Altered behaviour in adult mice exposed to a single low dose of DDT and its fatty acid conjugate as neonates

DDT, 1,1,1-trichloro-2,2-bis(p-chlorophenyl)-ethane is one of the best-known insecticides which produces neurotoxic syndrome in mammals. DDT is also a world-wide environmental contaminant which is still used in several countries. We have previously reported on pronounced retention of DDT in the neonatal mouse brain. We have also observed that DDT and a DDT metabolite, DDOH, conjugated to palmitic acid (DDOH-PA), which have been found in DDT-treated female rats, affect the muscarinic cholinergic receptors in the brain of the neonatal mouse. We now report that neonatal exposure to a single low oral dose of DDT and DDOH-PA (1.4 mumol/kg b.wt.) also can lead to a permanent hyperactive condition in the mice as adults.

Behavioral effects after intrathecal administration of cholinergic receptor agonists in the rat

Behavioral effects of nicotine and cytisine, and the cholinesterase inhibitors physostigmine and 9-amino-1,2,3,4-tetrahydroacridine (THA), administered intrathecally (IT) at the lumbar level in the rat have been evaluated. Antinociceptive dose relationships were established using the tail immersion test. Total activity, locomotion and rearing were also measured in computerized test boxes. The nicotinic receptor antagonist, mecamylamine, and the muscarinic receptor antagonist, atropine, were used to study the selectivity of the effects. Physostigmine and THA significantly decreased total activity, locomotion and rearing as compared to control animals. The motor effects of physostigmine were completely antagonized only partly. Mecamylamine had no antagonistic effect. Nicotine did not affect any activity parameter. Cytisin reduced total activity and locomotion 1-6 min after dose. IT physostigmine, 15 micrograms, increased tail immersion latency for 30 min. No significant increase in response latency in this test was observed after the IT administration of nicotine or THA, whereas cytisine elicited a small increase. The IT administration of THA, nicotine and cytisine was also associated with gnawing, vocalization and hyperactivity and in the case of THA, diarrhoea. These effects were blocked by mecamylamine. Physostigmine antinociception as well as the behavioral effects including total activity, locomotion and rearing caused by physostigmine and by THA are most probably due to an action on spinal muscarinic receptors. Nicotinic receptors do not seem to be involved in spinal antinociception. Some aversive behavioral effects caused by the IT administration of nicotinic receptor agonists could, however, be attenuated by the spinal administration of the antagonist mecamylamine, which may indicate the involvement of nicotinic receptors in afferent sensory transmission.

Adaptive changes in alpha-2 adrenoceptor mediated responses: analgesia, hypothermia and hypoactivity

The acute effects of the alpha-2 adrenoceptor agonists, clonidine and guanfacine, upon antinociception, hypothermia and motor activity were compared under conditions of receptor antagonism, denervation, and chronic administration of a tricyclic antidepressant compound. The analgesic actions of clonidine and guanfacine were antagonised by idazoxan, an alpha-2 receptor antagonist, but potentiated by pretreatment with the noradrenaline neurotoxin DSP4, and attenuated by chronic treatment with desipramine (DMI). Clonidine- and guanfacine-induced hypothermia was antagonised by idazoxan, potentiated by prior treatment with DSP4 and attenuated by chronic administration with DMI. Both clonidine and guanfacine produced decreases in motor activity that were attenuated by idazoxan but unaffected by prior DSP-4 treatment. Chronic DMI administration also attenuated clonidine-induced hypoactivity but potentiated guanfacine-induced hypoactivity. These diverse results describe both similar and differential adaptive mechanisms modulating the functional effect of alpha-2 receptor systems in the central nervous system.

Selective lesion of central dopamine or noradrenaline neuron systems in the neonatal rat: motor behavior and monoamine alterations at adult stage

Different parameters of motor behavior (locomotion, rearing and total activity counts) were studied in the adult rat following neonatal intracisternal 6-hydroxydopamine (6-OHDA, 50 micrograms) treatment combined with noradrenaline (NA) uptake blocker (desipramine) or dopamine (DA) uptake blockers (amfolenic acid or GBR 12909) to obtain selective DA or NA lesions respectively. At 61-65 days of age, selective DA-lesioned animals showed an initial decrease in spontaneous motor behavior at test days 1 and/or 2, while at test days 4 and 5 hyperactivity was observed. However, following amfolenic acid or GBR 12909 pretreatment leading to a selective NA lesion, no difference in spontaneous motor behavior was seen on any of the 5 test days. Determination of regional brain levels of NA and DA confirmed the type of lesion predicted from the various pretreatments with selective uptake blockers. These data suggest that changes in motor behavior in the adult rats, following neonatal 6-OHDA treatment, are specifically related to a DA-denervation, whereas an NA lesion does not seem to influence the spontaneous motor behavior. However, following the selective DA lesion, significant increases of serotonin levels in striatum and cerebellum were observed, while following selective NA lesions an increase of cerebellar NA levels was found concomitant with drastic reductions of NA levels in frontal cortex and spinal cord.

Ultrasound detection of axillary lymph node metastases in breast cancer

Presence or absence of lymph node metastases is the most accurate prognostic indicator in breast cancer. Clinical examination is unreliable in detecting involved nodes. Preoperative ultrasound scan of the axilla has been performed in 140 consecutive women with breast cancer. The sensitivity for involved nodes was 66% which was significantly higher than clinical examination (42%) (P = less than 0.01). However ultrasound gave more false positives than clinical examination and thus no overall improvement in prognostic information was achieved.

Behavior of mother rats in conflict tests sensitive to antianxiety agents

Previous studies of freezing and open-field activity have demonstrated that lactating rats are less fearful or less anxious than nonpregnant ones. The purpose of this investigation was to observe the behavior of mother rats in conflict tests, which are frequently used in studies on the neurobiology of anxiety. In the punished drinking test, in which licking from a water spout is punished by electric shocks, mothers (observed on Day 1 postpartum following 24 hr of water deprivation) were found to drink more than virgins. Mothers (Day 1 postpartum) also consumed more food than controls in an unfamiliar open field. In contrast, no difference between mothers (Day 5 postpartum) and virgins was present in the exploration of an electrified shock probe. The largest maternal anticonflict effects in the drinking and feeding tests were recorded when the females were tested with their pups. Increased punished drinking was also observed in virgin rats treated with the anxiolytic benzodiazepine midazolam. Water-deprived virgins and mothers did not differ in the shock titration test, a result suggesting that diminished pain reactivity was unlikely to account for the increased punished drinking in mothers. Moreover, females in late pregnancy, which are hypoalgesic (Gintzler, 1980), did not lick more than virgins in the punished drinking test. Following 24 hr of water deprivation, unpunished drinking was higher in lactating females than in virgins, so the increased acceptance of punishment by mothers might have been due to their being more thirsty than virgins.(ABSTRACT TRUNCATED AT 250 WORDS)

