Serotonergic innervation of the cerebral vasculature: relevance to migraine and ischaemia

Priorities for research on neuromodulatory subcortical systems in Alzheimer's disease: Position paper from the NSS PIA of ISTAART

The neuromodulatory subcortical system (NSS) nuclei are critical hubs for survival, hedonic tone, and homeostasis. Tau-associated NSS degeneration occurs early in Alzheimer's disease (AD) pathogenesis, long before the emergence of pathognomonic memory dysfunction and cortical lesions. Accumulating evidence supports the role of NSS dysfunction and degeneration in the behavioral and neuropsychiatric manifestations featured early in AD. Experimental studies even suggest that AD-associated NSS degeneration drives brain neuroinflammatory status and contributes to disease progression, including the exacerbation of cortical lesions. Given the important pathophysiologic and etiologic roles that involve the NSS in early AD stages, there is an urgent need to expand our understanding of the mechanisms underlying NSS vulnerability and more precisely detail the clinical progression of NSS changes in AD. Here, the NSS Professional Interest Area of the International Society to Advance Alzheimer's Research and Treatment highlights knowledge gaps about NSS within AD and provides recommendations for priorities specific to clinical research, biomarker development, modeling, and intervention. HIGHLIGHTS: Neuromodulatory nuclei degenerate in early Alzheimer's disease pathological stages. Alzheimer's pathophysiology is exacerbated by neuromodulatory nuclei degeneration. Neuromodulatory nuclei degeneration drives neuropsychiatric symptoms in dementia. Biomarkers of neuromodulatory integrity would be value-creating for dementia care. Neuromodulatory nuclei present strategic prospects for disease-modifying therapies.

Factors Determining Headache at Onset of Acute Ischemic Stroke

Headache is a frequent accompaniment of acute ischaemic stroke. The predisposing factors and underlying mechanisms are currently incompletely defined. We analysed prospectively collected data relevant to headache occurring at ischaemic stroke onset in consecutive patients included in the Henry Ford Hospital Stroke Data Bank. Patients with headache (HA+) and without headache (HA–) were compared for demographic factors, medical history, medications, examination findings, laboratory findings, and stroke localization and subtype. Group comparisons for categorical data were performed with χ2 test, and for continuous variables with two-sample t-tests. Stepwise logistic regression analysis, including all variables with P < 0.25, was used to define the independent predictors of onset headache. Three hundred and seventy-five patients had complete headache and clinical datasets and were included in the analysis (HA+, N = 118; HA–, N = 257). Multivariate analysis revealed that the independent predictors of HA+ were: infarct in the distribution of the posterior circulation [ P = 0.0076, odds ratio (OR) 2.15, 95% confidence interval (CI) 1.23, 3.77], absence of history of hypertension ( P = 0.0106, OR 0.48, 95% CI 0.27, 0.84), and treatment with warfarin at the time of the index stroke ( P = 0.0135, OR 4.89, 95% CI 1.39, 17.21). The occurrence of headache at onset of ischaemic stroke is determined by posterior circulation distribution of the ischaemic event, absence of history of hypertension and treatment with warfarin at the time of the index stroke. These results suggest that preserved elasticity and maintenance of the intracranial vasculature in a relaxed state, in combination with coagulation system derangements, and activation of dense perivascular afferent nerves, play a role in the pathogenesis of onset headache.

Mitochondrial monoamine oxidase-A-mediated hydrogen peroxide generation enhances 5-hydroxytryptamine-induced contraction of rat basilar artery

BACKGROUND AND PURPOSE

We evaluated the role(s) of monoamine oxidase (MAO)-mediated H₂O₂ generation on 5-hydroxytryptamine (5-HT)-induced tension development of isolated basilar artery of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto (WKY) rats.

EXPERIMENTAL APPROACH

Basilar artery (endothelium-denuded) was isolated for tension measurement and Western blots. Enzymically dissociated single myocytes from basilar arteries were used for patch-clamp electrophysiological and confocal microscopic studies.

KEY RESULTS

Under resting tension, 5-HT elicited a concentration-dependent tension development with a greater sensitivity (with unchanged maximum tension development) in SHR compared with WKY (EC(50) : 28.4 ± 4.1 nM vs. 98.2 ± 9.4 nM). The exaggerated component of 5-HT-induced tension development in SHR was eradicated by polyethylene glycol-catalase, clorgyline and citalopram whereas exogenously applied H₂O₂ enhanced the 5-HT-elicited tension development in WKY. A greater protein expression of MAO-A was detected in basilar arteries from SHR than in those from WKY. In single myocytes and the entire basilar artery, 5-HT generated (clorgyline-sensitive) a greater amount of H₂O₂ in SHR compared with WKY. Whole-cell iberiotoxin-sensitive Ca(2+) -activated K(+) (BK(Ca) ) amplitude measured in myocytes of SHR was approximately threefold greater than that in WKY (at +60 mV: 7.61 ± 0.89 pA·pF(-1) vs. 2.61 ± 0.66 pA·pF(-1) ). In SHR myocytes, 5-HT caused a greater inhibition (clorgyline-, polyethylene glycol-catalase- and reduced glutathione-sensitive) of BK(Ca) amplitude than in those from WKY.

CONCLUSIONS AND IMPLICATIONS

5-HT caused an increased generation of mitochondrial H₂O₂ via MAO-A-mediated 5-HT metabolism, which caused a greater inhibition of BK(Ca) gating in basilar artery myocytes, leading to exaggerated basilar artery tension development in SHR.

