Nerve fibers and perikarya containing gonadotropin-releasing hormone (GnRH-like) immunoreactivity were investigated in the brain of the three-week-old chick. Gallus domesticus using the technique of immunocytochemistry. Six major groups of perikarya were found to include the olfactory bulb, olfactory tubercle/lobus parolfactorius, nucleus accumbens, septal preoptic hypothalamic region (three sub-nuclei), lateral anterior thalamic nucleus and in and about the oculomotor complex. The immunostaining was unusual in the latter group, suggesting that the neurons may contain a GnRH-II like material. Immunoreactive fibers for GnRH were found throughout the entire brain extending from the olfactory bulbs to the caudal brainstem. Two anatomical areas, not emphasized in the past literature, which had distinct GnRH-like immunoreactivity, included the lateral anterior thalamic nucleus and the preoptic recess. The former included a group of GnRH perikarya that is also known to be a retino-recipient area while the latter contained neuronal terminals some of which appeared to be contacting the cerebrospinal fluid of the preoptic recess. An attempt was made to list all anatomical structures that contained or were juxta-positioned to sites that displayed immunoreactive perikarya and fibers including circumventricular organs.

The distribution of VIP-like perikarya and fibers was determined throughout the chick brain. The most rostral immunoreactive perikarya were found to be cerebrospinal fluid-contacting neurons in the pars medialis of the lateral septal organ. Additional data were presented supporting the idea that the lateral septal organ is another circumventricular organ within the brain of birds (Kuenzel and van Tienhoven 1982). A large group of immunoreactive perikarya was found in the lateral hypothalamic area and appeared continuous with immunoreactive neurons in the anterior medial and ventromedial hypothalamic nuclei (n). A few perikarya were located in the paraventricular hypothalamic n. A number of immunoreactive neurons were found within and about the infundibular and inferior hypothalamic n., none however was immunoreactive cerebrospinal fluid-contacting neurons. Immunoreactive perikarya were found predominantly in laminae 10-11 of the stratum griseum et fibrosum superficiale. A few scattered perikarya were found ventromedial to the n. tegmenti pedunculo-pontinus pars compacta and locus ceruleus. Some of the immunoreactivity was unusual, being very homogeneous within the cell body with little evidence of the material in the axon or dendrites. Perikarya were found in the central gray, n. intercollicularis, and area ventralis of Tsai. The most caudal structure showing immunoreactive neurons was the n. reticularis paragigantocellularis lateralis. Brain areas containing the most abundant immunoreactive fibers, listed from the rostral-most location, were found in the ventromedial region of the lobus parolfactorius and the lateral septal n. Continuing caudally, there were immunoreactive fibers within the periventricular hypothalamic n.; some of the fibers were found to travel for some distance parallel to the third ventricle. Dense immunoreactive fibers were found in the tractus cortico-habenularis et cortico-septalis, medial habenular n. and posterior and dorsal n. of the archistriatum. A number of areas had what appeared to be baskets of immunoreactive fibers (perhaps immunoreactive terminals) surrounding non-reactive perikarya. Brain areas containing terminals included the piriform cortex, area ventralis of Tsai, interpeduncular n., and specific regions of the stratum griseum et fibrosum superficiale. A very dense immunoreactivity occurred within the external zone of the median eminence, the dorsolateral parabrachial n., and n. tractus solitarii. Vasoactive intestinal polypeptide appears to be a useful peptide for defining the neuroanatomical constituents of the visceral forebrain in birds.

