Distribution of Brain-Derived Neurotrophic Factor in Rats and Its Changes with Development in the Brain

Abstract: A newly established, sensitive, two-site enzyme-immunoassay system for brain-derived neurotrophic factor (BDNF) is described. Using this system, we investigated the tissue distribution of BDNF and developmental changes in tissue levels of BDNF in rats. The minimal limit of detection of the assay was 3 pg/0.2 ml of assay mixture. BDNF was successfully solubilized from tissues in the presence of guanidine hydrochloride but not in any of the other buffers examined. In the rat brain at 1 month of age, the highest level of BDNF was detected in the hippocampus (5.41 ng/g of wet weight), followed by the hypothalamus (4.23 ng/g) and the septum (1.68 ng/g). In other regions, levels of BDNF ranged between 0.9 and 1.7 ng/g. The level of BDNF in the posterior lobes of the cerebellum from rats at 30 days of age was slightly higher than that in the anterior lobes. The concentration of BDNF increased in all regions of the brain with postnatal development. In peripheral tissues, BDNF was found at very low concentrations (0.65 ng/g in the spleen, 0.21 ng/g in the thymus, and 0.06 ng/g in the liver). The subfractionation of the hippocampal homogenate indicated that ∼50% of BDNF was contained in the crude nuclear fraction. Immunoblots of BDNF-immunoreactive proteins extracted from the hippocampus, hypothalamus, and cerebellum contained doublet bands of protein of ∼14 kDa, a value close to the molecular mass of recombinant human BDNF. Immunocytochemical investigations showed that, in the hippocampus, BDNF was localized in the nucleus of the granule cells in the dentate gyrus and of the cells in the pyramidal cell layer. The frequency of cells that were stained in the dentate gyrus was greater than that of cells in the pyramidal cell layer.     

Morphometric analysis of atrial natriuretic peptide-containing granules in atriocytes of rats with experimental congestive heart failure

The morphometric characteristics of atrial natriuretic peptide-containing granules were studied in atrial myoendocrine cells of rats with aorto-caval fistula, an experimental model of congestive heart failure. A total of 6680 granules of control and aorto-caval rats were analyzed by a computerized image analysis system that evaluated the number and sectioned surface area of granules and their subcellular location. Compared with control animals, rats with congestive heart failure displayed a slight increase in the number of peripheral granules, adjacent to the sarcolemma, but not centrally located in the Golgi areas. The mean sectioned surface area of granules in rats with congestive heart failure was about 50% of that in controls, both in the right and left atria. Rats with aortocaval fistula had a higher percent of small granules and lower percent of large granules compared with controls. The data demonstrate different morphometric characteristics in atrial natriuretic peptide-containing granules in atriocytes in rats with experimental congestive heart failure; this may reflect the enhanced synthesis and release of atrial natriuretic peptide in heart failure.     

Demonstration of high opioid-like activity in isolated peptides from wheat gluten hydrolysates

Because of a possible relationship between schizophrenia and celiac disease, a condition in some individuals who are sensitive to wheat gluten proteins in the diet, there has been interest in observations that peptides derived from wheat gluten proteins exhibit opioid-like activity in in vitro tests. To determine the origin of the peptides exhibiting opioid activity, wheat proteins were fractionated by size (gel filtration), by charge differences (ion exchange chromatography) and by differences in hydrophobicity (reversed-phase HPLC). These fractions were hydrolyzed by pepsin or pepsin and trypsin and the resulting peptides separated by gel filtration chromatography. The separated peptides were tested for opioid-like activity by competitive binding to opioid receptor sites in rat brain tissue in the presence of tritium-labeled dihydromorphine. The peptides showed considerable differences in activity; while some peptides exhibited no activity, 0.5 mg of the most active peptides were equivalent to 1 nM of morphine in the binding assay. The most active peptides were derived from the gliadin fraction of the gluten complex.     

Parallel bioassay of litorin and phyllolitorins on smooth muscle preparations

Phyllolitorin and Leu8-phyllolitorin, two nonapeptide amides from the skin of the South American frog Phyllomedusa sauvagei, are representatives of a novel bombesin subfamily, characterized by the occurrence in their molecule of a serine residue substituting the usual histidine residue at position 3 from the C-terminus. In parallel bioassay on ten different smooth muscle preparations and rat blood pressure, phyllolitorin and Leu8-phyllolitorin were virtually equiactive, but the two peptides appeared remarkably less potent that litorin in all test preparations, except the rat urinary bladder. The shape of contractions produced by the phyllolitorins and promptness of cessation of their action upon washing seem to indicate a looser binding of these peptides to their receptors and/or a more rapid inactivation, in comparison to litorin.     

Taenia taeniaeformis: characterization of larval metabolic products and growth of host gastric cells in vitro

Development of larvae of the cestode parasite Taenia taeniaeformis in the liver of rats induces gross hyperplasia of the gastric mucosa and excessive mucus production in the stomach without any direct contact with the stomach. Because the taeniid larvae are known to elaborate excretory-secretory (E-S) product in vivo and in vitro, the product was analyzed further, and its effects on cultured rat and dog stomach cells were investigated. In vitro E-S product contained less negatively charged glycosaminoglycan than either heparin or chondroitin sulfate, and proteins of various molecular weights. It stimulated the growth of both rat and dog stomach cells at concentrations of 3-9 micrograms protein/ml culture medium. At a concentration of 30 micrograms protein/ml culture medium, it stimulated hexosamine production in the cells up to 20 times, and multiple intracytoplasmic granules were found in both rat and dog cultured cells by light and electron microscopy. These results suggest that larval E-S product may be involved in the induction of gastric hyperplasia and hypermucus secretion.     

