- Email: [email protected]
Hypothalamic potentials evoked by stimulation of the optic chiasma
Brat:: Research, 177 (1979) 593-597 ~, Elsevier/North-Holland Biomedical Press
593
Hypothalamic potentials evoked by stimulation of the optic chiasma
FRI5 DI~RIC BREMER Bram Research Un#, Umver~tty of Brussels, B-IO00 Brusael6 ( Belgtum )
(Accepted August 9th, 1979)
Single electric pulses dehvered to the optic nerve fibers in 'enc6phale isol6" cats were found to regularly evoke in the basal preoptic area a field potential with a brief negative wave followed by a slower positive deflection z. The latter has been interpreted as an electrical sign of postsynaptic inhibition of the preoptic hypnogenic center. The present paper describes the potentials evoked by the same chiasma stimulation m the medlobasal hypothalamus. The experiments were performed on 23 young adult cats of either sex, prepared as ~enc6phale isolC. The condition of the operated animal was very good as tested by the brisk mast~catory reflexes maintained during mechanical stimulation of the gums, and by the regular heartbeat at 160/mm or more. The optic chiasma was stimulated through bipolar needle electrodes (1 mm interelectrode separation), inserted on the r~ght side, with single or double square pulses of 0.1 or 0.3 msec duration. Monopolar field potentmls from the left mediobasal hypothalamus and basal preopt~c area were recorded by means of steel microelectrodes varnished except at the tip of about l-3 #m, that were inserted stereotaxically. The potentials were displayed after amphficatJon with 0.1 sec t~me constant on an oscilloscope. Groups of 4 successive trmls were photographed and superimposed. The hlstologic location of electrode tips was verified in 9 experiments, and all of those are illustrated here. The pairs of traces in Fig. 1A and 1B, show the contrast between the potentmN evoked by the chmsma stimulus in the mediobasal hypothalamus (lower traces) and m the basal preoptic area respectively. The hypothalamic potentmls were both recorded with stereotaxic coordinates LI and H5, and with frontal coordinates A10 and A7 respectively. Both responses are characterized by slow negative field potentml of 7 msec latency, with a small hump on the wave summit. In Fig. IC and 1D simdar recordings m another experiment disclose a conspicuous N2 wave, m slightly different stereotaxlc coordinates (see legend). Although there is generally a positive correlation between the potential amplitude and the proximity of the recording electrode to the medioventral-arcuate complex and to the mldhne (Fig. 1E-G) the field potential happens here to be smaller for stereotaxlc coordinate H6. On the other hand, the recording of multmnit spike discharges at a distance from the ventromedial-arcuate complex, as in Fig. IH, may be related to the diffuse distribution of the perikarya
594
Fag 1. Responses of the mediobasal hypothalamus to electrical stimulation of optic nerve fibers Monopolar field potentials negativity upwards. The stimulus was a double pulse applied on the contralateral optic chiasma. A and B: the upper traces show the response of the basal preoptic area recorded for comparison, (stereotaxic coordinates in text). In all other traces the frontal plane was m A10; the other coordinates are: C, L1.5, H0; D: L1, H--6.5; E: L1.5, H - - 2 , F: L1.5, H - - 4 : G . L3, H - - 4 ; and H. L 1, H0. Voltage and time scale indications: 0. I mV, 50 msec. Same re&cations m Figs 2 and 3
