This document provides information about neurotransmitters from a presentation by Dr. Suresh Kumar Murugesan. It discusses key neurotransmitters like glutamate and GABA. Glutamate is an excitatory neurotransmitter that plays an important role in learning and memory formation. GABA is an inhibitory neurotransmitter that reduces neuronal excitability. The document also outlines the major neurotransmitter systems in the brain and criteria for identifying neurotransmitters.

1. Neurotransmitters
Dr.Suresh Kumar Murugesan PhD
Head, Department of Psychology, The American College, Madurai

2. About the Course Teacher
● Dr.Suresh Kumar Murugesan is a passionate Professor,
researcher and Mental Health Practitioner from
Madurai, Tamil Nadu, India
● He is very keen in learning new research studies in
behavioural Sciences and open to learn.
● His ultimate aim is to make impression in the field of
Knowledge
● His area of specializations are Psychotherapy, Positive
Psychology, Education Psychology, Cognitive
Psychology, Cyber Psychology etc

3. Contact
Dr. Suresh Kumar Murugesan PhD
sureshkumar800@yahoo.com
Home:
7, Vivekananda Street,
New Vilangudi,
Madurai, Tamil Nadu, India
WhatsApp: +91 9750 406463

4. Disclaimer
● This presentation is prepared for
learning purpose only and all the
photos used in this presentation are
taken from google image search.
● Due recognition was given to all the
material collected from the various
sources.
● Any name or reference is missed
kindly bring it to the notice of the
presenter for inclusion

5. Neurotransmitter
Neurotransmitters are
chemical messengers that
transmit a message from a
nerve cell across the synapse to
a target cell.
Image Credit: https://qbi.uq.edu.au/brain/brain-physiology/what-are-neurotransmitters

6. Neurotransmitters
Neurotransmitters are released
from synaptic vesicles in
synapses into the synaptic
cleft, where they are received
by neurotransmitter receptors
on the target cell.
Image Credit: https://www.drugabuse.gov/news-events/nida-notes/2017/03/impacts-drugs-neurotransmission

7. The exact number of
unique
neurotransmitters in
humans is unknown, but
more than 200 have
been identified.
Souce: https://beyondword.com/blogs/beyond-words-blog/neurotransmitters-and-how-to-
use-them

8. Neurotransmitters are
essential to the function
of complex neural
systems.
Source: https://www.wikiwand.com/en/Neurotransmitter

9. Neurotransmitters are often
referred to as the body’s
chemical messengers.
They are the molecules used by
the nervous system to transmit
messages between neurons, or
from neurons to muscles.

10. Until the early 20th century,
scientists assumed that the
majority of synaptic
communication in the brain
was electrical.

11. The gap between neurons,
known today as the synaptic
cleft, was discovered by
Ramón y Cajal and it was
found to be 20 to 40 nm gap
through histological
examination.

12. In 1921 German
pharmacologist Otto Loewi
confirmed that neurons can
communicate by releasing
chemicals

13. Otto Loewi is credited
with discovering
acetylcholine (ACh)—the
first known
neurotransmitter

14. A neurotransmitter influences a neuron in one of three ways: excitatory, inhibitory or modulatory.
Image Credit: http://rwjms1.umdnj.edu/pang/subpages/research.html

15. An excitatory transmitter promotes the generation of an electrical signal called an action potential in the
receiving neuron, while an inhibitory transmitter prevents it. Whether a neurotransmitter is excitatory or
inhibitory depends on the receptor it binds to.
Image Credit: https://www.sciencedirect.com/science/article/pii/B9780128023815000063

16. Neuromodulators are a bit different, as they are not
restricted to the synaptic cleft between two neurons,
and so can affect large numbers of neurons at once.
Neuromodulators therefore regulate populations of
neurons, while also operating over a slower time
course than excitatory and inhibitory transmitters.

