Biomedical subjects

G F Ball

Publications and source records attributed to G F Ball.

At least 91 records · Page 5Linked to original sources

PubMed1995

Autoradiographic localization of D1-like dopamine receptors in the forebrain of male and female Japanese quail and their relationship with immunoreactive tyrosine hydroxylase.

The distribution of D1-like dopamine receptors was studied in the brain of male and female Japanese quail (Coturnix japonica) by means of quantitative autoradiography with 3H-labelled D1 selective antagonist, SCH 23390, serving as a ligand. A specific, saturable, high affinity binding of this ligand was demonstrated. High densities of binding sites were detected in the lobus parolfactorius, olfactory tubercle, and paleostriatum augmentatum. Medium densities were observed in the entire neostriatum and in the external layers of the optic tectum. Similar levels of binding outlined the paleostriatum primitivum, the nucleus pretecalis and the nucleus intercollicularis. Low but significant levels of receptors were also present in the medial preoptic area at the level of the sexually dimorphic medial preoptic nucleus and throughout the infundibulum, as well as in the ectostriatum, medial and lateral septum, and nucleus accumbens. At the level of the medial septum, just dorsal to the anterior commissure, two circular areas of high receptor density corresponding to the nucleus of the septal commissure were also observed. No sex difference in receptor density could be detected in any of the areas. All areas containing high densities of D1 receptors also contained high densities of tyrosine hydroxylase (TH) fibers. However, certain areas characterized by a high density of TH-immunoreactive fibers did not contain appreciable densities of D1-like dopamine receptors. The distribution of this receptor and its relationship to TH-immunoreactivity is consistent with observations made in other vertebrates, suggesting that the dopaminergic system is evolutionarily highly conserved among amniote vertebrates.

Animals↗

PubMed1995

Appetitive as well as consummatory aspects of male sexual behavior in quail are activated by androgens and estrogens.

Appetitive male sexual behavior was measured in male quail with the use of a learned social proximity procedure that quantified the time spent by a male in front of a window providing a view of a female that was subsequently released into the cage, providing an opportunity for copulation. The learned response is not acquired by castrated males but can be acquired when castrates are treated with testosterone (T) or with the synthetic estrogen diethylstilbestrol or with the endogenous estrogen 17 beta-estradiol. Only birds that become sexually active acquire the response. Conversely, birds in which the consummatory copulatory behavior is disrupted by treatment with the antiestrogen tamoxifen lose the anticipatory response. These results demonstrate that appetitive sexual behavior is, like copulation, activated by T and by estrogens. This suggests that intracerebral aromatization of T also plays a critical role in the activation of this behavior.

Androgens↗

PubMed1994

Characterization and localization of D1 dopamine receptors in the sexually dimorphic vocal control nucleus, area X, and the basal ganglia of European starlings.

D1 dopamine receptors were pharmacologically characterized and localized by quantitative autoradiography in the basal ganglia of male and female European starlings (Sturnus vulgaris). The D1 selective antagonist SCH 23390 was used to label this receptor subtype. Starlings are songbirds and possess a neural circuit implicated in the learning and production of song. This circuit includes a sexually dimorphic nucleus, area X, that is a subregion of the parolfactory lobe of the basal ganglia and is known from work on zebra finches to receive dopaminergic input from the area ventralis of Tsai. We focused our investigation on the D1-like receptor subtype because they are abundant in the basal ganglia. Competition studies indicate that a variety of dopaminergic ligands compete with [3H] SCH 23390 for the binding site in an order of potency characteristic of a D1-like receptor. Autoradiographic studies of the basal ganglia revealed high D1 receptor densities in the avian homologues of the caudate-putamen and relatively low-receptor densities were observed in the avian homologue of the globus pallidus. In male starlings, area X could be reliably discerned on the autoradiograms by the higher density of D1 receptors compared to the surrounding parolfactory lobe (LPO). This was also true for females, though not as reliably as in males. When we compared the mean D1 receptor density in area X for males and females we did not find a significant sex difference. However, we also analyzed the data by comparing sex differences in the degree to which area X has a higher receptor density in comparison with the surrounding LPO. When we normalized D1 receptor density in area X relative to the LPO, we did find a significant sex difference. This sex difference in relative receptor density represents another neural sex difference in the song circuit that may mediate sex differences in the learning and production of song in starlings and other songbirds.

