Effects of variation in chronic dose of cocaine on contingent tolerance as assessed in a milk-drinking task

Sigma-1 Receptor Antagonist (BD1047) Decreases Cathepsin B Secretion in HIV-Infected Macrophages Exposed to Cocaine

Pathogenesis of HIV-associated neurocognitive disorders (HAND) is mediated through the infiltration of perivascular macrophages into the brain with the secretion of viral, neurotoxic and inflammatory proteins. One of these proteins is cathepsin B (CATB), a lysosomal cysteine protease that induces neuronal apoptosis, and increases in plasma and cerebrospinal fluid from HIV-1 infected patients (Cantres-Rosario et al. AIDS 27(3):347-356, 2013). Cocaine further potentiates CATB neurotoxicity in vitro and in vivo (Zenón et al. J NeuroImmune Pharmacol 9(5):703-715, 2014). Modulation of sigma-1 (Sig1R) by cocaine increases oxidative species, cytokines and other factors that promote lysosomal disruption. However, the role of Sig1R in CATB secretion and HIV-1 replication in macrophages exposed to cocaine is unknown. We hypothesized that pharmacological modulation of Sig1R would alter CATB secretion from HIV-1 infected macrophages in vitro and in vivo. To test our hypothesis, monocyte derived-macrophages (MDM) from HIV-1 seronegative donors were isolated, infected with HIV-1ADA, and pretreated with Sig1R antagonist (BD1047) or Sig1R agonist (PRE-084) prior to cocaine exposure and followed for 3,6,9 and 11 days post-infection (dpi). Experiments in vivo were conducted using the HIV encephalitis mouse model (HIVE) with BD1047 treatments prior to cocaine for 14 days. Results demonstrate that in presence of cocaine, BD1047 decreases CATB secretion at 11 dpi, while PRE-084 did not have an effect. In the mouse model, BD1047 treatment prior to cocaine decreased CATB expression, cleaved caspase-3 an p24 antigen levels, reduced astrocytosis, but did not increase MAP-2 or synaptophysin. Results demonstrate that Sig1R plays a role in the modulation of CATB levels in HIV-1 infected MDM exposed to cocaine in vitro and in vivo. Graphical Abstract ᅟ.

Tolerance to cocaine's effects following chronic administration of a dose without detected effects on response rate or pause

To observe tolerance to drug effects on operant behavior, the dose that researchers have often selected for chronic administration is one that disrupts, but does not abolish, responding. Some evidence suggests that tolerance may develop after chronic administration of relatively smaller doses. The purpose of the present experiment was to assess systematically effects of chronic administration of a dose without detected effect on responding. Specifically, response rates and post-reinforcement pauses of five pigeons key pecking under a three-component multiple fixed-ratio schedule of food reinforcement were observed under chronic cocaine administration. We evaluated the effects of a range of doses (1.0 mg/kg to 17.0  mg/kg) during acute administration. The largest dose that failed to alter responding acutely then was administered chronically (1.0  mg/kg for 1 pigeon, 3.0  mg/kg for 3 pigeons, and 5.6  mg/kg for 1 pigeon). After 30 consecutive sessions of chronic administration, smaller and larger doses occasionally were substituted for the chronic dose. Pigeons then received pre-session saline administration for 30 consecutive sessions, and the post-chronic effects of the series of doses on responding were determined. All subjects developed tolerance to doses of cocaine that initially had caused large decreases in rate, with the magnitude of the effects varying across components of the multiple schedule and subjects. Specifically, tolerance generally was greatest in the components with smaller ratios. Following post-chronic saline administration, tolerance was usually diminished. Overall, the results demonstrate that under these conditions, repeated experience with disruptive effects of cocaine on food-maintained responding is not a necessary factor in the development of tolerance.

Response topography in behavioral tolerance to cocaine with rats

Research conducted with rats has shown tolerance to the behavioral effects of psychomotor stimulants to be contingent on chronic drug administration occurring before the experimental session. Recent experiments with pigeons, however, resulted in tolerance when drug administration followed the experimental session. We hypothesized that the apparent species differences in tolerance may be a function of different operantly conditioned response topographies used in these experiments. Specifically, we propose that operantly reinforced consummatory responses, like pecking with pigeons, are less likely to reveal contingent tolerance. This experiment involved rats in a manner that paralleled earlier experiments with pigeons. Rats were subjected to daily sessions that required 20 licking responses to obtain 2.5-s access to water. Acute effects of cocaine were determined by administering precession doses ranging from 1.0 to 30.0 mg/kg, with dosing occurring every fifth day. Rats were then divided into two groups. One group received 17.0 mg/kg cocaine before the session and the other received 17.0 mg/kg cocaine after the session. After 30 daily sessions, the effects of the cocaine-dose range were reassessed. Tolerance to the rate-decreasing effects of cocaine was evident in both the groups, regardless of the temporal relationship between drug administration and the experimental session. The results support the hypothesis that operantly reinforced consummatory responses are less likely to show contingent tolerance.

