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A centrifugal visual system showing FMRF-amide-like immunoreactivity has been demonstrated in Lampetra fluviatilis by using immunocytochemical and hodological techniques. From 50 to 60 immunoreactive neurons, labelled after contralateral intraocular injection of rhodamine beta-isothiocyanate, form a small, clearly defined, nucleus in the lateral neural plate of the magnocellular preoptic nucleus. These cells give rise to immunoreactive axons which have been observed at the base of the nucleus, in the optic chiasma and in the optic nerve, to project into the intermediate plexiform layer of the retina, which separates the layer of internal horizontal cells from the layer of external horizontal cells. This FMRF-amide-like immunoreactive centrifugal visual system is compared to that described in Gnathostomes.

The circadian pacemaker of the suprachiasmatic nuclei (SCN) is entrained to the environmental light-dark cycle via the retinohypothalamic tract (RHT). It is unknown whether light activates or suppresses firing of the retinal ganglion cells which mediate photic entrainment. We therefore electrically stimulated the optic nerves and the anterior optic chiasm of hamsters with free-running activity rhythms in continuous darkness. These electrical stimulations are thought to induce a release of neurotransmitter at the RHT terminals. Electrical stimulation mimicked the phase dependent shifts induced by light pulses. The phase shifts were significantly larger than the shifts induced by sham stimulation in the same animals or by electrical stimulation in animals with an electrode outside the optic nerves and chiasm. Our results indicate that the retinal ganglion cells which project to the SCN are activated by light. Intraperitoneal administration of MK-801, a non-competitive antagonist of the NMDA-receptor, attenuated the phase delays induced by electrical stimulation in the early subjective night. This suggests that an excitatory amino acid mediates the effects of light upon the circadian pacemaker.

The optic fiber termination layer in the contralateral optic tectum was reinnervated and useful vision was recovered in the adult frog, after successful optic nerve regeneration through an autologous peripheral nerve-bridge used to replace the optic nerve and optic chiasma. During their course through the nerve-bridge, the optic fibers were associated with Schwann cells in the usual relationship observed in peripheral nerve.

Multiple sclerosis (MS) patients may suffer from optic disturbances. Toxin-induced demyelinations have frequently been developed to investigate the cellular and structural aspects of demyelination and remyelination processes, separately. The present study describes functional consequence of lysolecithin (LPC)-induced lesion in the adult rat optic nerves and chiasm by recording the visual evoked potentials (VEPs) from the visual cortex and its correlation with myelin basic protein (MBP) expression in lesion site. Records of VEP were obtained at 2, 7, 14 and 28 days post-injection. We observed that the VEPs generated by light stimuli progressively changed in both amplitude and latency after the lesion as well as in comparison with those generated in control animals. These observations were confirmed through measurement of mRNA expression level for MBP which is one of the important genes expressed in mature oligodendrocytes and Schwann cells. The level of MBP mRNAs in demyelinated chiasm and optic nerves decreased following lysolecithin injection with its least value on day 7, and then it increased to the control level 14 days post-lesion. However, it continued to increase even after that and reached a maximum level 28 days post lesion. Results of the present paper show that, LPC injection in the chiasm share functional and molecular alterations which are found in demyelinating disorders in both the optic nerves and chiasm and also these alterations were coming back to level of control animal on 28 days post lesion, which is typically seen in myelin repair process. The present paper provides new insights into the experimental toxin-induced models that may be useful for evaluating the functional recovery of demyelinated optic nerves and chiasm following various repairing strategies. It also seems to be useful for studying the protective or remyelinating effects of different therapies in e.g. optic apparatus which is more affected by MS.

Genetically mutant anophthalmic rats lacking a complete visual system due to the absence of eyeballs and optic nerves up to the optic chiasma were used as a model to study photo-regulated physiological activities. The photoreception in these mutant rats was determined by measuring the neuroendocrine response of the pineal gland-melatonin levels in the serum, and synaptic ribbon complexes (SRCs) in the pinealocytes. These parameters were studied in both normal and anophthalmic rats maintained under light-dark (LD 12:12), continuous dark (DD) and light (LL) conditions. Both normal and mutant anophthalmic animals showed nocturnal increases in serum melatonin levels and in the number and diameter of SRC and their vesicles in the pinealocytes in LD. The daily rhythms persisted even upon transfer to DD both in normal and mutant rats, whereas in LL, the nocturnal elevation of both the parameters disappeared. These observations suggested that congenitally blind rats can perceive light. The studies of these parameters in both normal and mutant rats in reversed-LD conditions confirmed that pineal rhythms can be entrained by light-dark cycles in congenitally anophthalmic mutant rats through a nonvisual system for light perception.

