Fetal brain damage in the rat following prenatal exposure to cocaine

The aim of this study was to identify fetal brain damage induced by 1) prenatal cocaine exposure or 2) physical procedures causing temporary constriction or occlusion of the uterine vessels in pregnant rats. Brains were examined from rat fetuses killed 48 hours after the dam was given one or more intraperitoneal doses of cocaine (50–70 mg/kg) on day 16 of gestation. Only brains from fetuses with hemorrhage in the extremities were examined, as this indicated they had undergone a circulatory disturbance. Four of the 10 brains examined showed bilateral necrosis and cavitation in the cerebral cortex. There were also hemorrhage and ectopic outgrowths in the corpus striatum, bilateral cavitation in the brainstem and vacuolization in the lens of the eye. A similar type and distribution of damage was seen in rat fetal brains from dams treated by temporary occlusion of the uterine vessels or direct handling of the pregnant uterus on day 16 of gestation and examined 48 hours later. It is proposed that the procedures act through the common mechanism of constriction/occlusion of the uterine vessels. The damage to the fetuses appears to be due to hemorrhage from the fetal vessels and ischemia. These findings are discussed in relation to cocaine use during human pregnancy.     

Cocaine binding sites in fetal rat brain: implications for prenatal cocaine action

Binding of [³H]cocaine to membrane preparations from whole fetal rat brain was studied. High-affinity binding (10 nM cocaine) was detected as early as gestational day (GD) 15 and steadily increased across subsequent development. Saturation studies comparing [³H]cocaine binding at GD20 and adulthood yielded similar K_D values, and LIGAND analyses favored a two-site model if an extended range of [³H]cocaine concentrations was used. Various monoamine uptake inhibitors displaced labeled cocaine with potencies consistent with the idea that [³H]cocaine labels the dopamine (DA), serotonin (5-HT), and possibly also the norepinephrine (NE) transporters in whole fetal brain preparations. Synaptosomal DA uptake was well developed by GD20, as was the potency of cocaine to inhibit such uptake. The results indicate that functional, monoamine transporter related cocaine binding sites are present in the fetal rat brain. Such sites are likely to play an important role in mediating the direct interactions of prenatally-administered cocaine with developing monoaminergic systems in both animals and humans.Some of these data were published in preliminary form in: Meyer JS (1992) Prenatal neurochemistry of cocaine. Ann NY Acad Sci 654:487–488     

Morphine tolerance and dependence in noradrenaline neurones of the rat cerebral cortex

Summary By subcutaneous implantation of 2 or 13 morphine pellets (75 mg morphine/pellet), rats were made tolerant to, and dependent on narcotic analgesics. Occipital cortex slices from dependent animals and placebo-implanted controls were incubated with (-)-³H-noradrenaline and subsequently superfused with physiological salt solution. The accumulation of ³H-noradrenaline was not changed by pretreatment with 2, but was slightly decreased by pretreatment with 13 morphine pellets. The overflow of tritium evoked by electrical field stimulation was higher in slices from morphine-implanted rats than in those from placebo controls. Morphine and levorphanol, added in vitro, inhibited the stimulation-induced overflow of tritium at, similar concentrations and to a similar degree in slices from morphine-and placebo-pretreated animals. —It is concluded that, during chronic treatment with morphine, an adaptation takes place in the brain to compensate for the acute effect of narcotic analgesics, i.e. inhibition of the release of noradrenaline by nerve impulses. The chain of events from the drug-receptor interaction to the depression of the release process can be excluded as substrate of this adaptation. During with-drawal, the compensatory changes provoke an enhanced increase of extracellular noradrenaline during nerve impulses.     

The effect of ketamine upon norepinephrine and dopamine levels in rabbit brain parts

Summary Ketamine (40 mg/kg, i.v.) significantly increased dopamine levels in the thalamus and hypothalamus brain areas, but not in the midbrain or caudate nucleus. The increase in dopamine occurred during the time when ketamine produced its maximal anesthetic action (10–30 min). Ketamine had no effect upon norepinephrine levels in whole brain or the select brain parts with the exception of caudate nucleus at any of the times studied. These results demonstrate an effect of ketamine upon dopamine levels in those brain regions previously suggested as the site of ketamine's anesthetic action.     

