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The role of nitric oxide (NO) in the activation-flow coupling (AFC) response to periodic electrical forepaw stimulation was investigated using signal averaged laser Doppler (LD) flowmetry. LD measures of calculated cerebral blood flow (CBF) were obtained both prior and after intra-peritoneal administration of the non-selective nitric oxide synthase (NOS) inhibitor, N(G)-nitro-L-arginine (L-NNA) (40 mg/kg). Characteristic baseline low frequency vasomotion oscillations (0.17 Hz) were observed after L-NNA administration. These LD(CBF) oscillations were synchronous within but not between hemispheres. L-NNA reduced the magnitude of the AFC response (p<0.05) for longer stimuli (1 min) with longer inter-stimulus intervals (2 min). In contrast, the magnitude of the AFC response for short duration stimuli (4 s) with short inter-stimulus intervals (20 s) was augmented (p<0.05) after L-NNA. An interaction occurred between L-NNA induced vasomotion oscillations and the AFC response with the greatest increase occurring at the stimulus harmonic closest to the oscillatory frequency. Nitric oxide may therefore modulate the effects of other vasodilators involved in vasomotion oscillations and the AFC response.

The cochlea receives its main blood supply from the basilar artery via the anterior inferior cerebellar artery and the spiral modiolar artery. Morphologic studies have shown sympathetic innervation along the spiral modiolar artery of the gerbil and the guinea pig and functional studies in the isolated in vitro superfused spiral modiolar artery of the gerbil have demonstrated norepinephrine-induced vasoconstrictions via alpha(1A)-adrenergic receptors. It is current unclear whether the sympathetic innervation is physiologically relevant. Stimulation of sympathetic ganglia in guinea pigs has been shown to alter cochlear blood flow in situ. Whether these changes originated from local or more systemic changes in the vascular diameter remained uncertain. The goal of the present study was to demonstrate the presence or absence of neurogenic changes in the diameter of the isolated in vitro superfused spiral modiolar artery, anterior inferior cerebellar artery and basilar artery from the gerbil and the guinea pig. Vascular diameter was monitored by videomicroscopy. Electric field stimulation was used to elicit neurotransmitter release. A reversible inhibitory effect of 10(-6) M tetrodotoxin was taken as criterion to discriminate between neurogenic and myogenic changes in vascular diameter. Mesentery arteries of comparable diameter, which are known to respond with a neurogenic vasoconstriction to electric field stimulation, served as controls. Basilar artery, anterior inferior cerebellar artery, spiral modiolar artery and mesentery arteries constricted in response to electric field stimulation. No dilations were observed. Myogenic and neurogenic vasoconstrictions were observed in all vessels. These observations suggest that the sympathetic innervation of the basilar artery, the anterior inferior cerebellar artery and branch points of the spiral modiolar artery is involved in a physiologically relevant control of the vascular diameter in the gerbil and the guinea pig.

We determined whether spinal 5-hydroxytryptamine 2A (5-HT2A) receptors contribute to resting cutaneous sympathetic vasomotor activity, and to increases in activity elicited by electrical stimulation of the medullary raphe/parapyramidal region, and whether these receptors are involved in the cutaneous vasoconstricting action of systemically administered MDMA (3,4-methylenedioxymethamphetamine, "Ecstasy") and its reversal by clozapine. Experiments were conducted in urethane-anesthetized rabbits and rats. Administration of the 5-HT2A antagonist, trans-4-((3Z)3-[(2-Dimethylaminoethyl)oxyimino]-3-(2-fluorophenyl)propen-1-yl)-phenol, hemifumarate (SR 46349B, 0.1 mg/kg, i.v.) inhibited resting ear pinna sympathetic vasomotor nerve discharge and reduced the extent to which raphe/parapyramidal electrical stimulation caused ear pinna (rabbit) and tail (rat) artery blood flow to fall. Clozapine (0.125-0.5 mg/kg, i.v.) also reduced the fall in ear pinna blood flow elicited by raphe/parapyramidal stimulation. In rabbits, after inactivation of raphe/parapyramidal function by local microinjection of muscimol (1 nmol in 100 nl), the 5-HT2A agonist R(-)-1-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane hydrochloride (DOI, 50 microg/kg, i.v.) increased ear pinna sympathetic nerve activity from 3+/-2% to 129+/-5% of pre-muscimol levels (P<0.01, n=6), and this increase was abolished by section of the ipsilateral cervical sympathetic nerve trunk. MDMA (2 mg/kg, i.v.) after muscimol decreased ear pinna blood flow from 33+/-10 to 2+/-1 cm/s (P<0.01, n=5) and increased ear pinna sympathetic nerve activity from 8+/-4% to 120+/-41% of pre-muscimol levels (P<0.01, n=6). The MDMA-elicited increase in nerve activity was abolished by SR 46349B. Data suggest that spinal 5-HT2A receptors contribute to sympathetically induced cutaneous vasoconstriction regulated by raphe/parapyramidal neurons in the brainstem, and that these receptors contribute to the cutaneous vasoconstricting action of MDMA and its reversal by clozapine.

