Size Of Neuronal Somata Research Articles

Quantitative morphology of human hippocampus early neuron development.

Previous findings in adults revealed significant hemispheric asymmetry in the size of neuronal somata in hippocampal subfield CA2 (the resistant sector) with no age-related changes. A paucity of quantitative data on the developmental status of these protected neurons has led to the investigation of their morphology in comparison to neurons in adjacent subfield CA3, bilaterally. Bilateral coronal sections from postmortem hippocampus, 24 to 76 weeks postmenstrual age (gestational age plus postnatal age), were studied. The neurons were digitized and measured on a computer. Soma size correlated positively and significantly with age in CA2 and CA3, bilaterally. CA2 somata were significantly larger (left, 34%; right, 32%) than adjacent CA3 somata. Variability in soma form or size increased appreciably with age, in both subfields, bilaterally, while variability in soma orientation was weakly correlated with brain growth. The results suggest that in early development there are similarities in hemispheric growth patterns in CA2 and CA3. Large CA2 soma size implies axonal connectivity to distantly located targets very early in development. The results have functional implications, including memory, to brain development.

Enlargement of Neuronal Somata in the LMAN Coincides with the Onset of Sensorimotor Learning for Song

The lateral magnocellular nucleus of the anterior neostriatum (LMAN) in the zebra finch (Taeniopygia guttata) has been shown to play a developmentally restricted role that is essential during song-learning processes. Dendritic spine frequencies and synapse numbers in LMAN have been reported to decline in males during early vocal motor learning and thereafter, but not in females, who do not sing. Nissl staining has shown the LMAN volume to be very similar in both sexes, however. To gain more insight into the development of sex-specific differences in LMAN, the size of neuronal somata and cell nuclei were analyzed in 1-μm semithin sections. Cell somata and nuclei were similar in males and females during the initial phases of sensory memory formation for song, but during early vocal motor learning cell size increased in males and decreased in females. Sex differences in neuronal somata size were present at 50 days and remained throughout life. This sex difference may be indicative of a difference in protein biosynthesis in LMAN, arising as a consequence of vocal learning in males.

Effect of sialectomy on the superior cervical ganglion sympathetic neurons in young adult and aged mice

The dependence of superior cervical ganglion (SCG) adrenergic neurons on their target organ submandibular salivary gland containing high concentrations of nerve growth factor was studied in adult and aged male mice. The submandibular salivary glands were removed (sialectomy) either uni- or bilaterally, and the SCG were studied by fluorescence microscopy and histochemically. Catecholamine fluorescence and tyrosine hydroxylase immunoreactivity decreased after sialectomy, suggesting reduced noradrenaline production. Neuronal density was lower in the aged controls than in the young controls. In both age groups, sialectomy reduced the density of catecholamine-producing neurons. In the mouse SCG, there was remarkable heterogeneity in the size of neuronal somata. In aged control mice there was a greater number of large-size neurons than in young adult control mice. Six weeks postoperatively, no large catecholamine-producing neurons could be observed in the ganglia. Yellow autofluorescent lipopigments accumulated with age in the adrenergic neurons. Sialectomy increased the accumulation of lipopigments in both young and aged neurons. Sialectomy resulted in (a) reduced catecholamine fluorescence, (b) reduced tyrosine hydroxylase immunoreactivity, (c) reduced number of catecholamine neurons, (d) increased autofluorescent lipopigment. Ageing resulted in (a) reduced number of neurons, (b) increased ratio of large to small neurons, (c) increased autofluorescent lipopigment. Alterations after sialectomy were more detrimental in the aged ganglia than in the young adult ganglia. The discontinuation of the retrograde supply of nerve growth factor may contribute to these alterations.

Antiestrogens fail to prevent the masculine ontogeny of the zebra finch song system

Early treatment with the antiestrogen, tamoxifen, fails to block the ontogeny of the male zebra finch song system which is hypothesized to occur as a result of early estradiol action. In Experiment 1, two other antiestrogens, LY117018 or CI628, or vehicle was administered daily to zebra finch chicks for the first 20 days after hatching at which time the males were castrated. Comparisons of experimental and control brains at 60 days revealed that neither antiestrogen prevented the masculinization of the song system in males. Rather, both compounds increased (hypermasculinized) neuronal soma area in male MAN (magnocellular nucleus of the anterior neostriatum), DLRA (dorsolateral portion of the robust nucleus of the archistriatum), and in HVc (caudal nucleus of the ventral hyperstriatum). In females both compounds masculinized by increasing neuronal soma area in HVc and inducing the formation of Area X. Experiment 2 showed that neither LY117018 nor CI628 was effective in preventing the masculinization of the song system typical of 25-day-old males when administered daily from hatching until sacrifice. Rather, both compounds masculinized females by inducing the formation of Area X, and LY117018 increased RA volume. LY117018 hypermasculinized males by increasing HVc volume and size of neuronal somata in MAN, HVc, and DLRA. CI628 also hypermasculinized males by increasing RA volume and neuronal soma size in HVc and RA. The failure of the present compounds to block masculinization of the song system and the paradox of hypermasculinization by antiestrogens are discussed with reference to the estradiol-masculinization hypothesis.