Cocaine-like effect of ketamine on vascular adrenergic neurones

The influence of ketamine on adrenergic and cholinergic responses was studied in the rabbit pulmonary artery in vitro. Ketamine and cocaine potentiated smooth muscle contractions elicited by nonadrenaline, adrenaline and transmural electrical stimulation of adrenergic neurone terminals. Arterial contractions elicited by tyramine were enhanced by ketamine, while cocaine blocked them. Ketamine moved the concentration-response curve of carbachol slightly to the right. Nicotine-induced contractions were blocked by ketamine and cocaine. The adrenergic neurone blocking effect of bretylium and dimethylphenylpiperazinium on the response to transmural stimulation was prevented by ketamine. The uptake of ³H-noradrenaline by rabbit isolated aorta was inhibited by ketamine and cocaine. It is concluded that ketamine inhibits the membrane amine pump in the terminals of postganglionic adrenergic neurones in a cocaine-like manner.     

Alpha-receptor-mediated modulation of transmitter release from central noradrenergic neurones

Summary Slices of rat cerebral cortex were preincubated with 10^–7 M (-)-³H-noradrenaline, and the outflow of tritium was determined. Oxymetazoline, phentolamine and cocaine did not change the spontaneous efflux. The overflow of tritium evoked by electrical field stimulation was decreased by oxymetazoline, and enhanced by phentolamine, phenoxybenzamine, and cocaine. Oxymetazoline did not counteract the increase of the stimulation-induced overflow caused by cocaine, but strongly antagonized the increase caused by phentolamine and phenoxybenzamine. When the stimulation-induced overflow was large under control conditions (high frequency of stimulation, addition of cocaine), the inhibitory effect of oxymetazoline was diminished. The results indicate that an -receptor-mediated feed-back control of noradrenaline release, previously demonstrated in postganglionic sympathetic nerves, also operates in central noradrenergic neurones.     

Influence of morphine and naloxone on the release of noradrenaline from rat brain cortex slices

Summary In slices of rat brain cortex preincubated with (–)-³H-noradrenaline, the influence of morphine and naloxone on the efflux of tritium was investigated. The spontaneous outflow of tritium was not changed by 10^–7–10^–5 M morphine and by 10^–6–10^–4 M naloxone, but was accelerated by 10^–4 M morphine. Electrical field stimulation augmented tritium outflow. The overflow evoked per ppulse decreased as the frequency of stimulation was increased from 0.3 to 3 Hz, but remained approximately constant when it was further increased to 10 Hz. At frequencies of 0.3, 1, and 3 Hz, but not at 10 Hz, morphine in concentrations of 10^–7–10^–5 M depressed the stimulation-induced overflow of tritium. 10^–4 M morphine did not influence the overflow induced by stimulation at 0.3 and 1 Hz and increased that evoked by stimulation at 10 Hz. Naloxone (10^–6–10^–4 M) did not change the response to stimulation. In the presence of 10^–4 M naloxone, 10^–6 M morphine did not diminish, and 10^–5 M morphine even enhanced the stimulation-induced overflow of tritium. The inhibitory effect of 10^–6 M morphine was not reduced, after tyrosine hydroxylase had been blocked by -methyltyrosine-methylester. It is concluded that morphine through an action on specific opiate receptors inhibits the release of transmitter from cerebrocortical noradrenergic neurones evoked by nerve impulses. By an action unrelated to opiate receptors, morphine at high concentrations increases the stimulation-induced overflow of noradrenaline, presumably by inhibiting its re-uptake into nerve endings.     

