Role of catecholaminergic neurones of the caudal ventrolateral medulla in cardiovascular responses induced by acute changes in circulating volume in rats

Several findings suggest that catecholaminergic neurones in the caudal ventrolateral medulla (CVLM) contribute to body fluid homeostasis and cardiovascular regulation. The present study sought to determine the effects of lesions of these neurones on the cardiovascular responses induced by changes in circulating volume. All experiments were performed in male Wistar rats (320-360 g). Medullary catecholaminergic neurones were lesioned by microinjection of anti-dopamine beta-hydroxylase-saporin (6.3 ng in 60 nl; SAP rats, n = 14) into the CVLM, whereas sham rats received microinjections of free saporin (1.3 ng in 60 nl, n = 15). Two weeks later, rats were anaesthetized (urethane, 1.2 g kg(-1), i.v.), instrumented for measurement of mean arterial pressure (MAP), renal blood flow (RBF) and renal vascular conductance (RVC), and infused with hypertonic saline (HS; 3 m NaCl, 0.18 ml (100 g body weight)(-1), i.v.) or an isotonic solution (volume expansion, VE; 4% Ficoll, 1% of body weight, i.v.). In sham rats, HS induced sustained increases in RBF and RVC (155 +/- 7 and 145 +/- 6% of baseline, at 20 min after HS). In SAP rats, RBF responses to HS were blunted (125 +/- 6%) and RVC increases were abolished (108 +/- 5%) 20 min after HS. Isotonic solution increased RBF and RVC in sham rats (149 +/- 10 and 145 +/- 12% of baseline, respectively, at 20 min). These responses were reduced in SAP rats (131 +/- 6 and 126 +/- 5%, respectively, at 20 min). Pressor responses to HS were larger in SAP rats than in sham rats (17 +/- 5 versus 9 +/- 2 mmHg, at 20 min), whereas during VE these responses were similar in both groups (6 +/- 3 versus 4 +/- 6 mmHg, at 20 min). Immunohistochemical analysis indicates that microinjections of anti-DbetaH-saporin produced extensive destruction within the A1/C1 cell groups in the CVLM. These results suggest that catecholaminergic neurones mediate the cardiovascular responses to VE or increases in plasma sodium levels.

Basal forebrain cholinergic lesions reduce heat shock protein 72 response but not pathology induced by the NMDA antagonist MK-801 in the rat cingulate cortex

Non-competitive N-methyl-D-aspartate (NMDA) antagonists, in addition to their neuroprotective potential, possess neurotoxic properties and induce seizures and psychosis. MK-801 induces cytoplasmic vacuoles and heat shock protein in pyramidal neurones in the rodent posterior cingulate and retrosplenial cortex. The mechanism of this neurotoxicity is unclear, involving many neurotransmitter systems. The aim of this study was to investigate the role of cholinergic pathways from the nucleus basalis of Meynert in mediating MK-801-induced neurotoxicity. Cholinergic projections from the nucleus basalis of Meynert were lesioned by focal injection of 192-IgG-saporin (80 ng), which after 7 days reduced the number of cholinergic cell bodies by 70% in the lesioned nucleus compared to the uninjected nucleus. Following a unilateral cholinergic lesion, MK-801 (5 mg/kg s.c.) induced expression of hsp72 mRNA (6 h) and HSP72 protein immunoreactivity (24 h) was reduced by 42 and 60%, respectively in the ipsilateral compared to the contralateral posterior cingulate. Despite this apparent protective effect, the unilateral cholinergic lesion did not affect the degree of neuronal vacuolation (6 h), necrosis (24 h) or the large and prolonged increase in cerebral blood flow which occurred over the first 9h following MK-801 administration. These results demonstrate that cholinergic neurones in the nucleus basalis of Meynert play an important role in the heat shock response to NMDA antagonist-induced neurotoxicity but also reveal an unexpected divergence between the heat shock response and the pathophysiological response. This suggests that other cholinergic pathways or non-cholinergic mechanisms are responsible for the pathological changes induced by MK-801.

