Nucleus Mesencephalicus Lateralis Research Articles

Enhancement and suppression in the auditory midbrain nucleus (MLD) of the pigeon

Auditory evoked potentials (AEPs) and spike responses were recorded from the same recording site in the nucleus mesencephalicus lateralis pars dorsalis (MLD) in pigeons with a tungsten microelectrode. Depending on the recording sites within the MLD, enhancement and suppression of the AEPs in response to clicks were observed at particular frequencies of a background continuous pure tone. Post stimulus time histograms (PSTs) of the spike responses, if available in such cases, were recorded from the same position by the same electrode. Suppression of the AEPs always occurred but enhancement occurred in only 21% of the trials. The frequencies of tone bursts that caused maximum AEP were vaguely related to the frequencies of continuous pure tones that elicited maximum suppression of the AEPs in response to clicks. However, enhancement was produced by a continuous pure tone of approximately 1.5 kHz, independent of the frequencies of tone bursts that produced maximum AEPs. Most of the PSTs in such instances showed parallel relations between the spike responses and the amplitudes of the AEPs. The nature of the enhancement and suppression of the click evoked AEPs during continuous pure tones was clearly different from those in recordings from the nucleus magnocellularis, nucleus angularis and Field L in respect to the probability of occurrence of enhancement and suppression.

Parvalbumin and calbindin-D28K immunoreactivity as developmental markers of auditory and vocal motor nuclei of the zebra finch

The posthatch developmental profiles of parvalbumin and calbindin-D28K immunoreactivity were compared for the auditory nucleus mesencephalicus lateralis pars caudalis in the midbrain, n. ovoidalis in the thalamus, and telencephalic field L, as well as for the telencephalic vocal motor nuclei hyperstriatum ventrale pars caudalis and n. robustus archistriatalis. The two calcium-binding proteins showed specific temporal patterns of expression in each nucleus, without following an ascending or descending sequence. Calbindin-D28K immunoreactivity usually preceded parvalbumin immunoreactivity. Onset of expression, especially of parvalbumin-immunostaining, was earlier in auditory nuclei than in vocal motor nuclei. The developmental order of appearance of immunoreactivity in somata, dendrites and axons was different in various brain regions. In some structures parvalbumin or calbindin-D28K immunoreactivity occurred only transiently. The two antibodies bound to separate but spatially complementary groups of cells in the nucleus mesencephalicus lateralis pars dorsalis and n. ovoidalis, as has previously been described in visual nuclei. This pattern was maintained into adulthood. These hitherto unknown subcompartments may reflect internal functional organization in these nuclei. A transitory neostriatal zone containing parvalbumin-positive neurons and fibres was observed between the immature field L and the emerging hyperstriatum ventrale pars caudalis. Some comparative aspects are discussed as to the way in which neurons distinguished by the two Ca-binding proteins may differ in energy metabolism, activity pattern and other functional mechanisms.