Animals↗

PubMed1994

Sex differences in the volume of avian song control nuclei: comparative studies and the issue of brain nucleus delineation.

Two goals of research on neural sex differences are to establish the behavioral function of such sex differences and to identify precisely what features differ between males and females. Comparative studies of sex differences in the volume of brain nuclei within the songbird vocal control circuit provide one way to address these goals. Informative comparisons can be either inter-specific or intra-specific. Inter-specific comparisons of species within the songbird suborder allow one to establish how species variation in the degree to which there is a sex difference in nuclear volume relates to species variation in the degree to which there is a sex difference in vocal behavior. Intraspecific comparisons of sex differences in nuclear volume involve the comparison of a variety of histochemical methods to define nuclei and describe a nucleus within a species. Sex differences in nuclear volume have now been measured for at least some song control nuclei in 10 different passerine species. In species with more complex male than female song, the volume of key song control nuclei is on average larger in males than in females. However, future studies will require more refined measures of vocal behavior and perceptual abilities to make more precise correlations between brain and behavior. In European starlings (Sturnus vulgaris), the volume of the vocal control nucleus, area X was found to be on average 1.95 times bigger in males than in females based on Nissl stained sections. Variation in neurotransmitter receptor density as determined by quantitative receptor autoradiography can also be used to define clearly the boundaries of a nucleus. When the boundaries of area X in male and female starlings were defined based on variation in muscarinic cholinergic and alpha 2-adrenergic receptor densities, volumetric estimates were obtained that are nearly identical to those obtained with the use of Nissl stains. Intra-specific comparisons of this sort extend our knowledge concerning the neurochemical basis of sex differences in nuclear volume. The wide application of this method would greatly increase our understanding of neural sex differences.

Animals↗

PubMed1994

Neurochemical specializations associated with vocal learning and production in songbirds and budgerigars.

Specialized neural circuitry has evolved in groups of birds where vocal learning is known to occur, such as in the oscine suborder of the Passeriformes (songbirds) and in the order Psittaciformes (parrots). These specializations are most prominent in the telencephalon, while the midbrain and medullary portions of the vocal control circuit are generally similar in all orders of birds. Specializations in songbirds have at least four components: 1) a set of distinct and interconnected vocal control nuclei in the forebrain; 2) unique connections between the auditory system and these vocal control nuclei; 3) the occurrence of receptors for sex steroid hormones in a subset of the vocal control nuclei; and 4) unique patterns in the distribution of various markers of the major classes of neurotransmitters within the vocal control nuclei. In the order Psittaciformes, as exemplified by budgerigars (Melopsittacus undulatus), it appears that neural specializations generally similar to those described in songbirds have evolved independently. Although anatomical studies have found a system of interconnected forebrain regions in budgerigars that are roughly similar to those described in oscines, detailed connectivity studies of this forebrain system suggest that it is only superficially similar to that of songbirds, and budgerigars also have unique connections between the auditory and motor systems. Also, analyses of the distribution of markers of neurotransmitter function in the budgerigar brain reveal patterns different from those described in songbird vocal control systems. This work suggests that songbirds and parrots have evolved separate neural 'solutions' to solve the problem of vocal plasticity. There are differences between these 'solutions' but also similarities that may be the result of convergent evolution. Although vocal behavior is learned in both songbirds and parrots, it differs in many respects. By taking advantage of this 'natural' experiment one can gain insight into the hormonal and neural events that mediate these different forms of vocal plasticity.

Animals↗

PubMed1993

Sexual dimorphism in the volume of song control nuclei in European starlings: assessment by a Nissl stain and autoradiography for muscarinic cholinergic receptors.

Previous studies have found that the volume of several song control nuclei is larger in male songbirds than in female songbirds. The degree of this volumetric sex difference within a given species appears to be systematically related to the degree of the behavioral sex difference. The largest volumetric differences have been reported in species in which the male sings and the female sings little, if at all, and the smallest sex differences in volume have been reported in species in which males and females both sing in nearly equal amounts. We compared the volume of three song control nuclei in male and female European starlings (Sturnus vulgaris), a species in which females are known to sing, though at a much lower rate than males. We investigated the volume of hyperstriatum ventrale, pars caudale, nucleus robustus archistriatalis, and area X of the lobus parolfactorius as defined with the use of a Nissl stain. In addition, we measured the volume of area X as defined by the density of muscarinic cholinergic receptors visualized by in vitro receptor autoradiographic methods. The volumes of all three of the song nuclei, as defined by Nissl staining, are significantly larger in males than in females. For area X, Nissl staining and receptor autoradiography indicate the same significant volumetric sex difference. The three nuclei are approximately one and one half to two times larger in males than in females, a degree of dimorphism that is intermediate to those reported for other species. Previous investigations of sex differences in the avian vocal control system have used only Nissl stains to define nuclear volumes. We demonstrate in this paper that receptor autoradiography can be used to assess dimorphisms in nuclear volume. Broad application of this approach to a number of neurotransmitter receptor systems will better characterize the dimorphisms in the song system, and therefore will provide greater insight into the neuroanatomical and neurochemical control of birdsong.

