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Dopamine modulation of activity of cat sensorimotor cortex neurons during conditioned reflexes
Neuroscience Letters 330 (2002) 171–174 www.elsevier.com/locate/neulet
Dopamine modulation of activity of cat sensorimotor cortex neurons during conditioned reflexes V.M. Storozhuk a,*, V.I. Khorevin a, N.M. Rozumna a, A.E.P. Villa b, I.V. Tetko c,d a Bogomoletz Institute of Physiology, Bogomoletz str. 4, 01024, Kyiv, Ukraine Institute of Physiology, University of Lausanne, Rue du Bugnon 7, CH-1005, Lausanne, Switzerland c Biomedical Department, Institute of Bioorganic & Petroleum Chemistry, Murmanskaya 1, Kyiv, 02094, Ukraine d Institute for Bioinformatics, MIPS, GSF, Ingolsta¨dter Landstraße 1, D-85764 Neuherberg, Germany b
Received 13 May 2002; received in revised form 8 July 2002; accepted 9 July 2002
Abstract The effects of iontophoretic application of dopamine and selective D1 or D2 dopamine receptor agonists and antagonists on impulse activity of neurons of the deep layers of the sensorimotor cortex of cat were investigated during performance of a conditioned paw movement task. The application of dopamine, Quinpirole (selective D2 receptor agonist) or SKF 38393 (selective D1 receptor agonist) increased both background (P , 0:001) and evoked impulse activity (P , 0:05 for selective agonists). Selective D2 and D1 receptor antagonists (Sulpiride and SKF 83566, respectively) both increased the latency of neural responses and significantly increased the latency of the conditioned paw movements (P , 0:01). These data suggest that during natural physiological functions subcortical dopamine neurons provide facilitation of activity pyramidal neurons of sensorimotor cortex. q 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Learning; Placing; Freely-moving animals; Dopamine; D1, D2 receptors; Agonists; Antagonists; Iontophoretic application
Deep and superficial layers of the sensorimotor cortex receive dopamine (DA) projections from the ventral tegmental area (VTA) and substantia nigra (SN), respectively. There is a particularly high density of DA receptors in the frontal and in the motor cortex areas [3]. Dopaminergic neurons of VTA and SN nuclei, that have axons projecting to the cortex, are activated during conditioning [8,10,11]. A facilitating role of the activation of D1 DA receptors in frontal cortical areas was shown in experiments with working memory-guided directional movements [9]. Some authors, however, reported that pyramidal neuron excitability is decreased in the presence of DA [3]. The purpose of our work was to determine the participation of the DA system in the modulation of the activity of sensorimotor cortex neurons during conditioning under natural conditions. The influence of selective agonists and antagonists of D1 and D2 receptors on the background and evoked activity of cortical neurons was studied. Adult male cats were trained to perform an instrumentally conditioned placing movement in response to a sound click of 2 ms duration and 60 dB intensity. Touch to dorsal * Corresponding author. Tel.: 1380-44-293-27-31; fax: 1380-44256-20-00. E-mail address: [email protected] (V.M. Storozhuk).
