Promoting functional plasticity in the damaged nervous system.

Damage to the central and peripheral nervous system often produces lasting functional deficits. A major focus of neuroscience research has been to enhance functional restitution of the damaged nervous system and thereby produce recovery of behavioral or physiological processes. Promising procedures include surgical, physical, and chemical manipulations to reduce scar formation and minimize the disruption of support elements, administration of growth-stimulating substances, tissue grafts to bridge gaps in fiber pathways, and embryonic brain tissue grafts to provide new cells with the potential to generate fiber systems. Two elements are required for functional nervous system repair: (i) neurons with the capacity to extend processes must be present, and (ii) the regenerating neurites must find a continuous, unbroken pathway to appropriate targets through a supportive milieu.

Calcitonin: inhibitory effect on eating in rats.

Subcutaneous and intracerebral injections of calcitonin inhibited feeding in rats. The anorectic activity of calcitonin was destroyed by exposing the hormone to heat, trypsin, or hydrogen peroxide. Calcitonin did not produce a conditioned taste aversion to saccharin, and maximum inhibition of feeding occurred 4.5 to 8.3 hours after subcutaneous administration. It is concluded that calcitonin inhibits feeding by acting directly on the central nervous system.

Brain grafts reduce motor abnormalities produced by destruction of nigrostriatal dopamine system.

In order to determine if brain tissue grafts can provide functional input to recipient central nervous system tissue, fetal rat dopamine-containg neurons were implanted adjacent to the caudate nucleus of adult recipients whose endogenous dopaminergic input had been destroyed. The grafts showed good survival and axonal outgrowth. Motor abnormalities, which had been induced by the destruction of the endogenous dopaminergic input to the caudate, were significantly reduced after grafting of the fetal brain tissue. These data suggest that such implants may be potentially useful in reversing deficits after circumscribed destruction of brain tissue.

Normalization of spiroperidol binding in the denervated rat striatum by homologous grafts of substantia nigra.

Transplantation of embryonic substantia nigra into the adult rat brain decreases the motor asymmetry that is produced by dopamine receptor supersensitivity after a unilateral lesion of the substantia nigra. The authors report that this effect of transplantation is specific to grafts of substantia nigra. They also report that, in conjunction with the decrease in motor asymmetry, these grafts cause postsynaptic dopaminergic binding sites to return to normal density as measured by tritiated spiroperidol autoradiography. Thus, in animals with brain lesions, grafts of substantia nigra produce a long-term alteration in the functional status of host brain cell receptors that is associated with a reduction in the behavioral deficit.

An immortalized rat ventral mesencephalic cell line, RTC4, is protective in a rodent model of stroke.

One therapeutic approach to stroke is the transplantation of cells capable of trophic support, reinnervation, and/or regeneration. Previously, we have described the use of novel truncated isoforms of SV40 large T antigen to generate unique cell lines from several primary rodent tissue types. Here we describe the generation of two cell lines, RTC3 and RTC4, derived from primary mesencephalic tissue using a fragment of mutant T antigen, T155c (cDNA) expressed from the RSV promoter. Both lines expressed the glial markers vimentin and S100beta, but not the neuronal markers NeuN, MAP2, or beta-III-tubulin. A screen for secreted trophic factors revealed substantially elevated levels of platelet-derived growth factor (PDGF) in RTC4, but not RTC3 cells. When transplanted into rat cortex, RTC4 cells survived for at least 22 days and expressed PDGF. Because PDGF has been reported to reduce ischemic injury, we examined the protective functions of RTC4 cells in an animal model of stroke. RTC4 or RTC3 cells, or vehicle, were injected into rat cortex 15-20 min prior to a 60-min middle cerebral artery ligation. Forty-eight hours later, animals were sacrificed and the stroke volume was assessed by triphenyl-tetrazolium chloride (TTC) staining. Compared to vehicle or RTC3 cells, transplanted RTC4 cells significantly reduced stroke volume. Overall, we generated a cell line with glial properties that produces PDGF and reduces ischemic injury in a rat model of stroke.

The use of microarrays to characterize neuropsychiatric disorders: postmortem studies of substance abuse and schizophrenia.

