The effects of reverse monocular deprivation in monkeys II. Electrophysiological and anatomical studies

Summary Monkeys had one eye closed at about 30 days of age for 14, 30, 60, or 90 days, then opened, and the fellow eye closed for another 120 days. The animals then had at least 10 months of binocular visual experience before extensive behavioral training and testing were carried out. In terminal experiments concluded more than 18 months later, microelectrode investigations of the striate cortex demonstrated that there was almost a complete absence of binocular neurons in all animals. The initially deprived eyes (IDEs) dominated the majority of cortical neurons, even when soma size measurements of lateral geniculate neurons indicated that the LGN cells driven by the IDE had not regained their normal size. The monkeys which had significant interocular differences in spatial vision also exhibited abnormalities in the distribution of the metabolic enzyme, cytochrome oxidase (CO), within the striate cortex. These results demonstrate that many of the severe alterations in cortical physiology and eye dominance produced by early monocular form deprivation can be reversed, with recovery of normal cortical function, via the reverse-deprivation procedure.Supported by National Eye Institute grants R01 EY01120, R01 EY03611, R01 EY01139, and EY02520     

Inhibitory interaction in the cat's lateral geniculate nucleus

Summary Spike activities of optic tract fibers and corresponding relay cells were recorded simultaneously in layers A and A₁ of the dorsal lateral geniculate nucleus of the cat. Light stimuli of various diameters were shone into the receptive field center of these unit pairs and their input/output ratios were determined. An increase of the stimulus size leads to an impairment of the input/output ratio in on-center and off-center relay cells. This suppressive effect has approximately the same latency as the excitatory response.Intracellular recordings suggest that the inhibitory effect of the surround is due to a postsynaptic process. Inhibitory postsynaptic potentials occur during and — under certain stimulus conditions —before the excitatory response. The short latency of these IPSPs suggests that they result from the activity of adjacent units with the same RF characteristics as the recorded neuron. This inhibitory input is not restricted to the RF periphery but may also be activated by stimulation within the RF center. Most neurons are also inhibited by units with antagonistic center responses.During the period of this research Ernst Pöppel held a training grant of the Stiftung Volkswagenwerk, Az. 11 1015.     

Indirect hypothalamo-cerebellar pathway? Demonstration of hypothalamic efferents to the lateral reticular nucleus

Summary Hypothalamic efferents to the lateral reticular nucleus (NRL) have been demonstrated in the cat by means of anterograde and retrograde axonal transport of the wheat germ agglutinin — horseradish peroxidase (WGA-HRP) complex. Pressure injections of the WGA-HRP complex into the hypothalamus resulted in anterograde labelling of branching terminal axons both in the NRL and in an adjacent area, presumably the ventrolateral catecholaminergic cell group (A1). After microiontophoretical ejections of the WGA-HRP complex into the NRL from a ventral approach, retrogradely labelled neurons were found in the lateral, dorsal, posterior and anterior hypothalamic areas and in the tubero-mammillary, dorsomedial and periventricular nuclei. The projection is bilateral with a clear ipsilateral predominance and has its main origin in the lateral hypothalamic area. The locations of hypothalamic cells projecting to the NRL are somewhat different from those giving rise to hypothalamo-cerebellar and hypothalamo-spinal connections. The present demonstration of a hypothalamic input to one of the major precerebellar relay nuclei introduces a new possible indirect route through which the cerebellum may be influenced by the hypothalamus. The different indirect and direct hypothalamo-cerebellar pathways and their potential functional importance are discussed.     

Visual and vestibular signals in the lateral mesencephalic tegmental region of the cat

Summary Single unit recordings from two alert cats were used in an attempt to further elucidate the function of the lateral mesencephalic tegmental region (LTR), a part of the mesencephalon forming a link between the superior colliculus and the lower brain stem. A total of 155 units recorded from the LTR were tested with visual, vestibular and acoustic stimuli. Of these, 54 cells (36%) were characterized as either visually (n=33) or vestibularly (n=21) responsive and an additional 13 cells were driven by complex acoustic stimuli. Visually responsive cells typically were directionally selective with large, mainly contralateral receptive fields. Vestibularly responsive cells were modulated by stimulation of either the horizontal canals (yaw stimulation; n = 16) or of both pairs of vertical canals (pitch stimulation; n=5). About half of the cells with activity modulated by rotation about the yaw axis increased discharge during ipsiversive (Type I), the other half during contraversive rotation (Type II). Of the 5 cells with activity modulated by pitch stimulation, 4 preferred the nose-down and only 1 the nose-up direction. Although the discharge of units responsive to yaw stimulation was roughly in phase with head velocity (mean phase lag with respect to head velocity: 10.6 deg), none of the vestibular cells had activity correlated with eye position, eye velocity or movement of visual stimuli. Our observations suggest that the LTR might introduce visual and vestibular signals into the tecto-facial pathway which may be used to adjust the size of pinna movements with respect to the size of ongoing head- or body movements.     

Stability of intracranial self-stimulation following hypophysectomy

The possibility of a hypothalamo-pituitary involvement in the intracranial self-stimulation phenomenon was investigated. Threshold and optimal stimulation currents were identified by means of the method of limits, in rats with bipolar electrodes implanted in the lateral hypothalamus. Total or sham hypophysectomies were performed after the establishment of these current values, and found to have no effect on reinforcing brain stimulation. It was concluded that a hypothalamo-pituitary mechanism does not subserve reinforcing brain stimulation.     

