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PubMed1982

Is a retrosplenial (cingulate) pathway involved in the mediation of high frequency hippocampal rhythmical slow activity (theta)?

In previous experiments we demonstrated that in rats there are two kinds of hippocampal rhythmical slow activity patterns (RSA or theta) as defined by the dominating EEG frequencies. RSA with a frequency of 6-8 Hz appeared during exploratory behavior (locomotion), whereas stimulation of the dorsomedial hypothalamus (DMH) elicited RSA with frequencies of 8-12 Hz. To determine the neural pathways involved in the mediation of these two types of RSA, local injections of tetracaine were made either in the medial septum or in the cingulate cortex in order to reversibly interrupt the functional activity of these loci. Blockade of the medial septum suppressed the 6-8 Hz 'walking-associated' RSA in the hippocampal EEG, but had no effect on the 8-12 Hz DMH-driven RSA. On the other hand, a tetracaine injection into the cingulate cortex selectively blocked the high-frequency RSA elicited by DMH stimulation, but had no effect on the 6-8 Hz 'walking-associated' RSA. Both effects disappeared between 30 and 90 min after tetracaine injection. We conclude that the DMH-driven RSA is mediated by the cingulum and/or fibers traveling through the cingulate cortex (retrosplenial region) and thus, that this type of RSA operates without septal involvement.

Animals↗
PubMed1990

Sex differences in corpus callosum: influence of prenatal alcohol exposure and maternal undernutrition.

The functional significance of sex differences in the size of the corpus callosum was investigated using a prenatal alcohol exposure paradigm that influences the fetal hormonal milieu. Adult male and female Long-Evans rats were selected from one of 3 prenatal treatment histories: prenatal alcohol-exposed (35% ethanol-derived calories), nutritional control (0% ethanol-derived calories) or standard control (lab chow). Subjects were assessed for open field activity at 85 days of age. At 100 days of age, midline sagittal areas of the corpus callosum and the anterior commissure were determined for these subjects. Male control subjects had significantly larger callosal areas than female controls. Prenatal alcohol exposure significantly decreased the total callosal area, and abolished this sexual dimorphism. When the callosal measurements were analyzed using Denenberg's regions, differential effects of prenatal alcohol exposure, undernutrition and sex were dissociable by subarea. There were no significant sex differences or effects of prenatal alcohol exposure in the midline sagittal area of the anterior commissure. Callosal size was negatively correlated to open field activity, suggesting a possible role in normal exploratory behavior and to the overactivity observed after prenatal alcohol exposure.

Animals↗
PubMed1993

Behavioural responses of bicucculline methiodide injections into the ventral hypothalamus of freely moving, socially interacting rats.

Several studies, using electrical stimulation of parts of the hypothalamus, have shown, that different parts of the hypothalamus yield different behavioural responses upon stimulation. In order to differentiate between stimulation of neuronal cell bodies and passing fibres and to investigate the role of GABA in hypothalamically elicited behaviour, 25 local injections with bicucculline methiodide, a GABA antagonist, (35 ng/0.2 microliter) were performed in the ventral parts of the hypothalamus of 16 freely moving rats in a social environment. A cannula system was used that allowed injection without interruption of the ongoing social interactions. Digging, gnawing, drinking and attack behaviour were elicited in different animals. By plotting the behavioural responses of the animals into a detailed hypothalamic atlas, we assessed the hypothalamic distribution of the elicited behavioural responses. A number of injections elicited a combination of two or three different responses, probably due to diffusion of the substance, thus disinhibiting more than one behavioural system. Our results are in general agreement with previous electrical stimulation data and show that, in an overlapping pattern, different populations of neurons are involved in the elicitation of digging, gnawing, drinking and attack behaviour. In the hypothalamus, a tonic GABAergic inhibition of neurons involved in the display of these types of behaviour appears to exist.

Aggression↗
PubMed1996

Morphology of identified corticospinal cells in the rat following motor cortex injury: absence of use-dependent change.

After unilateral injury to the forelimb area of the motor cortex, rats are reported to show relatively increased use of the ipsilateral forelimb during exploratory behavior and a concomitant transient increase in dendritic growth in neurons in the undamaged motor cortex. To identify the specific population of cells in motor cortex that undergo such use-dependent change, we examined the morphology of corticospinal pyramidal cells in the intact hemisphere 18 days following unilateral motor cortex damage. Corticospinal neurons in the motor cortex were retrogradely labeled with injections of the fluorescent tracer, DiO, into the cervical enlargement of the spinal cord. Seven days later, the rats received a lesion in the forelimb area of the contralateral motor cortex and 18 days following the lesion, limb use was assessed in two behavioral tests after which the rats were sacrificed. Under fluorescent light, corticospinal cells were visualized and injected with a horseradish peroxidase-fluorescein conjugate that was then reacted with diaminobenzidine. The labeled cells were reconstructed and the number and centrifugal order of the branches were analyzed. The increased use of the paw contralateral to the intact motor cortex was not associated with an increase in dendritic arborization in corticospinal motor neurons in the intact motor cortex. The results are discussed in light of methodological and theoretical considerations relevant to the study of neural plasticity in the motor system.

