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.

New nociceptive circuits to the hypothalamic perifornical area from the spinal cord and spinal trigeminal nucleus via the parabrachial nucleus.

Neurons of the parabrachial nucleus (PB) receive nociceptive input from the dorsal horn (DH) of the spinal cord and caudal part of the spinal trigeminal nucleus (Vc). Previously, we demonstrated that glutamatergic lateral PB neurons innervate orexin (ORX) neurons in the perifornical area (PeF) of the hypothalamus. However, the neural circuit via which ORX neurons receive nociceptive input from the DH and brainstem remains to be determined. In the present study, we aimed to clarify the potential nociceptive circuit from DH/Vc to PeF via lateral PB. We first examined the neuronal activity of fluorogold (FG)-labeled, PeF-projecting lateral PB neurons in Wistar rats following either saline or formalin injection to the forepaw or lips. We clearly detected more abundant c-Fos-positive, FG-labeled neurons in the PB nucleus. To investigate the relay from the DH/Vc to the PeF via the lateral PB, we injected FG into the PeF and biotinylated dextranamine (BDA) into the contralateral DH or ipsilateral Vc. We observed the most prominent overlap between BDA-labeled axon terminals and FG-labeled neurons in the dorsal lateral and central lateral subnuclei. Furthermore, we found that FG-labeled neurons formed close contact sites with BDA-labeled axons with synaptophysin immunoreactivity. Using electron microscopy, we confirmed that these contact sites were truly synapses. Taken together, our results indicate that the DH/Vc transmits nociceptive information to the PeF via the lateral PB, suggesting the involvement of ORX neurons in the pain pathway.

Lateral parabrachial neurons innervate orexin neurons projecting to brainstem arousal areas in the rat.

Orexin (ORX) neurons in the hypothalamus send their axons to arousal-promoting areas. We have previously shown that glutamatergic neurons in the lateral parabrachial nucleus (LPB) innervate ORX neurons. In this study, we examined potential pathways from the LPB to ORX neurons projecting to arousal-promoting areas in the brainstem by a combination of tract-tracing techniques in male Wistar rats. We injected the anterograde tracer biotinylated dextranamine (BDA) into the LPB and the retrograde tracer cholera toxin B subunit (CTb) into the ventral tegmental area, dorsal raphe nucleus, pedunculopontine tegmental nucleus, laterodorsal tegmental area, or locus coeruleus (LC). We then analyzed the BDA-labeled fibers and ORX-immunoreactive neurons in the hypothalamus. We found that double-labeled ORX and CTb neurons were the most abundant after CTb was injected into the LC. We also observed prominently overlapping distribution of BDA-labeled fibers, arising from neurons located in the lateral-most part of the dorsomedial nucleus and adjacent dorsal perifornical area. In these areas, we confirmed by confocal microscopy that BDA-labeled synaptophysin-immunoreactive axon terminals were in contiguity with cell bodies and dendrites of CTb-labeled ORX-immunoreactive neurons. These results suggest that the LPB innervates arousal-promoting areas via ORX neurons and is likely to promote arousal responses to stimuli.