Neuronotrophic activity for ciliary ganglion neurons. Induction following injury to the brain of neonatal, adult, and aged rats

The induction of neuronotrophic activity following injury to the brain of neonatal, adult, and aged Sprague-Dawley rats was compared using an improved in vitro assay. The maximal levels of activity in tissue surrounding the wound were reached at 3, 10-15, and about 15 days postlesion in neonatal, adult, and aged animals, respectively. Tissue neuronotrophic levels were always much lower in neonatal animals relative to the older animals. Accumulation of neuronotrophic activity in the gelfoam placed into the wound cavities in neonatal and adult animals lagged behind the levels in tissue by 4-5 days, suggesting that either the neuronotrophic factor itself or the cells which produce it are transferred from the tissue into the gelfoam. Relatively little activity accumulated in the gelfoam taken from aged Sprague-Dawley rats, and this observation was confirmed in aged Fischer rats. Aged animals seem to be unable to produce or release one of a number of neuronotrophic factors in response to injury.

The survival of brain transplants is enhanced by extracts from injured brain

Fragments of rat embryo corpus striatum implanted into wound cavities in the cortex of neonatal rat hosts showed very poor survival when transplantation was performed immediately after the cavity was made. Consistent survival of the transplants was made possible by supplying the implant with extracts from the injured brain of neonatal rats. These extracts also supported in vitro survival of embryonic striatal neurons, suggesting that transplanted cells benefit from injury-induced neuronotrophic factors.

Cell biology of synaptic plasticity

The nervous system of mammals retains throughout the animals' life-span the ability to modify the number, nature, and level of activity of its synapses. Synaptic plasticity is most evident after injury to the nervous system, and the cellular and molecular mechanisms that make it possible are beginning to be understood. Transplantation of brain tissue provides a powerful approach for studying mechanisms of synaptic plasticity. In turn, understanding the response of the central nervous system to injury can be used to optimize transplant survival and integration with the host brain.

Enhancing the self-repairing potential of the CNS after injury

Embryonic CNS tissues can now be successfully transplanted into most regions of the CNS in neonate, adult, or aged host animals. The transplants generally project to their correct target areas in the host brain. However, transplants appear to receive only partial innervation by host fibers. Replacement of lost host neurons by transplants has proven to be functionally most successful in the cases of neurosecretory, monoaminergic, or cholinergic neurons. Their success probably depends on their ability to deliver the proper neurotransmitter (and perhaps trophic factors) close to their targets rather than on their capacity to reestablish all lost connections. Efforts to achieve complete integration of the transplants will probably require interventive strategies to guide the natural repair response of CNS tissue. Survival and outgrowth of the transplants can be promoted by taking advantage of the natural increase of neurotrophic factors in response to injury. Neurotrophic factors and substrate guidance factors, once purified and completely characterized, promise to be powerful new therapeutic agents for enhancing the survival and regrowth of the injured CNS.

Injury-induced neuronotrophic activity in adult rat brain: correlation with survival of delayed implants in the wound cavity

Mechanical or chemical injury to adult rat brain elicited the accumulation in the affected area of trophic activity for cultured parasympathetic, sympathetic, and sensory neurons. Neuronotrophic activity was relatively low both in noninjured brain tissue extracts and in extracts prepared from the tissue surrounding an injury immediately after the lesion was made. However, trophic titers increased considerably over time, first in the brain tissue that formed the walls of the wound and then in the Gelfoam filling the wound cavity. In the tissue adjacent to the injury, trophic titers began to rise immediately after the lesion, reached a maximum 10 days later, and decayed thereafter. In the wound cavity, occupied by Gelfoam, neuronotrophic activity began to increase 6 days postlesion, reached a maximum at day 16 after injury, and decreased at later times. The levels of induced trophic activity appeared to be proportional to the size of the wound. Injury to various brain areas including temporal, entorhinal, occipital, parietal, and frontal cortices, hippocampus, corpus striatum, and cerebellum, all induced a similar increase in neuronotrophic factor(s). Damage to the myelinated fibers of the corpus callosum did not. High trophic titers decayed rapidly with distance from the wound except in areas heavily deafferented by the lesion, where activity also reached high levels. Extracts from all of the above-mentioned brain areas contained toxic activity for cultured spinal cord neurons. The level of neuronotoxic activity was similar both before the lesion and 15 days postlesion, with the possible exception of the corpus callosum. Intraventricular injections of kainic acid at doses which destroy areas CA4, CA3, and part of CA1 of the hippocampus also induced a time-dependent rise of neuronotrophic activity in this structure, comparable to that achieved by mechanical damage. Both kainic acid treatment and mechanical injury cause extensive glial proliferation in the injured and/or deafferented area. The apparent concurrence of glial reaction and increase in neuronotrophic activity suggests that glial cells may be a major source of the induced trophic activity. As an in vivo correlate of cell culture data, the survival of striatal transplants into host cortical wounds was examined. Fragments of embryonic corpus striatum did not survive when transplanted into a freshly made cavity in the entorhinal/occipital cortex of adult rats. Survival was enhanced by introducing a delay between the time at which the wound cavity was made and that at which the striatal tissue was implanted in it.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuronotrophic activity in brain wounds of the developing rat. Correlation with implant survival in the wound cavity