Bright oligothiophene N-succinimidyl esters for efficient fluorescent labeling of proteins and oligonucleotides

The synthesis of multicolor fluorescent oligothiophene N-succinimidyl esters (TSEs) is reported, and their optical properties are discussed with the aid of ab initio calculations. The esters were coupled to proteins and to 3'-amino-modified oligonucleotides in mild conditions and with similar modalities. A comparative study of the bioconjugate of IgG1 anti-CD3 antibody labeled with a blue fluorescent TSE and with fluorescein isothiocyanate (FITC) is reported, showing that the former achieves higher photoluminescence intensity and optical stability than the latter. Fluorescence resonance energy transfer experiments with TSE-labeled oligonucleotides and examples of cellular imaging via TSE-labeled proteins are reported.

Ablation of NK1 receptor bearing neurons in the nucleus of the solitary tract blunts cardiovascular reflexes in awake rats

The nucleus of the solitary tract (NTS) receives primary afferents involved in cardiovascular regulation. We investigated the role of NK(1)-receptor bearing neurons in the NTS on cardiovascular reflexes in awake rats fitted with chronic venous and arterial cannulae. These neurons were lesioned selectively with saporin conjugated with substance P (SP-SAP, 2 microM, bilateral injections of 20 nL in the subpostremal NTS, or 200 nL in both the subpostremal and the commissural NTS). Before, and 7 and 14 days after injection of SP-SAP, we measured changes in blood pressure and heart rate induced by i.v. injection of phenylephrine and nitroprusside (baroreceptor reflex), cyanide (arterial chemoreceptor reflex), and phenylbiguanide (Bezold-Jarisch reflex). The smaller injections with SP-SAP completely abolished NK1 receptor staining in the subpostremal NTS. The larger injections abolished NK1 receptor immunoreactivity in an area that extended from the commissural NTS to the rostral end of the subpostremal NTS. The lesions seemed to affect only a limited number of neurons, since neutral red stained sections did not show any obvious reduction in cell number. The smaller lesions reduced the gain of baroreflex bradycardia and the hypotension induced by phenylbiguanide. The larger lesions completely abolished the response to phenylbiguanide, blocked the baroreflex bradycardia induced by phenylephrine, severely blunted the baroreflex tachycardia, and blocked the bradycardia and reduced the hypertension induced by cyanide. Thus, these responses depend critically on NK(1)-receptor bearing neurons in the NTS.

Expression, purification and anti-tumor activity of curcin

Curcin, purified from the seeds of Jatropha curcas, can be used as a cell-killing agent. Understanding the anti-tumor activity of the recombinant protein of curcin is important for its application in clinical medicine. The segment encoding the mature protein of curcin was inserted into Escherichia coli strain M15, and the recombinant strain was induced to express by isopropyl-beta-D-thiogalactopyranoside at a concentration of 0.5 mM. The recombinant protein was expressed in the form of inclusion bodies and purified by Ni-NTA affinity chromatography. The target protein was incubated with the tumor cells at different concentrations for different times and the results demonstrated that the target protein could inhibit the growth of tumor cells (NCL-H446, SGC-7901 and S180) at 5 microg/ml.

Pokeweed antiviral protein depurinates the sarcin/ricin loop of the rRNA prior to binding of aminoacyl-tRNA to the ribosomal A-site

Ribosome-inactivating proteins, such as the pokeweed antiviral protein (PAP), inhibit translation by depurinating the conserved sarcin/ricin loop of the large ribosomal RNA. Depurinated ribosomes are unable to bind elongation factor 2, and, thus, the translocation step of the elongation cycle is inhibited. Though the consequences of depurination are well characterized, the ribosome conformation required for depurination to take place has not been described. In this report, we correlate biochemical and genetic data to conclude that pokeweed antiviral protein depurinates the sarcin/ricin loop when the A-site of the ribosomal peptidyl-transferase center is unoccupied. We show that prior incubation of ribosomes with puromycin, an analog of the 3'-terminus of aminoacyl-tRNA, inhibits both binding and depurination by PAP in a concentration-dependent manner. Expression of PAP in the yeast strain mak8-1 results in little depurination unless the cells are lysed, a process that would promote loss of aminoacyl-tRNA from the ribosome. The mak8-1 strain is known to exhibit a higher affinity for aminoacyl-tRNA compared with wild-type cells, and therefore, its ribosomes are more resistant to PAP in vivo. These data contribute to the mechanism of action of pokeweed antiviral protein; specifically, they have uncovered the ribosomal conformation required for depurination that leads to subsequent translation inhibition.