Animals↗

PubMed1993

Long-term potentiation in the avian hippocampus does not require activation of the N-methyl-D-aspartate (NMDA) receptor.

Evoked potentials recorded from slices of pigeon hippocampus were reversibly attenuated by 2 mM kynurenic acid. High frequency stimulation (3 x 200 Hz for 1 sec, with 1 sec intervals) evoked a persistent increase in the evoked potential, lasting in a nondecremental form for at least 2 hr. This increase in the magnitude of the potential was not blocked by antagonists of the NMDA receptor (APV and MK-801). These data suggest that the synaptic facilitation observed in the pigeon hippocampus, which appears to be a form of long-term potentiation, does not depend on the activation of NMDA receptors.

2-Amino-5-phosphonovalerate↗

PubMed1992

Immunocytochemical localization of androgen receptors in the male songbird and quail brain.

The distribution of androgen receptors was studied in the brain of the Japanese quail (Coturnix japonica), the zebra finch (Taeniopygia guttata), and the canary (Serinus canaria) by immunocytochemistry with a polyclonal antibody (AR32) raised in rabbit against a synthetic peptide corresponding to a sequence located at the N-terminus of the androgen receptor molecule. In quail, androgen receptor-immunoreactive cells were observed in the nucleus intercollicularis and in various nuclei of the preoptic-hypothalamic complex, namely, the nucleus preopticus medialis, the ventral part of the nucleus anterior medialis hypothalami, the nucleus paraventricularis magnocellularis, the nucleus ventromedialis hypothalami, and the tuberal hypothalamus. In the two songbird species, labeled cells were also observed in various nuclei in the preoptic-hypothalamic region, in the nucleus taeniae, and in the nucleus intercollicularis. Additional androgen receptor-immunoreactive cells were present in the androgen-sensitive telencephalic nuclei that are part of the song control system. These immunoreactive cells filled and outlined the boundaries of the hyperstriatum ventrale, pars caudalis, nucleus magnocellularis neostriatalis anterioris (both in the lateral and medial subdivisions), and nucleus robustus archistriatalis. The immunoreactive material was primarily present in cell nuclei but a low level of immunoreactivity was also clearly detected in cytoplasm in some brain areas. These studies demonstrate, for the first time, that androgen receptors can be detected by immunocytochemistry in the avian brain and the results are in general agreement with the binding data obtained by autoradiography with tritiated dihydrotestosterone. Immunocytochemical methods offer several advantages over autoradiography and their use for the study of the androgen receptor will greatly facilitate the analysis of steroid-sensitive systems in the avian brain.

Animals↗

PubMed1991

Long-term enhancement of synaptic responses in the songbird hippocampus.

Electrophysiological recordings from the hippocampus were taken using brain slices from 1-year-old, female, song sparrows (Melospiza melodia). The evoked responses were smaller and less stable as compared with those obtained from the mammalian hippocampus. They consisted of two spikes. The first spike had low calcium dependency and represented mainly fiber potential. The second spike demonstrated a clear calcium dependency proving its synaptic origin. Paired-pulse facilitation showed inhibition of the second response at latencies below 20 ms, facilitation at 30 ms and no changes above 30 ms. Train stimulation with 20 Hz (each train consisted of 1 s stimulation with 10-s intervals repeated 3 times) evoked a stable increase in the size of the evoked response lasting approximately 2 h. These data indicate that the avian hippocampus possesses several neurophysiological properties that typify the mammalian hippocampus including the long-term enhancement of the synaptic response following certain patterns of stimulation.

Animals↗

PubMed1991

Testosterone and avian life histories: the effect of experimentally elevated testosterone on corticosterone and body mass in dark-eyed juncos.

