Neuronal alpha-bungarotoxin receptors differ structurally from other nicotinic acetylcholine receptors.

We have characterized the alpha-bungarotoxin receptors (BgtRs) found on the cell surface of undifferentiated pheochromocytoma (PC12) cells. The PC12 cells express a homogeneous population of alpha7-containing receptors that bind alpha-Bgt with high affinity (Kd = 94 pM). The BgtRs mediate most of the response elicited by nicotine, because the BgtR-specific antagonists methyllycaconitine and alpha-Bgt block approximately 90% of the whole-cell current. The binding of nicotinic agonists to cell-surface BgtRs was highly cooperative with four different agonists showing Hill coefficients in the range of 2.3-2.4. A similar agonist binding cooperativity was observed for BgtR homomers formed from chimeric alpha7/5HT3 subunits expressed in tsA 201 cells. Two classes of agonist binding sites, in the ratio of 4:1 for PC12 cell BgtRs and 3:1 for alpha7/5HT3 BgtRs, were revealed by bromoacetylcholine alkylation of the reduced sites on both PC12 BgtRs and alpha7/5HT3 BgtRs. We conclude from this data that PC12 BgtRs and alpha7/5HT3 homomers contain at least three distinguishable agonist binding sites and thus are different from other nicotinic receptors.

Continuous darkness and continuous light induce structural changes in the rat thymus.

It is known that neuroendocrine responses to environmental stimuli, such as light, can influence immune responses through the pineal gland. It is also known that periods of constant darkness and constant light cause stimulation and inhibition of melatonin secretion from the pineal gland, successively. In this study, we provide experimental evidence that changes in the rhythm of the photoperiod have considerable effects on thymic structure of the rat. Male albino Wistar rats were divided into 3 groups. Group 1 rats were kept in a dark room, group 2 in a room under a bright artificial light and group 3 (control) animals were exposed to a 12:12 h light: dark cycle. All animals were killed after 4 wk. In group 1, thymus weight increased by 315%, the increase in volume affecting the medulla (cortex 190%, medulla 655%). The absolute number of epithelial cells and lymphocytes increased both in the cortex and medulla. Thymic cortical epithelial cells were hypertrophied and contained numerous large clear vesicles. Perivascular spaces were enlarged. In group 2 thymus weight decreased by 53%, the reduction in volume affecting mainly the cortex (cortex 61%, medulla 27%). The absolute numbers of cortical epithelial cells and lymphocytes were decreased, and pyknotic lymphocyte nuclei were frequent both in the cortex and medulla. It is concluded that constant darkness causes hypertrophy and increased cellularity of the thymus, while constant light causes involution of the thymus and death of lymphocytes. These changes possibly reflect the well known immunostimulatory effects of melatonin acting directly or indirectly, on the thymic lymphocytes and epithelial cells.

Localisation of the spinal nucleus of the accessory nerve in the rabbit.

The spinal nucleus of the accessory nerve (SNA) was localised in eight adult rabbits by a retrograde degeneration technique using thionine as a stain for the Nissl substance. The SNA was found to extend from the caudal one fifth of the medulla oblongata to the cranial one fourth of the sixth cervical segment. In the caudal part of the medulla oblongata, the SNA was located in the dorsal part of the detached ventral grey column. In the first cervical segment, the SNA was dorsolateral to the dorsomedial column and dorsal to the ventromedial column of the ventral grey column. In the cranial part of the second cervical segment, the SNA shifted laterally to the lateral margin of the ventral grey column. After this lateral shift, the SNA was located in the lateral part of the ventral grey column of the second, third and fourth cervical segments. In the fifth and cranial one fourth of the sixth cervical segments, the SNA was not a well defined column of cells but was represented by isolated cells scattered in the ventral part of the ventral grey column between the phrenic nucleus and the ventral border of the grey matter. The total number of chromatolysed cells found in the SNA of the right experimental side varied from 2723 to 3210.

Biostatistical study on the arrangement of the superficial veins of the cubital fossa in Iraqis.

A study of the arrangement of the superficial veins of the cubital fossa was made on 300 students and staff of the Military Medical College and the AlMustansiriya College of Medicine. Six types of variations of arrangement of the veins were found, two of which have not been mentioned before. The commonest type was that the median vein of the forearm divides in the cubital fossa into 2 veins, one of which joins the basilic vein, and the other the cephalic vein, although in a few cases this joining (or arrangement), occurred above the cubital fossa. The arrangements which have not been mentioned before were that the communication between basilic and cephalic veins was through a horizontal venous connection between 1 of the tributaries of these 2 veins and the basilic vein, and that the median vein of the forearm divides into median cephalic and median basilic, and a vein from the front of the forearm drains into the median basilic vein.

The attachments of the lateral and medial ends of the extensor retinaculum of the human wrist.

The attachments of the lateral and medial ends of the extensor retinaculum of the human wrist were observed in 52 human upper limbs (from 26 cadavers) by dissection. In all the specimens used in this study, the lateral end of the retinaculum was found to be attached to the distal part of the anterior border of the radius and its medial end was attached to the styloid process of the ulna, the pisiform and the triquetrum.