Behavior of mother rats in conflict tests sensitive to antianxiety agents

Previous studies of freezing and open-field activity have demonstrated that lactating rats are less fearful or less anxious than nonpregnant ones. The purpose of this investigation was to observe the behavior of mother rats in conflict tests, which are frequently used in studies on the neurobiology of anxiety. In the punished drinking test, in which licking from a water spout is punished by electric shocks, mothers (observed on Day 1 postpartum following 24 hr of water deprivation) were found to drink more than virgins. Mothers (Day 1 postpartum) also consumed more food than controls in an unfamiliar open field. In contrast, no difference between mothers (Day 5 postpartum) and virgins was present in the exploration of an electrified shock probe. The largest maternal anticonflict effects in the drinking and feeding tests were recorded when the females were tested with their pups. Increased punished drinking was also observed in virgin rats treated with the anxiolytic benzodiazepine midazolam. Water-deprived virgins and mothers did not differ in the shock titration test, a result suggesting that diminished pain reactivity was unlikely to account for the increased punished drinking in mothers. Moreover, females in late pregnancy, which are hypoalgesic (Gintzler, 1980), did not lick more than virgins in the punished drinking test. Following 24 hr of water deprivation, unpunished drinking was higher in lactating females than in virgins, so the increased acceptance of punishment by mothers might have been due to their being more thirsty than virgins.(ABSTRACT TRUNCATED AT 250 WORDS)

Behaviour in rats maintained by low differential reinforcement rate: effects of delta 1-tetrahydrocannabinol, cannabinol and cannabidiol, alone and in combination

Rats were trained to respond according to a low rate differential reinforcement (DRL) 72 sec schedule of operant behaviour. The animals were then tested with delta 1-tetrahydrocannabinol (delta 1-THC), cannabinol, and cannabidiol alone and in combination. Tests with single doses of delta 1-THC (dose-range: 0.3-5.6 mg/kg) and cannabinol (dose-range: 1-56 mg/kg) but not cannabidiol (dose-range 3-100 mg/kg), yielded a dose-related biphasic effect on the response rate. Small doses of delta 1-THC and cannabinol increased the rate of responding, large doses of these agents decreased it. Cannabidiol alone only decreased the rate of responding (occurring at large doses). The rate of reinforcement generally was decreased when response rates increased and vice versa. Cannabidiol (10 and 30 kg/kg), together with delta 1-THC (1 and 3 mg/kg), decreased the response output and increased the rate of reinforcement. Similar results were observed with combinations of cannabinol (10 and 30 mg/kg) and cannabidiol (10 and 30 mg/kg). Combinations of delta 1-THC (0.3 and 1 mg/kg) and cannabinol (1 and 3 mg/kg) also reduced the response rate and there were no significant changes in the rate of reinforcement. Hence the actions of delta 1-THC and cannabinol on behaviour in rats maintained by low rate differential reinforcement were similar (approximate difference in potency 1:10), whereas no stimulation of response rate was demonstrated with cannabidiol. Vehicle and day of testing (Tuesday or Friday) variables were found not to affect the results.

Effects of d-amphetamine and methylphenidate on hyperactivity produced by neonatal 6-hydroxydopamine treatment

Neonatal intracisternal administration of 6-hydroxydopamine (6-OHDA, 50 micrograms on day 1 after birth) caused a marked hyperactivity when the rats were tested as adults. These rats also showed severe DA depletions in striatum and nucleus accumbens. Pretreatment with the noradrenaline (NA) uptake inhibitor desipramine provided protection against NA depletion in frontal cortex and nucleus accumbens. Pretreatment with DA uptake inhibitors, amfolenic acid or GBR 12909, before 6-OHDA, provided full protection against DA depletion but produced marked NA depletion in frontal cortex. These rats did not demonstrate any degree of hyperactivity. Low doses of d-amphetamine (0.25 mg/kg SC) or methylphenidate (1 mg/kg SC) reversed the hyperactivity in DA-depleted rats but increased motor activity in vehicle-treated and NA-depleted rats. Higher doses of d-amphetamine (1 mg/kg) or methylphenidate (4 mg/kg) produced potentiated levels of locomotion but attenuated levels of rearing in DA-depleted animals. The results further suggest the utility of the neonatal DA lesion in rats as a potential animal model for derivation of therapeutic agents that may be efficacious in the treatment of the hyperkinetic syndrome.

Serotonin and depression: old problems and new data

1. Several lines of evidence implicating some dysfunction or alteration to brain serotonergic systems in depressive states are summarized. 2. Some aspects of the interactions between the 5-HT and catecholamine pathways in the action of antidepressant drugs are examined. 3. Finally, the important role of NA modulation of serotonergic activity in the action of antidepressants is suggested.

Noradrenergic and serotonergic involvement in brief shock-induced analgesia in rats

Four experiments were performed to investigate the effects of different techniques causing noradrenergic and serotonergic depletions in the brain and spinal cord on brief shock-induced analgesia. Newborn pups were administered N-2-choloroethyl-N-ethyl-2-bromobenzylamine systemically (2 x 50 mg/kg, ip) and 6-hydroxydopamine administered either systemically (100 micrograms/g, sc) or directly (8 micrograms in 1 microliter, bilaterally) into the locus coeruleus region, or intrathecally (20 micrograms in 10 microliter) into the lumbar subarachnoidal space, caused notable and consistent attenuations of the analgesia caused by brief shock. These treatments reduced noradrenaline concentrations in the spinal cord drastically. A potentiation of brief shock-induced analgesia was caused by the administration of p-chlorophenyl-alanine, whereas administration of 5,7-dihydroxytryptamine, into the nucleus raphe magnus or intrathecally into the subarachnoidal space, produced attenuation of the analgesic effect. Biochemical analyses revealed marked 5-hydroxytryptamine depletions in the spinal cord. The present findings are discussed with regard to the role of spinal noradrenaline and 5-hydroxytryptamine involvement in brief shock-induced analgesia and in reactions to stressful events.

