Autonomic mechanisms in the acute cardiovascular effects of cocaine in conscious rats

The Critical Role of Peripheral Targets in Triggering Rapid Neural Effects of Intravenous Cocaine

Direct interaction of cocaine with centrally located monoamine transporters is the primary mechanism underlying its reinforcing properties. It is also often assumed that this drug action is responsible for all the physiological and behavioral effects of this drug. The goal of this review is to challenge this basic mechanism and demonstrate the importance of peripheral actions of cocaine in inducing its initial, rapid neural effects. The use of high-resolution electrophysiological, neurochemical and physiological techniques revealed that the effects of intravenous cocaine at behaviorally relevant doses are exceptionally rapid and transient correlating with strong, quick, and transient increases in blood cocaine levels. Some of these effects are mimicked by cocaine-methiodide, a cocaine analog that cannot cross the blood-brain barrier and they are resistant to dopamine (DA) receptor blockade. Therefore, it appears that rapid neural effects of cocaine result from its direct interaction with receptive sites on afferents of sensory nerves densely innervating blood vessels. This interaction creates a rapid neural signal to the CNS that results in generalized neural activation and subsequent changes in different physiological parameters. This drug's action appears to be independent from cocaine's action on central neurons, which requires a definite time to occur and induce neural and physiological effects with longer latencies and durations. The co-existence in the same drug on two timely distinct actions with their subsequent interaction in the CNS could explain consistent changes in physiological and behavioral effects of cocaine following their repeated use, playing a role in the development of drug-seeking and drug-taking behavior.

Intravenous Cocaine Increases Oxygen Entry into Brain Tissue: Critical Role of Peripheral Drug Actions

Although it is well established that the direct action of cocaine on centrally located neural substrates is essential in mediating its reinforcing properties, cocaine induces very rapid immediate neural effects that imply cocaine's action on peripheral neural substrates. We employed oxygen sensors coupled with high-speed amperometery to examine the effects of standard cocaine HCl that easily enters the blood-brain barrier and its blood-brain barrier-impermeable methiodide analogue on oxygen levels in the nucleus accumbens in awake, freely moving rats. Both drugs induced strong increases in nucleus accumbens oxygen levels, which displayed similarly short, second-scale latencies and a general similarity with oxygen increases induced by an auditory stimulus. This study provides additional support for the view that the immediate neural effects of intravenous cocaine are triggered via its direct action on peripherally located neural substrates and fast neural transmission to the central nervous system via somatosensory pathways.

Lack of Reactive Oxygen Species Deteriorates Blood Pressure Regulation in Acute Stress

This study investigated the contribution of reactive oxygen species (ROS) to blood pressure regulation in conscious adult male Wistar rats exposed to acute stress. Role of ROS was investigated in rats with temporally impaired principal blood pressure regulation systems using ganglionic blocker pentolinium (P, 5 mg/kg), angiotensin converting enzyme inhibitor captopril (C, 10 mg/kg), nitric oxide synthase inhibitor L-NAME (L, 30 mg/kg) and superoxide dismutase mimeticum tempol (T, 25 mg/kg). Mean arterial pressure (MAP) was measured by the carotid artery catheter and inhibitors were administered intravenously. MAP was disturbed by a 3-s air jet, which increased MAP by 35.2±3.0 % vs. basal MAP after the first exposure. Air jet increased MAP in captopril- and tempol-treated rats similarly as observed in saline-treated rats. In pentolinium-treated rats stress significantly decreased MAP vs. pre-stress value. In L-NAME-treated rats stress failed to affect MAP significantly. Treatment of rats with P+L+C resulted in stress-induced MAP decrease by 17.3±1.3 % vs. pre-stress value and settling time (20.1±4.2 s). In P+L+C+T-treated rats stress led to maximal MAP decrease by 26.4±2.2 % (p<0.005 vs. P+L+C) and prolongation of settling time to 32.6±3.3 s (p<0.05 vs. P+L+C). Area under the MAP curve was significantly smaller in P+L+C-treated rats compared to P+L+C+T-treated ones (167±43 vs. 433±69 a.u., p<0.008). In conclusion, in rats with temporally impaired blood pressure regulation, the lack of ROS resulted in greater stress-induced MAP alterations and prolongation of time required to reach new post-stress steady state.