595 containing releasing factors in the median hypothalamus 1,7. As the figurine shows, the greatest spike density coincides with the summit of the N1 wave. A similar spatial diffusion has been found by Feldman 3 for short latency potentials evoked by brief photic stimuli in anterior hypothalamus. Like the preoptic ones 2, the hypothalamic responses, in the 'enc6phale ~sol~' preparation, were very sensitive to the depressive effect of pentobarbital. In 4 experiments a 3 m m high and 4.5 m m wide transection of the basal preoptic area was made electrolytically in the plane A14. This considerably reduced the amplitude of the ipsilateral hypothalamus potential evoked by the same chiasma stimulation, as well as the density of background spike discharges in the hypothalamus (Fig. 2A and 2B). Histological sections showed that the hypothalamic neuropil had not been involved by the preoptic lesion. The demonstrated projection of the suprachiasmatic nucleus (SCN) to the medioventral-arcuate complex 6, the strong spontaneous activity of SCN (shown in Fig. 2C and 2D), its photic reactivity, described in the rat 5 and shown for the cat in Fig. 2, account for these effects of the preoptic transection. Diffuse light had a weak excitatory action, shown in Fig. 3A and 3B, on the
Fig. 2 Hypothalamic reactivity to contralateral chlasma stimulation before (A) and after (B) transection of the brain on the basal preoptic area in an ~enc6phale ~so16'cat Recordings from the med~obasal hypothalamus with stereotaxlc coordinates A 10, L1, H--4 either with an electric pulse delivered to the optic chiasma (upper traces in A and B), or without any such stimulation (lower traces) C: another experiment showing spontaneous activity of the suprachlasmatlc nucleus; D. increase thereof by bilateral diffuse photlc stimulation, which evoked strong ON and OFF responses, location of the electrode tip was verified h~stologlcally
596
Fig. 3. Photic potentiation of mediobasal hypothalamus responses to chiasma stimulation. 'Enc6phales isol~s'. Preoptic response were recorded in A and B (upper traces) for comparison. The hypothaiamic responses coordinates wore in A and B: At0, LO.5, H---4.5; in C, D and E: A10.5, LI.5, H--6.5; in F and G: A10, L I.5, H--6. 5. A, C, E and F have been recorded in darkness, in a condition of light adaptation; B, D and G immediately after the onset of a binocular illumination by a beam of light from a scialytic lamp at 2 m distance. The eyes were closed in A and D, fixed open in F and G. In each row of traces the control and potentiated responses were recorded in quick succession.
background spike discharge of the mediobasal hypothalamus. But the same illumination potentiated regularly, and often strongly, the hypothalamus response to the chiasma shock. The facilitatory effect appeared immediately after the onset of the binocular illumination and did not increase during the 6 sec duration o f the latter. As shown by traces in Fig. 3, the potentiation was documented by an increase o f the fold potential amplitude, by an increase of the response complexity and eventually by its greater regularity in the group of 4 superimposed traces. It was generally less obvious for the preoptic response to the chiasma shock, as shown by Fig. 3A and 3B. In the experiments which have given the traces shown in Fig. 3A-3E, the eyes being¢losed at the time of the 'recordings', the intensity of the illumination at the cornea must not have much exceeded 350 lux (cf. ref. 2). In conclusion, experiments on enc6phale isol6 cats have shown that single-shock stimulation of optic nerve fibers evoked in the mediobasal hypothalamus two successive slow negative potentials and a long multiunit spike discharge. The response depends on the integrity of the basal preoptic area. Its regular potentiation by diffuse high or low intensity has a functional significance for neuroendocrine regulations.
597 T h e a u t h o r is grateful to Professor J. F l a m e n t - D u r a n d for her kind histological controls and to Mr. Ch. Libert for his technical assistance.
