An inexpensive computer-aided morphometric device for the analysis of dissociated brain cell cultures

Dendritic hypertrophy of Stach type VI neurons within experimentally altered ileum of pigs

Myenteric neurons were investigated morphometrically to answer the question if type-specific somal hypertrophy of type VI neurons in mechanically stressed ileum of pigs, which was known from an earlier study, is correlated with an increased dendritic arborization, that is, with dendritic hypertrophy. Muscular hypertrophy was induced in the ileum of two juvenile pigs by narrowing the gut circumference (mechanical stenosis) and by reversing a loop of ileum which results in an antiperistaltic segment (functional stenosis), respectively. After a survival time of 6 weeks, wholemounts from the pre- and poststenotic ileal regions, from the antiperistaltic segment as well as from an age matched control animal, were silver impregnated. Dendritic parameters of Stach types IV and VI neurons were recorded using a computer-aided morphometric program and analysed statistically. Type IV neurons showed no change of dendritic parameters, neither within control nor within stenosed ileal segments. In contrast, the type VI neurons displayed increased dendritic parameters within zones of muscular hypertrophy such as total dendritic length, numbers of dendrites, of dendritic branching points and of dendritic endings. We suggest that type VI neurons may participate as descending nitrergic interneurons or motorneurons in the control of muscular function, thus, undergoing plastic changes in case of experimental muscular hypertrophy. Type IV neurons which are involved in the regulation of mucosal processes were not affected by muscular hypertrophy.

Experimental hypertrophy of myenteric neurones in the pig: a morphometric study

Muscular hypertrophy in the ileum of two pigs aged 6 weeks was induced using two different surgical techniques, narrowing of the gut circumference (mechanical stenosis) and segmental reversal of an ileal loop which results in a persistent antiperistalsis of that segment (functional stenosis). These pigs were sacrificed 5-6 weeks postoperatively. Cross sections through the gut wall at various distances from the operation sites revealed marked muscular hypertrophy in the pre-stenotic regions and in the reversed segment. Whole mounts from pre- and post-stenotic, as well as reversed ileal regions, were silver- impregnated. The corresponding ileal region of a third, nonoperated pig served as control. Using a computer-aided morphometric device, somal areas of five morphological neurone types were measured at various distances orally and anally from the operation sites and along the control ileum. Values between hypertrophic and nonhypertrophic zones as well as between two corresponding zones of nonoperated ileum were compared statistically. Along the control ileum, values revealed no differences in soma sizes. Within the experimentally altered material, somal areas of type VI neurones showed marked hypertrophy related to the sites of muscular hypertrophy whereas the other types remained constant throughout (II, IV in segmental reversal) or showed slightly larger somal areas within the post-stenotic, nonhypertrophied zones (I, V, IV in stenosis). Additionally, within the reversed segment, neuronal perikarya of type I, II, IV and V neurones were larger as compared to the neighbouring regions. However, this enlargement of perikarya within the reversed segment may not be correlated with muscular hypertrophy but rather with the transections of intramural axons before reversing this segment. The results suggest that morphologically distinct neurone types may play different roles within the mechanically stressed small intestine and possibly also in the coordination of normal muscular function.

Neurofilament phosphorylation and axon diameter in the squid giant fibre system

Electron energy loss spectroscopic analysis of squid giant axons in a phosphorus energy window yielded bright signals, which were shown to originate from highly phosphorylated neurofilaments. The frequency and distribution of these signals were analysed at defined intervals in cross-sections of the giant axon, starting from its origin in the stellate ganglion and extending distally along the stellar nerve. The analysis revealed a proximodistal gradient of increasing neurofilament phosphorylation. Within the stellate ganglion and for some distance beyond, the increase in frequency of signals correlated with the widening of the neurofilament meshwork and the radial growth of the axon. This agrees with the hypothesis that neurofilament phosphorylation regulates axon calibre by affecting interfilament spacing. In distal axon domains where the axon diameter diminished, contrary to expectations, the spacing of signals increased and the signals were significantly larger. Hyperphosphorylation apparently compensated for a diminishing supply of neurofilament protein. Contrary to predictions, the presynaptic terminal of the giant synapse contained a distinct and highly phosphorylated neurofilament meshwork. We conclude that the growth of the axon diameter is a function of neurofilament phosphorylation, interfilament spacing and neurofilament density. A mature and highly phosphorylated neurofilament cytoskeleton completely filled the presynaptic terminal of the giant synapse.