To assess whether alterations in the normal pattern of testosterone (T) secretion might be beneficial or detrimental, we studied a breeding population of dark-eyed juncos in which we elevated T experimentally and measured its effect on potential correlates of fitness. We treated both free-living and captive males with implants that were either empty (C-males, controls) or packed with T (T-males, experimentals). Timing of implant varied and was designed to mimic natural peak breeding levels except that peaks were either prolonged or premature. We bled the birds at recapture and analyzed their plasma, and that of their female mates, for T and corticosterone (B). We also measured body mass and fat score in free-living T- and C-males. In the field, T-implants elevated T and kept it elevated for at least a month. Experimental males also had higher B than controls. In captives, the effect of the implants on plasma T was detectable within 24 hr. B in captive T-males was again higher than in captive C-males. In females, neither T nor B differed between mates of T- and C-males. T-males implanted in early spring lost more mass between implant and recapture in late spring than did controls and also had lower fat scores when recaptured. When implants were inserted in summer, treatment did not influence mass. Elevated T in early spring apparently hastened the transition from the winter to the breeding mode of fat storage. We suggest that prolonged elevation of testosterone might be selected against because of the association between T and B. Premature elevation of T might be costly because of the resultant loss of mass and fat reserves, which could lead to mortality when spring snowstorms prevent access to food.

Adipose Tissue↗

PubMed1991

Testosterone effects on staining density and autoradiographic investigations of the alpha 2-adrenergic receptor in the medial preoptic nucleus of the Japanese quail: relationship to the activation of reproductive behavior.

The effects of gonadectomy combined or not with testosterone (T) therapy on the sexual behavior, cloacal gland area, staining density and alpha 2-adrenergic receptors in the medial preoptic nucleus (POM) were studied in male and female Japanese quail. In castrated males, T increased the cloacal gland size and activated copulatory behavior. In agreement with previous reports, these effects were sexually differentiated: under the influence of T, cloacal gland growth was smaller and this treatment did not activate masculine sexual behavior in females. The optical density of the medial preoptic nucleus stained with thionein blue (Nissl stain) was decreased by castration and increased by T in both males and females. This suggests that T has a profound effect on the synthesis of proteins in the POM and, since POM is a critical site in the activation by T of masculine sexual behavior, these induced proteins are, in all probability, a part of the causal chain of biochemical events giving rise to copulatory behavior. The treatment with T had, by contrast, no clear effect on the number of binding sites and on the affinity of the alpha 2-adrenergic receptors in the POM. Therefore, if the noradrenergic transmission is involved in the induction by T of copulatory behavior, it is probably acting either through the alteration of another adrenergic receptor subtype or through the modulation of the baseline levels or turnover of the transmitter itself.

Animals↗

PubMed1990

Muscarinic cholinergic receptors in the songbird and quail brain: a quantitative autoradiographic study.

In order to clarify the neuroanatomical basis for postulated muscarinic cholinergic control of a wide array of physiological processes in birds, the distribution of muscarinic cholinergic receptors in the brain of three avian species was investigated by quantitative autoradiography. The species consisted of two passerines (songbirds), the European starling (Sturnus vulgaris) and the song sparrow (Melospiza melodia), and one galliform, the Japanese quail (Coturnix coturnix japonica). [3H]N-methyl scopolamine (NMS), a muscarinic cholinergic antagonist was used as the ligand to label the receptors. Initial experiments demonstrated that the binding of this ligand in the three species is saturable in the nanomolar range and has a high affinity (Kd = +/- 0.6 nM). Displacement experiments revealed that three muscarinic ligands competed in an order of potency characteristic of the mammalian muscarinic receptor (i.e., atropine greater than oxotremorine greater than carbachol) for NMS binding in the avian brain. In all three species, portions of the basal ganglia, such as the parolfactory lobe and the paleostriatum augmentatum, exhibited the highest density of binding. On the other hand, the paleostriatum primitivum, the avian homologue of the mammalian globus pallidus, contained very few binding sites. Other telencephalic sites, such as the ventral and dorsal hyperstriatum, also revealed relatively high receptor density. However, the neostriatum and especially the ectostriatum showed much lower levels. In the hypothalamus, in all three species, specific binding could be observed in the ventromedial nucleus and adjacent areas. The paraventricular nucleus also showed moderate levels of binding density, especially in the two songbird taxa. At a more rostral level, the preoptic area showed low levels of binding. In the quail, the sexually dimorphic nucleus of the preoptic area was clearly outlined in the autoradiograms by the low level of binding sites compared to the surrounding areas. In the two passerine species, nuclei of the song system were identified by either high or low levels of NMS binding. High binding defined area X and the mesencephalic nucleus, intercollicularis (ICo). In contrast, the robust nucleus of the archistriatum and the magnocellular nucleus of the anterior neostriatum showed low levels of binding in comparison with the surrounding tissue. None of these nuclei were visible in the quail autoradiograms except for ICo, which appeared as in the passerines as a heavily labelled area surrounding the lightly labelled nucleus mesencephalicus lateralis pars dorsalis. In all three species, the hippocampal complex was devoid of NMS binding except for two lateral dark bands that were present along the entire rostral to caudal extent of the hippocampus.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1990