Neural mechanisms of directional hearing in the pigeon

The directional sensitivity of single auditory neurons in the midbrain (Nucleus mesencephalicus lateralis pars dorsalis) of the pigeon (Columba livia) was studied, using acoustic free-field stimulation (usually pure tones) in the frontal hemifield. Of a total of 337 units, 84.6% showed statistically significant changes of their responses as a function of sound azimuth. Of these, most units respond maximally to sounds in a particular azimuthal range, each has its "best area". These neurons were classified into four classes according to the properties of their best areas: (1) contralateral neurons (53.4%); (2) ipsilateral neurons (6.2%); (3) frontal neurons (18.1%); and (4) complex neurons (3.3%). The first two showed only one border of the best area within the frontal hemifield, with an increase of response strength towards the contralateral and the ipsilateral side, respectively; with frontal neurons, the best area was bounded towards both sides within the frontal hemifield, whereas the complex neurons had two or more separated best areas or extensive frontal inhibitory areas. In the remaining units (3.6%), termed weakly directional neurons, changes of their discharge rate depending on sound azimuth were statistically significant, but too poor to determine any best areas. There was a significant under-representation of best frequencies in the mid-frequency range (1-2 kHz) with a minimum in the relative number of MLD neurons recorded from at 2 kHz. However, the directional sensitivity of the neurons quantified by analysing different parameters of the directional diagrams (dynamic range, roll-off steepness, best area width) was undiminished in the mid-frequency range. In several experiments, in addition to the neurons' directional sensitivity in free-field sound, their sensitivity to interaural ongoing time (phase) differences (OTDs) and interaural intensity differences (IIDs) were also tested, using dichotic stimulation (pure tones) by headphones. Directional sensitive neurons tuned to low frequencies (best frequency less than 2 kHz) were either sensitive exclusively to OTDs or to both OTDs and IIDs; the ranges of best OTDs were correlated significantly with the azimuthal position of the best area. "High frequency" units (best frequency greater than 2 kHz) were sensitive to IIDs but not to OTDs.(ABSTRACT TRUNCATED AT 400 WORDS)

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)

Localization and Quantitative Autoradiography of Glutamatergic Ligand Binding Sites in Chick Brain.

The anatomical localization of glutamate receptor subtype-selective ligand binding sites was investigated in 1-day-old chick brain using quantitative autoradiography. Under the conditions used, the regional distributions of [3H]glutamate, [3H]AMPA (a selective quisqualate receptor ligand) and [3H]kainate binding sites are manifestly different. [3H]l-glutamate binding is densely localized in the telencephalon, particularly in the neostriatum (2.8 pmol/mg protein). In addition, [3H]l-glutamate labels the thalamus, the nucleus mesencephalicus lateralis pars dorsalis, the superficial layers of the optic tectum and the molecular layer of the cerebellum. [3H]AMPA binding sites are most densely localized in the hippocampus (0.90 pmol/mg protein), with an otherwise relatively uniform distribution of binding within the telencephalon. [3H]AMPA also labels the striatum griseum et fibrosum superficiale of the optic tectum and the molecular layer of the cerebellum. [3H]Kainate binding sites are extremely densely packed in the molecular layer of the cerebellum (10 pmol/mg protein). Other regions of [3H]kainate binding include the hyperstriatum and the thalamus. The binding of the NMDA receptor channel blocker [3H]MK-801 is increased in the presence of 1 mM l-glutamate. [3H]MK-801 binding is generally widespread in the telencephalon but is notably absent from the ectostriatum. No evidence of [3H]MK-801 binding sites was detected in the cerebellum, even in the presence of 1 mM l-glutamate. The relatively high densities and the well-defined localizations of the glutamate receptor subtype binding sites suggest that chick brain provides a useful system for the further study of excitatory amino acid receptors.

Autoradiographic localization of nicotinic acetylcholine receptors in the brain of the zebra finch (Poephila guttata).