Aptamer:toxin conjugates that specifically target prostate tumor cells

We have used RNA aptamer:gelonin conjugates to target and specifically destroy cells overexpressing the known cancer biomarker prostate-specific membrane antigen (PSMA). Aptamer:toxin conjugates have an IC50 of 27 nmol/L and display an increased potency of at least 600-fold relative to cells that do not express PSMA. The aptamer not only promotes uptake into target cells but also decreases the toxicity of gelonin in non-target cells. These results validate the notion that "escort aptamers" may be useful for the treatment of specific tumors expressing unique antigen targets.

Detection of ricin and other ribosome-inactivating proteins by an immuno-polymerase chain reaction assay

Ribosome-inactivating proteins (RIPs) are plant proteins with enzymatic activity, classified as type 1 (single chain) or type 2 (two chains). They are identified as rRNA N-glycosidases (EC 3.2.2.22) and cause an irreversible inhibition of protein synthesis. Among type 2 RIPs, there are potent toxins (ricin is the best known) that are considered as potential biological weapons. The development of a fast and sensitive method for the detection of biological agents is an important tool to prevent or deal with the consequences of intoxication. In this article, we describe a very sensitive immuno-polymerase chain reaction (IPCR) assay for the detection of RIPs-a type 1 RIP (dianthin) and a type 2 RIP (ricin)-that combines the specificity of immunological analysis with the exponential amplification of PCR. The limit of detection (LOD) of the technique was compared with the LODs of the conventional immunological methods enzyme-linked immunosorbent assay (ELISA) and fluorescent immunosorbent assay (FIA). The LOD of IPCR was more than 1 million times lower than that of ELISA, allowing the detection of 10 fg/ml of dianthin and ricin. The possibility to detect ricin in human serum was also investigated, and a similar sensitivity was observed (10 fg/ml). IPCR appears to be the most sensitive method for the detection of ricin and other RIPs.

Effect of nucleus basalis magnocellularis cholinergic lesions on fear-like and anxiety-like behavior

Previous research has suggested that cholinergic neurons in the nucleus basalis magnocellularis and substantia innominata (NBM/SI) may be important in mediating aversive states. The authors investigated the effect of NBM/SI cholinergic lesions, induced with 192 IgG saporin, on behavioral measures of aversive states in rats. Behavior in the elevated plus maze and behavioral suppression induced by 2 fear-conditioned stimuli, a tone and a light, were evaluated. Lesions had no effect on any measures in the elevated plus maze but attenuated operant suppression induced by the light and attenuated freezing induced by the tone, though this last effect was not statistically significant. The results of the study suggest that NBM/SI cholinergic neurons may be important in mediating selective aspects of aversive states.

Selective lesions of the nucleus basalis magnocellularis impair cognitive flexibility

The authors tested the hypothesis that the cholinergic nucleus basalis magnocellularis (NBM) is involved in solving problems requiring cognitive flexibility. Rats with 192 IgG-saporin lesions of the NBM were assessed for perseveration (i.e., cognitive inflexibility) in the serial reversal of an operant discrimination and during subsequent extinction testing. It was hypothesized that the NBM lesion and control groups would not differ in the acquisition of the initial, simple discrimination, because this task does not demand cognitive flexibility. In contrast, it was hypothesized that the NBM lesion group would show perseveration during serial reversal and extinction testing. Results generally supported these hypotheses, suggesting that the NBM plays an important role in mediating cognitive flexibility.