Software implementation of statistical methods for the analysis of structure and patterns in neuroanatomical objects

Neuroanatomical research has greatly benefited from the availability of a large number of cell-specific and region-specific molecular markers. In fact, the analysis of spatial patterns of gene expression in individual cells or patterns within cell populations often provides an inroad into understanding the functional significance of distinct structures. However, it can be difficult to discern whether the arrangement of different morphologically or biochemically defined structures represents a defined pattern. To address this issue, we adapted a series of established statistical procedures for the analysis of uni- and bivariate point patterns in histological specimens. We implemented these statistical procedures in an easy-to-use computer program. The methods are scale independent and easy to expand for various applications. The utility of this approach is demonstrated with examples from tissue sections and cultured cells at the light and electron microscopical levels.

Differentiative effects of dopamine on striatal neurons involve stimulation of the cAMP/PKA pathway

The neurotransmitter dopamine (DA) stimulates neurite outgrowth and growth cone formation in cultures of embryonic rat striatum through activation of D1 but not D2 receptors. We show here that neurite outgrowth could be stimulated to a similar extent by elevating cellular cAMP levels. Second, the neuritotrophic effect of DA was completely abolished by inhibiting adenylate cyclase or protein kinase A (PKA) but not protein kinase C (PKC). Third, double staining of cultures with antibodies against growth-associated protein-43 (GAP-43) and the phosphorylated form of the cAMP response element binding protein (pCREB) showed that pCREB was nearly exclusively associated with GAP-43-positive, i.e., actively growing, neurons. Again, this effect depended on D1 receptor and PKA activation. Although cross-talk with other signaling pathways needs to be studied further, we conclude that DA promotes the differentiation of striatal neurons via stimulation of D1 receptors and the cAMP/PKA signal transduction pathway.

Androgens stimulate the morphological maturation of embryonic hypothalamic aromatase-immunoreactive neurons in the mouse

Gonadal steroids play an important role as developmental factors for the rodent brain and are implicated in the sexual differentiation of neural structures. Estrogens have been linked to survival and plasticity of central neurons, thereby regulating the development of hypothalamic and limbic structures associated with reproductive functions. Besides estrogens, androgens also contribute actively to CNS maturation. We have shown recently that androgens stimulate the receptor-mediated functional differentiation of cultured hypothalamic aromatase-immunoreactive (Arom-IR) neurons by stimulating the expression of Arom, the key enzyme in estrogen formation. In the present study, we investigated whether androgens are capable of influencing morphological differentiation of hypothalamic Arom-IR neurons. Androgen treatment, unlike estrogen, stimulated the morphological differentiation of cultured embryonic hypothalamic Arom-IR cells by increasing neurite outgrowth and branching, soma size, and the number of stem processes. This effect was brain region- and transmitter phenotype-specific; neither cortical Arom-IR neurons nor hypothalamic GABAergic neurons responded to androgens. Moreover, morphogenetic effects depended on androgen receptor (AR) activation, since morphological changes were completely inhibited by flutamide. Double-labeling of hypothalamic Arom-IR neurons revealed a considerable number of cells coexpressing AR, whereas cortical Arom-IR cells did not label for AR. Our data demonstrate that androgens function as morphogenetic signals for developing hypothalamic Arom-IR cells, thus being potentially effective in influencing plasticity and synaptic connectivity of hypothalamic Arom-systems.

Myenteric neurons with different projections have different dendritic tree patterns: a morphometric study in the pig ileum

Morphometric analysis was performed of two types of myenteric neurons with at first glance, very similar morphology, but different projections in the pig ileum. 50 type IV cells projecting vertically to the outer submucosal plexus, and 50 solitary type V neurons projecting aborally, within the myenteric plexus, were evaluated. Using a computer-aided morphometric device, the following parameters were recorded: somal area, longest somal diameter, number of primary dendrites, dendritic length, number of dendritic branching points and number of terminal segments. In addition to other significant differences, the most prominent discriminating parameter between the two populations of nerve cells estimated in this study was the length of the longest dendrite of each cell type. The longest dendrite of an individual type V neuron is a manifold longer than the corresponding somal diameter, in contrast to type IV neurons where it is at most twice the somal diameter. In addition, all type IV and type V single dendritic lengths were arranged in histogramms, where the type V dendrites showed two frequency peaks. Thus, we assume that solitary type V neurons can develop two populations of dendrites: a short and a long one. These results demonstrate that myenteric neurons with different projections (and hence different functions) display strikingly different dendritic morphology.