Environmental and pharmacological factors in the development of noncontingent tolerance to cocaine in pigeons

Previous research with rats and monkeys has shown that tolerance to behavioral effects of cocaine developed if the drug was administered before behavioral test sessions but not if it was administered after sessions, a finding known as contingent tolerance. In contrast, a recent experiment using pigeons found that they showed tolerance resulting from postsession drug administration (noncontingent tolerance). The 4 experiments reported in this article were conducted to examine that result more fully. Experiment 1 found that immediate presession administration of cocaine to pigeons reliably led to tolerance to effects on food-reinforced operant key pecking and that immediate postsession administration of cocaine also led to tolerance in half the subjects, those whose key pecking was not suppressed by postsession dosing. Experiment 2 showed that eating in the home cage under the effects of postsession cocaine was not necessary for tolerance to develop to effects of postsession cocaine and that the majority of subjects developed tolerance from postsession cocaine administration. Experiment 3 found that mere drug exposure in the home cage without exposure to an experimental session did not reliably produce tolerance during the behavioral session. Experiment 4 showed that tolerance from postsession cocaine administration could be observed even when daily dosing was discontinued during dose-response curve assessment. Therefore, the combined results showed that pigeons often developed tolerance to effects of cocaine during the behavioral session when cocaine was administered postsession and that this tolerance was not the result of feeding under effects of the drug.

Expression of c-fos mRNA in the basal ganglia associated with contingent tolerance to amphetamine-induced hypophagia

Tolerance to the hypophagic effect of psychostimulants is contingent on having access to food while intoxicated. Rats given chronic injections of such drugs with access to food learn to suppress stereotyped movements, which interfere with feeding. In contrast, controls given the drug after food access do not learn to suppress stereotypy and, therefore, do not become tolerant. To determine the role of the basal ganglia in this phenomenon, we used in situ hybridization to measure the expression of c-fos mRNA, a marker for neural activation, in the brains of tolerant and nontolerant rats. Rats given chronic amphetamine injections prior to food access learned to suppress stereotyped movements, whereas yoked controls given the drug after feeding did not. Following an acute injection of amphetamine, both of these groups had higher levels of c-fos mRNA than saline-treated controls throughout the striatum, in the nucleus accumbens core, the ventral pallidum and layers V-VI of the motor cortex. In contrast, tolerant rats, which had learned to suppress stereotypy, had higher levels of c-fos mRNA than both amphetamine- and saline-treated controls in the entopeduncular nucleus, globus pallidus, subthalamic nucleus, pedunculopontine nucleus, nucleus accumbens shell, olfactory tubercle, somatosensory cortex, and layers II-IV of motor cortex. These data suggest that the learned suppression of amphetamine-induced stereotypy involves the activation of dorsal striatal pathways previously implicated in response selection as well as the ventral striatum, long implicated in appetitive motivation and reinforcement.

Role of instrumental learning in tolerance to cathinone hypophagia

The effects of dl-cathinone on milk intake and motor activity were investigated in bottle- and cannula-fed rats. Acute injections of cathinone produced dose-dependent increases in activity in both groups but only produced decreased intake in bottle-fed rats. With chronic injections, tolerance to the suppression of intake developed in the bottle-fed group, accompanied by decreased activity. After the tolerance phase, switching from bottle to cannula feeding produced further increases in intake, whereas switching from cannula to bottle feeding produced decreased intakes. These results suggest that (a) cathinone suppresses intake by inducing locomotion and stereotypy, which interfere with the appetitive phase of feeding, and (b) tolerance to drug-induced hypophagia involves learning to suppress such movements, as proposed by the instrumental learning model.