Risk of ischemic stroke associated with antidepressant drug use in elderly persons

Competing hypotheses have been formulated about a possible association between selective serotonin reuptake inhibitors (SSRIs) and ischemic stroke. However, the relationship between antidepressant drug use and ischemic stroke is still unclear. The aim of the study was to assess the association between the use of different types of antidepressants and the risk of ischemic stroke in elderly outpatients. A population-based, nested, case-control study was conducted in persons 65 years and older in the Integrated Primary Care Information database (1996-2005). Cases were all patients with a validated first ischemic stroke. Controls were matched on year of birth, sex, and index date. Exposure to antidepressants was divided in current, past, and nonuse and further categorized by type (SSRI, tricyclic, and other antidepressants), dose, and duration. Conditional logistic regression was used to compare the risk of ischemic stroke between users of antidepressants and nonusers. Overall, 996 incident ischemic strokes were identified. Current use of SSRIs was associated with a significantly increased risk as compared with nonuse (odds ratio, 1.55; 95% confidence interval, 1.07-2.25) in elderly patients, particularly when used for less than six months. No associations were observed for current use of tricyclic and other antidepressant drugs. To summarize, compared with nonuse, only SSRI use seems to be associated with an increased risk of ischemic stroke in elderly patients, particularly as a short-term effect.

Fluoxetine and sertraline attenuate postischemic brain injury in mice

This study aimed to investigate whether selective serotonin reuptake inhibitors (SSRIs) attenuate brain injury and facilitate recovery following photothrombotic cortical ischemia in mice. Male ICR mice were anesthetized and systemically administered Rose Bengal. Permanent focal ischemia was induced in the medial frontal and somatosensory cortices by irradiating the skull with cold light laser. The animals were treated with fluoxetine or sertraline once a day for 14 d starting 1 h after ischemic insult. Treatment with fluoxetine and sertraline significantly reduced the infarct size. The Evans blue extravasation indices of the fluoxetine- and sertraline-treated groups were significantly lower than that of the vehicle group. Treatment with fluoxetine and sertraline shifted the lower limit of the mean arterial blood pressure for cerebral blood flow autoregulation toward normal, and significantly increased the expression of heme oxygenase-1 (HO-1) and hypoxia-inducible factor-1alpha (HIF-1alpha) proteins in the ischemic region. These results suggest that SSRIs, such as fluoxetine and sertraline, facilitate recovery following photothrombotic cortical ischemia via enhancement of HO-1 and HIF-1alpha proteins expression, thereby providing a benefit in therapy of cerebral ischemia.

Cocaine-induced breakdown of the blood-brain barrier and neurotoxicity

Role of cocaine in influencing blood-brain barrier (BBB) function is still unknown. Available evidences suggest that cocaine administration results in acute hyperthermia and alterations in brain serotonin metabolism. Since hyperthermia is capable to induce the breakdown of the BBB either directly or through altered serotonin metabolism, a possibility exists that cocaine may induce neurotoxicity by causing BBB disruption. This hypothesis is discussed in this review largely based on our own laboratory investigations. Our observations in rats demonstrate that cocaine depending on the dose and routes of administration induces profound hyperthermia, increased plasma and brain serotonin levels leading to BBB breakdown and brain edema formation. Furthermore, cocaine was able to enhance cellular stress as seen by upregulation of heat shock protein (HSP 72 kD) expression and resulted in marked neuronal and glial cell damages at the time of the BBB dysfunction. Taken together, these observations are the first to suggest that cocaine-induced BBB disruption is instrumental in precipitating brain pathology. The possible mechanisms of cocaine-induced BBB breakdown and neurotoxicity are discussed.

From migraine to stroke

An association between migraine and ischemic stroke has been observed for many years but the exact mechanisms by which migraine can lead to stroke are currently still under investigation. Migraine seems to affect neurovascular factors and substances that increase the risk of stroke during and in between migraine attacks. Ischemic stroke can occur as a complication of an attack of migraine with aura. Epidemiological studies suggest that vascular risk factors are increased in migraineurs, thus increasing the incidence of stroke. Another important issue is a patent foramen ovale (PFO), which is a well-known risk factor for stroke and which, on the other hand, seems to be more frequent in migraineurs than in people without. The purpose of this review is to summarize the current literature linking the two neurological diseases: migraine and stroke.

Neuroprotection for ischemic stroke: past, present and future

Neuroprotection for ischemic stroke refers to strategies, applied singly or in combination, that antagonize the injurious biochemical and molecular events that eventuate in irreversible ischemic injury. There has been a recent explosion of interest in this field, with over 1000 experimental papers and over 400 clinical articles appearing within the past 6 years. These studies, in turn, are the outgrowth of three decades of investigative work to define the multiple mechanisms and mediators of ischemic brain injury, which constitute potential targets of neuroprotection. Rigorously conducted experimental studies in animal models of brain ischemia provide incontrovertible proof-of-principle that high-grade protection of the ischemic brain is an achievable goal. Nonetheless, many agents have been brought to clinical trial without a sufficiently compelling evidence-based pre-clinical foundation. At this writing, around 160 clinical trials of neuroprotection for ischemic stroke have been initiated. Of the approximately 120 completed trials, two-thirds were smaller early-phase safety-feasibility studies. The remaining one-third were typically larger (>200 subjects) phase II or III trials, but, disappointingly, only fewer than one-half of these administered neuroprotective therapy within the 4-6h therapeutic window within which efficacious neuroprotection is considered to be achievable. This fact alone helps to account for the abundance of "failed" trials. This review presents a close survey of the most extensively evaluated neuroprotective agents and classes and considers both the strengths and weakness of the pre-clinical evidence as well as the results and shortcomings of the clinical trials themselves. Among the agent-classes considered are calcium channel blockers; glutamate antagonists; GABA agonists; antioxidants/radical scavengers; phospholipid precursor; nitric oxide signal-transduction down-regulator; leukocyte inhibitors; hemodilution; and a miscellany of other agents. Among promising ongoing efforts, therapeutic hypothermia, high-dose human albumin therapy, and hyperacute magnesium therapy are considered in detail. The potential of combination therapies is highlighted. Issues of clinical-trial funding, the need for improved translational strategies and clinical-trial design, and "thinking outside the box" are emphasized.