surface of the anterior paw evoked an unconditioned placing reflex. The conditioned response was achieved by pairing the touch with the click and rewarding the animal after each movement with food, until the click alone evoked the movement. Trained animals were anaesthetized with Nembutal (40 mg/kg intraperitoneally). A metal cylinder sealed with a plastic obturator was placed over an opening in the skull above the sensorimotor cortex and was fixed in place with dental acrylic cement. During recording sessions 5–10 days later the obturator was replaced by a directed cannula containing a multi-barrel glass micropipette linked to a micromanipulator. One barrel of the micropipette was used for extracellular recording of impulse activity (3.0 M NaCl, resistance 5–10 MV). Neuronal impulse activity was recorded in the projection zone of the contralateral forepaw sensorimotor cortex. Other barrels were filled with synaptic active drugs (Sigma) for the iontophoresis. The chemicals were dissolved in distilled water at the following concentrations: DA 100 mM (pH 4.0), Quinpirole 5 mM (pH 4.0), Sulpiride 150 mM (pH 5.0), SKF 38393 and SKF 83566 10 mM (pH 4.0). The ejection currents ranged from 10 to 20 nA; the retaining currents were between 8 and 15 nA. Impulse activity of isolated cortical neurons was recorded during responses to the conditioned stimulus in three series,
0304-3940/02/$ - see front matter q 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S03 04 - 394 0( 0 2) 00 77 5- 9
172
V.M. Storozhuk et al. / Neuroscience Letters 330 (2002) 171–174
namely before (first control), during and 10 min after (second control) the application of the investigated substances (ten trials in each series). The iontophoretic applications started 1 s before and finished 3 s after the sound stimulus. Biceps electromyogram response was used as an indicator of the initiation of the paw movement. The impulse activity of neurons, electromyogram responses, and times of stimulus and of iontophoretic application were digitally stored in a computer. Analysis of neuronal impulse activity was done using peristimulus histograms and histograms constructed from the onset of movement. Statistical significance of results was determined using Student’s t-test for paired or unpaired samples (quantitative changes) and non-parametric two-tails sign criterion (qualitative changes). The impulse activities of 78 neurons in 422 series were investigated. Examples of changes of the impulse activity of a pyramidal neuron are demonstrated in Fig. 1. The direction of changes in neuronal activity, behavior and statistic results for iontophoretic application of synaptic active substances are summarized in Tables 1 and 2. The significance changes according to the sign criterion (Table 1) are quite similar to those calculated using Student’s t-test and are used to better illustrate the qualitative effects of substances. The discussion is based on the quantitative results calculated using Student’s t-test. None of the dopamine agonists (DA, Quinpirole and SKF 38393) produced a significant change in paw movement latency, but both the D1 (SKF 83566) and D2 (Sulpiride) selective antagonists significantly slowed the reaction time. Thus, inhibition of DA receptors in a tiny area of the deep layer cortex significantly increased the latency of the movement of animals. The application of synaptic active substances evoked various changes of the impulse activity of different neurons. Selective DA agonists increased the background activity and the intensity of impulse neuronal responses but have no significant effect on the latency of neuronal responses and on movement latency. DA agonists also have a trend towards increasing the duration of the neuronal response that reaches significance for the D1 selective agonist. While the selective D2 antagonist does not change background activity, the selective D1 receptor antagonist also significantly increased background activity just like the agonist did. The D2 antagonist significantly increased the neural response latency and the duration for the neural response, even more strongly than the agonist. Both D1 and D2 antagonists significantly increased movement latency. Our experimental setup (i.e. use of glass micropipette and experimental settings) makes possible long-time recording only from large pyramidal cells that are located at least 1 mm deep from the surface of the cortex. That is why our results mainly concern the influence of axons of VTA dopaminergic cells on neurons in the deep layers of the sensorimotor cortex. DA increased background activity, and increased the dura-
Fig. 1. Influences of dopaminergic agonist (Quinpirole) and antagonist (Sulpiride) on the activity of sensorimotor cortex neurons during conditioned placing reaction. Each peristimulus histogram is a sum of impulse responses to ten conditioned stimuli in control or during iontophoretic application of dopaminergic substances. The iontophoretic currents are indicated for each substance. The moment of sound stimulus coincides with zero abscissa and bin size of the histogram is 50 ms. Numbers on the right of the histograms indicate the level of background activity measured as impulses/s.
V.M. Storozhuk et al. / Neuroscience Letters 330 (2002) 171–174
173
Table 1 Qualitative changes of neural responses and movement of animals following iontophoretic application of dopaminergic substances a Synaptic active substances N
DA Quinpirole SKF 38393 Sulpiride SKF 83566
Background activity
Latency of neuronal responses
" 22 9* 40 16 24 6* 23 2 32 6*
Duration of neuronal response
Intensity of neuronal responses
Latency of movement
<
#
"
<
#
"
<
#
"
<
#
"
<
#
12 19 18 19 26
1 5 0 2 0
2 4 3 12* 3
17 34 19 10 27
3 2 2 1 2
4 13* 8 10* 5
16 26 14 12 24
2 1 2 1 3
8 12* 3 2 1
12 28 21 21 28
2 0 0 0 3
3 5 2 7* 8*
17 32 22 16 23
2 3 0 0 1
a
N is the number of analyzed neurons. The columns indicate counts of neurons that increased ( " ), did not change ( < , if changes in value were within ^SD) and decreased ( # ) the corresponding parameter following iontophoretic application. Significance changes according to the non-parametric sign criterion (P , 0:05) are indicated with an asterisk (*).
