Variability of morphologic parameters of individual neurons and neuron clusters in the visceral ganglion of the mollusk Lymnaea stagnalis L

Quantitative investigations on variability of visual morphological parameters in neurons BB1, BB3-5 and clusters BBb have been performed on the ventral side of the visceral ganglion in 20 molluscs Lymnaea stagnalis L. (height of the shell -45.5-1.3 mm, variation coefficient -2.9%) cought in the same pond and on the same day. Statistical analysis of the data obtained is performed by means of the methods applied for analysing small independent samples. A probability character of visual identification and an essential variability are demonstrated for the parameters of the neuron BB1 (diameter, position, colour), of the number of giant and/or large neurons BB3-5 and the cluster BBb neurons. The variation character of the parameters mentioned is asymmetric. It is possible to speak on a greater determinancy of a preferable gradation of the parameters. The interconnection of the variability and the determinancy of the morphological signs with the identificity and functioning of the neuronal elements are discussed. A suggestion is made that identification of the neurons according to both their morphological and functional criteria, as a whole, can have a probability character. The data considered in the work make doubt the invariance of the neurons studied in the mollusc Lymnaea stagnalis L.     

Neurons Expressing Tyrosine Hydroxylase or Aromatic L-Amino Acid Decarboxylase in the Mediobasal Hypothalamus of Wistar Rats in Ontogeny: Topographic Interrelations and Axonal Projections to the Medial Eminence

Topographic interrelations of the arcuate nucleus (AN) neurons expressing the dopamine-synthesized enzymes, tyrosine hydroxylase (TH) and/or aromatic L-amino acid decarboxylase (AAD), as well as projections of axons of these neurons to the medial eminence were studied in male rats at the 21st embryonal and 9th postnatal days as well as in adult animals. The method of double immunocytochemical labeling and its modification were used to reveal these enzymes. For identification of immunoreactive neurons, a confocal microscope was used. At all ontogenetic stages, three populations of neurons were found, which differed by composition of the dopamine-synthesizing enzymes as well as by the character of topographic interrelations of the TH-expressing monoenzyme neurons with the AAD-expressing neurons. In ontogeny, the topographic tight junctions are formed between the monoenzyme TH- and AAD expressing neurons at the level of both the cell body and the distal axons, which seems to increase effectiveness of the L-dihydroxyphenylalanine (L-DOPA) transfer from the TH- to the AAD-expressing neurons. The TH- and AAD expressing monoenzyme neurons project their axons to the medial prominence to provide entrance of the products of the specific syntheses into the pituitary portal circulating system. Thus, the morphological data obtained confirm indirectly our hypothesis about a cooperative participation of the TH- and AAD-expressing monoenzyme neurons of the AN in the dopamine synthesis.     

Electrogenesis in molluscan giant neurons after treatment with ribonuclease

Electrical activity of identified and unidentified neurons ofHelix pomatia was recorded intracellularly after incubation of the ganglia for 0.5, 1, and 2 h in ribonuclease (RNAse) solution. Histochemical and cytophotometric analysis showed that after 30 min no RNA could be found in any of the neurons studied or in the glia and neuropil of the ganglia. At these times of incubation action potentials and spontaneous and evoked postsynaptic potentials could be recorded in all the neurons studied. The response to microapplication of acetylcholine to the neuron soma or to its direct electrical stimulation remained the same as in the control. In the identified neurons the addition of RNAse and its subsequent action did not alter their electrogenesis even after incubation for 2 h. It is concluded that electrogenesis is not directly dependent on the RNA content in the neuron. The primary role of RNA is considered to be participation in the synthesis of the specific proteins responsible for synaptic transmission.I. M. Sechenov Institute of Physiology, First Medical Institute, Moscow. Faculty of Psychology, Moscow State University, Moscow. Translated from Neirofiziologiya, Vol. 4, No. 4, pp. 423–428, July–August, 1972.     