Nitric oxide (NO) is a potent vasodilating agent implicated in cochlear blood flow regulation. We recently demonstrated that exogenously applied NO donor DPTA-NONOate hyperpolarizes both endothelial and smooth muscle cells of in vitro spiral modiolar artery (SMA) via activation of ATP-sensitive K+ channels (K(ATP)). Also, NO was detected in the SMA cells by NO indicator dye in the in vitro basal condition. Using intracellular recording techniques, electrochemical NO-sensing measurement, and a vaso-diameter video tracking method, we investigated the basal release of NO from the in vitro SMA and its role in the vascular function. We found that (1) 300 microM L-NAME, a NO synthase inhibitor, and 3 microM glipizide caused a depolarization of approximately 4.5 and approximately 3.2 mV, respectively, in cells with a resting potential less negative than -60 mV; (2) NO sensor in the close vicinity of the SMA detected a NO concentration of approximately 50 nM that was suppressed by L-NAME and enhanced by L-arginine (1-1000 microM); (3) NO donor DPTA-NONOate (0.1-30 microM) applications produced about 8-245 nM of NO in the recording bath. These data indicate a NO concentration-hyperpolarization relation, with an EC50 of 22 nM. (4) Finally, L-NAME but not glipizide produced a 4.8% reduction in SMA diameter (approximately 50 microm) in the majority of SMAs, whereas NONOate (10 microM) always caused a dilation. Both the induced constriction and dilation were not significantly affected by 3 microM glipizide. We conclude that a significant amount of NO (> 50 nM) is tonically released from the in vitro SMA, which is above the EC50 for activation of K(ATP), and thus contributes to the membrane polarization. The basal release of NO also contributes to vasotone relaxation, but the K(ATP) activation appears to play little role in the relaxation of the in vitro SMA.

Experiments were performed to test the hypothesis that subarachnoid hemorrhage (SAH) causes functionally relevant perturbations of cyclooxygenase activity in cerebral arteries. Four groups of rabbits were formed: (I) controls; (II) sham injected animals (2 ml physiological solution in the cisterna magna); (III) SAH group (2 ml blood in cisterna magna); (IV) indomethacin group (4 mg/kg i.v. 30 min before sacrifice). Animals of groups II and III were used 3 days after injection. The basilar arteries (BAs) were removed and perfused at a constant flow rate (after electrocoagulation of all branches) in vitro in a 2-ml bath at 37 degrees C. After 45 min equilibration, the arteries were subjected to a fixed protocol: first, in Krebs solution, contraction to increasing extraluminal concentrations of histamine (HA), followed by a single maximal extraluminal concentration of acetylcholine (ACh); then, after 30 min rest, the same tests were repeated in oxyhemoglobin (oxyHb) solution (extraluminal, 10-4 M). Perfusion pressure changes reflected changes in artery resistance. Although oxyHb alone increased pressure, indicating contraction of the arteries, its most important effect was to increase contraction to HA (in groups II, III, and IV but not controls) and to strongly inhibit ACh-induced relaxation in the SAH (-66.3%) and indomethacin (-46.9%) groups (III and IV) but not the control (-27.6%) group. The latter result suggests that a relaxing factor released by ACh in oxyHb solution in the control group was not present in groups III and IV. In conjunction with the results on HA, which is known to normally release prostacyclin (PGI2) from the endothelium, it is concluded that PGI2 was not or little released from arteries of the SAH group when they bathed in oxyHb solution. Alternatively, in the SAH group constrictor prostaglandins were released in response to HA and ACh in place of PGI2., (Copyright 1998 Elsevier Science B.V.)

In anesthetized and ventilated rats, activation of carotid chemoreceptors with intracarotid administration of 100 nmol sodium cyanide rapidly excited the spinal cord-projecting vasomotor neurons in the rostroventrolateral reticular nucleus (RVL) of the medulla oblongata and sympathetic nerves and increased arterial pressure. The chemoreflex sympathoexcitatory pressor responses were attenuated by an acute systemic administration of ethanol at 0.45 g/kg, but not at 45 mg/kg. The ethanol effects were observed at the level of RVL-spinal vasomotor neurons, in attenuating the neuronal responses to the chemoreflex excitation and direct iontophoresis of N-methyl-D-aspartic acid (NMDA) but without altering responses of the carotid sinus nerves to intracarotid cyanide. The effect of ethanol on the RVL neurons was further defined as blocking NMDA-evoked inward current in the corresponding spontaneously active RVL neurons in vitro. The results indicate that acute ethanol intoxication markedly influences NMDA receptor activation and arterial chemoreflexes. The relevance of the type of action to clinical hypertension in chronic and heavy drinkers is discussed.

The characteristics of regenerated fibres in the chorda tympani have been investigated in cats after nerve section without repair or after section followed by nerve repair twelve weeks later. In the unrepaired group the animals were allowed to recover for twenty four weeks and after delayed repair there was a further recovery period of twelve or twenty four weeks. The properties of gustatory, thermosensitive and mechanosensitive units and the return of vasomotor and secretomotor responses were then investigated and data compared with that from normal controls and from animals which had undergone immediate nerve repair. After nerve section, integrated whole-nerve activity recorded from the chorda tympani during gustatory or thermal stimulation of the tongue was reduced when compared to controls, but there were only small differences between the repaired and unrepaired groups. Recordings made from single units in the chorda tympani revealed that more units were spontaneously active after repair (P < 0.05) and the gustatory units produced more impulses when stimulated (P < 0.005). Twelve weeks after delayed repair the units had slower conduction velocities than those in the unrepaired nerves (P < 0.001), but by twenty four weeks after repair they were significantly faster (P < 0.05). There was little difference in the level of recovery twelve weeks after immediate or delayed repair. We conclude that delayed nerve repair results in better recovery than leaving the nerve unrepaired and that a twelve week delay before repair has little effect.