Interleukin-1beta (IL-1beta ) has anorectic, hyperthermic, and analgesic or hyperalgesic (depending on the studies) effects in the rat. These effects appear to be mediated by the central nervous system; however, the exact localization of action of IL-1beta in the brain has never been delineated with precision. The purpose of this study was to determine precisely where IL- IO acts in the hypothalamus and in the thalamus to modulate food intake, body temperature, and pain sensitivity. Animals were tested after local intracerebral microinjections of 5 ng of IL-1beta dissolved in 0.3 microl of saline, or of 0.3 microl saline alone. The results show that IL-1beta has anorectic effects in 3 diencephalic sites (the perifornical area, an area above the optic chiasma, and an area internal to the mamillo-thalamic tract), and not in 9 other sites tested. IL-1beta has hyperthermic effects in 7 sites (the media] and lateral preoptic area, the hypothalamic periventricular substance, the dorso-medial and arcuate nuclei of the hypothalamus, and the centro-medial and gelatinosus nuclei of the thalamus), and not in 6 other sites. IL-1beta has analgesic effects in the centro-medial and gelatinosus nuclei of the thalamus, and not in 7 other sites. IL-1beta also increases food intake and decreases pain sensation thresholds in the paraventricular nucleus of the hypothalamus. Therefore IL-1beta has very selective anatomical sites of action in the brain, and the paraventricular nucleus of the hypothalamus appears to have special properties regarding the effects of IL-1beta on food intake and pain sensation regulation.

Calcitonin is a peptide hormone which can act centrally to decrease food intake and locomotor activity, and increase body temperature and nociceptive thresholds. In a previous study we showed that the brain sites involved in the food intake and locomotion decreases were mostly the paraventricular nucleus, the perifornical area and the preoptic area above the optic chiasma. We now study the diencephalic sites involved in calcitonin-induced increases in body temperature and nociceptive thresholds. Salmon clacitonin (15 ng in 0.3 μl) was injected in several diencephalic sites, and the effects on body temperature and nociceptive thresholds compared with a saline injection. The results show that the sensitive sites are the dorsomedial nucleus of the hypothalamus, the preoptic area and the centromedial nucleus of the thalamus, and not the paraventricular nucleus and adjacent perifornical area. Therefore, different kinds of central effects of calcitonin can be differenciated on an anatomical basis.

We studied whether plasticity-induced callosal transfer exists after the critical period for sensitivity of visual cortex cells in kittens postnatally monocularly deprived and in which interocular competition was cancelled by chiasm transection during adulthood. Callosal transfer was studied acutely (n = 3 cats) and chronically (n = 7) following the chiasm transection (OCAMD). For comparison, adult cats in which chiasm transection only was performed (OCA) were also studied acutely (n = 3) and chronically (n = 9). The results were also compared to cats in which monocular deprivation and chiasm transection were simultaneously performed (OCKMD) during development (n = 6) and to normal control cats (n = 18). Unit recording was extracellularly carried out in visual cortex areas 17 and 18 and their boundary region, where the corpus callosum is represented. When no interocular competition was allowed between the non-deprived and the deprived eye via the thalamocortical direct visual pathways on cortical cells, such as in the OCKMD cats, the absolute majority of the cells were ipsilaterally driven, regardless of which hemisphere was studied. Only a minor proportion (4.1%) of the cells had some contralateral input from the non-deprived eye in the hemisphere ipsilateral to the deprived eye, indicating almost no interhemispheric callosal transfer. A slight increase in the proportion of cells callosally driven from the non-deprived eye (9.8%), was found in this hemisphere in cats in which interocular competition was allowed via the direct visual pathways prior to its cancellation by chiasm transection (OCAMD), if studied acutely after the chiasm transection. A remarkable increase in callosal transfer was found in this hemisphere under chronic conditions.(ABSTRACT TRUNCATED AT 250 WORDS)

The distribution of the cells of origin projecting from the substantia innominata to the caudate nucleus was studied in macaque monkeys by means of the retrograde axonal transport of horseradish peroxidase (HRP). The HRP was injected, after callosotomy, into the exposed head of the caudate nucleus. Labeled cells appeared in the ipsilateral substantia innominata, extending rostrally to the level of the optic chiasma.