We have localized nicotinic acetylcholine receptors in the zebra finch brain by using three 125I-labelled ligands: alpha bungarotoxin and two monoclonal antibodies to neuronal nicotinic receptors (MAb 35 of Tzardos et al., J. Biol. Chem., 250: 8635-8645, '81; and MAb 270 of Whiting and Lindstrom: J. Neurosci. 6: 3061-3069, '86). Unfixed brains from intact adult male and female zebra finches were prepared for in vitro autoradiography. Low-resolution film autoradiograms and high-resolution emulsion autoradiograms were prepared for each of the three ligands. The major brain structures that bind all three of the ligands are hippocampus; hyperstriatum dorsalis; hyperstriatum ventralis; nucleus lentiformis mesencephali; nucleus pretectalis, some layers of the optic tectum; nucleus mesencephalicus lateralis; pars dorsalis; locus ceruleus; and all cranial motor nuclei except nucleus nervi hypoglossi. The major structures labelled only by [125I]-alpha bungarotoxin binding included hyperstriatum accessorium and the nuclei: preopticus medialis, medialis hypothalami posterioris, semilunaris, olivarius inferior, and the periventricular organ. Of the song control nuclei, nucleus magnocellularis of the anterior neostriatum; hyperstriatum ventralis, pars caudalis; nucleus intercollicularis; and nucleus hypoglossus were labelled. The binding patterns of the two antibodies were similar to one another but not identical. Both labelled nucleus spiriformis lateralis and nucleus geniculatus lateralis, pars ventralis especially heavily and also labelled the nucleus habenula medialis; nucleus subpretectalis; nucleus isthmi, pars magnocellularis; nucleus reticularis gigantocellularis; nucleus reticularis lateralis; nucleus tractus solitarii; nucleus vestibularis dorsolateralis; nucleus vestibularis lateralis; nucleus descendens nervi trigemini; and the deep cerebellar nuclei. Lobus parolfactorius and nucleus vestibularis medialis were labelled by only MAb 270, whereas only MAb 35 labelled nucleus laminaris and the medial and lateral pontine nuclei. These data extend previous reports of cholinergic participation in the song system (Ryan and Arnold: J. Comp. Neurol. 202: 211-219, '81) to suggest that the zebra finch song system may contain several closely related nicotinic receptors. In several brain nuclei it appeared that certain anatomical portions of a nucleus or a certain class of neurons were specifically labelled. Furthermore, in certain cases, the labelling appeared to be clustered around Nissl-stained cell nuclei, thus suggesting that the receptors are concentrated on or in somata.

Auditory responses in the nucleus basalis of the pigeon

Single-unit responses and field potentials evoked by sound stimuli were recorded from the nucleus basalis in the frontal lobe of the pigeon brain. Auditory units in this nucleus showed phasic responses to tonal stimuli and sharp frequency tuning. The latency of responses was 5.8±0.6 ms. The response properties of these units were similar to those of units in the nucleus mesencephalicus lateralis, pars dorsalis (a mesencephalic auditory nucleus), where fibers from the auditory nuclei in the medulla terminate. This suggests that the nucleus basalis receives projections from medullary auditory neurons. Averaged auditory field potentials in the frontal lobe had three prominent components. Regional changes in the polarity of each component suggest that auditory neurons in the medulla project directly to the nucleus basalis, which in turn projects to the frontal neostriatum.

Ascending vocalization pathways in the female ring dove: Projections of the nucleus intercollicularis

Nest-coo (courtship) vocalization is an estrogen-dependent component of a sequence of behaviors leading to egg-laying in the ring dove ( Streptopelia risoria). Implantation of estrogen in the nucleus intercollicularis of ovariectomized females restores the ability to produce nest-coos. Lesion of n. intercollicularis specifically disrupts nest-cooing and inhibits follicular development. We used anterograde transport of tritiated leucine to identify regions that receive input from n. intercollicularis. As a control, isotope was injected in an auditory nucleus (nucleus mesencephalicus lateralis, pars dorsalis) neighboring the n. intercollicularis. A strong projection to the nucleus was observed, demonstrating a potential interaction between auditory and vocalization systems at the level of the midbrain. Local projections of n. intercollicularis were observed in midbrain and hind brain nuclei including the nucleus tegmenti pedunculo-pontinus, pars compacta and nucleus papillioformis. A conspicuous projection ascended centrally via the mesencephalic central gray. Proceeding rostrally, this pathway was traced to the nucleus periventricularis magnocellularis and tissue surrounding it. At its rostral extent, the pathway was found to project to the nucleus preopticus medialis, the anterior medial hypothalamus, and the lateral hypothalamus. These results are consistent with the possibility of a nucleus intercollicularis projection to regions that regulate reproductive function.

Effects of unilateral and bilateral cochlea removal on 2-deoxyglucose patterns in the chick auditory system.