17. Excitatory
neurotransmitters
Glutamate (Glu)
Acetylcholine (ACh)
Histamine
Dopamine (DA)
Norepinephrine (NE); also known as noradrenaline (NAd)
Epinephrine (Epi); also known as adrenaline (Ad)
Inhibitory
neurotransmitters
gamma-Aminobutyric acid (GABA)
Serotonin (5-HT)
Dopamine (DA)
Neuromodulators Dopamine (DA)
Serotonin (5-HT)
Acetylcholine (ACh)
Histamine
Norepinephrine (NE)
Neurohormones Releasing hormones from hypothalamus
Oxytocin (Oxt)
Vasopressin; also known as antidiuretic hormone (ADH)
Key facts about neurotransmitters

18. Excitatory and
inhibitory
neurotransmitters
Excitatory neurotransmitters function to activate receptors on the
postsynaptic membrane and enhance the effects of the action
potential, while inhibitory neurotransmitters function to prevent
an action potential.
Image Credit: https://umemorilab.wordpress.com/research-interests/
https://socratic.org/questions/do-neurotransmitters-either-increase-or-decrease-the-likelihood-the-next-neuron-

19. Neurotransmitters:
Classification
Neurotransmitters can also be classified based
on their chemical structure:
● Amino acids – GABA, glutamate
● Monoamines – serotonin, histamine
● Catecholamines (subcategory of
monoamines) – dopamine,
norepinephrine, epinephrine
Image credit: https://slideplayer.com/slide/7446846/

20. Identification Criteria of
Neurotransmitters
There are four main criteria for identifying
neurotransmitters:
1. The chemical must be synthesized in the
neuron or otherwise be present in it.
2. When the neuron is active, the chemical must
be released and produce a response in some
targets.
3. The same response must be obtained when
the chemical is experimentally placed on the
target.
4. A mechanism must exist for removing the
chemical from its site of activation after its
work is done.

21. Nuerotransmitters
● Carry messages between neurons via
influence on the postsynaptic membrane.
● Have little or no effect on membrane
voltage, but have a common carrying
function such as changing the structure of
the synapse.
● Communicate by sending reverse-
direction messages that affect the release
or reuptake of transmitters.

22. Types of Neurotransmitters
There are many different ways to classify neurotransmitters. Dividing them into amino acids, peptides, and
monoamines is sufficient for some classification purposes.[9]
Major neurotransmitters:
● Amino acids: glutamate,[10] aspartate, D-serine, gamma-Aminobutyric acid (GABA),[nb 1] glycine
● Gasotransmitters: nitric oxide (NO), carbon monoxide (CO), hydrogen sulfide (H2S)
● Monoamines: dopamine (DA), norepinephrine (noradrenaline; NE, NA), epinephrine (adrenaline),
histamine, serotonin (SER, 5-HT)
● Trace amines: phenethylamine, N-methylphenethylamine, tyramine, 3-iodothyronamine,
octopamine, tryptamine, etc.
● Peptides: oxytocin, somatostatin, substance P, cocaine and amphetamine regulated transcript,
opioid peptides[11]
● Purines: adenosine triphosphate (ATP), adenosine
● Catecholamines: dopamine, norepinephrine (noradrenaline), epinephrine (adrenaline)
● Others: acetylcholine (ACh), anandamide, etc.

23. Brain Neurotransmitter
Systems
1. Neurons expressing certain types of
neurotransmitters sometimes form distinct
systems, where activation of the system affects
large volumes of the brain, called volume
transmission.
2. Major neurotransmitter systems include the
noradrenaline (norepinephrine) system, the
dopamine system, the serotonin system, and the
cholinergic system, among others.
3. Trace amines have a modulatory effect on
neurotransmission in monoamine pathways (i.e.,
dopamine, norepinephrine, and serotonin
pathways) throughout the brain via signaling
through trace amine-associated receptor. A brief
comparison of these systems follows:

24. System Pathway origin and projections Regulated cognitive processes and
behaviors
Noradrenaline
system
Noradrenergic pathways:
● Locus coeruleus (LC) projections
● LC → Amygdala and Hippocampus
● LC → Brain stem and Spinal cord
● LC → Cerebellum
● LC → Cerebral cortex
● LC → Hypothalamus
● LC → Tectum
● LC → Thalamus
● LC → Ventral tegmental area
● Lateral tegmental field (LTF) projections
● LTF → Brain stem and Spinal cord
● LTF → Olfactory bulb
● anxiety
● arousal (wakefulness)
● circadian rhythm
● cognitive control and working
memory (co-regulated by dopamine)
● feeding and energy homeostasis
● medullary control of respiration
● negative emotional memory
● nociception (perception of pain)
● reward (minor role)