Epigenetic mechanisms of character origination

The close mapping between genotype and morphological phenotype in many contemporary metazoans has led to the general notion that the evolution of organismal form is a direct consequence of evolving genetic programs. In contrast to this view, we propose that the present relationship between genes and form is a highly derived condition, a product of evolution rather than its precondition. Prior to the biochemical canalization of developmental pathways, and the stabilization of phenotypes, interaction of multicellular organisms with their physicochemical environments dictated a many-to-many mapping between genomes and forms. These forms would have been generated by epigenetic mechanisms: initially physical processes characteristic of condensed, chemically active materials, and later conditional, inductive interactions among the organism's constituent tissues. This concept, that epigenetic mechanisms are the generative agents of morphological character origination, helps to explain findings that are difficult to reconcile with the standard neo-Darwinian model, e.g., the burst of body plans in the early Cambrian, the origins of morphological innovation, homology, and rapid change of form. Our concept entails a new interpretation of the relationship between genes and biological form.     

Identified target motor neuron regulates neurite outgrowth and synapse formation of aplysia sensory neurons in vitro

To determine the influence that an appropriate target cell has on the axonal structure of a presynaptic neuron in vivo, we examined the morphologies of individual Aplysia sensory neurons in dissociated cell culture in the presence or absence of identified target motor neurons. We find that an appropriate target, the motor cell L7, regulates the morphological differentiation of the presynaptic sensory neurons in two ways: the target induces the axons of the sensory neurons to develop a more elaborate structure and to form active zones, and the target guides the outgrowth of the sensory neurons. The influence of the appropriate target, L7, on the morphological differentiation of sensory neurons appears to be related to the formation of chemical synaptic connections between the sensory neurons and L7, since sensory neurons co-cultured with an inappropriate target motor neuron do not exhibit a comparable elaboration of their axonal processes.     

Effects of Some Organic Cations on Generator Potential of Crayfish Stretch Receptor

The generator potential of both slowly and rapidly adapting crayfish stretch receptor cells can still be elicited by mechanical stimuli when all the Na of the bathing medium is replaced by various organic cations. In the presence of tris(hydroxymethyl)aminomethane (Tris), the generator potential is particularly large, about 30–50 % of that in the control saline, while spike electrogenesis of the cell is abolished. Persistence of the generator response is not due to retention of Na by a diffusion barrier, and ionic contributions to the electrogenesis by Ca and Cl can also be excluded. Thus, whereas the electrogenesis of the generator membrane must be due to an increased permeability to monovalent cations, the active receptor membrane appears to be less selective for different monovalent cations than is the receptor component of some other cells, or the conductile component of the stretch receptor neuron.     

About Mechanisms of Transformation of Sensory Neurons into Associative Neurons in the Epidermal Plexus and Ganglia of Bilateria

Studies of morphological processes in culture of pulmonate mollusc neurons have allowed identifying structural criteria for the main morphogenetic mechanisms: growth and retraction of processes, their invagination into the cell body, and changes of neuronal orientation. By comparing these criteria with pictures of fixed preparations of epidermal plexus of phoroniids and of abdominal ganglion of polychaetes, stained supravitally with methylene blue, it has become possible to determine possible mechanisms of the initial evolutionary morphogenesis of the nervous system. Thus, it can be concluded that outcome of sensory neurons from epithelium (start of centralization) occurs as a result of retraction of their basal processes and translocation of the nucleus with the surrounding cytoplasm inside the processes to the center. This leads to a narrowing and thinning of the sensory cell apical pole that is transformed into a train process (the primary sensory dendrite). Subsequently, at the end of this process in a part of sensory neurons, a bulb of retraction appears, and the process contracts and is invaginated into the neuronal body. The loss of the sensory dendrite under conditions for formation of interneuronal connections in the nerve plexus converts the primary sensory cell into the associative neuron. A similar mechanism can also be placed in a part of sensory neurons of abdominal ganglion of polychaetes. Using morphogenetic criteria of mobility, it becomes possible to arrange a consecutive line of stages of neuronal structural reconstructions to show contraction of the receptor dendrite with its gradual invagination into the cellular soma. Loss of the dendrite in this case also transforms the sensory neuron into the associative one. All the above processes act as the inexorable cause-effect mechanisms of the single evolutionary process of centralization of the nervous system.     

