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Biomedical subjects

D F Cechetto

Publications and source records attributed to D F Cechetto.

At least 19 recordsLinked to original sources
PubMed2001

Connexin43 null mutation increases infarct size after stroke.

Glial-neuronal interactions have been implicated in both normal information processing and neuroprotection. One pathway of cellular interactions involves gap junctional intercellular communication (GJIC). In astrocytes, gap junctions are composed primarily of the channel protein connexin43 (Cx43) and provide a substrate for formation of a functional syncytium implicated in the spatial buffering capacity of astrocytes. To study the function of gap junctions in the brain, we used heterozygous Cx43 null mice, which exhibit reduced Cx43 expression. Western blot analysis showed a reduction in the level of Cx43 protein and GJIC in astrocytes cultured from heterozygote mice. The level of Cx43 is reduced in the adult heterozygote cerebrum to 40% of that present in the wild-type. To assess the effect of reduced Cx43 and GJIC on neuroprotection, we examined brain infarct volume in wild-type and heterozygote mice after focal ischemia. In our model of focal stroke, the middle cerebral artery was occluded at two points, above and below the rhinal fissure. Four days after surgery, mice were killed, the brains were sectioned and analyzed. Cx43 heterozygous null mice exhibited a significantly larger infarct volume compared with wild-type (14.4 +/- 1.4 mm(3) vs. 7.7 +/- 0.82 mm(3), P < 0.002). These results suggest that augmentation of GJIC in astrocytes may contribute to neuroprotection after ischemic injury.

Animals↗
PubMed2001

The effects of propofol in the area postrema of rats.

UNLABELLED: Propofol has an antiemetic effect that may be mediated by gamma-aminobutyric acid (GABA) influences on the serotonin system, the mechanism of which is not known. We used three techniques, immunohistochemistry, High Performance Liquid Chromatography, and electrophysiology, to define propofol's effects on the rat's brainstem. Paired male Wistar rats received propofol, 20 mg/kg/hr, or Intralipid for 6 h. The brains were then subjected to immunohistochemical analysis of serotonin. In a separate experiment after a propofol or Intralipid infusion, cerebrospinal fluid (CSF) was extracted from the fourth ventricle and analyzed for the amount of serotonin and 5-hydroxyindoleacetic acid. Electrophysiological neuronal recordings were made in the area postrema (AP) in response to propofol with and without a GABA or serotonin antagonist. Results showed that immunohistochemical staining for serotonin in the propofol rats was significantly increased (28 +/- 12%) in the dorsal raphe and decreased in the AP (17 +/- 6%) compared with control. There were no significant changes in the isoflurane-anesthetized animals. Both serotonin and 5-hydroxyindoleacetic acid in the CSF of the fourth ventricle at the level of the AP were significantly reduced by 63% and 36%, respectively. Both propofol and pentobarbital injections reduce AP neuronal activity, but only the propofol response was blocked by bicuculline, a GABA antagonist. We conclude that the reduced levels of serotonin in the AP and the CSF may explain the antiemetic property of propofol. Propofol may also directly act on AP neurons via a GABA(A) receptor to reduce their activity. IMPLICATIONS: Propofol may produce its antiemetic effect by depleting the area postrema of serotonin as well as by a direct gamma-aminobutyric acid-mediated inhibition.

Anesthetics, Intravenous↗
PubMed2001

Neurotransmitters in the thalamus relaying visceral input to the insular cortex in the rat.