25. System Pathway origin and projections Regulated cognitive processes and
behaviors
Dopamine system Dopaminergic pathways:
● Ventral tegmental area (VTA) projections
● VTA → Amygdala
● VTA → Cingulate cortex
● VTA → Hippocampus
● VTA → Ventral striatum (Mesolimbic pathway)
● VTA → Olfactory bulb
● VTA → Prefrontal cortex (Mesocortical pathway)
● Nigrostriatal pathway
● Substantia nigra pars compacta → Dorsal
striatum
● Tuberoinfundibular pathway
● Arcuate nucleus → Median eminence
● Hypothalamospinal projection
● Hypothalamus → Spinal cord
● Incertohypothalamic pathway
● Zona incerta → Hypothalamus
● arousal (wakefulness)
● aversion
● cognitive control and working memory (co-
regulated by norepinephrine)
● emotion and mood
● motivation (motivational salience)
● motor function and control
● positive reinforcement
● reward (primary mediator)
● sexual arousal, orgasm, and refractory
period (via neuroendocrine regulation)

26. System Pathway origin and projections Regulated cognitive processes
and behaviors
Histamine system Histaminergic pathways:
● Tuberomammillary nucleus (TMN)
projections
● TMN → Cerebral cortex
● TMN → Hippocampus
● TMN → Neostriatum
● TMN → Nucleus accumbens
● TMN → Amygdala
● TMN → Hypothalamus
● arousal (wakefulness)
● feeding and energy
homeostasis
● learning
● memory

27. System Pathway origin and projections Regulated cognitive processes
and behaviors
Serotonin system Serotonergic pathways:
Caudal nuclei (CN):
Raphe magnus, raphe pallidus, and raphe obscurus
● Caudal projections
● CN → Cerebral cortex
● CN → Thalamus
● CN → Caudate-putamen and nucleus accumbens
● CN → Substantia nigra and ventral tegmental area
● CN → Cerebellum
● CN → Spinal cord
Rostral nuclei (RN):
Nucleus linearis, dorsal raphe, medial raphe, and raphe pontis
● Rostral projections
● RN → Amygdala
● RN → Cingulate cortex
● RN → Hippocampus
● RN → Hypothalamus
● RN → Neocortex
● RN → Septum
● RN → Thalamus
● RN → Ventral tegmental area
● arousal (wakefulness)
● body temperature regulation
● emotion and mood, potentially including
aggression
● feeding and energy homeostasis
● reward (minor role)
● sensory perception

28. System Pathway origin and projections Regulated cognitive processes
and behaviors
Acetylcholine system Cholinergic pathways:
Forebrain cholinergic nuclei (FCN):
Nucleus basalis of Meynert, medial septal nucleus, and
diagonal band
● Forebrain nuclei projections
● FCN → Hippocampus
● FCN → Cerebral cortex
● FCN → Limbic cortex and sensory cortex
Brainstem cholinergic nuclei (BCN):
Pedunculopontine nucleus, laterodorsal tegmentum, medial
habenula, and
parabigeminal nucleus
● Brainstem nuclei projections
● BCN → Ventral tegmental area
● BCN → Thalamus
● arousal (wakefulness)
● emotion and mood
● learning
● motor function
● motivation (motivational salience)
● short-term memory
● reward (minor role)

29. Neurotransmitters

30. Glutamate

31. Glutamate (Glu)
Type Excitatory
Released from Sensory neurons and cerebral cortex
Functions Regulates central nervous system excitability, learning process, memory

32. Glutamate
Early research into functional properties of glutamate used a compound known
as proline to study responses in the avian (bird) retina.
Image Credit: https://en.wikipedia.org/wiki/Glutamate_(neurotransmitter)#/media/File:L-Glutamate_Structural_Formulae.png
https://www.quantamagazine.org/hyperuniformity-found-in-birds-math-and-physics-20160712/