Functional heterogeneity of the electroexcitable membrane of nerve cells

The own and literary data connected with a problem of functional heterogeneity of the electroexcitable membrane of the nerve cells is presented. The results which testify the peculiarities of spreading of excitability on somatic membrane of isolated neuronal somata and the form of somatic action potentials studied by using the micro-computer have been analysed. The morphological heterogeneity of the electroexcitable membrane is suggested to be the basis of the electrogenesis action potentials.     

Responses of caudate neurons to direct electrical stimulation of the medial geniculate body in cats

Activity of 124 neurons of the caudate nucleus during stimulation of the medial geniculate by infrequent (0.5 Hz) square electrical stimuli 0.3 msec in duration and ranging in intensity from 50 µA to 1 mA was investigated extracellularly in chronic experiments on cats. Responses were recorded from 54 neurons (43%). The main types of neuronal responses were phasic activation in the form of a single spike or spike discharge, initial activation followed by inhibition, and primary inhibition of unit activity. Responses of excitatory character predominated (81% of all responses). Their latent period varied in different neurons from 2.7 to 64 msec. Latent periods of responses of the same neuron always showed great variability, so that all the responses recorded could be considered to be orthodromic. The mode of the histogram of latent periods of excitatory responses lay between 9 and 12 msec. The latent period of the inhibitory response varied from 12 to 130 msec, and in most neurons with this type of response it was 40–60 msec. An increase in the strength of stimulation was accompanied by an increase in the regularity of the responses, an increase in the number of spikes in them, and shortening of their latent period. The character and structure of the response of the same caudate neuron to stimulation of the medial geniculate body and to presentation of clicks were usually identical. The latent period of responses to clicks was longer. The particular features of the functional connection of the medial geniculate body with the caudate nucleus as a polymodal nonspecific structure of the forebrain are discussed.     

A neuroanatomical study on the organization of the central antennal pathways in insects

1. Single unimodal (olfactory) or multimodal (olfactory and mechanosensory) neurons in the antennal lobe of the deutocerebrum of the American cockroach were characterized functionally by microelectrode recording, and their morphological types and positions in the brain were established by dye injection. Thus individual, physiologically identified neurons of known shape could be mapped in reference to the areas of soma groups, glomeruli, tracts and their projection regions in the brain. 2. All of these neurons send processes to deutocerebral glomeruli, i.e., the regions in which the axons of antennal sensory cells terminate. Output neurons have axons that leave the deutocerebrum whereas local interneurons are anaxonic. 3. An output neuron innervates only one glomerulus, sending its axon into the calyces of the corpora pedunculata (CP) in the protocerebrum, where by multiple branching they reach many CP neurons. The same axons send collaterals into the lateral lobe of the protocerebrum. Because of this arrangement, each deutocerebral glomerulus is represented individually and separately in the two projection regions. The fine structure of the endings of the deutocerebral axons in the protocerebrum is described. In the CP calyces they form microglomeruli with typical divergent connectivity. 4. A local interneuron innervates many glomeruli without sending processes to other parts of the brain. 5. Unimodal olfactory and multimodal neurons can be either output neurons or local interneurons; multimodal information is sent to the protocerebrum directly, in parallel with the unimodal information. 6. At least one glomerulus--the macroglomerulus of the male deutocerebrum--is specialized so as to provide an exclusive topographic representation of certain olfactory stimuli not represented elsewhere (female sexual pheromone).     

