Chronic inorganic arsenic exposure in vitro induces a cancer cell phenotype in human peripheral lung epithelial cells

Inorganic arsenic is a human lung carcinogen. We studied the ability of chronic inorganic arsenic (2 μM; as sodium arsenite) exposure to induce a cancer phenotype in the immortalized, non-tumorigenic human lung peripheral epithelial cell line, HPL-1D. After 38 weeks of continuous arsenic exposure, secreted matrix metalloproteinase-2 (MMP2) activity increased to over 200% of control, levels linked to arsenic-induced cancer phenotypes in other cell lines. The invasive capacity of these chronic arsenic-treated lung epithelial (CATLE) cells increased to 320% of control and colony formation increased to 280% of control. CATLE cells showed enhanced proliferation in serum-free media indicative of autonomous growth. Compared to control cells, CATLE cells showed reduced protein expression of the tumor suppressor gene PTEN (decreased to 26% of control) and the putative tumor suppressor gene SLC38A3 (14% of control). Morphological evidence of epithelial-to-mesenchymal transition (EMT) occurred in CATLE cells together with appropriate changes in expression of the EMT markers vimentin (VIM; increased to 300% of control) and e-cadherin (CDH1; decreased to 16% of control). EMT is common in carcinogenic transformation of epithelial cells. CATLE cells showed increased KRAS (291%), ERK1/2 (274%), phosphorylated ERK (p-ERK; 152%), and phosphorylated AKT1 (p-AKT1; 170%) protein expression. Increased transcript expression of metallothioneins, MT1A and MT2A and the stress response genes HMOX1 (690%) and HIF1A (247%) occurred in CATLE cells possibly in adaptation to chronic arsenic exposure. Thus, arsenic induced multiple cancer cell characteristics in human peripheral lung epithelial cells. This model may be useful to assess mechanisms of arsenic-induced lung cancer.

Silencing KRAS overexpression in arsenic-transformed prostate epithelial and stem cells partially mitigates malignant phenotype

Inorganic arsenic is a human carcinogen that likely targets the prostate. Chronic arsenic exposure malignantly transforms the RWPE-1 human prostate epithelial line to chronic arsenic exposed-prostate epithelial (CAsE-PE) cells, and a derivative normal prostate stem cell (SC) line, WPE-stem to arsenic-cancer SCs (As-CSCs). The KRAS oncogene is highly overexpressed in CAsE-PE cells and activation precedes transformation, inferring mechanistic significance. As-CSCs also highly overexpress KRAS. Thus, we hypothesize KRAS activation is key in causing and maintaining an arsenic-induced malignant phenotype, and hence, KRAS knockdown (KD) may reverse this malignant phenotype. RNA interference using shRNAmirs to obtain KRAS KD was used in CAsE-PE and As-CSC cells. Cells analyzed 2 weeks post transduction showed KRAS protein decreased to 5% of control after KD, confirming stable KD. KRAS KD decreased phosphorylated ERK, indicating inhibition of RAS/ERK signaling, a proliferation/survival pathway activated with arsenic transformation. Secreted metalloproteinase (MMP) activity was increased by arsenic-induced malignant transformation, but KRAS KD from 4 weeks on decreased secreted MMP-9 activity by 50% in As-CSCs. Colony formation, a characteristic of cancer cells, was decreased in both KRAS KD transformants. KRAS KD also decreased the invasive capacity of both cell types. KRAS KD decreased proliferation in As-CSCs, consistent with loss of rapid tumor growth. Genes predicted to impact cell proliferation (eg, Cyclin D1, p16, and p21) changed accordingly in both KD cell types. Thus, KRAS silencing impacts aspects of arsenic-induced malignant phenotype, inducing loss of many typical cancer characteristics particularly in As-CSCs.

