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As part of a study concerning the organization of premotor areas in the medullary reticular formation in birds we used a fluorescent retrograde double labeling technique to localize the premotor neurons of the trigeminal (mV) and supraspinal motor nucleus (SSp). Diamidino Yellow injections in mV and Fast Blue injections in SSp demonstrated that mV and SSp do not share premotor neurons, but the premotor neurons form a mixed population in the ventromedial part of the parvocellular reticular formation.

Aim of this paper is to give a concise overview of what is known about the trigeminal nociceptive system in birds. Several types of nociceptors have been discovered, thermal nociceptors and polymodal, i.e. mechanothermal and mechanochemical receptors. Information from these receptors reaches the Laminae I and II of the caudal subnucleus of the descending trigeminal system and of the dorsal horn of the rostral spinal cord. The organization of the afferents to the avian brainstem and of the primary nociceptive centers is largely the same as that in mammals. This is also true for a number of histochemical characteristics of these primary centers. The comparability of the ascending nociceptive system in birds and mammals is more problematic. This is due to the differences in organization of the forebrain in mammals and birds. The paper concludes with a short discussion on the sense of pain and the connection with nociception.

Horseradish peroxidase (HRP) histochemistry was used to identify the motoneurons innervating the tongue muscles in the mallard. Four nuclei are involved: the intermediate motor nucleus of N.VII innervating the stylohyoid, serpihyoid and ceratohyoid muscles, the retrofacial nucleus of N.IX innervating the m. geniohyoideus and the n. intermedius or motor nucleus of N.XII that innervates the mm. ceratoglossus and hyoglossus anterior and obliquus. The m. intermandibularis is innervated by a trigeminal motor subnucleus. There is no clear intranuclear organization. The results are summarized in Table I and discussed in connection with the role of each of the muscles during movements of the tongue.

We discovered in the brainstem of infrared-sensitive vampire bats,Desmodus rotundus, a specific nucleus not known in other species of bats. Because it corresponded in location and histological features to the infrared nucleus of infrared-sensitive snakes, we suggest the probability of its being part of the infrared processing system of vampire bats.

The trigeminal and glossopharyngeal ganglia of the adult mallard were studied following HRP injections into the principal trigeminal nucleus (PrV). The PrV consists of the principal trigeminal nucleus proper (prV) and the principal glossopharyngeal nucleus (prIX). After an injection into the prV, the labeled cells were found in the ipsilateral trigeminal ganglion. After an injection into the prIX, labeled cells were found in the ipsilateral distal glossopharyngeal ganglion, but not in the proximal ganglion of the IX and X cranial nerve (pGIX + X). In Nissl preparations, two types of ganglion cells in the trigeminal ganglion, pGIX + X, and distal ganglion of N IX could be distinguished: larger light cells and smaller dark cells. We could not determine whether the HRP-labeled cells belonged to both types or to one of them; but because all the labeled cells were over 20 microns, we concluded that the smallest cells (10-19 microns) in the trigeminal ganglion and distal ganglion of N IX did not project to the PrV. The labeling of the cells in the distal ganglion of N IX (average 34.5 microns) was uniformly moderate. In the trigeminal ganglion there were two types of labeled cells: heavily labeled cells (average 29.1 microns) and moderately labeled cells (average 35.1 l microns). These two types of labeling (moderate and heavy) may reflect two types of primary sensory neurons: cells with ascending, nonbifurcating axons, and cells with bifurcating axons. We speculate that the former are proprioceptive neurons and the latter tactile neurons. Labeled bifurcating axons in the sensory trigeminal complex gave off collaterals to all parts of the descending trigeminal nucleus except to the caudalmost laminated spinal part.

The central projections of the chorda tympani nerve in the duck were studied by means of the Fink-Heimer technique. Following section of the VIIth nerve proximal to the geniculate ganglion terminal projections of the CT are found in the sensory nucleus N VII (sVIId) on the dorsum of the descending trigeminal root, the n. presulcalis anterior solitarii, the n. sulcalis anterior solitarii p. dorsalis and p. ventralis, and the n. ventrolateralis anterior solitarii (Vla). Small quantities of terminal degeneration are also found in the n. intermedius anterior and the lateral substantia gelatinosa of the solitary complex. A number of fibers decussate to terminate contralaterally in corresponding portions of the opposite solitary complex. Comparison with data of the pigeon reveals a limited overlap of projections of the chorda tympani nerve and of the nodose ganglion, respectively, in the dorsal and ventral parts of the n. sulcalis anterior. We suggest that the regions sVIId and Vla alone may convey gustatory information.