The 2-deoxyglucose (2DG) method was used to map functional activity in the auditory system of chicks that had been subjected to unilateral or bilateral cochlea removal. Following survival times of 1 day to 4 weeks, chicks were exposed to continuous white noise in the 2DG experiments. In monaural subjects nucleus angularis and nucleus magnocellularis showed faint 2DG uptake on the side contralateral to the intact ear. In the binaural nucleus laminaris, the asymmetrical and almost mirror-imaged labeling pattern (Lippe, Stewart, and Rubel: Brain Res. 196:43-58, '80) was produced. The superior olive (OS) was strongly labeled on the ipsilateral side, whereas the contralateral OS showed only a slight 2DG uptake at its medial border. The lateral lemniscus and nucleus lemnisci lateralis, pars ventralis (LLv) showed stronger activation on the contralateral side. Both Nissl stains and 2DG patterns provide evidence that nucleus ventralis lemnisci lateralis (VLV) can be subdivided into an anterior (VLVa) and a posterior (VLVp) part. Whereas VLVp is labeled only contralaterally, VLVa is labeled on both sides with similar intensity. Nucleus mesencephalicus lateralis, pars dorsalis (MLD) is strongly labeled throughout contralaterally. The ipsilateral MLD shows a defined ventral portion of high 2DG uptake. Intensity of labeling here is symmetrical to the corresponding area of the contralateral MLD. These symmetrical patterns were related to the tonotopic organization of MLD, which was mapped in intact animals by using tone stimuli. Assuming that symmetrical 2DG uptake in monaural animals indicates excitatory input from both ears (EE-cells), it appears that these EE-cells occupy a sector of each isofrequency plane in MLD. Nucleus ovoidalis (Ov) generally was stronger labeled on the contralateral side. The columnar organization of field L as seen in monaural chicks has already been described (Scheich, Exp. Brain Res. 51:199-205, '83). In bilaterally deafened chicks, MLD, Ov, and layer L2 of field L showed strong but spatially restricted 2DG accumulation in contrast to absence of labeling in peripheral nuclei. The 2DG patterns in monaural chicks are likely to reflect excitatory input within the auditory system. In addition they reveal new insights into the functional organization of some of its nuclei. In particular, they support the notion that MLD contains maps of several interaural integration mechanisms similar to field L. Labeling in the auditory system of bilaterally deafened chicks may result from descending projections or from other than auditory inputs.

Origin of ascending auditory projections to the nucleus mesencephalicus lateralis pars dorsalis in the chicken

Ascending auditory projections to the nucleus mesencephalicus lateralis pars dorsalis (MLd) were studied in white Leghorn chickens by means of unilateral injections of horseradish peroxidase into the MLd and by injections of tritiated leucine into nucleus angularis or the combined nucleus magnocellularis and nucleus laminaris. The experiments showed that nucleus angularis sends an extensive projection to the contralateral MLd and a smaller projection to the rostral pole of the ipsilateral MLd; the lagenar region contributes to these bilateral connections. Nucleus angularis also projects bilaterally to the superior olive and nucleus ventralis lemnisci lateralis and to the contralateral nucleus lemnisci lateralis pars ventralis and dorsal nucleus of the lateral lemniscus. Projections from nucleus laminaris were demonstrated to the ipsilateral superior olive, to the contralateral lemniscal nuclei and a small medial region in MLd bilaterally; the contralateral projection is much denser than the ipsilateral one. Other nuclei having ascending connections with MLd include the contralateral superior olive, the ipsilateral nucleus lemnisci lateralis pars ventralis, the contralateral nucleus ventralis lemnisci lateralis and the contralateral MLd. The ipsilateral superior olive and nucleus ventralis lemnisci lateralis also project to MLd but much more sparsely than in their contralateral projection. Although several of these findings correspond with auditory connections previously shown in the pigeon brainstem, they differ fundamentally in that we find both nucleus angularis and nucleus laminaris projecting to different areas of the MLd on both sides of the brain. In particular, our observation that the cochlear nucleus has bilateral connections with MLd demonstrates an important avian similarity with the brainstem auditory pathways of other terrestrial vertebrates.