Acquisition and reversal of taste/tactile discrimination after forebrain noradrenaline depletion

Two experiments were performed to assess the role of noradrenaline (NA) on the acquisition of an aversively motivated discrimination task and its reversal. A conditioned taste aversion procedure was used. The NA depletions were achieved through two different pharmacological means: systemic N-2-chloroethyl-N-ethyl-2-bromo-benzylamine (DSP4) and destruction of the dorsal noradrenergic bundle (DNAB) with 6-hydroxydopamine. Both procedures caused marked reductions of NA in the frontal cortex and hippocampus. In neither of the studies (Experiment 1, DSP4, and in Experiment 2, DNAB) were there any significant changes between controls and NA-depleted rats in either the rate of acquisition of the original discrimination (Phase 1) or the subsequent reversal (Phase 2). This occurred irrespective of which of the two stimuli (a taste cue, i.e., saccharin presented in bottles with nozzles that do not have ball bearings, "silent bottles," or a tongue-tactile cue, i.e., water in bottles with nozzles that had ball bearings "noisy bottles") initially was used as the conditioned stimulus (CS1, i.e., the stimulus first followed by contingent administration of lithium chloride, and later, in Phase 2, followed by saline injections). Thus NA does not appear to be critically involved in the acquisition and reversal of a taste/tactile discrimination task. The significance of forebrain NA for other discrimination tasks is discussed.

Prenatal methylazoxymethanol treatment potentiates d-amphetamine- and methylphenidate-induced motor activity in male and female rats

The effects of the stimulant drugs, d-amphetamine and methylphenidate, upon the motor activity of male and female off-spring of pregnant rats, treated on gestation day 15 with the antimitotic agent methylazoxymethanol (MAM, 25 mg/kg) were studied in four experiments. Cortical and striatal hypoplasia induced by prenatal administration of MAM resulted in increased concentrations of catecholamines in those regions. Administration of d-amphetamine and methylphenidate caused significant increases in motor activity; this effect was markedly potentiated in the MAM-treated rats, both the male and female off-spring. Thus, the locomotion and total activity parameters showed similar, but not identical, drastic increases in behaviour induced by the stimulant drugs as a result of the prenatal MAM treatment whereas for the rearing parameter a lesser potentiation by the MAM treatment was observed. This potentiation of the excitatory effects of the stimulant compounds upon the behavioural parameters is interpreted in terms of a relative increase in the density of catecholaminergic terminals in the forebrain regions of the central nervous system. The present results are discussed with regard to the utility of prenatal MAM treatment as a possible animal model for certain neurological disorders.

Norepinephrine-stimulated inositol phospholipid breakdown in the rat cerebral cortex following serotoninergic lesion

Norepinephrine (NE)-stimulated inositol phospholipid hydrolysis ("PI breakdown") in rat cerebral cortical miniprisms was used as a measure of alpha 1-adrenoceptor function following serotonin and/or NE depletion. The use of ascorbic acid to prevent autooxidation of the NE during the PI breakdown assay was found to be warranted. Treatment of rats with 5,7-dihydroxytryptamine and DSP4 produced selective depletions of serotonin (79-95%) and NE (69-85%), respectively, in cortical and hippocampal brain regions. The degree of cortical NE-stimulated PI breakdown in the lesioned animals was not significantly different from that in the control animals, suggesting that under the conditions used, serotonin and NE depletion do not lead to a changed sensitivity of alpha 1-adrenoceptors coupled to PI breakdown in the rat cortex.

Neonatal 6-hydroxydopamine-induced dopamine depletions: motor activity and performance in maze learning

Three experiments were performed to study the effect of dopamine (DA) depletions, induced by neonatal intracerebroventricular (ICV) treatment with 6-hydroxydopamine (6-OHDA), upon measures of spontaneous motor activity. Instrumental learning for food reward in an Olton radial arm maze and escape learning from a large, circular water maze were studied also. Motor activity was measured by direct observation of rats in a modified radial arm maze and by use of automated test cages equipped with photocell devices. 6-OHDA-treated rats demonstrated considerable and long-lasting locomotor (ambulation) activity and total activity increases. 6-OHDA-treated rats showed notably less rearing activity than the vehicle-treated rats during the initial 20 min of each 60-min test period. However, over the second half of these 60-min test periods, the 6-OHDA-treated rats demonstrated significantly more rearing activity than the vehicle-treated rats. In the acquisition of the running response, to obtain the 8 food pellets placed in each of the 8 arms of the radial arm maze, 6-OHDA rats showed a retarded acquisition, as measured by the latency and number of arms visited to acquire all eight pellets. 6-OHDA-treated rats failed completely to acquire the Morris-type swim maze task by which they were required to locate a platform just under the water surface in a circular water tank. The neurochemical assays indicated severe DA depletion in several forebrain regions. The present findings add to existing indications of the potential of this DA depletion condition as an animal model of the minimal brain dysfunction syndrome.

Hyperactivity and instrumental learning deficits in methylazoxymethanol-treated rat offspring

Several changes of spontaneous motor and learned behaviours were obtained in the male offspring of pregnant rats that were treated on gestation day 15 with the antimitotic agent methylazoxymethanol (MAM, 25 mg/kg). MAM-treated offspring, when tested at adult ages, showed notable increases in motor activity parameters as measured by direct observation or in automated photocell test cages. This hyperactive state was accompanied by clear impairments by MAM offspring in the acquisition of instrumental learning in a radial arm maze and in a circular swim maze. In Skinner boxes, MAM offspring made fewer responses during the Fixed Ratio (FR) 1 schedule but did not differ from the saline offspring in the acquisition of the difficult differential-reinforcement-of-low-rates (DRL) 72 sec task. Neurochemical assays indicated that the MAM rats had elevated noradrenaline and dopamine levels in several brain regions. These findings are discussed with regard to possible alterations of habituation processes in MAM rats.

Galanin impairs acquisition but not retrieval of spatial memory in rats studied in the Morris swim maze

The effect of intraventricular administration of the neuropeptide galanin on acquisition and retrieval in a modified Morris swim maze was studied in rats. Galanin induced a significant deficit in the acquisition of the task while no effects on the retrieval were observed. No deficits were seen 24 h after the last treatment. Galanin did not increase the number of failures to reach the platform. It is suggested that endogenous galanin modulates learning possibly via the galanin-containing cholinergic neurons in the septum-basal forebrain area projecting to the hippocampus and cortex.