The effects of cocaine on heart rate and electrocardiogram in zebrafish (Danio rerio)

Zebrafish (Danio rerio) have been used as a model organism to explore the genetic basis for responsiveness to addictive drugs like cocaine. However, very little is known about how the physiological response to cocaine is mediated in zebrafish. In the present study electrocardiograms (ECGs) were recorded from adult zebrafish treated with cocaine. Treatment with cocaine resulted in a bell-shaped dose response curve with a maximal change in heart rate seen using 5mg/L cocaine. Higher doses resulted in a higher percentage of fish showing bradycardia. The cocaine-induced tachycardia was blocked by co-treatment with propranolol, a β-adrenergic antagonist, but potentiated by co-treatment with phentolamine, an α-adrenergic antagonist. Co-treatment with atropine, a classic cholinergic antagonist, had no effect on cocaine-induced tachycardia. Cocaine treatment of adult fish changed the ECG of treated fish, inducing a dose-dependent increase in QT interval after adjusting for heart rate (QTc), while not affecting the PR or QRS intervals. The acute effects of cocaine on heart rate were examined in 5-day old embryos to see if zebrafish might serve as a suitable model organism to study possible links of embryonic physiological response to subsequent adult behavioral response to the drug. Cocaine treatment of 5-day old zebrafish embryos also resulted in a bell-shaped dose response curve, with maximal tachycardia achieved with 10mg/L. The response in embryonic fish was thus comparable to that in adults and raises the possibility that the effects of embryonic exposure to cocaine on the developing cardiovascular system can be effectively modeled in zebrafish.

Central and peripheral contributions to dynamic changes in nucleus accumbens glucose induced by intravenous cocaine

The pattern of neural, physiological and behavioral effects induced by cocaine is consistent with metabolic neural activation, yet direct attempts to evaluate central metabolic effects of this drug have produced controversial results. Here, we used enzyme-based glucose sensors coupled with high-speed amperometry in freely moving rats to examine how intravenous cocaine at a behaviorally active dose affects extracellular glucose levels in the nucleus accumbens (NAc), a critical structure within the motivation-reinforcement circuit. In drug-naive rats, cocaine induced a bimodal increase in glucose, with the first, ultra-fast phasic rise appearing during the injection (latency 6–8 s; ~50 μM or ~5% of baseline) followed by a larger, more prolonged tonic elevation (~100 μM or 10% of baseline, peak ~15 min). While the rapid, phasic component of the glucose response remained stable following subsequent cocaine injections, the tonic component progressively decreased. Cocaine-methiodide, cocaine's peripherally acting analog, induced an equally rapid and strong initial glucose rise, indicating cocaine's action on peripheral neural substrates as its cause. However, this analog did not induce increases in either locomotion or tonic glucose, suggesting direct central mediation of these cocaine effects. Under systemic pharmacological blockade of dopamine transmission, both phasic and tonic components of the cocaine-induced glucose response were only slightly reduced, suggesting a significant role of non-dopamine mechanisms in cocaine-induced accumbal glucose influx. Hence, intravenous cocaine induces rapid, strong inflow of glucose into NAc extracellular space by involving both peripheral and central, non-dopamine drug actions, thus preventing a possible deficit resulting from enhanced glucose use by brain cells.

Ventral tegmental area neurons are either excited or inhibited by cocaine's actions in the peripheral nervous system

Cocaine's multiple pharmacological substrates are ubiquitously present in the peripheral and central nervous system. Thus, upon its administration, cocaine acts in the periphery before directly acting in the brain. We determined whether cocaine alters ventral tegmental area (VTA) neuronal activity via its peripheral actions. In urethane-anesthetized rats, we recorded VTA neuron's responses to intravenous injections of two cocaine analogs: cocaine-hydrochloride (HCl, 0.25 mg/kg), which readily cross the blood-brain barrier (BBB), and cocaine-methiodide (MI, 0.33 mg/kg), which does not cross the BBB. Both cocaine analogs produced sustained changes in discharge rates that began 5 s after the initiation of a 10-s drug infusion. Within the first 90 s post-injection, the magnitudes of neuronal responsiveness of both cocaine analogs were comparable, but later the effects of cocaine-HCl were stronger and persisted longer than those of cocaine-MI. The proportion of neurons responsive to cocaine-HCl was twice that of cocaine-MI (74% and 35%, respectively). Both analogs also differed in their response onsets. Cocaine-MI rarely evoked responses after 1 min, whereas cocaine-HCl continued to evoke responses within 3 min post-injection. VTA neurons were either excited or inhibited by both cocaine analogs. Most units responsive to cocaine-MI, regardless of whether they were excited or inhibited, had electrophysiological characteristics of putative dopamine (DA) neurons. Units inhibited by cocaine-HCl also had characteristics of DA neurons, whereas excited neurons had widely varying action potential durations and discharge rates. Cocaine-MI and cocaine-HCl each produced changes in VTA neuron activity under full DA receptor blockade. However, the duration of inhibition was shortened and the number of excitations increased, and they occurred with an earlier onset during DA receptor blockade. These findings indicate that cocaine acts peripherally with a short latency and alters the activity of VTA neurons before its well-known direct actions in the brain.

