatic efferents were those mainly inhibited in 71% of test cells. Inhibition of low-threshold response induced by tactile stimuli emerged less clearly or not at all. Potential mechanisms and the functional significance of these SN influences on reticular neurons are discussed.A. A. Bogomolets Institute of Physiology, Academy of Sciences of the Ukrainian SSR, Kiev. Translated from Neirofiziologiya, Vol. 21, No. 6, pp. 772–780, November–December.     

Glutamatergic neurons induce expression of functional glutamatergic synapses in primary myotubes

Background

The functioning of the nervous system depends upon the specificity of its synaptic contacts. The mechanisms triggering the expression of the appropriate receptors on postsynaptic membrane and the role of the presynaptic partner in the differentiation of postsynaptic structures are little known.

Methods and Findings

To address these questions we cocultured murine primary muscle cells with several glutamatergic neurons, either cortical, cerebellar or hippocampal. Immunofluorescence and electrophysiology analyses revealed that functional excitatory synaptic contacts were formed between glutamatergic neurons and muscle cells. Moreover, immunoprecipitation and immunofluorescence experiments showed that typical anchoring proteins of central excitatory synapses coimmunoprecipitate and colocalize with rapsyn, the acetylcholine receptor anchoring protein at the neuromuscular junction.

Conclusions

These results support an important role of the presynaptic partner in the induction and differentiation of the postsynaptic structures.     

Flotillin‐1 promotes formation of glutamatergic synapses in hippocampal neurons

Synapse malformation underlies numerous neurodevelopmental illnesses, including autism spectrum disorders. Here we identify the lipid raft protein flotillin‐1 as a promoter of glutamatergic synapse formation. We cultured neurons from the hippocampus, a brain region important for learning and memory, and examined them at two weeks in vitro, a time period rich with synapse formation. Double‐label immunocytochemistry of native flot‐1 with glutamatergic and GABAergic synapse markers showed that flot‐1 was preferentially colocalized with the glutamatergic presynaptic marker vesicular glutamate transporter 1 (VGLUT1), compared to the GABAergic presynaptic marker glutamic acid decarboxylase‐65 (GAD‐65). Triple‐label immunocytochemistry of native flot‐1, VGLUT1, and NR1, the obligatory subunit of NMDA receptors, indicates that Flot‐1 was preferentially localized to synaptic rather than extrasynaptic NR1. Furthermore, electrophysiological results using whole‐cell patch clamp showed that Flot‐1 increased the frequency of miniature excitatory postsynaptic currents (mEPSCs) but not miniature inhibitory postsynaptic currents (mIPSCs), whereas amplitude and decay kinetics of either type of synaptic current was not affected. Corresponding immunocytochemical data confirmed that the number of glutamatergic synapses increased with flot‐1 overexpression. Overall, our anatomical and physiological results show that flot‐1 enhances the formation of glutamatergic synapses but not GABAergic synapses, suggesting that the role of flot‐1 in neurodevelopmental disorders should be explored. © 2010 Wiley Periodicals, Inc. Develop Neurobiol 70: 875–883, 2010     

Ultrastructure of neurons and synapses in the tentacle gastrodermis of the sea anemone Calliactis parasitica

Little is known about gastrodermal neurons and synapses in the tentacles of sea anemones. Using transmission electron microscopy of serial thin sections of Calliactis parasitica, we have identified both a sensory cell and a ganglion cell with granular vesicles originating from the Golgi complex and have identified four types of synapses in the tentacular gastrodermal nerve plexus. The sensory cell has a recessed apical cilium with a basal body and a perpendicularly oriented centriole, below which are several strands of striated rootlets surrounded by mitochondria. The ganglion cell lacks a cilium and resembles a bipolar neuron, with oppositely directed processes lying parallel to the basally located circular smooth muscle. Both one-way and two-way interneuronal synapses are present with 60- to 90-nm granular vesicles of various densities aligned at the paired electron-dense membranes and fine cross filaments in the intervening 13-nm cleft. Two types of neuroeffector synapses have been located. Dense granular vesicles are present at neuromuscular synapses, whereas less dense vesicles are present at neuroglandular synapses. Most of the synaptic vesicles range from 60 to 120 nm in diameter. Two types of nerve cells and a variety of synaptic loci provide morphological substrates for the spontaneous SS2 conduction pulses in the tentacular gastrodermis of C. parasitica. J Morphol 231:217–223, 1997. © 1997 Wiley-Liss, Inc.     

