Hypothalamic dopaminergic neurons in prolactin-deficient Ames dwarf mice: localization and quantification of deficit by tyrosine hydroxylase immunocytochemistry

Hypothalamic tuberoinfundibular prolactin-inhibiting neurons show decreased levels and synthesis of dopamine in two types of genetically prolactin-deficient dwarf mice (Snell, Ames) which arise from separate mutations. A reduction to 2% of normal in this neuronal population has been quantified for Snell dwarfs. The present study was undertaken in order to quantify morphometrically the deficit and its distribution in Ames dwarf mice, including comparisons of sex and adult age. The brains of dwarf (df/df) and normal phenotypic (DF/?) sibling mice of both sexes from 4 to 16 months of age were immunostained for tyrosine hydroxylase, the rate-limiting enzyme in dopamine synthesis; neuronal perikarya were counted in coronal sections of tuberoinfundibular arcuate nucleus (area A12), medial zona incerta (A13) and anterior periventricular (A14) hypothalamic areas at 180 microns rostral-to-caudal intervals. Normal (DF/?) mice exhibited no differences in neuron numbers, with regard to age or sex, in any of the three dopaminergic areas. In dwarf mice, a tendency toward decreased neuron numbers with age was statistically significant for area A14 only, and the size of the neuronal population in A12 was reduced in males compared with females. Total A12 neuron number in dwarfs was 48% of that in normal mice (P < 0.001). Periventricular (A14) perikaryal numbers were reduced slightly (P < 0.05) in dwarfs compared with normals. Numbers of A13 neurons were comparable for DF/? and df/df.(ABSTRACT TRUNCATED AT 250 WORDS)

Postnatal reduction in number of hypothalamic tuberoinfundibular dopaminergic neurons in prolactin-deficient dwarf mice

Mice homozygous for the recessive 'Ames' dwarf mutation have undetectable serum or pituitary prolactin (PRL). Accompanying this pituitary deficiency is a marked reduction of dopamine (DA) and its rate-limiting synthetic enzyme tyrosine hydroxylase (TH) in PRL-regulating tuberoinfundibular hypothalamic neurons. In order to determine whether this deficit in adult Ames dwarf mice is congenital or arises postnatally, brains of dwarf (df/df) and normal (DF/?) littermate mice were assessed for TH immunoreactivity from 7 days through 2 months of age. Numbers of TH-positive neurons were counted in three hypothalamic DA areas: tuberoinfundibular A12, medial zona incerta A13, and anterior periventricular A14. There was an increase in the number of TH-positive neurons between 7 and 21 days of age in A12 and A14, but not in A13, for both DF/? and df/df mice. Between 21 days and 2 months of age, cell numbers were the same in all three areas in DF/? mice and in A13 and A14 in df/df mice. However, A12 TH-positive cell number in dwarfs decreased significantly (p < 0.01) between 21 days and 2 months, and was markedly lower (p < 0.001) in df/df than in DF/? mice at 2 months of age. The results emphasize the specificity of the dopaminergic neuron reduction in the Ames dwarf, which is restricted to the PRL-regulating tuberoinfundibular region. The data also indicate that the dwarf DA/TH deficit has an onset in late postnatal development, suggesting a response to absence of target PRL, rather than a primary hypothalamic effect of the dwarf mutation.

Developmental assessment of hypothalamic tuberoinfundibular dopamine in prolactin-deficient dwarf mice

Development of the hypophysiotropic hypothalamus in PRL-deficient Ames dwarf (df/df) mice was examined for steady state dopamine (DA) by visualization using formaldehyde-induced catecholamine histofluorescence and by quantification using catecholamine HPLC at selected postnatal ages (7, 14, 21, 30, and 90 days). Phenotypically normal (DF/?) littermate mice were compared with dwarfs by both methods at each age. The studies were designed to investigate whether the known deficiency in hypothalamic tuberoinfundibular DA in adult dwarfs is present neonatally or develops over the postnatal period. The anterior pituitary of each mouse was processed for GH and PRL immunocytochemistry. At 7 days of age, GH immunostaining was robust, and scattered PRL-positive cells were noted in DF/? pituitary. Homogeneously distributed PRL cells increased in number through 30 days of age in normal mice. Neither GH nor PRL immunoreactivity was present in df/df mice at any age. At 7, 14, and 21 days of age, hypothalamic DA tuberoinfundibular histofluorescence was comparable in df/df and DF/? mice. At 90 days of age, tuberoinfundibular histofluorescence in normal mice remained intense, but was virtually undetectable in dwarfs. The developmental change affected only tuberoinfundibular neurons, since DA histofluorescence in nonhypophysiotropic areas, such as substantia nigra (SN), was qualitatively comparable for df/df and DF/? for all ages examined. Norepinephrine (NE) fluorescence in hypothalamus was also comparable for df/df and DF/?. Catecholamine HPLC provided quantitative confirmation of histofluorescence observations. DA and NE levels in both hypothalamus and ventral midbrain, including SN, increased during development in both df/df and DF/? brains. NE levels were not different between dwarf and normal animals at any age in either medial basal hypothalamus (MBH) or SN. The DA concentration in SN was not different between df/df and DF/? at any age examined. MBH DA was comparable in df/df and DF/? mice at 7, 14, and 21 days of age; at 30 and 90 days, MBH DA was markedly lower (P < 0.001) in dwarf than in normal mice. Although MBH DA in dwarfs was comparable to that in normal mice at 21 days, the increase in dwarfs between 14 and 21 days was not statistically significant. Thus, the hypothalamic DA deficit that exists in adult dwarf mice is not present neonatally and represents a failure to increase DA compared with normal mice after 14 days of age. The failure of continued development of hypophysiotropic tuberoinfundibular DA neurons in dwarf mice is correlated chronologically with absent pituitary PRL production.

Differential recovery of prostacyclin and endothelium-derived relaxing factor after vascular injury

Differential recovery of prostacyclin and endothelium-derived relaxing factor after vascular injury. Am. J. Physiol. 262 (Heart Circ. Physiol. 31): H1449-H1457, 1992. The recovery of prostacyclin (prostaglandin I2, PGI2) synthesis and endothelium-derived relaxing factor (EDRF) activity, as demonstrated by acetylcholine (ACh)-induced relaxation, by rabbit aorta was examined up to 8 wk after balloon catheter-induced injury. Following injury, basal 6-keto-PGF1 alpha formation was decreased acutely; however, after 3 wk it was not different from control. Arachidonic acid-stimulated 6-keto-PGF1 alpha formation was decreased, returning to control levels at 3 and 8 wk for thoracic and abdominal aorta, respectively. ACh-induced relaxation did not return to control levels over the 8-wk study. Initiation of reendothelialization with a layer of hyperplastic endothelial cells overlying subendothelial fibrosis and intimal hyperplasia were present at 2-3 wk. Intimal hyperplasia appeared 2 wk after injury and progressed throughout the period of the study. These data indicate that following balloon catheter-induced injury the formation of both PGI2 and EDRF is reduced and that recovery follows a differential time course. In addition, the recovery of PGI2 formation did not coincide with the attenuation of intimal hyperplasia, whereas the relationship between EDRF formation and intimal hyperplasia is uncertain.