Cocaine action on peripheral, non-monoamine neural substrates as a trigger of electroencephalographic desynchronization and electromyographic activation following i.v. administration in freely moving rats

Many important physiological, behavioral and subjective effects of i.v. cocaine (COC) are exceptionally rapid and transient, suggesting a possible involvement of peripheral neural substrates in their triggering. In the present study, we used high-speed electroencephalographic (EEG) and electromyographic (EMG) recordings (4-s resolution) in freely moving rats to characterize the central electrophysiological effects of i.v. COC at low doses within a self-administration range (0.25-1.0 mg/kg). We found that COC induces rapid, strong, and prolonged desynchronization of cortical EEG (decrease in alpha and increase in beta and gamma activity) and activation of the neck EMG that begin within 2-6 s following the start of a 10-s injection; immediate components of both effects were dose-independent. The rapid effects of COC were mimicked by i.v. COC methiodide (COC-MET), a derivative that cannot cross the blood-brain barrier. At equimolar doses (0.33-1.33 mg/kg), COC-MET had equally fast and strong effects on EEG and EMG total powers, decreasing alpha and increasing beta and gamma activities. Rapid EEG desynchronization and EMG activation was also induced by i.v. procaine, a structurally similar, short-acting local anesthetic with virtually no effects on monoamine uptake; at equipotential doses (1.25-5.0 mg/kg), these effects were weaker and shorter in duration than those of COC. Surprisingly, i.v. saline injection delivered during slow-wave sleep (but not during quiet wakefulness) also induced a transient EEG desynchronization but without changes in EMG and motor activity; these effects were significantly weaker and much shorter than those induced by all tested drugs. These data suggest that in awake animals, i.v. COC induces rapid cortical activation and a subsequent motor response via its action on peripheral non-monoamine neural elements, involving neural transmission via visceral sensory pathways. By providing a rapid neural signal and triggering neural activation, such an action might play a crucial role in the sensory effects of COC, thus contributing to the learning and development of drug-taking behavior.

Rapid EEG desynchronization and EMG activation induced by intravenous cocaine in freely moving rats: a peripheral, nondopamine neural triggering

Many important physiological, behavioral, and psychoemotional effects of intravenous (IV) cocaine (COC) are too fast and transient compared with pharmacokinetic predictions, suggesting a possible involvement of peripheral neural mechanisms in their triggering. In the present study, we examined changes in cortical electroencephalogram (EEG) and neck electromyogram (EMG) induced in freely moving rats by IV COC administration at low, reinforcing doses (0.25-1.0 mg/kg) and compared them with those induced by an auditory stimulus and IV COC methiodide, which cannot cross the blood-brain barrier. We found that COC induces rapid, strong, and prolonged EEG desynchronization, associated with decrease in alpha and increase in beta and gamma activities, and EMG activation and that both begin within 2-6 s following the start of a 10-s injection; immediate components of this effect were dose independent. The rapid COC-induced changes in EEG and EMG resembled those induced by an auditory stimulus; the latter effects had shorter onset latencies and durations and were fully blocked during urethane anesthesia. Although urethane anesthesia completely blocked COC-induced EMG activation and rapid components of EEG response, COC still induced EEG desynchronization that was much weaker, greatly delayed (approximately 60 s), and associated with tonic decreases in delta and increases in alpha, beta, and gamma activities. Surprisingly, IV saline delivered during slow-wave sleep (but not quite wakefulness) also induced a transient EEG desynchronization but without changes in EMG activity; these effects were also fully blocked during anesthesia. Peripherally acting COC methiodide fully mimicked rapid EEG and EMG effects of regular COC, but the effects at an equimolar dose were less prolonged than those with regular COC. These data suggest that in awake animals IV COC, like somato-sensory stimuli, induces cortical activation and a subsequent motor response via its action on peripheral neural elements and involving rapid neural transmission. By providing a rapid neural signal and triggering transient neural activation, such an action might play a crucial role in the sensory effects of COC, thus contributing to the learning and development of drug-taking behavior.