Impact of increased plasma serotonin levels and carotid atherosclerosis on vascular dementia

Serotonin (5-HT), a potent vasoconstrictor in the large cerebral arteries, is considered to play a key role in atherothrombosis and to be implicated in ischemic cerebrovascular events followed by delayed neuronal death. The present study aims at evaluating the relationship between plasma levels of 5-HT and vascular dementia (VaD) caused by stroke or atherosclerotic small vessel disease. Carotid artery intima-media thickness (IMT), plaques, plasma 5-HT levels and atherosclerotic parameters were determined in 20 patients with VaD and 40 age-matched controls. Age, gender, body mass index, systolic and diastolic blood pressure, fasting plasma glucose levels and serum levels of insulin, triglycerides, high-density lipoprotein cholesterol, leptin, adiponectin and interleukin-6 and plasma levels of plasminogen activator inhibitor-1 were not significantly different between the two groups. Serum levels of insulin-like growth factor-1 (IGF-1) were significantly lower in VaD patients than in controls. Plasma 5-HT levels, serum levels of hepatocyte growth factor (HGF), low-density lipoprotein (LDL) cholesterol and high-sensitive C-reactive protein (hs-CRP), max IMT and plaque frequency were significantly greater in VaD patients than in controls. There was a significant positive correlation of max IMT with 5-HT or HGF levels. Multiple logistic regression analysis revealed that increased plasma levels of 5-HT and carotid plaque prevalence had significantly independent association with VaD as compared with serum levels of IGF-1, HGF, LDL cholesterol and hs-CRP. These results suggest that increased plasma levels of 5-HT and carotid atherosclerotic plaques may be involved in the pathogenesis and progression of VaD.

Effect of estrogen therapy on cerebral arteries during stroke in female rats

OBJECTIVE

To investigate the effect of estrogen therapy on the structural and functional properties of the middle cerebral artery during ischemia and reperfusion.

DESIGN

Ovariectomized (OVX; n = 8) and ovariectomized with estrogen therapy (OVX+EST; n = 8) female Sprague-Dawley rats were exposed to 1 hour of ischemia using a model of temporary focal ischemia of the middle cerebral artery with 24 hours of reperfusion and compared to sham controls (CTL; n = 8). After occlusion and reperfusion, right middle cerebral arteries were removed from the brain and mounted on glass cannulas in a chamber that allowed for control over transmural pressure and measurement of lumen diameter. Lumen diameter was measured in response to increased transmural pressure (myogenic tone) as well as response to nitro-L-arginine, serotonin, and nifedipine. Cerebrovascular reactivity was compared to other stroke outcome measures, including infarct volume (%) and neurologic deficit.

RESULTS

Serum estrogen was increased in OVX+EST rats (60.5 +/- 18.2 pg/mL) compared to OVX (0.2 +/- 0.2 pg/mL P < 0.05 vs OVX+EST) and CTL animals (1.3 +/- 1.0 pg/mL P > 0.05 vs OVX). OVX showed significantly less myogenic tone at 75 mm Hg (13.8 +/- 3.6%, P < 0.05 vs CTL) than CTL (29.8 +/- 4.7%) that was partially restored by estrogen therapy (21.2 +/- 4.5; P > 0.05). At serotonin concentrations of 10(-7) M, 3 x 10(-7) M, and 10(-6) M, the vessels from ischemic OVX rats showed significantly greater constriction (20.9 +/- 2.1%, 35.0 +/- 3.9%, and 39.4 +/- 3.4%, respectively) compared to nonischemic CTL rats (6.3 +/- 1.1%, 11.3 +/- 1.8%, and 16.8 +/- 2.5%, respectively P < 0.05). Estrogen therapy resulted in intermediate responses (18.2 +/- 5.3%, 25.2 +/- 6.6%, and 28.2 +/- 6.5%, respectively) that were not significantly different from the other groups. In addition, ischemia resulted in significantly greater dilation in response to 0.01 microM nifedipine in vessels from OVX animals (51.1 +/- 8.0%) compared to nonischemic CTL (18.0 +/- 3.8%; P < 0.05) and estrogen therapy resulted in an intermediate response (38.0 +/- 10.6; P > 0.05). Both reactivity to nitro-L-arginine and passive distensibility were not different among groups. There were no differences in percent infarct or neurologic deficit between ischemic groups.

CONCLUSIONS

The influence of ischemia and reperfusion on vessel function was more dominant than that of estrogen therapy. However, estrogen therapy seemed to partially restore vessel function to similar levels as nonischemic vessels.

Fetal cerebrovascular acclimatization responses to high-altitude, long-term hypoxia: a model for prenatal programming of adult disease?

During the past several decades, many risk factors for cerebrovascular and cardiovascular disease have been identified. More recently, it has been appreciated that inadequate nutrition and/or other intrauterine factors during fetal development may play an important role in the genesis of these conditions. An additional stress factor that may "program" the fetus for disease later in life is chronic hypoxia. In studies originally designed to examine the function of developing cerebral arterial function in response to long-term hypoxia (LTH), it has become clear that many cellular and subcellular changes may have important implications for later life. Here we review some of the significant alterations in fetal cerebral artery structure and function induced by high-altitude (3,820 m, 12,470 ft) LTH ( approximately 110 days). LTH is associated with augmentation or upregulation of presynaptic functions, including responses to perivascular (i.e., sympathetic) nerve stimulation, and structural maturational changes. In contrast, many postsynaptic functions related to the Ca(2+)-dependent contractile pathway tend to be downregulated, whereas elements of the Ca(2+)-independent contraction pathway are upregulated. The results emphasize the role of high-altitude LTH in modulating many aspects of electromechanical and pharmacomechanical coupling in the developing cerebral vasculature. A complicating factor is that the regulation of cerebrovascular tone by Ca(2+)-dependent and Ca(2+)-independent pathways changes significantly as a function of maturational age. In addition to highlighting independent regulation of various elements of the signal transduction cascade, the studies demonstrate the potential for LTH to program the fetus for cerebrovascular and other disease as an adult.

