Calcium-binding protein-immunoreactive projection neurons in the caudal subnucleus of the spinal trigeminal nucleus of the rat

It has been reported that calcium-binding proteins are good markers for dif ferent sets of neurons in various brain regions. We examined expression of the main calcium-binding proteins in projection neurons in the rat medullar y dorsal horn (MDH) by combining immunofluorescence histochemistry for calb indin D28k (CB), calretinin (CR) and parvalbumin (PV) with the retrograde t ract-tracing method. A fluorescence tracer, tetramethylrhodamine-dextran am ine (TMR-DA), was injected into the parabrachial, thalamic or hypothalamic region. After such injections, a number of PV-, CR-, and/or CB-immunoreacti ve MDH neurons were labeled retrogradely with TMR-DA. Triple-immunofluoresc ence histochemistry further revealed that a number of CB-, CR-, or PV-immun oreactive TMR-DA-labeled MDH neurons showed immunoreactivity for substance P receptor (NK1), and that they expressed immunoreactivity for c-fos protei n in the rats which were injected with formalin into the lips. Thus, it was indicated that some of CB-, CR- or PV-containing projection neurons in the MDH might be involved in the transmission of nociceptive stimuli. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.