Experimental production of congenital malformation of the central nervous system in rat fetuses by single dose intragastric administration of ethylenethiourea

Ethylenethiourea (ETU) is a degradation product from ethylenebisdithiocarbamate such as Zineb and Maneb which have been extensively used in food crops and ornamental plants. Khera (1973, 1975, 1977) reported that administration of ETU to pregnant rats could induce anomalies in the visceral organs and the central nervous system of fetuses in food toxicology. From this point, in an attempt to better understand the pathomechanism of teratogenesis in the central nervous system, we have studied the effects of ETU on the central nervous system of rat fetuses. In this study, pregnant Sprague Dawley (SD) rats were used and subjected to ETU. Various types of congenital malformations of the central nervous system are presented in rat fetuses including spinal dysraphism associated with hindbrain crowding, exencephaly, meningoencephalocele, microencephaly, hydraencephaly and hydrocephalus. Each depended on the gestation days of the ETU administration and dosages.     

Glycoproteins associated with myelin in the central nervous system

Purified myelin fractions from the central nervous system contain one major myelin-associated glycoprotein and approximately 16 minor glycoproteins. While the genuine association of the major myelin-associated glycoprotein with the oligodendroglial myelin unit is demonstrated, the possibility exists that several of the minor glycoproteins have their origin in contaminating membranes not related to myelin. The major myelin-associated glycoprotein is probably not present in compacted myelin, but immunocytochemical and subfractionation studies indicate that it is confined to the periaxonal and paranodal region of the myelin sheath. In experimental demyelination and multiple sclerosis, the major glycoprotein is the first myelin constituent to be affected. Its localization on the membrane surface where myelin and axolemma are in close contact, and other indirect evidence indicate that the major glycoprotein, and possibly other myelin-associated glycoproteins, could play a role in the process of myelination and myelin maintenance.     

A novel magnesium-independent neutral sphingomyelinase associated with rat central nervous system meylin.

Purified myelin fractions prepared from young adult rat brain contain a novel sphingomyelinase which has a pH optimum of 7.0 and does not require divalent cations. This sphingomyelinase is different from the two previously known sphingomyelinases in the brain--the acidic sphingomyelinase and the magnesium-dependent neutral sphingomyelinase. When the distributions of the sphingomyelinases among the purified myelin, the total subcellular fractions heavier than myelin (greater than 0.85 M sucrose), and the microsomes were examined, the magnesium-independent sphingomyelinase was detected only in myelin, while the magnesium-dependent sphingomyelinase was present in the other two fractions but not in myelin. Therefore, this new sphingomyelinase appears to be specifically localized in the myelin sheath.     

Systemic administration of kainic acid produces elevations in TRH in rat central nervous system

Several studies have suggested that the concentration of thyrotropin releasing hormone (TRH) in the central nervous system (CNS) is influenced by the level of CNS activation. Hibernation in the ground squirrel and estivation in the lungfish result in region-specific decreases in TRH concentrations. Repeated electroconvulsive shock (ECS) and amygdaloid kindling have been shown to result in elevations of TRH in limbic brain regions. In the present study, limbic seizures induced by systemic administration of kainic acid resulted in substantial increases in the TRH content of posterior cortex and of dorsal and ventral hippocampus, and in moderate elevations in anterior cortex, amygdala/piriform cortex and corpus striatum. Maximal elevations in TRH were observed 2-4 days after kainic acid administration, and by 14 days TRH levels were similar to control values, with the exception of the dorsal hippocampus, which exhibited more prolonged elevations in TRH levels. Prior exposure to limbic seizure activity attenuated the magnitude of TRH elevation in response to a second administration of kainic acid in the posterior cortex but in no other region. These results indicate that seizure-related processes or events influence TRH systems in the CNS. Neuronal populations involved in limbic seizure induced damage may be involved in the modulation of posterior cortical TRH levels.     

Acetaminophen distribution in the rat central nervous system

Based on the evidence that the antinociceptive effects of acetaminophen could be mediated centrally, tissue distribution of the drug after systemic administration was determined in rat anterior and posterior cortex, striatum, hippocampus, hypothalamus, brain stem, ventral and dorsal spinal cord. In a first study, rats were treated with acetaminophen at 100, 200 or 400 mg/kg per os (p.o.), and drug levels were determined at 15, 45, 120, 240 min by high performance liquid chromatography (HPLC) coupled with electrochemical detection (ED). In a second study, 45 min after i.v. administration of [3H]acetaminophen (43 microCi/rat; 0.65 microg/kg), radioactivity was counted in the same structures, plus the septum, the anterior raphe area and the cerebellum. Both methods showed a homogeneous distribution of acetaminophen in all structures studied. Using the HPLC-ED method, maximal distribution appeared at 45 min. Tissue concentrations of acetaminophen then decreased rapidly except at the dose of 400 mg/kg where levels were still high 240 min after administration, probably because of the saturation of clearance mechanisms. Tissue levels increased with the dose up to 200 mg/kg and then leveled off up to 400 mg/kg. Using the radioactive method, it was found that the tissue/blood ratio was remarkably constant throughout the CNS, ranking from 0.39 in the dorsal spinal cord to 0.46 in the cerebellum. These results, indicative of a massive impregnation of all brain regions, are consistent with a central antinociceptive action of acetaminophen.     

