properties ofratprimary afferent neurones withcarbonic anhydrase activity

izations (AHPs) weremadefromtheL3,L4andL5dorsal rootganglia (DRGs)of6-to8-week-old anaesthetized female Wistar ratsinvitro at36-5+ 1 QC.Neurones wereclassified by their conduction velocities (CVs) asAa/,/? (>12m s-1), Ad(13-12m s')orC fibre neurones (<1P3m s-1). 2. Following therecording, fluorescent dyewasinjected intracellularly. Sections ofinjected neurones weretested forcarbonic anhydrase (CA)activity histochemically. Reaction product intensity andcell size weremeasured. Control experiments showedthatintracellular dye,timeinvitro, axotomy andelectrical stimulation didnotaffect proportions ofCA-positive neurones ortheir size distributions. 3. Approximately 28-30%ofDRG neurones wereCApositive. Theirsizes wereapproximately normally distributed andcovered theentire size rangeofDRGneurones withno correlation between size andCAintensity. Agreater proportion ofAx/,/ cells (62%)than ofAd(32%)orCcells (38%)wereCApositive, butCAintensity wasnotcorrelated with CV. 4. InA neurones meanAPduration wassignificantly shorter inCA-positive cells; forCApositive andCA-negative cells, respectively, these values were16and2-8msforAd cells; 11and1-7ms forAa/,/. cells; andwere1-2and2-3msforallA cells. CAintensity wasnegatively correlated withAPduration atbaseinallthese groups. 5. AgaininA neurones, themeanAHP durations weresignificantly shorter intheCApositive cells: themeanAHPdurations to80% recovery forpositive andnegative cells were8-8and36ms,respectively, forAc//, cells andwere8-6and26ms,respectively, for allA cells. CAintensity wasnegatively correlated withAHP duration inAa/,/I cells and allAcells together. 6. Afibre cells withthelonger APandAHPdurations wereallCAnegative, while cells with theshorter durations included bothCA-positive andCA-negative cells. 7. CA-positive andCA-negative A fibre neurones therefore havedifferent electrophysiological characteristics. Itissuggested thatCA-negative A fibre neurones mayhave slower somatic firing ratesanddifferent sensory functions fromtheCA-positive neurones.