SSRI Treatment—Associated Stroke: Causality Assessment in Two Cases

OBJECTIVE:

To assess the probability of cerebrovascular adverse drug reactions (CV-ADRs) due to treatment with selective serotonin-reuptake inhibitors (SSRIs) using 2 causality methods.

CASE SUMMARIES:

Two patients with the possibility of SSRI-related stroke were referred for causality assessment. Causality assessment was performed using an adverse drug reaction probability scale, as well as clinical and radiologic parameters. A 31–year-old white man, who had been receiving paroxetine 200 mg/day over a period of 3 years, developed ischemic stroke involving left middle cerebral artery. The second patient was a 46–year-old white woman with a history of recurrent depression who developed delirium and ischemic stroke while she was taking a combination of paroxetine 50 mg/day, trazodone 200 mg/day, and bupropion 150 mg/day.

DISCUSSION:

Carotid and cardiothromboembolism were found to be the major etiological factors for ischemic stroke. Accounting for the temporal relation, prior reports of SSRI treatment—associated CV-ADRs, and the pharmacologic action of serotonin on coagulation and the vascular system, the possible contribution of SSRIs to stroke in these patients was considered. An objective causality assessment using the Naranjo probability scale revealed that a CV-ADR was possible. However, the nature of the stroke, plus clinical and radiologic findings, were inconsistent with known pathophysiologic mechanisms linking SSRIs and stroke in these patients.

CONCLUSIONS:

Causality assessment may improve unbiased recognition, management, and voluntary reporting of infrequent adverse effects such as SSRI treatment—related cerebrovascular accident.

Fetal cardiac and cerebrovascular acclimatization responses to high altitude, long-term hypoxia

In response to high altitude long-term hypoxemia, the heart of fetal sheep shows a decrease in cardiac output that is secondary to a decrease in myocardial cell contractile function. The intracellular mechanisms responsible for these reductions might include reduced myofibrillar Mg(2+)-activated ATPase. There is also a decrease in beta(1)-adrenergic receptor stimulated augmentation of myocardial contraction. An overproduction of cAMP by beta(1)-adrenergic receptor stimulation, resulting in overphosphorylation of troponin I, may reduce calcium binding by troponin C. Fetal coronary arteries have a reduced contractile response to K(+) depolarization and a reduced sensitivity to a thromboxane A(2) receptor agonist-stimulated contraction. Cerebral arteries of adult sheep (but not the fetus) show decreased responses to both K(+)-depolarization and norepinephrine-induced contraction. Nonetheless, cerebral arteries in the long-term hypoxic fetus demonstrated a number of significant changes from control. For the cerebral arteries in general, high altitude hypoxia is associated with augmented or upregulation of presynaptic functions. In contrast, postsynaptic functions tend to be significantly depressed or downregulated. The results emphasize the role of high altitude, long-term hypoxemia in modulating adrenergic- and serotonergic-mediated signal transduction in the cerebral vasculature. They specifically highlight the significant differences in acclimatization responses between the fetus and adult.

Diabetic ketoacidosis depletes plasma tryptophan

Diabetic ketoacidosis (DKA) is a severe metabolic disturbance of insulin-dependent diabetes mellitus (IDDM) which has a significant effect on amino acid metabolism. Amino acids serve as precursors for various neurotransmitters which are involved in affective disorders, and patients with IDDM are known to have an increased prevalence of affective disorders. We monitored the plasma concentrations of 23 amino acids in six adolescents prior to treatment of DKA and at 6, 24 and 120 hours after initiation of treatment. The well-known increase in the concentrations of the glucogenic amino acids and the decrease in the branched-chain amino acids were observed in response to treatment of DKA. Low levels of tryptophan were found prior to treatment of DKA. Treatment increased the plasma tryptophan levels, but the mean concentration remained low throughout the sampling period. Only the glutamate-derived amino acids (glutamate, proline and glutamine) from the Krebs cycle pool were significantly affected by treatment. Glutamine declined initially, but recovered as the plasma pH normalized. Our results indicate that DKA causes a depletion of plasma tryptophan. This depletion may predispose some patients with IDDM to have affective disorders secondary to a neurotransmitter imbalance.

Expression of the 5-HT1B receptor by subtypes of rat trigeminal ganglion cells

The type of trigeminal ganglion cells that express 5-HT1B receptors has not been well characterized, despite the fact that these receptors are important targets for anti-migraine drugs. We have therefore used combined in situ hybridization and immunofluorescence to examine the expression of 5-HT1B receptor messenger RNA in identified subpopulations of rat trigeminal ganglion cells. 5-HT1B-expressing cells accounted for 15% of all trigeminal ganglion cells, were medium sized, and showed immunoreactivity for either 200,000 mol. wt neurofilament, calcitonin gene-related peptide, or nerve growth factor receptor (trkA). In contrast few 5-HT1B cells showed immunoreactivity for substance P or binding of the lectin Griffonia simplicifolia IB4. Our results are consistent with 5-HT1B receptors acting to control the release of calcitonin gene-related peptide from trigeminal neurons with finely myelinated axons. 5-HT1B receptor agonists may reduce neurogenic vasodilation by activating such receptors. However many nociceptive trigeminal neurons, including the substance P and IB4-binding populations, do not express the 5-HT1B receptor.

Local treatments of dorsal raphe nucleus induce changes in serotonergic activity in rat major cerebral arteries

BACKGROUND AND PURPOSE

Rat major cerebral arteries seem to receive serotonergic fibers originating from the dorsal raphe nucleus (DRN), but little is known about their function. The aim of our present work was to establish a functional relationship between this brain stem nucleus and the cerebral blood vessels by studying the effects of several treatments in the DRN on cerebrovascular serotonergic activity.