Myeloid precursors and acute myeloid leukemia cells express multiple CD33-related Siglecs

OBJECTIVES

CD33 is a cell surface marker of committed myelomonocytic precursors and circulating monocytes, and is also found on acute myeloid leukemia (AML) cells. CD33 belongs to a family of sialic acid-binding cell surface proteins named Siglecs, among which there are 7 other functional CD33-related Siglecs (CD33rSiglecs). We sought to characterize the spectrum of expression of the other CD33rSiglecs on bone marrow precursors and AML cells and asked if they can potentially serve as targets for therapy.

METHODS

Cell surface CD33rSiglecs were analyzed by flow cytometry. The ability of certain anti-Siglec antibodies to target toxin-mediated cell killing of Siglec-expressing cell lines was characterized and compared.

RESULTS

We demonstrate that Siglecs-3, -5, -6, -7, and -9 are expressed on subsets of normal bone marrow precursors, including promonocytes and myelocytes. Furthermore, most AML (but not ALL) cells express these Siglecs. There is substantial variability in Siglec type and expression level between cases, with each having a unique "CD33rSiglec fingerprint." Individual anti-Siglec antibodies along with a saporin toxin-conjugated secondary antibody can target myelomonocytic leukemia cells for death, and targeting of multiple Siglecs improves cell killing. Cytotoxicity was further enhanced by sialidase treatment of target cells, which improves antibody binding. We also confirmed that antibody binding induced rapid internalization of Siglecs from the cell surface, which is a requirement for cell killing via saporin.

CONCLUSIONS

Multiple CD33rSiglecs are expressed on normal and malignant myelomonoyctic cells. Targeting these Siglecs, possibly in combinations, could improve anti-CD33 antibody therapy or be used as an alternative to anti-CD33.

Targeted anticancer immunotoxins and cytotoxic agents with direct killing moieties

Despite the progress of the bioinformatics approach to characterize cell-surface antigens and receptors on tumor cells, it remains difficult to generate novel cancer vaccines or neutralizing monoclonal antibody therapeutics. Among targeted cancer therapeutics, biologicals with targetable antibodies or ligands conjugated or fused to toxins or chemicals for direct cell-killing ability have been developed over the last 2 decades. These conjugated or fused chimeric proteins are termed immunotoxins or cytotoxic agents. Two agents, DAB389IL-2 (ONTAKTM) targeting the interleukin-2 receptor and CD33-calicheamicin (Mylotarg), have been approved by the FDA for cutaneous T-cell lymphoma (CTCL) and relapsed acute myeloid leukemia (AML), respectively. Such targetable agents, including RFB4(dsFv)-PE38 (BL22), IL13-PE38QQR, and Tf-CRM107, are being tested in clinical trials. Several agents using unique technology such as a cleavable adapter or immunoliposomes with antibodies are also in the preclinical stage. This review summarizes the generation, mechanism, and development of these agents. In addition, possible future directions of this therapeutic approach are discussed.

The anti-CD20 antibody rituximab augments the immunospecific therapeutic effectiveness of an anti-CD19 immunotoxin directed against human B-cell lymphoma

The chimaeric anti-CD20 antibody rituximab (Rituxan) sensitises lymphoma cells to small molecule cytotoxic drugs and to protein toxins. We have explored the augmentive effect of rituximab on the anti-CD19 immunotoxin BU12-SAPORIN in a model of human lymphoma. Intact rituximab and its F(ab)2 derivative both augmented the immunospecific protein synthesis inhibitory effects of BU12-SAPORIN in a complement-independent manner. A combination of rituximab + BU12-SAPORIN completely abolished the proliferation of Ramos cells in vitro and also induced a significantly greater degree of apoptosis in these cells. Treatment with rituximab, BU12-SAPORIN or a combination of both induced poly(ADPribose) polymerase and caspase 3 cleavage, although this was always consistently greater in combination-treated cells. zVAD almost completely inhibited apoptosis in rituximab- or BU12-SAPORIN-treated cells but only partially in combination-treated cells. In severe combined immunodeficient (SCID)-Ramos mice the combination of rituximab + BU12-SAPORIN was significantly better therapeutically than either single agent. The immunological fidelity of the therapeutic effect because of combination treatment was demonstrated through the failure of rituximab to augment an irrelevant anti-CD7 immunotoxin. The therapeutic efficacy of rituximab and combination treatment was reduced in SCID-Ramos mice depleted of serum complement while natural killer cell depletion failed to show any convincing role for antibody-dependent cellular cytotoxicity. This study shows a clear therapeutic advantage from using rituximab to immunospecifically augment immunotoxin cytotoxicity warranting further investigation.