Brain temperature responses to salient stimuli persist during dopamine receptor blockade despite a blockade of locomotor responses

We examined how an acute dopamine (DA) receptor blockade affects locomotor and brain (nucleus accumbens or NAcc), muscle and skin temperature responses to three arousing stimuli (procedure of sc injection, tail-pinch and social interaction with another male rat) and intravenous cocaine (1 mg/kg). DA receptor blockade was induced by mixture of D1- (SCH23390) and D-2 selective (eticlopride) DA antagonists at 0.2 mg/kg doses. Each arousing stimulus and cocaine caused locomotor activation, prolonged increase in NAcc and muscle temperature (0.6-1.0 degrees C for 20-50 min) and transient skin hypothermia (-0.6 degrees C for 1-3 min) in drug-naive conditions. DA receptor blockade strongly decreased basal locomotor activity, but moderately increased brain, muscle and skin temperatures. Therefore, selective interruption of DA transmission does not inhibit the brain, making it more metabolically active and warmer despite skin vasodilatation and the enhanced heat loss to the body and the external environment. DA antagonists strongly decreased locomotor responses to all stimuli and cocaine, had no effects on acute skin vasoconstriction, but differentially affected stimuli- and drug-induced changes in NAcc and muscle temperatures. While brain and muscle temperatures induced by cocaine were fully blocked and both temperatures slightly decreased, temperature increases induced by tail-pinch and social interaction, despite a significant attenuation, persisted during DA receptor blockade. These data are discussed to define the role of the DA system in regulating the central activation processes and behavioral responsiveness to natural arousing and drug stimuli.

Cocaine-induced reinstatement in rats: evidence for a critical role of cocaine stimulus properties

RATIONALE

The exact behavioral nature of drug-induced reinstatement of drug seeking is still debated. As an incentive, the drug can have general facilitatory influences on appetitive behaviors. As an interoceptive stimulus, the drug can acquire discriminative properties and control behavior.

OBJECTIVE

This study assessed the relative contribution of the incentive versus discriminative properties of cocaine in food-seeking reinstatement.

METHODS

In Experiment 1, eight groups of rats were trained to press a lever for food pellets and experienced cocaine (0, 5, 10, or 15 mg/kg; i.p.), either during the operant conditioning sessions or 4 h after, in another environment without food access. In Experiment 2, to dissociate the role of the operant response per se from the consummatory response, two groups of rats experienced food consumption under cocaine (10 mg/kg; i.p.) either during operant conditioning sessions or during alternate sessions of free access to the food. Then, for both experiments, food pellets were withheld and cocaine injections ceased (extinction). The reinstating effects of noncontingent cocaine (10 mg/kg; i.p.) and food pellet delivery were assessed. Locomotor activity was recorded to probe expression of behavioral sensitization.

RESULTS

Cocaine reinstated lever pressing only in rats having previously performed the operant responses under cocaine. In contrast, food pellet delivery reinstated lever pressing independently of rats' history with cocaine. Locomotor sensitization was evidenced for all cocaine-pre-exposed rats, dissociating sensitization from reinstatement.

CONCLUSIONS

When present during operant conditioning, the stimulus "cocaine" acquires conditioned properties which can then promote reinstatement of the extinguished behavior.

Sensory effects of intravenous cocaine on dopamine and non-dopamine ventral tegmental area neurons