Taste preferences induced by trains of rewarding lateral hypothalamic stimulation of differing durations

The question of whether prolonged stimulation of the lateral hypothalamic area (LH) simply diminishes in rewarding effect or becomes aversive was tested in 32 rats using a taste preference technique. The animals were allowed to drink novel, coffee-flavoured water for 10 min, and then received 60 trains of LH stimulation with differing durations, at an intensity proven to be rewarding at 0.5 sec duration. In a test 24 hours later, those animals that had been stimulated with 1 or 5 sec trains showed a shift in preference from tap water to coffee water, but those stimulated with 10 sec trains did not. The results show that prolonged stimulation not only loses its positive reinforcement effect but becomes negative.     

Lateralized rewarding brain stimulation affects forepaw preference in rats

Rats trained to reach for food pellets into a narrow tubular feeder consistently prefer to perform this stereotype instrumental movement with either the left or right forepaw. In 16 rats with established handedness electrodes were implanted into both lateral hypothalami. The animals were rewarded by intracranial self stimulation (ICSS, 300 msec, 50 Hz, 20-60 microA) for reaching into a modified feeder for a plastic ball operandum, the movement of which between the bottom and entrance of the feeder was monitored by mechanical contacts. The rats readily continued to reach when ICSS was delivered immediately after the photoelectrically detected reach or after the displacement of the operandum. Most rats learned in a single session to modify the movement when ICSS delivery was made contingent upon holding the operandum between the bottom and entrance of the feeder for 256 or 512 msec. The efficiency of reaching (ratio of successful reaches to all reaches) decreased with increasing holding time; only a few animals were able to master a 1024 msec delay. Reaching was supported by ICSS of either lateral hypothalamus. Whereas in 8 rats the strongly expressed forepaw preference was not changed by lateralized ICSS, in 8 latently ambidextrous animals stimulation of the lateral hypothalamus ipsilateral to the preferred forepaw increased reaching with the normally non-preferred forepaw from 15% to 60%. Stimulation of the lateral hypothalamus contralateral to the preferred forepaw did not change the preference. The preference shift was equally well expressed in simple and difficult versions of the task. It is concluded that lateralization of motivational influences can be reflected in the asymmetry of the neural mechanisms processing the lateralized sensory signals and/or elaborating the lateralized motor output.     

Excitation of units in the lateral geniculate and contiguous nuclei of the cat by stretch of extrinsic ocular muscles

Summary In cats, anaesthetized with chloralose and paralysed, the responses of units in the right lateral thalamus were recorded while the extrinsic ocular muscles (EOM) of the right eye were stretched in the dark. Phasic responses were found in all layers of the dorsal lateral geniculate nucleus (LGNd) and in the perigeniculate nucleus (PGN). A given unit usually responded to stretch of more than one EOM and thus to more than one direction of rotation of the eye in the orbit. LGNd. Of a sample of 76 units in LGNd, 55 (72%) gave visual but no muscle responses and 21 (28%) responded to EOM stretch. In all, 40 units with EOM responses were examined and 25 of the 27 tested (93%) also had visual responses. Of the 40 units, 32 could be allocated to layers, thus: layer A, 8 (25%); layer A1, 20 (63%); layer B, 3 (9%); central interlaminar nucleus, 1 (3%). It is interesting that most of the EOM responses were found in layer A1 which receives the excitatory visual input from the eye whose EOM were stretched. Muscle responsive units occurred with ON- and OFF-centre visual responses of sustained and transient types. PGN. In PGN, 21 units gave EOM responses and most of them were also excited by visual input.The conclusion is that the LGNd and PGN recieve an extraretinal proprioceptive signal which should be present during at least large saccadic eye movements. The anatomical pathways which may be involved and the significance of the signal are discussed briefly.     

Mouse killing and hyperreactivity following lesions of the medial hypothalamus, the lateral septum, the bed nucleus of the stria terminalis, or the region ventral to the anterior septum

Electrolytic lesions in the medial hypothalamus, the lateral septum, or the region ventral to the anterior septum induced home cage mouse killing in 85 to 100% of rats when tested 2 days postoperatively and in 50 to 70% when tested at 21 days. When tested in a novel and larger test chamber, 100% of the rats with medial hypothalamic lesions killed mice at 2 days postoperatively but only 30% killed at 21 days postoperatively. Ten to thirty percent of animals with lesions of the lateral septum or of the region ventral to the anterior septum killed at any time in the novel environment. Lesions of the stria terminalis produced a slight increase in mouse killing in both the home cage and the novel environment. A high level of reactivity was produced by lesions of the medial hypothalamus, the lateral septum or the region ventral to the anterior septum but only that caused by the medial hypothalamic lesions was sustained over the 21 day test period. These results support previous evidence that the lateral septum, the region ventral to the anterior septum, and the medial hypothalamus are each important areas modulating mouse killing.     

Effects of intracerebroventricular injections of 2-deoxy-D-glucose,d-glucose and xylose on operant feeding in pigs

The effects, on operant feeding, of injection into the lateral cerebral ventricle of 50 μmoles CaCl₂, 4 mmoles D-glucose, 2-deoxy-D-glucose (2DG) or xylose, or NaCl, have been studied in five pigs. All the sugars and CaCl₂ were given in 1 ml of normal saline. Each of the sugar solutions produced transient drinking. Only CaCl₂ and 2DG significantly increased food intake during the hour following injection. The results show that the mechanism by which the pig responds to intracerebroventricular 2DG is similar to that of the rat and different from that of the sheep.