Aberrant microRNA expression likely controls RAS oncogene activation during malignant transformation of human prostate epithelial and stem cells by arsenic

Inorganic arsenic (iAs), a human carcinogen, potentially targets the prostate. iAs malignantly transforms the RWPE-1 human prostate epithelial line to CAsE-PE cells, and a derivative normal stem cell (SC) line, WPE-stem, to As-Cancer SC (As-CSC) line. MicroRNAs (miRNA) are noncoding but exert negative control on expression by degradation or translational repression of target mRNAs. Aberrant miRNA expression is important in carcinogenesis. A miRNA array of CAsE-PE and As-CSC revealed common altered expression in both for pathways concerning oncogenesis, miRNA biogenesis, cell signaling, proliferation, and tumor metastasis and invasion. The KRAS oncogene is overexpressed in CAsE-PE cells but not by mutation or promoter hypomethylation, and is intensely overexpressed in As-CSC cells. In both transformants, decreased miRNAs targeting KRAS and RAS superfamily members occurred. Reduced miR-134, miR-373, miR-155, miR-138, miR-205, miR-181d, miR-181c, and let-7 in CAsE-PE cells correlated with increased target RAS oncogenes, RAN, RAB27A, RAB22A mRNAs, and KRAS protein. Reduced miR-143, miR-34c-5p, and miR-205 in As-CSC correlated with increased target RAN mRNA, and KRAS, NRAS, and RRAS proteins. The RAS/ERK and PI3K/PTEN/AKT pathways control cell survival, differentiation, and proliferation, and when dysregulated promote a cancer phenotype. iAs transformation increased expression of activated ERK kinase in both transformants and altered components of the PI3K/PTEN/AKT pathway including decreased PTEN and increases in BCL2, BCL-XL, and VEGF in the absence of AKT activation. Thus, dysregulated miRNA expression may be linked to RAS activation in both transformants.

Chronic cadmium exposure in vitro induces cancer cell characteristics in human lung cells

Cadmium is a known human lung carcinogen. Here, we attempt to develop an in vitro model of cadmium-induced human lung carcinogenesis by chronically exposing the peripheral lung epithelia cell line, HPL-1D, to a low level of cadmium. Cells were chronically exposed to 5 μM cadmium, a noncytotoxic level, and monitored for acquired cancer characteristics. By 20 weeks of continuous cadmium exposure, these chronic cadmium treated lung (CCT-LC) cells showed marked increases in secreted MMP-2 activity (3.5-fold), invasion (3.4-fold), and colony formation in soft agar (2-fold). CCT-LC cells were hyperproliferative, grew well in serum-free media, and overexpressed cyclin D1. The CCT-LC cells also showed decreased expression of the tumor suppressor genes p16 and SLC38A3 at the protein levels. Also consistent with an acquired cancer cell phenotype, CCT-LC cells showed increased expression of the oncoproteins K-RAS and N-RAS as well as the epithelial-to-mesenchymal transition marker protein Vimentin. Metallothionein (MT) expression is increased by cadmium, and is typically overexpressed in human lung cancers. The major MT isoforms, MT-1A and MT-2A were elevated in CCT-LC cells. Oxidant adaptive response genes HO-1 and HIF-1A were also activated in CCT-LC cells. Expression of the metal transport genes ZNT-1, ZNT-5, and ZIP-8 increased in CCT-LC cells culminating in reduced cadmium accumulation, suggesting adaptation to the metal. Overall, these data suggest that exposure of human lung epithelial cells to cadmium causes acquisition of cancer cell characteristics. Furthermore, transformation occurs despite the cell's ability to adapt to chronic cadmium exposure.

Recruitment of normal stem cells to an oncogenic phenotype by noncontiguous carcinogen-transformed epithelia depends on the transforming carcinogen

BACKGROUND

Cancer stem cells (CSCs) drive tumor initiation, progression, and metastasis. The microenvironment is critical to the fate of CSCs. We have found that a normal stem cell (NSC) line from human prostate (WPE-stem) is recruited into CSC-like cells by nearby, but noncontiguous, arsenic-transformed isogenic malignant epithelial cells (MECs).

OBJECTIVE

It is unknown whether this recruitment of NSCs into CSCs by noncontact co-culture is specific to arsenic-transformed MECs. Thus, we used co-culture to examine the effects of neighboring noncontiguous cadmium-transformed MECs (Cd-MECs) and N-methyl-N-nitrosourea-transformed MECs (MNU-MECs) on NSCs.