tion and intensity of impulse reactions of most part investigated neurons. However, these effects of DA could not be explained by only the direct influence of this substance on the activity of the investigated neurons. Some investigators indicated that DA has depression action on the neuronal activity [2,4]. The current study suggests that facilitation effects of DA and of its selective agonist on impulse activity of investigated neurons can be associated with their depressing influence on GABA-ergic transmission. In the human cortex approximately 60% of DA synapses were coupled with the dendrite spines and 40% with dendrite shafts. The DA synapses are usually symmetrical and only 13% of them are asymmetrical [6,11]. D1 receptors were also found in parvalbumin- and in carletinin-containing interneurons [7]. Most dense DA receptors on neuronal cell bodies were concentrated in the V and VI layers of the rat prefrontal cortex [12]. Joint localization of D1 and D2 receptors on the same neurons was found only in 25% of neurons. Cells with only D1 receptors were non-pyramidal neurons. The cells that had only D2 receptors were big interneurons and little pyramidal neurons [13]. The facts on the different distribution of DA receptors can partially explain the heterogeneity of the data recorded in our experiments. In the intracellular recordings about 50% of the frontal cortex neurons responded to DA application [1]. The intracellular recording in the rat brain slices has shown that SKF 38393 reduced the
latency of the first spike and decreased the firing threshold of neurons in prefrontal cortex as a response to the depolarizing current pulses. Quinpirole did not produce any effect on the same neurons. The action on DA receptors in premotor cortex is produced through their influence on the calcium currents. This action changes the latency and the number of spikes in the response to depolarization [13]. The suppressive effect of DA on the glutamate transmission was partially mimicked by the D1 receptor agonist SKF 38393. It was also suggested that DA decreased glutamate synaptic transmission in neurons located in layer V of rat prefrontal cortex [5]. DA enhanced inhibitory neuron excitability but decreased pyramidal cell excitability, through depolarization and hyperpolarization, respectively [14]. According to our data DA and its selective agonist increased background and evoked impulse activity of the majority of investigated cortical neurons coupled with the conditioned movement. The latency of some part of neuronal reactions on conditioned stimulus decreased, but the latency of movement increased. Iontophoretic influences of Sulpiride with high probability increased the latency of the neuronal reaction and conditioned movement. It is possible to conclude that an increase of the VTA activity through DA receptors evoked depression of the nearest inhibitory interneurons that evoked increasing excitation of pyramidal neurons during conditioned placing reaction.
Table 2 Quantitative changes of neural responses and movement of animals following iontophoretic application of dopaminergic substances a Drug
N
Background activity
Control DA Quinpirole SKF 38393 Sulpiride SKF 83566
22 9 ^ 0.7 40 12 ^ 0.7 24 13 ^ 1 23 11 ^ 1 32 8.6 ^ 0.7
Latency of neuronal responses
Duration of neuronal responses
Intensity of neuronal responses
Latency of paw movement
Iontophoresis Control
Iontophoresis Control
Iontophoresis Control
Iontophoresis Control
Iontophoresis
12 ^ 1*** 14 ^ 0.6*** 16 ^ 2*** 10 ^ 1 10 ^ 1*
570 ^ 30 640 ^ 20 690 ^ 30 780 ^ 30*** 610 ^ 30
1220 ^ 90 1110 ^ 80 870 ^ 50* 870 ^ 50** 1270 ^ 90
33 ^ 3 36 ^ 3** 26 ^ 2* 18 ^ 2 29 ^ 3
780 ^ 50 800 ^ 40 870 ^ 60 1070 ^ 70*** 930 ^ 50**
570 ^ 40 650 ^ 20 700 ^ 30 650 ^ 30 570 ^ 40
1150 ^ 80 880 ^ 50 800 ^ 40 740 ^ 40 1290 ^ 90
28 ^ 2 26 ^ 2 20 ^ 2 19 ^ 2 30 ^ 2
760 ^ 40 750 ^ 40 850 ^ 60 840 ^ 60 820 ^ 40
a Background activity is indicated as number of impulses/s. The intensity of neuronal responses is measured as the number of impulses in responses. The other values are measured in ms. Asterisks indicate the significance level: *P , 0:05, **P , 0:01, ***P , 0:001 calculated using Student’s t-test.