Effect of cocaine and pentylenetetrazol on cortical kindling

The effect of drug-induced convulsions on subsequent cortical kindling was studied in male Long-Evans rats. Animals experienced three intravenous infusions of physiological saline at 3 day intervals, or three convulsions induced by the infusion of cocaine or pentylenetetrazol (PTZ). Beginning eight days after the last infusion, all animals were kindled by stimulation of the anterior neocortex (area 6). PTZ-induced convulsions facilitated the development of both the behavioral convulsion and the electrographic seizure during cortical kindling, while cocaine-induced convulsions facilitated only the development of the electrographic seizure. Comparison of these results with previous research indicates that convulsions induced by these two drugs have long-lasting effects on brain function which differ both in their anatomical distribution and in the nature of the effects produced. These drugs also differed in their acute effects at subconvulsant doses on the expression of cortically kindled seizures. Cocaine (and lidocaine, another local anesthetic) substantially elevated afterdischarge (AD) threshold and inhibited the focal component of the cortically kindled seizure. PTZ had no significant effect on either of these variables but significantly increased AD duration. In addition to these drug effects, a substantial inhibitory effect on seizure expression was observed, both during kindling and afterwards, when ADs were elicited daily but not when they were separated by 3 days or more. This finding suggests that the large number of ADs typically required for cortical kindling may be due in part to daily stimulation.     

Phencyclidine increases the affinity of dihydropyridine calcium channel antagonist binding in rat brain

Summary Phencyclidine (PCP) significantly reduces the apparent dissociation constant (K _D) of the dihydropyridine (DHP) calcium channel antagonist, [³H]nitrendipine, in synaptosomal membranes of rat and mouse brain without significantly effecting the maximum binding capacity (B _max). At an optimum concentration of PCP (10 M) the apparentK _D of [³H]nitrendipine was reduced from 178±9 pM to 112±9 pM in rat forebrain, a 58% increase in affinity. The structural derivatives of PCP, P-Br-PCP {1-[1-(4-bromophenyl-cyclohexyl)piperidine]}, m-NH₂-PCP {1-[1-(3-anilo)-cyclohexyl]piperidine}, (±)-PCMP [1-(1-phenyl)-cyclohexyl-3-methylpiperidine] also increased the apparent affinity of [³H]nitrendipine in the following order, p-Br-PCP PCMp>PCP>m-NH₂-PCP. Local anesthetics either reduced the apparent affinity of [³H]nitrendipine or had no effect. Kinetic analysis revealed that PCP both increased the microassociation rate constant and decreased the microdissociation rate contant of [³H]nitrendipine. The magnitude of this enhanced binding varied with the brain region studied; the greatest increase in apparent affinity of [³H]nitrendipine was observed in striatum, while no significant increase in affinity was observed in brainstem. In some brain areas, PCP was more effective in reducing theK _D in crude homogenates than in washed tissue. PCP (10 M) did not alter theK _D of [³H]nitrendipine to rat cardiac tissue. Both Ca²⁺ and Mg²⁺ inhibited the effect of PCP, while monovalent ions were ineffective in this regard. These data are consistent with an allosteric modulation of DHP calcium channel antagonist binding sites by PCP and structural derivatives that is not mediated through the brain PCP binding site. This modulation of DHP binding sites may account for some of the psychopharmacologic actions PCP and related compounds in vivo.     

Effects of cocaine microinjections into the nucleus accumbens and medial prefrontal cortex on schedule-induced behaviour: comparison with systemic cocaine administration

The effects of cocaine HCl infusions into either the nucleus accumbens (NACC) or medial prefrontal cortex (PFC) were compared on the performance of schedule-induced polydipsia (SIP) and related behaviours. Food-deprived rats were exposed to a fixed-time 60-s schedule of food delivery in daily 30-min sessions until stable levels of behaviour were obtained (14 days). Rats were then bilaterally infused with cocaine into either the NACC or PFC via chronically indwelling guide cannulae. Each subject received a sequence of five cocaine infusions (0, 12.5, 25, 50, 100 µg) according to a Latin Square design. For comparison, following these intracranial infusions each rat received a sequence of five IP injections of cocaine (0, 2.5, 5, 10, 20 mg/kg) also in a counterbalanced order. NACC and PFC infusions of cocaine and IP cocaine dose-dependently reduced SIP. Cocaine infusions into the NACC, but not the PFC, increased locomotor activity but the characteristic temporal profile of locomotor activity during SIP was retained. IP cocaine also increased locomotor activity in a dose-dependent manner, but the temporal profile of activity was flattened following 20 mg/kg cocaine. NACC and PFC infusions of cocaine had little effect on the total number of panel presses to gain access to the food pellets, but did slightly decrease the high rates of responding immediately prior to the pellet delivery. IP cocaine increased the total number of panel presses at the higher doses, mainly by increasing the low rates of responding. The effects of cocaine infusions into the PFC were behaviourally the most selective, as they reduced SIP without having substantial effects either on locomotor activity or panel pressing. These data therefore implicate a role for the PFC in the performance of SIP.     

