A complete motivated or goal-oriented behavioral act can be viewed as consisting of initiation, procurement, and consummatory phases. In order to gain some insight into the organizing principles of neural circuitry that underlies the expression of motivated behavior, certain basic pathways thought to play an important role in two specific classes of such behavior, hypovolemic thirst and reproductive behavior, are reviewed. In both cases, humoral factors participate in the initiation phase, and their sites of action have been rather clearly defined. Circuitry underlying the procurement phase, which involves foraging behavior, is much more complex, but can be thought of as involving two fundamentally different systems, one concerned with the processing of specific sensory information and the production of refined motor responses, and the other concerned with modulating behavioral state. The former is associated primarily with the thalamocortical-lateral forebrain system whereas the latter is associated primarily with the medial forebrain system. Finally, evidence favoring the hypothesis that "biochemical switching" may take place in fixed neuroanatomical circuitry associated with ingestive and reproductive behaviors is reviewed.
A light and electron-microscopic study was performed concerning the effects of hypophysectomy (HP) followed by cyproterone acetate (CA) treatment on the adrenal chromaffin cells of the rat. The latter drug is reported to interfere with steroid biosynthesis. When given following HP, CA was found to induce degeneration in the inner cells of the zona fasciculata and a marked fall in the blood corticosterone level. The adrenal chromaffin cells which were depleted after the administration of reserpine at the beginning of the experiment failed to recover two weeks later. In addition, some of the depleted chromaffin cells migrated towards the outer cells of the zona fasciculata, had the appearance of pheochromoblasts and showed features of increased synthetic activity. The results are discussed in the light of the generally accepted functional relationship between the cells of the adrenal cortex and the medulla and following a marked fall in the concentration of blood corticosterone, a chemobiotaxis is suggested between the chromaffin and adrenal cortical cells.
A review is given of what is known about the functional significance of variation of the morphology of the human mandible and jaw muscles. First, the mandible is a lever transferring muscular forces to the teeth. The angle between corpus and ramus and the width of the ramus are particularly relevant in this respect as they determine the mechanical advantage of the lever system and the capacity for sagittal (open-close) movement. The stability of the mandible in asymmetric bites is especially affected by the ratio between the intermolar and intercondylar distances. The repertoire of bite forces that can be generated at any tooth and the loading pattern of the temporomandibular joint are strongly dependent on the relative size of the masseter, temporalis and medial pterygoid muscles. Second, executing its function as a lever, the mandible is subjected to shearing, bending and torsional forces. The bony parts harbouring the teeth, joints and muscle attachments serve to counter these forces; additional strength is needed in three areas i.e. in the symphysis, the condylar neck and in the transition area between corpus and ramus. In human populations there are clear-cut patterns of correlation between some facial skeletal traits, jaw joint morphology and strength and line of action of the jaw muscles. As a result, facial morphologies can be distinguished with marked differences in mechanical performance of their masticatory apparatus. It is suggested that they emerge as a result of diverging environmental influences during postnatal growth.
Different types of release site were studied ultrastructurally with tannic acid and immunohistochemical techniques in the central nervous system (CNS) of the invertebrate pond snail Lymnaea stagnalis and in two neuromediator rich core regions in the CNS of the rat, viz., the median eminence (ME) and the mesencephalic central grey substance (MCG). In the CNS of the snail, release of the contents of the secretory granules could be clearly demonstrated in (1) neurohaemal axonterminals, (2) synapses and (3) in nonsynaptic release sites: neuronal processes without morphological synaptic specializations. In the ME, release of secretory products by exocytosis was found in neurohaemal axonterminals in the external part of the palisade layer and in nonsynaptic release sites in all other layers of the median eminence. It was found that oxytocine and vasopressin were released by exocytosis into the extracellular space from such (preterminal) nonsynaptic release sites. Serial section analysis revealed three types of fibre in the MCG, viz. (1) varicose fibres that made synaptic contacts with MCG dendrites on every varicosity, (2) fibres with two types of varicosity, viz. synapse-bearing varicosities and varicosities without synaptic specializations, and (3) varicose fibres without any synaptic specializations. It has been discussed that the nonsynaptic release sites in the CNS of the snail Lymnaea stagnalis, and the nonsynaptic varicosities in the rat brain are the morphological correlates of nonsynaptic communication in the CNS. The results further indicate that particular peptidergic neuromediators are released from such nonsynaptic varicosities, and may reach via the extracellular space receptors located at some distance.