174
V.M. Storozhuk et al. / Neuroscience Letters 330 (2002) 171–174
This study was partially supported by INTAS-OPEN 970173 and SNSF 7-IP-062620 grants. We thank Professor Brian Hyland (University of Otago, New Zealand) for his useful remarks. [1] Bernardi, G., Cherubini, E., Marciani, M.G., Mercuri, N. and Stanzione, P., Responses of intracellularly recorded cortical neurons to the iontophoretic application of dopamine, Brain Res., 425 (1982) 267–274. [2] Delgado, A., Sierra, A., Querejeta, E., Valdiosera, R.F. and Aceves, J., Inhibitory control the GABAergic transmission in the rat neostriatum by D2 dopamine receptors, Neuroscience, 95 (2000) 1043–1048. [3] Gaspar, P., Stepniewska, I. and Kaas, J.H., Topography and collateralization of the dopaminergic projections to motor and lateral prefrontal cortex in owl monkeys, J. Comp. Neurol., 325 (1992) 1–21. [4] Gulledge, A.T. and Jaffe, D.B., Multiple effects of dopamine on layer V pyramidal cell excitability in rat prefrontal cortex, J. Neurophysiol., 86 (2001) 586–595. [5] Lawtho, D., Hirsch, J.C. and Crepel, F., DA modulation of synaptic transmission in rat prefrontal cortex: an in vitro electrophysiological study, Neurosci. Res., 21 (1994) 151– 160. [6] Lidow, M.S., Goldman-Rakic, P.S., Gallager, D.W. and Rakic, P., Distribution of dopaminergic receptors in the primate cerebral cortex: quantitative autoradiographic analysis using [3H]raclopride, [3H]spiperone and [3H]SCH23390, Neuroscience, 40 (1991) 657–671.
[7] Muly 3rd, E.C., Szigeti, K. and Goldman-Rakic, P.S., D1 receptor in interneurons of macaque prefrontal cortex: distribution and subcellular localization, J. Neurosci., 18 (1998) 10553–10565. [8] Nishino, H., Ono, T., Muramoto, K., Fukuda, M. and Sasaki, K., Neuronal activity in the ventral tegmental area (VTA) during motivated bar press feeding in the monkey, Brain Res., 413 (1987) 302–313. [9] Sawaguchi, T., The role of D1-dopamine receptors in working memory-guided movements mediated by frontal cortical areas, Parkinsonism Relat. Disord., 7 (2000) 9– 19. [10] Schultz, W., Apicella, P. and Ljungberg, T., Responses of monkey DA neurons to reward and conditioned stimuli during successive steps of learning a delayed response task, J. Neurosci., 13 (1993) 900–913. [11] Smiley, J.F., Williams, S.M., Szigeti, K. and Goldman-Rakic, P.S., Light and electron microscopic characterisation of DAimmunoreactive axons in human cerebral cortex, J. Comp. Neurol., 321 (1992) 325–335. [12] Vincent, S.L., Khan, Y. and Benes, F.M., Cellular colocalization of dopamine D1 and D2 receptors in rat medial prefrontal cortex, Synapse, 19 (1995) 112–120. [13] Yang, C.R., Seamans, J.K. and Gorelova, N., Electrophysiological and morphological properties of layers V-VI principal pyramidal cells in rat prefrontal cortex in vitro, J. Neurosci., 16 (1996) 1904–1921. [14] Zhou, F.M. and Hablitz, J.J., DA modulation of membrane and synaptic properties of interneurons in rat cerebral cortex, J. Neurophysiol., 81 (1999) 967–976.