33. Glutamate
Cherkin, Eckardt and Gerbrandt (1976), found the
administration of proline would reduce learning and
memory in birds
Image credit: https://www.pinterest.com/pin/47991552250211093/

34. Glutamate
Researchers found that the
proline acts as a glutamate
antagonist (reducing the
release of glutamate in the
synapse), glutamate must be
involved in some process
related to learning and
memory.
Image credit: https://www.eurekalert.org/pub_releases/2020-01/cuot-git012020.php

35. Glutamate
Further studies used other glutamate
antagonists to demonstrate that overall,
reducing the amount of glutamate in the
synapse reduces the ability to learn and form
memories.
Image credit: https://www.pinterest.com/pin/460633868131751211/

36. Glutamate
Studies have summarized a critical process related to
learning and memory known as long term
potentiation. This process relies on the stimulation of
glutamate pathways in the brain (Malenka and Nicoll,
1999).
Image credit:
https://www.sciencedirect.com/science/article/pii/S2589004219301117

37. Human conditions related to major disruption of learning and memory have consistently tended to be related
to significant absences of glutamate neurotransmitters and receptors.
Image Credit:
https://www.researchgate.net/publication/24247865_The_role_of_microRNAs_in_synaptic_development_and_function/figures?lo=1

38. Glutamate
Squire (1986) found reduced numbers of
glutamate receptors in the hippocampus of
amnesic patients,
Image credit: https://medicalxpress.com/news/2019-10-decipher-glutamate-receptors-importance-memory.html

39. Glutamate
Hyman and colleagues (1987) documented that
extreme reductions in glutaminergic neurons in
the entorhinal cortex and hippocampus represent
a distinct feature of Alzheimer’s disease.
Image Credit: http://sciencemission.com/site/index.php?page=news&type=view&id=health-science%2Fhow-moderate-sunlight

40. GABA

41. GABA
Gamma-Aminobutyric acid (GABA) is the most
powerful inhibitory neurotransmitter produced by the
neurons of the spinal cord, cerebellum, basal ganglia,
and many areas of the cerebral cortex.
Image Credit: https://human-memory.net/gaba/

42. GABA
GABA is derived from
glutamate plays a vital role in
memory and learning.
Image Credit: https://www.kurzweilai.net/discovery-of-abnormal-gaba-levels-may-lead-to-improvements-in-diagnosing-treating-alzheimers-disease

43. Gamma-Aminobutyric acid (GABA)
Type Inhibitory
Released from Neurons of the spinal cord, cerebellum, basal ganglia, and many
areas of the cerebral cortex
Functions Reduces neuronal excitability throughout the nervous system and
memory process

44. GABA (γ-
Aminobutyric
Acid)
Until the discovery of benzodiazepines, GABA
had been relatively ignored in terms of its effects
on learning and memory processes.
Image Credit: https://www.news-medical.net/health/What-is-GABA.aspx

45. GABA (γ-Aminobutyric Acid)
Benzodiazepines were eventually found to drive
activity of GABA at one of its various types of
receptors (GABAA), as well as produce dramatic
learning impairments (Lister, 1985).

46. Neurotransmitter GABA predicts tactile learning
ability
Image Credit: https://alchetron.com/GABA-receptor

47. Researchers at Baylor College of
Medicine (BCM) have discovered
that when the activity of PKR — a
molecule normally elevated during
viral infections — is inhibited in
the brain, mice learn and
remember dramatically better.

48. GABA (γ-
Aminobutyric Acid)
McGaugh (1989) used
local administration of
GABA producing
compounds (agonists) or
inhibiting compounds
(antagonists)
demonstrating they
could selectively
produce learning and
memory impairments or
enhancements
depending on whether
they used.
Image Credit: https://egpat.com/questions/alprazolam-is-not-gaba-agonist

49. GABA (γ-
Aminobutyric
Acid)
The GABA agonist (learning
and memory impairments) or
GABA antagonists (learning
and memory enhancements).
Image Credit: https://www.pngegg.com/en/png-ilyoa

50. GABA (γ-
Aminobutyric Acid)
Research suggests GABA’s inhibitory nature. Specifically, a
reduction of GABA in the synapse or great inhibition of the
release of GABA can increase rates of firing between cells
leading to greater long term potentiation and thus learning
and memory consolidation.
Image credit: https://www.sciencedirect.com/science/article/pii/S0960076015301217