Intravenous (iv) cocaine mimics salient somato-sensory stimuli in their ability to induce rapid physiological effects, which appear to involve its action on peripherally located neural elements and fast neural transmission via somato-sensory pathways. To further clarify this mechanism, single-unit recording with fine glass electrodes was used in awake rats to examine responses of ventral tegmental area (VTA) neurons, both presumed dopamine (DA) and non-DA, to iv cocaine and tail-press, a typical somato-sensory stimulus. To exclude the contribution of DA mechanisms to the observed neuronal responses to sensory stimuli and cocaine, recordings were conducted during full DA receptor blockade (SCH23390+eticloptide). Iv cocaine (0.25 mg/kg delivered over 10 s) induced significant excitations of approximately 63% of long-spike (presumed DA) and approximately 70% of short-spike (presumed non-DA) VTA neurons. In both subgroups, neuronal excitations occurred with short latencies (4-8 s), peaked at 10-20 s (30-40% increase over baseline) and disappeared at 30-40 s after the injection onset. Most long-(67%) and short-spike (89%) VTA neurons also showed phasic responses to tail-press (5-s). All responsive long-spike cells were excited by tail-press; excitations were very rapid (peak at 1 s) and strong (100% rate increase over baseline) but brief (2-3 s). In contrast, both excitations (60%) and inhibitions (29%) were seen in short-spike cells. These responses were also rapid and transient, but excitations of short-spike units were more prolonged and sustained (10-15 s) than in long-spike cells. These data suggest that in awake animals iv cocaine, like somato-sensory stimuli, rapidly and transiently excites VTA neurons of different subtypes. Therefore, along with direct action on specific brain substrates, central effects of cocaine may occur, via an indirect mechanism, involving peripheral neural elements, visceral sensory nerves and rapid neural transmission. Via this mechanism, cocaine, like somato-sensory stimuli, can rapidly activate DA neurons and induce phasic DA release, creating the conditions for DA accumulation by a later occurring and prolonged direct inhibiting action on DA uptake. By providing a rapid neural signal and triggering transient neural activation, such a peripherally driven action might play a crucial role in the sensory effects of cocaine, thus contributing to learning and development of drug-taking behavior.

Thrombotic microangiopathy in cocaine abuse-associated malignant hypertension: report of 2 cases with review of the literature

Cocaine is one of the most commonly used illicit drugs. Acute renal failure is an emergent complication in patients with acute cocaine intoxication. It is well known that rhabdomyolysis and vasoconstriction can be important pathogenetic mechanisms resulting in acute renal failure in these patients. Clinically, although cocaine abuse is associated with elevated blood pressure, persistent accelerated hypertension reaching levels diagnostic of malignant hypertension is uncommon. Cocaine-induced malignant hypertension associated with morphologic features of thrombotic macroangiopathy has been rarely mentioned in the literature. We report 2 cases of cocaine abuse-associated malignant hypertension with renal failure. Kidney biopsies revealed thrombotic microangiopathy with fibrinoid necrosis of arterioles and glomerular tufts. Cocaine-mediated endothelial injury and platelet activation may play important pathogenetic roles in cocaine abusers who develop acute renal failure and malignant hypertension.

Electrophysiological evaluation of the time-course of dopamine uptake inhibition induced by intravenous cocaine at a reinforcing dose

Cocaine effectively inhibits dopamine (DA) uptake and this action appears to be the primary cause for increased DA transmission following systemic cocaine administration. Although this action had been reliably demonstrated in vivo with cocaine at high doses, data on the extent and the time-course of DA uptake inhibition induced by i.v. cocaine at low, reinforcing doses remain controversial. To clarify this issue, we examined how cocaine affects striatal neuronal responses to repeated iontophoretic DA applications in urethane-anesthetized rats. Because most striatal neurons during anesthesia have low, sporadic activity, DA tests were performed on cells tonically activated by continuous glutamate application. DA phasically decreased the activity of most dorsal and ventral striatal neurons; these responses in control conditions (i.v. saline) were current (dose) -dependent and remained highly stable following repeated DA applications at the same currents. DA also consistently decreased the activity of striatal neurons after i.v. cocaine (1 mg/kg); the magnitude of DA-induced inhibition slowly increased from approximately 5 min, became significantly larger from approximately 9 min, and peaked at 13-15 min after a single i.v. injection. Then, the difference in the DA response slowly decreased toward the pre-cocaine baseline. A similar enhancement of DA induced-inhibition was also seen after i.p. cocaine administration at a high dose (15 mg/kg). In this case, the DA response became significantly stronger at 7-9 min and remained enhanced vs. a pre-drug control up to 24-26 min after the injection. Both regimens of cocaine treatment did not result in evident changes in either onset or offset of the DA-induced inhibitions. Our data confirm that cocaine at low, reinforcing doses inhibits DA uptake, resulting in potentiation of DA-induced neuronal inhibitions, but they suggest that this effect is relatively weak and delayed from the time of i.v. injection. These slow and prolonged effects of i.v. cocaine on DA-induced neuronal responses are consistent with previous binding and our electrochemical evaluations of DA uptake, presumably reflecting the total time necessary for i.v.-delivered cocaine to reach brain microvessels, cross the blood-brain barrier, passively diffuse within brain tissue, interact with the DA transporters, and finally inhibit DA uptake.