Many inflammatory conditions show topographically precise symmetrical responses. In this study we assessed vascular and cellular responses of apparently normal knees following induction of monoarthritis on the opposite side. A strictly localised monoarthritis was induced in the right knee of experimental animals using intra-articular latex spheres. In both knee joints bradykinin-induced plasma extravasation was significantly enhanced increasing from 0.52 +/- 0.07 micrograms/ml Evans blue to 0.99 +/- 0.07 micrograms/ml and 0.88 +/- 0.1 micrograms/ml in the injected and uninjected, contralateral, knees respectively (P < 0.05). A bilateral increase in cellularity was also apparent with cell counts in the uninjected, and apparently normal, knee increasing from 512 +/- 42 cells/mm2 to a maximum of 812 +/- 125 cells/mm2 on day 10 (P < 0.05). Immunohistological analysis demonstrated that the infiltrating cells in both the ipsilateral and contralateral joints were predominantly macrophages. Cell counts were not increased in the other peripheral joints. Levels of the sensory neuropeptide substance P were significantly elevated in both the ipsilateral and contralateral dorsal root ganglia and prior inhibition of small unmyelinated nerve activity inhibited the cellular infiltrate on the contralateral side, suggesting that the effect was mediated, at least partially, by a specific neurogenic pathway. The data suggests the presence of a neurogenic mechanism able to induce a topographically precise response. This may serve to upregulate the cellular defences of at-risk tissues following a potentially damaging stimulus at another site.

The membrane properties of visually identified, DiI retrogradely labeled bulbospinal neurons of the C1 adrenergic cell group were studied by whole-cell recordings in brainstem slices from 7- to 10-day-old rats. A post-hoc histochemical analysis allowed us to evaluate the electrophysiological properties of the C1 adrenergic neurons, a group of cells known to project to the sympathetic preganglionic neurons. Two types of cells were labeled: pacemaker and non-pacemaker neurons. In voltage-clamp mode, C1 pacemaker neurons exhibited a TTX-sensitive, persistent inward current that was activated between -55 and -50 mV and reached a peak between -40 and -30 mV. This current was significantly larger in the pacemaker neurons as compared to the non-pacemaker neurons and appeared to be a principal conductance driving the C1 pacemaker activity. Two other conductances modulated the frequency of pacemaker discharge: (1) an anomalous rectifier accelerated pacemaker frequency by three synergistic actions: (a) depolarizing it at rest, (b) increasing the slope of the pacemaker potentials, and (c) limiting hyperpolarizing membrane excursions; and (2) an A-type current which had two opposing actions: (a) slowing it by decreasing the slope of the pacemaker potential, and (b) accelerating it by repolarizing the fast action potential. Persistent sodium current functions as the driver potential responsible for the tonic firing pattern of the C1 bulbospinal neurons providing a cellular mechanism responsible for the descending excitatory drive imposed onto sympathetic preganglionic neurons. Thus, it may explain how C1 neurons may function to maintain vasomotor tone or modulate other autonomic functions. This study is the first attempt to analyze voltage-activated membrane conductances of RVLM neurons of known phenotype and axonal connections.

Extracellular single unit recordings were made from barosensitive neurons in the subretrofacial nucleus (SRF) of the rostral ventrolateral medulla in chloralose-anaesthetised cats. At the same time, single preganglionic neuron activity was recorded from filaments of the cervical sympathetic trunk (CST); barosensitive units were selected for study. Evidence for monosynaptic connections between the two neuron groups was sought by cross-correlation analysis of their ongoing activity. Cross-correlograms of 16/16 SRF/CST neuron pairs showed a broad peak (100-200ms wide), reflecting the synchronizing action of arterial baroreceptors on both neurons' activity. Two of the 16 cross-correlograms additionally showed a robust, statistically significant, narrow peak of a single 2 ms bin width, providing the first physiological demonstration that ventrolateral medullary neurons monosynaptically excite preganglionic sympathetic neurons. Deductions are made about the strength, convergence and divergence of the connection.

Effects of a single cortical spreading depression (CSD), elicited by KCl microinjection, on diameter of pial arterioles and venules in the parieto-occipital cortex were examined in urethane-anesthetized adult rabbits using a closed cranial window. The velocity of CSD propagation was 2.7 +/- 0.1 mm/min (mean +/- S.E.M.). All arterioles (n = 39) except for those in the retrosplenial region (n = 6) increased their diameter significantly during CSD. The arteriolar dilation lasted for 1.5 +/- 0.1 min. Location of dilating arteriole and propagating CSD showed that they were always closely associated temporally. As a percentage change, diameters of smaller arterioles significantly increased (from 60 +/- 1 to 103 +/- 2 microns, 71%, n = 12) more than those of larger ones (from 82 +/- 2 to 129 +/- 3 microns, 57%, n = 27). While venules with initial diameter of 85 +/- 4 microns (n = 5) did not dilate, those with initial diameter of 49 +/- 3 microns increased to 57 +/- 3 microns (16%, n = 8) for 1.4 +/- 0.2 min during CSD. The majority of the dilated venules started to increase their diameter after nearby arterioles had dilated maximally. Pial arterioles, which dilated during ipsilateral CSD, decreased their diameter significantly from 78 +/- 2 to 72 +/- 3 microns (8%, n = 11) during contralateral CSD for 13.8 +/- 3.6 min with similar onset latencies as those observed for the dilation. Indomethacin pretreatment significantly enhanced arteriolar dilation during CSD (from 73 +/- 4 to 138 +/- 6 microns, 89%, n = 4).(ABSTRACT TRUNCATED AT 250 WORDS)