1 Barry, J Glrod, C et Dubois, M P, Topographle des neurones 61aborateurs de LRF chez les Primates, Bull As~. Anat (Nancy), 59 (1975) 103-140. 2 Bremer, F , Photlc responses of the basal preoptlc area in the cat, Brain Research, 115 (1976) 145-149 3 Feldman, S, Visual projections to the hypothalamus and preoptic area, Ann. N. Y. Acad. Set, 117 (1964) 53-68. 4 N~shmo, R Y , KoJzum, K. and Brooks, McC, The role of suprachlasmatlC nuclei of the hypothalamus m production of circadian rhythm, Brain Research, 112 (1976) 45-59 5 Sawaki, Y , Retmohypothalamus projection: electrophyslological evidence for the existence m female rats, Brain Research, 120 (1977) 336-341 6 Swanson, J W. and Cowan, W. M , The efferent connections of the suprachiasmatlc nucleus of the hypothalamus, J comp Neurol., 160 (1975) 1-12 7 Zlmmerman, E. A. and Antunes, J L., Orgamzatlon of the hypothalamo-pltuitary system Current concepts from lmmunohlstochemical studies, J. Histochem Cytochem, 24 (1976) 807 815 ,
593
Hypothalamic potentials evoked by stimulation of the optic chiasma
FRI5 DI~RIC BREMER Bram Research Un#, Umver~tty of Brussels, B-IO00 Brusael6 ( Belgtum )
(Accepted August 9th, 1979)
Single electric pulses dehvered to the optic nerve fibers in 'enc6phale isol6" cats were found to regularly evoke in the basal preoptic area a field potential with a brief negative wave followed by a slower positive deflection z. The latter has been interpreted as an electrical sign of postsynaptic inhibition of the preoptic hypnogenic center. The present paper describes the potentials evoked by the same chiasma stimulation m the medlobasal hypothalamus. The experiments were performed on 23 young adult cats of either sex, prepared as ~enc6phale isolC. The condition of the operated animal was very good as tested by the brisk mast~catory reflexes maintained during mechanical stimulation of the gums, and by the regular heartbeat at 160/mm or more. The optic chiasma was stimulated through bipolar needle electrodes (1 mm interelectrode separation), inserted on the r~ght side, with single or double square pulses of 0.1 or 0.3 msec duration. Monopolar field potentmls from the left mediobasal hypothalamus and basal preopt~c area were recorded by means of steel microelectrodes varnished except at the tip of about l-3 #m, that were inserted stereotaxically. The potentials were displayed after amphficatJon with 0.1 sec t~me constant on an oscilloscope. Groups of 4 successive trmls were photographed and superimposed. The hlstologic location of electrode tips was verified in 9 experiments, and all of those are illustrated here. The pairs of traces in Fig. 1A and 1B, show the contrast between the potentmN evoked by the chmsma stimulus in the mediobasal hypothalamus (lower traces) and m the basal preoptic area respectively. The hypothalamic potentmls were both recorded with stereotaxic coordinates LI and H5, and with frontal coordinates A10 and A7 respectively. Both responses are characterized by slow negative field potentml of 7 msec latency, with a small hump on the wave summit. In Fig. IC and 1D simdar recordings m another experiment disclose a conspicuous N2 wave, m slightly different stereotaxlc coordinates (see legend). Although there is generally a positive correlation between the potential amplitude and the proximity of the recording electrode to the medioventral-arcuate complex and to the mldhne (Fig. 1E-G) the field potential happens here to be smaller for stereotaxlc coordinate H6. On the other hand, the recording of multmnit spike discharges at a distance from the ventromedial-arcuate complex, as in Fig. IH, may be related to the diffuse distribution of the perikarya
594
Fag 1. Responses of the mediobasal hypothalamus to electrical stimulation of optic nerve fibers Monopolar field potentials negativity upwards. The stimulus was a double pulse applied on the contralateral optic chiasma. A and B: the upper traces show the response of the basal preoptic area recorded for comparison, (stereotaxic coordinates in text). In all other traces the frontal plane was m A10; the other coordinates are: C, L1.5, H0; D: L1, H--6.5; E: L1.5, H - - 2 , F: L1.5, H - - 4 : G . L3, H - - 4 ; and H. L 1, H0. Voltage and time scale indications: 0. I mV, 50 msec. Same re&cations m Figs 2 and 3