RESULTS

After 2 weeks of noncontact Cd-MEC co-culture, NSCs showed elevated metalloproteinase-9 (MMP-9) and MMP-2 secretion, increased invasiveness, increased colony formation, decreased PTEN expression, and formation of aggressive, highly branched duct-like structures from single cells in Matrigel, all characteristics typical of cancer cells. These oncogenic characteristics did not occur in NSCs co-cultured with MNU-MECs. The NSCs co-cultured with Cd-MECs retained self-renewal capacity, as evidenced by multiple passages (> 3) of structures formed in Matrigel. Cd-MEC-co-cultured NSCs also showed molecular (increased VIM, SNAIL1, and TWIST1 expression; decreased E-CAD expression) and morphologic evidence of epithelial-to-mesenchymal transition typical for conversion to CSCs. Dysregulated expression of SC-renewal genes, including ABCG2, OCT-4, and WNT-3, also occurred in NSCs during oncogenic transformation induced by noncontact co-culture with Cd-MECs.

CONCLUSIONS

These data indicate that Cd-MECs can recruit nearby NSCs into a CSC-like phenotype, but MNU-MECs do not. Thus, the recruitment of NSCs into CSCs by nearby MECs is dependent on the carcinogen originally used to malignantly transform the MECs.

Oxidative DNA damage after acute exposure to arsenite and monomethylarsonous acid in biomethylation-deficient human cells

The carcinogen inorganic arsenic (iAs) undergoes biomethylation (BMT) in some cells. The methylated metabolite, monomethylarsonous (MMA(3+)), may cause oxidative DNA damage (ODD). With chronic iAs exposure, BMT-competent cells show ODD while BMT-deficient do not. To further define these events, we studied ODD produced by acute iAs or MMA(3+) in the BMT-deficient human prostate cell line, RWPE-1. ODD, measured by the immuno-spin trapping method, was assessed after exposure to iAs or MMA(3+) alone, with the arsenic BMT inhibitor selenite or after glutathione (GSH) depletion. The expression of oxidative stress-related genes (HO-1, SOD-1, SOD-2, Nrf2 and Keap-1) was also assessed. Exposure to iAs at 24 h (0-20 µM), stimulated ODD only at levels above the LC50 of a 48 h exposure (17 µM). If iAs induced ODD, it also activated oxidative stress-related genes. Selenium did not alter iAs-induced ODD. MMA(3+) at 24 h (0-0.5 µM) caused ODD at levels below the LC50 of a 48 h exposure (1.5 µM), which were greatly increased by GSH depletion but not selenite. MMA(3+) induced ODD at levels not activating oxidant stress response genes. Overall, iAs induced ODD in BMT-deficient cells only at toxic levels. MMA(3+) caused ODD at non-toxic levels, independently of cellular BMT capacity and in a fashion not requiring further BMT.

Chronic exposure of renal stem cells to inorganic arsenic induces a cancer phenotype

Inorganic arsenic in the drinking water is a multisite human carcinogen that potentially targets the kidney. Recent evidence also indicates that developmental arsenic exposure impacts renal carcinogenesis in humans and mice. Emerging theory indicates that cancer may be a disease of stem cells (SCs) and that there are abundant active SCs during early life. Therefore, we hypothesized that inorganic arsenic targets SCs, or partially differentiated progenitor cells (PCs), for oncogenic transformation. Thus, a rat kidney SC/PC cell line, RIMM-18, was chronically exposed to low-level arsenite (500 nM) for up to 28 weeks. Multiple markers of acquired cancer phenotype were assessed biweekly during arsenic exposure, including secreted matrix metalloproteinase (MMP) activity, proliferation rate, colony formation in soft agar, and cellular invasiveness. Arsenic exposure by 10 weeks and after also induced marked and sustained increases in colony formation, indicative of the loss of contact inhibition, and increased invasiveness, both cancer cell characteristics. Compared to the passage-matched control, chronic arsenic exposure caused exposure-duration dependent increases in secreted MMP-2 and MMP-9 activity, Cox-2 expression, and more rapid proliferation (all >2-fold), characteristics typical of cancer cells. Dysregulation of SC maintenance genes and signaling pathways are common during oncogenesis. During arsenite exposure, expression of several genes associated with normal kidney development and SC regulation and differentiation (i.e., Wt-1, Wnt-4, Bmp-7, etc.) were aberrantly altered. Arsenic-exposed renal SCs produced more nonadherent spheroid bodies that grew much more aggressively in Matrigel, typical of cancer SCs (CSCs). The transformed cells also showed gene overexpression typical of renal SCs/CSCs (CD24, Osr1, Ncam) and arsenic adaptation such as overexpression of Mt-1, Mt2, Sod-1, and Abcc2. These data suggest that inorganic arsenic induced an acquired cancer phenotype in vitro in these rat kidney SCs potentially forming CSCs and, consistent with data in vivo, indicate that these multipotent SCs may be targets of arsenic during renal carcinogenesis.