Song acquisition in photosensitive and photorefractory male European starlings.

We tested the ability of 1-year-old European starlings (Sturnus vulgaris) to acquire songs while in different physiological states. Photorefractory males, with low testosterone levels, learned songs as completely and as accurately as photosensitive males in full reproductive condition. This indicates that song acquisition in 1-year-old males does not depend on high levels of androgens. The ability to learn songs during the nonbreeding season may reflect the high song output of potential tutors through most of the year, including the photorefractory period, and may facilitate increases in song repertoire size in adulthood.

Animals↗

PubMed1989

Effects of the noradrenergic neurotoxin DSP-4 on luteinizing hormone levels, catecholamine concentrations, alpha 2-adrenergic receptor binding, and aromatase activity in the brain of the Japanese quail.

Previous investigations have established that DSP-4 reliably enhances the activating effects of testosterone on copulatory behavior in adult male quail. In the present study, we wanted to clarify the neurochemical changes that parallel these behavioral effects and to determine whether DSP-4 also affects non-behavioral steroid-dependent sexually dimorphic reproductive processes. We first showed using the Palkovits microdissection technique combined with assay by high-performance liquid chromatography (HPLC) that DSP-4 specifically depletes norepinephrine in several nuclei of the brain such as the medial preoptic nucleus, the ventromedial nucleus of the hypothalamus or the intercollicular nucleus but leaves intact the noradrenergic innervation in other areas such as the infundibulum or nucleus accumbens. Other amines such as dopamine and serotonin were not affected by the drug. Surprisingly DSP-4 did not decrease the binding of tritiated p-aminoclonidine in any of the brain areas which were studied by quantitative autoradiography. This suggests that most of the alpha 2-adrenergic receptors are located at the postsynaptic level but alternative interpretations are discussed. Testosterone treatment of castrated birds specifically reduced the density of alpha 2-adrenergic receptors in the dorsal infundibulum and in the medial mammillary nucleus. The possible relations of this receptor change to the control of luteinizing hormone (LH) secretion are discussed. Finally it was shown that DSP-4 treatment decreases plasma LH levels (which reveals the stimulatory effect of norepinephrine on LH secretion) but increases the testosterone-induced aromatase activity in the preoptic area. This latter effect could be one of the mechanisms by which DSP-4 potentiates copulatory behavior in testosterone-treated quail.

Adrenergic alpha-Agonists↗

PubMed1989

Distribution of alpha 2-adrenergic receptors in the brain of the Japanese quail as determined by quantitative autoradiography: implications for the control of sexually dimorphic reproductive processes.

With the use of [3H]p-aminoclonidine (PAC), alpha 2-adrenergic binding sites were mapped in the brain of the Japanese quail (Coturnix coturnix japonica). The sites were labeled with the use of in vitro quantitative autoradiography. Special attention was given to areas implicated in the control of sexually dimorphic reproductive processes including sexual behavior. Preliminary competition experiments found that [3H]PAC binding on tissue sections exhibited a pharmacology appropriate to the alpha 2 receptor. Binding sites were found to be heterogeneously distributed throughout the brain. Some of the highest levels of specific binding were found in several areas regulating reproductive function such as the preoptic area, the supraoptic nucleus, the infundibulum, and the medial mammillary nucleus of the infundibulum. [3H]PAC labeled precisely the morphologically dimorphic preoptic medial nucleus but no sexual dimorphism in density of receptor binding was identified. However, dimorphism in density of receptor binding was identified in two areas: the medial mammillary nucleus and the mesencephalic intercollicular nucleus. The former area appears to be involved in the regulation of gonadotrophin secretion and the latter area has been implicated in the control of vocal behavior. These neurochemical dimorphisms may contribute to the regulation of two sexually dimorphic reproductive processes, gonadotropin secretion and courtship vocalizations.