Animals↗
PubMed1982

Neuroanatomical site specific modulation of spontaneous motor activity by neurotensin.

Immunohistofluorescent neurotensin (NT) is found in the ventral tegmental area (VTA), and bilateral injection of NT into the VTA produces an increase in exploratory behaviors. The VTA also contains dopaminergic cell bodies with axonal projections to the nucleus accumbens. In this study it was shown that bilateral microinjection of NT (4.0 micrograms/side) into the nucleus accumbens blocked the behavioral hyperactivity produced by intra-VTA injection of NT (2.5 micrograms/side).

Animals↗
PubMed1991

Characterization of tiagabine (NO-328), a new potent and selective GABA uptake inhibitor.

Tiagabine (NO-328) (R(-)-N-[4,4-bis(3-methylthien-2-yl)but-3-enyl]nipecotic acid, hydrochloride) is a new centrally acting GABA uptake inhibitor. The anticonvulsant activity of tiagabine was evaluated against seizures induced by methyl 6,7-dimethoxy-4-ethyl-beta-carboline-3-carboxylate (DMCM), pentylenetetrazol, bicuculline, maximal electrostimulation (MES), or high intensity sound. The sedative actions of tiagabine were evaluated in tests for traction, rotarod performance and exploratory behavior. Finally, interoceptive properties of tiagabine were assessed using diazepam-, CGS 9896-, pentylenetetrazol-, or amphetamine-discriminating rats. Tiagabine was an effective anticonvulsant in doses which did not produce sedation or motor debilitation, although it was not potent against MES. In a manner similar to other anti-epileptic drugs, tiagabine potentiated dopaminergic function (methylphenidate-induced gnawing in mice) although it did not substitute for amphetamine in amphetamine-trained animals. Furthermore, although tiagabine antagonized DMCM-induced convulsions, it exhibited neither CGS 9896 or diazepam-like interoceptive effects, nor did it block (or potentiate) pentylenetetrazol-discrimination. Thus, GABA uptake inhibition represents a novel rationale for a valproate-like anticonvulsant drug therapy.

Animals↗
PubMed1996

Prenatal exposure to cocaine selectively disrupts motor responding to D-amphetamine in young and mature rabbits.

Acute administration of D-amphetamine probed the functional effects of prenatal exposure to cocaine on the integrity of monoaminergic systems in preweanling (48-56 days old) and adult (> or = 140 days old) Dutch belted rabbits. D-Amphetamine sulfate (0, 0.3, 1.0, 3.3 and 6.0 mg/kg, s.c.) produced equivalent dose-related reductions in food intake in 180 day-old rabbits that had been exposed in utero on gestational days 8-29 to cocaine or saline. Intrauterine exposure to cocaine also did not alter the incidence of exploratory behaviors stimulated by D-amphetamine during the anorexia test. In contrast, however, prenatal cocaine virtually eliminated stereotyped head bobbing elicited by the highest dose of D-amphetamine. When responses to 5.0 mg/kg D-amphetamine were measured during a 90-min open field test, prenatal cocaine prevented head bobbing in preweanling rabbits and reduced this behavior by 92% in 140 day-old adults. Prenatal cocaine also diminished the intensity of other motor responses in the open field in the adults but not in preweanlings. In normal rabbits, the D1 antagonist R(+)-SCH 23390 (0.01 mg/kg, s.c.) blocked D-amphetamine-induced head bobbing. Thus, prenatal exposure to cocaine produces an early and persistent deficit in behavioral responding to a high dose of D-amphetamine. The deficit is especially selective at the time of weaning, broadens to affect more motor behaviors with maturation and may reveal impaired D,-mediated dopaminergic neurotransmission in the brain.

Age Factors↗
PubMed1985

The roles of information reactivation and nonassociative arousal in recovery from ECS-induced retrograde amnesia.

Restoration of memory by pretest reminder treatments following ECS-induced amnesia in principle could be mediated by nonassociative arousal and/or reactivation of information by the reminder stimuli. In the present research, arousal value of the reminder treatment was largely a function of the novelty of the context in which the reminder cues occurred. After producing ECS-induced amnesia in rats for a signaled passive avoidance task, presentation of the signal outside of the training and test context proved to be an effective reminder cue. However, prereminder familiarization with the reminder location, which was sufficient to reduce exploratory behavior suggestive of a decrease in the arousal value of the context, did not influence recovery from amnesia. These data indicate that reminder treatments are capable of reversing experimental amnesia by initiating further processing of previously acquired information even when the treatment does not produce appreciable arousal.