Temporal aspects of bilateral sympathetic nerve stimulation on cerebral blood flow (CBF) were examined in anesthetized rabbits (n = 7). CBF ranged from 32 to 50 ml/min per 100 g. Bilateral stimulation reduced blood flow by 17-31% to cerebrum, diencephalon-mesencephalon and cerebellum, and responses were constant between 2 and 6 min of stimulation. Sustained cerebral vasoconstriction is consistent with an important role for sympathetic nerves in the regulation of CBF.

Pharmacologic experiments were carried out to test the degree of interdependence of rostral vasopressor and caudal vasodepressor neuron pools in the ventrolateral medulla (VLPA and VLDA, respectively). In two groups of urethane-anesthetized rats, the gamma-aminobutyric acid (GABA) agonist muscimol (10 ng/site) was bilaterally microinjected into both the VLPA and VLDA to inhibit neuronal activity at these sites. In one group of experiments, muscimol was microinjected first into the VLPA and then into the VLDA. Following muscimol microinjection in the VLPA the mean arterial pressure (MAP) and heart rate (HR) decreased to 40 +/- 6 mm Hg and 310 +/- 21 beats/min (bpm) from a control level of 90 +/- 3 mm Hg and 403 +/- 23 bpm. Subsequent microinjection of muscimol in the VLDA had no significant effect on BP or HR. This lack of response was not due to severe fall in BP caused by microinjection of muscimol into the VLPA. In the second group of experiments muscimol was first injected into the VLDA followed by muscimol microinjection into the VLPA. In the VLDA muscimol significantly increased MAP and HR to 139 +/- 4 mm Hg and 427 +/- 4 bpm from a control level of 87 +/- 2 mm Hg and 356 +/- 23 bmp. The aortic depressor nerve response (-37 +/- 1 mm Hg and -47 +/- 4 bpm) was converted to an aortic 'pressor' response (+20 +/- 1 mm Hg and -13 +/- 6 bpm). Subsequent microinjection of muscimol into the VLPA caused MAP and HR to fall to 43 +/- 5 mm Hg and 338 +/- 17 bpm. The aortic 'pressor' response was also abolished (2 +/- 2 mm Hg). These results indicate that neuronal activity in the rostral VLPA is an important determinant for changes in BP and its reflex regulation mediated by the VLDA. However, BP changes mediated by the rostral VLPA are independent of the level of neuronal activity in the VLDA. Sites of VLPA and VLDA interaction are discussed.

The thickness and area of rat sciatic endoneurial microvessel components (endothelial cells, basement membranes and wall) were assessed to test whether collapse or vasoconstriction was typical of immersion (I) as compared to perfusion (P) or in situ (S) fixation and to determine whether area, but not thickness, would be unaffected by collapse or vasoconstriction. In S and in P fixation there was no apparent collapse or vasoconstriction; in fact, none of the measurements were significantly different between themselves except for index of circularity (IC), which was a little lower in S than in P fixation. By contrast to S or P, in I fixation, the lumen was much smaller and more irregular and the wall was thicker. Area of wall (and of its components) was not significantly different among I, P or S fixation, but thickness was significantly greater in I than in P or S fixation. For comparison to such properties of vessels as permeability, thickness may be the appropriate measurement, but for other purposes, such as determining the amount of basement membrane in diabetes mellitus, area may be a better measurement as it is less affected by collapse or vasoconstriction.

Microinjections of D,L-homocysteic acid into the ventrolateral medulla, in the region of nucleus paragigantocellularis lateralis (PGL) which lies caudal to the facial nucleus and adjacent to the rostral third of the inferior olive, evoke a rise in arterial blood pressure and vasoconstriction in hindlimb muscle. Activation of a group of neurones located in a more rostral strip of tissue ventral to the facial nucleus produces vasodilatation in the hindlimb but no significant change in blood pressure. It appears that the ventrolateral medulla contains several subpopulations of neurones which can alter resistance to blood flow and hence distribution of flow and level of blood pressure by selective control of individual vascular beds.

An inexpensive method is described which permits simultaneous quantification of the cerebrovascular extraction (E) of diffusion-limited compounds and cerebral blood flow (CBF) in rats. This method involves the use of two radioisotopic tracers: (a) a diffusion-limited, test tracer such as [3H]water; and (b) a reference tracer. The reference tracer is also used in the measurement of CBF. In the development and validation of this technique, results using two different types of reference tracers were compared. The reference tracers employed were: (a) [14C]butanol, a flow-limited (i.e. freely diffusible) compound; and (b) [141Ce]microspheres which embolize in the cerebromicrocirculation. Inclusion of [3H]water in the injection bolus permitted simultaneous measurement of Ew using both butanol and microspheres as the reference as well as concomitant measurement of CBF. Both tracers provided estimates of these values which behaved physiologically with respect to increasing arterial CO2 content (paCO2). In addition, the simultaneous measurement of Ew and CBF permitted calculation of the effective permeability of water across the blood-brain barrier (PwS) which was discovered to increased with increasing paCO2.

