Projecto nº:016588

Referência do Projecto:PTDC/NEU-NMC/1259/2014 (POCI-01-0145-FEDER-016588)

Título:Pre- and postsynaptic interactions between afferents supplying lamina I projection neurons in

the lumbar and cervical spinal cord: impact for somatic pain and migraine

Montante envolvidos:

Investimento total: 173.604,00€

Apoio FEDER: 147.563.40€

Apoio OE: 26.040,60€

Localização do projecto: Porto, Portugal

Sintese do projecto:

Chronic pain affects 19 % of the adult European population and more than 100 million people in the U.S. where its annual cost exceeds $500 billion (Breivik et al 2006; Institute of Medicine 2011). It highly impairs patients? mood, quality of life and performance at work, yet available treatments are often inadequate and elicit numerous side effects. This is a direct consequence of our limited knowledge about the spinal and supraspinal neuronal circuitries processing pain. Therefore, better understanding of the nociceptive processing network and its alterations causing chronic pain is urgently required. The most superficial layer of the spinal dorsal horn, lamina I, plays a key role in the nociceptive processing. It receives input from thin myelinated Aδ and unmyelinated C afferents, and projects to specific areas of the brainstem and thalamus. Lamina I is a complex network where projection neurons form about 5 % of the neuron population. In the lumbar spinal cord, alterations in the processing mode of lamina I neurons result in a chronic pain. In the upper cervical cord, considered as a part of the trigeminocervical complex, lamina I neurons relay afferent inputs from the cranial meninges and cervical somatic structures, and serve as the neural substrates of primary headache syndrome, e.g. migraine. Organization of the inputs to projection neurons, their pre- and postsynaptic interactions underlying nociception and functional disorders are poorly understood. Presynaptic inhibition of nociceptive afferents by the low-threshold afferents is critically important for the control of pain. It was  ostulated to function as a gate regulating nociceptive information flow into the spinal cord. However, until now the presynaptic inhibition by low-threshold fibers was not described for afferent inputs to lamina I neurons. Furthermore, the presynaptic inhibition of trigeminal and cervical afferents as a mechanism controlling migraine associated symptoms, such as allodynia, has not been considered so far. Postsynaptic interaction of afferent inputs is necessary for the signal integration and polymodal processing. We have recently shown that lamina I neurons receive broad afferent inputs (Pinto et al 2010) and that visceral and somatic C fibers converge directly onto individual projection neurons (Attachment 1) providing the neural substrate of referred pain. Trigeminal inputs from the cranial dura mater to the neurons in the upper cervical cord are currently considered as major contributors to primary headache, such as migraine. These neurons also receive somatic inputs from their cervical afferents providing the neural substrate for the spread and referral of pain accompanying headache. Unfortunately, we know little about the trigeminal and cervical afferent inputs to spinal lamina I neurons. Lack of knowledge about the pre- and postsynaptic interactions between afferents supplying lamina I neurons reflectslimitations of the methods used so far. It was not possible to record from identified neurons in the isolated spinal cord and trigeminocervical complex with preserved afferent pathways. During the last years our laboratory established several new approaches allowing solution of this problem. We developed methods of: 

-imaging and patch-clamp recording from lamina I neurons in the isolated spinal cord and brainstem (Szucs et al 2009):

-classification of projection neurons based on their local axon collaterals (Szucs et al 2010),

-identifying mono- and polysynaptic inputs to lamina I neurons from several dorsal roots (Pinto et al 2010; Luz et al 2014) or peripheral nerves (Attachment 1),

-studying the afferent-driven presynaptic inhibition of C fiber inputs to lamina I neurons (Attachment 2),

-recording the trigeminal nerve inputs to cervical neurons (Attachment 3).

The aim of this proposal is to study mechanisms of presynaptic inhibition and postsynaptic integration in anatomically classified lamina I projection neurons. Projection neurons in the lumbar and cervical cord will be labelled by injecting a retrograde tracer into their supraspinal projection areas. Task 1, we shall study low-threshold Aβ/Aδ-fiberdriven presynaptic inhibition of nociceptive Aδ and C fiber inputs to projection neurons in the lumbar cord. Task 2, in the isolated trigeminocervical complex we shall characterize cervical neurons receiving inputs from the trigeminal and spinal nerves. Task 3, the presynaptic interactions between the trigeminal and spinal nerve inputs to the cervical lamina I neurons will be studied. Neurons labelled with biocytin in Tasks 1-3 will be classified on the basis of their somatodendritic architecture and course of major axon and collaterals.

Galeria de fotos do projeto