51. Acetylcholine

52. Type Excitatory in all cases except in the heart (inhibitory)
Released from Motor neurons, basal ganglia, preganglionic neurons of the autonomic nervous
system, postganglionic neurons of the parasympathetic nervous system, and
postganglionic neurons of the sympathetic nervous system that innervate the
sweat glands
Functions Regulates the sleep cycle, essential for muscle functioning, memory
Acetylcholine (ACh)

53. Acetylcholine
Studies using pharmachological methods to
reduce the amount of acetylcholine in the
synapse (by way of compounds that inhibit
acetylcholine, or compounds that completely
block acetylcholine receptors) within human
learning tasks and animal models have found
cognitive impairment related to learning and
memory (Deutsch, 1983, Coyle et al., 1983).
Image Credit: https://drjockers.com/improve-memory/

54. Chapoutier (1989) additionally
found that memory impairment in
individuals with Parkinson’s
disease is correlated with
acetylcholine functioning in the
frontal cortex.

55. Winson (1990) has provided evidence that
acetylcholine function can modulate rhythmic
electrical brain activity (specifically in the theta
and gamma frequencies) that are important for
producing optimal firing rates leading to long
term potentiation.

58. Catecholamines and Serotonin
Catecholamine systems such as epinephrine, norepinephrine and dopamine have
been documented to be recruited during spatial learning and memory recall, and
blockage of acetylcholine release has been demonstrated to reduce catecholamine
system function (Brandeis, Brandys & Yehuda, 1989).

59. Hatfield and McGaugh (1999) demonstrated
using a water maze task depletion of
noradrenaline affected consolidation processes
making the memory trace less stable (worse
later recall) and more susceptible to
interference.

60. Other chemical compounds that act as
neurotransmitters to bind with
receptor sites have been demonstrated
to play a role in memory consolidation
and recall (D’Hooge & De Deyn, 2001)
suggesting many different systems
work together and in opposition to
modulate our ability to encode and
consolidate long term memories.

61. Norepinephrine (NE)
Type Excitatory
Released from Brainstem, hypothalamus, and adrenal glands
Functions Increases the level of alertness and wakefulness, stimulates various processes of the
body

62. Epinephrine (Epi)
Type Excitatory
Released from Chromaffin cells of the medulla of adrenal gland
Functions The fight-or-flight response (increased heart rate, blood pressure, and glucose
production)

63. Dopamine (DA)
Type Both excitatory and inhibitory
Released from Substantia nigra
Functions Inhibits unnecessary movements, inhibits the release of prolactin, and stimulates the
secretion of growth hormone

64. Serotonin (5-hydroxytryptamine, 5-HT)
Type Inhibitory
Released from Neurons of the brainstem and gastrointestinal tract, thrombocytes
Functions Regulates body temperature, perception of pain, emotions, and sleep cycle

65. Histamine
Type Excitatory
Released from Hypothalamus, cells of the stomach mucosa, mast cells, and basophils in the blood
Functions Regulates wakefulness, blood pressure, pain, and sexual behavior; increases the
acidity of the stomach; mediates inflammatory reactions

66. References
1. https://en.wikipedia.org/wiki/Neurotransmitter#:~:text=Neurotransmitters%20are%20chemical%20messengers%20that,specifically%20to%20transmit%20the%20mess
age.
2. https://qbi.uq.edu.au/brain/brain-physiology/what-are-neurotransmitters
3. https://www.kenhub.com/en/library/anatomy/neurotransmitters
4. https://www.sciencedirect.com/topics/agricultural-and-biological-sciences/neurotransmitters
5. https://www.khanacademy.org/science/biology/human-biology/neuron-nervous-system/a/neurotransmitters-their-receptors
6. https://www.britannica.com/science/neurotransmitter
7. https://teachmephysiology.com/nervous-system/components/neurotransmitters/
8. https://www.dana.org/article/neurotransmitters/
9. https://www.ncbi.nlm.nih.gov/books/NBK539894/
10. https://www.verywellmind.com/what-is-a-neurotransmitter-2795394