Intrathecal noradrenaline restores 5-methoxy-N,N-dimethyltryptamine induced antinociception abolished by intrathecal 6-hydroxydopamine

Intrathecal administration of 6-hydroxydopamine (6-OHDA) abolished the antinociceptive effects of acute administration of 5-methoxy-N,N-dimethyltryptamine (5-MeODMT, 1 mg/kg, s.c.) in the hot-plate, tail-flick and shock titration tests of nociception. The antinociceptive effects of 5-MeODMT, abolished by the prior intrathecal 6-OHDA treatment, were restored by intrathecal administration (2 or 1 microgram) of noradrenaline (NA), immediately prior to 5-MeODMT, in all three tests of nociception. Biochemical analysis confirmed severe NA depletions (95 percent loss) in the lumbar and thoracic regions of the spinal and much lesser dopamine depletions (25-35 percent loss). Intrathecal 5,7-dihydroxytryptamine (5,7-DHT) attenuated 5-MeODMT induced antinociception in the tail-flick test and combined NA + 5-MeODMT induced antinociception in the hot-plate and tail-flick tests. Intrathecal administration of 5,7-DHT caused a severe depletion of 5-hydroxytryptamine in the lumbar region of the spinal cord. The present findings demonstrate further the modulatory role of NA upon serotonergic systems in nociception and indicate the necessity of NA availability for induction of 5-MeODMT analgesia.

Evidence for crosstolerance to the analgesic effects between morphine and selective alpha 2-adrenoceptor agonists

Rats were injected subcutaneously (s.c.) with morphine (5 mg/kg) until tolerance developed to its antinociceptive action, or with 0.9% saline which was used as vehicle for morphine. Subsequently, both groups of animals were given an intrathecal (i.th.) dose of either noradrenaline (2 micrograms), clonidine (12.5 micrograms) or guanfacine (12.5 micrograms), that had been found previously to be reliably antinociceptive. In the saline-treated animals, these doses of noradrenaline, clonidine or guanfacine induced clear antinociceptive effects, but not in the morphine-group. It is therefore concluded that cross-tolerance to the antinociceptive effects of systemic morphine and the alpha-adrenoceptor agonists was obtained. The cross-tolerance between morphine on one hand, and noradrenaline, clonidine and guanfacine on the other, implies that a substantial opiate-adrenoceptor interaction exists in antinociceptive processes.

Acquisition and reversal of taste/tactile discrimination after forebrain noradrenaline depletion

Two experiments were performed to assess the role of noradrenaline (NA) on the acquisition of an aversively motivated discrimination task and its reversal. A conditioned taste aversion procedure was used. The NA depletions were achieved through two different pharmacological means: systemic N-2-chloroethyl-N-ethyl-2-bromo-benzylamine (DSP4) and destruction of the dorsal noradrenergic bundle (DNAB) with 6-hydroxydopamine. Both procedures caused marked reductions of NA in the frontal cortex and hippocampus. In neither of the studies (Experiment 1, DSP4, and in Experiment 2, DNAB) were there any significant changes between controls and NA-depleted rats in either the rate of acquisition of the original discrimination (Phase 1) or the subsequent reversal (Phase 2). This occurred irrespective of which of the two stimuli (a taste cue, i.e., saccharin presented in bottles with nozzles that do not have ball bearings, "silent bottles," or a tongue-tactile cue, i.e., water in bottles with nozzles that had ball bearings "noisy bottles") initially was used as the conditioned stimulus (CS1, i.e., the stimulus first followed by contingent administration of lithium chloride, and later, in Phase 2, followed by saline injections). Thus NA does not appear to be critically involved in the acquisition and reversal of a taste/tactile discrimination task. The significance of forebrain NA for other discrimination tasks is discussed.

Comparison of desipramine, amitriptyline, zimeldine and alaproclate in six animal models used to investigate antidepressant drugs

In the present paper the acute actions primarily of the tricyclic antidepressants amitriptyline and desipramine, the atypical antidepressant zimeldine and the potential antidepressant alaproclate were evaluated in six models used for studying antidepressant agents. These included the forced swim test, a modified learned helplessness procedure, the clonidine hypothermia test, the social dominance test (using the interaction with clonidine), a differential-reinforcement-of-low-rates (DRL-72s) schedule and conditioned avoidance response. The results showed desipramine to be effective in all the tests employed. Zimeldine was effective in the learned helplessness, DRL-72s and domination tests, but also caused notable deficits in two-way active avoidance response. Alaproclate was effective in all the tests except the domination paradigm. Amitriptyline was effective in all tests employed. The results are discussed in relation to the possible mechanism of action of these compounds in the test models employed.

Some aspects of stress and depression

1. The role of stress in depressive illness is discussed together with utility of the "learned helplessness" model and some neuropharmacological correlates of uncontrollable shock. 2. Similarities and differences between chronic antidepressant treatment and chronic stress treatment regimes are reviewed. 3. Finally the role of adaptive process in stress on antidepressant treatments is discussed.

Noradrenergic and serotonergic involvement in brief shock-induced analgesia in rats

Four experiments were performed to investigate the effects of different techniques causing noradrenergic and serotonergic depletions in the brain and spinal cord on brief shock-induced analgesia. Newborn pups were administered N-2-choloroethyl-N-ethyl-2-bromobenzylamine systemically (2 x 50 mg/kg, ip) and 6-hydroxydopamine administered either systemically (100 micrograms/g, sc) or directly (8 micrograms in 1 microliter, bilaterally) into the locus coeruleus region, or intrathecally (20 micrograms in 10 microliter) into the lumbar subarachnoidal space, caused notable and consistent attenuations of the analgesia caused by brief shock. These treatments reduced noradrenaline concentrations in the spinal cord drastically. A potentiation of brief shock-induced analgesia was caused by the administration of p-chlorophenyl-alanine, whereas administration of 5,7-dihydroxytryptamine, into the nucleus raphe magnus or intrathecally into the subarachnoidal space, produced attenuation of the analgesic effect. Biochemical analyses revealed marked 5-hydroxytryptamine depletions in the spinal cord. The present findings are discussed with regard to the role of spinal noradrenaline and 5-hydroxytryptamine involvement in brief shock-induced analgesia and in reactions to stressful events.