Electrical stimulation of hypothalamic and midbrain defence area sites eliciting a cholinergic vasodilatation in the hindlimb activates vasodilator fibres supplying skeletal muscle. Simultaneous baroreceptor mediated suppression of sympathetic vasoconstrictor activity to the muscle and postfiring depression of vasoconstrictor activity contribute to the development of the vasodilatation during and after the stimulus. The observation of a differential pattern of activation of muscle and renal vasoconstrictor fibres implies a reciprocal influence exerted on these sympathetic outflows by neurones in the defence areas of the brain.

Substantial concentrations of serotonin (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA), comparable to those found in brain tissue, were measured in the small pial vessels of the rat, rabbit and cat. Both rat and rabbit pial vessels exhibited a high affinity uptake process with kinetic parameters similar to those identified for the cerebral cortex. Labelled 5-HT, taken up by isolated rabbit pial vessels was released, in a calcium-dependent manner, by potassium-induced depolarization. Various pharmacological manipulations were carried out in the rat. Systemic administration of the 5-HT precursor, 5-hydroxytryptophan and the monoamine oxidase inhibitor, pargyline, significantly increased the concentration of 5-HT in the pial vessels; in contrast, two depleting agents (p-chloroamphetamine and reserpine) and the tryptophan hydroxylase inhibitor, p-chlorophenylalanine, all decreased the perivascular 5-HT levels. A serotonergic antagonist (methysergide) and a 5-HT receptor agonist (MK 212) respectively increased and decreased the concentrations of 5-HIAA in the pial vessels. These pharmacologically induced changes observed in pial vessels were not dissimilar from those noted for cortical tissue. Electrolytic lesions of the nuclei raphes medianus and/or dorsalis markedly decreased the levels of 5-HT and 5-HIAA in these small cerebral arterioles. Electrical stimulation of these nuclei decreased 5-HT although 5-HIAA concentrations tended to increase. A number of conclusions may be drawn from these studies. Thus, there is a serotonergic innervation of the cerebral circulation in several laboratory species which unequivocally originates in the raphé nuclei. Furthermore, these perivascular fibres possess synthetic, storage, release, inactivation and autoregulatory processes for 5-HT which, when further elucidated, may offer some rationale for the treatment of those cerebrovascular diseases in which this neurotransmitter and vasoactive agent is believed to be of pathological importance.

Experiments were performed to test the hypothesis that A1 noradrenergic neurons, in the caudal ventrolateral medulla, have an inhibitory cardiovascular function. The lateral portion of the caudal medulla was systematically explored, using focal electrical stimulation, in anesthetized, paralyzed rabbits and arterial pressure and heart rate responses were recorded. Since electrical stimulation activates fibers of passage as well as neuronal cell bodies, we also determined cardiovascular responses to microinjections of L-glutamate, a neuroexcitatory amino acid with minimum effects on fibers of passage. Histological studies of stimulation sites were combined with catecholamine fluorescence histochemical studies to localize the A1 cells. A decrease in arterial pressure and heart rate, restricted to the region containing A1 cells, was observed with low frequency stimulation and with microinjections of L-glutamate. In contrast, when GABA, an inhibitory amino acid, was microinjected into the A1 region, we observed an increase in arterial pressure and heart rate. L-Glutamate and GABA responses were dose-related. The fall in pressure was independent of the fall in heart rate. Results support our hypothesis, providing evidence that neurons in the A1 area tonically inhibit sympathetic vasomotor tone.

In anaesthetized cats, stimulation of the lumbar sympathetic trunk inconsistently elicited small increases in the contraction of fatigued Peroneus Longus muscles (Orbeli phenomenon). Facilitation of this anti-fatigue effect was regularly observed following close intra-arterial injection of isoprenaline, a beta-adrenergic agonist. Injection of the drug by itself exerted a marked anti-fatigue effect on muscle contraction.

The purpose of the present study was to identify which catecholamine-containing neurons (norepinephrine (NE) or dopamine (DA)) and which central nervous system (CNS) region(s) innervated by them might participate in the pressor and drinking responses produced by central drug stimulation. Forebrain NE was reduced in rats by injecting 4 micrograms of 6-hydroxydopamine (6-OHDA) into the ascending noradrenergic bundles. Spinal cord NE was depleted by intracisternal injection of 50 micrograms 6-OHDA. Depletion of forebrain DA was produced by bilateral injection of 4 micrograms 6-OHDA into the substantia nigra of desipramine-pretreated rats. Pressor responses to various doses of angiotensin II (AII), carbachol or hyperosmolar NaCl injected into the lateral ventricles (LVT); and drinking responses to LVT AII and carbachol were examined. Injection of 6-OHDA into the noradrenergic bundles reduced telencephalic and hypothalamic NE by more than 80% without significantly affecting brain DA or spinal cord NE. Intracisternal 6-OHDA depleted spinal cord NE by 80% and forebrain NE by 20-25% without reducing brain DA. Injection of 6-OHDA into the substantia nigra reduced telencephalic DA by 86% and NE by 29% without significantly affecting NE in other CNS regions. Substantia nigra 6-OHDA injected animals evidenced attenuated drinking to both LVT AII and carbachol. Pressor responses to LVT AII, carbachol and hypertonic saline were largely unaffected. Almost complete depletion of brain and/or spinal cord NE failed to alter centrally mediated drinking or pressor responses. These data indicate that the integrity of brain DA neurons is required for the behavioral but not hypertensive responses produced by central drug stimulation.