Neuropsychiatric disorders are generally diagnosed based on a classification of behavioral and, in some cases, specific neurological deficits. The lack of distinct quantitative and qualitative biological descriptors at the anatomical and cellular level complicates the search for and understanding of the neurobiology of these disorders. The advent of microarray technology has enabled large-scale profiling of transcriptional activity, allowing a comprehensive characterization of transcriptional patterns relating to the pathophysiology of neuropsychiatric disorders. We review some of the unique methodological constraints related to the use of human postmortem brain tissue in addition to the generally applicable requirements for microarray experiments. Microarray studies undertaken in neuropsychiatric disorders such as schizophrenia and substance abuse by the use of postmortem brain tissue indicate that transcriptional changes relating to synaptic function and plasticity, cytoskeletal function, energy metabolism, oligodendrocytes, and distinct intracellular signaling pathways are generally present. These have been supported by microarray studies in experimental models, and have produced multiple avenues to be explored at the functional level. The quality and specificity of information obtained from human postmortem tissue is rapidly increasing with the maturation and refinement of array-related methodologies and analysis tools, and with the use of focused cell populations. The development of experimental models of gene regulation in these disorders will serve as the initial step towards a comprehensive genome-linked analysis of the brain and associated disorders, and help characterize the integration and coordinate regulation of complex functions within the CNS.

Glutamatergic mechanisms mediating stimulant and antipsychotic drug effects.

This paper presents an hypothesis regarding the functions of striatal dopaminergic and glutamatergic neurotransmission. It is suggested that the principal functional role of dopaminergic neurotransmission is to regulate the efficacy of cortico-striatal and cortico-accumbens neurotransmission. Increased activity at dopamine-mediated synapses is suggested to interact with neurotransmission at adjacent cortically derived glutamate-mediated synapses, facilitating communication from the cerebral cortex, and thereby causing behavioral stimulation. Decreased activity at dopaminergic synapses, as produced by neuroleptic drugs, causes changes in the activation of cortically derived synapses in the corpus striatum and nucleus accumbens which result in behavioral sedation and decreased activity. This hypothesis suggests that activity at dopaminergic synapses produces behavioral effects only insofar as these changes modulate cortico-striatal (or cortico-accumbens) activity, and further, that the manifestations of activity in cortico-striatal systems are modulated by activity at dopaminergic synapses. It is further suggested that when neuroleptics are administered chronically, adjustments in the efficacy of cortico-striatal neurotransmission are responsible for the antipsychotic effect of neuroleptic drugs.

Functional brain tissue transplantation: reversal of lesion-induced rotation by intraventricular substantia nigra and adrenal medulla grafts, with a note on intracranial retinal grafts.

Using a rotational behavior animal model, it has been found that embryonic substantia nigra (SN) can be homologously transplanted to the brain lateral ventricles to reverse the effects of SN lesions. These grafts were found to decrease the lesion-induced rotational behavior that was provoked either by apomorphine or amphetamine. This effect was not duplicated by grafts of other embryonic brain regions. The SN grafts produced a dopaminergic reinnervation of the dorsomedial striatum that appeared to be responsible for the behavioral amelioration. Long-term studies demonstrated that behavioral efficacy and survival continued for at least 6 months to 1 1/2 years. The catecholaminergic "chromaffin" cells of the adrenal medulla possess a remarkable ability to change morphologically and biochemically in response to their environmental hormonal milieu. This plasticity was exploited by transplanting adrenal medulla to the rat brain to reverse the effects of SN lesions. This tissue changed biochemically by producing large amounts of dopamine, and morphologically, by extending coarse fiber processes. Although these grafts appeared to secrete catecholamines, they did not reinnervate the striatum. Rotational behavior was reduced by these grafts, apparently as a consequence of the catecholamine secretion. When adrenal chromaffin tissue was obtained from 1- or 2-year-old donors, however, lesion-induced rotational behavior was not reduced. It is suggested that adrenal chromaffin cell grafts from young donors possess a biochemical plasticity that is the basis for the behavioral effect, but that this plasticity is lost with maturity of the tissue. An important issue for future applications of these procedures is the immunological privilege of the brain lateral ventricles. We found that both embryonic brain tissue and adult adrenal medulla "allografts" from Brown Norway rat donors consistently survived for at least 6 months in the ventricles of Fisher 344-strain rat hosts. These strains differ in major histocompatibility antigens and, as expected, Fisher 344 rats rapidly rejected Brown Norway skin grafts. Skin graft survival times were not influenced by the presence of established brain grafts, nor did brain grafts elicit systemic humoral immunity. Conversely, however, independent elicitation of systemic immunity by skin grafting resulted in the rejection of long-established brain grafts concomitant with rejection of the skin grafts. Rotational behavior in Fisher 344 hosts was reduced by brain grafts from Brown Norway donors; yet, after rotation had been reduced it could be brought back to baseline levels through systemic immunization and associated brain graft rejection.(ABSTRACT TRUNCATED AT 400 WORDS)