Dynorphin immunocytochemistry in the rat central nervous system

The distribution of dynorphin in the central nervous system was investigated in rats pretreated with relatively high doses (300–400 μg) of colchicine administered intracerebroventricularly. To circumvent the problems of antibody cross-reactivity, antisera were generated against different portions as well as the full dynorphin molecule (i.e., residues 1–13, 7–17, or 1–17). For comparison, antisera to [Leu]enkephalin (residues 1–5) were also utilized. Dynorphin was found to be widely distributed throughout the neuraxis. Immunoreactive neuronal perikarya exist in hypothalamic magnocellular nuclei, periaqueductal gray, scattered reticular formation sites, and other brain stem nuclei, as well as in spinal cord. Additionally, dynorphin-positive fibers or terminals occur in the cerebral cortex, olfactory bulb, nucleus accumbens, caudate-putamen, globus pallidus, hypothalamus, substantia nigra, periaqueductal gray, many brain stem sties, and the spinal cord. In many areas studied, dynorphin and enkephalin appeared to form parallel but probably separate anatomical systems. The results suggest that dynorphin occurs in neuronal systems that are immunocytochemically distinct from those containing other opioid peptides.     

Behavioral recovery associated with central nervous system regeneration in the snail Melampus

The pulmonate snail Melampus bidentatus regenerates central nervous tracts following commissurotomy, connective transection, and cerebral ganglion ablation. Our goal was to determine whether or not neural regrowth within the central nervous system restored behaviors disrupted by lesions. One behavior that is disrupted by commissurotomy is retraction of facial structures that are contralateral to a stimulated facial region, a response that normally accompanies the ipsilateral retraction. Tentacle withdrawal on the side contralateral to stimulation reappeared on a timescale that was correlated with growth of a commissural link (8-19 days post-lesion). Electrophysiological recordings from a labial nerve pathway that has a contralateral component similar to the contralateral tentacle response showed that development or strengthening of an alternative pathway could also mediate contralateral responses. Thus, a major conclusion of this study was that both tract regeneration and changes in existing CNS pathways can underlie recovery. The percentage (approx. 75%) of snails that regenerate the cerebral commissure and show behavioral recovery is established early in the period following commissure transection. Behavioral recovery and anatomical evidence of regeneration were also correlated in the other two operations: single cerebral ganglion removal and unilateral cerebropleural and cerebropedal connective transection. We conclude that Melampus is able to regenerate neuronal connectivity that can restore normal behavior.     

Snapin deficiency is associated with developmental defects of the central nervous system

The autophagy-lysosomal pathway is an intracellular degradation process essential for maintaining neuronal homoeostasis. Defects in this pathway have been directly linked to a growing number of neurodegenerative disorders. We recently revealed that Snapin plays a critical role in co-ordinating dynein-driven retrograde transport and late endosomal-lysosomal trafficking, thus maintaining efficient autophagy-lysosomal function. Deleting snapin in neurons impairs lysosomal proteolysis and reduces the clearance of autolysosomes. The role of the autophagy-lysosomal system in neuronal development is, however, largely uncharacterized. Here, we report that snapin deficiency leads to developmental defects in the central nervous system. Embryonic snapin-/- mouse brain showed reduced cortical plates and intermediate zone cell density, increased apoptotic death in the cortex and third ventricle, enhanced membrane-bound LC3-II staining associated with autophagic vacuoles and an accumulation of polyubiquitinated proteins in the cortex and hippocampus. Thus our results provide in vivo evidence for the essential role of late endocytic transport and autophagy-lysosomal function in maintaining neuronal survival and development of the mammalian central nervous system. In addition, our study supports the existence of a functional interplay between the autophagy-lysosome and ubiquitin-proteasome systems in the protein quality-control process.     