The adrenal gland of the camel consists of an outer cortex and an inner medulla. The general disposition of the cortex and medulla, however, differs occasionally from that of other mammals. Extensions of medulla could reach as far as the periphery of the cortex. Islet of medullary tissue may be found in sections of the cortex and cortical tissue consisting of all zones of the cortex may occur around arteries or nerves in the medulla. The medulla may be separated from the cortex by connective tissue especially in old camels. The arrangement of noradrenaline-secreting cells is different from that in other ruminants; they are found in groups scattered between the adrenaline-secreting cells. Bundles of smooth muscle occur in venules at the corticomedullary interface. Accessory adrenal glands are found embedded in the renal fat. They are similar in structure to the adrenal gland. The adrenal cortex forms 74% of the volume of the gland and the ratio of the cortex to medulla is 4:1. The zona glomerulosa, fasciculata and reticularis constitute about 13%, 53%, and 29% by volume of the cortex, respectively.
Coronary arterial development was studied in complete microseries of 20 human embryos and microseries of the hearts from 18 rat embryos. We never observed more than two coronary arterial orifices; these always originated from the facing aortic sinuses. In the human embryos these coronary orifices were variably identified between 16-19 mm crown-rump length, but were invariably present above 19 mm crown-rump length. In rat embryos, the orifices were variably identified at 13-17 mm and invariably present above 17 mm crown-rump length. In both human and rat embryos the left coronary orifice was observed significantly earlier. In all the embryos septation at arterial orifice level was complete. At the stages in which identification of the coronary orifices was variable, the proximal epicardial segments of the left and right coronary arteries could usually already be identified, in human as well as in rat embryos. On the other hand, a coronary orifice was never seen in the absence of a proximal coronary artery. At all stages studied (in human embryos from 10 mm crown-rump length and in rat embryos from 11 mm crown-rump length) vascular structures could be identified in the epicardial covering of the heart. The present theories on proximal coronary artery development are inadequate to explain either these data or the known possible congenital abnormalities of the coronary arteries. Our study offers a detailed chronology of development of these proximal coronary arteries and mostly supports dual coronary arterial development. The process by which the coronary orifices are brought into contact with the main coronary arteries still remains to be explained.
A case of a single coronary artery is described in a 50-year-old male, who died of asphyxia. The artery originated in the right aortic sinus and from it another artery emerged which crossed the crista supraventricularis and the interventricular septum and returned to occupy a subepicardial position in the lower half of the anterior interventricular sulcus. This partially intramyocardial artery was considered as the anterior interventricular artery. A literature survey showed only five cases with similar characteristics. The importance of this anomaly derives from the risk of damage occurring to the intramyocardial artery during a manipulation of the infundibulum of the right ventricle in a cardiac surgery or from problems of perfusion during coronary bypass procedures.
A study of the attachments of the musculotendinous fibres of the levator ani muscle shows that it is made of two portions: a thick anterior portion which is mostly fleshy and a thin posterior portion which is mostly aponeurotic. The anterior portion consists of two layers: a superficial perineal layer and a deep pelvic layer. Both layers have a common origin from the back of the body of the pubic bone and the anterior part of the tendinous arch. In addition both layers make a U-shaped loop around the recto-anal junction. The posterior fibres of the deep pelvic layer received nerve supply only from the third and fourth sacral nerves. The rest of the muscle was supplied from the sacral nerves as well as the perineal branches of the pudendal nerve. The role of the anterior fibres in reinforcing the sphincters of the anal canal and fixation of the pelvic viscera is stressed. The close anatomical relation between the posterior portion of the muscle and the obturator internus suggests that the latter may play a role in supporting the weak posterior portion of the levator ani, especially during straining positions associated with lateral rotation at both hips.