Anomalous behavioral response to imidazoleacetic acid, a GABA agonist, in animals treated chronically with haloperidol.

Short-term haloperidol treatment decreases the stimulant effects of drugs with dopaminelike actions, while withdrawal from long-term haloperidol treatment enhances the effects of such drugs. In the present study, we have shown that withdrawal from long-term haloperidol treatment decreases or eliminates the tendency for imidazole-4-acetic acid, a GABA agonist, to decrease the locomotor activity of mice. Acute haloperidol treatment did not duplicate these effects. It is suggested that chronic administration of haloperidol causes changes in a variety of systems in the brain, and that the GABA system in particular is profoundly altered by such treatment.

Neuropathology of bipolar disorder.

The literature on the neuropathology of bipolar disorder (BD) is reviewed. Postmortem findings in the areas of pathomorphology, signal transduction, neuropeptides, neurotransmitters, cell adhesion molecules, and synaptic proteins are considered. Decreased glial numbers and density in both BD and major depressive disorder (MDD) have been reported, whereas cortical neuron counts were not different in BD (in Brodmann's areas [BAs] 9 and 24). In contrast, MDD patients showed reductions in neuronal size and density (BA 9, BA 47). There are a number of findings of alterations in neuropeptides and monoamines in BD brains. Norepinephrine turnover was increased in several cortical regions and thalamus, whereas the serotonin metabolite, 5-hydroxyindoleacetic acid, and the serotonin transporter were reduced in the cortex. Several reports further implicated both cyclic adenosine monophosphate and phosphatidylinositol (PI) cascade abnormalities. G protein concentrations and activity increases were found in the occipital, prefrontal, and temporal cortices in BD. In the PI signal cascade, alterations in PKC activity were found in the prefrontal cortex. In the occipital cortex, PI hydrolysis was decreased. Two isoforms of the neural cell adhesion molecules were increased in the hippocampus of BD, whereas the synaptic protein marker, synaptophysin, was not changed. The findings of glial reduction, excess signal activity, neuropeptide abnormalities, and monoamine alterations suggest distinct imbalances in neurochemical regulation. Possible alterations in pathways involving ascending projections from the brain stem are considered. Larger numbers of BD brains are needed to further refine the conceptual models that have been proposed, and to develop coherent models of the pathophysiology of BD.

Further studies of elevated cerebrospinal fluid neuronal cell adhesion molecule in schizophrenia.

BACKGROUND: The purposes of the present study were to attempt to replicate a previous finding of increased cerebrospinal fluid (CSF) neuronal cell adhesion molecule (N-CAM) in schizophrenia, and to assess whether the increases could be related to medication, clinical state effects, or brain structural measures. METHODS: CSF N-CAM was measured by the Western blot technique in 45 DSM-III-R diagnosed male schizophrenic patients both on and off haloperidol treatment and in 20 healthy male control subjects. RESULTS: CSF N-CAM was significantly increased in schizophrenic patients, with no overlap in the ranges, when compared to controls. There were no significant effects of medication or exacerbation on CSF N-CAM. No associations with measures of brain structure were found. CONCLUSIONS: Because N-CAM levels were not shown to be different on and off treatment or in exacerbated versus nonexacerbated patients, the higher levels seen in schizophrenic patients may be inherent to the disorder and possibly related to neurodevelopment.

The role of cholinergic supersensitivity in the medical symptoms associated with withdrawal of antipsychotic drugs.