METHODS

Serotonin, clomipramine, 8-OH-DPAT, and WAY-100635 were administered in DRN. A stereotaxically localized electrode allowed the electrical stimulation of this brain stem nucleus. Serotonergic activity was appraised in major cerebral arteries, striatum, and hippocampus from 5-hydroxytryptophan accumulation after aromatic L-amino acid decarboxylase inhibition with NSD-1015.

RESULTS

Serotonin significantly decreased serotonergic activity in major cerebral arteries and striatum without affecting it in hippocampus. This reduction was blocked by previous injection of WAY-100635 in DRN. Local administration of 8-OH-DPAT or clomipramine elicited an effect similar to that of serotonin, whereas that of WAY-100635 did not modify serotonergic activity in either of the tissues. Electrical stimulation of DRN significantly increased serotonergic activity in major cerebral arteries and striatum but not in hippocampus.

CONCLUSIONS

These results confirm the presence of a serotonergic innervation in rat major cerebral arteries functionally related to DRN. 5-HT(1A) receptor activation partly mediates the action of serotonin in DRN. A serotonergic tone acting on these somatodendritic receptors was not clearly found.

Effects of maturation, artery size, and chronic hypoxia on 5-HT receptor type in ovine cranial arteries

To test the hypothesis that variations in cerebrovascular reactivity to 5-HT among arteries of different size or type, during maturation, or during acclimatization to high altitude involve differences in serotonergic receptor subtype, we determined relative agonist potency orders and antagonist affinities in common carotid (Com), main branch middle cerebral (Main), and second branch middle cerebral (2BR) arteries from term fetal lambs and nonpregnant adult sheep acclimatized at sea level or at an altitude of 3,820 m for approximately 110 days. In normoxic adult Com segments, agonist potency order was 5-hydroxytryptamine (5-HT) > 5-carboxamidotryptamine (5-CT) >/= 8-hydroxy-2(di-n-propylamino)tetraline (8-OH-DPAT); sumatriptan (Suma) produced no contractile response; and antagonist dissociation constant (pKb) values were 9.4 and 9.5 for ketanserin against 5-HT and 5-CT, 7.5 for GR-127935 against 5-HT, and 7.2 for SB-206553 against 5-HT. In normoxic adult Main segments, agonist potency order was 5-HT > 5-CT >/= Suma >/= DPAT, and pKb values were 9.1 and 9.2 for ketanserin against 5-HT and 5-CT and 7.4 and 8.5 for GR-127935 against 5-HT and Suma, respectively. In the 2BR segments from normoxic adults, agonist potency order was 5-CT > 5-HT > Suma > DPAT and pKb values were 7.4 and 7.2 for ketanserin against 5-HT and 5-CT and 10.0 and 8.7 for GR-127935 against 5-HT and Suma, respectively. Compared with normoxic adults, none of these values were significantly different in hypoxic adults and in fetuses only the pKb values for ketanserin against 5-HT in the 2BR segments (8.8) were greater. From these results we propose that the ratio of 5-HT2 to 5-HT1 receptors is greatest in the Com and decreases progressively to its smallest values in 2BR or smaller segments. Because this gradient appears stable and relatively resistant to the effects of maturation and chronic hypoxia, changes in reactivity associated with these perturbations may involve alterations in receptor density and/or coupling efficiency for 5-HT in ovine cranial arteries.

Role of tyrosine kinase in serotonin-induced constriction of the basilar artery in vivo

BACKGROUND AND PURPOSE

Serotonin is one of the most potent constrictors of cerebral blood vessels and is implicated in several pathological conditions, including migraine and cerebral ischemia. Recent evidence has suggested that tyrosine kinase is involved in vasocontractile responses. The objective of this study was to test the hypothesis that activation of tyrosine kinase contributes to serotonin-induced constriction of the basilar artery in vivo.

METHODS

Using a cranial window in anesthetized Sprague-Dawley rats, we examined effects of inhibitors of tyrosine kinase and tyrosine phosphatase on constrictor responses of the basilar artery to serotonin in vivo.

RESULTS

Serotonin (10(-8), 10(-7), and 10(-6) mol/L) produced constriction of the basilar artery by 12+/-2%, 27+/-2%, and 37+/-3%, respectively. Genistein (3 x 10(-6) mol/L), an inhibitor of tyrosine kinase, did not affect baseline diameter of the basilar artery but attenuated serotonin-induced vasoconstriction (P<.05 versus control responses). Daidzein, an inactive analogue of genistein, did not affect serotonin-induced constriction of the basilar artery. Tyrphostin 47 (10(-5) mol/L), another inhibitor of tyrosine kinase, also attenuated serotonin-induced vasoconstriction, and tyrphostin 63, an inactive analogue of tyrphostin 47, did not affect the vasoconstriction. Sodium orthovanadate (10(-5) mol/L), an inhibitor of tyrosine phosphatase, enhanced serotonin-induced vasoconstriction. Phorbol 12,13-dibutyrate, a direct activator of protein kinase C, also caused constriction of the basilar artery, which was not affected by genistein or sodium orthovanadate.

CONCLUSIONS

These results suggest that serotonin-induced constriction of the basilar artery is mediated, at least in part, by activation of tyrosine kinase in vivo.