Prenatal cocaine exposure: effects on locomotor activity in rat offspring

This study examines the developmental effects of prenatal exposure to cocaine in the rat, evaluated during the first month of life through open-field behavior. The offspring of Wistar dams that received 60 mg/kg of cocaine, from gestational day 8 to 22, were examined in the open-field during the second, third and fourth weeks of postnatal life in three consecutive 15-min daily sessions, starting on postnatal day (PND) 14, (PND 14–16), PND 21 (PND 21–23) and PND 28 (PND 28–30). Results show that prenatal exposure to cocaine increased total activity and rearing behavior on PND 22 and PND 29. Also, on PND 14, cocaine-exposed animals reared significantly more than control rats. There were no significant differences in the frequency of center and peripheral ambulation, nor in the defecation rate. The present results evidence alterations in the emotional behavior of rats prenatally exposed to cocaine. The delayed onset of exploration in the open-field observed in cocaine-exposed animals suggests that they take more time to become habituated to a novel and open environment.     

Effects of phencyclidine and ketamine on punished and unpunished responding by pigeons

Pigeons responded under a multiple fixed-interval fchedule of food presentation in which responding in one component was suppressed by presentation of electric shock (punishment). High doses of pentobarbital, ketamine and phencyclidine produced decreases inn rates of unpunished responding. At least two doses of each drug produced mean rates of punished responding greater than 200% of control rates. All three drugs disrupted normal patterning of both unpunished and punished fixed-interval responding. These results demonstrate that phencyclidine and ketamine have activity qualitatively similar to that of pentobarbital on schedule-controlled responding suppressed by electric shock presentation.     

Cocaine-like discriminative stimulus effects of novel cocaine and 3-phenyltropane analogs in the rat

RATIONALE: Cocaine dependence is a major health concern and there are no effective pharmacotherapies currently available. Although cocaine is an indirect DA agonist that binds to all three monoamine transporters, there is much evidence implicating a greater role for the dopamine (DAT) than norepinephrine (NET) and serotonin (SERT) transporters in the behavioral effects of cocaine. As such, several groups have developed compounds that exhibit high affinity and selectivity for the DAT. OBJECTIVE: The present investigation examined the cocaine-like discriminative stimulus effects in rats of novel cocaine analogs (RTI 12, 13, 15) and 3-phenyltropane analogs (RTI 111, 112, 113, 114, 117 120, 121, 123, 134 and 152) of which several exhibit high affinity (e.g., <7 nM) and selectivity for the DAT. RESULTS: During dose-effect testing all drugs produced 75-100% cocaine-lever responding. Analyses indicated that the potency of the compounds to produce cocaine-like discriminative stimulus effects was correlated with their affinity for the DAT and the NET but not SERT. Due to the extremely large concentrations (e.g., 10,000-31,024 nM) needed to occupy the NET in vitro, it is doubtful if the doses administered had meaningful NET activity. The selectivity at the DAT, relative to the other transporters, was not indicative of the potency with which these drugs substituted for cocaine. CONCLUSIONS: The cocaine-like discriminative stimulus of the RTI compounds tested appear to be mediated by the DAT, however the extent to which the NET is involved remains unclear. Additionally, several of the RTI compounds had properties consistent with those thought desirable in a pharmacotherapeutic for cocaine dependence.     