From a review of the clinical literature, the authors determined that the medical symptoms of neuroleptic withdrawal occurred more frequently with neuroleptics having potent anticholinergic effects than with those having weak anticholinergic actions. When antiparkinsonian agents were not simultaneously withdrawn, there was a striking difference between these two categories of neuroleptics. Experiments with mice showed that withdrawal of haloperidol, a neuroleptic with weak anticholinergic effects, produced subsensitivity (depression of locomotor activity and seizure thresholds) to the cholinergic effects of physostigmine. These findings support the theory that the medical side effects of neuroleptic withdrawal are due to rebound cholinergic hypersensitivity associated with the anticholinergic actions of these drugs, rather than being related to their dopamine-blocking activity.

Eye-blinking and cerebral ventricular size in chronic schizophrenic patients.

Spontaneous eye-blinking, a possible measure of central dopaminergic activity, was studied in 55 drug-free chronic schizophrenic patients subdivided by cerebral ventricular size. Blink rates were higher in schizophrenic patients than in normal control subjects, regardless of cerebral ventricle size. Neuroleptics lowered blink rates in patients with normal ventricles but did not affect blink rates in patients with large ventricles. Insofar as blinking is a dopaminergic parameter, these findings suggest that the dopamine hypothesis of schizophrenia is most relevant in patients with normal ventricles.

Partial reversal of the iminodipropionitrile-induced hyperkinetic syndrome in rats by alpha-tocopherol (vitamin E).

Rats were treated with the neurotoxin iminodipropionitrile (IDPN), which causes an irreversible movement disorder accompanied by axonal damage similar to that seen in vitamin E deficiency. Animals that received 2 g/kg vitamin E concurrently with 100 mg/kg IDPN for 10 days demonstrated a significantly reduced severity of IDPN-induced dyskinesia (as measured by vertical head movements) compared to animals that received IDPN alone. When animals were treated with 100 mg/kg IDPN for 10 days and then given either 2 g/kg vitamin E or an equivalent volume of sesame oil for 7 days, vitamin E produced a significant reduction in the severity of IDPN-induced dyskinesia. In both experiments, locomotor activity was unchanged by vitamin E. These data suggest a possible involvement of free radical formation in the neurotoxicity of IDPN.

Transforming growth factors beta 1 and beta 2 in the cerebrospinal fluid of chronic schizophrenic patients.

Transforming growth factor beta s (TGF beta s) are potent immunosuppressive molecules released in the brain after injury. We hypothesized that TGF beta levels in cerebrospinal fluid (CSF) of schizophrenic patients would be altered because TGF beta can influence neural cell adhesion molecule (N-CAM) expression in vitro. The levels of TGF beta 1 and beta 2 in CSF of patients with schizophrenia and normal controls measured by ELISA showed no differences. There was evidence that the stability of TGF beta in CSF may be altered in schizophrenia. For a limited sample, TGF beta 1 and N-CAM concentrations were significantly correlated in normal patients (r = 0.98) but not in schizophrenics. The results do not support an active neurodegeneration or anti-inflammatory response in the central nervous system, which is reflected in the CSF of chronic schizophrenics.

Effects of neuroleptics on phencyclidine (PCP)-induced locomotor stimulation in mice.

A variety of neuroleptics were compared for their ability to block phencyclidine (PCP)-induced behavioral stimulation in mice. Methiothepin, fluphenazine, trifluoperazine, and chlorpromazine were highly effective in blocking phencyclidine-induced stimulation at doses that did not decrease spontaneous behavioral activity. Clozapine, thioridazine and haloperidol were moderately effective, while sulpiride, molindone, and pimozide were completely ineffective. The effectiveness of the drugs was found to be correlated with their ability to block tryptamine-induced seizures and with several other measures of antidopaminergic and antiserotonergic potency. it is concluded that a combination of antidopaminergic and antiserotonergic activity is important for blocking the stimulating effects of phencyclidine.

A comparison of intraventricular and intraparenchymal cerebellar allografts in rat brain: evidence for normal phosphorylation of neurofilaments.