Effects of butyltin exposures on MAP kinase-dependent transcription regulators in human natural killer cells

Natural killer (NK) cells are a major immune defense mechanism against cancer development and viral infection. The butyltins (BTs), tributyltin (TBT) and dibutyltin (DBT), have been widely used in industrial and other applications and significantly contaminate the environment. Both TBT and DBT have been detected in human blood. These compounds inhibit the lytic and binding function of human NK cells and thus could increase the incidence of cancer and viral infections. Butyltin (BT)-induced loss of NK function is accompanied by activation of mitogen activated protein kinases (MAPKs) and decreases in expression of cell-surface and cytolytic proteins. MAPKs activate components of the transcription regulator AP-1 and activate the transcription regulator Elk-1. Based on the fact that BTs activate MAPKs and alter protein expression, the current study examined the effect of BT exposures on the levels and phosphorylation states of the components of AP-1 and the phosphorylation state of Elk-1. Exposure to 300 nM TBT for 10 min increased the phosphorylation of c-Jun in NK cells. One hour exposures to 300 nM and 200 nM TBT increased the phosphorylation and overall level of c-Jun. During a 300 nM treatment with TBT for 1 h the binding activity of AP-1 was significantly decreased. There were no significant alterations of AP-1 components or of Elk-1 with DBT exposures. Thus, it appears that TBT-induced alterations on phosphorylation, total levels, and binding activity of c-Jun might contribute to, but are not fully responsible for, TBT-induced alterations of NK protein expression.

Effects of tributyltin on protein tyrosine kinases and phospholipase C gamma in human natural killer cells

ABSTRACT Tributyltin (TBT) has been used in wood preservation, marine antifouling paints, disinfection of circulating industrial cooling waters, and slime control in paper mills. Detectable levels have been found in human blood. Exposure to TBT decreases the tumor cell lysing (lytic) function of human natural killer (NK) lymphocytes. In this study we assessed the effects of concentrations of TBT that have been shown to decrease NK lytic function on protein tyrosine kinases (PTKs) (Syk, Zap-70, Src, and Pyk) and phospholipase C gamma (PLC-gamma) in NK cells. Exposure to 500 nM TBT caused no change in phosphorylation of any of the PTKs. A 60-min exposure of NK cells to 500 nM TBT did not significantly affect the phosphorylation state of PLC-gamma at any of the lengths of exposure. However, total levels of PLC-gamma were increased by almost 50% after this exposure. Exposure of NK cells to 300 nM TBT for 5 to 60 min caused no significant changes in the phosphorylation state PTKs or PLC-gamma. Exposure of NK cells to 200 nM TBT for 24 h caused no significant changes in the PTK phosphorylation state or total levels. Cells that were exposed to 300 nM TBT for 1 h followed by 24 h or 48 h in TBT-free media showed a significant increase in the phosphorylated forms of Syk and Zap-70 after 24 h in TBT-free media but not after 48 h. These data indicate that in vitro exposure to TBT caused no changes in PTK or PLC-gamma phosphorylation under most conditions.

Ventrolateral medullary lesions and fastigial cardiovascular response in beagles

These studies were designed to verify that the putative vasomotor center in the rostral ventrolateral medulla (RVLM) contained the outflow paths for the fastigial nucleus (FN) sympathoexcitatory cardiovascular response. If so, then lesions placed by radiofrequency heating (75 degrees C) or application of kainic acid (40 mM) pledgets would reduce or ablate the pressor-tachycardia response after electrical stimulation of FN. Anesthetized beagles (alpha-chloralose, 115 mg/kg) were used in this study to maintain consistency in medullary brain stem anatomy. A ventral brain stem approach exposed the three chemosensitive zones of Mitchell, Schlaefke, and Loeschcke. In other species the intermediate zone and a portion of the rostral zone underlie the Hokfelt C1 cell group and the putative RVLM vasomotor center. Heart rate, arterial and left ventricular (LV) pressures, and maximal rate of pressure development (LV dp/dt) increased 14-84% above control levels in response to stimulating FN 5-10 times the stimulation threshold. The cardiovascular response was abolished in four of six dogs that received bilateral radiofrequency lesions at a depth of 1-2 mm. In five of seven dogs that received kainate surface lesions, the response was substantially reduced but not abolished. These lesions were effective only in the RVLM, above the corresponding intermediate, but not adjacent rostral or caudal chemosensitive areas. The data support the hypotheses of others that an epinphrine-containing cell group in this region is a final common pathway of sympathoexcitation. Expression of the FN cardiovascular response is primarily mediated through this vasomotor region previously identified by others in the rat, cat, rabbit, and primate.(ABSTRACT TRUNCATED AT 250 WORDS)

