Formalin hindpaw injection induces changes in the [3H]prazosin binding to α1-adrenoceptors in specific regions of the mouse brain and spinal cord

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Abstract
Involvement of the α1-adrenoceptor subtypes in early and late phases of formalin pain was investigated by quantitative in vitro autoradiography in the spinal cord and brain structures of CD-1 mice. Total α1-adrenoceptors binding (including all α1-adrenoceptor subtypes) was assessed with [3H]prazosin; α1B-adrenoceptor was assessed with [3H]prazosin in the presence of 10 nM WB4101 to mask remaining α1-adrenoceptor subtypes. Early after formalin injection the α1-adrenoceptors (mainly α1B receptor) binding was reduced in the contralateral hind limb area of the somatosensory cortex and in the secondary motor cortex. A reduction occurred also in the ipsilateral laminae I–III of the spinal cord (both α1B- and non-α1B-adrenoceptors). Lately an increase of α1-adrenoceptors binding (mostly subtypes other than α1B) appeared in discrete amygdaloid and thalamic nuclei. These results provide the first description of changes at the level of central α1-adrenoceptors’ binding during the formalin-induced pain in mice. Their distribution suggests that they may have a functional meaning.