In this (semi) quantitative animal study the reaction of the periodontal ligament (PDL) to experimental tooth movement is described. To this end, rabbit first incisors were moved sideways with helical torsion springs for periods varying from 3-24 hours. The initial force of the springs was 50 gf. The histomorphology of the PDL was studied in 5 microns thick plastic sections. Comparison with control animals and animals wearing passive springs showed that tooth movement leads to an increased trauma in the PDL within only a few hours. This trauma is characterized by hyalinization, tears and ruptures in the fibres and blood vessels, and by the presence of extravascular erythrocytes and pyknosis. Tissue damage significantly increased with time. After 24 hours of tooth movement, the PDL fibers are compressed or stretched in 68% of the sections and the blood vessels in the PDL are compressed or stretched in 62% of the sections. Even in the controls, more than 15% of the sections displayed slightly stretched or compressed fibers, and about 10% showed slightly compressed or stretched blood vessels. This indicates that some damage is regularly present in a normally functioning PDL. Increases in the percentage of sections with blood vessel compression are found in all groups wearing passive springs, especially after 6 hours. A high concordancy in compression and tension patterns of blood vessels and fibers is present in 83% of the sections. Pyknotic cells are practically confined to areas with compressed PDL fibers in rabbits wearing active springs. Extravascular erythrocytes were found in sections with all types of fiber patterns. A significant majority of extravascular erythrocytes, however, was found in areas with compressed fibers.
The ultrastructure of portions of the arterial and venous systems of the 11.5 day old Wistar rat embryos has been studied by scanning and transmission electron microscopy. The vessels at this stage of development are in the form of capillaries, and the arterial and venous types can be distinguished by the morphology of the endothelial cells by SEM. The endothelial cells of the arterial vessels gave prominent nuclear bulges and numerous microvilli apart from their spindle shape, whilst those of the veins appear flattened, are polygonal in shape, and have few microvilli. Transmission electron microscopy shows that the endothelial cells of the arteries and veins are identical in structure. The ultrastructure of these cells resembles that of endothelial cells at later stages of development including the adult type in that mature forms of cytoplasmic organelles are obtained. In studies on the intercellular junctions and fenestrations with lanthanum nitrate, the impression is formed that the vessels at this stage are impermeable to small molecular size particles, compared with adult capillaries. This suggests that cytoplasmic vesicles must play a major role in the transport of macromolecules in the 11.5 day embryonic vessels.
Sections from different parts along the facial vein of the camel (Camelus dromedarius) were examined by light microscopy. The results demonstrated heterogeneity among the various segments. Particular attention was paid to a specific area in the buccal region which was previously shown by physiological experiments to have a temperature-dependent myogenic tone. The morphology of that area showed highly thickened media with prominent bands of circularly disposed smooth muscles infiltrating both the intima and the adventitia. The morphology described in this study correlates well with the function and gives further credence to the proposed role of the facial vein in cranial thermoregulation particularly under heat stress.