The efferent connections of the nuclei of the descending trigeminal tract in the mallard ( Anas platyrhynchos L.)

The efferent and intranuclear connections of the nuclei of the descending trigeminal tract of the mallard have been studied with lesion methods, and by axonal transport techniques following injections of tritiated leucine, and of horseradish peroxidase. The large subnucleus oralis neurons, including those belonging to the nucleus of the ascending glossopharyngeal tract, have proven to be the sole origin of trigeminocerebellar connections. The cerebellar afferents are of the mossy fiber type, and terminate predominantly in lobules V, VI and VII, and possibly, lobule IV. Trigeminocerebellar projections are ipsilateral except for the vermal area. Subnucleus interpolaris is the main source of intratrigeminal fibers that terminate in subnucleus oralis and the ventral part of the main sensory nucleus. These intranuclear connections are bilateral, but the medium-celled caudal part of subnucleus interpolaris in particular contains the majority of bi- and/or contralaterally projecting neurons. Additionally, the small cells in the rostral part of subnucleus interpolaris project ipsilaterally upon the parabrachial region, and upon the lateral reticular formation. Projections upon the parabrachial region furthermore emanate bilaterally from layer I of the rostral subnucleus caudalis. A minor part of layer I neurons sends its axons contralaterally along with those of the dorsal column nuclei toward the thalamic nucleus dorsolateralis posterior. Associated with the medial lemniscus, contralateral termination is also present in the lateral part of the ventral lamella of oliva caudalis, in the marginal zone of nucleus mesencephalicus lateralis, pars dorsalis and immediately surrounding intercollicular grey and, finally, in the nucleus intercalatus thalami. Furthermore, a bilaterally descending projection from subnucleus caudalis upon layers I and II of the rostral cervical cord was observed. Close to their origin subnucleus caudalis neurons project upon the adjoining caudal part of the lateral reticular formation.

Vocalization after electrostimulation of the brain of pigeons in relation to heart- and breathing-rates

Vocalizations elicited by electrical stimulation in the midbrain of pigeons were studied in connection with heart- and breathing-rates. Most of the sites where sound production could be elicited were found in the nucleus intercollicularis (ICo), lying rostromedial to the nucleus mesencephalicus lateralis, pars dorsalis (Mld). All vocalizations were accompanied by an increase of heart- and breathing-rates. Electrical stimulation elicits predominantly changes in breathing-rate which can be accompanied by passive vocalization.

Distribution of methionine-enkephalin immunoreactivity in the chick brain: an immunohistochemical study.

The distribution of Met-enkephalin-like immunoreactivity in the brains of 2-week-old domestic chicks was studied with immunohistofluorescence and the unlabeled antibody peroxidase-antiperoxidase technique, using antibodies to Met-enkephalin generated in rabbits. Immunoreactive cell bodies were found in the telencephalon, diencephalon, and mesencephalon in areas as yet uncharacterized as discrete nuclei in birds (E-1, E-2, E-3, E-4, E-5); further cells were located in the diencephalic nucleus spiriformis lateralis, the midbrain medial intercollicular nucleus (E-6), the nucleus mesencephalicus lateralis, pars dorsalis, the Edinger-Westphal nucleus and dorsal occulomotor nucleus; and in the nucleus of cranial nerve X and an uncharacterized area in the dorsolateral medulla (E-7). Immunoreactive fibers and/or terminals were located around the immunoreactive cell bodies and, in addition in the lateral septal area of the telencephalon; in the preoptic and hypothalamic areas of the diencephalon; in the anterior intercollicular area, periaqueductal central gray, area C, and the midventral tegmentum of the mesencephalon; in the nucleus solitarius, nucleus IX-X, nucleus intercalatus, nucleus intermedius, and ventrolateral areas of the rhombencephalon. The pattern of distribution of met-enkephalin in the chick is compared with that in the rat. A possible functional role for Met-enkephalin in neural mechanisms mediating some behaviors of the chick is suggested.