Neurotransmitters relaying ascending visceral information were examined by comparing the response of neurons in the insular cortex to vagal stimulation (0.8 Hz, 2 mA) before and after neurotransmitter antagonist injections (200 nl) in the ventroposterior parvocellular nucleus of the thalamus (VPpc). Cobalt (10 mM; presynaptic blocker) and kynurenate (100 microM; nonspecific excitatory amino acid antagonist) injections in the VPpc resulted in an attenuation (73-100 and 38-98%, respectively) of the evoked cortical response. Injections of the specific N-methyl-D-aspartate (NMDA) antagonist DL-2-amino-5-phosphonopentanoic acid (200 microM and 2 mM) did not affect the vagally evoked response, whereas the nonspecific non-NMDA antagonist L-glutamic acid diethylester (200 microM) attenuated the vagally evoked response by 66-100%. Three concentrations of the DL-alpha-amino-3-hydroxy-5-methylisoxazole-propionic acid (AMPA)-specific antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (20 and 200 microM and 2 mM) attenuated the vagally evoked cortical response by 29 +/- 9, 31 +/- 10, and 59 +/- 8%, respectively. The more selective AMPA antagonist 6-nitro-7-sulphamoylbenzo(f)quinoxaline-2,3-dione (200 microM and 2 mM) inhibited the vagally evoked cortical response by 53 +/- 8 and 52 +/- 3%, respectively. Phentolamine (0.1 and 1.0 microM), a general alpha-adrenergic antagonist, and picrotoxin (0.1 and 1.0 microM), a GABA(A) antagonist, did not affect the vagally evoked response. Atropine, a muscarinic cholinergic antagonist, decreased the vagally evoked response by 40 +/- 2% at a concentration of 0.1 microM, but a higher concentration of 1.0 microM had no effect. These results indicate that the non-NMDA excitatory amino acid receptor is necessary for the relay of visceral information in the VPpc. Muscarinic receptors may modulate visceral neuronal excitability in the VPpc, although the exact interaction between the inhibitory (m2) and excitatory (m3 or m5) muscarinic receptor types found in the thalamus is not known.

2-Amino-5-phosphonovalerate↗
PubMed2000

Neuropeptide Y-Y1 receptor antisense oligodeoxynucleotide increases the infarct volume after middle cerebral artery occlusion in rats.

An antisense oligodeoxynucleotide selective for the rat neuropeptide Y1 receptor gene was given into the left lateral ventricle in the experimental group of rats, whereas a missense oligodeoxynucleotide or saline was given in the control groups. Some rats were decapitated at 1-2h after the last injection of the oligodeoxynucleotides to examine their effects on the Y1 receptor density in the insular cortex. When compared to the Y1 and Y2 binding density of the untreated rats, the antisense-treated rats had reduced Y1 binding in the insular cortex but the Y2 binding was unaffected; treatment with missense oligodeoxynucleotide had no effect. Other rats underwent a right-sided middle cerebral artery occlusion at 1-2h after the last injection of the oligodeoxynucleotides or saline to examine the effect on the infarction volume at three days following stroke. The antisense treatment resulted in a doubling of the mean infarction volume when compared to the missense or saline treatment.Thus, reducing the Y1 receptor density prior to middle cerebral artery occlusion is harmful. Neuropeptide Y may mediate neuroprotection against focal ischemia via the cortical Y1 receptor, since the immunoreactivity for neuropeptide Y has been shown to increase within the peri-infarct cortex after middle cerebral artery occlusion.

Animals↗
PubMed1999

Human forebrain activation by visceral stimuli.

Visceral function is essential for survival. Discreet regions of the human brain controlling visceral function have been postulated from animal studies (Cechetto and Saper [1987] J. Comp. Neurol. 262:27-45) and suspected from lethal cardiac arrythmias (Cechetto [1994] Integr. Physiol. Behv. Sci. 29:362-373). However, these visceral sites remain uncharted in the normal human brain. We used 4-Tesla functional magnetic resonance imaging (fMRI) to identify changes in activity in discrete regions of the human brain previously identified in animal studies to be involved in visceral control. Five male subjects underwent heart rate (HR) and/or blood pressure (BP) altering tests: maximal inspiration (MX), Valsalva's maneuver (VM), and isometric handgrip (HG). Increased neuronal activity was observed during MX, VM, and HG, localized in the insular cortex, in the posterior regions of the thalamus, and in the medial prefrontal cortex. To differentiate special visceral (taste) regions from general visceral (HR, BP) regions in these areas, response to gustatory stimulation was also examined; subjects were administered saline (SAL) and sucrose (SUC) solutions as gustatory stimuli. Gustatory stimulation increased activity in the ventral insular cortex at a more inferior level than the cardiopulmonary stimuli. The observed neural activation is the first demonstration of human brain activity in response to visceral stimulation as measured by fMRI.

Autonomic Nervous System↗
PubMed1999

Propofol prevents peroxide-induced inhibition of glutamate transport in cultured astrocytes.