A study of the recent neuromorphological, neurophysiological and neuroethological literature, and data from the current research in our own laboratory have led us to a new classification of entities in the mammalian neuraxis. This classification comprises the core and the median and lateral paracores. The core of the neuraxis may be considered as a caudally extended limbic system. It extends throughout the central nervous system and, as its name implies, most of it is situated close to the ventricular cavity. This entity is characterized by the presence of (1) numerous diffuse grisea, (2) enormous amounts of thin, unmyelinated, varicose axons, many of which are arranged in diffuse fibre systems, (3) large numbers of different neuromediators, particularly neuropeptides, and (4) large numbers of neurons which concentrate estrogen and androgen hormones. Ethophysiological studies have shown that the core region contains numerous loci from which on stimulation quite characteristic behavioral patterns, like eating, drinking, fear, attack, reproductive behavior etc., can be elicited. The core region appears to be involved most directly in the organization of behavior and is of paramount importance for the regulation of processes aimed at the survival of the individual (organism) and of the species. The median and lateral paracores represent extensions of the core at the level of the brain stem. The median paracore includes the raphe nuclei, whereas the (bilateral) lateral paracore is constituted by a ventrolaterally extending lamella of tissue. Both paracores contain sets of monoaminergic cells giving rise to networks of fibres that pervade virtually all grisea of the neuraxis, i.e. the serotoninergic neurons in the median paracore and the catecholaminergic cells in the lateral paracore. The lateral paracore contains a series of grisea, including the substantia nigra, the ventral tegmental area, the nucleus reticularis parvocellularis, the tegmental pedunculopontine nucleus and the catecholaminergic cell groups A1, A2, A5, A7 and C1 and C2. It harbours a large bundle of loosely arranged, thin fibres, which forms a direct caudal continuation of the hypothalamic medial forebrain bundle. This lateral paracore bundle contains numerous catecholaminergic and peptidergic fibres. Three typical core centres, viz. the nucleus centralis amygdalae, the bed nucleus of the stria terminalis and the lateral hypothalamic area contribute substantially to this bundle. The lateral paracore contains, just like the core region, a large number of functionally defined centres related to integrated somatomotor and visceromotor responses. It is postulated that non-synaptic interneuron
Various levels of organisation in the central nervous system can be distinguished, ranging from the molecular, the cellular, the multicellular and the neuronal system level. The relationship between receptor function and behaviour is focussed to the dopamine D2 type receptor of the striatal complex in relation to extrapyramidal and limbic systems. In the striatal complex a striosomal and a matrix compartment can be distinguished. The matrix compartment can be considered as a part of the extrapyramidal system and is innervated by the motor cortex and by the dopaminergic neurons of the ventral tegmental, the dorsal substantia nigra and the retrorubral area. This compartment has a relatively high density of D2 receptors. The striosomes are innervated by e.g. the prelimbic cortex and dopamine neurones of the ventral part of the substantia nigra; here the density of D2 receptors are lower. Under normal conditions most of the D2 receptors are occupied by endogenous dopamine, and postsynaptic (e.g. cholinergic) function is therefore sensitive to antagonists; e.g. antipsychotics. Exposure to drugs such as amphetamine produces a substantial overflow of dopamine from nerve terminals leading to the activation of remote dopamine receptors, that may belong to the system that normally is not influenced by these nerve terminals (defined here as extra synaptic receptor activation). A loss of the normal spatial-temporal relationships may also occur during L-DOPA therapy in Parkinson's disease. In this illness, due to degeneration of dopaminergic innervation, several dopamine receptors have become non-synaptic. In these states of intoxication the normal spatial/temporal organization is lost and such a loss may contribute to behavioural impairments.
Two classes of substances exist within the extracellular space: energetic and informational. Examples of the former are glucose, dissolved oxygen and CO2 while the latter include excitatory amino acids, cathecholamines and opiates. The simple ions Na+ and Cl- are generally associated with energetic processes while extracellular K+ and Ca2+ tend to be informational in function. Local release of an informational substance brings about a concentration gradient that causes the substance to be dispersed in the extracellular space by diffusion. This process is modified relative to a free aqueous medium by the constraints of volume fraction, tortuosity and uptake. Volume fraction is defined simply as the fraction of a brain region that is extracellular. If a given quantity of substance is released into a region with a reduced volume fraction then the substance will reach a higher concentration than it would in a free medium. Tortuosity is related to the increase in the path length of the random walk of a diffusing particle due to the necessity to navigate around cellular obstructions. Tortuosity manifests itself as a decrease in the diffusion coefficient. Uptake represents the movement of a substance from the extracellular space to the intracellular. Since initially a concentration gradient exists in this direction and all membranes have some permeability some concentration-dependent uptake always occurs. In addition there exist specific carrier-mediated uptake processes for some substances such as amino acids or catecholamines. In some regions the dispersal process can be dominated by uptake rather than diffusion. While volume fraction, tortuosity and uptake have all been demonstrated by a technique based on the use of radiolabels and other methods, these classical techniques have limited spatial and temporal resolution. The advent of methods based on micro-injection of substances by iontophoresis or pressure and subsequent detection with ion-selective microelectrodes (ISMs) or voltammetric microsensors (VMs) has opened a new window onto the dynamic local behavior of the extracellular space. In the last decade our laboratory and others have studied the migration of the test substances tetramethylammonium, tetraethylammonium, AsF6- and alpha naphthalene sulfonate, the endogenous ions K+ and Ca2+, the epileptogenic agent penicillin and the neurotransmitter dopamine. These studies have been carried out on the cerebellum and some other regions in a variety of species that include rat, turtle, skate and an intervertebrate, the cuttlefish.(ABSTRACT TRUNCATED AT 400 WORDS)
Nine aphakic eyes from human embryos infected with Rubella or Parvovirus B19 during early pregnancy were histologically examined. One of the eyes conformed with the classical description of primary congenital aphakia (PCA), namely, that no structures of the anterior eye segment are present. However, the other eight eyes did reveal such structures. In these eyes embryological development and differentiation of the anterior eye segment had taken place, despite the fact that no lens had formed previously. On the basis of this study it is concluded that PCA is not necessarily associated with aplasia of the anterior eye segment.
