SCH 23390 decreases self-stimulation of the medial prefrontal cortex in the rat

Medial prefrontal cortex and anteromedial thalamus interaction regulates goal-directed behavior and dopaminergic neuron activity

The prefrontal cortex is involved in goal-directed behavior. Here, we investigate circuits of the PFC regulating motivation, reinforcement, and its relationship to dopamine neuron activity. Stimulation of medial PFC (mPFC) neurons in mice activated many downstream regions, as shown by fMRI. Axonal terminal stimulation of mPFC neurons in downstream regions, including the anteromedial thalamic nucleus (AM), reinforced behavior and activated midbrain dopaminergic neurons. The stimulation of AM neurons projecting to the mPFC also reinforced behavior and activated dopamine neurons, and mPFC and AM showed a positive-feedback loop organization. We also found using fMRI in human participants watching reinforcing video clips that there is reciprocal excitatory functional connectivity, as well as co-activation of the two regions. Our results suggest that this cortico-thalamic loop regulates motivation, reinforcement, and dopaminergic neuron activity.

The prefrontal cortex is involved in goal-directed behaviour. Here the authors show that medial prefrontal cortex activates goal-directed motivation and dopamine neurons via a feedback loop with the anteromedial thalamus.

Pharmacology and behavioral pharmacology of the mesocortical dopamine system

The prefrontal cortex (PFC) has long been known to be involved in the mediation of complex behavioral responses. Considerable research efforts are directed towards refining the knowledge about the function of this brain area and the role it plays in cognitive performance and behavioral output. In the first part, this review provides, from a pharmacological perspective, an overview of anatomical, electrophysiological and neurochemical aspects of the function of the PFC, with an emphasis on the mesocortical dopamine system. Anatomy of the mesocortical system, basic physiological and pharmacological properties of neurotransmission within the PFC, and interactions between dopamine and glutamate as well as other transmitters within the mesocorticolimbic circuit are included. The coverage of these data is largely restricted to what is relevant for the second part of the review which focuses on behavioral studies that have examined the role of the PFC in a variety of phenomena, behaviors and paradigms. These include reward and addiction, locomotor activity and sensitization, learning, cognition, and schizophrenia. Although the focus of this review is on the mesocortical dopamine system, given the intricate interactions of dopamine with other transmitter systems within the PFC and the importance of the PFC as a source of glutamate in subcortical areas, these aspects are also covered in some detail where appropriate. Naturally, a topic as complex as this cannot be covered comprehensively in its entirety. Therefore this review is largely limited to data derived from studies using rats, and it is also specifically restricted to data concerning the medial PFC (mPFC). Since in several fields of research the findings concerning the function or role of the mPFC are relatively inconsistent, the question is addressed whether these inconsistencies might, at least in part, be related to the anatomical and functional heterogeneity of this brain area.

Mediation by neurotensin-receptors of effects of neurotensin on self-stimulation of the medial prefrontal cortex

1 Intracortical microinjections of neurotensin (NT) selectively decreased intracranial self-stimulation (ICSS) of the medial prefrontal cortex in the rat. 2 To elucidate whether this effect is mediated by NT receptors or by the formation of NT-dopamine complexes, we investigated the effects on ICSS of intracortical microinjections of neurotensin (1-11), an NT fragment that forms extracellular complexes with dopamine but does not bind to NT receptors. 3 We also studied the effects of the peripheral administration of SR 48692, a selective antagonist of NT receptors, on the inhibition of ICSS produced by the intracortical administration of NT. 4 Unilateral microinjections of neurotensin (1-11) at doses of 10, 20 and 40 nmol into the medial prefrontal cortex did not change the basal ICSS rate of this area. 5 The intraperitoneal administration of SR 48692 at doses of 0.08 and 0.16 mg kg-1 30 min before microinjection of 10 nmol of NT into the medial prefrontal cortex, antagonized the inhibition of ICSS produced by the neuropeptide. 6 These results demonstrate that the inhibitory effect of NT on ICSS is mediated by NT receptors.

Neuropharmacological evidence for the role of dopamine in ventral pallidum self-stimulation

The present study examines the role of dopaminergic neurotransmission in modulating the reinforcing effect of ventral pallidum (VP) intracranial self-stimulation (ICSS). Fifty four adult rats were implanted with a monopolar moveable stimulating electrode in the VP. Rate-frequency functions were determined by logarithmically decreasing the number of pulses in a stimulation train from a value that sustained maximal responding to one that did not sustain responding. After the ICSS thresholds stabilized, the animals received treatments with several doses of cocaine and of various selective drugs acting at the level of DA receptor subtypes. Their effects on threshold and asymptotic rate were analyzed. Cocaine produced a significant decrease in ICSS threshold but had no significant effect on the asymptotic rate. A significant decrease in ICSS threshold was also seen with the D3 agonist 7-OH-DPAT. This was associated with a decrease rather than an increase in performance. D1 and D2 DA receptor blockers (haloperidol, SCH-23390, raclopride and sulpiride) produced a dose dependent increase in ICSS threshold and a decrease in the maximal rate. The results suggest that DA plays a modulatory role in VP intracranial self-stimulation, and that D1, D2 and D3 receptors are involved in the mediation of this effect, although to different extents.

Modulation of memory fields by dopamine D1 receptors in prefrontal cortex

Dopamine has been implicated in the cognitive process of working memory but the cellular basis of its action has yet to be revealed. By combining iontophoretic analysis of dopamine receptors with single-cell recording during behaviour, we found that D1 antagonists can selectively potentiate the 'memory fields' of prefrontal neurons which subserve working memory. The precision shown for D1 receptor modulation of mnemonic processing indicates a direct gating of selective excitatory synaptic inputs to prefrontal neurons during cognition.