A newly recognized fossil coelacanth highlights the early morphological diversification of the clade

Previously considered an actinopterygian or an osteichthyan incertae sedis, the Devonian (Givetian-Frasnian) Holopterygius nudus is reinterpreted as a coelacanth. This genus is among the oldest coelacanths known from articulated remains, but its eel-like morphology marks a considerable departure from the conventional coelacanth body plan. A cladistic analysis places Holopterygius as the sister taxon of the Carboniferous (Serpukhovian) genus Allenypterus. Despite the specialized morphology of these genera, they occupy a surprisingly basal position in coelacanth phylogeny; only Diplocercides and Miguashaia are further removed from the crown. A morphometric analysis reveals that coelacanths were anatomically disparate early in their history. Conflicts between this result and those of previous studies challenge the adequacy of systematic character sets for describing historical patterns of morphological variety. Coelacanths have long had an iconic place in the study of vertebrate evolution for their apparent anatomical conservatism over geological time, but Holopterygius provides clear evidence for rapid morphological evolution early in the history of this clade.     

Multivariate morphometries of the Ethiopian populations of harsh-furred rat (Lophuromys: Mammalia, Rodentia)

We investigated the geographic variation of eight Ethiopian populations of the rodent Lophuromys flavopunctatus and compared them to the Bale endemic species L. melanonyx. We used multivariate morphometrics and analysed independently skull and external body linear measurements, in an attempt to relate morphological variability to geography (latitude, longitude, altitude). There is a high morphological diversity in these Ethiopian populations, which form three distinct recognizable groups, with the Bale population being the most distinct. The results of analyses on the two character sets corroborate each other and indicate that the kind of variation is not 'ecological' but rather there is a phylogenetic cause, and relations at higher taxonomic level are suggested. There is a homogeneous group with five populations within which there is a recognizable pattern of clinal variation related to altitude, with a decrease in body size and a change in skull shape.     

Tiling of the Drosophila epidermis by multidendritic sensory neurons

Insect dendritic arborization (da) neurons provide an opportunity to examine how diverse dendrite morphologies and dendritic territories are established during development. We have examined the morphologies of Drosophila da neurons by using the MARCM (mosaic analysis with a repressible cell marker) system. We show that each of the 15 neurons per abdominal hemisegment spread dendrites to characteristic regions of the epidermis. We place these neurons into four distinct morphological classes distinguished primarily by their dendrite branching complexities. Some class assignments correlate with known proneural gene requirements as well as with central axonal projections. Our data indicate that cells within two morphological classes partition the body wall into distinct, non-overlapping territorial domains and thus are organized as separate tiled sensory systems. The dendritic domains of cells in different classes, by contrast, can overlap extensively. We have examined the cell-autonomous roles of starry night (stan) (also known as flamingo (fmi)) and sequoia (seq) in tiling. Neurons with these genes mutated generally terminate their dendritic fields at normal locations at the lateral margin and segment border, where they meet or approach the like dendrites of adjacent neurons. However, stan mutant neurons occasionally send sparsely branched processes beyond these territories that could potentially mix with adjacent like dendrites. Together, our data suggest that widespread tiling of the larval body wall involves interactions between growing dendritic processes and as yet unidentified signals that allow avoidance by like dendrites.     

The fine structure of the rat pineal and the influence of anti-androgens and castroation]