The striatum receives massive dopaminergic projections from neurons in the ventral tegmental area, the substantia nigra and the retro-rubral cell group. Dopaminergic neurons in the arcuate nucleus and periventricular hypothalamic nuclei project to the median eminence and the neuro-intermediate lobe of the pituitary gland. The anterior lobe of the pituitary gland is not innervated by dopaminergic neurons, but receives dopamine via a vascular route from the median eminence. Two categories of dopamine receptors (D-1 and D-2) can be identified on the basis of the ability of various drugs to discriminate between these two entities. Dopamine stimulates both D-1 and D-2 receptors. The affinity of dopamine for the D-2 receptor is approximately 1000 times higher than for the D-1 receptor. Dopamine is involved in synaptic as well as non-synaptic communication. Examples of non-synaptic communication via D-2 receptors are the dopamine induced inhibition of prolactin release from the anterior pituitary gland and most likely the D-2 receptor mediated inhibition of the release of acetylcholine in the striatum. Examples of synaptic communication have been found in the striatum where (with ultrastructural techniques) synaptic contacts between dopaminergic nerve terminals and elements from cells containing GABA, substance P or enkephalin have been demonstrated. It is tempting to speculate that synaptic and non-synaptic communication occurs via D-1 and D-2 receptors respectively.
On the basis of the contrasting evolutionary patterns of the Teleostei and the "Chondrostei" the merit of phylogenetic testing is summarized as a non-arbitrary method for assessing the possible role of various designs in producing differential morphological diversity in different lineages. Arguments are presented for the recognition of a genealogical (reproductive, informational) and an ecological hierarchy. Various levels are proposed within hierarchies, because there are processes intrinsic to each level that are not reducible to those of lower levels or subsumed by higher levels. Mutual influences exist between successive levels within a hierarchy and possible interhierarchical mutual influences are hypothesized between organisms, demes, and avatars, and from the germ line to functional units. The term symecomorphosis is proposed to denote the balanced symmetry of the co-existing and mutually interdependent ecological and genealogical hierarchies. Symecomorphosis predicts that a disturbance in environmental systems can destroy this balance with profound effects on the genealogical hierarchy. Using the evolutionary differentiation of four lineages of air breathing teleosts as an example, it is demonstrated how the principle of symecomorphosis can be included in tests establishing a causal relationship between design and differential diversity among lineages.
This paper analyses the role of constructional morphology in explaining the limitations on the interactions between an organism and those factors in its environment which are potentially relevant to its inclusive fitness. Constructional morphology deals with the relations between functionally relevant anatomical units (apparatuses or functional components) and thereby demonstrates what quantitative and qualitative constraints there are on combining units necessary for environmental interactions. It is argued that investigations on the relations between form and environment (ecological morphology) should (1) consider three types of relations: form-form, form-function and function-environment factor, (2) include behavioral and physiological ecology and (3) not be limited to a particular stage, but include as much of ontogeny as possible.