Endogenous proteinases modulate the function of the β-adrenergic receptor-adenylate cyclase system

Photoaffinity labeling techniques have recently demonstrated that mammalian β₁- and β₂-adrenergic receptors reside on peptides of M_r 62 000–64 000. These receptor peptides are susceptible to endogenous metalloproteinases which produce peptides of M_r 30 000–55 000. Several proteinase inhibitors markedly attenuate this process, specifically EDTA and EGTA. In this study we investigated the functional significance of this proteolysis (and its inhibition) in the β₂-adrenergic receptor-adenylate cyclase system derived from rat lung membranes. Membrane preparations containing proteolytically derived fragments of the receptor of M_r 40000–55 000 are fully functional with respect to their ability to bind β-adrenergic antagonist radioligands such as [³H]dihydroalprenolol and β-adrenergic antagonist photoaffinity reagents such as p-azido-m-[^{125I]iodobenzylcarazolol}. They retain the ability to form a high-affinity, agonist-promoted, guanine nucleotide-sensitive complex thought to represent a ternary complex of agonist, receptor and guanine nucleotide regulatory protein. Nonetheless, after proteolysis, GTP is less able to revert this high-affinity receptor complex to one of lower affinity, and all aspects of adenylate cyclase stimulation are reduced. In addition, the functional integrity of the N protein in membranes prepared without proteinase inhibitors is reduced as assessed by reconstitution studies with the cyc[su− variant of S49 lymphoma cell membranes. These results suggest that endogenous proteolysis does not directly impair the ability of β-adrenergic receptors to either bind ligands or interact with the guanine nucleotide regulatory protein. However, they imply that endogenous proteolysis likely impairs the functionality of other components of the adenylate cyclase system, such as the nucleotide regulatory protein.     

Ultrastructure of rat pituitary LH gonadotrophs in relation to serum and pituitary LH levels following repeated LH-RH stimulation

The effects of single and repeated LH-RH injections at 120 min intervals on female rat LH gonadotrophs and on pituitary and serum LH levels were investigated using electronmicroscopy and radioimmunoassay. A temporary stimulation of granule release, of protein and new granule synthesis and of the accumulation of lysosomal structures was found in LH cells after the first LH-RH injection. The temporary stimulations were massively enhanced after the second injection. These consecutive yet in their time-sequence overlapping processes account for the initial depletion of secretory granule content (3--15 min after LH-RH injection), for the subsequent regranulation and accumulation of granules above control levels (60--120 min after injection) and also for the reduction in the number of granules to control levels (150 min after LH-RH injection and thereafter). Increased polymorphic lysosomal structures are believed to be responsible for this reduction of excess granules. The amount of assayable pituitary and serum LH generally corresponds with the morphological changes observed in LH-gonadotrophs, thus further substantiating the above observations. A schema which summarizes the observed morphological and hormonal changes in their time-sequence in response to LH-RH stimulation depicts the short-term regulation of secretory processes in female gonadotrophs.     

The preparation of a sarcolemmal fraction from evacuated muscle slices

A novel procedure is described for preparing a plasma membrane fraction from skeletal muscle (i.e., sarcolemma). The procedure entails evacuating the myoplasm from muscle slices as a preliminary step to homogenization and fractionation. The evacuated muscle slices are composed of a stroma-containing sarcolemma, which is then homogenized and fractionated, utilizing a sequence of differential and discontinuous sucrose density gradient centrifugations. On the basis of electron microscopy, selective enzyme markers and α-bungarotoxin binding in innervated and denervated muscles, the fraction most enriched with sarcolemma is recovered from the 0.5/0.7 M interface of a discontinuous sucrose gradient.     

Architecture of normal pancreas as revealed by retrograde injection

Summary The architecture of the pancreas was revealed by retrograde injection of the pancreatic ductal system of normal rats with a silicone rubber compound, and subsequent study of the preparation by light microscopy and scanning electron microscopy. The injected material became associated with both ducts and acinar areas. Examination of these specimens suggests that the arrangement of the exocrine pancreas is that of a complexly curving and branching system of tubules which anastomose and end blindly. This architecture, which is not that of a true acinar gland, provides a rational basis for the understanding of the simple dedifferentiative changes that accompany pancreatic carcinogenesis, and which have been generally interpreted as representing ductular proliferation.Supported by Grant Number CA22063, awarded by the National Cancer Institute, DHEW, through the National Pancreatic Cancer ProjectI thank Mr. Jackson Rhoads and Dr. J. Michael Barrett for information on preparative procedures     

The effect of a liquid elemental diet on cell proliferation in the colon of rats

Summary A liquid elemental diet (Vivonex) was given to rats for 6 days while control animals received a normal diet. At the end of the experiment each animal received one intraperitoneal injection of tritiated thvmidine at 8a.m. Animals from each group were killed hourly during the first 24h after the injection and the proliferative activity was studied by autoradiography of the mucosa of the colon using the labeled mitoses-wave method.The epithelial cell proliferation was significantly decreased in the colon of the Vivonex-fed animals.