BACKGROUND: Glutamate transporters located in the plasma membrane of cerebral astrocytes take up excitatory neurotransmitters from the synaptic cleft. In diseases characterized by oxidative stress, the extracellular glutamate concentration increases and contributes to neuronal death. The authors wanted to determine whether propofol defends brain cells against oxidant-induced changes in their transport of glutamate. METHODS: Primary cultures of rat cerebral astrocytes were exposed to tert-butyl hydroperoxide (1 mM) to serve as an in vitro model of oxidative stress. Astrocytes were incubated with propofol for 2 h and tert-butyl hydroperoxide was added for the final hour. Alternatively, astrocytes were incubated with tert-butyl hydroperoxide for 30 min and then with propofol for another 30 min. Control cells received drug vehicle rather than propofol. The rate of uptake of glutamate, the efflux of the nonmetabolizable analog D-aspartate, and the intracellular concentration of the endogenous antioxidant glutathione were measured. RESULTS: Tert-butyl hydroperoxide decreased the glutathione concentration and inhibited glutamate uptake but had a negligible effect on D-aspartate efflux. At clinically relevant concentrations, propofol did not affect the glutathione concentration but did prevent the effect of tert-butyl hydroperoxide on glutamate transport. Furthermore, the addition of propofol after tert-butyl hydroperoxide reversed the inhibition of glutamate uptake. CONCLUSIONS: Propofol prevents and reverses the inhibition of excitatory amino acid uptake in astrocytes exposed to tert-butyl hydroperoxide. The ability of propofol to defend against peroxide-induced inhibition of glutamate clearance may prevent the pathologic increase in extracellular glutamate at synapses, and thus delay or prevent the onset of excitotoxic neuronal death.

Anesthetics, Intravenous↗
PubMed1998

Rilmenidine elevates cytosolic free calcium concentration in suspended cerebral astrocytes.

Rilmenidine, a ligand for imidazoline and alpha2-adrenergic receptors, is neuroprotective following focal cerebral ischemia. We investigated the effects of rilmenidine on cytosolic free Ca2+ concentration ([Ca2+]i) in rat astrocytes. Rilmenidine caused concentration-dependent elevation of [Ca2+]i, consisting of a transient increase (1-100 microM rilmenidine) or a transient increase followed by sustained elevation above basal levels (1-10 mM rilmenidine). A similar elevation in [Ca2+]i was induced by the imidazoline ligand cirazoline. The transient response to rilmenidine was observed in Ca2+-free medium, indicating that rilmenidine evokes release of Ca2+ from intracellular stores. However, the sustained elevation of Ca2+ was completely dependent on extracellular Ca2+, consistent with rilmenidine activating Ca2+ influx. Pretreatment with thapsigargin, an inhibitor of the endoplasmic reticulum Ca2+-ATPase, abolished the response to rilmenidine, confirming the involvement of intracellular stores and suggesting that rilmenidine and thapsigargin activate a common Ca2+ influx pathway. The alpha2-adrenergic antagonist rauwolscine attenuated the increase in [Ca2+]i induced by clonidine (a selective alpha2 agonist), but not the response to rilmenidine. These results indicate that rilmenidine stimulates both Ca2+ release from intracellular stores and Ca2+ influx by a mechanism independent of alpha2-adrenergic receptors. In vivo, rilmenidine may enhance uptake of Ca2+ from the extracellular fluid by astrocytes, a process that may contribute to the neuroprotective effects of this agent.

Adenosine Triphosphate↗
PubMed1998

Receptors in lateral hypothalamic area involved in insular cortex sympathetic responses.