I.v. cocaine induces rapid, transient excitation of striatal neurons via its action on peripheral neural elements: single-cell, iontophoretic study in awake and anesthetized rats

Cocaine's (COC) direct interaction with the dopamine (DA) transporter is usually considered the most important action underlying the psychomotor stimulant and reinforcing effects of this drug. However, some physiological, behavioral and psycho-emotional effects of COC are very rapid and brief and they remain intact during DA receptor blockade, suggesting possible involvement of peripheral non-DA neural mechanisms. To assess this issue, single-unit recording with microiontophoresis was used to examine changes in impulse activity of dorsal and ventral striatal neurons to i.v. COC (0.25-0.5 mg/kg) in the same rats under two conditions: awake with DA receptor blockade and anesthetized with urethane. In the awake preparation approximately 70% striatal neurons showed rapid and transient (latency approximately 6 s, duration approximately 15 s) COC-induced excitations. These effects were stronger in ventral than dorsal striatum. During anesthesia, these phasic effects were fully blocked and COC slowly decreased neuronal discharge rate. Cocaine-methiodide (COC-M), a derivative that cannot cross the blood-brain barrier, also caused phasic excitations in the awake, but not anesthetized condition. In contrast to regular COC, COC-M had no tonic effect on discharge rate in either preparation. Most striatal neurons that were phasically excited by both COC forms also showed short-latency excitations during tail-touch and tail-pinch in the awake preparation, an effect strongly attenuated during anesthesia. Finally, most striatal neurons that in awake conditions were phasically excited by somato-sensory stimuli and COC salts were also excited by iontophoretic glutamate (GLU). Although striatal neurons were sensitive to GLU in both preparations, the response magnitude at the same GLU current was higher in awake than anesthetized conditions. These data suggest that in awake animals i.v. COC, like somato-sensory stimuli, transiently excites striatal neurons via its action on peripheral neural elements and rapid neural transmission. While the nature of these neuronal elements needs to be clarified using other analytical techniques, they might involve voltage-gated K(+) and Na(+) channels, which have a high affinity for COC and are located on terminals of visceral sensory nerves that densely innervate peripheral vessels. Therefore, along with direct action on specific brain substrates, central excitatory effects of COC may occur via indirect action, involving afferents of visceral sensory nerves and rapid neural transmission. By providing a rapid sensory signal and triggering transient neural activation, such a peripherally triggered action might play a crucial role in the sensory effects of COC, thus contributing to learning and development of drug-taking behavior.

The role of peripheral Na(+) channels in triggering the central excitatory effects of intravenous cocaine

While alterations in dopamine (DA) uptake appear to be a critical mechanism underlying locomotor and reinforcing effects of cocaine (COC), many centrally mediated physiological and affective effects of this drug are resistant to DA receptor blockade and are expressed more quickly following an intravenous (i.v.) injection than expected based on the dynamics of drug concentration in the brain. Because COC is also a potent local anesthetic, its rapid action on Na+ channels may be responsible for triggering these effects. We monitored temperatures in the nucleus accumbens, temporal muscle and skin together with conventional locomotion during a single i.v. injection of COC (1 mg/kg), procaine (PRO, 5 mg/kg; equipotential anesthetic dose), a short-acting local anesthetic drug that, like COC, interacts with Na+ channels, and cocaine methiodide (COC-MET, 1.31 mg/kg, equimolar dose), a quaternary COC derivative that is unable to cross the blood-brain barrier. In this way, we explored not only the importance of Na+ channels in general, but also the importance of central vs. peripheral Na+ channels specifically. COC induced locomotor activation, temperature increase in the brain and muscle, and a biphasic temperature fluctuation in skin. Though PRO did not induce locomotor activation, it mimicked, to a greater degree, the temperature effects of COC. Therefore, Na+ channels appear to be a key substrate for COC-induced temperature fluctuations in the brain and periphery. Similar to PRO, COC-MET had minimal effects on locomotion, but mimicked COC in its ability to increase brain and muscle temperature, and induce transient skin hypothermia. It appears therefore that COC's interaction with peripherally located Na+ channels triggers its central excitatory effects manifested by brain temperature increase, thereby playing a major role in drug sensing and possibly contributing to COC reinforcement.