Stimulation of the locus coeruleus in 11 Macaca nemestrina monkeys resulted in a frequency-dependent increase in internal carotid resistance (vasoconstriction) and a frequency-dependent decrease in external carotid resistance (vasodilation). The internal carotid constrictor response is maximal at low frequency stimulation (5 s-1), and decreases as frequency of stimulation is increased or decreased. It is blocked by the non-specific alpha-adrenoceptor blocker phentolamine and the alpha-2 adrenoceptor blocker yohimbine, but is unaffected by the alpha-1 adrenoceptor blocker prazosin. It is concluded that the cerebral vasoconstrictor response to locus coeruleus stimulation is mediated by alpha-2 adrenoceptors.

Single-unit recording experiments were done in chloralose-anesthetized, paralyzed and artificially ventilated cats to identify neurons in ventrolateral medulla (VLM) that send efferent axons directly to the region of the nucleus of the solitary tract (NTS) and receive cardiovascular afferent inputs from the carotid sinus (CSN) and aortic depressor (ADN) nerves and the NTS. Units in VLM were identified by antidromic excitation to stimulation of functionally and histologically verified sites in the NTS complex. Antidromic potentials were recorded from 34 units in VLM. Units responded with a mean antidromic latency of 4.37 +/- 0.32 ms corresponding to a mean conduction velocity of 0.93 +/- 0.07 m/s. Of these 34 units, 18 were excited orthodromically by stimulation of the CSN and/or ADN. Furthermore, 10 of the 18 units responding to stimulation of the buffer nerves were also orthodromically excited by stimulation of NTS. An additional 76 units were identified in VLM that only responded orthodromically to stimulation of NTS with a mean latency of 9.75 +/- 2.93 ms, of which 33 also responded orthodromically to stimulation of the buffer nerves. These data provide electrophysiological evidence of a bidirectional connection between neurons in VLM that receive and integrate peripheral cardiovascular afferent inputs and send efferent axons directly back to the region of NTS. These results suggest that neurons in the VLM may be part of a medullary feedback reflex loop through which afferent information from cardiovascular receptors exerts an influence on NTS neurons involved in the control of the circulation.

Spinally-projecting A5 noradrenergic neurons were recorded in urethane-anesthetized rats. All A5 neurons sampled were inhibited by raising the mean arterial blood pressure (mBP) in the 110-160 mm Hg range. Similar elevations of mBP in baroreceptor-denervated rats were without effect. Clonidine inhibited A5 neurons and enhanced the inhibitory effect of increasing peripheral blood pressure.

Experiments were done in chloralose anesthetized, paralyzed and artificially ventilated cats to identify single units in ventrolateral medulla (VLM) projecting directly to the intermediate gray (IG) region of the upper thoracic cord and responding to inputs from pressor sites in the anterior lateral hypothalamus (Hla) and carotid sinus (CSN) and aortic depressor (ADN) nerves. Forty-eight units were antidromically activated in VLM to stimulation of the IG at the level of T2. Of these 48 units, 15 (31%) were orthodromically excited by stimulation of the Hla with a mean latency of 15.8 +/- 2.1 ms. In addition, 8 of the 15 units responding to Hla stimulation were also excited orthodromically by stimulation of either the CSN or ADN or both. Of the remaining 33 units, 15 responded to stimulation of only the buffer nerves and 18 were unresponsive to the tested inputs. These results provide electrophysiological evidence for the existence of neurons in VLM which receive hypothalamic and buffer nerve inputs and suggest that the VLM plays a role in integrating and relaying cardiovascular afferent information from peripheral baroreceptors and chemoreceptors and from supramedullary centers to provide effector signals to spinal autonomic neurons involved in the control of the circulation.

Substance P (SP) has been determined by radioimmunoassay in the sciatic nerve and its fibular, tibial and sural branches; and in a red, slow-twitch and a white, fast-twitch muscle supplied by the sciatic nerve. The mixed sciatic nerve contained 25 ng SP per g tissue wet wt., while the sural branch, which is supplying mainly skin, and thus is rich in sensory fibres, had a significantly higher content (49 ng/g). The mixed fibular and tibial branches contained approximately the same amount as the sciatic nerve proper. SP was also found in the skeletal muscles. The red m. soleus had a significantly higher content (0.61 ng/g) than the white m. extensor digitorum longus (0.22 ng/g). A dorsal root lesion which leads to degeneration of sensory fibres, reduced the SP level more than 90% both in nerves and muscles. Ventral root section, which leads to degeneration of somato-motor fibres and terminals, had, on the other hand, no effect. We conclude that sensory neurons are the only source of importance for SP in the sciatic nerve and in skeletal muscles. Based on the above findings, the possibility that SP may function as a mediator of an axon reflex in skeletal muscle is discussed.