This electrophysiological study complements neuroanatomical work from our department on the somatotopy of the trigeminal system of the mallard. Peripheral areas of mechanoreceptors in bills and tongue were mapped in the telencephalic nucleus basalis, a second-order relay nucleus in the ascending trigeminal pathway. The multi-unit responses recorded under Equithesin anaesthesia did not show spontaneous activity and all animals adapted rapidly after mechanical stimulation. They showed well-circumscribed receptive fields whose peripheral position did not change when the electrode was lowered in the vertical stereotaxic plane, but changes immediately when its position was changed in the horizontal XZ-plane. The somatotopic picture presented here corresponds in many details to that obtained with combined neuroanatomical techniques (Dubbeldam et al., '81). In the discussion the structural point-to-point relationship between the peripheral mechanoreceptive areas and the nucleus basalis is tentatively changed to a division into areas related to the functional units involved in the subsequent sensory events during feeding. The somatotopy provides a basis for future chronic experiments to investigate this postulated role of the various areas in the nucleus basalis.

The paleostriatal complex (PC) of the pigeon lies in the basolateral wall of telencephalon, and consists of three major subdivisions: the paleostriatum augmentatum (PA), paleostriatum primitivum (PP), and nucleus intrapeduncularis (INP). The lobus parolfactorius (LPO) lies on the medial aspect of PA and has often been considered to be part of PA. The present study of afferent and efferent connections of the paleostriatal complex supports earlier previous suggestions that the PC is directly comparable to the basal ganglia of mammalia. High concentrations of acetylcholinesterase were found in the PA, LPO and INP. Intense yellowish green fluorescence, probably dopamine, was confined to the PA and LPO. Stereotaxic lesions were placed in either the dorsal ventricular ridge structures above the PC (neo- and hyperstriatum), PA, LPO or PP-INP, and animals sacrificed from one to six days postoperatively. The brains were stained with the Fink-Heimer methods for the demonstration of degenerating axons and terminals. The region of the neo- and hyperstriatum was found to project upon the PA, in a seemingly topographic manner. PA was found to project topographically upon the PP and INP. In contrast, the LPO contributed to the medial forebrain bundle, terminating in the rostral lateral hypothalamus. LPO does not appear to project to the PP or INP. Lesions of PP-INP resulted in massive degeneration of a descending tract, the ansa lenticularis. Terminal degeneration was found in the anterior and posterior nuclei of the ansa lenticularis of the ventral diencephalon, nucleus dorsalis intermedius posterior and nucleus spiriformis lateralis of the dorsal thalamus, and the nucleus tegmenti pedunculopontinus pars compacta et disseminata of the isthmic tegmentum. In these several features of histochemical and hodological organization the PC alone appears similar to the caudate-putamen and globus pallidus complex of mammalian brains. More specifically, the PA resembles the caudate-putamen, whereas PP and INP resemble the external and internal divisions of the globus pallidus, respectively. Similarities and differences between avian and mammalian brains, and the relationship of the present study of the PC and previous studies of the dorsal ventricular ridge structures are discussed (Karten, '69; Nauta and Karten, '70).

The primary vagal axons and terminals within the lateral descending trigeminal tract (dlv) and nucleus (DLV) of two species of Boidae are studied following HRP injections of the vagal nerve. Labeled fibers and terminals are found in the tail portion of the dlv and DLV, partly forming a neuropil at its margin. The labeled thin fibers and neuropil seem to correspond to the C-fibers and marginal neuropil of Crotalinae.

The ascending projections from the principal sensory nuclues V (PrV) have been studied by tracing degeneration after lesions in the PrV and by injections of HRP into the projection zone of PrV. The quintofrontal tract arises from PrV, ascends into the forebrain, and terminates in the ipsilateral and the contralateral nucleus basalis (NB). The contralateral fibers decussate in the the tegmentum at the level of the trochlear-oculomotor nuclei. NB is a laminar nucleus lying over the rostral part of the paleostriatal complex. Dorsally NB is bounded by the neostratum. NB consists of small neurons. In the dorsal part of NB, these neurons are arranged in vertical columns; the afferents ascend through these columns, and clusters of degenerated boutons are found around the cells. It is possible to distinguish regions in NB receiving ophthalmic, maxillary, mandibular, or glossopharyngeal afferents. The rostral part of NB receives an exclusive ipsilateral projection; the intermediate part, a bilateral projection; and the caudal part, a contralateral projection, with the exception of the most caudal area, which also receives a bilateral projection. It is not clear whether NB should be considered a thalamic, a telencephalic, or even a pallial structure. The hypothesis that the columnar organization of the NB is a prerequisite to preserve a precise somatotopy of the tactile system of the oral region is discussed. In this respect the organization of NB can be compared to that of layer IV of the somatosensory (SI) cortex of mammals. Knowledge of the structure and functions of the peripheral tactile sense system opens the possibility of subdividing the NB into functional units.