Effects of lingual nerve section on morphometric characteristics of reticular nucleus neurons in the kitten brain stem

Computerized morphometric techniques were used to investigate each of 23 parameters in three types of brain stem reticular nucleus neurons in Golgi-stained frontal slices from the brain of 30-day-old kittens after uni- and bilateral lingual nerve section 5–7 days after birth. Particular statistically significant differences in some parameters were discovered in all types of cell. Certain group-specific differences in parameters could be most frequently distinguished in each category: distribution of loose dendritic endings through the dendritic area in reticular neurons, length of dendritic segments in branching cells, and distribution of foci of dendritic arborization in giant multipolar neurons. Unilateral lingual nerve section results in quantitatively more marked deviation from the normal state. It was only under these circumstances, moreover, that differences in overall length of dendrites could be seen, which could indicate a difference in the surface area of the cell.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 23, No. 4, pp. 409–418, July–August, 1991.     

Nature of the distribution of synapses in the neurons of the reticular formation and some afferent nuclei]

Under study was the morphology of synaptic terminations of the brain reticular formation in cats and dogs as well as that of the afferent nuclei of the cat's posterior columns. The neurons of the Goll's and Burdach's nuclei have a richly ramified dendritic network. In this connection the main mass of synapses is disposed on the dendrites and their different branchings. The dendrites of the multipolar cells of the reticular formation have the main type of branching, but the cells are distributed from the nerve cell body at a considerable distance (up to 50 mu and more). The synapses are observed at the total length of the dendrite, so the axo-dendritic contacts quantitatively prevail over axo-somatic ones. The morphological data are compared with physiological axo-somatic and axo-dendritic concepts of the role of synapses in conducting the nerve impulse.     

Morphometric parameters of neurons in reticular nuclei of the brain stem in kittens

Three types of Golgi-stained neurons were discovered in brain stem reticular nuclei of 30-day-old kittens: sparsely branching reticular neurons, those with densely branching dendritic trees, and giant multipolar neurons (Leontovich's classification). Adopting computerized morphometric techniques enabled 23 different parameters to be measured in cells of these types. The measurements taken from the neuronal groups investigated revealed statistically significant differences between them for most parameters. It was concluded from this that each of the neuronal types distinguished has its own morphological identity (or stability). Characteristics of structural differences and properties of differing cell types in reticular nuclei are discussed in relation to their functional properties.Institute of Higher Nervous Activity and Neurophysiology, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 23, No. 4, pp. 399–409, July–August, 1991.     

Ultrastructural parameters of GABA-ergic and non-GABA-ergic synaptic contacts on neurons of the catsubstantia nigra

Nigrothalamic neurons were identified in the reticular part of thesubstantia nigra using labelling by the retrograde axonal transport of horseradish peroxidase. Nine parameters of the synaptic contacts (n=195) were analyzed, including the size and shape of terminals and size and type of synaptic vesicies. Sixty-six percent of axon terminals studied formed symmetric contacts and contained large polymorphic vesicles (group I). Two-thirds of these synapses were located on the distal dendrites, while one-third was distributed on the perikarya and proximal dendrites. Synapses of group II (29% of all synapses analyzed) exhibited asymmetric contacts and contained round agranular vesicles. Among these synapses, 79% were located on the distal dendrites, 19% were located on the proximal dendrites, and only 2% were located on the neuronal perikarya. Axon terminals of group III (5% of total population) exhibited symmetric contact and contained small polymorphic vesicles. High-resolution immunogold EM histochemistry indicated that 63% of the group-I axon terminals were GABA-positive. The majority of synapses on the labelled nigrothalamic neurons (21 contacts of 25) belonged to group I. Among these 21 synapses, 19 were axo-somatic and mostly GABA-positive. Within group II, 30% of synapses showed slightly expressed GABA-positivity.Neirofiziologiya/Neurophysiology, Vol. 27, No. 2, pp. 147–157, March–April, 1995.     