Cortical and hippocampal EEG power spectra in animal models of schizophrenia produced with methamphetamine, cocaine, and phencyclidine

Cortical and hippocampal EEGs in animal models of schizophrenia were compared to those obtained with psychotomimetics or antipsychotic agents by utilizing power spectral analysis. Models of positive schizophrenic symptoms were created with methamphetamine (MAP) and cocaine, and a model of both negative and positive symptoms was created with PCP. MAP caused a prolonged decrease in the cortical EEG power spectra, cocaine caused a marked decrease for a short time, and PCP produced no significant changes. In the hippocampal spectra, MAP induced a marked increase in the T2(6.0–7.9 Hz)/ T1(4.0–5.9 Hz) ratio, PCP caused a decrease of this ratio after an initial increase, and cocaine produced no significant change. (An increase in the T2/T1 ratio represents a shift of theta waves to higher frequencies.) Since apomorphine (a DA agonist) and MK-801 (an NMDA antagonist) caused the T2/T1 ratio to increase, positive schizophrenic symptoms caused by MAP may be related to the DA and NMDA systems. 3-PPP (a σ agonist) caused biphasic changes similar to those induced by PCP. Haloperidol and chlorpromazine caused a decrease of the T2/T1 ratio. These results indicate that cortical and hippocampal EEG power spectra (especially the hippocampal T2/T1 ratio) can be used to characterize both qualitatively and quantitatively models of schizophrenia. Received: 21 October 1996/Final version: 2 January 1997     

Effect of desipramine on rat cortex slices incubated with 3H-dopamine

Rat cortex slices were incubated with ³H-dopamine (³H-DA), and the effect of desipramine (DMI) was studied on the accumulation of ³H-DA and ³H-noradrenaline (³H-NA) in the tissue and the concentrations of ³H-DA and ³H-NA in the incubation medium. This effect was compared with the effect of cocaine, reserpine and FLA 63 studied by the same technique, in order to elucidate the mechanisms of action of DMI.All the drugs induced a significant decrease of ³H-NA accumulation in the cortical tissue. The ³H-DA retention varied: cocaine and reserpine caused a significant decrease, FLA 63 a marked, significant increase, and DMI a slight, but significant increase. In the incubation medium, ³H-DA significantly increased after DMI, cocaine and reserpine, and remained unchanged after FLA 63. In all experiments ³H-NA in the medium was very low.It is suggested that DMI in cortex slices may exert a double mechanism of action on the final step in the noradrenaline biosynthesis: 1. an inhibition of the ³H-DA uptake at the level of the noradrenergic cell membrane, and 2. an inhibition of the intraneuronal transport of ³H-DA to sites where it is converted to ³H-NA, concomitant with an increased intraneuronal ³H-DA accumulation. Other possibilities are discussed.     

Patterns of functional activity associated with cocaine self-administration in the rat change over time

Rationale Although imaging studies in human addicts have been valuable for identifying the neural substrates of the effects of abused drugs, few studies have used this approach in animal models where conditions can be carefully controlled.Objective To define the substrates that mediate the effects of cocaine in a rodent model of cocaine self-administration using the 2-[¹⁴C]deoxyglucose method and to assess changes in these patterns over the course of drug exposure.Methods Male Sprague-Dawley rats self-administered cocaine (0.75 mg/kg per injection; FR2; 21 injections/session) and control rats received saline infusions in the same pattern as the cocaine rats for 5 or 30 days. Metabolic mapping was applied immediately after the final session.Results Following 5 days of self-administration, rates of glucose utilization were decreased in the nucleus accumbens, and increased in autonomic brainstem structures and in sensorimotor regions. After 30 days of cocaine exposure, self-administration reduced glucose utilization throughout the dorsal and ventral striatum, central nucleus of the amygdala, medial forebrain bundle, and infralimbic and prelimbic prefrontal cortices. In addition, at this time point glucose utilization was no longer elevated in any autonomic or sensorimotor brain regions.Conclusions These data demonstrate that the distribution of functional activity associated with self-administered cocaine undergoes considerable change over the course of drug exposure. While increases in metabolic rates were largely found in autonomic and sensorimotor structures after short-term cocaine access, decreases were prominent in mesocorticolimbic regions after prolonged exposure. These differences in the patterns of brain activity that develop with long-term cocaine self-administration may play a role in the transition to habitual drug seeking behavior.     