Descending facilitation from the rostral ventromedial medulla maintains visceral pain in rats with experimental pancreatitis

BACKGROUND & AIMS

Pain is a main complaint of patients with pancreatitis. We hypothesized that such pain is mediated through ascending pathways via the nucleus gracilis (NG) and is dependent on descending facilitatory influences from the rostral ventromedial medulla (RVM).

METHODS

A rat model of persistent experimental pancreatitis was used. After establishment of pancreatitis, rats received microinjection of lidocaine in the NG or in the RVM to determine the importance of neural activity at these supraspinal sites in the expression of abdominal hypersensitivity evoked by von Frey filaments (ie, pancreatic pain). Rats also were pretreated for 28 days before induction of pancreatitis with a single RVM microinjection of dermorphin-saporin to eliminate cells that drive descending facilitation. Dynorphin content was measured in the spinal cord of pancreatitic rats and the effects of spinal antidynorphin antiserum in pancreatic pain were assessed.

RESULTS

Microinjection of lidocaine into either the NG or the RVM produced a time-related reversal of pancreatitis-induced pain. Pancreatitis significantly increased thoracic spinal dynorphin content and spinal antidynorphin antiserum elicited a time-related reversal of abdominal hypersensitivity. RVM dermorphin-saporin injection prevented the maintenance, but not the expression, of pancreatitis abdominal hypersensitivity and also prevented the increase of spinal dynorphin content in animals with pancreatitis.

CONCLUSIONS

Our findings suggest that descending facilitation from the RVM plays a critical role in the maintenance, but not the expression, of pancreatic pain. These results provide a novel insight into the role of descending pathways and spinal plasticity in the maintenance of visceral pain from pancreatitis.

Ribosome-inactivating proteins in edible plants and purification and characterization of a new ribosome-inactivating protein from Cucurbita moschata

The basic protein fraction of tissue extracts from 40 edible plants inhibited cell-free protein synthesis and released adenine from herring sperm DNA, thus having adenine glycosylase activity. This suggested the presence of ribosome-inactivating proteins (RIPs) in the plant extracts. This indication was further strengthened by the presence of the two activities after a partial chromatographic purification of three extracts, including that from Lycopersicon esculentum (tomato), which had very low activity. From the extract of Cucurbita moschata (pumpkin), the most active one, a glycoprotein of 30,665 Da was purified which had the properties of a RIP, in that (i) it inhibited protein synthesis by a rabbit reticulocyte lysate with IC50 (concentration giving 50% inhibition) 0.035 nM (1.08 ng ml(-1)) and by HeLa, HT29 and JM cells with IC50 in the 100 nM range, (ii) deadenylated hsDNA and other polynucleotidic substrates, and (iii) depurinated yeast rRNA at a concentration of 0.1 ng ml(-1), all values being comparable to those of other RIPs. The C. moschata RIP gave a weak cross-reaction only with an antiserum against dianthin 32, but not with antisera against other RIPs, and had superoxide dismutase, antifungal and antibacterial activities.

Purkinje cell loss by OX7-saporin impairs acquisition and extinction of eyeblink conditioning

The current study examined the effects of globally depleting Purkinje cells in the cerebellar cortex with the immunotoxin OX7-saporin on acquisition and extinction of delay eyeblink conditioning in rats. Rats were given OX7-saporin or saline 2 wk before the start of eyeblink conditioning. The rats that reached a performance criterion of two consecutive days with 80% or greater conditioned responses were given 5 d of extinction training followed by 2 d of reacquisition training. Rats that received infusions of OX7-saporin had 77.2%-97.9% Purkinje cell loss and exhibited impaired acquisition and extinction. The amount of Purkinje cell loss was correlated with the magnitude of the acquisition and extinction impairments. The highest correlations between Purkinje cell number and the rate of acquisition were in lobule HVI and the anterior lobe. The highest negative correlation between Purkinje cell number and the percentage of conditioned responses during extinction was in the anterior lobe. The results indicate that cerebellar Purkinje cells, particularly in the anterior lobe and lobule HVI, play significant roles in acquisition and extinction of eyeblink conditioning.

