Tetsuro Sugisaki

Presence of a Somatomedin-C-Immunoreactive Substance in the Central Nervous System: Immunohistochemical Mapping Studies

Somatomedin C (SMC; insulin-like growth factor I) is thought to mediate the effects of growth hormone (GH) mainly on skeletal growth. SMC is produced in the liver but its production by various other fetal tissues including the brain, suggests a local regulatory role rather than a general one. A substance cross-reacting with recombinant human SMC (rSMC) was localized in the central nervous system (CNS) of the normal control and Snell dwarf mice by the unlabeled antibody peroxidase-antiperoxidase technique. rSMC-immunoreactive substance (rSMC-IRS) was found in the neuronal cells of forebrain structures. These included the caudate nucleus/putamen, hippocampus, thalamus, hypothalamus, globus pallidus and amygdala. No positive cells were found in the cerebral cortex. Investigation of the dwarf brain showed rSMC-IRS distributed in identical areas of the brain, although the intensity of the staining of rSMC-IRS was found to be weaker than that of the positive cells in the normal brain. Moreover, the number of positive cells was found to be less than in the normal brain. After treatment with bovine GH for 3 days the reduced number of positive cells and weaker staining in the cerebral sections of the dwarf mice did not change. Thus, rSMC may represent another peptide which is common to both the endocrine and the nervous system, with a potential neurotransmitter/neuromodulator function in the CNS.

Hypomyelination in the cerebrum of the congenitally hypothyroid mouse (hyt)

Abstract: 2′,3′‐Cyclic nucleotide 3′‐phosphohydrolase activity in the cerebrum of the inherited primary hypothyroid mouse (hyt/hyt) is reduced in comparison with the normal heterozygate (hyt/+). No differences were observed with regard to DNA and RNA content and the RNA/DNA ratio. The results of this study indicate that hypomyelination in the hypothyroid mouse is restricted to the cerebrum, and is not related to arrested glial proliferation.

Partial restoration of cerebral myelination of the congenitally hypothyroid mouse by parenteral or breast milk administration of thyroxine.

Abstract: We attempted to define whether thyroid hormone can ameliorate the cerebral hypomyelination present in the congenitally hypothyroid (hyt) neonatal mouse, and to define the critical time period during early postnatal life when thyroxine (T4) is essential for myelin formation. We administered T4) to the hyt mouse by breast milk during the first 20 days of postnatal life, and through the diet during the second 20 days of postnatal life. Positive results were obtained only when hormone was given during the first 20 days of postnatal life. A distinct increase in cerebral 2′,3′‐cyclic nucleotide 3′‐phosphohy drolase activity was noted, and brain sections stained for myelin basic protein correlated with the biochemical findings. The later administration of hormone through diet was ineffective.

Factors contributing to cerebral hypomyelination in the growth hormone-deficientlittle mouse

We attempted to delineate the events leading to hypomyelination in the brain of thelittle mouse, a promising murine model of isolated growth hormone deficiency. At 20 days of age, the mutant mouse brain weighed less than its normal counterpart, and this difference in brain weight persisted. Increase in CNPase activity was found to be suppressed in the cerebrum throughout the developmental stage, but not in the other parts of the brain. Differences in cerebral DNA content between thelittle and normal mice first became apparent on the 10th day of age. Thereafter, the rate of increase in thelittle brain consistently lagged behind the normal. [3H]Thymidine incorporation into the DNA fraction in vivo on the 7th day of age, when glial cell proliferation in the normal cerebrum is most active, was approximately half that of the controls in all parts of thelittle brain. These findings indicate that the hypomyelination of the mutant cerebrum might result from reduced oligodendroglial proliferation due to growth hormone deficiency.

Abnormal neuronal growth in the Little (lit) cerebrum

Mice genetically deficient in growth hormone were compared with normal littermates for evidence of altered neuronal development. In the lit/lit motor cortex, area 6 of Caviness, cell number, stratification of neurons, and the proportionate layer widths were identical to those of the controls (lit/+). Examined by the Golgi-Cox method modified by Ramon-Moliner, however, the pyramidal neuron was found to have short primary dendrites with sparse branchings. This result was confirmed in sections stained for neuron-specific enolase. Therefore, we conclude that growth hormone has an independent action on neuronal development.

