Substance P and its tachykinin NK1 receptor: a novel neuroprotective target for Parkinson's disease

Parkinson＇s disease （PD） is the most common motor neurode- generative disorder affecting approximately 4 million people worldwide. Although PD presents primarily with motor dysfunction, non-motor symptoms including cognitive decline, mood disorders, reduced olfaction and constipation are also of- ten present, with some of these non-motor symptoms even pre- senting prior to the onset of motor symptoms. It is well known that PD is largely caused by the gradual degeneration of dopa- minergic neurons within the substantia nigra pars compacta （SNc）, along with the presence of protein aggregates called Lewy bodies, which consist primarily of ct-synuclein and are found in the cytoplasm of surviving neurons. This ongoing cell loss and Lewy body pathology is not confined to the SNc, but is also seen in other brain regions implicated in PD pathogenesis such as the locus ceruleus.

Functional dissection of parabrachial substrates in processing nociceptive information

Painful stimuli elicit first-line reflexive defensive reactions and,in many cases,also evoke second-line recuperative behaviors,the latter of which reflects the sensing of tissue damage and the alleviation of suffering.The lateral parabrachial nucleus(lPBN),composed of external-(elPBN),dorsal-(dlPBN),and central/superior-subnuclei(jointly referred to as slPBN),receives sensory inputs from spinal projection neurons and plays important roles in processing affective information from external threats and body integrity disruption.However,the organizational rules of lPBN neurons that provoke diverse behaviors in response to different painful stimuli from cutaneous and deep tissues remain unclear.In this study,we used region-specific neuronal depletion or silencing approaches combined with a battery of behavioral assays to show that slPBN neurons expressing substance P receptor(NK1R)(lPBNNK1R)are crucial for driving pain-associated self-care behaviors evoked by sustained noxious thermal and mechanical stimuli applied to skin or bone/muscle,while elPBN neurons are dispensable for driving such reactions.Notably,lPBNNK1R neurons are specifically required for forming sustained somatic pain-induced negative teaching signals and aversive memory but are not necessary for fear-learning or escape behaviors elicited by external threats.Lastly,both lPBNNK1R and elPBN neurons contribute to chemical irritant-induced nocifensive reactions.Our results reveal the functional organization of parabrachial substrates that drive distinct behavioral outcomes in response to sustained pain versus external danger under physiological conditions.