[Effect of protein synthesis inhibitors on sensitization of defence reaction and on cholinosensitivity of command neurons in Helix lucorum]

We studied influence of protein synthesis inhibitors on short-term sensitization of Helix escape reaction and potentiation cholinosensitivity in command neurons. Inhibitor of protein synthesis anisomycin does not prevent behavioral sensitization. Anisomycin and irreversible inhibitor of protein synthesis saporin change the dynamics of cholinosensitivity potentiation in command neurons. The results Suggest that investigated sensitization of Helix escape reaction does not require synthesis of new proteins.

Aversive stimulus attenuates impairment of acquisition in a delayed match to position T-maze task caused by a selective lesion of septo-hippocampal cholinergic projections

Infusion of 192 IgG-saporin (SAP) into the medial septum (MS) of rats selectively destroys cholinergic neurons projecting to the hippocampus and impairs acquisition of a delayed matching to position (DMP) T-maze task. The present study evaluated whether introduction of a mild aversive stimulus 30 min prior to training would attenuate the deficit in DMP acquisition caused by the SAP lesions. Male Sprague-Dawley rats received medial septal infusions of either artificial cerebrospinal fluid or SAP (0.22 microg in 1.0 microl). Fourteen days later, all animals were trained to perform the DMP task. Half of the SAP-treated animals and controls received an intraperitoneal injection of saline each day, 30 min prior to training. Results show that intraperitoneal saline attenuated the impairment in DMP acquisition in SAP lesioned rats. These results suggest that a mild aversive stimulus can attenuate cognitive deficits caused by medial septal cholinergic lesions.

Medullary noradrenergic neurons release norepinephrine in the medial amygdala in females in response to mating stimulation sufficient for pseudopregnancy

In the female rat, stimuli from the uterine cervix and vagina are carried to the brain areas involved in the mating-induced pseudopregnancy (PSP) response via the ventral noradrenergic bundle. Noradrenergic neurons projecting through this tract synapse in many forebrain areas including the amygdala, and neurons in the posterodorsal medial amygdala (MePD) are activated following mating. The goal of this experiment was to investigate whether norepinephrine (NE) is released into the MePD after mating using microdialysis and to determine the origin of this release. Ovariectomized estrogen- and progesterone-treated rats were implanted unilaterally with guide cannulae aimed at the MePD. Females were placed with males until they received 15 intromissions (15I), 5 intromissions (5I) or 15 mounts-without-intromission (MO). Dialysate samples collected every 20 min for 2 h before to 3 h after mating were analyzed for NE using HPLC with electrochemical detection. A significant increase in mean NE release in the MePD was seen at 80 min after mating onset in females receiving 15I, and no increase was seen in animals receiving 5I or MO. The time of peak NE release varied in 15I animals from 60 to 160 min after mating. Mean baseline levels of NE did not differ between groups. The retrograde tracer FluoroGold (FG), administered through the probe after cessation of dialysis sampling, was observed within identified noradrenergic cells primarily within the A1 and A2 cell groups. Infusion of anti-dopamine-beta-hydroxylase-saporin (DBH-SAP) into the MePD lesioned noradrenergic neurons located in the A1 and A2 cell groups. Because high levels of NE release occurred in the MePD only after the females received a number of intromissions sufficient to induce PSP, these results suggest that NE release within the MePD may be important for the establishment of PSP.