The role of peripheral and central sodium channels in mediating brain temperature fluctuations induced by intravenous cocaine

While cocaine's interaction with the dopamine (DA) transporter and subsequent increase in DA transmission are usually considered key factors responsible for its locomotor stimulatory and reinforcing properties, many centrally mediated physiological and psychoemotional effects of cocaine are resistant to DA receptor blockade, suggesting the importance of other non-DA mechanisms. To explore the role of cocaine's interaction with Na+ channels, rats were used to compare locomotor stimulatory and temperature (NAcc, temporal muscle and skin) effects of repeated iv injections of cocaine (1 mg/kg) with those induced by procaine (PRO 5 mg/kg), a short-acting local anesthetic with negligible effect on the DA transporter, and cocaine methiodide (COC-MET 1.31 mg/kg), a quaternary cocaine derivative that is unable to cross the blood-brain barrier. While PRO, unlike cocaine, did not induce locomotor activation, it mimicked cocaine in its ability to increase brain temperature following the initial injection and to induce biphasic, down-up fluctuations following repeated injections. This similarity suggests that both these effects of cocaine may be driven by its action on Na+ channels, a common action of both drugs. While COC-MET also did not affect locomotor activity, it shared with cocaine and PRO their ability to increase brain temperature but failed to induce temperature decreases after repeated injections. These findings point toward activation of peripheral Na+ channels as the primary mechanism of rapid excitatory effects of cocaine and inhibition of centrally located Na+ channels as the primary mechanism for transient inhibitory effects of cocaine. DA receptor blockade (SCH23390+eticlopride) fully eliminated locomotor stimulatory and temperature-increasing effects of cocaine, but its temperature-decreasing effects remained intact. Surprisingly, DA receptor blockade also altered the temperature fluctuations caused by PRO and COC-MET, suggesting that some of the central effects triggered via Na+ channels are in fact DA-dependent. Finally, repeated administration of PRO to animals that had previous cocaine experience led to conditioned locomotion and potentiated temperature-increasing effects of this drug. It appears, therefore, that, in addition to the central effects of cocaine mediated via interaction with the DA transporter and potentiation of DA uptake, interaction with peripheral and central Na+ channels is important for the initial physiological and, perhaps, affective effects of cocaine, likely contributing to the unique abuse potential of this drug.

Dopamine-dependent and dopamine-independent actions of cocaine as revealed by brain thermorecording in freely moving rats

Brain temperature fluctuates biphasically in response to repeated, intravenous (i.v.) cocaine injections, perhaps reflecting cocaine's inhibiting effect on both dopamine (DA) transporters and Na+ channels. By using a DA receptor blockade, one could separate these actions and determine the role of DA-dependent and DA-independent mechanisms in mediating this temperature fluctuation. Rats were chronically implanted with thermocouple probes in the brain, a non-locomotor head muscle and subcutaneously. Temperature fluctuations associated with ten repeated i.v. cocaine injections (1 mg/kg with 8-min inter-injection intervals) were examined after a combined, systemic administration of selective D1-like and D2-like receptor blockers (SCH-23390 and eticlopride) at doses that effectively inhibit DA transmission. In contrast to the initial temperature increases and subsequent biphasic fluctuations (decreases followed by increases) seen with repeated cocaine injections in saline-treated control, brain and muscle temperatures during DA receptor blockade decreased with each repeated cocaine injection. DA receptor blockade had no effects on skin temperature, which tonically decreased and biphasically fluctuated (decreases followed by increases) during repeated cocaine injections in both conditions. DA receptor blockade by itself slightly increased brain and muscle temperatures, with no evident effect on skin temperature. DA antagonists also strongly decreased spontaneous movement activity and completely blocked the locomotor activation normally induced by repeated cocaine injections. Although our data confirm that cocaine's inhibitory action on presynaptic DA uptake is essential for its ability to induce metabolic and behavioral activation, they also suggest that the physiological effects of this drug cannot be explained through this system alone. The continued hypothermic effect of cocaine points to its action on other central systems (particularly blockade of Na+ channels) that may be important for the development of cocaine abuse and adverse effects of this drug.

Etiology and management of hypertension in chronic kidney disease

The kidneys are vital in the pathogenesis of hypertension and are also pathologically affected by the presence of hypertension. The prevalence of hypertension in chronic kidney disease (CKD) depends on age, the severity of renal failure, and proteinuria. The intricate and inextricable relationship between CKD and hypertension seems to cause cardiovascular disease that has assumed epidemic proportions. This article discusses the etiology and treatment of hypertension in CKD so that it can be better controlled.