Characterization of 5-hydroxytryptamine receptors mediating contractions in basilar arteries from stroke-prone spontaneously hypertensive rats

1. The 5-hydroxytryptamine (5-HT) induced-contraction in ring preparations of basilar arteries from Wistar-Kyoto rats (WKY) and stroke-prone spontaneously hypertensive rats (SHRSP) was pharmacologically characterized in vitro. 2. Contractile responses to 5-HT (1 nM-100 nM) and their pD2 values in arteries from SHRSP at 6 months of age were significantly greater than those in age-matched WKY, although the maximum response did not differ between the two groups. 3. There were no significant differences in contractile responses to U-44619, endothelin-1, neuropeptide Y, and angiotensin II between WKY and SHRSP arteries. 4. Spiperone (1 nM-1 microM, a 5-HT2 receptor antagonist), produced biphasic displacement of the 5-HT curves in WKY and SHRSP arteries. The response to high concentrations of 5-HT was concentration-dependently antagonized by spiperone, while the response to low concentrations of 5-HT was resistant to blockade by spiperone, and the spiperone-resistant contractile responses induced by 5-HT were greater in SHRSP than in WKY. Ketanserin (1-100 nM, 5-HT2) also produced a biphasic shift of the 5-HT curves for both arteries. 5. Methiothepin (10 and 100 nM, 5-HT1 and 5-HT2) potently inhibited 5-HT-induced contractions in both groups. In addition, methiothepin (100 nM) produced a parallel shift to the right of the component of 5-HT-induced contractile responses that was resistant to blockade by spiperone in both groups. 6. The contractile effects of 5-HT in WKY and SHRSP arteries were not affected by MDL 72222 (1 microM, 5-HT3) and SDZ 205-557 (1 microM, 5-HT4). In addition, cocaine (10 microM), pargyline (50 microM), prazosin (10 microM), indomethacin (3 microM) and SQ 29,548 (1 microM) did not affect the contractile effects of 5-HT in either artery. 7. Contractile responses to 5-carboxamidotryptamine, CGS 12066B, pindolol and propranolol were greater in SHRSP arteries than in WKY arteries, whereas contractions in response to 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), alpha-methyl-5-HT and 2-methyl-5-HT did not differ between the two groups. Cisapride failed to contract basilar arteries in both groups. Furthermore, a correlation analysis showed a highly significant correlation between the pD2 values of 5-HT agonists in WKY and SHRSP arteries and their published binding affinities at the 5-HT1B subtype. 8. These findings suggest that 5-HT elicits vasoconstriction in rat basilar arteries by stimulation of a mixed receptor population of 5-HT2 and 5-HT1-like receptors (similar to the 5-HT1B receptor subtype), and that the contraction mediated by 5-HT1-like receptors is enhanced in the basilar artery from SHRSP.

Focal ischemia due to traumatic contusions documented by stable xenon-CT and ultrastructural studies

A traumatic cerebral contusion causes a zone of perifocal neuronal necrosis, the cause of which is not known; the surgical management of these lesions remains controversial. To determine the pathophysiological mechanisms responsible for brain damage after contusions, the authors performed cerebral blood flow (CBF) mapping studies and related these to change in local cerebral blood volume (CBV) and ultrastructure. In 11 severely head injured patients with contusion, CBF and CBV were measured in pericontusional areas using stable xenon-computerized tomography (CT). These studies demonstrated a profound reduction in perilesional CBF (mean 17.5 +/- 4 ml/100 g/min), which was always accompanied by a zone of edema defined by CT density measurements. Mean CBV in these regions was 2.3 +/- 0.4 ml/100 g, a reduction to approximately one-half the value of 4.8 ml/100 g found in the nonedematous regions, and to approximately 35% of the value of 6.0 ml/100 g found in normal volunteers. Ultrastructural analysis of the pericontusional tissue, taken at surgery in four patients with high intracranial pressure showed glial swelling with narrowing of the microvascular lumina due to massive podocytic process swelling. Additionally, some suggestion of vascular occlusion due to erythrocyte and leukocyte stasis was seen. These data support the conclusion that microvascular compromise by compression and/or occlusion is a major event associated with profound perilesional hypoperfusion, which is a uniform finding within edematous pericontusional tissue.

Cholinergic and vasoactive intestinal polypeptidergic innervation of the cerebral arteries

Acetylcholine and vasoactive intestinal polypeptide are not only two vasoactive agonists that predominantly induce a vasodilatation of the cerebral arteries, but also correspond to neurotransmitters that innervate the various anatomical segments of the cerebral vasculature. The distinct patterns of the cerebrovascular cholinergic and vasoactive intestinal polypeptidergic innervation, their neurochemistry, in vitro and in vivo pharmacology, as well as the putative pathophysiological implications of these neurotransmission systems are critically summarized on the basis of the most recently published literature.

Enhancement of serotonergic immunoreactivity in sympathetic cerebrovascular nerve fibers after experimental embolic stroke

We examined 5-hydroxytryptamine-like immunoreactive cerebrovascular nerve fibers in rats after experimental thromboembolic stroke. Although there were no visible 5-hydroxytryptamine-like immunoreactive nerve fibers in normal animals, we found many of these fibers near the clot emboli 30 min after the stroke, and the number of fibers increased slightly with time. In immunohistochemical double staining, these fibers corresponded to neuropeptide Y-like immunoreactive nerve fibers. And they were not observed in animals after superior cervical ganglionectomy. These findings suggest that the sympathetic nerves take up serotonin released from intraluminal aggregating platelets.

Serotonin (5-HT) fibers of the rat dura mater: 5-HT-positive, but not authentic serotoninergic, tryptophan hydroxylase-like fibers

Serotonin (5-HT)-positive, but not tryptophan-5-hydroxylase (TPOH)-positive, authentic serotoninergic fibers were shown in the rat dura mater. 5-HT immunoreactive fibers in the dura are postulated to result from 5-HT uptake from circulating blood elements (e.g. platelets, mast cells) by perivascular sympathetic nerve fibers. A robust TPOH-immunoreactive mast cell population was identified in the dura; this result confirms the TPOH antibody specificity to cells known to synthesize 5-HT. While these results indicate that there are no authentic serotoninergic fibers in the dura mater, the mast cells, platelets and cerebrospinal fluid can serve as a source of 5-HT activating 5-HT receptors known to be present in this tissue.