Somatic and vagal afferent convergence on solitary tract neurons in cat: electrophysiological characteristics

Electrophysiological characteristics are described for 67 neurones localized to subnuclei of the solitary tract or the area of the dorsal motor nucleus of the vagus in alpha-chloralose-anesthetized, paralysed cats which received vagal and hindlimb sural or peroneal nerve excitation. The peroneal and sural nerves were stimulated in an exposed hindlimb preparation; the ipsilateral vagus was stimulated at the cervical level. Compound action potentials were recorded from all three nerves. Neurons were recorded with extracellular microelectrodes from the brain stem solitary area contralateral to the stimulated somatic nerves. Ninety-one percent of the recorded neurons were spontaneously active. Eighteen percent and 5% of the neurons received only peroneal or sural excitation, respectively, while 59% of the neurons received convergent peroneal and sural excitation. Thirty-nine of the 67 neurons were also tested for vagal input of which 41% responded with excitation. All of the neurons tested for vagal input also received converging excitation from one or both of the somatic nerves. Thirty-one percent of the vagal-excited neurons received converging input from both the peroneal and sural nerves. The combined mean minimal conduction velocity for peroneal and sural input was 31 +/- 1 m/s (mean +/- 1 S.E., range 9-54 m/s). Thirty-six percent of the peroneal and 31% of the sural afferents were Group II fibers. Significant periods of inhibition of spontaneous neuronal spike activity followed peroneal and sural excitation in 43 and 39% of the neurons, respectively. In many neurons, both excitation and inhibition of spike activity could be elicited at stimulus intensities as low as 1.2 times threshold for the lowest threshold fibers in each nerve. Somatic nerve-induced inhibition of spontaneous neuron activity without prior excitation was also observed. These results suggest that neurons of the solitary tract nuclei receive Group II and Group III somatic afferents which converge on neurons also receiving excitatory vagal input. Consequently, somesthetic and kinesthetic as well as visceral receptor activation may directly modulate solitary tract neurons. A possible conclusion is that the nucleus tractus solitarius is the initial central site of mediation of somatosympathetic reflexes. Modulation of the nucleus tractus solitarius by somatic afferents may then adjust sympathetic tone, via modulation of other medullary centers, in visceral and somatic tissues to match somatic metabolic needs.

Fastigial nucleus modulation of medullary parasolitary neurons

Input from the cerebellar fastigial nuclei to neurons at the lateral margin of the nuclei of the solitary tract, particularly to the area identified as the nucleus parasolitarius was investigated in acutely prepared, anesthetized dogs. Fastigial nucleus stimulation led to short latency excitation of nucleus parasolitarius units often followed by prolonged inhibition of spontaneous activity. Excitation from deep skeletal muscle afferents, converged on 25% of the spontaneously active units excited from the fastigial nuclei; these afferents originated primarily from the ipsilateral forelimb muscles. This study provides electrophysiological evidence for fastigial modulation of neurons previously demonstrated autoradiographically to receive presumed monosynaptic fastigial nucleus efferents. The convergence of forelimb muscle afferent information tentatively identified as being from Group Ia or Group II pressure stretch receptors suggests that the nucleus parasolitarius may be an integrative area for cerebellar, sensorimotor and/or autonomic information.