Previous evidence has shown that sympathetic nerve responses to insular cortical (IC) stimulation are mediated by synapses within the lateral hypothalamic area (LHA) and ventrolateral medulla. The present study determined the receptor(s) involved at the synapse in the LHA associated with stimulation-evoked IC sympathetic responses. Twenty-seven male Wistar rats were instrumented for renal nerve activity, arterial pressure, and heart rate recording. The right IC was stimulated with a bipolar electrode (200-1,000 microA, 2 ms, 0.8 Hz) resulting in sympathetic nerve responses. Antagonists were then pressure injected into the ipsilateral LHA (300-500 nl). Kynurenate (250 mM) injections resulted in 51 +/- 8% (range 0-100%) block of IC-stimulated sympathetic nerve responses. Similarly, the N-methyl-D-aspartic acid (NMDA)-receptor antagonist DL-2-amino-5-phosphonopentanoic acid (200 microM) resulted in an inhibition (82 +/- 8%; range 51-100%) of IC-stimulated sympathetic responses. Injection of the non-NMDA antagonist 6-cyano-7-nitroquinoxaline-2,3-dione (200 microM) had no effect on IC sympathetic responses. Injection of antagonists to GABA, acetylcholine, and adrenergic receptors was also without effect. No antagonist injections had any effects on baseline sympathetic nerve discharge, arterial pressure, or heart rate. These results suggest that the IC autonomic efferents projecting to the LHA utilize NMDA glutamatergic receptors.

2-Amino-5-phosphonovalerate↗
PubMed1998

Complementary antihypertensive action of rilmenidine on the pressure-natriuresis relationship and sodium preference in spontaneously hypertensive rats.

Previously, changes in position and slope of the pressure-natriuresis relationship have been used to characterize antihypertensive drugs in basic research. Rilmenidine may chronically reduce arterial pressure via central nervous system and renal imidazoline receptors. The present experiments were used to examine the shift in the pressure-natriuresis relationship during rilmenidine administration. We examined the effects of twice daily doses (1 and 3 mg/kg) for 6 days on the pressure-natriuresis relationship determined for control and treated spontaneously hypertensive rats (SHR) drinking tap water or 1% NaCl. The pressure-natriuresis relationship was shifted to the left for the 3 mg/kg dose and the slope was no different from the control. These experiments also indicated that rilmenidine might have an effect on sodium preference which was confirmed in a third series of experiments by permitting control and treated (3 mg/kg) SHR access to both tap water and 1% NaCl. This lack of change in slope indicates that, during rilmenidine treatment, the arterial pressure is relatively insensitive to sodium intake. The shift to the left indicates a restoration of the pressure-natriuresis relationship after chronic treatment with rilmenidine and a resetting of the long-term blood pressure control. Rilmenidine also reduces salt appetite in the SHR.

Animals↗
PubMed1997

Colchicine affects cortical and amygdalar neurochemical changes differentially after middle cerebral artery occlusion in rats.

Recently, we have shown increases in the immunoreactivity for neuropeptide Y and tyrosine hydroxylase in the insular cortex surrounding the focal infarction after middle cerebral artery occlusion. In addition, the immunoreactivity for neuropeptide Y, leucine-enkephalin, dynorphin, and neurotensin increased ipsilaterally in the amygdala. Increases in immunoreactivity were observed in nerve terminals and fibers; changes in the neuropeptides were maximal 3 days after stroke. Local excitotoxic injury of the insular cortex also elicited similar neuropeptide changes unilaterally in the same regions. In this study, immunohistochemistry was used following intracerebroventricular injection of colchicine and stroke to determine whether blockade of axonal transport would prevent these neurochemical changes. These experiments would also locate the putative cellular origins of the neurochemicals involved. Control rats received either colchicine injection or middle cerebral artery occlusion alone. Injection of colchicine enhanced the periinfarct increase in neuropeptide Y but did not alter the increase in tyrosine hydroxylase. The neuropeptide Y increase was observed in local cortical neurons. Colchicine prevented the increases in immunoreactivity for the neuropeptides in the amygdala on the side of stroke, although there were small perikarya that showed immunoreactivity for these neuropeptides within the amygdala on both sides. We conclude that local cortical neurons are responsible for the increase in neuropeptide Y in the periinfarct region, that the cortical increase in tyrosine hydroxylase is not dependent on fast axonal transport, and that axonal transport of signals from the insular cortex to the amygdala is critical in mediating the amygdalar neuropeptide changes seen after stroke.

Amygdala↗
PubMed1997

Effect of rilmenidine on arterial pressure and urinary output in the spontaneously hypertensive rat.