The effects of hyperbaric oxygenation with 2 atm. pressure and 100 percent oxygen on cerebrovascular tone were assessed by the reactivity of the cerebral vessels to CO2 and vasomotor capacitance index (the cranial pressure divided by the mean arterial pressure) in 50 anaesthetized artifically ventilated dogs, in which intracranial pressure was raised by slow inflation of an extradural balloon. Hyperbaric oxygenation reduced the intracranial pressure only at the stage when the cerebral vessels were still responsive to CO2, as indicated by a rise in intracranial pressure of 30-70 mmHg; under these circumstances, both the reactivity of CO2 and the vasoconstrictor tone of cerebral vessels were improved by hyperbaric oxygenation. At this stage, rapid decrease of the intracranial pressure produced by deflation of the extradual balloon showed no rebound, and hyperbaric oxygenation rapidly restored the vasomotor tone. When CO2 failed to influence the intracranial pressure of about 100 mmHg hyperbaric oxygenation did not aid the recovery of the reactivity of the cerebral vessels to CO2 or the vasoconstrictor tone. In extreme intracranial hypertension (above 100 mmHg) when there was reactivity to CO2 and the electroencephalogram was flat, rapid balloon deflation was followed by a further gradual increase of intracranial pressure and hyperbaric oxygenation did not restore the cerebrovascular tone. The effect of hyperbaric oxygenation in experimental intracranial hypertension appeared to be dependent upon the vasoconstrictor tone of the cerebral vessels, which would be indicated by a vasodilator response to CO2.

Electrical stimulation of the subfornical organ (SFO) in urethane anesthetized male Sprague-Dawley rats was associated with intensity and frequency dependent increases in arterial blood pressure. Stimulation in the hypothalamic paraventricular nucleus (PVN) also evoked increases in arterial blood pressure. Electrolytic lesions of the PVN significantly reduced SFO induced pressor responses, suggesting that the PVN constitutes part of the efferent pathways through which SFO stimulation elicits increases in blood pressure.

Application of gamma-aminobutyric acid (GABA) antagonist drugs (bicuculline, picrotoxinin) to the intermediate region of the ventral surface of the medulla oblongata of gallamine paralyzed, alpha-chloralose anesthetized cats produced a dose-dependent blockade of the baroreceptor reflex. GABA antagonists applied to the rostral and caudal areas did not block the baroreceptor reflex. When strychnine was applied to the ventral medulla, it did not block the baroreceptor reflex. The diffusion of [3H]bicuculline was studied by scintillation counting and autoradiography and found not to penetrate more than 2 mm from the ventral medullary surface. These results suggest that a GABAergic synapse lies within the first 2 mm of the ventral medulla and is involved in baroreceptor modulation of the sympathetic outflow.

Adrenaline-containing neurons of the rostral ventrolateral medulla (the C1 group) project selectively to autonomic spinal neurons in rats. Stimulation of these neurons electrically or chemically elevates arterial pressure, while neuronal blockade by microinjection of tetrodotoxin bilaterally drops arterial pressure to levels comparable to those produced by spinal cord transection. Adrenaline neurons of the ventral medulla appear necessary for maintaining normal levels of blood pressure, and thus may constitute a tonic vasomotor center.

Electrical stimulation within discrete sites of the spinal trigeminal complex in anesthetized or decerebrated rabbits results in arterial hypotension, often over 50 mm Hg, bradycardia of up to 60 beats/min, apnea, and gastric hypermotility, collectively termed the trigeminal depressor response (TDR). The threshold for the TDR is less than or equal to 10 muA and is graded up to 3-6 times threshold. It can only be elicited by trains of stimuli of low frequency (0.5-20 Hz); at 50 Hz the response disappears or becomes pressor. The bradycardia is only abolished by bilateral vagotomy combined with beta-adrenergic blockade, and thus results from combined excitation of cardio-vagal and inhibition of cardiac sympathetic nerves. The hypotension is unassociated with changes in cardiac output, does not change after blockade of the bradycardia, but disappears after alpha-adrenergic blockade and hence is entirely attributable to inhibition of ongoing sympathetic vasoconstrictor nerve activity. Below threshold stimulation the TDR can only be elicited from the root entry zone of the Vth nerve, from dorsal portions of the spinal tract of the Vth nerve, and to portions of the nucleus of the spinal tract, notably the nucleus caudalis. A TDR of reduced magnitude can also be elicited by low frequency stimulation of numerous branches of the Vth nerve arising from all three divisions and including the supra- and infra-orbital, the inferior alveolar, and lingual nerves. Bilateral electrolytic lesions of the nucleus tractus solitarii at the obex, with complete abolition of baroreceptor reflexes from carotid sinus and aortic depressor nerves, fail to alter the TDR elicited from the brain or from branches of the Vth nerve, or the vasodepressor responses elicited by electrical stimulation of the central ends of the IXth and Xth cranial nerves transescted distal to the branches of baro-receptor nerves. In contrast, caudal lesions of the trigeminal complex abolish the TDR elicited from brain and Vth nerve and substantially reduces the vasodepressor responses from the IXth and Xth nerves, without altering baroreceptor reflexes. We conclude that the TDR represents a heretofore recognized vasodepressor response dependent upon the spinal trigeminal complex which is at least in part anatomically distinct from pathways subserving arterial baroreceptor and somatic vasodepressor reflexes. The TDR can be reflexly elicited from widely distributed but yet unidentified receptors innervated by branches of the Vth and of the IXth and Xth cranial nerves other than those innervating arterial baroreceptors. It is of unknown function, but may be related to pain mechanisms.