Dopamine modulation of activity of cat sensorimotor cortex neurons during conditioned reflexes V.M. Storozhuk a,*, V.I. Khorevin a, N.M. Rozumna a, A.E.P. Villa b, I.V. Tetko c,d a Bogomoletz Institute of Physiology, Bogomoletz str. 4, 01024, Kyiv, Ukraine Institute of Physiology, University of Lausanne, Rue du Bugnon 7, CH-1005, Lausanne, Switzerland c Biomedical Department, Institute of Bioorganic & Petroleum Chemistry, Murmanskaya 1, Kyiv, 02094, Ukraine d Institute for Bioinformatics, MIPS, GSF, Ingolsta¨dter Landstraße 1, D-85764 Neuherberg, Germany b
Received 13 May 2002; received in revised form 8 July 2002; accepted 9 July 2002
Abstract The effects of iontophoretic application of dopamine and selective D1 or D2 dopamine receptor agonists and antagonists on impulse activity of neurons of the deep layers of the sensorimotor cortex of cat were investigated during performance of a conditioned paw movement task. The application of dopamine, Quinpirole (selective D2 receptor agonist) or SKF 38393 (selective D1 receptor agonist) increased both background (P , 0:001) and evoked impulse activity (P , 0:05 for selective agonists). Selective D2 and D1 receptor antagonists (Sulpiride and SKF 83566, respectively) both increased the latency of neural responses and significantly increased the latency of the conditioned paw movements (P , 0:01). These data suggest that during natural physiological functions subcortical dopamine neurons provide facilitation of activity pyramidal neurons of sensorimotor cortex. q 2002 Elsevier Science Ireland Ltd. All rights reserved. Keywords: Learning; Placing; Freely-moving animals; Dopamine; D1, D2 receptors; Agonists; Antagonists; Iontophoretic application
Deep and superficial layers of the sensorimotor cortex receive dopamine (DA) projections from the ventral tegmental area (VTA) and substantia nigra (SN), respectively. There is a particularly high density of DA receptors in the frontal and in the motor cortex areas [3]. Dopaminergic neurons of VTA and SN nuclei, that have axons projecting to the cortex, are activated during conditioning [8,10,11]. A facilitating role of the activation of D1 DA receptors in frontal cortical areas was shown in experiments with working memory-guided directional movements [9]. Some authors, however, reported that pyramidal neuron excitability is decreased in the presence of DA [3]. The purpose of our work was to determine the participation of the DA system in the modulation of the activity of sensorimotor cortex neurons during conditioning under natural conditions. The influence of selective agonists and antagonists of D1 and D2 receptors on the background and evoked activity of cortical neurons was studied. Adult male cats were trained to perform an instrumentally conditioned placing movement in response to a sound click of 2 ms duration and 60 dB intensity. Touch to dorsal * Corresponding author. Tel.: 1380-44-293-27-31; fax: 1380-44256-20-00. E-mail address: [email protected] (V.M. Storozhuk).