Rilmenidine is an antihypertensive agent acting at the imidazoline receptor that may have both central effects in the ventral lateral medulla and direct effects on the kidney to alter Na+ excretion. The present experiments examined whether rilmenidine induces a leftward shift or change in the slope of the pressure-natriuresis curve in the spontaneously hypertensive rat (SHR). A single oral gavage dose indicated that 3 and 10 mg/kg rilmenidine significantly lowers arterial pressure at 4-12 h after administration by oral gavage. The effect of rilmenidine on pressure-natriuresis was studied using twice daily doses of 1 and 3 mg/kg for control and treated SHR drinking tap water or 1% NaCl for 3 days. Na+ excretion was measured over 24 h, and mean arterial pressure was measured 6-8 h after the morning dose of rilmenidine. The results indicate that 1 mg/kg had no effect, while the pressure-natriuresis relationship for the rats receiving the 3 mg/kg dose was shifted to the left and was not significantly different from the vertical slope of the untreated SHR. This experiment also suggested that rilmenidine may attenuate the salt preference of the rats. This was confirmed in an additional series of experiments in which the rats had access to both tap water and 1% NaCl. Thus, rilmenidine shifts the pressure-natriuresis relationship to the left and reduces salt preference in SHR.

Administration, Oral↗
PubMed1997

Cardiovascular response to stress after middle cerebral artery occlusion in rats.

Previously, we have shown cardiovascular and autonomic disturbances in male Wistar rats following middle cerebral artery occlusion (MCAO). Using this model, neurochemical changes, that were maximal at 3-5 days and subsiding by day 10, were observed unilaterally in the insular cortex and amygdala. The amygdalar neurochemical changes may be related to the stroke-induced cardiovascular disturbances, since the amygdala is critical in mediating the cardiovascular responses to stress. We examined the cardiovascular responses to intermittent and continuous noise and air-jet stimulation in male Wistar rats on days 2-10 after right-sided MCAO or sham MCAO. Compared to the sham MCAO rats, intermittent noise elicited significant tachycardiac responses on days 5 and 7 after stroke. Air-jet stimulation also elicited a significant tachycardic response on day 5, whereas continuous noise produced significant tachycardiac and pressor responses at days 5 and 7, respectively, in the MCAO rats compared to the control rats. Analyses on the heart rate variability using fast Fourier transformation revealed significant increases in the normalized mid-frequency spectral power on day 7 for intermittent noise and air-jet stimulation, suggesting increases in the sympathetic activity. These results indicate a time-course of exaggerated cardiovascular responses to stress and suggest a state of susceptibility to cardiac perturbations in rats following stroke.

Amygdala↗
PubMed1997

Cerebral hemispheric lateralization in cardiac autonomic control.

OBJECTIVE: To identify cerebral hemispheric lateralization in cardiac autonomic control. PATIENTS: Eight patients undergoing an intracarotid amobarbital sodium test as a presurgical evaluation of temporal lobe epilepsy. DESIGN: Power spectral analysis of heart rate variability before and after intracarotid amobarbital injection. SETTING: University hospital and research center. MAIN OUTCOME MEASURE: The changes in the ratio of low-frequency (LF) (sympathetic) to high-frequency (HF) (parasympathetic) power (LF/HF ratio), a measure of sympathovagal balance, after hemispheric inactivation. RESULTS: The LF/HF ratio changed as follows: right preinactivation = 3.81 +/- 0.96, postinactivation = 3.40 +/- 1.23; left preinactivation = 2.74 +/- 0.49, postinactivation = 4.34 +/- 0.59 (mean +/- SEM). The test of interaction between laterality and inactivation using a 2-way repeated-measures analysis of variance was statistically significant (P = .001). The increased ratio on the left side (1.61 +/- 0.70) was statistically significant (P = .03), but the decrease on the right side (-0.40 +/- 0.46) was not (P < or = .70). CONCLUSIONS: These findings suggest that there is a cerebral lateralization in cardiac autonomic control and that the right cerebral hemisphere predominantly modulates sympathetic activity. This study may help identify subgroups of patients with intracranial disease at high risk of cardiac complications.

Adolescent↗
PubMed1997

Cardiovascular consequence of experimental stroke.