Barn owls can use ongoing‐time disparities to determine the azimuth of a sound source

A class of auditory neurons in the owl's nucleus mesencephalicus lateralis pars dorsalis (MLD), a midbrain auditory nucleus, have small spatial receptive fields. We sought our relationships between the spatial receptive fields of these neurons (measured under free‐field conditions) and sensitivities to binaural disparities (presented dichotically). To switch easily between free‐field and dichotic stimulation we constructed threaded, miniature earphones, which could be inserted into threaded rings implanted into the owl's ear canals. Neurons with spatial receptive fields were found to be sensitive to a narrow range of ongoing‐time disparities in the biologically significant range of tens of microseconds. There was a strong correlation between the azimuth of the spatial receptive fields and the magnitude of the ongoing‐time disparities. Freely behaving owls were presented with similar ongoing‐time disparities through identical earphones. They reacted to the stimuli in a manner consistent with the conclusion that ongoing‐time disparities were used to ascertain the azimuth of a sound source.

The Nucleus mesencephalicus lateralis, pars dorsalis in Neotropical Passerines

The volume of the nucleus mesencephalicus lateralis, pars dorsalis and the optic lobe were determined in 8 species of neotropical birds in the order Passeriformes: Pyrocephalus rubinus, Pitangus sulphuratus, Atticora fasciata, Molothrus bonariensis, Tangara nigrocincta, Ramphocelus dimidiatus, Euphonia xanthogaster and Spinus magellanicus. The ratio of the volume of the nucleus to the volume of the optic lobe was calculated for each species, and was found to be larger in all 8 species than in a series of nonpasserine species examined previously by Cobb. A possible relationship between the relative size of this nucleus and the auditory capabilities of birds is discussed.

A map of auditory space in the midbrain of the owl

Auditory units that responded to sound only when it originated from a limited area of space were found in the lateral and anterior portions of the midbrain auditory nucleus (nucleus mesencephalicus lateralis pars dorsalis, MLD) of the owl. The response properties of these units were studied in five barn owls (Tyto alba) using a remotely controlled, movable sound source under free‐field, anechoic conditions. The area of space to which such a unit responded was virtually independent of the nature (tone, click, or noise) and the intensity of the sound stimulus, and was defined as the unit's receptive field. Within a unit's receptive field could be found a small area to which the unit would respond with greatest vigor. This area of space was termed the unit's best area. Units in the lateral and anterior portions of MLD were systematically arranged according to the azimuth and elevation of their best areas. Units with contralateral best areas were located posterolaterally; units with ipsilateral best areas were located anteromedially. Elevation was arrayed along the dorsoventral axis with high best areas located dorsally and low best areas ventrally. [Work supported by NIH.]

Electrically elicited vocalization from the brain of the house finch (Carpodacus mexicanus).

AbstractVocalizations were electrically elicited from the brains of thirty-eight male and female house finches (Carpodacus mexicanus) using acute procedures and local anesthetic. Nine types of call notes were produced including notes which sounded like song elements, but complete normal song was never evoked. Vocalizations could be electrically elicited from all parts of the brain except the cerebellum, but the widest variety of calls and the points yielding vocalizations at the lowest threshold were located in the midbrain around the nucleus mesencephalicus lateralis pars dorsalis. Precise anatomical localization of call type was not found and all calls were elicited from both males and females.

Anatomical distribution of estrogen target cells in the avian CNS: a comparison with the mammalian CNS.