Fastigial nucleus projections in the midbrain and thalamus in dogs

Efferent connections to midbrain and thalamus from portions of the cerebellar fastigial nucleus were investigated using autoradiographic techniques. Bipolar stimulating electrodes were placed in the fastigial nucleus of anesthetized beagles and the area which produced maximal increases in blood pressure and heart rate was localized in each dog. A mixture of [3H]leucine and [3H]proline (4:1) was injected into that area and autoradiograms were prepared. Injections filled the rostral and various parts of the caudal fastigial nucleus. The rostral-caudal extent of injection sites were mapped in the horizontal plane from sequential coronal, thionin-stained sections and "primary" and "secondary" injection zones were defined according to specific criteria. Labeled axons reached the mesencephalon via the contralateral uncinate fasiculus. Ascending fibers assembled in a diffuse contingent at the prerubral level adjacent to the ventrolateral periaqueductal gray. The heaviest projections were contralateral to the injection site, but ipsilateral terminals were observed as well. In the midbrain, axons entered the contralateral and ipsilateral superior colliculus to branch repeatedly and terminate in the deep and intermediate layers. Additional terminals were observed bilaterally in the nuclei of the posterior commissure and pretectal areas at the midbrain-diencephalic junction. In the thalamus, labeled axons formed into three groups which terminated in: the contralateral paraventricular complex and medial dorsal nucleus; the contralateral central medial, paracentral, parafasicular and central lateral nuclei, and the contralateral ventral medial and ventral lateral nuclei. There was a sparse projection to the ipsilateral ventral lateral nucleus. The contralateral projection to the ventral medial and ventral lateral nuclei was marked by dense clusters of label ventral to the internal medullary lamina extending, in the dorsal ventral lateral nucleus, to its rostral pole. Projections to specific somesthetic thalamus or the hypothalamus were not observed. These ascending projections in the canine brain generally conform to those described in other nonprimate mammals. The fastigial nucleus presumably provides information concerning equilibrium and body proprioception to the superior colliculus and to thalamic nuclei including both specific motor relay and "nonspecific" midline and intralaminar nuclei, much the same as reported in the cat. The projection to the ventral medial and ventral lateral thalamic nuclei terminate in areas known to participate in the control of axial and proximal limb muscle activity.(ABSTRACT TRUNCATED AT 400 WORDS)

Fastigial nucleus cardiovascular response and brain stem lesions in the beagle

Changes in the excitatory cardiovascular response (heart rate, arterial blood pressure, left ventricular pressure, and LV dP/dt as an index of myocardial contractility) resulting from electrical stimulation of the cerebellar fastigial nucleus (FN) were recorded after placement of DC or radio-frequency lesions or after microinjections of kainic acid into brain stem areas that receive FN projections and have been shown to be involved in central cardiovascular control. FN-induced increases in heart rate, blood pressure, and contractility were reduced or abolished by lesions made in the restiform body or the A5 area, which is homologous to the catecholamine-containing region in cats and rats. Lesions in the paramedian reticular nucleus, rostral and caudal to obex, failed to reduce the FN cardiovascular response. Nucleus of the solitary tract lesions augmented the FN pressor response and tachycardia. Kainic acid (1 microliter of 100 mM solution) caused profound depression of heart rate, blood pressure, and contractility and reduced or eliminated the FN-induced cardiovascular response when injected into the A5 area, previously identified by the pressor response following electrical stimulation. We concluded from these observations that a descending fastigiobulbar sympathoexcitatory pathway courses through a previously identified A5 pressor area that is also capable of a depressor response when the cell bodies alone are activated.

Fastigial nucleus projections to the brain stem in beagles: pathways for autonomic regulation

Efferent connections from a portion of the cerebellar fastigial nucleus were investigated using autoradiography. Bipolar stimulating electrodes were placed in the fastigial nucleus of anesthetized beagles and the area that produced increases in blood pressure and heart rate was localized. A mixture of [3H]leucine and [3H]proline (4:1) was injected into the area and autoradiograms of transported material were prepared. Injections filled the rostral and various parts of the caudal fastigial nucleus. Labeled axons reached the brain stem via two routes, the ipsilateral juxtarestiform body and the contralateral uncinate fasciculus. Ventral portions of the lateral vestibular nucleus were labeled bilaterally, projections to the inferior vestibular and medial vestibular nuclei are contralateral. Nucleus tractus solitarius was heavily labeled on the side opposite the injection. The contralateral medial reticular formation contained many labeled terminals and axons. Label was found in the nucleus reticularis ventralis, lateral reticular nucleus, nucleus gigantocellularis, nucleus pontis caudalis and the paramedian reticular nucleus. No terminal labeling was found in nucleus parvocellularis or nucleus ambiguous. Stimulation of the rostral fastigial nucleus produces increases in blood pressure and heart rate by generalized sympathoexcitation. Many cell groups which facilitate the activity of preganglionic sympathetic neurons do not receive direct fastigial input. It is suggested that that sympathoexcitation resulting from stimulation of the fastigial nucleus occurs through multisynaptic connections in the brain stem.