Effects of dorsal raphe nucleus stimulation on cerebral blood flow and flow-metabolism coupling in the conscious rat

In the present study, we have investigated the effects of an activation of the ascending serotonergic pathway on the cerebral blood supply to a number (63) of well-defined neuroanatomical structures. To this end, we have measured the local cerebral blood flow during electrical stimulation of the dorsal raphe nucleus. Measurement of regional blood flow was performed in the conscious rat through the use of the [14C]iodoantipyrine autoradiographic technique. Stimulation of the dorsal raphe nucleus induced increases (> 15% compared to control) in cerebral blood flow in 17 structures of which statistical significance (P < 0.05) was achieved in nine; raphe stimulation significantly decreased flow in three regions. The greatest increases (+71 and +46%) were found in the frontal sensorimotor and posterior parietal cortices. Other increases were noted in relay stations of the extrapyramidal and limbic systems. Stimulation induced a decrease in two regions of the primary auditory system and in the lateral habenular nucleus. These results show that activation of the serotonergic pathway in the conscious rat effects regional cerebral blood flow heterogeneously, differing from the widespread increase in glucose utilization that we previously observed using the same experimental paradigm. Statistical analyses indicated that activation of the dorsal raphe nucleus resulted in a global modification of the flow-metabolism ratio. Moreover, in 19 out of 31 regions analysed, this ratio is significantly altered as compared to control. The dichotomy between raphe-induced changes in flow and glucose-metabolism could be explained by one or both of two hypotheses; firstly there could be a direct serotonergic innervation of cerebral resistance vessels; secondly, during raphe stimulation it could be that glucose use is not the primary determinant of tissue perfusion.

Absence of serotonergic innervation from raphe nuclei in rat cerebral blood vessels--II. Lack of tryptophan hydroxylase activity in vitro

Neurochemical studies performed in vivo have suggested that serotonin-containing and -synthesizing nerves, originating in the raphe nuclei, directly innervate pial blood vessels. Nerve fibres of these vessels have been shown by immunocytochemistry to contain tryptophan hydroxylase (the rate-limiting enzyme of serotonin synthesis) but no serotonin. The present study examines this contradiction by measuring in vitro the tryptophan hydroxylase activity of rat cerebral vessels and femoral arteries (which also contain tryptophan hydroxylase-immunopositive nerves), and comparing them to the tryptophan hydroxylase activity of the rat pineal body, raphe nuclei and brain cortex under identical conditions. Oxygenated incubation solutions contained either [14C]- or "cold" L-tryptophan (2 x 10(-5) to 5 x 10(-4) M) and NSD-1015 (3-hydroxybenzylhydrazine) which inhibits the decarboxylation of 5-hydroxytryptophan, the second step of serotonin synthesis. Tissue fragments were incubated for 35-60 min. High-performance liquid chromatography (on tissue extracts and incubation solutions) as well as determination of 14C activity in the 5-hydroxytryptophan fraction of elution from tissue extracts showed that the pineal body, the raphe nuclei and cortical slices synthesize various amounts of 5-hydroxytryptophan under our experimental conditions. All these tissues contained serotonin. Femoral arteries, but not cerebral vessels, also contained small amounts of serotonin stored before incubation, probably in mast cells. In contrast to brain tissues, no measurable amounts of "cold" or [14C]5-hydroxytryptophan were found in cerebral blood vessel and femoral artery extracts or incubation solutions. Under identical experimental conditions, sympathetic nerves of both types of vessels were able to synthesize large amounts of L-DOPA when incubation solutions contained L-tyrosine instead of L-tryptophan.(ABSTRACT TRUNCATED AT 250 WORDS)

Immunohistochemical evidence for the absence of central neuron projection to pial blood vessels and dura mater

The present work shows that, in rat pial vessels and dura mater, all the nerve fibres observable by confocal fluorescence microscopy belong to the peripheral nervous system. It has been postulated that central nervous structures such as the raphe nuclei and the locus coeruleus could send direct projections to meningeal blood vessels. Mature neurons, whose perikaryons and axons are entirely located within the central nervous system, express the low molecular mass neurofilament protein and not the 57,000 mol. wt intermediate filament protein called "peripherin". This is the case for both raphe nuclei and locus coeruleus neurons [Leonard et al. (1988) J. Cell Biol. 106, 181-193]. Neurons which send axons outside the central nervous system or ganglionic neurons of the peripheral nervous system systematically express both proteins [Portier et al. (1984) Devl Neurosci. 6, 335-344]. Double labelling of pial vessels and meningeal tissue with antibodies directed against low molecular mass neurofilament and peripherin revealed nerve fibres immunoreactive to both antibodies and no nerve fibres reactive only to the low molecular mass neurofilament antibody. Conversely, cortical nerve fibres were immunoreactive only to the low molecular mass neurofilament antibody. It is thus concluded that the raphe nuclei and the locus coeruleus do not directly innervate meningeal tissues and, therefore, that these nuclei cannot directly intervene in cerebrovascular pathologies such as migraine headache or vasospasm. Secondarily, the present work also allowed for the first time the accurate observation of the spatial organization of the complete cerebrovascular innervation. Three main types of nerves can be defined on a morphological basis. A high proportion of these nerve fibres, either isolated or grouped in bundles, are varicose nerve fibres. Contacts between adjacent varicosities of the same type, which have been occasionally observed by electron microscopy, appear to be a very frequent feature.

