Nerve growth factor depletion by autoimmunization produces thermal hypoalgesia in adult rats

Nerve growth factor (NGF) plays a role in mechanisms of inflammation and hyperalgesia in adult animals. We sought to determine if NGF depletion produced by autoimmunization of adult rats altered their thermal sensitivity to an acute noxious thermal stimulus. Anti-NGF IgG was not detected in the cerebrospinal fluid of any tested samples. Only those rats with the highest anti-NGF serum titers showed significant (P < 0.05) thermal hypoalgesia measured using the hot plate test (52 degrees C): the mean (+/-S.D.) hind paw lick latency of rats in the high anti-NGF titer group was 18.0 +/- 4.6 s compared to means of 10.8 +/- 4.3 s, 9.2 +/- 2.6 s and 10.1 +/- 3.0 s in the medium, low and control groups, respectively. Thus, NGF depletion by autoimmunization is a useful model for investigating the role of NGF in behavioral responses of adult rats to noxious stimuli, providing high titers of antibody are present.