Haemodynamic responses to sensory stimulation are enhanced following acute cocaine administration

Cocaine enhances neural activity in response to sensory stimulation, an effect that may play a role in the development of drug craving. However, cocaine-induced sensory enhancement may be difficult to study in humans using neuroimaging if the global increases in baseline haemodynamic parameters, which cocaine produces, interfere with the ability of enhanced sensory-related neural activity to lead to enhanced haemodynamic responses. To investigate the effect of cocaine-induced baseline haemodynamic changes on sensory-related haemodynamic (and electrophysiological) responses, field potential (FP) and haemodynamic responses (obtained using optical imaging spectroscopy and laser-Doppler flowmetry) in the barrel cortex of the anaesthetised rat were measured during mechanical whisker stimulation following cocaine (0.5 mg/kg) or saline administration. During cocaine infusion, the relationship between blood flow and volume transiently decoupled. Following this, cocaine caused large baseline increases in blood flow (133%) and volume (33%), which peaked after approximately 6 min and approached normal levels again after 25 min. During the peak baseline increases, FP responses to whisker stimulation were similar to saline whereas several haemodynamic response parameters were slightly reduced. After the peak, significant increases in FP responses were observed, accompanied by significantly enhanced haemodynamic responses, even though the haemodynamic baselines remained elevated. Hence, the haemodynamic response to sensory stimulation is transiently reduced in the presence of large increases in baseline but, after the baseline peak, enhanced neural responses are faithfully accompanied by enhanced haemodynamic responses. The findings suggest that any cocaine-induced enhancement of sensory-related neural activity in humans is likely to be detectable by neuroimaging.

Hemodynamic response profile predicts susceptibility to cocaine-induced toxicity

Cocaine evokes pressor responses due either to a large increase in systemic vascular resistance despite a decrease (>8%) in cardiac output (vascular responders) or to small increases in both cardiac output and vascular resistance (mixed responders) in conscious rats. These studies were designed to determine (1) if the hemodynamic response pattern to cocaine correlates with relative sensitivity to toxicity and (2) if altering the hemodynamic response pattern to cocaine using propranolol enhances toxicity. Rats were instrumented for determination of cardiac output and arterial pressure. After recovery, rats were classified as vascular or mixed responders to cocaine (5 mg/kg, i.v., four to six trials). Two weeks later, cocaine was infused (1.5 mg/kg/min) until death after pretreatment with saline or propranolol (1 mg/kg). Saline-pretreated mixed responders (n=6) had greater tolerance to cocaine toxicity compared to vascular responders (n=11). Furthermore, saline-pretreated vascular responders were less sensitive than propranolol-pretreated vascular responders (n=9) to cocaine toxicity. Therefore, we propose that the initial hemodynamic response pattern to cocaine predicts sensitivity to cocaine toxicity. In addition, propranolol, a drug that enhances the increase in vascular resistance to cocaine, also increases toxicity to cocaine in vascular responders.

Cardiovascular disorders associated with cocaine use: myths and truths

Cocaine produces a pattern of cardiovascular responses that are associated with apparent myocardial ischemia, arrhythmias, and other life-threatening complications in some individuals. Despite recent efforts to better understand the causes of cocaine-induced cardiovascular dysfunction, there remain a number of unanswered questions regarding the specific mechanisms by which cocaine elicits hemodynamic responses. This review will describe the actions of cocaine on the cardiovascular system and the evidence for the mechanisms by which cocaine elicits hemodynamic and pathologic responses in humans and animals. The emphasis will be on experimental data that provide the basis for our understanding of the mechanisms of cardiovascular toxicity associated with cocaine. More importantly, this review will identify several controversies regarding the causes of cocaine-induced cardiovascular toxicity that as yet are still debated. The evidence supporting these findings will be described. Finally, this review will outline the obvious deficits in our current concepts regarding the cardiovascular actions of cocaine in hope of encouraging additional studies on this grave problem in our society.

Amlodipine reduces blood pressure and headache frequency in cocaine-dependent outpatients

Blood pressure and headache frequency were evaluated in normotensive male and female cocaine-dependent patients (N=43) participating in a placebo-controlled, double-blind trial of amlodipine for the treatment of cocaine dependence. Amlodipine produced a significant reduction in both systolic (p=0.04) and diastolic (p=0.01) blood pressures without producing dizziness or faintness. Placebo subjects had about three times the frequency of headaches compared to the amlodipine-treated subjects (p=0.004). The high frequency of headaches reported by cocaine-dependent individuals was significantly reduced by amlodipine and may reflect improved cerebrovascular tone.