The anterior hypothalamus has been implicated in the higher centre control of blood pressure and more recently in hydromineral balance regulation. Using a glass recording electrode with and without a 7-barrelled iontophoretic electrode we investigated this region for blood pressure-sensitive cells. We used a ventral approach through the optic chiasma. We found 36 cells out of 91 tested that increased their firing rate in response to a spontaneous or induced decrease in blood pressure. Of these 19 increased firing in response to angiotensin II (AII) injected into the lateral cerebral ventricle and 10 of these increased firing in response to local iontophoretic application of AII. Cells responsive to an increase in blood pressure were never found. Thus cells in this area respond to hypovolaemia and hypotension as well as to AII, which could link this area with higher centre responsiveness to stimuli of extracellular thirst.

Flash-evoked potentials (FEPs) in the cat's optic chiasma and superior colliculus were recorded under the following two conditions: complete darkness and background illumination. Special attention was paid to a specific late component of FEP'S and comparison in the behavior of the late component was made between the two conditions. It was found that a late component of FEPs in the optic chiasma appeared in the presence of background illumination while it was not observed under the condition of complete darkness. A corresponding late component of FEPs was detected in the superior colliculus. The late component might be supposed to be driven from a class of W-cells in the cat's retina.

Summary Cats were trained to differentiate between a wide range of visual stimuli associated with an audio stimulus and tone alone. They learned to demonstrate this differentiation by turning a pedal on the left side of the conditioning ☐ in the event of the former, or a pedal on the right side in the event of the latter. Electrodes were then implanted in optic chiasma, lateral geniculate nuclei, and at various depths in the optic radiations, as well as in the superior colliculus and on the surface of the visual cortex. Stimulation of these electrodes with biphasic pulses in association with the audio stimulus resulted in the cats' striking the left pedal with greatest frequency for stimulation of the optic chiasm and lateral geniculate bodies, followed by the optic radiations and superior colliculus. Stimulation of surface electrodes on the striate cortex had the poorest performance in terms of a preconditioned visual response.

Ventromedial forebrain structures were stimulated electrically with short (10-ms) trains of pulses to test for effects on a viscerosomatic reflex. Stimulation at many hypothalamic sites led to an attenuation or even a complete inhibition of reflex activity. The most sensitive sites, however (i.e. those requiring currents of 50 μA or less to inhibit the reflex), were located in the anterior hypothalamus/preoptic area (AH/POA) and rostrally in the diagonal band of Broca (DBB). At certain sites the effects of electrical stimulation were compared with those of microinjection of an excitatory amino acid (DL-homocysteic acid) which is known to excite neuronal cell bodies and not axons. The results of this part of the study indicated that activation of cell bodies located in the ventromedial AH/POA (from the level of the optic chiasma caudally to the level of DBB rostrally) mediate, at least in part, the inhibitory effects on visceral afferent processing. These data are discussed in relation to a possible role of AH/POA in the spinal processing of nociceptive information of visceral origin.

The supraoptic decussation plays an important role in the development of asymmetry of brain function for visual discrimination learning in the chicken. Lesioning the decussation on day 2 has no effect on the asymmetry normally revealed by unilaterally treating either the left or right forebrain hemisphere with cycloheximide on day 4 of life. However, the lesion removes the asymmetry revealed by cycloheximide treatment on day 8 and reverses that revealed by treatment on day 10, albeit to a lesser extent. The asymmetry of learning performance between the left and right eyes present in untreated chickens tested monocularly in the second week of life is also removed by lesioning the supraoptic decussation. Thus, in the first week of life functional asymmetry is present but not dependent on left-to-right side coupling via the supraoptic decussation. The difference between lesioning during the first and second week of life may relate to the relative degree of maturation in the supraoptic decussation.