Although the existence of two somatostatin variants (SS1 and SS2) has now been demonstrated in the brain of mammals, amphibians, and fish, only one isoform of somatostatin (SS1) has been characterized to date in the brain of birds. Here we report cloning of the cDNA encoding a 101-amino-acid protein (PSS2) that encompasses the somatostatin variant [Pro(2)]somatostatin-14 (SS2) at its C-terminus. Sequence analysis indicated that chicken PSS2 is more closely related to fish PSS2 than to mammalian cortistatin precursors. Northern blot analysis showed that the chicken PSS1 gene is expressed in the central nervous system (CNS) and in the pancreas, whereas the PSS2 gene is expressed only in the CNS and not in peripheral organs. In situ hybridization histochemistry revealed that, in the chicken brain, PSS1 mRNA is more widely distributed than PSS2 mRNA. In particular, PSS1 mRNA expression was found in the hippocampus, the hyperstriatum, the preoptic area, the ventricular hypothalamic nuclei, the optic tectum, and several nuclei of the mesencephalon and rhombencephalon. In contrast, the distribution of PSS2 mRNA was restricted to a few regions of the brain, including the paraolfactory lobe, the paleostriatum, and some nuclei of the mesencephalon and rhombencephalon. The fact that the PSS1 and PSS2 genes are differently expressed in the brain and in peripheral organs indicates that, in chicken, the two somatostatin variants likely exert distinct functions. In particular, the observation that PSS1 mRNA, but not PSS2 mRNA, occurs in the preoptic area and in the ventral hypothalamic nuclei suggests that, of the two somatostatin isoforms, only SS1 acts as a hypophysiotropic factor.

The peptidergic melanin‐concentrating hormone (MCH) system was investigated by immunocytochemistry in several birds. MCH perikarya were found in the periventricular hypothalamic nucleus near the paraventricular organ and in the lateral hypothalamic areas. Immunoreactive fibers were very abundant in the ventral pallidum, in the nucleus of the stria terminalis, and in the septum/diagonal band complex, where immunoreactive pericellular nets were prominent. Many fibers innervated the whole preoptic area, the lateral hypothalamic area, and the infundibular region. Some fibers also reached the dorsal thalamus and the epithalamus. The median eminence contained only sparse projections, and the posterior pituitary was not labeled. Thus, in birds, a neurohormonal role for MCH is not likely. Immunoreactive fibers were observed in other regions, such as the intercollicular nucleus, stratum griseum periventriculare (mesencephalic tectum), central gray, nigral complex (especially the ventral tegmental area), reticular areas, and raphe nuclei. Although no physiological investigation concerning the role of MCH has been performed in birds, the distribution patterns of the immunoreactive perikarya and fibers observed suggest that MCH may be involved in functions similar to those described in rats. In particular, the projections to parts of the limbic system (ventropallidal ganglia, septal complex, hypothalamus, dorsal thalamus, and epithalamus) and to structures concerned with visceral and other sensory information integration suggest that MCH acts as a neuromodulator involved in a wide variety of physiological and behavioral adaptations (arousal) with regard to feeding, drinking, and reproduction. J. Comp. Neurol. 411:239–256, 1999. © 1999 Wiley‐Liss, Inc.

Changes in the content of vasopressin-immunoreactive material in neurons and their projections were examined in pregnant and nonpregnant guinea pigs as well as in mother and newborn animals. Before sacrifice all animals used in the present study were submitted to a pyrogen test, during which the pregnant animals displayed a reduced fever response to exogenous pyrogen. The unlabeled enzyme-immunoperoxidase method was used in the present study. Light microscopic examination showed that, in comparison to all other groups examined, the pregnant animals exhibited a reduced content of the vasopressin-immunoreactive substance in the supraoptic nucleus (SON), in the neuronal pathways extending between the paraventricular nucleus (PVN) and the SON, as well as in the axons projecting to the neural lobe of the pituitary. An increased amount of vasopressin-immunoreactive material was observed during pregnancy especially in the medial portion of the PVN, in axonal distensions in the external zone of the median eminence and in the extrahypothalamic projection sites of the PVN in the lateral septum and in the amygdala. In the pregnant animals neurovascular contacts of vasopressinergic perikarya and fibers were abundant in the PVN; in the lateral septum and in the amygdala vasopressinergic terminals appeared to contact neurons of other types. It is suggested from the present immunocytochemical results that activation of neurons in the medial portion of the PVN and the increased number of vasopressinergic terminals and preterminals in the lateral septum and in the amygdala might be functionally involved in fever suppression at the term of pregnancy.