Morphological Differences among Luteinizing Hormone Releasing Hormone Neurons from Postpartum and Estrous Cycling Cows

Abstract

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 µm) 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 medial 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 < 0.01) and average or total length of process per neuron (p < 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 < 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 < 0.05) in EPP cows than in MPP or CYC cows. For all groups, the area of LHRH immunostaining was greater (p < 0.001) in the external layer of lateral regions of the ME, but was similar in both internal and external layers of medial regions of the ME. Although additional ultrastructural studies are necessary to distinguish between de novo structural changes of neurons and the reduced filling of preexisting processes with immunoreactive LHRH, these data support the hypothesis of reduced activity of LHRH neurons during early to middle stages of the puerperium.

Distribution of β-Endorphin Immunoreactivity in the Arcuate Nucleus and Median Eminence of Postpartum Anestrus and Luteal Phase Cows

“…Finally, suckled anestrous cows had higher concentrations of opioid binding sites in tissue ho mogenates containing the preoptic-anterior hypothal amic regions than suckled cows that reinitiated estrous cycles [21 ]. In a companion study [23], we found in these same cows that LHRH dendritic lengths and ME innervation by LHRH axons and terminals were both reduced in EPP cows compared to CYC cows. In this study, irp-END was lowest in the ARC of EPP cows.…”

“…[32,33] and about 30% bind P4 [34]. These findings may account for the vast heteroge neity in POMC mRNA levels among individual ARC neurons following steroid treatments [35,36], In postpar tum cows, similar heterogeneity may have masked differ ences of POMC mRNA levels between suckled and nonsuckled cows [37], Possibly, an individual cell analysis, such as performed for LHRH neurons in the postpartum cow [23], might have revealed additional differences in ir-P-END neurons between postpartum groups. EPP MPP CYC Postpartum interval Previous studies demonstrated that the ME contains specific opioid binding sites and is a site of opioid inhibi tion of LHRH secretion [22], In postpartum cows, as pre viously described in heifers [20], ir-p-END in ME formed a well-defined band in the external layer.…”

“…Parts of these tissues were used previously to describe morphological differences among LHRHimmunoreactive neurons [23]. Primiparous and multiparous cows were randomly assigned to two treatment groups within 1 week after calving: early postpartum (EPP, days 10-16 postpartum, n = 5) or midpostpartum (MPP, days 33-43 postpartum, n = 4).…”

Origen y migración de las neuronas GnRH en el bovino (<i>Bos taurus</i>)

“…El número de neuronas y fibras GnRH en los mamíferos es escaso y existen variaciones en diferentes especies de animales (81, 107-109, 115, 116), las mutaciones genéticas (122), el período de desarrollo (106,(108)(109)(110), el sexo (118,121,123), la estación reproductiva en especies cuya reproducción es estacional (124) y diferentes acontecimientos reproductivos tales como la ciclicidad, el parto y el puerperio, entre otros (125) son posibles causas para explicar estas diferencias. También, la distribución de los somas neuronales y los axones GnRH difieren notoriamente en las áreas y núcleos de la región hipotalámica entre las diferentes especies animales.…”

“…En la hembra bovina (Bos taurus), el porcentaje del área ocupado por las fibras GnRH-ir en la eminencia media fue significativamente menor en las vacas durante el período puerperal temprano con respecto a las hembras que se hallaban en el período puerperal tardío y al grupo de hembras cíclicas (125).…”