Effect of central catecholamine depletion on 3H-dexamethasone binding in the dog

Dogs were bilaterally adrenalectomized (Adx) or sham adrenalectomized 2 weeks after the administration of 6-hydroxydopamine (6-OHDA) or saline-ascorbic acid vehicle directly into the third ventricle (3V). Hypothalamic and hippocampal cytosols were assayed in vitro for high affinity binding of 3H-dexamethasone (3H-DM). 6-OHDA treatment resulted in a significant reduction of norepinephrine concentration in the hypothalamus, but not in the hippocampus, when measured 2 weeks after the second dose. Treatment with this neurotoxin also caused a decrease in 3H-DM binding in the hypothalamus that was detectable after adrenalectomy. A statistically significant reduction in bound DM was not observed in the hypothalamus after 6-OHDA treatment of dogs with intact adrenals, perhaps because of a masking effect of endogenous corticosteroids. No change was observed in the hippocampus. Saturation analysis of binding data revealed the total maximum number of available binding sites in hypothalamic cytosol was lower after 6-OHDA treatment, compared to saline-injected controls. Calculated values for dissociation constants revealed no differences between dogs treated with Adx, saline and Adx, and 6-OHDA. The data support the suggestion that catecholamines may act, in part, by altering the specific binding of a glucocorticoid to its hypothalamic receptor.

Depression of spontaneous and ionophore-induced transmitter release by ruthenium red at the neuromuscular junction

The effects on spontaneous and ionophore-induced transmitter release of the inorganic dye, ruthenium red (RuR), a known inhibitor of calcium binding sites, were observed at the frog sartorius neuromuscular junction using intracellular recording techniques. Both crude and purified RuR, at concentrations of 1 and 5 micron depressed or blocked spontaneous release of acetylcholine (ACh) and reduced postsynaptic sensitivity to ACh, the crude dye being more potent than the pure. Pretreatment of muscles with RuR prevented the catastrophic reaction of junctions to 100 micron X537A ionophore. Increased levels of Ca2+ restored spontaneous transmitter release to control levels after depression or blockade by RuR. It was concluded that RuR blocks a critical membrane-bound binding site for calcium which is necessary for quantal release of transmitter.

Depression of spontaneous and ionophore-induced neurotransmitter release by Salmonella

Exposure of frog neuromuscular junctions to heat-killed, lyophilized Salmonella typhimurium (SR 11) produces an early increase in spontaneous transmitter release followed by depression of release and blockade of the obligatory release usually induced by ionophore X537A.

Bacterial lipopolysaccharide depresses spontaneous, evoked, and ionophore-induced transmitter release at the neuromuscular junction

The neurotoxocity of RNA-free lipopolysaccharide (LPS) extracted from Salmonella Typhimurium (SR-11) was tested at the frog neuromuscular junction using intracellular recording techniques. Spontaneous miniature endplate potential (MEPP) frequency was reduced to 45% of control after 60 minutes in the presence of 10 and 50 micrograms LPS/ml Ringer's solution. Elevation of extracellular [Ca] to 10 mM converted the MEPP frequency response to a biphasic pattern of early acceleration followed by late depression. Evoked endplate potentials (EEPs) were reduced in quantal content until phasic release of transmitter was abolished, while MEPP amplitude and endplate resting potential remained constant. Effects of the potent cation ionophore X537A on MEPP frequency were blocked by 45 minutes of pre-exposure to LPS. Because of its extremely lipophilic character, LPS apparently alters the physical structure of the presynaptic terminal membrane, eventually reducing resting and phasic Ca influx, and isolating the presynaptic terminal from ionophore action.