Impaired performance of rats in the Morris swim-maize test late in abstinence following long-term sodium barbital treatment

Rats were tested for place learning in the Morris swim maze on days 110-114 of abstinence following 48 weeks of treatment with sodium barbital. A retarded acquisition of the swim-maze task, that could not be ascribed to motor impairments, was found in the barbital-treated rats. There was a significant difference in brain weight, but there were no significant differences between the control and barbital-treated rats in the frontal cortical concentrations of noradrenaline (NA), dopamine (DA), 5-hydroxytryptamine (5-HT) and 5-hydroxyindoleacetic acid (5-HIAA), nor in the intra- and extrasynaptosomal activities of cerebral cortical monoamine oxidase towards NA and 5-HT. Postsynaptically, neither the cerebral cortical inositol phospholipid breakdown responses to carbachol and NA (mediated by muscarinic and alpha 1-adrenergic receptors, respectively), nor the striatal and cortical densities of muscarinic receptors labelled by [3H]quinuclidinyl benzilate [( 3H]QNB) were found significantly to be altered in the barbital-treated rats. A strong correlation between the density of striatal and cortical [3H]QNB binding sites was seen for the barbital-treated (r = 0.91) but not for the control (r = -0.05) rats. It is suggested that the deficit in performance of the barbital-treated rats in the Morris maze may be related to a cholinergic dysfunction.

Lack of effects of prenatal exposure to lidocaine on development of behavior in rats

The objective of this investigation was to study the effects of lidocaine upon postnatal development of the rat. Lidocaine, 6 mg/kg (21 mumol/kg), was given to a group of 12 rats. Injections were administered intramuscularly, bilaterally in the masseter muscles, once a day on days 10 and 11 of pregnancy. Twelve control rats were given physiologic saline. Clinical signs, mortality, body weight, and food consumption were recorded during pregnancy and lactation. The duration of gestation was also recorded. The development of the offspring was monitored by tests of spontaneous activity, nociception, learning ability, and physical development. No clinical signs of adverse reactions were seen in any of the groups. In the majority of the learning ability tests, the control and lidocaine-treated groups showed similar results. However, in the schedule of differential reinforcement of low rates of responding (DRL 20), the lidocaine-exposed males received more reinforcements than the controls and made fewer responses. In the tests of nociception, a significant difference between sexes was recorded, in that the females were more sensitive than the males in the shock-titration test. Physical development, as monitored by swimming ability and spontaneous activity, showed no inter-group difference. The present results indicate that prenatal exposure to lidocaine fails to result in postnatal impairment of the development of behavioral performance of a wide range of tasks.

Increased antinociception by alpha-adrenoceptor drugs after spinal cord noradrenaline depletion

Animals depleted of the bulbospinal NA fiber tracts have been reported to be supersensitive to antinociceptive effects of intrathecally administered noradrenaline (NA) in vivo. In the present investigation, the antinociceptive effects were determined after systemic or intrathecal injections of noradrenergic agents. NA and the selective alpha 2-adrenoceptor agonists guanfacine and clonidine were used. NA depletion was performed by treatment neonatally with 6-hydroxydopamine (6-OHDA), or in adult animals by intrathecal 6-OHDA administration or systemic N-2-chloroethyl-N-ethyl-2-bromobenzylamine hydrochloride (DSP4). The neurotoxins were found to cause a severe depletion of spinal NA without affecting dopamine (DA) or 5-hydroxytryptamine (5-HT) levels. The antinociceptive effects of intrathecal injection of NA, clonidine and guanfacine were more strongly enhanced in the depleted than in the control rats. It was also found that clonidine and guanfacine given systemically had a stronger effect in depleted than in control animals. In conclusion, depletion of descending NA pathways induces functional supersensitivity both to intrathecally administered NA and to the selective alpha 2-adrenoceptor agonists clonidine and guanfacine. It was also found that systemically administered clonidine and guanfacine had a stronger effect in NA-depleted than in control animals.

Antinociceptive effects and spinal cord tissue concentrations after intrathecal injection of guanfacine or clonidine into rats

In the present study, the antinociceptive effects of intrathecal injections of the alpha 2-adrenoceptor agonists clonidine and guanfacine in rats was determined to establish their dose-response curves. Spinal cord tissue concentrations were also determined in a separate group of animals. Guanfacine was found to be more potent than clonidine and had a considerably longer duration of action. Thus, whereas the analgesic effect of clonidine declined to baseline by 4 hr after injecting doses of up to 50 micrograms, guanfacine still showed a considerable effect 18 hr after injecting both 25 and 50 micrograms. With both compounds, concentration gradients existed within the spinal cord. In the experiments with guanfacine, the region in the spinal cord tissue with the highest concentrations 10 min after injection contained around 30 pmol/mg wet weight. At 3 hr, this figure was around 20 pmol/mg. With clonidine, on the other hand, the concentration decreased from the maximal level of 200 pmol/mg at 10 min to 10 pmol/mg at 3 hr. On all occasions, except 10 min after injecting clonidine, it was found that the maximal tissue concentrations for both drugs remained below the cervical spinal cord, i.e., the rostral spread was less than expected, especially with drugs with such a long duration of action. The present investigation demonstrates analgesic effects of both clonidine and guanfacine after intrathecal administration, with guanfacine proving more potent and longer acting; the difference in duration of action is probably attributable to differences in rates of elimination of the drugs from spinal cord tissue.

Chronic treatment with antidepressant drugs and ECT differentially modifies the hypothermic action of clonidine and guanfacine

The hypothermia inducing action of clonidine and guanfacine was abolished by yohimbine and idazoxan pretreatment which suggests an alpha 2-adrenoceptor involvement in this effect. The effects of acute and chronic treatment with the antidepressant drugs desipramine (DMI), amitriptyline (AMI), maprotiline (MAP), mianserin (MIAN), iprindol (IPR), alaproclate (ALA) and electroconvulsive treatment (ECT) on the hypothermic action of the alpha 2-adrenoceptor agonists clonidine and guanfacine were studied. Acute administration of MIAN potentiated clonidine induced hypothermia whereas acute MIAN, IPR and ALA potentiated guanfacine induced hypothermia. Repetitive DMI, AMI and MAP treatment attenuated clonidine-induced hypothermia whereas guanfacine-induced hypothermia was potentiated by chronic treatment with DMI, AMI, MAP and MIAN, ECT applied without anaesthesia attenuated both clonidine and guanfacine hypothermia, however, under ethyl ether anaesthesia ECT was effective only towards guanfacine hypothermia. This discrepancy is discussed in terms of the relative selectivity of the agonists used, the reliability of agonist studies for indexing receptor function, and possible pharmacokinetic interaction.

