Ventral striatum and nucleus accumben

Smoking-related images elicited greater activation in ventral striatum and nucleus accumbens in smokers than nonsmokers. Among smokers, smoking-related cues produced bilateral activation in the ACC, OFC, SFG, and occipital cortex. 

Somatostatin inhibits secretion of growth hormone and other hormones such as prolactin from the anterior pituitary and is widely distributed in the brain in interneurons and projection pathways. All parts of the cortex contain local circuit somatostatin positive neurons, concentrated in layers V and VI, as does the amygdala and striatum. The nucleus accumbens and adjacent ventral putamen and caudate—designated limbic striatum—have particularly high concentrations of fibres. By contrast, TRH which regulates release of thyroid stimulating hormone and prolactin by the pituitary is generally confined to nuclei in and around the hypothalamus. 

Fig. 27. Comparison of the general topography of the expression of Di, D2 and D3 receptor genes in the dorsal and ventral striatum, as shown by in situ hybridization. Note the overall similar distribution of the D and D2 mRNAs in the caudate-putamen (cp) and nucleus accumbens (Acb) in contrast, note the restricted distribution of D3 mRNA in the nucleus accumbens, and the major (arrow) and minor (arrowheads) islands of Calleja. Scale bar. 1 mm. Reproduced with permission from LeMoine and Bloch (1996).

The striatum comprises the caudate, putamen and nucleus accumbens. In mammals in which corticofugal fibers coalesce into the internal capsule within the striatum, the caudate nucleus and putamen nucleus are separated by this partition. In animals in which corticofugal fibers are dispersed there is no clear separation between these nuclei, thus the term caudate-putamen is often used. The caudate and putamen, in most species, generally occupy the dorsal part of the striatum. The nucleus accumbens is the rostro-ventral extension of the striatum, and occupies the area surrounding the anterior commissure in the rostral part of the striatum. The term ventral striatum is generally used to refer to the nucleus accumbens and more caudally, the ventral most part of the striatum (Fleimer and Wilson 1975). The olfactory tubercle is sometimes included as a part of the ventral striatum, but in this review will not be discussed. 

Dopaminergic mechanisms within the ventral striatum (i.e., nucleus accumbens) subserve the ability of amphetamine and methylphenidate in low to moderate doses to increase locomotor activity. In contrast, very low dosages in animals seem to cause hypoactivity presumably by stimulation of autoreceptors, a finding that would be compatible with the clinical impression that methylphenidate might be usefiil in some patients with mania. 

D2 Mostly in striatum, nucleus accumbens and olfactory tubercle but also on neuron cell bodies in substantia nigra and ventral tegmentum where they are the autoreceptors for locally (dendritic) released DA. The loss of specific D2 antagonist binding in the striatum after lesions of the afferent nigro-striatal tract indicates their presynaptic autoreceptor role on terminals there. Other lesion studies have also established D2 receptors on other inputs such as the cortico striatal tract. 

There is some loss (40-60%) of DA in the nucleus accumbens of the mesolimbic system in the ventral tegmentum (AlO) and cortex at post-mortem but nowhere is it as marked as in the striatum. Some loss of NA, 5-HT, CCK and the enkephalins and of the markers GAD and ChAT (for GABA and ACh) have been reported in the striatum, SN and other areas but these rarely exceed 50% and could be secondary to DA loss. 

David SP, Munafo MR, Johansen-Berg H, Smith SM, Rogers RD, Matthews PM, et al (2005) Ventral striatum/nucleus accumbens activation to smoking-related pictorial cues in smokers and nonsmokers a functional magnetic resonance imaging study. Biol Psychiatry 58(6) 488 94... 

Robinson, Terry E, Phillip A. Jurson, Julie A. Bennett, and Kris M. Bentgen. 1988. "Persistent Sensitization of Dopamine Neur transmission in Ventral Striatum (Nucleus Accumbens) Produced by Prior Experience with (+)-Amphetamine A Microdialysis Study in Freely Moving Rats." Brain Research 462 211-22. 

A final general observation on Table 1 is that, in several cases, both facilitation through Di-like and inhibition by D2-like receptors have been reported. This holds true for noradrenaline release in rat nucleus accumbens, acetylcholine release in rat striatum, GABA release in rat striatum, nucleus accumbens, and ventral tegmental area (VTA), and glutamate release in rat substantia nigra pars reticulata. 

Robinson and Kolb (1997) treated rats with amphetamine twice a day for 5 days a week for a total of 5 weeks with a dose that was gradually increased from 1 mg/kg to 8 mg/kg. Thirty-eight days later, they found lasting structural modifications in the nucleus accumbens and prefrontal cortex neurons, including increased length of dendrites and density of spines. In a microdialysis study, Weiss et al. (1997) treated rats with amphetamine (1.5 mg/kg injected twice a day for 14 days). Seven days after withdrawal, the animals continued to show a reduced dopamine release in the ventral striatum in response to stress. 

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