Allografts of embryonic (E14-E15) rat cerebellum in adult brain were compared using the intraparenchymal and intraventricular transplantation techniques. We studied the expression and distribution of phosphorylated neurofilament (PNF) epitopes, nonphosphorylated neurofilament (nPNF) epitopes, synapse-associated antigens, glial fibrillary acidic protein (GFAP) and myelin basic protein (MBP). Both intraventricular and intraparenchymal grafts developed a clear trilaminar organization. Intraparenchymal grafts were much smaller and showed a large GFAP-positive glial scar and demyelination of host tissue. Nevertheless, myelinated fibers were present more often crossing the host-transplant border in intraparenchymal grafts. PNF and nPNF epitopes were present in both types of grafts. Staining patterns characteristic of normal rat cerebellum were seen. nPNF epitopes were present in Purkinje cell bodies and dendrites and PNF epitopes in basket cell axons surrounding Purkinje neurons. The appearance and distribution of PNF epitopes resembled that seen in normal postnatal cerebellar development and both PNF and nPNF epitopes were present at the same times in early development in both intraventricular and intraparenchymal grafts. In contrast to the situation in trauma and disease, PNF epitopes never appeared in perikarya of transplanted cerebellar neurons. The expression of synapse-associated antigens in grafted tissue was also similar to that seen in normal cerebellum.

Effects of intraventricular glutamic acid on the acquisition, performance, and extinction of an operant response, and on general activity.

This study was designed to investigate the effects of intracerebral injections of glutamic acid on acquisition and extinction of a bar-press response, performance of that response, and behavior activity. Nineteen food-deprived rats bearing chronic ventricular cannulae were tested in operant conditioning chambers or in an open field. Just prior to each testing session each animal was injected intraventricularly with 10 mul of either normal or acidified saline solution (control groups), or 10 mul of 100 mMol glutamic acid solution. Acquisition of the bar-pressing response by the glutamic acid group was significantly retarded as compared to the control groups, and the responding of the glutamic acid group was suppressed during the beginning of the first few sessions of testing on a fixed-interval schedule and during extinction. Other behavioral measures, such as operant level, performance of the response on a continuous schedule, performance on fixed-interval and extinction schedules except during the start of the first few sessions, and behavioral activity, were either unaffected or only slightly affected. It is concluded that interference with the normal neurophysiological activity of glutamic acid in the central nervous system interferes with learning and suppresses behavioral output in certain situations.

A possible role of AA2 excitatory amino acid receptors in the expression of stimulant drug effects.

GDEE, an antagonist of the AA2 or quisqualic acid category of excitatory amino acid receptor, decreases behavioral activity and locomotor stimulation induced by cocaine and amphetamine when locally injected into the nucleus accumbens. The present experiment was intended to examine the effects of systemic GDEE and other excitatory amino acid antagonists on stimulant-induced locomotor activity. GDEE markedly attenuated the stimulant effect of amphetamine, and partially blocked the effects of phencyclidine (PCP). Apomorphine-induced cage climbing behavior was partially decreased by lower dosages of GDEE, but was almost completely blocked by the highest dosage tested. Amphetamine-induced stimulation of locomotor activity was not decreased by any of the other excitatory amino acid antagonists that were tested, including MK-801, 2-amino-7-phosphonoheptanoic acid (APH), or CNQX. APH decreased stereotypy only at a high dosage (250 mg/kg), which also produces ataxia. Several other compounds, including L-glutamic acid gamma ethyl ester (GMEE), L-glutamic acid, glycine, and L-glutamine did not block amphetamine-induced stimulation in molar dosages equivalent to the highest dosage of GDEE (8 mmol/kg). It is concluded that the AA2 excitatory amino acid receptor is important in the expression of activating effects of stimulant drugs.

Production of convulsions in mice by the combination of methionine and homocysteine.

Behavioral effects of methionine have been attributed to either increased availability of methyl groups for the production of methylated amines or accumulation of convulsive metabolites. If the second hypothesis is correct, methionine would be expected to have convulsive properties either by itself or in combination with subconvulsive dosages of other known convulsants. Methionine alone did not induce convulsions when administered by various routes in dosages of 250--13,000 mg/kg, although larger doses of methionine (500--4,000 mg/kg) decreased behavioral activity. However, methionine pretreatment (125--1,000 mg/kg) markedly enhanced convulsions in animals challenaed with subconvulsine dosages of homocysteine. Pentylenetetrazol was less effective than homocysteine in promoting convulsions in methionine-pretreated animals. Although the convulsive effects of methionine were not shared by other natural amino acids (glutamate, asparate, cysteine, tryptophan, and others), ethionine enhanced homocysteine-induced convulsions almost as effectively as did methionine. Methionine thus promotes convulsions under certain conditions, plerhaps due to an accumulation of homocysteine or of other metabolites with convulsive properties.U