Summary The responses to sensory stimuli and to shocks to the optic pathways have been studied for 399 units in the hippocampal region of 19 cats. 172 units were recorded from anaesthetised cats and 229 from 7 unanaesthetised cats. In theunanaesthetised animals the proportions of units responding were high (∼60%) and did not differ significantly between regions for each type of stimulation investigated: visual, auditory and optic chiasma shocks. The proportion of units responsive to chiasmatic stimulation was related to the background firing rate. The latencies and durations of the responses were relatively long and variable. Both increases and decreases in responsiveness occurred. In a number of units responses were erratic, sometimes being brisk and at other times totally absent. Responses during one series of stimuli were not always similar to those during a subsequent series. A higher proportion of units responded decrementally to a series of sensory stimuli than to a series of shocks to the optic chiasma. Movement by the animal was without consistent affect on unit activity. Responses were markedly influenced according to whether or not the cat looked intently at an object. An important determinant of HR unit responses was the state of arousal, the effect being regionally distributed. Inanaesthetised animals the proportions of responding units were substantially lower and the responses were weaker than those in the unanaesthetised cats.

We examined the degree to which conduction velocity differences between X- and Y-cells are preserved during transmission through the retinogeniculate synaptic zone. This analysis focused upon two measures: (1) axon time; and (2)_perisynaptic time. The first is the time required for an action potential to travel from the optic chiasm to the point of major branching in the optic tract. The second is the sum of terminal invasion time, synaptic delay, and the time required for postsynaptic processes which precede the generation of an action potential. The X- and Y-cell distributions of axonal conduction times differed markedly. In contrast, the X- and Y- distributions of perisynaptic conduction times overlapped extensively. Therefore, the overlap in optic chiasm latency distributions between geniculate X- and Y-cells arises primarily from the perisynaptic zone. Further, on a unit-by-unit basis, we observed small but significant negative correlations between axon conduction times and perisynaptic times within both the X- and Y-cell classes. That is, units innervated by faster conducting afferents tended to have longer perisynaptic processing times, and vice versa. This sort of relationship may act to enhance within-class synchrony in postsynaptic activity.

Gonadotropic areas were located in the quail hypothalamus by means of stereotaxic coordinates. Destruction of two regions (posterior tuber and dorsal hypothalamus) inhibited the photosexual reflex. Flash-evoked potentials were recorded in unanesthetized, unrestrained quails through chronically implanted bipolar electrodes. Characteristics of hypothalamic responses to light flashes were homogeneous throughout tuberal and dorsal gonadotropic areas, their latency being markedly longer (14 msec) than in the optic chiasma (7 msec) and shorter than in the other hypothalamic regions explored (20 msec). Changing the lighting pattern from a short to a long daily photoperiod led to classical testicular growth, whereas the latency of photically evoked responses from the gonadotropic areas became shorter (12 msec). Testosterone treatment resulted in the same decrease in latency of these evoked potentials. Bilateral section of optic nerves suppressed all hypothalamic responses to light flashes but unilateral (homo- or contralateral) optic severance affected them differently. The results are discussed in terms of mechanisms of gonadal stimulation and of nervous structures and pathways through which light elicits a gonadotropic activation.

The first synaptic region of the fly's visual system contains sets of climbing fibres enclosing each optic cartridge in a double basket-like arrangement of processes. The two sets of processes, termed α and β, can be separately identified by their fine structure. αfibres are more electron dense than β; they are postsynaptic to receptor endings from the retina and contain synaptic specializations apposed to epithelial cell membranes, to β fibres and to the distal processes of the L4 monopolar neurone. β is postsynaptic to receptors and to α. It has a lighter cytoplasm and contains peculiar glial invaginations called ‘gnarls’. Degeneration experiments, where the optic chiasma between the 1st and 2nd synaptic regions has been severed, demonstrate that α fibres are intrinsic to the lamina. Golgi impregnation and electron microscopy of Golgi-impregnated cells have demonstrated that β fibres belong to a type of medulla-to-lamina cell, T1, whereas α fibres belong to an intrinsic (amacrine) cell in the lamina. The amacrine cells have wide fields through several cartridges. However, Golgi—EM studies show that each cartridge must be invaded by the processes of at least two cells. The synaptology of these elements is discussed with respect to previous data about the lamina, and certain analogies with the vertebrate plexiform layer are drawn.