(+)-8-OH-DPAT and 5-MeODMT induced analgesia is antagonised by noradrenaline depletion

In experiments with both rats and mice the 5-HT agonists 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and 5-methoxy-N,N-dimethyl-tryptamine (5-MeODMT) were shown to produce reliable analgesic effects after acute administration (1 mg/kg SC) in the tail-flick, hot-plate and shock-titration tests of nociception. Prior treatment with the noradrenaline neurotoxin, N-2-chloroethyl-N-ethyl-2-bromobenzylamine (DSP4), systemically administered to both rats and mice abolished the analgesic effects of both the 5-HT agonist compounds in all the tests of nociception used. Intrathecal 6-hydroxydopamine (6-OHDA) treatment also abolished the analgesic effects of 8-OH-DPAT and 5-MeODMT; in the tail-flick test the analgesia induced by 8-OH-DPAT was reversed to an hyperalgesia. Biochemical analyses confirmed notable noradrenaline depletions in the spinal cord. It is concluded that an important interaction between presynaptic noradrenergic terminals and serotonergic receptor sites, possibly 5-HT1A, mediates spinal nociception processes.

5-Hydroxytryptamine antagonists and the 5-methoxy-N,N-dimethyltryptamine-induced changes of postdecapitation convulsions

The ability of various compounds to antagonise the 5-MeODMT induced prolongations of latency and duration of postdecapitation convulsions (PDCs) were compared. The 5-hydroxytryptamine (5-HT) receptor antagonists, mianserin, methergoline, cinanserin and methysergide antagonised the 5-MeODMT (0.5 to 4.0 mg/kg) induced prolongations of latency to onset of convulsions substantially and to a lesser extent the prolongation of duration. The efficacy of the 5-HT antagonists for blocking 5-MeODMT changes of PDCs was roughly of the order mianserin greater than cinanserin greater than methysergide greater than methergoline. Pirenperone, the 5-HT2 antagonist, and pimozide, the dopamine receptor antagonist did not antagonise the 5-MeODMT induced changes. Mianserin, methergoline, cinanserin and methysergide, by themselves, prolonged the duration of PDCs but did not affect latency. Pirenperone (0.25 mg/kg) prolonged both the latency and duration of the PDCs while pimozide (0.5-2.0 mg/kg) had no effect upon PDCs. This evidence suggests that 5-MeODMT induced changes of PDCs are mediated via 5-HT1 receptors and thus a reliable model to combine with other measures of spinal function is suggested.

Selective attention and place navigation in rats treated prenatally with methylazoxymethanol

Prenatal treatment of rats on gestation day 15 with methylazoxymethanol (MAM) caused forebrain microencephaly. The behavioral analyses included measures of spontaneous motor activity and tests for cognitive deficits, and were performed when the rats had reached adult age. Female MAM-treated rats failed to demonstrate contextual control of latent inhibition, which confirms earlier findings with male rats. Male MAM-treated rats demonstrated a notable impairment of place navigation in a swim-maze, but showed as strong sensory preconditioning as the control animals. Biochemical analyses indicated considerable increases in catecholamine levels in the cerebral cortex, hippocampus and striatum. The cognitive deficits, characterised by the various conditioning (taste-aversion) and instrumental learning (swim-maze) tasks, suggested that the MAM rats are deficient in their capacity to attend selectively to the relevant stimulus in complex arrangements of the stimulus situation.

Selective lesioning of forebrain noradrenaline neurons at birth abolishes the improved maze learning performance induced by rearing in complex environment

The effect of selective destruction of forebrain noradrenaline (NA) neurons induced by 6-hydroxydopamine (6-OHDA) at Day 1 after birth on Hebb-Williams maze performance was investigated in adult rats housed after weaning in a complex environment (EC) or an isolated (IC) environment for 35 days. Saline treated control rats raised in the EC made fewer errors than those raised in the IC. This effect of EC was completely abolished in 6-OHDA treated rats; for these animals no improved performance due to the housing condition was obtained. Protection of the NA neurons against 6-OHDA neurotoxicity by pretreatment with desipramine (DMI) resulted in an effect of EC identical to that seen in saline-treated controls. Postweaning housing in the IC led to an increased locomotion as compared to housing in EC, but this effect was not affected by neonatal 6-OHDA and/or DMI treatment. Neurochemical analysis confirmed cortical NA and metabolite depletion as well as a good protection by the DMI pretreatment. The present results indicate that central NA neurons are involved critically in mediating mainly the cognitive components of behavioral alterations induced by EC.

Noradrenaline and sensory preconditioning in the rat

Two experiments were performed to investigate the effect of noradrenaline (NA) depletion following systemic administration of the neurotoxin N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4; 50 mg/kg, ip) on sensory preconditioning in the rat. For sensory preconditioning, a taste (saccharin, CS2) and a special type of drinking bottle (noisy bottle) were paired during Phase 1. During Phase 2, the noisy bottle (CS1) was paired with lithium chloride, and, finally, during Phase 3 the aversion to saccharin (CS2) was tested for in saccharin preference tests. The DSP4 treatment disrupted rats' ability to form sensory preconditioning, and this effect could not be explained on the basis of enhanced neophobia, stimulus generalization, or a deficit in first-order conditioning in DSP4-treated rats. These findings are closely related to these and other issues of associative learning such as contextual control of latent inhibition and extinction. The evidence from the present data suggests that NA-depleted rats fail to form associations between the CS1 and CS2 during sensory preconditioning and, as such, are consistent with other data from various compound conditioning experiments on the functional role of NA in learning and memory.

5-Methoxy-N,N-dimethyltryptamine-induced analgesia is blocked by alpha-adrenoceptor antagonists in rats

The effects of the alpha-adrenoceptor antagonists prazosin, phentolamine and yohimbine upon 5-methoxy-N,N-dimethyltryptamine (5-MeODMT)-induced analgesia were tested in the hot-plate, tail-flick and shock-titration tests of nociception with rats. Intrathecally injected yohimbine and phentolamine blocked or attenuated the analgesia produced by systemic administration of 5-MeODMT in all three nociceptive tests. Intrathecally administered prazosin attenuated the analgesic effects of 5-MeODMT in the hot-plate and tail-flick tests, but not in the shock titration test. Intrathecal yohimbine showed a dose-related lowering of pain thresholds in saline and 5-MeODMT-treated animals. Phentolamine and prazosin produced normal dose-related curves in the hot-plate test and biphasic effects in the shock titration and tail-flick tests. These results demonstrate a functional interaction between alpha 2-adrenoceptors and 5-HT agonist-induced analgesia at a spinal level in rats.

