Janet Allen

Direct excitatory effects of neuropeptide Y (NPY) on rat hippocampal neurones in vitro

Intracellular recordings from granule cells of the rat dentate gyrus show neuropeptide Y (NPY) applied by pressure ejection from pipettes containing 1.2-12 microM by pressures of less than 200 kPa for 1-5 s in duration to consistently evoke membrane depolarisations accompanied by a reduction in membrane resistance. The depolarisations were accompanied by an increase in excitability. Since the depolarisations evoked by NPY were not attenuated by either tetrodotoxin or kynurenic acid a direct excitatory action of NPY is postulated.

Neuropeptide Y (NPY) and vasopressin (AVP) in the hypothalamo-neurohypophysial axis of salt-loaded or Brattleboro rats.

A close anatomical relationship between nerve terminals containing neuropeptide Y (NPY) and vasopressin (AVP) has been demonstrated in the hypothalamic paraventricular (PVN) and supraoptic nuclei (SON). Furthermore, injections of NPY into the SON increased plasma concentrations of AVP in the rat. These data suggest a potential involvement of hypothalamic NPY in fluid homeostasis in the rat. Therefore, we have studied the effect of elevated plasma osmolality on the concentration of NPY and AVP in the hypothalamus and neurointermediate lobe (NIL) of the pituitary gland. Furthermore, we measured the concentration of NPY in the AVP-deficient Brattleboro rat, which suffers from diabetes insipidus and hyperosmolality. Salt-loading increased plasma osmolality and the concentration of AVP from 2.0 +/- 0.5 to 4.1 +/- 0.6 pg/ml after 7 days. The concentration of NPY in the NIL doubled after 7 days of salt-loading, from 7.9 +/- 0.6 ng/mg protein to 15.2 +/- 1.4 ng/mg protein, whereas AVP concentrations fell from 2285.7 +/- 210.9 ng/mg protein to 187.5 +/- 2.5 ng/mg protein. AVP concentrations in the ME increased transiently after 2 days of salt-loading and returned to control levels after 7 days. In contrast, NPY concentrations in the ME were unchanged at 2 days and were increased 61% after 7 days. NPY concentrations also were significantly elevated after 7 days of salt-loading in the preoptic area (POA) and mediobasal hypothalamus (MBH). The concentration of NPY in the NIL of the homozygous Brattleboro rat was 2-fold greater than in the heterozygous Brattleboro rat and 4-fold greater than in Sprague-Dawley rats used as controls.(ABSTRACT TRUNCATED AT 250 WORDS)

Sex differences in vasoactive intestinal peptide (VIP) concentrations in the anterior pituitary and hypothalamus of rats

Recent evidence suggests that vasoactive intestinal peptide (VIP), a putative prolactin (PRL)-releasing factor, is both synthesized and released by anterior pituitary cells, to act as a paracrine or autocrine factor. We have investigated the hypothesis that hypothalamic or pituitary VIP levels differ in male and female rats, since neuroendocrine control of PRL is sexually differentiated. Opposite sex differences were found in the hypothalamus and anterior pituitary. Random-cycle female rats had one-third higher VIP levels in the hypothalamus than males. In contrast, anterior pituitary VIP levels were 3 times as high in male rats as in females. Median eminence VIP levels were similarly low in both sexes. These results support a possible role of VIP in the sexually dimorphic regulatory mechanisms of PRL secretion. Moreover, demonstration that hypothalamic and pituitary VIP levels vary in opposite directions suggests that VIP is differentially regulated at the two sites.