surface of the anterior paw evoked an unconditioned placing reflex. The conditioned response was achieved by pairing the touch with the click and rewarding the animal after each movement with food, until the click alone evoked the movement. Trained animals were anaesthetized with Nembutal (40 mg/kg intraperitoneally). A metal cylinder sealed with a plastic obturator was placed over an opening in the skull above the sensorimotor cortex and was fixed in place with dental acrylic cement. During recording sessions 5–10 days later the obturator was replaced by a directed cannula containing a multi-barrel glass micropipette linked to a micromanipulator. One barrel of the micropipette was used for extracellular recording of impulse activity (3.0 M NaCl, resistance 5–10 MV). Neuronal impulse activity was recorded in the projection zone of the contralateral forepaw sensorimotor cortex. Other barrels were filled with synaptic active drugs (Sigma) for the iontophoresis. The chemicals were dissolved in distilled water at the following concentrations: DA 100 mM (pH 4.0), Quinpirole 5 mM (pH 4.0), Sulpiride 150 mM (pH 5.0), SKF 38393 and SKF 83566 10 mM (pH 4.0). The ejection currents ranged from 10 to 20 nA; the retaining currents were between 8 and 15 nA. Impulse activity of isolated cortical neurons was recorded during responses to the conditioned stimulus in three series,
0304-3940/02/$ - see front matter q 2002 Elsevier Science Ireland Ltd. All rights reserved. PII: S03 04 - 394 0( 0 2) 00 77 5- 9
172
V.M. Storozhuk et al. / Neuroscience Letters 330 (2002) 171–174
namely before (first control), during and 10 min after (second control) the application of the investigated substances (ten trials in each series). The iontophoretic applications started 1 s before and finished 3 s after the sound stimulus. Biceps electromyogram response was used as an indicator of the initiation of the paw movement. The impulse activity of neurons, electromyogram responses, and times of stimulus and of iontophoretic application were digitally stored in a computer. Analysis of neuronal impulse activity was done using peristimulus histograms and histograms constructed from the onset of movement. Statistical significance of results was determined using Student’s t-test for paired or unpaired samples (quantitative changes) and non-parametric two-tails sign criterion (qualitative changes). The impulse activities of 78 neurons in 422 series were investigated. Examples of changes of the impulse activity of a pyramidal neuron are demonstrated in Fig. 1. The direction of changes in neuronal activity, behavior and statistic results for iontophoretic application of synaptic active substances are summarized in Tables 1 and 2. The significance changes according to the sign criterion (Table 1) are quite similar to those calculated using Student’s t-test and are used to better illustrate the qualitative effects of substances. The discussion is based on the quantitative results calculated using Student’s t-test. None of the dopamine agonists (DA, Quinpirole and SKF 38393) produced a significant change in paw movement latency, but both the D1 (SKF 83566) and D2 (Sulpiride) selective antagonists significantly slowed the reaction time. Thus, inhibition of DA receptors in a tiny area of the deep layer cortex significantly increased the latency of the movement of animals. The application of synaptic active substances evoked various changes of the impulse activity of different neurons. Selective DA agonists increased the background activity and the intensity of impulse neuronal responses but have no significant effect on the latency of neuronal responses and on movement latency. DA agonists also have a trend towards increasing the duration of the neuronal response that reaches significance for the D1 selective agonist. While the selective D2 antagonist does not change background activity, the selective D1 receptor antagonist also significantly increased background activity just like the agonist did. The D2 antagonist significantly increased the neural response latency and the duration for the neural response, even more strongly than the agonist. Both D1 and D2 antagonists significantly increased movement latency. Our experimental setup (i.e. use of glass micropipette and experimental settings) makes possible long-time recording only from large pyramidal cells that are located at least 1 mm deep from the surface of the cortex. That is why our results mainly concern the influence of axons of VTA dopaminergic cells on neurons in the deep layers of the sensorimotor cortex. DA increased background activity, and increased the dura-
Fig. 1. Influences of dopaminergic agonist (Quinpirole) and antagonist (Sulpiride) on the activity of sensorimotor cortex neurons during conditioned placing reaction. Each peristimulus histogram is a sum of impulse responses to ten conditioned stimuli in control or during iontophoretic application of dopaminergic substances. The iontophoretic currents are indicated for each substance. The moment of sound stimulus coincides with zero abscissa and bin size of the histogram is 50 ms. Numbers on the right of the histograms indicate the level of background activity measured as impulses/s.
V.M. Storozhuk et al. / Neuroscience Letters 330 (2002) 171–174
173
Table 1 Qualitative changes of neural responses and movement of animals following iontophoretic application of dopaminergic substances a Synaptic active substances N
DA Quinpirole SKF 38393 Sulpiride SKF 83566
Background activity
Latency of neuronal responses
" 22 9* 40 16 24 6* 23 2 32 6*
Duration of neuronal response
Intensity of neuronal responses
Latency of movement
<
#
"
<
#
"
<
#
"
<
#
"
<
#
12 19 18 19 26
1 5 0 2 0
2 4 3 12* 3
17 34 19 10 27
3 2 2 1 2
4 13* 8 10* 5
16 26 14 12 24
2 1 2 1 3
8 12* 3 2 1
12 28 21 21 28
2 0 0 0 3
3 5 2 7* 8*
17 32 22 16 23
2 3 0 0 1
a
N is the number of analyzed neurons. The columns indicate counts of neurons that increased ( " ), did not change ( < , if changes in value were within ^SD) and decreased ( # ) the corresponding parameter following iontophoretic application. Significance changes according to the non-parametric sign criterion (P , 0:05) are indicated with an asterisk (*).