Endotoxin alters spontaneous transmitter release at the frog neuromuscular junction

The direct neurotoxic effects of E. coli endotoxin (ETX) on spontaneous transmitter release were tested at the frog sartorius muscle neuromuscular junction. Spontaneous transmitter release was monitored by intracellularly recording miniature end-plate potentials (MEPPs). Junctions were continuously exposed to standard concentrations of 10 microgram/ml of 3 ETX samples, 2 of which produced a significant elevation of MEPP frequency followed by a decline of frequency to very low rates. The third ETX sample, known to have a decreased canine lethality, was without effect on MEPP frequency. No significant changes in MEPP amplitude were evident. The rate of change in MEPP frequency, but not the peak frequency, was reduced by lowering ETX concentrations. Alterations in MEPP frequency induced by ETX were prevented by removing Ca++ and antagonized by high [K+]out. The results suggest that ETX alters ion conductance channels, particularly those for Ca++, in the presynaptic terminal membrane.

Uptake and binding of [3H]hydrocortisone by various pig brain regions

The cytosol fraction of septum, hypothalamus, and hippocampus of intact and adrenalectomized pigs possessed greater concentrations of radioactivity than the cytosol fraction of amygdala, pituitary, and cortex after an intraventricular injection of [1,2-3H]hydrocortisone. Nuclear extracts from the same brain regions possessed higher concentrations of radioactivity than nuclear extracts of the other brain regions of intact pigs. Nuclear extracts of amygdala, pituitary and hypothalamus from adrenalectomized pigs exhibited the greatest increase over intact pigs in labeled hormone concentration. When adrenalectomized pigs were administered dexamethasone prior to [3H]hydrocortisone, uptake of label was most depressed in hippocampal cytosol and cuclear extract. Also sensitive to the competitive effects of dexamethasone were septal and pituitary nuclear extracts. In intact pigs, pituitary, hippocampus and cortex exhibited higher ratios of bound to total hormone in the cytososl fraction than the other brain regions. Hippocampal and amygdala cytosol possessed the greater magnitude of increase in the ratio of bound to total hormone in adrenalectomized versus intact pigs. The pituitary, septum, amygdala, and cortex of intact and adrenalectomized pigs possessed a ratio of bound to total hormone in nuclear extract 5-10 times greater than that in hippocampus and hypothalamus. However, the latter two regions exhibited a greater increase in bound: total hormone after administration of labeled hormone to adrenalectomized pigs than nuclear extracts of the other brain regions.

Metyrapone inhibition of 3H-hydrocortisone uptake and binding in various brain regions of the pig

Metyrapone (MET) inhibition of hydrocortisone (3H-HC) uptake binding in the cytosol and nucleus of various brain regions of the pig was demonstrated in vivo. The hippocampus, hypothalamus and septum were the regions most sensitive to the inhibition by MET. The hippocampus exhibited the greatest reduction in 3H-HC concentration in whole homogenate, bound in cytosol and in nuclei. The anterior pituitary and cerebral cortex were the least sensitive to MET. In vitro incubation of hypothalami with 3H-HC and MET substantiated the results obtained in vivo with regard to the inhibitory action of MET on 3H-HC uptake and binding. These results were interpreted to indicate the MET may act directly in certain brain regions and that this inhibitory aciton has important implications for both experimental and clinical uses of this drug.

Effects of hippocampal and amygdalar stimulation on uptake and binding of 3H-hydrocortisone in the hypothalamus of the cat

Stimulation of the hippocampus or amygdala of adrenalectomized cats occurred for 10 sec followed by a 50 sec period of no stimulation, beginning 30 min prior to and ending 30 min after administration of 100 muCi of 3H-hydrocortisone into a lateral ventricle. Sixty min after administration of labeled hormone, the hypothalamus was excised and homogenized. Cytosol and nuclear extract fractions were obtained and analyzed for radioactivity and protein content. Separation of bound from free hydrocortisone was achieved by charcoal and adsorption assay. Results reveal that stimulation of the hippocampus resulted in a greater concentration of 3H-hydrocortisone taken up into hypothalamic cells. Also, a greater percentage of total hormone found in the nuclear extract was assayed as bound 3H-hydrocortisone, and the concentration of bound radioactivity in the nuclear extract was increased over control values. Amygdalar stimulation, in general, yielded results similar to those obtained from control cats. However, although a lesser percentage of total hormone in the hypothalamic cytosol was assayed as bound hormone, there was a greater concentration of nuclear bound hormone than in controls, but less than that determined in the hippocampal stimulation group. These results add to the evidence that hippocampus and amygdala have a modulating influence upon the hypothalamo-hypophyseal axis. They also suggest that one manner in which these limbic structures may influence hypothalamic function is to modulate the uptake and binding of hydrocortisone in hypothalamic cells.