Neuronotrophic activity accumulates in a wound cavity created in the entorhinal/occipital cortex of developing rats. These trophic factors support the survival of neurons in monolayer cultures of chick embryo spinal cord, ciliary ganglion, sympathetic ganglion and dorsal root ganglion, as well as of mouse dorsal root ganglion. Trophic activity was very low both in non-injured brain tissue and in the wound cavity 1 day post-lesion, but it increased 15- to 300-fold during the subsequent 2-5 days. Together with the trophic activity in the wound fluid were other substances which interfered with the survival of spinal cord neurons. The neuronotrophic factors appeared to be proteins immunologically distinct from mouse submaxillary nerve growth factor. Fragments of rat embryo corpus striatum placed in the cortical wound cavity immediately after its formation showed very poor subsequent survival and no innervation of the host hippocampus. However, if implantation was delayed by 3 or 6 days with respect to the time at which the receiving cavity was made, the survival was greatly improved and innervation of the host took place. The time course for the accumulation of the trophic factors in the cavity paralleled the delay leading to increased survival of brain grafts. It is suggested that the neuronotrophic activity accumulating in the wound cavity during the delay period may be responsible for the increased survival of the implants.

Perforated postsynaptic densities: probable intermediates in synapse turnover

The molecular layer of the dentate gyrus of normal rats shows a large incidence of perforated postsynaptic densities (PSDs). The perforations or discontinuities occur almost exclusively in PSDs located in spines showing a U- or W-shaped junctional profile (complex PSDs). Perforated PSDs account for 16-25% of the total complex PSD profiles in young adult rats and 12-29% of those in aged animals. The frequency of perforations in the inner molecular layer of the dentate gyrus undergoes significant changes during a cycle of nondegenerative synapse turnover induced by ipsilateral ablation of the entorhinal cortex. During the first 2 days postlesion nonperforated PSDs (simple PSDs) decrease sharply, whereas perforated PSDs change little. However, at later times (4-10 days) there is a significant increase in the number of perforated PSDs that balances the number of simple PSDs lost. Beyond 10 days postlesion the proportion of both types of PSD is restored slowly to normal--i.e., nonperforated PSDs increase in number and perforated PSDs decrease, returning to the values in unoperated animals by 120 days postlesion. This inverse relationship between small nonperforated PSDs and large perforated PSDs suggests a precursor-product relationship between them. We propose that perforated PSDs are intermediates in an ongoing cycle of synapse turnover that is a part of the normal maintenance and adaptation of the nervous system.

Brain injury causes a time-dependent increase in neuronotrophic activity at the lesion site

A cavity was made in the brain (entorhinal cortex) of developing or adult rats, and a small piece of Gelfoam was emplaced to collect fluid secreted into the wound. The neuronotrophic activity of the fluid was assayed with sympathetic and parasympathetic neurons in culture. The results show that wounds in the brain of developing or adult rats stimulate the accumulation of neuronotrophic factors and that the activity of these factors increases over the first few days after infliction of the damage.