tion and intensity of impulse reactions of most part investigated neurons. However, these effects of DA could not be explained by only the direct influence of this substance on the activity of the investigated neurons. Some investigators indicated that DA has depression action on the neuronal activity [2,4]. The current study suggests that facilitation effects of DA and of its selective agonist on impulse activity of investigated neurons can be associated with their depressing influence on GABA-ergic transmission. In the human cortex approximately 60% of DA synapses were coupled with the dendrite spines and 40% with dendrite shafts. The DA synapses are usually symmetrical and only 13% of them are asymmetrical [6,11]. D1 receptors were also found in parvalbumin- and in carletinin-containing interneurons [7]. Most dense DA receptors on neuronal cell bodies were concentrated in the V and VI layers of the rat prefrontal cortex [12]. Joint localization of D1 and D2 receptors on the same neurons was found only in 25% of neurons. Cells with only D1 receptors were non-pyramidal neurons. The cells that had only D2 receptors were big interneurons and little pyramidal neurons [13]. The facts on the different distribution of DA receptors can partially explain the heterogeneity of the data recorded in our experiments. In the intracellular recordings about 50% of the frontal cortex neurons responded to DA application [1]. The intracellular recording in the rat brain slices has shown that SKF 38393 reduced the
latency of the first spike and decreased the firing threshold of neurons in prefrontal cortex as a response to the depolarizing current pulses. Quinpirole did not produce any effect on the same neurons. The action on DA receptors in premotor cortex is produced through their influence on the calcium currents. This action changes the latency and the number of spikes in the response to depolarization [13]. The suppressive effect of DA on the glutamate transmission was partially mimicked by the D1 receptor agonist SKF 38393. It was also suggested that DA decreased glutamate synaptic transmission in neurons located in layer V of rat prefrontal cortex [5]. DA enhanced inhibitory neuron excitability but decreased pyramidal cell excitability, through depolarization and hyperpolarization, respectively [14]. According to our data DA and its selective agonist increased background and evoked impulse activity of the majority of investigated cortical neurons coupled with the conditioned movement. The latency of some part of neuronal reactions on conditioned stimulus decreased, but the latency of movement increased. Iontophoretic influences of Sulpiride with high probability increased the latency of the neuronal reaction and conditioned movement. It is possible to conclude that an increase of the VTA activity through DA receptors evoked depression of the nearest inhibitory interneurons that evoked increasing excitation of pyramidal neurons during conditioned placing reaction.
Table 2 Quantitative changes of neural responses and movement of animals following iontophoretic application of dopaminergic substances a Drug
N
Background activity
Control DA Quinpirole SKF 38393 Sulpiride SKF 83566
22 9 ^ 0.7 40 12 ^ 0.7 24 13 ^ 1 23 11 ^ 1 32 8.6 ^ 0.7
Latency of neuronal responses
Duration of neuronal responses
Intensity of neuronal responses
Latency of paw movement
Iontophoresis Control
Iontophoresis Control
Iontophoresis Control
Iontophoresis Control
Iontophoresis
12 ^ 1*** 14 ^ 0.6*** 16 ^ 2*** 10 ^ 1 10 ^ 1*
570 ^ 30 640 ^ 20 690 ^ 30 780 ^ 30*** 610 ^ 30
1220 ^ 90 1110 ^ 80 870 ^ 50* 870 ^ 50** 1270 ^ 90
33 ^ 3 36 ^ 3** 26 ^ 2* 18 ^ 2 29 ^ 3
780 ^ 50 800 ^ 40 870 ^ 60 1070 ^ 70*** 930 ^ 50**
570 ^ 40 650 ^ 20 700 ^ 30 650 ^ 30 570 ^ 40
1150 ^ 80 880 ^ 50 800 ^ 40 740 ^ 40 1290 ^ 90
28 ^ 2 26 ^ 2 20 ^ 2 19 ^ 2 30 ^ 2
760 ^ 40 750 ^ 40 850 ^ 60 840 ^ 60 820 ^ 40
a Background activity is indicated as number of impulses/s. The intensity of neuronal responses is measured as the number of impulses in responses. The other values are measured in ms. Asterisks indicate the significance level: *P , 0:05, **P , 0:01, ***P , 0:001 calculated using Student’s t-test.