Synaptic processes evoked in red nucleus neurons by stimulation of the substantia nigra in cats

Synaptic processes in red nucleus neurons evoked by stimulation of different parts of the substantia nigra and nucleus interpositus of the cerebellum were investigated by an intracellular recording method in acute experiments on cats. Stimulation of this sort was shown to induce mono- and polysynaptic activation of rubrospinal neurons. Monosynaptic cerebellar and nigral excitatory influences were found to be very similar. These influences were shown to converge on the same rubrospinal neurons. The functional significance of inputs from the substantia nigra to the red nucleus for movement performance is discussed.L. A. Orbeli Institute of Physiology, Academy of Sciences of the Armenian SSR, Erevan. Translated from Neirofiziologiya, Vol. 13, No. 2, pp. 149–158, March–April, 1981.     

Ultrastructure and distribution of somatostatin-like immunoreactive neurons and nerve fibres in the coeliac ganglion of cats

Summary Somatostatin-like immunoreactivity was localized in nerve cell bodies and nerve terminals in the cat coeliac ganglion. Two types of somatostatin-immunoreactive cell bodies were revealed, the first being large (diameter 35 m), numerous and weakly labelled, where—as the second was considerably smaller (diameter 10.4 m), sparsely distributed and heavily stained. The immunoreactive nerve terminals were in synaptic contact with many immunonegative large neurons and dendrites. However, in a few cases, somatostatin-immunoreactive nerve terminals could also be observed on the surface of lightly stained neurons. Transection of vagal or mesenteric nerve failed to affect the distribution or density of somatostatin-like immunoreactive nerve terminals. These results demonstrate the existence of a synaptic input to the principal neurons of the coeliac ganglion of the cat by somatostatin-containing nerve terminals and suggest that this peptide may act as a neuromodulator or neurotransmitter. It is proposed that somatostatin-positive neurons provide intrinsic projections to other somatostatin-positive and to somatostatin-negative neurons throughout the coeliac ganglion, thereby creating a complex interneuronal system.     

Changes in the ultrastructure and morphometric parameters of the cortical axospinal synapses as affected by a calcium-free medium

Slice preparations of the white mouse sensorimotor cortex were examined for the morphometry of axospinal synapses in the material obtained under a standard experimental procedure and in sections perfused in calcium-free medium. The calcium-free medium in slice preparations was shown to reduce considerably the spine length and to increase the amount of spines with a negative curvature of the spine head in the contact area. Besides, it is noticed that the postsynaptic thickening grows, the active zone length decreases, the number of perforated contacts drops and the spine apparatus moves to the dendritic zone. It is supposed that the spine apparatus transfer is probably due to the reorganization of spine cytoskeleton, i.e., it is determined by both the motor activity of dendritic microtubules and the polymerization level of spine microfilaments.     

Impulse response of neurons of the thalamic reticular nucleus to extraneous stimulation in conditioned-reflex trained cats

During heteromodal extraneous stimulation (ES), a large part of responding neurons of the thalamic reticular nucleus (RN) exhibit selectivity by responding with excitation to the stimulation of only one type of sensory input. To visual ES, 12 of 32 tested neurons responded; and 4 of 21 tested neurons responded to auditory ES. Response of neurons to ES diminished during the process of habituation to these stimuli; and after habituation was completed, the number of neurons responsive to the ES also diminished. Use of ES led to disappearance of high-frequency, grouped discharges in the responses of the RN neurons. Initial responses to ES and to the following conditioning stimulus (CS) appeared during external inhibition of the conditioned reflex (CR), but the later components of impulse responses that ordinarily accompany realized CR were suppressed in nearly one half of the studied neurons. We reach the conclusion that RN neurons participate in external inhibition of CR and in habituation to ES.A. A. Bogomolets Physiology Institute, Academy of Sciences of the USSR, Kiev. Translated from Neirofiziologiya, Vol. 23, No. 2, pp. 189–199, March–April, 1991.     

Ultrastructure of neurons of the human sympathetic ganglia after sudden death (morphometric study)

Six cases of urgent autopsies after a sudden cardiac death (SCD) of persons at the age 40-60 years and 5 control cases have been investigated. Osmiophilic mitochondria with inclusions make 1% of the whole neuronal cytoplasm volume. If we take all mitochondria as 100%, volumetric density of mitochondria with osmiophilic inclusions makes 9.6%. Volumetric density of mitochondria at SCD in comparison with the control is significantly higher in connection with increase of their size. In other components of cytoplasm, in particular in lysosomes and lipofuscin, no changes are revealed.