Central pathways converging upon the trigeminofacial motor nuclei of the mallard were studied in order to elucidate neuroanatomically the presumed influence of primary sensory trigeminal afferents upon jaw muscle activity. The techniques used included the Fink-Heimer I method after lesions, and axonal transport labeling following injections of 3H-leucine or of HRP for retrograde identification of the neurons of origin. A general description is given of the trigeminofacial motor complex. Jaw closer muscles are innervated by trigeminal motor neurons, and facial motor neurons innervate the jaw depressor muscles. Two afferents premotor systems, one including the mesencephalic trigeminal nucleus (MesV) and the other the rhombencephalic reticular formation, are distinguished. The proprioceptive neurons of the mesencephalic trigeminal nucleus project upon the ipsilateral trigeminal motor nucleus and upon the nucleus supratrigeminalis. The latter cell group bilaterally projects upon the dorsal and intermediate parts of the facial motor nucleus and upon the dorsal and intermediate parts of the facial motor nucleus and upon part of the trigeminal motor nucleus. Exteroceptive information, relayed through the primary sensory trigeminal column (PrV and nTTD), ultimately reaches the motor nuclei via the reticular formation. The reticular formation forms the final link of three separate circuits: a telencephalic one entered through the principal trigeminal sensory nucleus, a cerebellar one via subnucleus oralis of the descending trigeminal system, and a direct one via subnucleus interpolaris. No direct connections between the principal trigeminal sensory nucleus or subnuclei of the descending trigeminal system and the motor nuclei of the trigeminal (NV) and facial (NVII) nerves have been observed, nor are such direct projections present in the outflow of the presumed telencephalic and cerebellar circuits, viz. of the archistriatum and the central cerebellar nuclei, respectively. The archistriatum projects via the occipitomesencephalic tract upon the lateral rhombencephalic reticular formation as far down as the rostral cervical cord, as well as upon the subnucleus interpolaris of the descending trigeminal system. Similarly, efferents from the central cerebellar nuclei reach the reticular formation, which in turn projects bilaterally upon the motor nuclei. Finally, commissural intermotor connections apparently are mediated by reticular cells surrounding the motor nuclei of NV or NVII, rather than emanating from these nuclei directly.

SIR: Much time and effort have been devoted to elucidate the role of muscle spindles, but still there are no definite answers I. I wonder whether this may be partly due to the fact that many studies have too narrow a focus. The following reaction is triggered by the recent paper by Stein and Capaday 2 in

The projections from the ophthalmic, maxillary, and mandibular parts of the trigeminal ganglion upon the principal sensory trigeminal nucleus (PrV) in the mallard have been studied with the Fink-Heimer I method. PrV is a large nucleus subdivided in cell groups by layers of fibers. The orientation of the dentritic arborizations differs in the different parts of the nucleus. A dorso-caudal cell group sIX is an exclusive glossopharyngeal terminal field. A second, caudo-ventral projections area of NIX also receives trigeminal afferents. A small n. supratrigeminalis lies medial to PrV in the pathway of the mesencephalic trigeminal root. This nucleus seems to be part of the proprioceptive trigeminal system. The rostralmost part of PrV receives ophthalmic projections, the caudalmost part receives mandibular projections, the maxillary area being intermediate. Taking the stereotaxic plane of the mallard atlas (Zweers, '71) into account, it can be concluded that the situation is essentially not different from that in the pigeon and from the situation described for mammals.

The central projections of the glossopharyngeal and vagus nerves in the mallard have been studied with the Fink-Heimer I method and are compared to those of the trigeminal and facial nerves. The N. vagus projects ipsilaterally and contralaterally upon the central nuclei of the solitary complex, except the most rostral part of it, upon the n. sulcalis dorsalis, the parasolitary nuclei and the n. commissuralis. The glossopharyngeal nerve contributes to the rostral pole of the n. centralis anterior and to the n. ventrolateralis anterior of the solitary complex, but it has also terminal fields in a cellgroup sIX of the principal sensory trigeminal nucleus, in a small cellgroup sIXd on the dorsum of the descending trigeminal tract, in the n. interpolaris of this tract and in nuclei of the cuneate complex. There is hardly any overlap of the respective terminal fields. The convergence of projections from N VII and N IX can be connected with the presence of tastebuds in upper and lower bill and in the soft palate. The converging projections from N V and N IX in "trigeminal" nuclei may reflect the functional coherence of the mechanoreceptors in bill and tongue. It is suggested that these nuclei play a role in the feeding behavior.