Activation of dopaminergic D1 receptors promotes morphogenesis of developing striatal neurons

The early dopaminergic input from the midbrain may play an important role in the development of the basal ganglia. We therefore investigated whether and how dopamine affects the morphogenesis of striatal target neurons. Dissociated cell cultures of embryonic day 17 rat striatum were raised for seven days. Cells were then incubated with dopamine or various receptor-specific ligands for 1 h. At various times after termination of the treatment, cells were immunostained for growth-associated protein-43. Morphological parameters including numbers of growth cones, length of neurites, number of bifurcations, and neuronal soma size were assessed by means of a computer-based morphometric device. Treatment with dopamine in low concentrations as well as with the D1-like receptor agonist SKF 38393 increased the numbers of growth cones and neurite length and arborization. The morphogenetic effect took several hours to evolve and remained stable for at least 24 h. It could be blocked by the D1-like receptor antagonist SCH 23390 or by cycloheximide but not by pretreatment of the cultures with tetrodotoxin. The D2-like receptor agonist quinpirole had no effect on the morphological parameters and did not contribute to that of SKF 38393. Dopamine and SKF 38393 but not quinpirole also induced an increase in the number of neurons immunoreactive for Fos-like proteins. However, this effect was restricted to growth-associated protein-43-negative neurons. This is the first observation of a positive regulatory effect of D1-like receptors on neuronal morphogenesis. We conclude that the changes reflect true differentiation rather than short-term modulation of cellular properties and that c-fos induction is not an obligatory step in the transduction pathway coupling D1-like receptors to neurite outgrowth. Our results suggest that the differentiation of embryonic striatal neurons is promoted by the dopaminergic nigrostriatal projection through D1-like receptors.

Pre- and postnatal development of dopaminergic neuron numbers in the male and female mouse midbrain

Quantitative information about dopaminergic neuron numbers in the mesencephalon is needed to assess the significance of physiological cell death in the regulation of the development of this neural system. Therefore, stereological techniques were applied to determine absolute numbers of mesencephalic neurons immunoreactive to tyrosine hydroxylase during the ontogenetic period between embryonic day (E) 13 and postnatal day (P) 90. Male and female CBA/J mice were examined separately. The most rapid development with a 2.5-fold increase of total counts of immunostained cells per midbrain took place in the prenatal period. Beginning at E21, immunostained cells were counted separately in their three main locations, substantia nigra (SN), ventral tegmental area (VTA), and retrorubral field (RRF). Neuron numbers in RRF and VTA reached adult levels perinatally. In contrast, counts of immunostained cells in SN continued to increase postnatally. The only sign of cell loss was a transient decrease in VTA cell numbers (but not in total numbers of immunostained midbrain neurons) between E21 and P14. There were no statistically significant sex differences in cell numbers at any time point investigated. It is concluded that physiological cell death is not a major factor in the developmental regulation of dopaminergic cell numbers in the mouse midbrain.

Simple PC-based system for morphometric analysis of synapses

The computer system designed for synaptic morphometry of aksosomatic and aksospine synapses of brain is described in the present paper. It is based on an AT-comparable personal computer equipped with low-cost frame grabber. This hardware configuration allows to input images from any TV source such as TV camera, videorecorder for further processing. The appropriate software was written in Microsoft Quick Basic to measure the main morphometric parameters of axon ending, dendritic spines, total contact, active zone and mitochondria. Number of synaptic vesicles (total and active) were also counted using a mouse as a pointing device. The derivative parameters (vesicle density, mitochondrial density) are then calculated. All measured data are stored in ASCII format, allowing ease in editing and export into other application programs. Statistical evaluation and calculation of histograms is performed by associated program also written in Quick Basic. The advantages and disadvantages of this approach are discussed.