Noradrenaline and the context-dependent extinction effect

Three experiments were performed to examine the effects of noradrenaline (NA) depletion upon the context-dependent extinction effects in conditioned taste-aversion learning. Three different methods were used to deplete NA: lesions of the dorsal noradrenergic bundle (DNAB) with 6-hydroxydopamine (6-OHDA), lesions induced by neonatal treatment with 6-OHDA and lesions induced by systemic administration with the NA neurotoxin, N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4). In each experiment, novel saccharin was presented in novel noisy bottle followed by lithium chloride. Later, during the extinction phase, half the control and half the NA depleted rats received saccharin in noisy bottles while the other half received saccharin in silent bottles. In the control condition, the rats that received saccharin in the noisy bottles (same context as conditioning) showed considerably more aversion than those that received saccharin in the silent bottles (different context to conditioning); NA depletion attenuated this effect. Reinstatement of the conditioning context (noisy bottle) resulted in a stronger aversion in the case where the different context (silent bottle) was present during extinction; this effect was attenuated in the NA depletion condition. These findings maintain a role for noradrenaline in compound conditioning tasks.

5-HT agonist induced analgesia modulated by central but not peripheral noradrenaline depletion in rats

The antinociceptive effect elicited by the 5-hydroxytryptamine (5-HT) agonist 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) was reversed or blocked in animals which had previously sustained severe spinal noradrenaline (NA) depletion via either systemic N-2-chlorethyl-N-ethyl-2-bromobenzylamine hydrochloride (DSP 4), neonatal 6-hydroxydopamine (neon. 6-OHDA), or intrathecal 6-OHDA treatment. Biochemical analysis of the lumbar spinal cord samples confirmed severe central NA depletions. Animals were tested with nondamaging heat pain (tail-flick test, hot-plate test) and electric footshock titration to determine the amount of antinociception or nociception. Peripheral NA depletion following intravenous (i.v.) 6-OHDA injection to adult rats had no effect on the antinociception induced by 5-MeODMT, but did cause severe NA depletions in the left heart atrium. These results suggest a modulatory effect of central and not peripheral noradrenergic system upon 5-HT agonist induced analgesia, and also give evidence that this effect is spinally mediated.

The inhibition of the cage-leaving response--a model for studies of the serotonergic neurotransmission in the rat

It was observed that rats that had been given drugs that enhance serotonergic neurotransmission, e.g. the serotonin releasing compounds p-chloroamphetamine (PCA) and fenfluramine, the MAO-A inhibitors and serotonin releasing agents amiflamine and alpha-ethyltryptamine and the serotonin agonists 5-methoxy-N, N-dimethyltryptamine (5-MeODMT), 8-hydroxy-2-(di-n-propylamino) tetraline (8-OH-DPAT), m-chlorophenyl piperazine (m-CPP) and 5-methoxy-3 (1,2,3,6-tetrahydropyridin-4-yl)1H-indole (RU 24969), did not leave their home-cages when the grid-covers were removed in contrast to normal rats who almost immediately left the cages. The association between the serotonin neurotransmission and the inhibitory effect of PCA on the cage-leaving response was indicated by the findings that 1. Serotonin uptake inhibitors (alaproclate and citalopram) antagonized the effect of PCA. 2. High, neurotoxic doses of PCA antagonized the effect of PCA when tested one week after the former administration. The serotonin uptake inhibitor zimeldine counteracted the effect of neurotoxic PCA. 3. Depletion of brain serotonin with p-chlorophenylalanine counteracted the effect of acute PCA. 4. Repeated treatment of rats for 7 days with zimeldine, amiflamine, alpha-ethyltryptamine or clorgyline plus a low dose of PCA counteracted the effect of acute PCA probably due to a functional down-regulation at postsynaptic receptors. Clorgyline or a low dose of PCA by themselves had no effect. 5. Compounds interacting with dopamine or noradrenaline mechanisms, e.g. alpha-methyltyrosine, N-2-chloroethyl-N-ethyl-2-bromobenzylamine (DSP 4), pimozide, remoxipride and prazosin did not antagonize the effect of PCA nor did (+)-amphetamine inhibit the cage-leaving response. None of the serotonin receptor antagonists (cinanserin, ketanserin, metergoline, methysergide, metitepine, mianserin, pirenperone) blocked the inhibition of the cage-leaving response produced by PCA, indicating that the receptors involved may not be of the S1- and S2- types. Observation of the cage-leaving response may be a valuable technique in studies of drugs that enhance the serotonin neurotransmission in the rat brain.

Noradrenaline-stimulated inositol phospholipid breakdown as a measure of alpha 1-adrenoceptor function in rat hippocampal miniprisms after repeated antidepressant treatment

Noradrenaline-stimulated inositol phospholipid (PI) breakdown in rat hippocampal miniprisms was used as a measure of alpha 1-adrenoceptor function after repeated antidepressant treatment. After 24-29 days of oral treatment with either desipramine, mianserin, maprotiline or zimeldine (all at doses of 10 mg/kg b.i.d.), there was no significant difference in the degree of stimulation of hippocampal PI breakdown by 0.4, 2, 10 or 100 microM noradrenaline. It is concluded that there is no supersensitivity of hippocampal alpha 1-adrenoceptors coupled to PI breakdown after repeated antidepressant treatment under the conditions used.

Chronic treatment with antidepressant drugs and the analgesia induced by 5-methoxy-N,N-dimethyltryptamine: attenuation by desipramine

The effect of chronic and acute oral or intraperitoneal treatment with the antidepressant drugs, desipramine, amitriptyline, alaproclate and iprindole, upon pain thresholds in the tail flick, hot plate and shock titration tests of nociception in saline- and 5-MeODMT-treated rats was studied. Chronic desipramine treatment increased the pre-test tail flick latencies. In the saline-treated rats, chronic oral desipramine treatment increased tail flick latencies, whereas chronic oral amitriptyline treatment decreased tail flick latencies. In 5-MeODMT-treated rats, chronic oral desipramine treatment attenuated the effects of 5-MeODMT (1 mg/kg) in all three tests of nociception, whereas chronic amitriptyline caused a potentiation in the tail flick and hot plate tests. Chronic oral iprindole treatment attenuated 5-MeODMT-induced analgesia in the hot plate test. Chronic intraperitoneal desipramine treatment attenuated 5-MeODMT analgesia in the tail flick and shock titration tests. In a different chronic treatment experiment, oral desipramine treatment attenuated 5-MeODMT analgesia in the tail flick test and zimeldine did for both the tail flick and hot plate tests, whereas mianserin potentiated 5-MeODMT-induced analgesia in both the tail flick and hot plate tests. In the saline-treated rats, acute treatment with all four drugs, desipramine, amitriptyline, iprindole and alaproclate, elevated the shock thresholds, whereas in 5-MeODMT-treated rats, desipramine and amitriptyline elevated shock thresholds. Two main conclusions can be drawn: chronic desipramine caused a quite consistent attenuation of 5-MeODMT-induced analgesia and the effects of acute treatment differed strongly from that of the chronic treatment. The effects of chronic administration with these antidepressants were compared with other findings using different measures of behavioural and receptor function.