Adrenergic alpha-Agonists↗

PubMed1989

An autoradiographic study of alpha 1-adrenergic receptors in the brain of the Japanese quail (Coturnix coturnix japonica).

The neuroanatomical distribution of alpha 1-adrenergic receptors was studied in Japanese quail by quantitative in vitro autoradiography using the specific antagonist [3H]prazosin as the ligand. The presence of saturable (Bmax less than 200 fmol/mg protein) high affinity (Kd less than 0.12 nM) binding sites was detected by saturation analysis. High concentrations of [3H]prazosin binding sites were detected in the archistriatum/pars ventralis, the hippocampus, the cortex piriformis, the area corticoidea dorsolateralis, the dorsal thalamus, and the nucleus praetectalis. Lower concentrations were seen in the intercollicular nucleus, the lateral septum, and the posterior and tuberal hypothalamus. Very little binding was seen in the preoptic and anterior hypothalamic areas. The relatively high number of binding sites identified in the telencephalic structures agrees well with previous mammalian studies. This is in contrast with the pattern in the anterior hypothalamus where, in mammals, a number of nuclei have been reported to contain a high receptor density.

Animals↗

PubMed1989

A dorsomedial subdivision within the nucleus intercollicularis identified in the Japanese quail (Coturnix coturnix japonica) by means of alpha 2-adrenergic receptor autoradiography and estrogen receptor immunohistochemistry.

The nucleus intercollicularis is an important site in the control of vocalization in birds. In oscines, a subregion of the nucleus intercollicularis called the dorso-medial intercollicular nucleus appears to play a key role in this process because it receives the majority of the projections from the nucleus robustus archistriatalis and sends most of the projections to the motor nucleus of the hypoglossal nerve. In this paper, we present neurochemical studies of the nucleus intercollicularis in the Japanese quail which suggest the presence of heterogeneity within this structure. One rostral band contains high densities of cholinergic muscarinic receptors identified by quantitative autoradiography using tritiated N-methylscopolamine as the ligand. A caudal dorso-medial region is specifically labeled by estrogen receptors identified using immunocytochemistry and by alpha 2-adrenergic receptors which were quantified by autoradiography using tritiated para-amino-clonidine. This latter subregion is possibly equivalent to the dorso-medial intercollicular nucleus of oscines. Additional track-tracing studies should be performed to confirm this homology. The coexistence of estrogen and alpha 2-adrenergic receptors within the same structure suggests important functional connections between steroid action and catecholaminergic systems in the brain.

Animals↗

PubMed1989

Immunohistochemical localization of corticotropin-releasing factor in selected brain areas of the European starling (Sturnus vulgaris) and the song sparrow (Melospiza melodia).

Corticotropin-releasing factor (CRF) was localized in the brains of two passerine species, the European starling (Sturnus vulgaris) and the song sparrow (Melospiza melodia), by means of immunohistochemistry. The hypothalamic distribution of this peptide in these species includes a complex of immunoreactive perikarya observed in the paraventricular nucleus (PVN), in both its medial and lateral divisions. Nerve fibers were also seen running from these areas to the anterior median eminence (AME) where a terminal field is apparent. A wide variety of extrahypothalamic nuclei containing CRF-immunoreactive cells and fibers were identified. An apparent CRF terminal field can be visualized in the lateral septum. A dense fiber plexus is present in the nucleus accumbens (Ac) and more caudally in the nucleus of the stria terminalis (nST). In colchicine-pretreated animals, it was revealed that these areas also contain CRF-stained perikarya. The pattern of CRF immunoreactivity in the Ac-nST complex is continuous, with no distinction apparent between the nuclei. The medial preoptic area (mPOA) and the adjacent diagonal band of Broca contain CRF-fibers, while cells are apparent in the mPOA. In the mesencephalon, cells were visualized in the midbrain central gray; a terminal field and scattered positively stained perikarya were found in areas more ventral to the central grey that are adjacent to the third cranial nerve. Scattered cells were also seen at the border of the nucleus intercollicularis-nucleus mesencephalicus lateralis, pars dorsalis complex. In contrast to mammalian studies, no immunoreactive nerve fibers or perikarya were observed in telencephalic areas homologous to the mammalian neocortex.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