Cortical choline transporter function measured in vivo using choline-sensitive microelectrodes: clearance of endogenous and exogenous choline and effects of removal of cholinergic terminals

The capacity of the high-affinity choline transporter (CHT) to import choline into presynaptic terminals is essential for acetylcholine synthesis. Ceramic-based microelectrodes, coated at recording sites with choline oxidase to detect extracellular choline concentration changes, were attached to multibarrel glass micropipettes and implanted into the rat frontoparietal cortex. Pressure ejections of hemicholinium-3 (HC-3), a selective CHT blocker, dose-dependently reduced the uptake rate of exogenous choline as well as that of choline generated in response to terminal depolarization. Following the removal of CHTs, choline signal recordings confirmed that the demonstration of potassium-induced choline signals and HC-3-induced decreases in choline clearance require the presence of cholinergic terminals. The results obtained from lesioned animals also confirmed the selectivity of the effects of HC-3 on choline clearance in intact animals. Residual cortical choline clearance correlated significantly with CHT-immunoreactivity in lesioned and intact animals. Finally, synaptosomal choline uptake assays were conducted under conditions reflecting in vivo basal extracellular choline concentrations. Results from these assays confirmed the capacity of CHTs measured in vivo and indicated that diffusion of substrate away from the electrode did not confound the in vivo findings. Collectively, these results indicate that increases in extracellular choline concentrations, irrespective of source, are rapidly cleared by CHTs.

Effect of N-methyl-d-aspartate receptor blockade on plasticity of frontal cortex after cholinergic deafferentation in rat

Cholinergic projections from the nucleus basalis play a critical role in cortical plasticity. For instance, cholinergic deafferentation increases dendritic spine density and expression of the GluR1 subunit of the alpha-amino-3-hydroxy-5-methylisoxazole-4-propionate receptor in frontal cortex. Acetylcholine modulates glutamatergic activity in cortex, and the N-methyl-d-aspartate subtype of glutamate receptor plays a role in many forms of synaptic plasticity. To assess whether N-methyl-d-aspartate receptors mediate the increase in GluR1 and spine density resulting from cholinergic deafferentation, we examined the effect of N-methyl-d-aspartate receptor blockade on nucleus basalis lesion-induced upregulation of GluR1 and dendritic spines. Rats received unilateral sham or 192 IgG saporin lesions of the nucleus basalis. Half of the rats in each group were treated with the N-methyl-d-aspartate antagonist MK-801 or phosphate-buffered saline. Two weeks later, brains were processed for either immunohistochemical staining of the GluR1 subunit or Golgi histology. In layer II-III of frontal cortex, neuronal GluR1 expression was assessed using an unbiased stereological technique, and spine density was assessed on basilar branches of pyramidal neurons. GluR1 expression was increased after nucleus basalis lesion, but this increase was prevented with MK-801. Similarly, nucleus basalis-lesioned animals had significantly higher spine densities, and this effect was also prevented by treatment with MK-801. Thus, N-methyl-d-aspartate receptor blockade prevented both GluR1 and spine density upregulation following cholinergic deafferentation, suggesting that these effects are N-methyl-d-aspartate receptor-mediated.

Tyrosine hydroxylase is expressed in a subpopulation of small dorsal root ganglion neurons in the adult mouse

The expression of tyrosine hydroxylase (TH) was studied in adult mouse dorsal root ganglia (DRGs) and spinal cord by means of immunohistochemistry and in situ hybridization. TH immunoreactivity and TH mRNA were present in 10-15% of lumbar DRG neurons, in most cases being small/medium-sized. Only very few of these neurons coexpressed calcitonin gene-related peptide (CGRP), and only around 6% bound isolectin B4 (IB4). Dopamine beta-hydroxylase-positive(+) or aromatic amino acid decarboxylase (AADC)+ DRG neurons were rare and did not colocalize TH. No evidence for dopamine transporter expression was obtained. Axotomy of the sciatic nerve only showed a tendency towards reduction in the number of TH+ neurons. In the dorsal horn of the spinal cord, moderately dense and widespread TH+ nerve terminals were observed, mainly in the gray matter and they did not show a typical primary afferent pattern. Also, dorsal rhizotomy or peripheral axotomy had no apparent effect on TH-LI in the dorsal horn. In the skin, along with an abundant TH+ innervation of blood vessels and sweat gland acini, a number of fibers was observed in close relation to the skin surface, some even penetrating into the epithelium. These results demonstrate presence, in normal adult mouse DRGs, of a subpopulation of TH+, essentially CGRP- and IB4-negative small/medium-sized neurons. No evidence for transport of TH into central afferents was obtained, but the enzyme may be present in some sensory fibers in the skin. The fact that neither AADC nor the dopamine transporter could be visualized suggests of non-dopaminergic transmitter phenotype, but the levels of these two dopaminergic markers may be too low to be detected with the present methodology. A further alternative is that L-DOPA after release is extracellularly converted to dopamine.