595 containing releasing factors in the median hypothalamus 1,7. As the figurine shows, the greatest spike density coincides with the summit of the N1 wave. A similar spatial diffusion has been found by Feldman 3 for short latency potentials evoked by brief photic stimuli in anterior hypothalamus. Like the preoptic ones 2, the hypothalamic responses, in the 'enc6phale ~sol~' preparation, were very sensitive to the depressive effect of pentobarbital. In 4 experiments a 3 m m high and 4.5 m m wide transection of the basal preoptic area was made electrolytically in the plane A14. This considerably reduced the amplitude of the ipsilateral hypothalamus potential evoked by the same chiasma stimulation, as well as the density of background spike discharges in the hypothalamus (Fig. 2A and 2B). Histological sections showed that the hypothalamic neuropil had not been involved by the preoptic lesion. The demonstrated projection of the suprachiasmatic nucleus (SCN) to the medioventral-arcuate complex 6, the strong spontaneous activity of SCN (shown in Fig. 2C and 2D), its photic reactivity, described in the rat 5 and shown for the cat in Fig. 2, account for these effects of the preoptic transection. Diffuse light had a weak excitatory action, shown in Fig. 3A and 3B, on the
Fig. 2 Hypothalamic reactivity to contralateral chlasma stimulation before (A) and after (B) transection of the brain on the basal preoptic area in an ~enc6phale ~so16'cat Recordings from the med~obasal hypothalamus with stereotaxlc coordinates A 10, L1, H--4 either with an electric pulse delivered to the optic chiasma (upper traces in A and B), or without any such stimulation (lower traces) C: another experiment showing spontaneous activity of the suprachlasmatlc nucleus; D. increase thereof by bilateral diffuse photlc stimulation, which evoked strong ON and OFF responses, location of the electrode tip was verified h~stologlcally
596
Fig. 3. Photic potentiation of mediobasal hypothalamus responses to chiasma stimulation. 'Enc6phales isol~s'. Preoptic response were recorded in A and B (upper traces) for comparison. The hypothaiamic responses coordinates wore in A and B: At0, LO.5, H---4.5; in C, D and E: A10.5, LI.5, H--6.5; in F and G: A10, L I.5, H--6. 5. A, C, E and F have been recorded in darkness, in a condition of light adaptation; B, D and G immediately after the onset of a binocular illumination by a beam of light from a scialytic lamp at 2 m distance. The eyes were closed in A and D, fixed open in F and G. In each row of traces the control and potentiated responses were recorded in quick succession.
background spike discharge of the mediobasal hypothalamus. But the same illumination potentiated regularly, and often strongly, the hypothalamus response to the chiasma shock. The facilitatory effect appeared immediately after the onset of the binocular illumination and did not increase during the 6 sec duration o f the latter. As shown by traces in Fig. 3, the potentiation was documented by an increase o f the fold potential amplitude, by an increase of the response complexity and eventually by its greater regularity in the group of 4 superimposed traces. It was generally less obvious for the preoptic response to the chiasma shock, as shown by Fig. 3A and 3B. In the experiments which have given the traces shown in Fig. 3A-3E, the eyes being¢losed at the time of the 'recordings', the intensity of the illumination at the cornea must not have much exceeded 350 lux (cf. ref. 2). In conclusion, experiments on enc6phale isol6 cats have shown that single-shock stimulation of optic nerve fibers evoked in the mediobasal hypothalamus two successive slow negative potentials and a long multiunit spike discharge. The response depends on the integrity of the basal preoptic area. Its regular potentiation by diffuse high or low intensity has a functional significance for neuroendocrine regulations.
597 T h e a u t h o r is grateful to Professor J. F l a m e n t - D u r a n d for her kind histological controls and to Mr. Ch. Libert for his technical assistance.
1 Barry, J Glrod, C et Dubois, M P, Topographle des neurones 61aborateurs de LRF chez les Primates, Bull As~. Anat (Nancy), 59 (1975) 103-140. 2 Bremer, F , Photlc responses of the basal preoptlc area in the cat, Brain Research, 115 (1976) 145-149 3 Feldman, S, Visual projections to the hypothalamus and preoptic area, Ann. N. Y. Acad. Set, 117 (1964) 53-68. 4 N~shmo, R Y , KoJzum, K. and Brooks, McC, The role of suprachlasmatlC nuclei of the hypothalamus m production of circadian rhythm, Brain Research, 112 (1976) 45-59 5 Sawaki, Y , Retmohypothalamus projection: electrophyslological evidence for the existence m female rats, Brain Research, 120 (1977) 336-341 6 Swanson, J W. and Cowan, W. M , The efferent connections of the suprachiasmatlc nucleus of the hypothalamus, J comp Neurol., 160 (1975) 1-12 7 Zlmmerman, E. A. and Antunes, J L., Orgamzatlon of the hypothalamo-pltuitary system Current concepts from lmmunohlstochemical studies, J. Histochem Cytochem, 24 (1976) 807 815 ,