Clinically, it has been observed that stroke causes a number of cardiovascular disturbances that are detrimental to prognosis and may cause death. We have developed an experimental model of stroke, a middle cerebral artery occlusion in the rat, that can mimic the acute cardiovascular responses observed clinically. This model has clearly demonstrated that the insular cortex is necessary to produced the autonomic changes and that these changes are exacerbated by right-sided infarcts and increasing age. In addition, we have demonstrated that there are neurochemical changes associated with our stroke model that may mediate the cardiovascular complications. In particular, an increase in dynorphin in the central nucleus of the amygdala occurs with a peak at 3 to 5 days after the stroke and is directly due to damage in the insular cortex. Finally, we have shown that there is a similar time course in the exaggerated cardiovascular responses to stress following middle cerebral artery occlusion. Direct injection of dynorphin into the central nucleus of the amygdala can enhance the cardiovascular response obtained by stimulation of the acoustic stress pathway. These observations have direct relevance to clinical stroke.

Animals↗
PubMed1996

Peptide changes in the parabrachial nucleus following cervical vagal stimulation.

Previous studies in our laboratory have shown that the peptides, neurotensin (NT), cholecystokinin (CCK), substance P (SP), somatostatin (SOM), and calcitonin gene-related peptide (CGRP), have a role in modulating ascending visceral sensory information from the nucleus of the solitary tract to the thalamus via a mandatory synapse in the parabrachial nucleus (PB). In this investigation, we examined the changes in the levels of these peptides detected by immunohistochemistry in response to cervical vagal stimulation in the inactin-anesthetized male Wistar rat. Paired control and experimental animals were instrumented to monitor blood pressure and heart rate. The vagus nerve was stimulated for 0.5, 2, or 4 hours, after which time the animals were perfused and the brains processed immunohistochemically for the Fos protein and the peptides NT, CCK, SP, SOM, and CGRP. Vagal stimulation for 1 hour produced large numbers of Fos-positive cells in the external lateral (el), external medial (em), and central lateral (cl) subnuclei of the PB (N = 3). Vagal stimulation produced a reduction in the level of immunolabeling for NT, SOM, and CCK in the el and em subnuclei of the PB. This depletion was present at 0.5 hour and increased in magnitude with the length of vagal stimulation, reaching a maximum after 4 hours. In contrast, the immunolabeling for SP and CGRP increased after 0.5 hour, reaching a maximum after 2 hours of vagal stimulation in the el and em subnuclei of the PB. After 4 hours of vagal stimulation, the immunolabeling for SP and CGRP was depleted in the two PB subnuclei. Thus, the neuropeptides NT, CCK, SP, SOM, and CGRP, which modulate the visceral sensory information in the PB, are influenced somewhat differentially by the level of activity in the vagus nerve.

Afferent Pathways↗
PubMed1995

Neuropeptide changes following excitotoxic lesion of the insular cortex in rats.

Following middle cerebral artery occlusion in Wistar rats, the immunoreactivity of neuropeptide Y increased ipsilaterally in the insular cortex and basolateral nucleus of the amygdala. In addition, the immunoreactivity of leucine-enkephalin, dynorphin, and neurotensin increased in the ipsilateral central nucleus of the amygdala. The amygdalar neurochemical changes are likely the result of damage to the insular cortex, although other cortical areas were also affected by the ischemia. To investigate whether damage to the insular cortex is essential in eliciting these changes, a localized lesion of the right or left insular cortex was produced by microinjection of D,L-homocysteic acid. Control animals received injections of vehicle into the right or left insular cortex or D,L-homocysteic acid into the right primary somatosensory cortex. Neurochemical changes were examined immunohistochemically with the peroxidase-antiperoxidase reaction 5 days after the injection. The immunoreactivity of neuropeptide Y increased locally after excitotoxic damage to the insular cortex or primary somatosensory cortex. The amygdalar neurochemical changes, including neuropeptide Y increase in the basolateral nucleus and leucine-enkephalin, dynorphin, and neurotensin increase in the central nucleus, were seen only when the ipsilateral insular cortex was lesioned. These neurochemical changes were similar to those seen 5 days after middle cerebral artery occlusion. Our findings indicate that damage to the insular cortex is essential in eliciting the neurochemical changes in the ipsilateral amygdala. In addition, the change in neuropeptide Y in the cortex appears to be a local reaction occurring irrespective of location of the lesion and glutamate receptor activation may be involved.

Amygdala↗