January 25, 2025	PSY 340 Brain and Behavior Class 08: Chemical Events at the Synapse [Outline]

Some thought questions:

• What did you have for breakfast this morning? Coffee? Why?
• Why is it a bad idea to drink alcohol when you are also taking a Valium?
• Why do you give someone with pain due to cancer a drug like morphine (in the US) or heroin (in the UK)?
• What is happening to your grandparents who may be on the road to developing Alzheimer's disease?
• How might people who kill themselves with guns differ from those who kill themselves with sleeping pills?

To answer these questions, we must understand the chemical events at the synapse & what happens with the neurotransmitters secreted there.

---

Chemical Activity at the Synapse: Summary

Illustrating the Synapse

---

A. Types of Neurotransmitters

• More than 100 neurotransmitters have been identified or suspected
• Many neurons release 2, 3, or more neurotransmitters in the same combination along all branches of the axon

Type	Neurotransmitters	Some Important (but not all) Functions & Facts
Amino Acids	Glutamate (Glu)	excitatory
	GABA (Gamma-aminobutyric acid)	inhibitory
Modified Amino Acid	Acetylcholine (ACh)
Monoamines	Indoleamine	• derived from tryptophan (an amino acid from diet)
	Serotonin (5-HT or 5-hydroxytryptamine)	modulation of emotion
	Catecholamines	• derived from phenylalanine (an amino acid from diet)  Tyrosine  Dopa  DA/NE/Epinephrine (see below)
	Dopamine (DA)	Muscle coordination Reinforcement Creates salience/urgency/captures attention
	Norepinephrine (NE)	modulation of emotion
	Epinephrine (Adrenaline)	stimulates sympathetic nervous system

Other Peptides (> 100 different types)	Endorphins (& enkephalins)	• suppresses transmission of pain by hyperpolarizing neurons which send out Substance P
	Substance P	dull chronic pain (e.g., cancer, nerve tissue damage)
	Neuropeptide Y	stimulates feeding and fat storage
Purines	Adenosine, ATP, et al.	Adenosine => signals onset of sleep ATP => basic energy in cell
Gases	NO (Nitric Oxide)	dilates blood vessels; created as needed
		Sources: Kalat (2005, 2007, 2009. 2016), Kimball (2005)

B. Transport & Storage of Neurotransmitter/Release and Diffusion of Neurotransmitters

• synaptic vesicles
  
• exocytosis. 

C. Receptor Activation on the Postsynaptic Cell

1. Ionotropic

• Depolarization (EPSP): Glutamate
    
• Hyperpolarization (IPSP): GABA
    

2. Metabotropic & Second Messenger Systems

Neuropeptides (endorphins, substance P, neuropeptide Y, etc.) = neuromodulators

Variations in Receptors

Drugs Binding to Receptors

• Nicotine stimulates a family of acetylcholine receptors call nicotinic receptors. 
   
  

• Opiate drugs (heroin, morphine, etc.) bind to the same receptors as the brain's endogenous morphines (i.e., endorphins)
  

D. Inactivation and Reuptake of Neurotransmitters

• Reuptake
    
  • Serotonin molecules experience reuptake. Prozac and other SSRI (selective serotonin reuptake inhibitor)
     
    
  • methylphenidate (Ritalin), a mild stimulant used for persons with attention deficit hyperactivity disorder (ADHD), as well as cocaine block the reuptake of dopamine.
    
    
• Inactivated or broken apart (a process technically called hydrolysis) by enzymes
   
  
  • Acetylcholine (ACh) is used by motor neurons to signal movement. ACh is broken up by the enzyme Acetylcholinesterase (AChE) into two smaller molecules ­ acetic acid and choline.
  • Monoamine oxidase (MAO)
    

• Float away from synaptic cleft or inactivated by glial astrocytes
  

E. Negative Feedback from Postsynaptic Cell

• Autoreceptors
  

• Postsynaptic neuron can release chemicals that affect the presynaptic terminal and inhibit further release of neurotransmitters. Three chemicals have been identified: nitric oxide (NO), anandamide and 2-AG (sn-2 arachidoylglycerol).
  

F. Electrical Synapse (Gap Junction)

G. Hormones

   
 

    Pituitary Gland and the Hypothalamus

• Posterior pituitary (= an extension of the hypothalamus): made of neural tissue and secretes two hormones - oxytocin and vasopressin (or antidiuretic hormone) - which are first made in the hypothalamus - into the blood stream
  

• Anterior pituitary: made of glandular tissue that makes six different "releasing" hormones (= hormones which flow through the bloodstream and stimulate or inhibit the release of other hormones): ACTH (adrenocorticotropic hormone), TSH (thyroid stimulating hormone), prolactin, somatotropin (= "growth hormone"), FSH (follicle-stimulating hormone), and LH (luteinizing) hormone.

---

This page was first posted January 18, 2005.