This report deals with substance P (SP) mechanisms involved in regulation of vasomotor tone at the spinal cord levels in normotensive Wistar-Kyoto (WKY) and spontaneously hypertensive rats (SHR). Our results indicate the following. (1) Intrathecal injections of the SP antagonist, D-Pro,D-Trp-SP cause dose-dependent decreases in mean arterial pressure and heart rate in Sprague-Dawley rats, WKYs and SHRs; the maximal blood pressure decreases are equal to those seen after cervical spinal cord transection. (2) Intrathecal injections of this antagonist into the L1 spinal level in WKYs or SHRs that had previously had their C8 spinal cords transected caused a rise in blood pressure and heart rate, suggesting that intrinsic spinal SP mechanisms are probably not involved in vasomotor tone. (3) The intermediolateral cell column region (IML) of 16-week-old WKYs and SHRs has a single high affinity and saturable binding component with approximately the same dissociation constant (Kd = 1.21 nM for WKYs; Kd = 1.25 nM for SHRs); the SHRs showed a higher number of sites (Bmax = 24.5 fmol/mg protein) than WKY rats (Bmax = 19.9 fmol/mg protein). The Kd and Bmax obtained from IML sections from 4-week-old WKYs and SHRs exhibit no differences, although their binding values with 2 nM [3H]SP are higher than those obtained from the 16-week-old animals. (4) D-Pro4,D-Trp7,9-SP4-11 has the same relatively low (micromolar range) potency for displacing [3H]SP binding in the IML of WKYs and SHRs. (5) SHRs (16 weeks old) contain 20% more SP immunoreactivity in the IML than WKY rats (834 +/- 36 pg/mg protein vs 694 +/- 50 pg/mg protein); 4-week-old rats do not show such differences. The potential significance of these results is discussed in relation to the control of vasomotor tone.

Microinjections of N-methyl-D-aspartate (NMDA) into the caudal ventrolateral medulla of the rat led to a decrease in arterial pressure whereas 2-amino-5-phosphonovalerate injected bilaterally into this region produced hypertension and blocked the depressor effect of aortic nerve stimulation. High K+ stimulation via push-pull cannula caused a calcium-dependent release of endogenous glutamate from the region. These results provide evidence for the NMDA receptor system involved in tonic vasodepressor control in the rat caudal ventrolateral medulla.

Pooled antisera to vasoactive intestinal polypeptide were used to block neurogenic extracranial vasodilatation elicited from either brainstem (locus coeruleus) or pterygopalatine ganglion stimulation in the cat. Vasodilatation was not inhibited by sham immune sera, or by antisera to bradykinin or substance P. The efferent pathway for vasodilatation from the locus coeruleus traverses the facial nerve (greater superficial petrosal branch) and the pterygopalatine and otic ganglia. Its blockade demonstrates a novel action of a peptide transmitter in the expression of a central neurogenic response.

Extensive plexuses of serotonin axons form a supra- and subependymal system in the walls of the ventricles, in the arachnoid sheath around major cerebral blood vessels, and in the pia over the spinal cord. These have been demonstrated by autoradiography after continuous intraventricular perfusions of exogenous [3H]5-HT in rats and monkeys. The axons accumulate 5,6-DHT rendering them electron opaque, but have no uptake systems for [3H]NE. After treatment with MAO inhibitors and [3H]5-HT, the axonal boutons contain large (70nm) variably dense synaptic vesicles, and small (35 nm) vesicles each equipped with a dense dot. The latter vesicles are not seen in untreated controls. Electrical stimulation in the raphe nuclei causes significant increases in axonal [3H]5-HT uptake indicating that the fibers originate in the raphe. Quantitatively, the supraependymal plexus is variable, profuse over the dorsal and ventral aqueductal surfaces, sparse over the lateral aspects. Individual raphe neurons have their specific uptake affinities for [3H]5-HT that are independent of tracer concentration or diffusion gradient. It is suggested that raphe neurons with low 5-HT uptake may utilize other neurotransmitters. Two new functional roles are proposed: (1) the serotonin ventricular and pial axons are probably important modifiers of local cerebrospinal fluid (CSF) composition so that regional CSF variations in 5-HT and its metabolites are highly probable; (2) the subarachnoid plexus around major cerebral vessels may contribute to local vasomotor action, thus affecting the cerebral blood flow. The possible significance of these serotonin systems for an understanding of certain neurological entities such as migraine and hemodynamic regulation in cerebral vascular disease is indicated.

GABA antagonists blocked, and diazepam potentiated, inhibition of spontaneous sympathetic activity elicited by electrical stimulation of classic midline medullary depressor sites. Picrotoxin often converted inhibitory effects of raphe stimulation into sympathoexcitatory responses. Serotonin antagonists blocked these sympathoexcitatory responses. The midline medullary raphe complex is heterogeneous in respect to autonomic function with sympathoinhibitory elements mediated at least in part by GABA and sympathoexcitatory pathways mediated by serotonin.