Binding sites forl-glutamate in the central nervous system of the rat

The regional distribution of 2-amino-4-phosphonobutyrate (APB)/chloride-insensitivel-[³H]glutamate binding sites in the rat central nervous system was compared with that of APB/chloride-sensitive and with sodium-dependent binding sites. The distribution of APB-sensitive and APB-insensitive sites was not corelated, but the latter was identical to that of the sodium-dependent sites. The pharmacological specificity of the APB-insensitive sites was not consistent with that of an N-methylaspartate-preferring receptor, and was also different from the specificity determined for the sodium-dependent sites. The APB-insensitive sites appear to be unrelated to any other previously described excitatory amino acid binding site.Dedicated to K. A. C. Elliott on his 80th birthday.     

Corticosteroid receptors in the central nervous system of the rat.

Corticosteroid receptors were demonstrated in the medial hypothalamus, the hippocampus and the parietal cortex of the rat while no such receptors were found in the hypophysis, the amygdala and the anterior hypothalamus. The findings suggest the role of extrahypothalamic regions in the perception of corticosteroid feedback as well as in the regulation of the hypothalamo-hypophysial-adrenal function and do not support the assumption that corticosteroids would inhibit corticotrophin secretion by acting directly on the hypophysis.     

Atrial natriuretic peptide in the central nervous system of the rat

1. Studies of the presence of atrial natriuretic peptide immunoreactivity and receptor binding sites in the central nervous system have revealed unusual sites of interest. 2. As a result, numerous studies have appeared that indicate that brain atrial natriuretic peptide is implicated in the regulation of blood pressure, fluid and sodium balance, cerebral blood flow, brain microcirculation, blood-brain barrier function, and cerebrospinal fluid production. 3. Alteration of the atrial natriuretic peptide system in the brain could have important implications in hypertensive disease and disorders of water balance in the central nervous system.     

Distribution of tripeptidyl-peptidase II in the central nervous system of rat

Tripeptidyl-peptidase II (TPP II) is a high molecular weight serine peptidase which removes tripeptides from a free N-terminus of longer peptides. Since it had previously been demonstrated that the enzyme can inactivate enkephalins and dynorphins in vitro by removing the N-terminal Tyr-Gly-Gly peptide, we wanted to see whether TPP II could be involved in this process also in vivo. Therefore, the localization of TPP II in different cerebral regions of rat was investigated by immunoblot analysis and activity measurements. It could be shown that TPP II is relatively evenly distributed in the central nervous system of rat. This indicates that the physiological role of the enzyme is probably not a specific degradation of enkephalins, but rather pertains to the general turnover of proteins.     

Distribution of glutamine synthetase in the rat central nervous system.

The results of a light microscopic immunohistochemical study of glutamine synthetase in rat nervous system are presented. In all sites studied the enzyme was confined to astrocytes. Except for trace amounts in ependymal cells, the enzyme was not observed in other cells of the nervous system including neurons, choroid plexus, third ventricular tanycytes, subependymal cells and mesodermally-derived elements. The intensity of astrocyte staining varied in different regions with the greatest degree noted in the hippocampus and cerebellar cortex while the least was noted in brain stem, deep cerebellar nuclei and spinal cord. The glutamine synthetase content correlated well with sites of suspected glutamergic activity in keeping with the view of a critical role of astrocytes in the regulation of the putative neurotransmitter glutamic acid.     

Immunocytochemical localization of acyl-CoA oxidase in the rat central nervous system

Peroxisomal β-oxidation, consisting of four steps catalysed by an acyl-CoA oxidase, a multifunctional protein and a thiolase, is responsible for the shortening of a variety of lipid compounds. The first reaction of this pathway is catalysed by a FAD-containing acyl-CoA oxidase, three isotypes of which have been so far recognised. Among these, straight-chain acyl-CoA oxidase (ACOX) acts on long and very long chain fatty acids, prostaglandins and some xenobiotics. We investigated ACOX localisation by means of a sensitive, tyramide based, immunocytochemical technique, thus obtaining a complete distribution atlas of the enzyme in adult rat CNS. Granular immunoreaction product was found in the cytoplasm of neuronal and glial cells, both in the perikarya and in the cell processes. ACOX immunoreactive neurons were present to variable extent, in either forebrain or hindbrain areas. Specifically, the strongest signal was detected in the pallidum, septum, red nucleus, reticular formation, nuclei of the cranial nerves, and motoneurons of the spinal cord. We then compared the ACOX immunoreactivity pattern with our previous distribution maps of other peroxisomal enzymes in the adult rat brain. While ACOX appeared to colocalise with catalase in the majority of cerebral regions, some differences with respect to d-amino acid oxidase were noted. These observations support the hypothesis of heterogeneous peroxisomal populations in the nervous tissue. The wide distribution of the enzyme in the brain is consistent with the severe and generalised neurological alterations characterising the peroxisomal disorder caused by ACOX deficiency (pseudo-neonatal adrenoleukodystrophy).