UNILATERAL ABSENCE OF THE TERMINAL NERVE AND DISTRIBUTION OF GONADOTROPIN-RELEASING-HORMONE IMMUNOREACTIVE NEURONS IN THE BRAIN OF THE COMMON MOLE-RAT (CRYPTOMYS, RODENTIA)

A paired terminal nerve with gonadotropin-releasing hormone-immunoreac tive (GnRHir) neurons was found in five of six specimens of the Zambia n common mole-rat (Cryptomys sp.). In these animals the distribution o f GnRHir neurons in the CNS was approximately even on both sides. One adult female lacked a right terminal nerve, yet exhibited a comparable total number of GnRHir neurons, most of which were located on the lef t side of the brain, i.e., on that side where the terminal nerve was p resent. An additional population of GnRHir cells was detected in the a rea of the parafascicular and dorsomedial thalamic nuclei of three non -reproductive adult females, but not in young animals (one female, two males). The additional GnRHir cells, referred to as dark spot cells ( DSCs) since their perikarya exhibit large or small strongly immunoreac tive vacuoles, were present on both sides of the brain in equal number s even in the specimen with unilateral absence of the terminal nerve. Obviously, the lack of one terminal nerve correlates with a drastic re duction in the number of ipsilateral genuine neurons but leaves the DS Cs unaffected. (C) 1998 Elsevier Science B.V. All rights reserved.