Rewarding effects of the electrical stimulation of the parabrachial complex: taste or place preference?

Place preferences induced by electrical stimulation of the external lateral parabrachial subnucleus in a sequential learning task: Place preferences induced by NLPBe stimulation

It is known that electrical stimulation of the external lateral parabrachial nucleus (NLPBe) can sustain concurrent taste and place learning. Place preferences can be learned through different procedures. Previous studies demonstrated that electrical stimulation of the PBNLe can generate aversive and preference place learning using concurrent procedures. In the concurrent procedure, the animals can move freely in the maze, and intracranial electrical stimulation is associated with their voluntary stay in one of the two maze compartments. However, the rewarding properties of most stimuli, whether natural or drugs of abuse, have usually been investigated using the sequential procedure, in which animals are confined while receiving the unconditioned stimulus and then undergo a choice test without stimulation in a later phase. This study examined whether this stimulation can sustain place preference learning in sequential tasks. Results demonstrated that place preferences can also be induced by the electrical stimulation of the NLBe using sequential procedures. These findings suggest that the NLPBe may form part of a brain reward axis that shares certain characteristics with those observed in the processing of natural rewarding agents and especially of drugs of abuse.

Differential rewarding effects of electrical stimulation of the lateral hypothalamus and parabrachial complex: Functional characterization and the relevance of opioid systems and dopamine

BACKGROUND

Since the discovery of rewarding intracranial self-stimulation by Olds and Milner, extensive data have been published on the biological basis of reward. Although participation of the mesolimbic dopaminergic system is well documented, its precise role has not been fully elucidated, and some authors have proposed the involvement of other neural systems in processing specific aspects of reinforced behaviour.

AIMS AND METHODS

We reviewed published data, including our own findings, on the rewarding effects induced by electrical stimulation of the lateral hypothalamus (LH) and of the external lateral parabrachial area (LPBe) - a brainstem region involved in processing the rewarding properties of natural and artificial substances - and compared its functional characteristics as observed in operant and non-operant behavioural procedures.

RESULTS

Brain circuits involved in the induction of preferences for stimuli associated with electrical stimulation of the LBPe appear to functionally and neurochemically differ from those activated by electrical stimulation of the LH.

INTERPRETATION

We discuss the possible involvement of the LPBe in processing emotional-affective aspects of the brain reward system.

Tolerance to repeated rewarding electrical stimulation of the parabrachial complex

The parabrachial complex has been related to various rewarding behavioral processes. As previously shown, electrical stimulation of the lateral parabrachial external (LPBe) subnucleus induces opiate-dependent concurrent place preference. In this study, two groups of animals (and their respective controls) were subjected to sessions of rewarding brain stimulation daily or on alternate days. The rats stimulated every other day maintained a consistent preference for the place associated with the brain stimulation. However, as also found in the Insular Cortex, there was a progressive decay in the initial place preference of animals receiving daily stimulation. These data suggest that the rewarding effects induced by electrical stimulation of LPBe subnucleus may be subject to tolerance. These findings are discussed with respect to other anatomical areas showing reward decay and to the reinforcing effects induced by various electrical and chemical rewarding agents.

Altered neural connectivity in adult female rats exposed to early life social stress

The use of a variety of neuroanatomical techniques has led to a greater understanding of the adverse effects of stress on psychiatric health. One recent advance that has been particularly valuable is the development of resting state functional connectivity (RSFC) in clinical studies. The current study investigates changes in RSFC in F1 adult female rats exposed to the early life chronic social stress (ECSS) of the daily introduction of a novel male intruder to the cage of their F0 mothers while the F1 pups are in the cage. This ECSS for the F1 animals consists of depressed maternal care from their F0 mothers and exposure to conflict between their F0 mothers and intruder males. Analyses of the functional connectivity data in ECSS exposed adult females versus control females reveal broad changes in the limbic and reward systems, the salience and introspective socioaffective networks, and several additional stress and social behavior associated nuclei. Substantial changes in connectivity were found in the prefrontal cortex, nucleus accumbens, hippocampus, and somatosensory cortex. The current rodent RSFC data support the hypothesis that the exposure to early life social stress has long term effects on neural connectivity in numerous social behavior, stress, and depression relevant brain nuclei. Future conscious rodent RSFC studies can build on the wealth of data generated from previous neuroanatomical studies of early life stress and enhance translational connectivity between animal and human fMRI studies in the development of novel preventative measures and treatments.