Safety Evaluation of Intrathecal Substance P-Saporin, a Targeted Neurotoxin, in Dogs

Intrathecal (IT) substance P-Saporin (SP-SAP), a 33-kDa-targeted neurotoxin, produces selective destruction of superficial neurokinin 1 receptor (NK1r)-bearing cells in the spinal dorsal horn. In rats, SP-SAP prevents the formation of hyperalgesia and can reverse established neuropathic pain behavior in rodents. To determine the safety of this therapeutic modality in a large animal model, beagles received bolus IT lumbar injections of vehicle, SP-SAP (1.5, 15, 45, or 150 microg), or a nontargeted preparation of saporin (SAP, 150 microg) for immunohistological analysis of spinal cords. Doses of 15 microg SP-SAP and above produced a significant and equivalent loss of NK1r-bearing cells and dendrites in lumbar laminae II and I compared to vehicle- or SAP-treated animals. Cervical regions in all animals displayed no loss of NK1r immunoreactivity as compared to controls. Total numbers of neurons in the lumbar dorsal horn or alpha-motor neurons in the ventral horn demonstrated no significant changes. No increases in the astrocytic marker glial fibrillary acidic protein were noted following treatment with SP-SAP, suggesting a lack of generalized neurotoxicity. Additional dogs received doses of 1.5-150 microg SP-SAP or SAP and were sacrificed after 28 or 90 days to assess behavioral and physiological parameters. Although some acute motor signs were observed with both SP-SAP and SAP, no long-lasting significant events were noted in any of these animals. These data indicate no adverse toxicity at doses up to 10 times those necessary for producing loss of superficial NK1r-bearing neurons in a large animal model.

A novel interaction of pokeweed antiviral protein with translation initiation factors 4G and iso4G: a potential indirect mechanism to access viral RNAs

Pokeweed antiviral protein (PAP) is a ribosome inactivating protein recognized primarily for its ability to depurinate the sarcin/ricin loop of the large rRNA. Studies have demonstrated that PAP also depurinates other RNA templates, such as Human immunodeficiency virus-1 RNA and Brome mosaic virus RNAs. However, the mechanism by which PAP accesses viral RNAs is not known. Considering that PAP was shown recently to bind the m(7)G of the cap structure, we speculated that PAP may interact with other factors involved in translation initiation. By far western analysis, we show that PAP binds specifically to eIF4G and eIFiso4G of wheat germ and analysis with truncation mutants of eIFiso4G indicates that a region of this protein, between amino acids 511 and 624, is required for PAP binding activity. The yeast two-hybrid system supports these results by showing reduced growth and alpha-galactosidase expression with truncation in this region of eIFiso4G. PAP binds m(7)GTP-Sepharose and this interaction does not diminish the binding of PAP to purified eIFiso4G, indicating that a complex can form among the cap structure, PAP and eIFiso4G. We incubated PAP with uncapped and non-polyadenylated transcripts containing a 3' translation enhancer sequence (TE) known to increase translation of the RNA in an eIF4F dependent manner. We show that in the presence of wheat germ lysate, PAP depurinates the uncapped and non-polyadenylated transcripts containing a functional wild-type 3'TE, but does not depurinate messages containing a non-functional mutant 3'TE. These results support our hypothesis that binding of PAP to eIF4G and eIFiso4G can provide a mechanism for PAP to access both uncapped and capped viral RNAs for depurination.