Subcortical Projections of Area V2 in the Macaque

To investigate the subcortical efferent connections of visual area V2, we injected tritiated amino acids under electrophysiological control into 15 V2 sites in 14 macaques. The injection sites included the fovea representation as well as representations ranging from central to far peripheral eccentricities in both the upper and lower visual fields. The results indicated that V2 projects topographically to different portions of the inferior and lateral pulvinar and to the superficial and intermediate layers of the superior colliculus. Within the pulvinar, the V2 projections terminated in fields P1, P2, and P4, with the strongest projection being in P2. Central visual field injections in V2 labeled projection zones in P1 and P2, whereas peripheral field injections labeled P1, P2, and P4. No projections were found in P3. Both central and peripheral field injections in V2 projected topographically to the superficial and intermediate layers of the superior colliculus. Projections from V2 to the pulvinar and the superior colliculus constituted cortical–subcortical loops through which circuits serving spatial attention are activated.

Peripheral and ovarian IGF-I concentrations during the ovine oestrous cycle

IGF-I was measured by RIA in plasma samples collected 8-hourly for 24 days which included two consecutive preovulatory surges of LH. In a separate study, ovarian venous blood was collected from animals undergoing ovariectomy on day 10 of the oestrous cycle, or 36 h later after being treated with prostaglandin with or without steroid-free bovine follicular fluid. Jugular venous blood samples were collected before, during and after surgery. Follicles were dissected from ovaries of these animals and sorted into categories of small, intermediate and large, non-atretic or atretic, and the follicular fluid was pooled and assayed for IGF-I. From another population of ovaries recovered from the slaughterhouse, granulosa, theca and corpora lutea were isolated, homogenized and assayed for IGF-I. Finally ovarian corpora lutea and granulosa cells were each incubated with tritiated amino acids overnight at 37 °C. Thereafter the tissues and media were sonicated, IGF-I extracted from the supernatant and tritiated IGF-I precipitated using a specific IGF-I antibody. The absence of any significant change in peripheral IGF-I concentrations following ovariectomy and the finding that the ovarian venous IGF-I concentrations (161 ± 10 μg/l) were not significantly different from levels seen in peripheral blood (157 ± 10 μg/l) indicated that the ovary is not a net exporter of IGF-I. However, the ovary does synthesize IGF-I, as evidenced by granulosa and luteal synthesis, but probably not in quantities in excess of that utilized by ovarian tissues per se. Although the plasma IGF-I levels increased around the second preovulatory LH surge, the results overall indicated that the IGF-I concentrations in plasma are not strictly related to any major ovarian event during the oestrous cycle in the sheep. This view is based on the findings that the concentration of IGF-I in follicular fluid was not related to follicular health but correlated with those in peripheral plasma and that the ovarian venous concentrations did not vary between left and right ovaries irrespective of whether the ovaries contained a corpus luteum, dominant follicle or neither. Collectively, these results are consistent with the notion that IGF-I of ovarian origin fulfils an autocrine/paracrine function and does not have an endocrine role. Moreover, the results show that the concentrations of IGF-I in follicular fluid reflect those in peripheral plasma. Journal of Endocrinology (1996) 148, 281–289

Visual-field map in the callosal recipient zone at the border between areas 17 and 18 in the cat

The representation of the visual field in the callosal fiber recipient zone of area 17 and the adjacent area 17/18 transition zone was determined in the cat. The callosal fiber recipient zone was identified by anterograde transport of tritiated amino acids that had been injected into transcallosal sending zone of the opposite hemisphere. Application of autoradiographic procedures revealed that transcallosal projections are densest in the area 17/18 transition zone, and that their density in area 17 diminishes within 1–2 mm of the transition zone. Of 980 sites sampled in the visual-field mapping part of the study, 507 proved to be in the zone demarcated by transcallosally transported label. In this zone, both ipsilateral- and contralateral-field positions are represented, and the representation of the visual field at the different elevations is not equal. When ipsilateral-field positions are considered, the representation extends to about 4 deg close to the visual axis, and to 15–20 deg at elevations >±30 deg, the representation is approximately mirror-symmetric about the horizontal meridian, and the representation is concordant with that of the representation in the area 17 transcallosal sending zone of the opposite hemisphere.

Distribution of combination-sensitive neurons in the ventral fringe area of the auditory cortex of the mustached bat

1. The orientation sound (pulse) of the mustached bat, Pteronotus parnellii parnellii, consists of long constant-frequency components (CF1-4) and short frequency-modulated components (FM1-4). The auditory cortex of this bat contains several combination-sensitive areas: FM-FM, DF, VA, VF, and CF/CF. The FM-FM area consists of neurons tuned to a combination of the pulse FM1 and the echo FMn (n = 2, 3, or 4) and has an echo-delay (target-range) axis. Our preliminary anatomical studies with tritiated amino acids suggest that the FM-FM area projects to the dorsal fringe (DF) area, which in turn projects to the ventral fringe (VF) area. The aim of our study was to characterize the response properties of VF neurons and to explore the functional organization of the VF area. Acoustic stimuli delivered to the bats were CF tones, FM sounds, and their combinations mimicking the pulse emitted by the mustached bat and the echo. 2. Like the FM-FM and DF areas, the VF area is composed of three types of FM-FM combination-sensitive neurons: FM1-FM2, FM1-FM3, and FM1-FM4. These neurons show little or no response to a pulse alone, echo alone, single CF tone or single FM sound. They do, however, show a strong facilitative response to a pulse-echo pair with a particular echo delay. The essential components in the pulse-echo pair for facilitation are the FM1 of the pulse and the FMn of the echo.(ABSTRACT TRUNCATED AT 250 WORDS)

Lethality of a tritiated amino acid in early mouse embryos

2- to 4-cell and morula- to blastocyst-stage mouse embryos were cultured for 1 h in tritiated leucine at two specific activities and their subsequent development followed in vitro and in vivo (after transfer to recipients), respectively. 2- to 4-cell embryos that incorporated an average of 42 d.p.m. per embryo were impaired in their ability to develop to the morula and blastocyst stage. Recipients receiving morulae and blastocysts that had incorporated an average of 384 d.p.m. per embryo failed to produce young. Reduction of the specific activity improved the viability of embryos both in vitro and in vivo but development was still less than that of unlabelled embryos. Protein degradation curves were different for both 2- to 4-cell and morulato blastocyst-stage embryos labelled at the two different specific activities. Most studies using tritiated amino acids have employed higher specific activities than those used here and they may have to be reevaluated due to the possibility of radiation-induced artifacts.