Absence of serotonergic innervation from raphe nuclei in rat cerebral blood vessels--I. Histological evidence

Anterograde tracing from dorsal raphe neurons by Phaseolus vulgaris leucoagglutinin and serotonin immunocytochemistry revealed no serotonergic projections from raphe nuclei to cerebral pial vessels in the rat. However, cerebrovascular nerve fibres, mainly located in major pial arteries, were immunoreactive to tryptophan-5-hydroxylase antibodies as previously shown by others. It thus seems that the rate-limiting enzyme catalysing the biosynthesis of serotonin, tryptophan-5-hydroxylase, is present in cerebrovascular nerve fibres which do not originate in the dorsal raphe nucleus and which do not contain enough serotonin to be labelled by serotonin immunocytochemistry. We also observed tryptophan hydroxylase-immunoreactive but no serotonin-immunoreactive nerve fibres in the femoral artery and, occasionally, in the dura mater. The femoral artery, like the dura mater, contained numerous mast cells reacting positively to both tryptophan hydroxylase and to serotonin immunocytochemistry. The colocalization of the enzyme and its final product thus appears to be a general feature, since it has already been demonstrated within the central nervous system. The only exception appears to be the tryptophan hydroxylase-immunoreactive nerves present in cerebral and peripheral vessels. These results suggest that there is not a true serotonergic (i.e. serotonin-containing) innervation in cerebral blood vessels. They also strongly suggest that the cerebrovascular nerve fibres which appear to contain tryptophan hydroxylase do not originate in the raphe nuclei.

5-HT1C/5-HT2 receptor blockade prevents 1-(2,5-dimethoxy-4-iodophenyl)2-aminopropane-, but not stress-induced increases in brain tryptophan

We have previously shown that acute administration of the 5-HT1C/5-HT2 receptor agonist, 1-(2,5-dimethoxy-4-iodophenyl)2-aminopropane (DOI), elevates brain tryptophan levels. The present work aimed to investigate the mechanisms responsible for this elevation. Acute s.c. administration of a 2-mg/kg dose of DOI increased brain tryptophan levels but did not affect either plasma free tryptophan, plasma total tryptophan, brain 5-HT, or brain 5-hydroxyindoleacetic acid. Pretreatment with the 5-HT1C/5-HT2 receptor antagonist, LY 53857, prevented the DOI-induced increase in brain tryptophan levels, whilst the increase was reduced by the 5-HT2 receptor/alpha 1-adrenoceptor antagonist, ketanserin, and to a lesser extent, by the ganglionic blocker, chlorisondamine. On the other hand, pretreatment with either the peripherally acting 5-HT1C/5-HT2 receptor blocker, BW 501C67, the 5-HT uptake enhancer, tianeptine, the 5-HT uptake blocker, paroxetine, or the beta 2-adrenoceptor antagonist, ICI 118.551, proved ineffective. Lastly, pretreatment with LY 53857 did not affect the immobilization-induced elevation in brain tryptophan levels. It is concluded that the elevation in brain tryptophan levels induced by DOI but not that induced by stress is due to central 5-HT1C and 5-HT2 receptor stimulation.

Regulation of cerebral blood flow--a brief review

Cerebral blood flow is largely independent of perfusion pressure when autoregulation is intact. Cerebral circulation is regulated mainly by changes of vascular resistance. Resistance can be modulated by local-chemical and endothelial factors, by autacoids, and by release of transmitters from perivascular nerves. Local-chemical factors such as H(+)-, K(+)-, Ca(2+)-ions, adenosine, and osmolarity are involved in the regulation of cerebrovascular resistance during cortical activation and under pathological conditions such as hypoxia or ischaemia. Endothelial factors such as thromboxane A2, endothelin (ET), endothelium derived constrictor factor and endothelium derived relaxing (EDRF, identified as nitric oxide, NO) or hyperpolarizing (EDHF) factor, and prostacyclin (PGI2), can be released by physical stimuli such as shear stress or haemorrhage, by autacoids, by neurotransmitters, and by cytokines. Several of these factors (NO, PGI2, ET) can also be released from neurons and astrocytes thus enabling a coupling between parenchymal function and flow. Autacoids like histamine, bradykinin, eicosanoids, and free radicals influence cerebrovascular resistance, capacitance vessels and the permeability of the blood-brain barrier under pathological conditions. They are released by trauma, ischaemia, seizures and inflammation. Cerebral arteries are innervated by several systems. The sympathetic-noradrenergic fibres originate from the superior cervical ganglion. By releasing the constricting transmitters norepinephrine and neuropeptide Y this system extends the range of autoregulation. The parasympathetic cholinergic system with the dilating transmitters acetylcholine and vasoactive intestinal polypeptide may prevent ischaemia. Besides the intracerebral noradrenergic and serotonergic perivascular innervation with an unclear function, a trigeminal innervation has been described.(ABSTRACT TRUNCATED AT 250 WORDS)

Physiopharmacological interactions between stress hormones and central serotonergic systems

The present review tries to delineate some mechanisms through which the sympathetic nervous system (SNS) and the hypothalamo-pituitary-adrenal (HPA) interact with central serotonergic systems. The recent progress in 5-hydroxytryptamine (5-HT) receptor pharmacology has helped to define the means by which central serotonergic activity may alter the respective activities of the SNS (sympathetic nerves and adrenomedulla) and of the HPA axis. These pharmacological findings have also helped to characterize the differential effects of central 5-HT upon different branches of the SNS and the numerous sites at which 5-HT exerts stimulatory influences upon the HPA axis. Although relevant to stress-related neuroendocrinology, the extent to which these interactions are involved in the antidepressant/anxiolytic properties of some serotonergic agents still remains to be clarified. Beside these findings, there is also abundant evidence for a tight control of central serotonergic systems by stress hormones. Activation of the SNS increases, by numerous means, central availability of tryptophan, whereas glucocorticoids exert differential actions upon the intra- and the extraneuronal regulation of 5-HT function. Actually, a significant number of these mechanisms is involved in the maintenance of homeostasis during stressful events, thereby conferring to these mechanisms a key role in adaptation processes.