Role of central noradrenaline neurons in the contextual control of latent inhibition in taste aversion learning

Three experiments were performed to examine the effects of noradrenaline (NA) depletion, using 3 different methods: lesions of the dorsal noradrenergic bundle (DB) with 6-hydroxydopamine (6-OHDA), lesions induced by neonatal treatment with 6-OHDA and lesions induced by systemic DSP4 upon latent inhibition, using the taste-aversion learning procedure. NA depleted and control (sham, vehicle or saline) rats were given pre-exposure trials to either novel saccharin or to novel saccharin in a novel type of drinking bottle (the noisy bottle). Later, during conditioning trials saccharin was presented in the noisy bottles for all the rats, followed by lithium chloride injections. Saccharin aversions, tested for in the noisy bottles, indicated considerably weaker saccharin aversions (i.e. more latent inhibition) by the control groups pre-exposed to both saccharin and the noisy bottles. These context-dependent latent inhibition effects were clearly attenuated by all 3 treatments that depleted central NA. Biochemical assays confirmed the NA depletions in each case. The results, demonstrating the intimate role of central NA neurons in contextual control of latent inhibition in taste-aversion learning, appear to conform with current attentional theories of NA function in the forebrain.

Noradrenaline-serotonin interactions in the control of sexual behavior in the male rat: DSP4-induced noradrenaline depletion antagonizes the facilitatory effect of serotonin receptor agonists, 5-MeODMT and lisuride

The present communication reports how depletion of central noradrenaline neurons of DSP4 treatment antagonizes the facilitatory actions of 5-MeODMT and lisuride on male rat sexual behavior. In males with intact noradrenaline, 5-MeODMT facilitated sexual behavior by reducing the number of intromissions required for ejaculation; inhibitory actions were also noted, since 5-MeODMT prolonged intromission and ejaculation latencies. In DSP4-pretreated animals the inhibitory effect of 5-MeODMT remained unchanged, whereas its facilitatory action was abolished. Consistent with previous research, lisuride also reduced intromission frequency prior to ejaculation. This facilitation of sexual behavior was not observed in DSP4-treated animals. In the male rat, ejaculations following the first have a lower latency and are preceded by a lower number of intromissions. This naturally occurring facilitation of sexual behavior was not prevented by DSP4-induced noradrenaline depletion. Our results suggest that serotonin and noradrenaline interact in the control of sexual behavior in the male rat.

Spinal and locus coeruleus noradrenergic lesions abolish the analgesic effects of 5-methoxy-N,N-dimethyltryptamine

Two experiments were performed on Sprague-Dawley rats to study the effects of noradrenaline and 5-hydroxytryptamine depletion upon the antinociceptive effects of acute 5-methoxy-N,N-dimethyltryptamine (5-MeODMT) administration. 6-Hydroxydopamine-induced lesions following microinjections to either the locus coeruleus or the spinal cord (lumbar) abolished completely 5-MeODMT-induced analgesia in the tail-flick, hot-plate, and shock titration tests whereas 5,7-dihydroxytryptamine-induced lesions of the nucleus raphe magnus and the lumbar spinal cord attenuated 5-MeODMT analgesia in the tail-flick and shock titration tests. Thus, the experiments serve to demonstrate an important interaction between descending noradrenergic and serotonergic pathways, possibly at a spinal locus.

The effect of selective noradrenergic lesions upon the stimulation by noradrenaline of inositol phospholipid breakdown in rat hippocampal miniprisms

The breakdown of inositol phospholipid (PI) stimulated by hippocampal noradrenaline in rat miniprisms in vitro was used as an index of alpha 1-adrenoceptor function after selective noradrenergic denervation. Selective denervation was produced by microinjections of 6-hydroxydopamine (6-OHDA) into either the dorsal noradrenergic bundle (DNAB) or the locus coeruleus (LC), or by systemic treatment with the noradrenergic neurotoxin DSP4 (N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine). Fourteen days after these treatments, there was a large depletion of cortical noradrenaline but no change in the stimulation of hippocampal PI breakdown by noradrenaline. It is concluded that selective noradrenergic denervation under the conditions used here does not lead to hippocampal alpha 1-adrenoceptor supersensitivity as assessed by noradrenaline-stimulated PI breakdown.

Attenuation of sensory preconditioning by noradrenaline depletion in the rat

In order to investigate the effect of noradrenaline (NA) depletion upon an associative learning phenomenon, sensory preconditioning, rats were inflicted with either 6-hydroxydopamine-induced lesions of the dorsal noradrenergic bundle (DNAB) or the locus coeruleus (LC), or with systemic injections of the NA neurotoxin, N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP4). Using appropriate controls (the UP groups) sensory preconditioning was demonstrated clearly in the non-lesion conditions (Sham or saline), but was blocked or strongly attenuated in the DNAB and DSP4 conditions. LC lesions did not affect sensory preconditioning. These findings suggest that the loss of central NA may cause some disruption of some aspects of complex associative learning. The role of NA in sensory preconditioning may be relevant to current notions of NA function.

Impaired selective attention in methylazoxymethanol-induced microencephalic rats

Prenatal treatment of rats on gestation day 15 with methylazoxymethanol (MAM) caused forebrain microencephaly. Several behavioral tests were performed when the rats had reached an adult age. MAM treated rats were hyperactive, and were severely impaired in the acquisition of successive position reversal in a T-maze. The microencephalic rats failed also to demonstrate contextual control of latent inhibition (the stimulus preexposure effect) in taste-aversion conditioning. These results indicate that MAM treatment disrupts attentional processes and that this may account for the learning impairment.

Central noradrenaline depletion attenuates amphetamine-induced locomotor behavior

Male rats were given 6-hydroxydopamine-induced lesions of the locus coeruleus (LC) or the dorsal noradrenergic bundle (DNAB), prior to the measurement of locomotor and rearing activity induced by D-amphetamine. The increased locomotor activity induced by D-amphetamine (1.8 mg/kg) was significantly attenuated by both the LC and the DNAB lesions. The stimulatory effect of the 7.2 mg/kg dose of amphetamine was attenuated by the LC lesion, whereas the DNAB lesion potentiated this effect. The LC lesion also attenuated rearing induced by the 7.2 mg/kg dose of amphetamine. These results suggest some involvement of central noradrenergic neurons in the activity induced by amphetamine in the rat.