174
V.M. Storozhuk et al. / Neuroscience Letters 330 (2002) 171–174
This study was partially supported by INTAS-OPEN 970173 and SNSF 7-IP-062620 grants. We thank Professor Brian Hyland (University of Otago, New Zealand) for his useful remarks. [1] Bernardi, G., Cherubini, E., Marciani, M.G., Mercuri, N. and Stanzione, P., Responses of intracellularly recorded cortical neurons to the iontophoretic application of dopamine, Brain Res., 425 (1982) 267–274. [2] Delgado, A., Sierra, A., Querejeta, E., Valdiosera, R.F. and Aceves, J., Inhibitory control the GABAergic transmission in the rat neostriatum by D2 dopamine receptors, Neuroscience, 95 (2000) 1043–1048. [3] Gaspar, P., Stepniewska, I. and Kaas, J.H., Topography and collateralization of the dopaminergic projections to motor and lateral prefrontal cortex in owl monkeys, J. Comp. Neurol., 325 (1992) 1–21. [4] Gulledge, A.T. and Jaffe, D.B., Multiple effects of dopamine on layer V pyramidal cell excitability in rat prefrontal cortex, J. Neurophysiol., 86 (2001) 586–595. [5] Lawtho, D., Hirsch, J.C. and Crepel, F., DA modulation of synaptic transmission in rat prefrontal cortex: an in vitro electrophysiological study, Neurosci. Res., 21 (1994) 151– 160. [6] Lidow, M.S., Goldman-Rakic, P.S., Gallager, D.W. and Rakic, P., Distribution of dopaminergic receptors in the primate cerebral cortex: quantitative autoradiographic analysis using [3H]raclopride, [3H]spiperone and [3H]SCH23390, Neuroscience, 40 (1991) 657–671.
[7] Muly 3rd, E.C., Szigeti, K. and Goldman-Rakic, P.S., D1 receptor in interneurons of macaque prefrontal cortex: distribution and subcellular localization, J. Neurosci., 18 (1998) 10553–10565. [8] Nishino, H., Ono, T., Muramoto, K., Fukuda, M. and Sasaki, K., Neuronal activity in the ventral tegmental area (VTA) during motivated bar press feeding in the monkey, Brain Res., 413 (1987) 302–313. [9] Sawaguchi, T., The role of D1-dopamine receptors in working memory-guided movements mediated by frontal cortical areas, Parkinsonism Relat. Disord., 7 (2000) 9– 19. [10] Schultz, W., Apicella, P. and Ljungberg, T., Responses of monkey DA neurons to reward and conditioned stimuli during successive steps of learning a delayed response task, J. Neurosci., 13 (1993) 900–913. [11] Smiley, J.F., Williams, S.M., Szigeti, K. and Goldman-Rakic, P.S., Light and electron microscopic characterisation of DAimmunoreactive axons in human cerebral cortex, J. Comp. Neurol., 321 (1992) 325–335. [12] Vincent, S.L., Khan, Y. and Benes, F.M., Cellular colocalization of dopamine D1 and D2 receptors in rat medial prefrontal cortex, Synapse, 19 (1995) 112–120. [13] Yang, C.R., Seamans, J.K. and Gorelova, N., Electrophysiological and morphological properties of layers V-VI principal pyramidal cells in rat prefrontal cortex in vitro, J. Neurosci., 16 (1996) 1904–1921. [14] Zhou, F.M. and Hablitz, J.J., DA modulation of membrane and synaptic properties of interneurons in rat cerebral cortex, J. Neurophysiol., 81 (1999) 967–976.