The pineal body, along with the hypothalamus-hypophysis system, is in the centre of sexual hormone regulation and, in addition to other functions, develops an antigonadotropic action through its organ specific hormone (melatonin). In order to clarify further open questions and to analyse more closely the morphology of the fine structure of the organ, light and electron microscopic studies were made of the pineal bodies of sexually mature male rats after hormonal castration by the administration of cyproterone and cyproterone acetate. The findings were compared with results obtained in the pineal bodies of surgically castrated animals of the same strain. Epiphysectomy was performed 3, 6, 9 and 12 weeks after castration or application of antiandrogen. In the pineal bodies, "light" and "dark" pineal cells and an interstitial cell form could be detected electronmicroscopically. The interstitial cells are found localised near the vessels in particular; their ramifications reach into the perivascular cleft. The light pineal cells preponderate and react essentially in the series; they are therefore considered as the really active form of parenchyma cells. Increased cell activity is already observed three weeks after treatment with antiandrogen: the nucleoli are enlarged, the ribosomes, the mitochondria and ergastoplasm are increased, the endoplasmic reticulum quantified and extended, and also the Golgi regions. The cells are consequently enlarged. Lysosomes also appear which frequently enter the liposomes. The changes in the liposomes after application of antiandrogen are remarkable. Initially they are evacuated, partially drawn out. Later the liposomes are enlarged and increased and often fill the cell body. These pineocytes form an appendage to the castration cells of the hypophysis. The liposomes are in a very close spatial, formal genetic relationship to the Golgi apparatus and to the rough walled reticulum. The larger liposomes apparently arise also through the confluence of smaller ones. Three structural elements of the liposomes could be indentifed: a homogenous, a lamellar and a granular component. The fine morphological reactions are most marked after cyproterone acetate. For the first time, bundles of "microtubuli" are described, the significance of which is not yet clear. They probably arise from the endoplasmic reticulum, they are only found after cyproterone acetate and are presumably due to the gestagen component of the cyproterone acetate. These structures have not previously been observed, either in pineal bodies or in other organs. The structures found after antiandrogen are not so outstandingly recognisable after surgical castration. The biological differences of the surgical compared with hormonal castration therefore seem to be reflected in the cell picture of the pineocytes. Consequently, the pineal body, after treatment with antiandrogen, shows cytostructural changes similar to those of increased anabolism...     

Characterization of pancreas-projecting rat dorsal motor nucleus of vagus neurons

The electrophysiological and morphological properties of rat dorsal motor nucleus of the vagus (DMV) neurons innervating the pancreas were examined by using whole cell patch clamp recordings from brain stem slices and postfixation morphological reconstructions of Neurobiotin-filled neurons. Recordings were made from 178 DMV neurons whose projections had been identified by previous apposition of the fluorescent neuronal tracer DiI to the body of the pancreas. DMV neurons projecting to the pancreas had an input resistance of 434 +/- 14 M omega, an action potential duration of 3 +/- 0.1 ms, and an afterhyperpolarization of 18 +/- 0.4 mV amplitude and 108 +/- 7 ms time constant of decay; these electrophysiological properties resembled those of gastric-projecting neurons but were significantly different from those of intestinal-projecting neurons. Interestingly, 14 of 178 pancreas-projecting neurons showed the presence of a slowly developing afterhyperpolarization whose presence was not reported in DMV neurons projecting to any other gastrointestinal area. The morphological characteristics of pancreas-projecting neurons (soma area 274 +/- 12 microm2; soma diameter of 25 +/- 0.7 microm; soma form factor 0.74 +/- 0.01; segments 9.7 +/- 0.41), however, were similar to those of intestinal- but differed from those of gastric-projecting neurons. In summary, these results suggest that pancreas-projecting rat DMV neurons are heterogeneous with respect to some electrophysiological and morphological properties. These differences might underlie functional differences in the vagal modulation of pancreatic functions.     

Neuronal organization of the periamygdaloid cortex in the cat brain

Neuronal organization of the fields Pmm, Pml2, Pe and epm of the periamygdaloid cortex of the cat brain has been studied by means of Golgi and Nissl methods. The field Pmm essentially differs from other fields of this cortex by primitiveness of its cytoarchitectonic an neuronal organization (two layers uniform by the composition of their neurons are distinguished, the structure of the latter is relatively primitive). In the medial part of this field long axonal rarely branching short dendritic, and in the lateral part--poorly differentiating pyramidal and spindle-like cells predominate. The field Pmm can be considered as a transitional formation between the subcortex (the medial nucleus of the amygdaloid body) and other fields of the periamygdaloid cortex. The fields Pml2, Pe and epm are built more complexly: the cells are organized in 4 layers, more complexly differentiated by their form and size than in the field Pmm and correspondingly more various (long axonal densely branching cells are observed: pyramidal and spindle-like--of the cortical type and bushy--of the subcortical type, as well as long axonal rarely branching reticular cells). The short axonal cells in the fields Pml2, Pe and epm are rather variable in their form, size and direction of axons; in the field Pmm they are less numerous. The field Pmm and the complex of the fields Pml2, Pe and epm are perhaps different in their function, this is evident from different projection of their neurons. Axons of the cells in the field Pmm get into less differentiated and the most ancient medial nucleus of the amygdaloid body and into the ancient system of connections of the latter--terminal strip, and neurons of the fields Pml2, Pe and epm are projected into the basolateral part of the amygdaloid body and into the external capsule--phylogenetically younger structures. Besides, poverty of the axonal collateralies in the long axonal neurons and a small amount and uniformity of the forms of the short axonal cells in the field Pmm and contrary, rich collateralies and variety of short axonal cells in the composition of other fields demonstrate more complex internal integrative function, performing in that composition.     