Repeated post- or presession cocaine administration: roles of dose and fixed-ratio schedule

Effects of repeated administration of cocaine to animals behaving under operant contingencies have depended on when the drug is given. Moderate doses given presession have generally led to a decrease in the drug's effect, an outcome usually referred to as tolerance. When these same doses have been given after sessions, the usual result has been no change or an increase in the drug's effects, with the latter usually referred to as sensitization. In the present study, repeated postsession administration of a relatively small dose of cocaine (3.0 or 5.6 mg/kg) to pigeons responding under a multiple fixed-ratio 5, fixed-ratio 100 schedule of food presentation generally resulted in tolerance to the rate-decreasing effects of the drug. When the same dose was given before sessions, little additional tolerance was observed, although some subjects showed further tolerance in the small-ratio component. A regimen of repeated postsession injection of larger (10.0-23.0 mg/kg) doses suppressed key pecking during the session; responding resumed following discontinuation of postsession administrations. Effects of postsession administration of cocaine, therefore, depended on the dose, with smaller doses leading to tolerance and larger ones to suppression of behavior during the session. Effects of postsession drug administration of either small or large doses were not related to whether effects of postsession drug were experienced mainly in the operant test chamber or in the pigeon's home cage. The results with large postsession doses are compatible with a view that the drug acted as a Pavlovian unconditional stimulus, with the session-related stimuli acting as a long-duration Pavlovian conditional stimulus. Tolerance following postsession administration of the smaller doses challenges the view that it depended on experiencing the drug's effects while the arranged reinforcement contingencies were in effect.

Tolerance to amphetamine hypophagia: a real-time depiction of learning to suppress stereotyped movements in the rat

To analyze how tolerance develops to amphetamine-induced hypophagia, the authors recorded real-time licking responses in rats given chronic injections of the drug and access to milk for 30 min. Initially, licking was greatly reduced and occurred only late in the session. The acquisition of tolerance was characterized by a decrease in the latency to initiate licking, a gradual increase in the number of licks, and a reorganization of the temporal licking pattern such that licks were distributed throughout the session, interspersed with pauses. On post-tolerance dose-response tests, licking was directly proportional to drug dose in some rats. The results support the view that tolerance to amphetamine hypophagia involves a behavioral adaptation to the motor effects of the drug.

Tolerance to the effects of cocaine on performance under behavior-correlated reinforcement magnitude

Four pigeons responded under a fixed-interval 8-min schedule of food delivery in which the amount of food delivered at the end of each interval depended on performance during the interval (i.e., a correlated schedule). Specifically, duration of access to grain was contingent upon the number of responses made during the first 4 min of the interval. This differential outcome did not affect response rates or patterning relative to performance under a simple fixed-interval 8-min schedule. Behavior under the correlated schedule was then investigated under doses of cocaine ranging from 0.3 to 10.0 mg/kg. A bitonic dose-response function was obtained for response rates and the time with head in the food hopper, whereas dose-dependent decreases were observed in the mathematical index of curvature (Fry, Kelleher, & Cook, 1960). The dose that produced the greatest increase in the head-in-hopper time was then administered prior to each session. Following repeated administration of cocaine, disruptions in response patterning were attenuated for all 4 pigeons; tolerance was also observed to the rate-increasing effects and increased head-in-hopper time for 2 pigeons after chronic cocaine administration. Tolerance therefore developed despite the fact that the initial effect of cocaine was to increase the amount of food obtained.

A comparison of fixed and variable doses of cocaine in producing and augmenting tolerance to its effects on schedule-controlled behavior