Stimulation of Snell Dwarf Mouse Neuronal Growth by GH and T4

An investigation of the Snell dwarf motor cortex, area 6 of Caviness, was carried out by means of a modified Golgi silver impregnation method. The pyramidal neurons located in layer V were found to have small perikarya, short primary dendrites with sparse branchings. Following administration of bovine growth hormone (bGH) and thyroxine (T4) during the first 20 d of postnatal life, this retarded neuronal growth was restored to normal: neuronal perikarya were enlarged, and the dentrites were thicker with denser branchings. These results were confirmed in the sections stained for neuron specific enolase (NSE). These findings demonstrate that exogenous GH and T4, will enhance neuronal growth in the Snell dwarf cerebrum, and restore neuronal arborization to normal.

Restoration of microcephalic cerebrum with hypomyelination in the growth hormone-deficient mouse (lit): Stimulatory effects of GH restricted to the first 20 days of postnatal life

We administered bovine growth hormone to the Little (lit), a promising model of isolated growth hormone deficiency, during the first and second 20 days after birth. Positive results were obtained only when bovine growth hormone was given during the first 20 days of postnatal life. We observed a distinct increase in cerebral weight, DNA content, and 2′, 3′-cyclic nucleotide 3′-phosphohydrolase activity. The latter administration of bovine growth hormone was ineffective. These data prove that growth hormone has an independent action on cerebral development, apart from the complementary or synergistic action of thyroid hormones, and that the administration of exogenous growth hormone led to increased myelinogenesis through its stimulatory effects on glial proliferation, as evidenced by the increase in cerebral DNA content.

Retarded growth of the suprachiasmatic nucleus and pineal body in dw and lit dwarf mice

The suprachiasmatic nucleus (SCN) and the pineal body in 3 types of inherited hormone-deficient mice, the dw, lit and hyt mice were examined by morphological, morphometric and biochemical techniques. In the dw and lit mice the SCN was underdeveloped. In the ventral part of the SCN, where most of the retinal fibers appeared to terminate, both cell number and cell size were decreased, although the size of the SCN was unaltered. In addition, the pineal bodies of both mice were morphologically underdeveloped and showed low levels of N-acetyltransferase activity. In contrast, the hyt SCN was comparable to the normal controls in every respect. The hyt pineal was well developed and showed levels of enzyme activity comparable to the controls. However, in all the deficient mice, the optic nerve appeared to be normal in morphological and biochemical studies. These results suggest that the underdevelopment of the pineal body, the reduced levels of spontaneous locomotion and the indistinct diurnal periodicity of the dw and lit mice might be related to the retarded neuronal growth of the SCN, and that growth hormone likely is indispensable for the development of the SCN.

Stimulatory Effects of Growth Hormone and Thyroxine on the Concentration of Gangliosides in the Snell Dwarf Cerebrum

Abstract: The concentration of gangliosides in the Snell dwarf mouse cerebrum was monitored from postnatal day 5 to day 40. In the dwarf cerebrum, the concentration of total gangliosides increased up to postnatal day 20 and then stopped, whereas in the control cerebrum, it continued to increase up to postnatal day 40. At postnatal day 40, the ganglioside level in the dwarf cerebrum was 70% of that in the control cerebrum. Among the ganglioside species, the concentrations of GM4, GM2, GM1, GD1a, GD3, GD1b, GT1b, and GQ1b were significantly lower in the dwarf cerebrum than in the controls at postnatal day 40. The reduced concentrations of ganglioside species GM2, GD1a, GD3, GD1b, and GQ1b, were completely restored by administration of bovine growth hormone (GH) during the first 20 days of postnatal life. The reduced concentration of the GM1 and GM4 species were most efficiently restored by administration of bovine GH plus thyroxine (T4) during the second 20 days of postnatal life. These results indicate that the lower ganglioside concentrations in the dwarf cerebrum can be elevated by hormone therapy and that there exist distinct GH and T4 actions on the enzymes participating in ganglioside metabolism.

Microcephalic cerebrum with hypomyelination in the congenital goiter mouse (cog).

Abstract2′,3′-Cyclic nucleotide 3′-phosphohydrolase activity in the cerebrum of the congenital goiter mouse (cog/cog) is reduced in comparison with the normal heterozygote (cog/+). The weight of thecog/cog cerebrum and cerebellum were significantly less than those of the normal controls, 89.0% less for the cerebrum, and 81.1% less for the cerebellum. However, no differences were observed with regard to DNA and RNA content and the RNA/DNA ratio. The results of this study indicate that hypomyelination in the congenital goiter mouse is restricted to the cerebrum, and is not related to arrested glial proliferation.