IMMUNOHISTOCHEMICAL LOCALIZATION OF DELTA SLEEP-INDUCING PEPTIDE-LIKE IMMUNOREACTIVITY IN THE CENTRAL NERVOUS SYSTEM AND PITUITARY OF THE FROG RANA RIDIBUNDA
Abstract
The purpose of the present study was to investigate the distribution of delta sleep-inducing peptide in the brain and pituitary of the frog RMa ridibmaiz and to determine the possible effect of this nonapeptide on adrenocorticotropic hormone and corticosteroid secretion. Delta sleep-inducing peptide-like immunoreactive fibres were observed throughout the brain of the frog. These fibres generally exhibited the characteristics of glial cell processes. Scarce delta sleep-inducing peptide-positive fibres were seen in the olfactory bulb and in the periventricular areas of the telencephalon. In the diencephalon, numerous delta sleepinducing peptide-containing processes were noted in the preoptic nucleus, the infundibular nuclei and the median eminence. A few cerebrospinal fluid-contacting cells were visualixed in the ventral nucleus of the infundibulum. Delta sleep-inducing peptide-positive fibres were also observed in the mesencephalon, radiating through the different layers of the tectum. In the cerebellmn, all Purkinje cells exhibited delta sleep-inducing peptide-like immtmoreactivity. More caudally, numerous delta sleep-inducing peptide-positive fibres were noted in the vestibular nucleus of the rhombencephalon. A dense network of delta sleep-inducing peptide-containing fibres was seen in the pars nervosa of the pituitary. In the distal lobe., a population of endocrine cells located in the anteroventral region contained delta sleep-inducing peptide-immunoreactive material. Labelling of consecutive sections of the pituitary by delta sleep-inducing peptide and adrenocorticotropic hormone antiserum revealed that a delta sleep-inducing peptide-related peptide is expressed in corticotroph cells. The possible role of delta sleep-inducing peptide in the control of adrenocorticotropic hormone and corticosteroid release was studied in vitro, using the perifusion system technique. Administration of graded doses of delta sleep-inducing peptide (from lo-* to 10e6 M) to perifused frog anterior pituitary cells did not alfect the spontaneous release of adrenocorticotropic hormone. In addition, prolonged infusion of delta sleep-inducing peptide (10m6 M) did not alter the stimulatory effect of corticotropin-releasing factor (lo-' M) on adrenocorticotropic hormone secretion. Similarly, exposure of frog interrenal slices to delta sleepinducing peptide did not induce any m&cation of spontaneous or adrenocorticotropic hormone-evoked secretion of corticosterone and aldosterone. Our results provide the tlrst evidence for the presence of a delta sleep-inducing peptide-related peptide in lower vertebrates. The occurrence of delta sleep-inducing peptidolike immunoreactivity in specific areas of the brain suggests that the peptide may act as a neuromodulator. Although delta sleep-inducing peptide was detected in pituitary corticotrophs, we did not observe any effect of exogenous delta sleep-inducing peptide on adrenocorticotropic hormone or corticosteroid secretion in oitro. The nonapeptide delta sleep-inducing peptide (DSIP) was originally characterized from the cerebral venous blood of the rabbit for its hypnogenic activity.43 Immunocytochemical and biochemical studies have demonstrated that DSIP is widely distributed in the CNS of man," cat,') rabbit" and rat.
Keywords
Abbreuiations: ACTH
adrenocorticotropic hormone
ANF
atria1 natriuretic factor
CRF
corticotropin-releasing factor
DSIP
delta sleep-inducing peptide
GH
growth hormone
HBPES
N-2 hydroxyethylpiperaxine-N-2- ethanesulphonic acid
LH
~lutei&ing hormone
LH- RI-I luteinixing hormonareleasing hormone
a-MSH
01 melanocyte-stimulating hormone
MCH
melanin- concentrating hormone
NPY
neuropeptide Y
PBS
phosphate-buffered saline
RIA
radioimmunoassay
SRIF
somatotropin-release inhibiting factor
TRH
thyrotropin-releasing hormone