Functional activity in the brain of socially deprivated rats produced by an active avoidance test after razobazam (Hoe 175) treatment: a 2-deoxyglucose study

Recognition of Mother's voice evokes metabolic activation in the medial prefrontal cortex and lateral thalamus of Octodon degus pups

In a variety of animal species, including primates, vocal communication is an essential part to establish and maintain social interactions, including the emotional bond between the newborn, its parents and siblings. The aim of this study in pups of the trumpet-tailed rat, Octodon degus, was to identify cortical and subcortical brain regions, which are involved in the perception of vocalizations uttered by the mother. In this species, which is characterized by an elaborated vocal repertoire, the (14C)-2-fluoro-deoxyglucose autoradiography was applied to measure region-specific metabolic activation in response to the presentation of a learned emotionally relevant acoustic stimulus, the maternal calls. Already at the age of eight days the precentral medial cortex, anterior cingulate cortex and the lateral thalamus could be identified by their enhanced metabolic activation in response to the presentation of the emotionally relevant maternal nursing calls, whereas other brain areas, such as the hippocampus and amygdala did not show stimulus-induced activation. Since in humans changes of activity patterns in relation to the emotional content of spoken language have been observed in similar brain regions, e.g. in the anterior cingulate cortex, Octodon degus may provide a suitable animal model to study the cellular and synaptic mechanisms underlying perception, production and processing of conspecific vocalizations.

Early auditory filial learning in degus (Octodon degus): behavioral and autoradiographic studies

Degu mothers (Octodon degus) utter specific maternal calls during nursing which presumably stimulate and reinforce suckling. Pups from surgically muted mothers show a reduced gain of body weight during postnatal development compared to pups from normally vocalizing mothers. Our behavioral studies suggest that the pups have to learn the meaning of the maternal calls during the first two weeks of life. Two-week-old pups from normally vocalizing mothers expressed a preference for the maternal call in a behavioral discrimination test, in contrast to pups from surgically muted mothers. Investigation of brain activities using the 2-[14C]fluoro-deoxyglucose (2-FDG) method revealed that pups from normal mothers display a significantly higher 2-FDG uptake in precentral medial, anterior cingulate cortex and a slight, non-significant increase in the prelimbic cortex and orbital PFC upon presentation of the maternal call, compared to pups from muted mothers, for which the maternal call was unfamiliar and meaningless. These prefrontal cortical areas are known to be involved in associative learning processes and our data suggest that they are involved in the association between the maternal call and the positive emotional situation during nursing.

Metabolic activation of the brain of young rats after exposure to environmental complexity

Autoradiography with 14C-2-deoxyglucose was used to determine brain metabolic activity during the quiet period that follows after daily exploratory experiences in new complex environments. Eight 1-month-old, male Tryon rats were selected from two litters. Pairs of littermates matched by body weight were assigned to one of two conditions: rats housed individually in small home cages as the "impoverished condition," or rats exposed twice daily to changing and complex environments of two large cages with inanimate objects and conspecifics as the "enriched condition." After 4 days, rats were injected with 2-deoxyglucose, placed individually in a home cage and left undisturbed for 90 min until sacrificed. The brains of "enriched" rats were heavier than their "impoverished" littermates, and showed a global trend for metabolic enhancement. They also showed significantly greater amounts of 2-deoxyglucose in occipital cortex (27%), hippocampal subiculum (36%), and nucleus accumbens (40%).

Structural modeling of functional neural pathways mapped with 2-deoxyglucose: effects of acoustic startle habituation on the auditory system

This paper describes the first application of structural modeling to neuroscience. Structural modeling (also known as path analysis) is a method to assess the relative impact of directional links in a system and how these interrelations may change under different conditions. The objective was to demonstrate how structural modeling can be used to determine the functional interrelationships between brain structures that form the auditory system. Using structural modeling, changes in auditory system 2-DG uptake were examined during long- and short-term habituation of the acoustic startle reflex. Models were based on the anatomical connections between central auditory system structures. Using functional 2-DG data, the correlations between these structures were calculated and numerical weights were computed for each anatomical link. The analysis revealed that the lemniscal path was dominant during short-term habituation, while during long-term habituation this influence was modified through extra-lemniscal pathways. The models are discussed in the context of previous findings to demonstrate how structural modeling can not only complement, but also extract more information from 2-DG mapping experiments.

Effect of heroin-conditioned auditory stimuli on cerebral functional activity in rats

Cerebral functional activity was measured as changes in distribution of the free fatty acid [1-14C]octanoate in autoradiograms obtained from rats during brief presentation of a tone previously paired to infusions of heroin or saline. Rats were trained in groups of three consisting of one heroin self-administering animal and two animals receiving yoked infusions of heroin or saline. Behavioral experiments in separate groups of rats demonstrated that these training parameters imparts secondary reinforcing properties to the tone for animals self-administering heroin while the tone remains behaviorally neutral in yoked-infusion animals. The optical densities of thirty-seven brain regions were normalized to a relative index for comparisons between groups. Previous pairing of the tone to heroin infusions irrespective of behavior (yoked-heroin vs. yoked-saline groups) produced functional activity changes in fifteen brain areas. In addition, nineteen regional differences in octanoate labeling density were evident when comparison was made between animals previously trained to self-administer heroin to those receiving yoked-heroin infusions, while twelve differences were noted when comparisons were made between the yoked vehicle and self administration group. These functional activity changes are presumed related to the secondary reinforcing capacity of the tone acquired by association with heroin, and may identify neural substrates involved in auditory signalled conditioning of positive reinforcement to opiates.

Learning and memory processes of an ACTH4-9 analog (ebiratide; Hoe 427) in mice and rats

These experiments investigated the effects of the new ACTH4-9 analog ebiratide (Hoe 427) [H-Met(O2)-Glu-His-Phe-D-Lys-Phe-NH-(CH2)8-NH2 X 3 CH3COOH] on memory processes in mice and rats in five training tasks. With all five training and testing procedures (inhibitory avoidance test with ECS- or scopolamine-induced amnesia, up-hill avoidance, one-way shuttle box avoidance and eight-arm radial maze) ebiratide was most effective in a dose range of 1-10 micrograms/kg SC.