Fetal and maternal brain and plasma levels of cocaine and benzoylecgonine following chronic subcutaneous administration of cocaine during gestation in rats

The distribution of cocaine and the cocaine metabolite benzoylecgonine (BE) in brain and plasma of Sprague-Dawley rat dams and their near-term fetuses was assessed 0.5 and 2 h post-injection on gestational day 20 following chronic daily subcutaneous injections of 10, 20, or 40 mg/kg/3 ml cocaine hydrochloride beginning on gestational day 8. Plasma concentrations of cocaine reached in the dams were found to be in the range of, or to exceed, those reported in human cocaine users. Dose-related increases in plasma and brain levels of cocaine in the dams and the fetuses were observed, particularly at 2 h post-injection. Fetal concentrations of cocaine in brain and plasma were approximately 2–3-fold less than those of the dams, suggesting that the placenta may somewhat restrict cocaine entry into fetal circulation. Brain/plasma cocaine ratios, however, were generally equivalent in the dams and fetuses, suggesting that once cocaine enters the circulation, its affinity for brain tissue is similar in the fetus and dam. Whereas plasma levels of BE, like cocaine levels per se, were greater in the dams than fetuses, BE concentrations in fetal brain were greater than those observed in maternal brain. These high levels of BE may contribute to the production of neurobehavioral alterations in cocaine-exposed offspring, given that this active cocaine metabolite has been shown to form molecular complexes with calcium ions (Misra and Mule 1975), thereby having the potential to influence a multiplicity of calcium-regulated developmental events. Taken together, the results of the present study suggest that the subcutaneous route may prove to be an appropriate means in rats for administering cocaine prenatally in investigations designed to assess potential neurobehavioral ramifications of gestational cocaine exposure.     

Parametric determinants in pre-stimulus modification of acoustic startle: interaction with ketamine

Prepulse inhibition of the acoustic startle response is a form of reflex modification known to be sensitive to drugs and to subtle procedural manipulations. The present study examined the importance of prepulse length and prepulse-pulse interval in the expression of prepulse inhibition and its modification by the noncompetitive N-methyl-d-aspartate antagonist, ketamine. In contrast to a previous report, ketamine disrupted prepulse inhibition at doses of 5.6 and 10 mg/kg when its short time course was taken into consideration. In a second experiment, the amount of prepulse inhibition was found to be directly related to prepulse length, with prepulse inhibition produced by shorter prepulse durations slightly more sensitive to disruption by ketamine. A third experiment examined prepulse-pulse time intervals (30–2000 ms). While prepulse inhibition produced by prepulses occurring 60–500 ms before the startle stimulus was disrupted by 10 mg/kg of ketamine, prepulses preceding the startle stimulus by only 30 ms produced either no effect or slight prepulse facilitation under control conditions, and significant prepulse facilitation when ketamine was administered. A fourth experiment examined the time course of prestimulus modification by continuous lead stimuli, ranging in onset from 15 to 75 ms before the startle stimulus. Prepulse facilitation, when observed, tended to occur in earlier portions of the session and was enhanced by ketamine. These results suggest that prestimulus modification of the startle reflex has important parametric and experiential determinants that may influence the effects of drugs. Some of these temporal determinants may have relevance to sensorimotor function in schizophrenia.     

Phencyclidine: Effects on motor activity and brain biogenic amines in the guinea pig

Previous reports suggesting that the behavioral response of the guinea pig to phencyclidine (PCP) administration is more similar to the effects of PCP observed in higher animals than those observed in mice and rats prompted us to investigate the effects of PCP on spontaneous motor activity and brain biogenic amine levels in the guinea pig. Doses of 2.5 and 5.0 mg/kg PCP were found to significantly elevate spontaneous motor activity; however, 7.5 mg/kg PCP produced highly variable results which were not significantly different from control. The concentrations of tryptophan, serotonin, 5-hydroxyindoleacetic acid, and norepinephrine were measured in the forebrain and hindbrain of previously drug naive animals 30min after administration of 5 mg/kg PCP. As compared to saline injected control animals, PCP was observed to have no effect on any of the neurochemical determinants measured. Contrary to previous reports, these data suggest that PCP produces behavioral effects in the guinea pig which are not unlike those observed in mice and rats. Furthermore, the effects which we report on spontaneous motor activity are not related to changes in the regional concentration of any of the neurochemical variables which were measured.