Morphological differences among luteinizing hormone releasing hormone neurons from postpartum and estrous cycling...

Deficiency in secretion of luteinizing hormone releasing hormone (LHRH) from the median eminence (ME) is one of the factors limiting reinitiation of estrous cycles following parturition in cows. This study employs quantitative light microscopy to describe morphological changes in LHRH neurons obtained from cows at three postpartum times. Tissues were obtained from anestrous early postpartum (EPP; days 10-16, n = 5), midpostpartum (MPP; days 33-43, n = 4), and multiparous cycling (CYC; months 12-14, n = 4) cows. Following perfusion fixation, cryostat sections (60 microns) of the ventral forebrain were immunostained with anti-LHRH serum via the biotin-avidin-peroxidase method. In all cows, LHRH perikarya formed a loosely arranged continuum, extending from anterior to posterior within the diagonal band of Broca, the lateral and medical preoptic areas, and the anterior hypothalamus. Width and length of perikarya were similar between postpartum groups. The number of dendrite-like processes per neuron (p less than 0.01) and average or total length of process per neuron (p less than 0.001) were greater in the CYC than in the EPP and MPP cows. Although all groups of cows contained a spectrum of lengths of dendrite-like processes, both EPP and MPP cows obtained a greater (p less than 0.05) percentage of neurons with shorter processes and a smaller percentage of neurons with longer processes. Within the ME, the percentage area occupied by immunostained fibers was less (p less than 0.05) in EPP cows than in MPP or CYC cows.(ABSTRACT TRUNCATED AT 250 WORDS)