Twelve pigeons were trained to peck a key under a fixed-ratio 20-response schedule of food presentation. Acute effects of cocaine (03-10.0 mg/kg), determined by administering the drug once per week, revealed dose-dependent decreases in frequency of key pecking. The pigeons were then divided into six pairs, matched with respect to acute dose-response curves. One of each pair received one of five different doses before each daily session (variable-dosing condition) and the other received a fixed dose equal to the arithmetic average of the doses experienced by its pair mate (fixed-dosing condition). Following 50 days of exposure, subjects in the variable-dosing condition were then switched to the fixed-dosing condition. Dose-response functions were then determined in both groups by substituting doses for the fixed daily dose, once per week. Rate-decreasing effects were attenuated similarly in both groups of subjects, both at the end of the variable-dosing regimen and during subsequent fixed dosing. Next, an attempt was made to increase the degree of tolerance. Specifically, pigeons in the variable-dosing condition were exposed repeatedly to a range of doses in which the largest dose was 1/8 to 1/4 log unit larger than in the original variable-dosing phase. Pigeons in the fixed-dosing group were exposed daily to the largest dose that did not eliminate key pecking by the end of the initial repeated-dosing regimen. Dose effects were determined after at least 35 days of exposure. If the dose-response function had shifted to the right, the largest dose for the variable-dosing subjects was increased by 1/8 to 1/4 log unit and the smallest dose in the sequence was eliminated, and another period of variable dosing commenced. For the fixed-dosing subjects, if the curve had shifted to the right, the fixed dose was increased by 1/8 to 1/4 log unit and the process repeated. Only very modest shifts of the dose-response function to the right were observed, and in several cases curves shifted left after exposure to larger doses. Overall the results suggest that a variable-dosing regimen holds promise as a technique for investigating the development of tolerance to the effects of cocaine, and that the magnitude of tolerance cannot be increased to any great degree by increasing the dose or doses repeatedly experienced. Additionally, it appears that experience with relatively large doses of cocaine may limit the degree to which tolerance can be developed, or decrease the magnitude of tolerance previously observed.

Tolerance and sensitization to the behavioral effects of cocaine in rats: relationship to benzodiazepine receptors

Tolerance and sensitization to the behavioral effects of cocaine were investigated in rats responding under a fixed-consecutive-number eight schedule of food reinforcement. The development of tolerance or sensitization was induced by delivering the drug either immediately before or after each behavioral session during chronic administration. Chronic cocaine administered before each session resulted in tolerance, as indicated by the shift to the right in the cocaine dose response curve. This tolerance was more likely to develop in the presence of an external discriminative stimulus. On the other hand, when cocaine was delivered after each session, the injections did not disrupt responding and sensitization or increased sensitivity rather than tolerance developed. This sensitization was more likely to occur when the external discriminative stimulus was not present. These data suggest that either tolerance or sensitization to the behavioral effects of cocaine can occur following the same number of chronic injections, with the effect dependent on the context under which the drug is delivered. Significant differences in benzodiazepine receptor binding measured autoradiographically using [3H]flumazenil were observed between rats that received cocaine before or after each session, suggesting that the development of tolerance and sensitization may be mediated through changes in benzodiazepine receptors in discrete brain regions.

Alteration of cataleptic responses induced by dopamine receptor antagonists after chronic cocaine administration in mice

The influence of chronic treatment of mice with cocaine, an indirect dopamine receptor agonist, on the cataleptic effects of R-(+)-chloro-2,3,4,5-tetrahydro-3-methyl-5-phenyl-1H-3-benzazepin- 7ol hydrochloride (SCH23390), a dopamine D1 receptor antagonist, or haloperidol, mainly a dopamine D2 receptor antagonist, was investigated. Mice were given cocaine (10 mg/kg s.c.) once every other day for 7 (4 injections), 15 (8 injections) or 21 (11 injections) days. The cataleptic effects of SCH23390 (0.3 mg/kg i.p.) were significantly reduced when it was given 1-7 days after the last dose of a 7- or 15-day pretreatment course of cocaine. When SCH23390 was given 14-21 days after the cocaine the cataleptic effect was increased in the 15-day, but not the 7-day, cocaine-pretreated mice. However, after a 21-day treatment with cocaine, a challenge dose of SCH 23390 given 1-3 days thereafter produced a decreased cataleptic response, but an increased response after 7-21 days. The cataleptic effects of haloperidol (o.3 mg/kg i.p.) were reduced when it was given 1-7 days after the last dose of a 7-day pretreatment, but increased 1-3 days after that of a 15-day pretreatment with cocaine (10 mg/kg s.c.) The pretreatment with cocaine for 21 days did not affect the haloperidol catalepsy during a 1- to 3-day withdrawal period. However, haloperidol catalepsy was decreased only 7 days, then reversed 14 days and gradually increased 21 days after the last injection of a 15- or 21-day pretreatment course of cocaine. These results suggest that chronic treatment with the indirect dopamine receptor agonist, cocaine, caused supersensitivity of dopamine D1 receptors (a decrease in SCH23390 catalepsy) during the early withdrawal period and subsensitivity (an increase in SCH23390 catalepsy) after a longer period of withdrawal. It was apparent that the longer the period and the higher the dose of pretreatment with cocaine, the less were the alterations in initial responses and the greater were the alterations in subsequent responses to the dopamine D1 receptor antagonists.