Intrategmental infusion of cocaine decreases dopamine release and enhances norepinephrine release in the medial prefrontal cortex

Specificity and impact of adrenergic projections to the midbrain dopamine system

Dopamine (DA) is a neuromodulator that regulates different brain circuits involved in cognitive functions, motor coordination, and emotions. Dysregulation of DA is associated with many neurological and psychiatric disorders such as Parkinson's disease and substance abuse. Several lines of research have shown that the midbrain DA system is regulated by the central adrenergic system. This review focuses on adrenergic interactions with midbrain DA neurons. It discusses the current neuroanatomy including source of adrenergic innervation, type of synapses, and adrenoceptors expression. It also discusses adrenergic regulation of DA cell activity and neurotransmitter release. Finally, it reviews several neurological and psychiatric disorders where changes in adrenergic system are associated with dysregulation of the midbrain DA system. This article is part of a Special Issue entitled SI: Noradrenergic System.

Lidocaine attenuates anisomycin-induced amnesia and release of norepinephrine in the amygdala

When administered near the time of training, protein synthesis inhibitors such as anisomycin impair later memory. A common interpretation of these findings is that memory consolidation requires new protein synthesis initiated by training. However, recent findings support an alternative interpretation that abnormally large increases in neurotransmitter release after injections of anisomycin may be responsible for producing amnesia. In the present study, a local anesthetic was administered prior to anisomycin injections in an attempt to mitigate neurotransmitter actions and thereby attenuate the resulting amnesia. Rats received lidocaine and anisomycin injections into the amygdala 130 and 120 min, respectively, prior to inhibitory avoidance training. Memory tests 48 h later revealed that lidocaine attenuated anisomycin-induced amnesia. In other rats, in vivo microdialysis was performed at the site of amygdala infusion of lidocaine and anisomycin. As seen previously, anisomycin injections produced large increases in release of norepinephrine in the amygdala. Lidocaine attenuated the anisomycin-induced increase in release of norepinephrine but did not reverse anisomycin inhibition of protein synthesis, as assessed by c-Fos immunohistochemistry. These findings are consistent with past evidence suggesting that anisomycin causes amnesia by initiating abnormal release of neurotransmitters in response to the inhibition of protein synthesis.

Rostral-caudal differences in the effects of intra-VTA muscimol on cocaine self-administration

We have found that dopamine (DA) in the ventral tegmental area (VTA) plays an important role in cocaine self-administration. DA in the VTA acts at D1-type receptors on the terminals of GABA afferents causing release of this neurotransmitter. Thus, the neurochemical pathways whereby VTA DA might be involved in cocaine self-administration may include GABA neurotransmission. In the present study, we investigated this possibility. Rats were prepared with intravenous catheters and bilateral guide cannulae positioned to allow microinjections directly into the VTA or a site 1 mm dorsal to it. The rats were then trained to self-administer cocaine (1.0 mg/kg/injection) under a fixed-ratio 1 schedule of reinforcement and tested with microinjections of muscimol (0, 0.05 and 0.1 microg/0.25 microl) or picrotoxin (0, 0.025 and 0.05 microg/0.25 microl) or trained under a progressive ratio (PR) schedule and tested with vehicle and 0.05 microg/0.25 microl muscimol. Muscimol in the VTA, but not immediately dorsal to it, significantly reduced cocaine intake under the FR1 schedule. Furthermore, when analyzed by rostral/caudal site of injection, it was found that rostral injections of muscimol significantly reduced cocaine self-administration whereas caudal injections produced non-significant decreases in self-administration. Inspection of individual records revealed no signs of non-specific behavioral effects of the muscimol treatments. Muscimol in the rostral VTA also significantly increased break points in responding under the PR schedule. Intra-VTA picrotoxin did not significantly affect cocaine self-administration. These data suggest that stimulation of GABA-A receptors in the VTA is involved in cocaine self-administration and reward and that this involvement is more pronounced in the rostral than in the caudal VTA.

Difference in magnitude of psychostimulant-induced extracellular norepinephrine in the ventral tegmental area contributes to discrepant prefrontal dopamine outflow

The dopamine (DA) efflux in the medial prefrontal cortex (mPFC) can be modulated by the interaction between afferent norepinephrine (NE) and somatodendritic DA in the ventral tegmental area (VTA). However, it is unclear how locally administered amphetamine (AMPH) or cocaine in the VTA results in discrepant response of DA efflux in the mPFC. In this study, intra-VTA infusion of AMPH (1000 microM) or cocaine (200 microM) in anesthetized rats was employed to study the concurrent profile of extracellular DA level in the VTA and mPFC. In addition, the extracellular NE levels during the intra-VTA infusion of these two psychostimulants were analyzed to compare their effects on prefrontal DA efflux. During the intra-VTA infusion of AMPH, both extracellular DA and NE increased significantly in the VTA (270 +/- 12% and 819 +/- 40%, respectively). Meanwhile, the DA efflux in the mPFC elevated significantly. During the intra-VTA infusion of cocaine, the extracellular DA and NE in the VTA also increased (271 +/- 21% and 150 +/- 15%, respectively). However, the DA efflux decreased significantly in the mPFC. Noteworthy, the increase of extracellular NE in the VTA was much more robust via AMPH infusion, as compared with cocaine. It is suggested that AMPH and cocaine enhance the extracellular NE concentrations in the VTA in different magnitudes, which in turn contribute to discrepant profiles of distal DA efflux in the mPFC.

Cerebral Activity in the Perception of Visceral Pain

Specific patterns of cerebral activity have recently been identified in relation to acute and chronic visceral pain experiences in humans. Activity may occur in a brain region as a consequence of receiving and processing neurally encoded information perceived to be arising from the viscera. (This includes, but is not necessarily limited to, information actually arising from the viscera.) Observed cerebral activity may also represent the mobilization and output of instructions emanating from the cerebrum, which helps create and respond to visceral events. Functional neuroanatomy underlying the transmission of both kinds of neuronally encoded information is outlined. Recent research and ideas on cerebral activity associated with visceral pain perceived to be arising from within the abdomen, chest, or pelvis are considered. Finally, the relationships of pain perception and cerebral activity to depression, autonomic function, and sex are discussed.