The distribution of labeled cells was investigated in the brain of the ring dove one hour after administration of 3H-estradiol. Major areas of concentration of labeled cells were found in (1) the preoptico-strial region: nucleus preopticus medialis and nucleus interstitialis of the dorsal olfactory projection, (2) the basal hypothalamic region: nucleus hypothalamicus posterior medialis and nucleus inferior, (3) the amygdaloid region: nucleus taeniae and adjacent portions of the archistriatum, and (4) the midbrain: substantia grisea surrounding the nucleus mesencephalicus lateralis, pars dorsalis. The findings support the phylogenetic homologies between the avian nucleus interstitialis of the dorsal olfactory projection and the mammalian nucleus interstitialis of the stria terminalis, the avian nucleus hypothalamicus posterior medialis and the mammalian nucleus ventromedialis hypothalami, as well as the avian nucleus inferior and the mammalian nucleus infundibularis-premammillaris ventralis. The results also suggest that the nucleus medialis and other more differentiated labeled areas of the mammalian amygdala.

Heart rate and blood pressure responses to electrical stimulation of the central nervous system in the pigeon (Columba livia).

AbstractAn extensive stereotaxic stimulation study of the pigeon brain was conducted with monitoring of heart rate, arterial blood pressure and respiration. Rostrally, short latency tachycardia, hypertension and hyperpnea were elicited from the archistriatum, occipitomesencephalic tract and hypothalamus. In addition, blood pressure decreases followed by long latency tachycardia were elicited from the septal complex, although occasionally slight bradycardia occurred.Tachycardia, hypertension and hyperpnea were elicited from many midbrain sites including the lateral reticular formation, ventrolateral tegmentum, ventral area of Tsai, the midline region between nucleus interpeduncularis and the oculomotor complex, and nucleus mesencephalicus lateralis, pars dorsalis. In addition, moderate tachycardia and hypotension were elicited from the central gray and nucleus intercollicularis while tachycardia, hypertension and hyperpnea were elicited from the tegmental area in the region of the occipitomesencephalic tract.At pontine levels, hypertension and cardioacceleration were elicited from a sparsely celled region lateral to the nucleus abducens and from a ventrolateral tegmental region. With respect to respiratory responses, hyperpnea was elicited from the ventrolateral brainstem at all pontine levels and from the dorsomedial region at rostral pontine levels. In caudal pons apnea was the consistent respiratory response to stimulation of the dorsomedial brainstem. In addition, cardio‐acceleration, hypertension and apnea were elicited from the region of the deep cerebellar nucleus cerebellus internus and from its major outflow, the uncinate fasciculus.Finally, stimulation in the medulla elicited bradycardia and hypotension from the vagal rootlets, solitary complex, descending vestibular nucleus and lateral aspect of the dorsal motor nucleus just rostral to the obex. Tachycardia and hypertension were elicited from the medial aspect of the dorsal motor nucleus, medullary reticular formation ventral to the vagal rootlets and ventrolateral medulla.

Development of mesencephalic nuclei in the chick embryo (Gallus domesticus).

1. The mesencephalic borders in the chick have been analysed and reconstructed. It is stated that the di-mesencephalic border corresponds to the border between postneuromeres 5 and 6, and the mes-rhombencephalic border with the border between postneuromeres 7 and 8. 2. The migration areas have been carefully analysed and reconstructed. 3. The ontogenesis of the mesencephalic brain nuclei has been traced from migration areas by means of reconstructions of successive series of stages. Some facts may be taken into consideration: a) The pretectal nuclear complex originates from the diencephalic region, close to the di-mesencephalic border, and during its expansion this nuclear complex passes the di-mesencephalic border, so the nuclei come to lie in both the diencephalic and mesencephalic regions. b) Some mesencephalic nuclei originate from a mixed cell material of different migration areas. Brain nuclei from a mixed cell material seem to be: the nucleus mesencephalicus lateralis, the nucleus isthmii, pars principalis complex, the nucleus of the basal optic root, the nuclei of the lateral genicular complex. 4. The mesencephalic anatomical topography is seen to change as follows: The optic tectum starts a rotation caudorostrally; it divides into two separate lobes, which are pushed away laterally along the tegmental sides. The tegmentum expands very greatly and there is tegmental axial straightening. The agueduct comes to lie horizontally.