Isolation, morphology, and protein and glycoprotein composition of synaptic junctional fractions from the brain of lower vertebrates: antigen PSD-95 as a junctional marker

Synaptic junction (SJ) fractions were isolated from the brains of the gray shark, bonito, common frog, several reptiles, and common chicken and compared to those prepared from mammalian brain. All SJ preparations, as judged by electron microscopic analysis, were at least 85% pure, consisting primarily of postsynaptic densities (PSDs) with or without an overlying plasma membrane and, to a lesser extent, of complete synaptic junctions. Complete junctions were less abundant in preparations from lower vertebrates. The electrophoretic pattern of SJs from different vertebrate species showed considerable conservation of the major protein bands. The most abundant were fibrous proteins, especially tubulins, actin, and the PSD-specific polypeptide with a molecular weight of 52,000 (PSD-52). Glycoproteins capable of binding concanavalin A were present in SJs from all vertebrates; their apparent molecular weight and relative abundance were characteristic of each animal order examined, showing more similarities in species more closely related phylogenetically. Finally, a protein (antigen PSD-95) previously shown to be located specifically in the postsynaptic densities of the mammalian brain was present in all species. The binding of antibody specific to this protein decreased with descending phylogenetic order from mammals to shark. Nonetheless, PSD-95 was present in all vertebrate species and appeared to be a general specific marker for PSDs.

Optimal concentration of iodonitrotetrazolium for the isolation of junctional fractions from rat brain

The yield and purity of synaptic plasma membranes (SPM) and synaptic junctions (SJ) from rat brain has been examined as a function of the concentration of rho-iodonitrotetrazolium (INT)--succinate used during their preparation. An INT concentration of 1 mg/g brain tissue (wet weight) was sufficient to obtain SPM and SJ of purity comparable to that obtained using 4--6 times that concentration of dye (1--3). At this lower level of INT the yield of SPM increased by about 100%, whereas mitochondrial contamination remained at 10--13% of the total SPM protein. At concentrations of INT below 0.5 mg/g brain tissue (wet weight) the contamination of SPM by mitochondria increased rapidly. At very low concentrations of INT (0.13 mg/g tissue) the contaminating protein of mitochondrial origin was 40--50% of the total protein in the SPM fraction. Examination by gel electrophoresis of SPM, SJ, and mitochondrial fractions with different degrees of cross-contamination allowed the assignment of marker polypeptides for mitochondrial, junctional, and nonjunctional plasma membranes. Under the conditions used to prepare SJ, a variable amount of particulate material floated over 1.0 M sucrose. It consisted of SJ and many membrane vesicles and had a protein composition similar to that of SJ contaminated by extrajunctional membrane proteins. An analogous fraction arose during in the preparation of postsynaptic densities.

Specific binding of kainic acid to purified subcellular fractions from rat brain

The subcellular distribution of kainic acid (KA) binding sites in rat brain has been studied using a microcentrifugation assay. KA did not bind to myelin or brain cytosol and had few or no binding sites in the nuclear fraction. However, it bound to microsomal components (Kd = 128-136 nM; 2.5-4.8 pmol/mg protein), purified synaptic plasma membranes (SPM)(Kd = 45-71 nM; 5.8-6.5 pmol/mg), and purified cell-body and intraterminal mitochondria (Kd = 11-31 nM; 0.4-1.1 pmol/ng). Bound KA could be totally displaced by L-glutamate or L-asparate, but several putative antagonists of these amino acids (nuciferin, compound HA-966, 2-amino-4-phosphonobutyrate, and 2-amino-3-phosphonoproprionate) failed to displace KA or did so at very high concentrations (greater than or equal to 4 mM). Glutamic acid diethyl ester (GDEE) and D,L-alpha-aminoadipate (alpha-AA) were more effective (IC50, 0.2-0.8 mM) and showed differential effects in their capacity to displace KA bound to the various subcellular fractions. Thus, GDEE only displaced 40-60% of the KA bound by SPM or mitochondria and did not prevent the binding of KA to microsomes. alpha-AA, on the other hand, was more effective in preventing the binding of KA at high concentrations and displaced between 80 and 100% of the drug. Both compounds showed biphasic curves of KA displacement from synaptic plasma membranes and mitochondria. The overall results indicate the presence of multiple binding sites for KA in brain cells and suggest that KA does not act exclusively as synaptic glutamate receptors. The mechanism of KA action is most likely quite complex, and the drug probably acts at multiple binding sites affecting a number of processes.