Cyclic GMP alters the firing rate and thermosensitivity of hypothalamic neurons

The rostral hypothalamus, especially the preoptic-anterior hypothalamus (POAH), contains temperature-sensitive and -insensitive neurons that form synaptic networks to control thermoregulatory responses. Previous studies suggest that the cyclic nucleotide cGMP is an important mediator in this neuronal network, since hypothalamic microinjections of cGMP analogs produce hypothermia in several species. In the present study, immunohistochemisty showed that rostral hypothalamic neurons contain cGMP, guanylate cyclase (necessary for cGMP synthesis), and CNG A2 (an important cyclic nucleotide-gated channel). Extracellular electrophysiological activity was recorded from different types of neurons in rat hypothalamic tissue slices. Each recorded neuron was classified according to its thermosensitivity as well as its firing rate response to 2-100 microM 8-bromo-cGMP (a membrane-permeable cGMP analog). cGMP has specific effects on different neurons in the rostral hypothalamus. In the POAH, the cGMP analog decreased the spontaneous firing rate in 45% of temperature-sensitive and -insensitive neurons, an effect that is likely due to cGMP-enhanced hyperpolarizing K(+) currents. This decreased POAH activity could attenuate thermoregulatory responses and produce hypothermia during exposures to cool or neutral ambient temperatures. Although 8-bromo-cGMP did not affect the thermosensitivity of most POAH neurons, it did increase the warm sensitivity of neurons in other hypothalamic regions located dorsal, lateral, and posterior to the POAH. This increased thermosensitivity may be due to pacemaker currents that are facilitated by cyclic nucleotides. If some of these non-POAH thermosensitive neurons promote heat loss or inhibit heat production, then their increased thermosensitivity could contribute to cGMP-induced decreases in body temperature.     

Neuron-specific phosphorylation of Alzheimer's beta-amyloid precursor protein by cyclin-dependent kinase 5

The mature form of Alzheimer's beta-amyloid precursor protein (APP) is phosphorylated specifically at Thr(668) in neurons. In mature neurons, phosphorylated APP is detected in neurites, with dephosphorylated APP being found mostly in the cell body. In vitro, active cyclin-dependent kinase 5 (Cdk5) phosphorylated the cytoplasmic domain of APP at Thr(668). Treatment of mature neurons with an antisense oligonucleotide to Cdk5 suppressed Cdk5 expression and significantly diminished the level of phosphorylated APP. The expression of APP was unaffected in antisense-treated neurons. These results indicate that in neurons APP is phosphorylated by Cdk5, and that this may play a role in its localization.     

Ultrastructural analysis of interneuronal syncytial perforations

The structural regularities of the organization of interneuronal syncytial cytoplasmic connections between neuronal bodies in gyrus dentatus and CA1 and CA2 (CA is cornu ammonis) of hippocampus, as well as between cell neurites of the caudal mesenteric ganglion were studied by transmission electron microscopy. The syncytial perforations are located only on the base of tight junctions. The perforations have rounded edges corresponding to the fusion edges of perforated membranes of adjacent neurons – or where their edges have a form of thinned plate – a remnant of the tight junction. In the lumen of the perforations, remnants of contact membranes – residual bodies – are revealed. On living neurons in tissue culture, the syncytial connection of two contacting processes of different neurons is found during the death of the body of one of them, but with preservation of viability of its processes that contact with other neurons.