Amnesia↗
PubMed1987

Effects of cerebellar vermal lesions on species-specific fear responses, neophobia, and taste-aversion learning in rats.

The cerebellar vermis has extensive anatomical connections with many brain stem and forebrain structures which have been implicated in emotional or affective behavior. Previous reports indicate that lesions of the vermis in a variety of experimental animals result in altered emotional behavior. The studies reported here attempted to clarify the nature of the change in emotional behavior following vermal lesions in rats by testing the animals in a variety of fear-eliciting situations. As compared with controls, vermal-lesioned rats froze less in the presence of a cat and showed fewer signs of fear in an open field. However, their responses to footshock did not differ fundamentally from controls. They recovered more quickly than controls from the neophobic response to a novel taste but showed robust taste-aversion learning. The results are discussed in terms of the role of the cerebellum in the modulation of fear-related behaviors and in terms of similarities and differences with the effects of amygdala lesions. The results expand the body of data implicating the cerebellum in the modulation of complex motivational behavior.

Animals↗
PubMed1987

Handling facilitates the acquisition of lever-pressing for brain self-stimulation in the posterior hypothalamus of rats.

Adult male rats implanted with stimulating electrodes in the posterior hypothalamus-ventral tegmental area (PH-VTA) were allowed to learn to lever press for intracranial self-stimulation (ICSS) without any priming by the experimenter or use of external cues. Animals that had been handled for seven days prior to testing acquired the lever-pressing task more rapidly than non-handled animals. Prior handling had no effect on the amount of locomotor activity in a novel environment nor on the number of non-reinforced lever presses. This suggested that the effect of handling on ICSS acquisition was not due to a change in locomotor activity or exploratory behavior. Implanted rats that were injected before each session with d-amphetamine (0.25 mg/kg) or saline did not differ in their rates of acquisition of ICSS in PH-VTA. However, injected animals acquired ICSS more slowly than the non-injected (handled and non-handled) animals. These results suggest that mild stressors applied before acquisition testing can alter the rate of learning of an operant task for ICSS in the posterior hypothalamic region and that small routine manipulations of animals can affect learning in operant training situations.

Amphetamine↗
PubMed1989

Forebrain norepinephrine involvement in selective attention and neophobia.

It has been reported that depletion of forebrain norepinephrine via 6-hydroxydopamine infusion into the dorsal bundle decreases the rat's ability to selectively attend to relevant stimuli and thus increases the rat's responsiveness to novelty. In this study we measured 6-hydroxydopamine lesion effects on 1) selective attention via the nonreversal shift task and extinction of continuous reinforcement bar pressing and on 2) neophobia via consumption of a novel solution in a familiar environment; exploratory behaviors and consumption of a familiar food in a novel environment; and consumption of familiar and novel foods in a novel environment. Our data do not support a role for the dorsal bundle in selective attention. Our data do support a role for forebrain norepinephrine in neophobia and suggest that the lesion effects on neophobia result from an interaction between novelty of environment and novelty of food.

Animals↗
PubMed1992

The effects of continuous naltrexone infusions on diet preferences are modulated by adaptation to the diets.

Two groups of male rats were placed on a feeding regimen in which a fat/protein diet and a carbohydrate/protein diet were available ad lib. Naltrexone was infused via osmotic minipumps either at the time the diets were introduced or after one week of adaptation to the diets. In rats adapted to the diets, naltrexone caused a decrease in the intakes of fat/protein and carbohydrate/protein diets. Relative preferences for the two diets were generally unchanged. In contrast, when naltrexone was infused at the time of introduction of the diets, a polarization phenomenon was observed: rats tended to consume nearly all of their daily calories from either one diet or the other. Six rats (out of 10) showed a stronger preference for the carbohydrate/protein diet than did any of the saline-treated rats, while 3 showed a stronger preference for the fat/protein diet than did any of the saline-treated rats. Thus, the effect was not diet- or macronutrient-specific. These preferences became significantly less extreme after termination of naltrexone infusions. Conditioned aversions and naltrexone-induced reductions in exploratory behavior are discussed as potential explanations for this polarization effect. These results indicate that naltrexone has differential effects on the development versus the maintenance of diet preferences. Further, they emphasize the importance of examining individual differences as well as baseline preferences in studies on the control of intake and diet selection.

Adaptation, Psychological↗